airah da13 fans publicreviewdraft

DA13 Review 2012 Public Review Draft ©AIRAH

AIRAH APPLICATION MANUAL

DA13 - FANS – SELECTION, APPLICATION, OPERATION AND MAINTENANCE

PUBLIC REVIEW DRAFT

Introduction

This draft is open for industry/public review from 30th November 2012 until 5pm 11th January 2013. The draft is available in WORD and PDF formats.

Comments are invited on the technical content, wording and general arrangement of the DA.

Comments may be submitted using WORD (track changes), PDF (comment facility) or separately from the document. Please indicate relevant clause numbers for each comment.

Where you consider that specific content is too simplistic, too complex or incorrect please suggest an alternative. Please provide supporting reasons and suggested alternative wording for each comment. Where appropriate, changes will be incorporated before the manual is published. If the draft is acceptable without change, an acknowledgment to this effect would be appreciated.

If you know of other persons or organisations that may wish to comment on this draft Standard, please advise them of its availability.

Further copies of the draft are available for download from AIRAH www.airah.org.au

All comment should be submitted to [email protected] before

5pm 11 th January 2013

Vince AherneProject manager

©AIRAH DA13 - FANS – SELECTION, APPLICATION, OPERATION AND MAINTENANCE PUBLIC REVIEW Draft – 301112

mailto:[email protected]

http://www.airah.org.au/


Mechanical Engineering Services Application Manual

FANS – SELECTION, APPLICATION, OPERATION AND MAINTENANCE

__________________________________________________________________________

Contents1. SCOPE AND INTRODUCTION................................................................................................................. 5

1.1. INTRODUCTION.........................................................................................................................................51.2. SCOPE....................................................................................................................................................51.3. PURPOSE.................................................................................................................................................51.4. APPLICATION............................................................................................................................................61.5. THE SYSTEMS APPROACH............................................................................................................................61.6. FAN TERMINOLOGY...................................................................................................................................7

2. FANS, AN OVERVIEW............................................................................................................................ 8

2.1. SECTION INTRODUCTION............................................................................................................................82.2. HOW A FAN WORKS..................................................................................................................................82.3. FAN TYPES...............................................................................................................................................82.4. CENTRIFUGAL FANS...................................................................................................................................92.5. AXIAL FANS............................................................................................................................................132.6. JET FANS...............................................................................................................................................162.7. MIXED-FLOW FANS.................................................................................................................................162.8. ROOF MOUNTED FANS.............................................................................................................................172.9. CROSS-FLOW/TANGENTIAL-FLOW FANS.......................................................................................................172.10. HIGH PRESSURE FANS..........................................................................................................................172.11. SMOKE-SPILL FANS..............................................................................................................................182.12. BIFURCATED FANS...............................................................................................................................182.13. INDUSTRIAL FANS................................................................................................................................182.14. FAN DRIVES.......................................................................................................................................212.15. ELECTRIC MOTORS..............................................................................................................................222.16. MOTOR VENTILATION AND PROTECTION..................................................................................................242.17. FAN ACCESSORIES...............................................................................................................................252.18. OTHER ACCESSORIES...........................................................................................................................282.19. STANDARD FAN ARRANGEMENTS...........................................................................................................28

3. FANS AND ENERGY USE....................................................................................................................... 30

3.1. SECTION INTRODUCTION..........................................................................................................................303.2. FANS AND ENERGY..................................................................................................................................303.3. FAN MOTORS AND ENERGY.......................................................................................................................303.4. MINIMUM ENERGY PERFORMANCE STANDARDS............................................................................................313.5. BCA SECTION J......................................................................................................................................313.6. SYSTEM DESIGN AND ENERGY....................................................................................................................323.7. SELECTING FANS FOR OPTIMUM ENERGY USE................................................................................................343.8. FAN CONTROL AND ENERGY......................................................................................................................353.9. RIGHT SIZING.........................................................................................................................................353.10. FAN EFFICIENCY.................................................................................................................................353.11. ESTIMATING FAN ENERGY USE...............................................................................................................353.12. CALCULATING ENERGY SAVINGS WITH VARIABLE SPEED DRIVES (VSDS)..........................................................363.13. CALCULATING RETURN ON INVESTMENT..................................................................................................373.14. LIFE CYCLE ANALYSIS (LCA).................................................................................................................38

4. FAN PERFORMANCE............................................................................................................................ 39

4.1. SECTION INTRODUCTION..........................................................................................................................394.2. FAN TESTING..........................................................................................................................................394.3. TEST CONFIGURATIONS............................................................................................................................404.4. FAN PERFORMANCE.................................................................................................................................404.5. FAN PERFORMANCE CURVES......................................................................................................................414.6. PUBLISHED AND CERTIFIED PERFORMANCE CURVES........................................................................................43



4.7. FAN SELECTION AIDS................................................................................................................................434.8. INTERPRETING FAN MANUFACTURER DATA...................................................................................................434.9. DERATING MANUFACTURERS DATA.............................................................................................................444.10. FAN LAWS.........................................................................................................................................44

5. SYSTEM DESIGN AND SPECIFICATION..................................................................................................46

5.1. SECTION INTRODUCTION...........................................................................................................................465.2. CONSTANT AIR VOLUME...........................................................................................................................465.3. VARIABLE AIR VOLUME.............................................................................................................................465.4. THE SYSTEMS APPROACH..........................................................................................................................465.5. THE ‘SYSTEM EFFECT’..............................................................................................................................485.6. SAFETY FACTORS.....................................................................................................................................495.7. DEFICIENT FAN/SYSTEM PERFORMANCE.......................................................................................................495.8. FANS IN SERIES.......................................................................................................................................505.9. FANS IN PARALLEL...................................................................................................................................515.10. FAN STALL.........................................................................................................................................535.11. FAN SURGE........................................................................................................................................535.12. SYSTEM HUNTING...............................................................................................................................535.13. SYSTEM STABILITY...............................................................................................................................545.14. OPTIMISING SYSTEM DESIGNS...............................................................................................................54

6. FAN SELECTION................................................................................................................................... 55

6.1. SECTION INTRODUCTION..........................................................................................................................556.2. FAN SELECTION.......................................................................................................................................556.3. FANS AND SYSTEMS.................................................................................................................................556.4. FAN PERFORMANCE.................................................................................................................................556.5. THE SYSTEM RESISTANCE CURVE.................................................................................................................556.6. OPERATING POINT...................................................................................................................................566.7. BEST EFFICIENCY POINT (BEP)...................................................................................................................576.8. MATCHING FANS TO SYSTEM DUTY.............................................................................................................576.9. SELECTION FOR SMOKE-SPILL APPLICATIONS.................................................................................................596.10. FAN NOISE........................................................................................................................................59

7. CONTROLLING FANS........................................................................................................................... 62

7.1. SECTION INTRODUCTION..........................................................................................................................627.2. THE CONTROL IMPERATIVE........................................................................................................................627.3. METHODS OF CONTROLLING FANS..............................................................................................................627.4. FACTORS AFFECTING CHOICE OF CONTROL METHOD.......................................................................................627.5. SPEED CONTROL.....................................................................................................................................637.6. VARIABLE SPEED ELECTRIC MOTORS............................................................................................................647.7. MULTI-SPEED CONTROL............................................................................................................................657.8. ON-OFF CONTROL...................................................................................................................................657.9. VARIABLE PITCH BLADES...........................................................................................................................657.10. INLET VANE CONTROL..........................................................................................................................657.11. MULTI-STAGED FAN OPERATION............................................................................................................667.12. CONTROL BY CHANGING FAN CHARACTERISTICS.........................................................................................667.13. CONTROL BY VARYING SYSTEM RESISTANCE..............................................................................................667.14. CONTROL USING A BYPASS....................................................................................................................677.15. MEASUREMENT FOR CONTROL..............................................................................................................677.16. INTELLIGENT FANS...............................................................................................................................677.17. MONITORING FANS.............................................................................................................................68

8. INSTALLATION AND COMMISSIONING................................................................................................69

8.1. SECTION INTRODUCTION..........................................................................................................................698.2. GENERAL INSTALLATION REQUIREMENTS......................................................................................................698.3. INSTALLATION SPECIFICATION....................................................................................................................698.4. FAN INSTALLATION..................................................................................................................................698.5. COMMISSIONING....................................................................................................................................708.6. COMMISSIONING RECORDS.......................................................................................................................728.7. DESIGNERS ROLE IN COMMISSIONING..........................................................................................................738.8. OPERATING AND MAINTENANCE MANUALS..................................................................................................73



9. OPERATION AND MAINTENANCE........................................................................................................ 75

9.1. SECTION INTRODUCTION..........................................................................................................................759.2. TRANSITION FROM CONSTRUCTION TO OPERATION........................................................................................759.3. OPERATION...........................................................................................................................................759.4. MONITORING OPERATIONS.......................................................................................................................769.5. INTELLIGENT FAN/SYSTEM DIAGNOSTICS......................................................................................................769.6. MAINTENANCE.......................................................................................................................................779.7. SYSTEM TUNING.....................................................................................................................................799.8. SYSTEM MANAGEMENT............................................................................................................................799.9. RECOMMISSIONING.................................................................................................................................809.10. UPGRADES........................................................................................................................................809.11. OPTIMISING EXISTING FAN SYSTEMS.......................................................................................................80

10. THE FAN DUTY AND SYSTEM EFFECT...............................................................................................82

10.1. SECTION INTRODUCTION......................................................................................................................8210.2. THE SYSTEM EFFECT...........................................................................................................................8210.3. FAN INSTABILITY.................................................................................................................................8210.4. SYSTEM EFFECT FACTOR......................................................................................................................8210.5. SYSTEM EFFECT FOR DUCTS AT THE FAN INLET..........................................................................................8310.6. SYSTEM EFFECTS AT FAN OUTLET...........................................................................................................8610.7. SYSTEM EFFECT OF PLENUMS OR ENCLOSURES..........................................................................................9010.8. EXAMPLE CALCULATION OF SYSTEM EFFECT.............................................................................................93

APPENDICES............................................................................................................................................... 95

APPENDIX A FAN LAWS.......................................................................................................................... 96

APPENDIX B MEASURING PRESSURE AND FLOW.....................................................................................97

APPENDIX C SPECIFYING FANS.............................................................................................................. 101

APPENDIX D FAN PERFORMANCE TROUBLE SHOOTING.........................................................................105

APPENDIX E GLOSSARY AND ACRONYMS.............................................................................................107

APPENDIX F INGRESS PROTECTION AND IMPACT RESISTANCE RATING.................................................109

APPENDIX G RESOURCES...................................................................................................................... 111



1. Scope and introduction

1.1. IntroductionWelcome to the AIRAH Application Manual on the selection, design, installation, operation and maintenance of fans, fan products and fan systems.

Fans are an increasingly important consideration in new building design and existing building renovation because of direct links to thermal comfort, indoor air quality, building performance and energy management. Fans are an essential feature of most HVAC&R systems. Whether installed in a free intake, free discharge or ducted configuration, fans move the air necessary to ventilate and to achieve the heat transfer required in both internal climate control and external heat rejection. Building ventilation systems, toilet and kitchen exhausts, air conditioning systems, car park ventilation systems and the list goes on; fans surround us. Fans are ubiquitous in modern society and, combined, consume significant quantities of electrical energy.

Fan energy use is now a significant issue for the Heating, Ventilation Air conditioning and Refrigeration (HVAC&R) industry. The primary energy efficiency opportunities for fan applications include the use of high efficiency motors, the application of speed variation for system control, improved design and installation of the air distribution system, and the sealing of ducts and buildings to achieve the full system performance potential.

New fan motor designs and minimum energy performance standards, new international fan classification standards, new control strategies, new or revised energy efficiency requirements for fan applications in the National Construction Code, and mandatory requirements for smoke spill fans are all issues that need to be considered and understood by system designers, installers, operators and maintainers.

This Application Manual provides an overview of the entire fans in HVAC&R story. The manual begins with first principles and examines some of the fundamentals of fans. It then addresses the issues around implementing fans in systems including, system design and optimisation, fan selection and specification, system installation and commissioning continuing through to handover, operation and maintenance.

1.2. ScopeFans are ubiquitous in modern society and are particularly common in HVAC&R systems where they are used to promote heat transfer or move air. This Application Manual outlines a generic process for the design and implementation of fans and fan systems in HVAC&R applications and includes specific detailed and technical information relating to fans for HVAC&R and related services as they are applied in buildings, including industrial ventilation applications. The principles and processes outlined in this Application Manual can generally be applied to any fan system and to any building type or size.

1.3. PurposeThe primary purpose of this Application Manual is to standardise and promote best practice design and installation practices within the HVAC&R industry. The overall objective is to assist industry to improve the sustainability of fan applications in the HVAC&R and associated industries by addressing the following issues:

Provide new information on fan and motor technologies, new fan designs and applications (jet fans, plug fans, fire/smoke fans) and typical best practice efficiencies.

Promote speed control over other forms of fan control. Discuss mandatory energy requirements, minimum energy performance standards

(MEPS), National Construction Code (NCC) minimum fan energy standards, International fan classification standards, and energy reporting options for fans and fan applications.



Address the evaluation and optimisation of existing fan systems. Outline the role of monitoring and maintenance in achieving efficient fan system

operation. Underpin the skills and update the knowledge of HVAC&R system designers,

installers, operators and maintainers. Improve the accessibility of best practice fan design, installation and operating

information and expand the content of the application manual for non-technical users.

1.4. ApplicationDepending on the reader’s requirements and area of interest, reading this Application Manual from front to back may not be the most effective way to extract the required information. Table 1.1 provides a guide to the application of the various sections and appendices of this Application Manual, and directs readers and stakeholders in fans to where they may find the information most relevant to their fields of interest.

Table 1.1 APPLICATION OF DA13

Stakeholder Sections of most relevance

Topic Location

Drafting note: to be filled in at publication stage

1.5. The systems approachAll ventilation and air distribution systems have the following five fundamental components:

1. The driving force – The fan, motor and drive combination that imparts energy to the air

2. The distribution system – Ducts in a ducted system (but may be just vanes and grilles) including the fan suction and discharge connections.

3. The inlets and outlets – Locations for air to enter and exit the system4. The system controls – Monitors, sensors, electronic controllers, supervisory systems.5. The air path – If air is introduced to a space there must be a path for it to leave (air

relief or return), if air is exhausted from a space there must be a path for it to enter (make-up/infiltration or supply).

If all five system components exist and are operating properly, the ventilation system will be working under defined design conditions. Solutions to most ventilation problems are found by identifying which of the system components is missing or operating improperly.

Best practice fan application in the HVAC&R industry requires practitioners to take a ‘systems approach’ to fan selection, control, installation and commissioning. In a systems approach attention shifts away from individual components to focus on total system performance. Best practice fan application methods should include the following steps:

Document system operating conditions and system performance or outcome requirements (in conjunction with owner or client).

Develop designs and design options that achieve the performance requirements or optimise the system outcomes (see Section 5, 6, 7 for design development)

Assess alternative designs and options and select and document the option which provides the most benefits for the least cost (see Section 3 for energy and life cycle cost assessments)



Implement the selected option in accordance with the design documentation (install, commission and handover system, see section 8)

Assess installed system energy consumption and relate it to system performance (see Section 3)

Monitor and fine tune the system over time (see Section 7 for monitoring and 9 for system assessment information)

Operate and maintain the system for optimum performance (see Section 9 for operation and maintenance information)

In particular the fan selection, the fan connection to the system (discussed in detail in Section 10), and the method of fan control can have a significant impact on the system performance outcomes.

1.6. Fan terminologyA list of the acronyms used in this application manual and a glossary of common terms related to fans is provided for reference in Appendix E.

Figure 1.1 Best practice fan application in HVAC&R systems



2. Fans, an overview

2.1. Section IntroductionThis section provides an overview of fan types, motor types and fan accessories, including their application and effect on system performance. The first point in the fan story is to look at how a fan works.

2.2. How a fan worksA fan is a rotating bladed machine which continuously supplies energy to the air or gas passing through it. There are three main components in a fan: the impeller (sometimes referred to as the wheel or rotor), the means of rotating it (the motor), and the casing or volute it is contained inside, if any. Some fan types do not include casings but may include a rotating diffuser that aids air separation from the blades converting velocity pressure to static pressure.

Energy is transferred to the air by rotation of the impeller which may be of the centrifugal, axial, mixed-flow or cross-flow type. In centrifugal fan types it is the centrifugal force generated by the mass of air contained within the impeller at any one instance, as well as the force exerted by the angle of the blades to the entering air, which gives it both static and velocity pressure and therefore moves the air through the system. In the axial types there is little or no centrifugal action; the blades, being set at an angle relative to the direction of air entry, generate a lift or pressure difference. In mixed-flow and cross-flow types energy is imparted to the air in a combination of centrifugal force and lift.

The casing must not be regarded only as an enclosure for the impeller to channel the air in a certain direction. It plays a very important part in the aerodynamic performance, particularly in the case of centrifugal, cross-flow and mixed-flow fans when it is often the major element which converts velocity energy to useful potential energy (static pressure) and in axial fans where impeller tip clearance is important.

For the purpose of this manual it is assumed that the flow through the fan follows the adiabatic process and therefore is incompressible. To satisfy this condition the total pressure developed by the fan should not exceed 2500 Pa. To forecast with reasonable accuracy the installed performance of a fan the designer must know:

The performance characteristics of the fan The resistance characteristics of the system/application The effects the system/fan connections will have on the fan’s performance.

Each fan has an individual performance characteristic and fans in different ventilation products have differing performance characteristics. Fans of different types and fans of the same type but supplied by different manufacturers may not interact with the system in exactly the same way. In all cases the system design and fan selection should be based on the performance characteristics of the proposed fan and not an assumed generic characteristic based on a specified fan type, size or manufacture.

2.3. Fan typesIn order to cover a very wide range of applications, fans are manufactured in a variety of configurations or types. The various types of fans can broadly be classified under following categories:

1. Centrifugal – with either forward-curved, radial, backward-curved, backward-inclined (backward-flat) or aerofoil blading.

2. Axial – with or without (inlet and/or outlet) guide vanes.3. Mixed-flow – in essence a combination of centrifugal and axial types.4. Cross-flow – special centrifugal fans with a forward-curved blade5. High pressure fans – utilising high speed centrifugal or turbo technology.



Axial and centrifugal fans are the most common fan types used in HVAC&R applications. Within these broad fan types are many variations and these are discussed in the following clauses.

2.4. Centrifugal fansIn centrifugal fans air enters the impeller axially and is discharged radially generally into a volute casing but also into a plenum or chamber. Duties covered are generally medium to low volume flow rates at medium to high pressures. The main varieties are characterised by the type and angle of the impeller blades.

Impeller blades can be configured in a variety of ways providing the fan with different performance and operating characteristics. The performance of a flat blade can be improved by curving the blade with further performance improvements available when an aerofoil shape is used. Fan blades can be backward-curved, backward-inclined, backward-inclined aerofoil, radial, and forward curved, see Figure 2.1.

Figure 2.1 Blade designs for centrifugal impellers.

Drafting note: Figure to be redrawn - The backward-curved blades should follow along the same line as the backward-inclined although curved. The forward curved example should have shorter blades and many of them. Should show radial tipped also. Also hyphens.

Backward-curved impellers generally have between 6 and 16 blades and forward-curved, between 30 and 60 blades. Centrifugal fans can be made single-width single-inlet (SWSI) or can be manufactured with back to back impellers producing double-width double-inlet (DWDI) devices. Backward-curved centrifugal fans are more tolerant of inadvertent stall operation than other types of fans.

2.4.1.Backward-curved and backward-inclined fansBackward-curved or backward-inclined fans may consist of aerofoil section blades or single thickness blades, the latter being either curved or straight, that tilt away from the direction of rotation. The impeller is characterised by few blades. The pressure curve has a non overloading characteristic, see Figure 2.2. These fans are capable of very high efficiencies. They are used in HVAC systems for low, medium and high pressure applications and are supplied in a range of sizes from small to very large.



Typical configuration Typical performance

Figure 2.2 Typical characteristics of a backward-curved centrifugal fan

Drafting note: Figure to be redrawn: Add image for backward-inclined impeller. Normalise all fan curves to static (or other) pressure on y axis. Curves past the stall point should be dotted and marked as ‘unstable area of operation’

Backward-inclined aerofoil blade fans are the most efficient of all centrifugal fan designs, when static pressure is above 50 Pa. They are similar to standard backward-inclined fans but operate at a higher speed and with increased performance and efficiency. Total efficiencies of up to 90% are possible and the high efficiency operating zone also corresponds to a stable operating area. The power characteristic of this configuration is non-overloading, see Figure 2.3.

Drafting note: Separate figure required for aerofoil blading?


Figure 2.3 Typical characteristics of an aerofoil bladed backward-curved fan

Drafting note: Figure to be sourced: Normalise all fan curves to static/total pressure on y axis.

2.4.2.Forward-curved fansForward-curved fans are characterised by a large number of curved shallow blades sloping forward in the direction of rotation. These fans are used in HVAC systems for low volume, low to medium pressure applications. Forward-curved fans handle relatively large volumes of air at lower operating speeds and lower noise generation, but the total efficiency of up to 70%, is less than that of backward-inclined blading



As the power curve rises steeply from zero flow to maximum flow, this fan is liable to overload its driving motor if operated significantly beyond its rated operating point, see Figure 2.4.


Figure 2.4 Typical characteristics of a forward-curved centrifugal fan

Drafting note: Figure to be redrawn: Normalise all fan curves to static/total pressure on y axis.

2.4.3.Radial blade fansRadial blades or radial tip blading produce a high pressure characteristic and a power curve which is almost a straight line rising from a minimum at zero flow to a maximum at maximum flow, i.e. power characteristic is the overloading type. The blades tend to be self cleaning and can handle moderately dirty conditions. Efficiencies tend to be lower than other centrifugal types (less than 70%) and these fans are not used widely in HVAC but do have many industrial applications, see Figure 2.5.


Figure 2.5 Typical characteristics of a radial blade fan


2.4.4.Plug fansPlug fans are specially designed centrifugal impellers that have no housing and can be used directly in a plenum or duct. They provide some space advantages due to the lack of housing, but with a reduced impeller efficiency compared to standard backward-bladed fans with housings. Plug fans are direct drive and as a consequence have the advantage that belt drive losses are eliminated. Plug fans draw air in through the inlet cone (in the same way as a housed fan) but then discharges the air radially around the whole 360° outer circumference of the impeller. They can provide great flexibility in outlet connections (from the plenum), meaning a reduced need for immediate bends or sharp transitions in the ductwork connections.



Because the plenum is used to convert the kinetic energy in the airflow into a velocity pressure raising the static pressure capability, the operating efficiency will be very dependent on the fan’s location within the plenum and the relationship of the fan to its outlet. It is important to treat the plenum as part of the ductwork and the duct connection should be as large as possible rather than reduced down to the fan discharge dimensions. Maximising the duct opening will minimise the box losses and improve the aerodynamic efficiency of the air movement system.

One of the major benefits of the plug fan is that the even velocity profile discharging from the plenum allows bends to be fitted without a high pressure drop. Lack of turbulence in the discharge also affords them with good acoustic performance. Substantially different performance and different stabilities of operation will depend on the impeller type (aerofoil, backward-curved etc). Plug fan designs vary greatly with standard backward-curved impellers through to specialised high performance impellers designed specifically to operate without the scroll enclosure used.

As the impeller is typically mounted directly on the motor shaft it is common for a variable frequency drive (VFD) to be used to operate the fan at a speed required to meet the duty point. Some plug fans are designed to operate far in excess of the motor name plate rating without any issue with motor or impeller life. Plug fans are mainly used in air handling units, computer room air conditioning units and industrial applications; although they have also been used for car park exhaust systems, see Figure 2.6.

Note: If plug fans are used in industrial applications with elevated gas temperatures then direct drive may not be suitable. Instead include belt drive with/without a heat slinger for bearing cooling.


Figure 2.6 Typical characteristics of a plug fan


2.4.5.In-line centrifugalIn-line centrifugal fans comprise a conventional aerofoil or backward-curved/inclined or mixed-flow impeller but installed in a wide range of configurations including cylindrical, square and rectangular housings. These fans are generally less efficient than the conventional cased type centrifugal fans but the straight through casing design provides some advantages, see Figure 2.7. In-line centrifugal fans are generally only used on low pressure HVAC&R applications.


Figure 2.7 Typical characteristics of an in-line centrifugal fan



Drafting note: Figure to be sourced. Normalised performance curves possible for these fans?

2.5. Axial fansIn axial fans, air enters and leaves the fan axially in a ‘straight through’ configuration. Duties are usually medium to high volume flow rate at medium to low pressures. Most axial fan types have non-overloading power characteristics although some with high pitch angled impellers can overload, but not as severely as forward-curved centrifugals. Axial fans can have very high efficiencies and the maximum efficiency is often achieved across a broad operating range, see Figure 2.8.

Axial fans generate swirl in the discharge airstream and the removal of the swirl improves fan efficiency. Swirl can be reduced by using guide vanes or by using twin impellers independently driven in opposite directions within the same casing, see Clause 2.5.6.

Downstream guide vanes can increase the pressure development capability of the axial flow fan by as much as 30% without any increase in the power required form the fan. Upstream guide vane units can provide an even higher pressure development but the power requirements increase correspondingly. The noise levels from the fan are generally increased with the downstream guide-vane unit having the least impact, see Clause 2.5.3.

Many axial fans are reversible, i.e. they can operate in the both the forward and reverse directions, often with a performance reduction when in reverse. The impeller blades can be configured in such a manner that the fan can be deemed truly reversible, although the performance achieved will not be as high as from an impeller with all blades installed in the normal manner. However, the performance achieved from such an arrangement is higher than that achieved from an axial fan simply rotated in the reverse direction. In all variations from the standard configuration the efficiency is lower and noise levels are generally increased, see Clause 2.5.5

Axial fans can exhibit stall at a lower static pressure than many other fan types and further information on this is provided in Section 5. Axial fans generally rotate faster than centrifugals to achieve the same airflow and they tend to generate more noise, particularly in the higher frequencies, which are however easier to attenuate than the low frequencies generated by centrifugals. Axial fans deliver more air at zero pressure than a centrifugal fan, of the same size and running at the same speed, but the centrifugal fan will develop more pressure. A significant feature of axial fans is their lower costs when compared to other types of fans.


Figure 2.8 Typical characteristics of an Axial Fan

Drafting note: Figure to be redrawn. Normalise all fan curves to static/total pressure on y axis. Should the adjustable pitch feature of the fan also be shown?



2.5.1.Plate mounted fansPlate mounted fans are basically an axial flow impeller running in a square or round plate suitable for wall, ceiling or panel mounting.

Because of the air entry conditions they develop less pressure than an axial flow fan of the same size and speed. Applications include moving air through a partition from one open space to another and they are also widely used in heat exchange systems in HVAC&R and industrial applications. These fans can move large volumes of air but only generate low pressures, see Figure 2.9. Complex blade designs can be incorporated to address noise and performance. The design of the orifice the impeller is mounted in can greatly affect the efficiencies and noise generated by these fans. Plate mounted fans can have an adjustable pitch impeller.


Figure 2.9 Typical characteristics of a plate mounted fan

Drafting note: Is this Figure required/available? Figure to be sourced: Normalise all fan curves to static/total pressure on y axis.

2.5.2.Tube axialIn its simplest form a single impeller is direct-driven by a motor mounted within a cylindrical frame. The fans (also called ducted propeller fans) move large volumes of air but only generate small pressures.

In the tube axial configuration the axial fan is mounted centrally within a cylindrical casing producing high flow rates at medium pressure generation. The discharge flow contains a pronounced swirl which may, if not corrected, materially increase the resistance of the downstream portion of the system. Used in low to medium pressure ducted HVAC where downstream airflow pattern is not critical and industrial applications.

2.5.3.Vane axial fansIn vane axial fans the swirl is removed by fitting either upstream or downstream guide vanes. The removal of the swirl can improve the fan efficiency and the downstream air distribution. These fans can produce low, medium and high pressures in a ducted or in-line configuration and are used in HVAC&R and industrial applications.

Upstream guide vanes can increase the pressure development of the axial flow fan, typically by more than 30%, with an equivalent increase in power consumed. There is also an increase in noise level. As the power increases at the same rate as the pressure development increases, there is no increase in efficiency

Downstream guide vanes can increase the pressure development capability of the axial flow fan, typically by more than 20%, with no increase in power consumed. This means an increase in the fan efficiency however there is also an increase in noise level.

There is increase in the noise level generated with both guide vane configurations but more with upstream guide vanes than with downstream guide vanes



When applied to fans arranged in series the downstream guide vanes act as upstream guide

vanes for the fan following and improves pressure development for each additional fan. This configuration provides less pressure development per ‘double’ stage than multi-stage axial flow fans (see Clause 2.5.7) but more flexibility and less noise.

2.5.4.Variable pitch fansBy varying the pitch of the blades of an axial fan the output can be varied while still maintaining a high efficiency. Varying the pitch has two different applications:

Controllable pitch fans (also called variable-pitch-in-motion fans) – Adjustment of the vane (blade) pitch during operation for automatic control purposes was once common but with the advent of energy efficient motor speed control only very specialised applications still require this technology and it is no longer a practical economic solution in most HVAC&R applications.

Adjustable pitch fans – These fans have impeller blades whose angles can be reset by manual adjustment with the fan at rest for a permanent performance adjustment. This technique can be used during commissioning or when fine tuning the fan to meet the system requirement.

2.5.5.Reversible axial fansAlthough many fans are strictly unidirectional, axial fans can be operated in reverse in one of two distinct methods.

Standard fan - A normal fan may be reversed, with a reduction in performance compared to standard flow performance.

Reversible fan - known as a ‘truly reversible’ fan, the impeller is configured to provide equal performance in either flow direction.

Both methods have limitations and efficiency and performance are reduced in reversing scenarios. Refer to Table 2.1 for an approximate or typical reduction in performance for each method. As both methods alter the fan’s performance curve, it is also important to verify stable operation in the reverse flow application and advice should be sought from the manufacturer where necessary.

Table 2.1 – Typical performance reduction for reversal of axial fans

Performance parameterReduction when compared to catalogue performance

Standard fan in reverse Truly reversible fan

Volume flow Reduced by 30% Reduced by 15%

Pressure developed Reduced by 55% Reduced by 25%

Power consumed Reduced by 25% Reduced by 20%

2.5.6.Contra-rotating axial fansThe contra-rotating axial flow fan typically has two separate impellers in series arranged to have opposite rotation. Swirl developed by the first impeller is removed and converted into useful static pressure by the second impeller. The resulting static pressure development is more than twice, and can be up to three times, that developed by a corresponding single impeller fan. These fans can be noisy when compared to other types.

2.5.7.Multi-stage axial flow fansAxial flow fans can be mounted in series, generally with contra-rotating impellers. With a two stage unit pressure development can be increased by approximately 2.5 times the pressure capability of a single-stage fan because the second stage eliminates the swirl component leaving the first stage. However, a 3-stage unit would re-impose the swirl but a 4th stage



would eliminate it again and so on. The greater the number of stages the greater the pressure developed.

2.6. Jet fansSome axial and centrifugal fan designs are called a ‘Jet Fan’ because a high velocity jet of air is produced from the unit. The high velocity jet discharged by the fan entrains surrounding air and these types of fans are commonly used in tunnel and car park ventilation systems where air movement over a large area or distance is required.

The jet fans applied for tunnel ventilation are generally axial jet fans. The jet fans applied for car park ventilation systems are generally mixed-flow or centrifugal jet fans. Noise is often an issue when jet fans are applied in occupied areas.

Drafting note: Figure and/or curve required/available


Figure 2.10 Typical characteristics of a jet fan

2.7. Mixed-flow fansMixed-flow fans have an air path through the impeller which is between that of the axial and centrifugal types. Mixed-flow fans are capable of being constructed to provide either axial or radial discharge and they produce more pressure than a comparable axial flow fan. Impellers are shrouded and more robust than axial impellers and most designs are of a compact nature. They also have a less severe stall characteristic than axial fans, see Figure 2.11. Better efficiencies tend to be achieved with the radial discharge design, but these types have an overloading power characteristic.


Figure 2.11 Typical characteristics of a Mixed-flow Fan

Drafting note: Normalise all fan curves to static/total pressure on y axis.



2.8. Roof mounted fansRoof ventilators, for exhaust applications, can be designed for vertical up-flow or down-flow discharge and fitted with axial, backward-curved bladed centrifugal or mixed-flow impellers.

Roof ventilators for supply air applications are generally fitted with backward-curved bladed impellers.

Drafting note: Figure and/or curve required/available?

Centrifugal Axial Mixed flow

Figure 2.12 Typical characteristics of a roof ventilator/exhaust fan


2.9. Cross-flow/Tangential-flow fansCross-flow or Tangential-flow fans are centrifugal fans with a forward curve bladed impeller of very long axial length in relation to its diameter. The impeller is fitted to a special casing wherein the air enters and discharges through the full length of the rotor and normally through an outlet diffuser. Efficiencies and noise levels are typically low and these fans are used where their long narrow rectangular inlets and outlets are advantageous. These fans are of limited application in commercial HVAC&R but are used in wall mounted split air conditioners and air curtains as well as used in industrial applications. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.

Drafting note: Figure and/or curve required/available?

Figure 2.13 Typical characteristics of a Cross-flow/Tangential-flow fan


2.10. High pressure fansKnown as high pressure fans, or industrial blowers, these fans have high discharge pressures for relatively low flow rates. Common designs include the use of multi-stage centrifugal or high speed turbo technologies. Rarely used in standard HVAC&R applications but used in industrial applications such as combustion air, fluid bed aeration, blow off, cooling, conveying, drying and high pressure industrial process systems, heat recovery, incineration, process air, and pollution control.



2.11. Smoke-spill fansFans utilised in smoke control systems that are designed to move smoke and the products of combustion, are called smoke-spill fans. AS/NZS 1668.1 specifies minimum performance requirements for these fans to ensure that they can continue to operate at high temperatures. Different requirements are specified depending on whether the building is protected by a sprinkler system or not, as smoke temperatures are expected to be lower in sprinkler protected buildings. AS/NZS 1668.1 requires a longer duration but lower temperature rating for application in sprinkler protected buildings and a higher temperatures but shorter duration rating for application in non-sprinkler protected buildings. Refer to AS/NZS 1668.1 for specific requirements.

2.12. Bifurcated fansBifurcated fans are axial fans constructed so that the direct drive electric motor is isolated from the airstream, by being enclosed within a central “pod”. The motor is ventilated only with ambient air delivered from outside the casing by means of a sideways tunnel or bifurcation see Figure 2.14. They are often used in explosive, corrosive, high temperature or aggressive applications, and selection requires an allowance to be made for the casing losses.

Figure 2.14 Typical bifurcation arrangement

2.13. Industrial fansIndustrial fans can include the types of fans used in HVAC&R as well as high pressure fans.

Industrial applications include process ventilation applications, dust collection, pneumatic conveying, spot cooling and ventilation, local fume exhaust and fume cupboards. The design and construction of industrial ventilation systems and their fans should be in accordance with the requirements of relevant regulations, standards, and industry guidelines. In the absence of local requirements the recommendations of the American Conference of Governmental Industrial Hygienists (ACGIH) Industrial Ventilation manual should be adopted.

Where flammable atmospheres could be present as a consequence of dusts, gases or vapours (e.g. grain milling, spray painting) the ventilation systems, including the fans, should be designed and constructed to mitigate ignition, flammability or explosion risks.



Table 2.2 Fan types and typical characteristics

Fan type Typical Characteristics Typical Applications

Centrifugal fansBackward-curved

and

Backward-inclined

Low, medium and high pressure applicationsCapable of very high efficiencies. Peak efficiency at 50 to 75% of free discharge flow, total efficiencies of 85 to 90%.Aerofoil blades provide highest efficiency (also highest cost and less durable than flat blade fans). Dirty blades or erosion will reduce performance.Stable and efficient operating characteristic to the right of peak pressure flow rateNon-overloading power characteristic

Used on large heating and ventilation systems

Large industrial/process applications (clean air for aerofoil blade, plate blades more robust)

Used where energy use is significant design criteria.

Forced draft applications.

Forward-curved

Works at a lower speed and with lower efficiencyMedium air volumes at low pressure/low noiseLight weight, low cost, small impellerLimited mechanical strengthPronounced stall region on fan curveHas overloading power characteristic

Used on Low pressure HVAC, room air conditioners, small ducted ventilation and heating systems

Applications where low noise is important Only suitable for clean air

Radial blade

and

Radial tip

Low/medium volume, high pressure applicationsLeast efficient centrifugal fan, radial tip design improves efficiencySelf cleaning blades in dirty air streamsSimple design, low cost, simple to repair impeller. High mechanical strength. Durable.Overloading power characteristic

Not common in HVAC&R Moderate to high pressure industrial

processes, materials handling, (dust collection, pneumatic conveying).

Induced draft applications

Plug fans Premium efficiency versions have rotating diffuser and aerofoil blades.Lower efficiency than backward inclined fans with scroll.Use less space than standard centrifugal and have flexible choice of discharge position.Significantly reduced pressure losses for bends close to discharge.Good acoustic characteristics.Non-overloading power characteristic

Used for high volume flow at medium pressures applications such as:

Air handling unit fans, Computer room air conditioner fans. Car park ventilation

In-line centrifugal

Standard impeller in annular casingLower efficiency than conventional centrifugalSome designs with forward curved blades may exhibit stall.Overloading and non-overloading power characteristics, depending on design

In-line configuration for ducted applications Low to medium pressure ducted HVAC, often

in return air or exhaust applications

Axial fansPlate mounted

High flow rates at low pressuresGenerally low efficiencies with maximum at free discharge. Efficiency significantly improved with shroud and inlet bell.Larger fans operate at lower speedsLow power use, non-overloading characteristic

Low pressure high volume non-ducted applications such as air transfer, cooling/heat exchange (coils and tubes) and air movement.

Cheap, basic product with medium efficiency Common in refrigeration plant.

Tube axial High flow rates at low to medium pressuresProduces turbulent downstream flow so potential issue with noise.Dip in fan curve indicates stall region In-line configuration, quick to reach full speedCompact fan often direct driven from motorNon-overloading power characteristics

Low to medium pressure small ducted HVAC Common in exhaust applications Low pressure Industrial ventilation including

drying ovens, spray booth ventilation, fume exhaust.

Used where reverse airflow is required, e.g. emergency supply/exhaust systems

Vane axial Highest efficiency/pressure capacity of any axialMore compact than comparable centrifugalDip in fan curve indicates stall regionIn-line configuration, quick to reach full speed

Low, medium and high pressure supply and exhaust ventilation

Ducted HVAC Industrial supply and exhaust applications



Often belt driven from motorNon-overloading power characteristics, except at high pitch angles.

Emergency ventilation (quick response) systems

Used where reverse airflow is requiredContra-rotating

2 to 3 times higher pressure development than single fanCompact design but can be noisy

Medium and high pressure supply and exhaust Ducted HVAC

Industrial supply and exhaust applications

Jet fansHigh velocity/high pressure airstream generatedHigh noise levels, may require attenuation

Used in tunnel ventilation; road, rail, mining Car park ventilation/air movement, Loading

docs

Mixed flow fansMedium - high pressure/Medium - high efficiencyNormally fitted with guide vanes.Available in axial or radial discharge.Axial discharge: shrouded impeller, non-overloading power characteristic, higher pressure and less severe stall than axial fans Radial discharge: unshrouded impeller, more efficient, overloading power characteristic, prone to surge if misapplied

Axial discharge types: Small sizes used for low volume ducted

HVAC systems Larger sizes not common in HVAC&R

Radial discharge types: Used in industrial processes

Cross-flow fansLow efficiency fansLow volume and low pressure developedVery quiet for the fan duty

Used in residential air conditioning products

Roof mounted fan unitsCentrifugal Aerofoil or backward-inclined bladed impellers

High volume airflow at medium to high pressuresNon-overloading power characteristic

Medium to high static pressure exhaust systems

Mainly ducted systemsAxial Axial impeller used to generate high volume

airflow at low to medium pressureLouder than centrifugal units.Non-overloading power characteristic (except at high pitch angles)

Most common configuration Low to medium static pressure exhaust

systems Mainly ducted systems

Mixed flow Multi-bladed shrouded mixed flow impellers offers good compatibility with weather cowl.Quieter than axial unitsNon-overloading power characteristic

Low to medium static pressure exhaust systems

Used for ducted systems

High pressure fans/blowersRelatively low efficienciesLow air volumes/high pressures

Rare in HVAC&R Used in industrial for pneumatic conveying

Notes

1. For the purposes of this table Low, Medium, High pressure ranges are characterised as:

Low pressure HVAC: 0-200 pa : Heat rejection, Air transfer, small scale supply and exhaust ventilation

Medium pressure HVAC: 201- 450 pa: Heat exchange, ventilation and air conditioning, car park ventilation

High pressure HVAC: above 450 pa: Industrial process, high pressure supply and exhaust, pneumatic conveying.

2. Power characteristic: For fans with an overloading fan characteristic (e.g. Figures 2.4 and 2.5), increasing power consumption with higher airflow rates may mean the driving motor will overheat or burnout if not appropriately selected. Motor ventilation is particularly important when dealing with fans that have overloading power characteristic.



2.14. Fan drives

2.14.1. Power sourcePrime movers or drivers for fans can include a variety of power sources including electric, combustion, turbine, pneumatic and gearbox. Fan drive by electric motor is the most common in HVAC&R applications. Fan drives are also classified by the configuration of their connection to the impeller.

2.14.2. Direct-driveIn the direct–drive configuration the fan impeller is either fitted directly onto the shaft of an electric motor, or it may be connected via a separate shaft and a drive coupling (also known as direct-coupled). The impeller speed is identical to the motor's rotational speed. With this type of fan drive mechanism, the fan speed cannot be varied unless the motor speed is adjustable. To enable speed adjustment motors are fitted with either voltage or frequency controlled speed controllers or the motor is of EC construction. Due to the direct-drive configuration transmission losses are minimised so efficiencies are higher than other arrangements.

2.14.3. Belt-driveIn the belt–drive configuration a set of pulleys (which may have an adjustable operating diameter) are mounted on the motor shaft and the fan impeller shaft. A belt (or number of belts) transmits the mechanical energy from the motor to the fan. The impeller speed depends upon the ratio of the diameter of the motor pulley to the diameter of the fan impeller shaft pulley. As the drive energy passes through mechanical components transmission losses occur, efficiencies are reduced and losses impact on overall fan efficiencies.

Belts used come in a range of designs; flat belt, V-belt, cogged V-belt and synchronous belt and belt selection must account for the power of the motor as well as site specific factors such as operating temperature, arc of contact (with the pulley) and service factor derating (due to acceleration forces)

2.14.4. External motor terminal boxFor axial fans, where the motor terminal box is moved to outside of the fan casing, less resistance is imposed on the airflow and this can improve the performance of a small fan. The magnitude of the performance improvement depends on the size of the impeller hub in relation to the motor size and the size of terminal box removed from the design.

2.14.5. Motor mountingAxial fans can be further differentiated according to the method of motor mounting as per the following descriptors:

T-piece mounting (using foot mounted motor) – Where the foot mounted motor is bolted to T-piece shaped plate longitudinally welded on the sides and bottom on the inside of the fan casing.

Spider rod mounting (using rod/pad mounted motor) - Where smaller motors are provided with holes on the motor body for demountable feet. These holes can also be used for threaded rods which would extend radially through holes in the casing and secured to the casing and thus forming a spider mounting with the motor in the centre.

Flange mounting - where the motor flange of a flange mounted motor is bolted to a mating fan casing mounting flange inside the fan casing.



2.15. Electric motors

2.15.1. Single-phase alternating current motorsSingle-phase alternating current (AC) power does not naturally create a rotating magnetic field so single-phase motors include additional means to start the rotor moving. The moving rotor then induces the magnetic field that maintains motor operation. In some single-phase motors, the starting circuit is “opened” after the rotor reaches a predetermined speed. In other types, the start circuit remains engaged. How single-phase motors are started affects the torque generated, and is often the factor that determines which single-phase motor type best fits the application.

Shaded pole motors have only one main winding and no start winding. Starting is accomplished through a design that uses a copper ring around a small portion of each motor pole. The shaded pole motor is electrically very simple and inexpensive. Speed can be controlled by varying the voltage. These motors offer poor starting torque, typically 25 to 75 % of rated load, and very low efficiency. These motors typically have sleeve bearings.

Permanent split capacitor (PSC) motors have a run-type capacitor that is permanently connected in series with the start winding. This makes the start winding an auxiliary winding after the motor reaches running speed. Maintenance is low due to the lack of a starting switch. The run capacitor must be designed for continuous use, it cannot provide the short-term boost of a starting capacitor. Therefore, starting torque of a PSC motor is low, ranging from 30 to 150 % of rated load, which makes the motors unsuitable for hard-to-start loads. PSC motors can be designed for easy reversing, and can be speed controllable. They are considered to be the most reliable single-phase motor, primarily because a starting switch is not required. These motors typically have ball bearings.

Split phase motors have two types of coils; one is called the run winding and the other the start winding. The start winding has much higher resistance than the run winding resulting in different currents and magnetic fields in the two windings. These form a rotating field that causes the rotor to turn. The split phase motor design is simple and typically less expensive than other types and can be speed controllable. Starting torque is low; typically 100 to 175 % of rated load. The split phase motor develops high locked rotor current and has unreliable thermal protection. These motors are usually designed for a single voltage and have ball bearings.

Capacitor start motors are similar to a split phase motors, but have a much heavier starting winding with a capacitor placed on the path of the electrical current to the winding to provide a starting boost and are usually fitted with centrifugal switch to isolate the capacitor at normal speed. These motors create more starting torque; typically in the range of 200 to 400% of rated load, with a lower starting current allowing higher cycle rates and reliable thermal protection. Capacitor start motors are more expensive than a split phase design (because of the additional cost of the capacitor and centrifugal switch) but the application range is much wider. Capacitor start motors cannot be speed controlled. They typically have ball bearings.

2.15.2. Three-phase alternating current motorsThree-phase alternating current (AC) power naturally creates a rotating magnetic field, no additional windings or switches are needed within the motor for starting. The increase and decrease of the current in each phase produces the rotating magnetic field. In turn, the rotation of the magnetic field produces the twisting motion in the motor shaft. These motors have high efficiencies and typically have ball bearings.

The most common three-phase motors used in fans for HVAC&R are squirrel cage designs. They are suitable for both direct-on-line and star/delta starting. These motors come in a range of sizes and efficiencies with the efficiency ratings tending to increase with increasing motor size. Most can be speed controlled using Variable Frequency Drives (VFDs). VFDs



not only vary the voltage like a speed controller, but they also change the frequency with the voltage. Motors used in conjunction with VFDs require heavier insulation on the internal wires, due to the extra heat generated within the windings when used with a VFD.

The use of three-phase external rotor motors is also very common, especially with centrifugal impellers. These have a compact design, and are able to be speed controlled using variable voltage control. They may also be controlled using VFD’s fitted with suitable electrical filters.

Table 2.3 outlines the major differences between single-phase and three-phase motor types.

Table 2.3 Comparison of single-phase and three-phase motors

Motor Type CapitalCost

Nominal Efficiency

Starting Torque

SpeedControl

Reversible Application notes

Shaded Pole

Lowest Lowest Lowest Yes No Used on small direct-drive fans only

Permanent split capacitor

Low Low Low Yes Yes • Constant torque • Used on small direct-drive fans only

Split Phase Average Good Medium No Yes • Separate start windings to control starting amps• Used on medium sized fans

Capacitor Start

Average 55% to 75% depending on motor size

High No Yes • Used for higher starting torque requirements• Used on medium and large fans• Most common

Three-phase

Average 65% to 97% depending on motor size

High Yes Yes • Efficient motor• Used on large fans• Wide range of available motor options

2.15.3. Direct current motorsDirect current (DC) motors have a DC supply and utilise a permanent magnet rotor with either brushed or brushless commutators. Motor sizes are typically available up to 500 W and efficiencies are between 50 to 90 %. These motors are rarely used in stationery HVAC&R fan applications but are used for transport refrigeration and air conditioning applications.

2.15.4. Electronic commutation (EC) motorsElectronic commutation (EC) technology combines highly efficient DC motors with an AC power supply. These motors convert AC supply to DC and switch the electrical supply at varying frequencies to drive the permanent magnet brushless DC motors at the required speed. EC motors produce reduced operating temperatures and can include integrated control logic and integrated electronics to provide remote communication and control possibilities. EC motors also contain internal motor protection so external contactors and overloads are not required. Some also include visual fault diagnosis indication to simplify trouble shooting should a fault occur within the motors. EC motors are available in sizes up to 7.5kW and efficiencies are typically between 80 – 95%.

Table 2.4 outlines some of the advantages and disadvantages associated with EC motors types.



Table 2.4 Advantages and disadvantages of EC motorsAdvantages Disadvantages

On-board motor protection Initial costs (can be offset by savings due to reduced control equipment requirement)

Extremely high efficiencies May not be suitable for high temperature or aggressive environments

Compact dimensions

Simple speed control/commissioning

On-board controls

2.16. Motor ventilation and protection

2.16.1. Open motorsAn open motor has ventilation openings which permit the passage of cooling air over and around the windings of the motor. The term ‘open’ means having no restriction to ventilation other than that necessitated by mechanical construction. Open motors are suitable for indoor use in relatively clean dry atmospheres. They do not offer protection from airborne dust or vapour. Open motors are typically used on small centrifugal roof fans with the motor out of airstream where the air is clean and dry.

2.16.2. Totally enclosed fan cooled (TEFC) motorsA totally enclosed fan cooled (TEFC) motor (also known as totally enclosed fan ventilated (TEFV) motor) is equipped for motor cooling by means of a fan integral to the motor but external to the enclosed parts. Air-cooled totally enclosed fan-cooled motors are inherently self sufficient in the manner which cooling is provided as the ventilation fan is driven by the motor shaft and no external cooling is required.

Note: Care needs to be taken if there is an adjustable motor speed to ensure adequate cooling if no auxiliary motor cooling is provided.

2.16.3. Totally enclosed air over (TEAO) motorsTEAO motors are similar to TEFC motors but do not contain an integral cooling fan, relying upon the airflow of the fan which they are driving to cool them. Where an axial fan is provided with a direct-drive motor this may be of aerodynamic design and may not require cooling fins. A totally enclosed air over motor is not self ventilated and in this case the airflow provided by the fan acts to cool the motor.

In such applications a standard TEFC motor may be used with its integral cooling fan removed provided the quantity of cooling air available is sufficient for motor cooling. Generally in TEAO fan applications the process air quantity exceeds the motor’s cooling requirements by a large margin, and in some cases it is possible to utilise this additional cooling to allow motor output to be increased by up to 15% (also known as “Airstream rating”). These motors are typically used on plate mounted propeller fans, direct-drive axial fans, and vane axial fans, and can operate in either Form A (motor upstream) or Form B (motor downstream).

2.16.4. Ingress protection ratingsApplications involving airstreams contaminated with dust or moisture can preclude the use of some motors. Motors can be sealed for protection from contaminants. There are varying degrees of motor protection against dust and moisture known as “IP” (Ingress Protection) ratings. For further information on IP ratings refer to Appendix F.

2.16.5. Hazardous location motorsThere are various classes of hazardous environments in which fans and motors may be required to operate. The correct classification of the hazard requires considerable skill and



judgement, particularly to the extent of the hazardous area, the probability of hazardous materials being present and their likely concentrations. This is best carried out by a specialist assessor.

Motors designed for one hazardous area are not necessarily suitable for use in another. In many cases, hazardous location motors will not fit on the originally selected fan due to the increased size.

When hazardous location motors are required, there are many classes, divisions, and groups to consider. Commonly encountered Hazardous Classifications are:

Ex’d’ (Flameproof) - An explosion resistant motor which is designed and constructed to withstand an internal explosion of specified gases or vapours, and not allow the internal flame or explosion to escape.

Ex’e’ (Increased Safety) Ex’n’ (Non-Sparking) DIP (Dust Ignition Proof)

2.16.6. Motor service factorThe service factor is a measure of continuous overload capacity at which a motor can operate without damage, provided the other design parameters such as rated voltage, frequency, and ambient temperature are within specification. For example a 2kW motor with a 1.15 service factor can operate at 2.3kW (2kW x 1.15 = 2.3kW) without overheating or otherwise damaging the motor if the rated voltage and frequency are supplied. General purpose open motors usually have a service factor greater than 1.0 and totally enclosed motors usually have a service factor not exceeding 1.0.

2.17. Fan accessories

2.17.1. Effect on performanceOften factory fitted extras (such as belt-guards or control dampers) are fitted to the fan at the request of the customer. These are sometimes specified with little thought or understanding of the aerodynamic affects and the consequent reduction of fan performance.

Unless the fan manufacturer’s catalogue clearly states to the contrary, it should be assumed that published fan performance does not include the effects of any accessories. If doubt exists about performance effects, it is best to seek advice from the fan manufacturer.

The following comments primarily apply to centrifugal fans, but may apply to any fan type.

2.17.2. Drive accessories

Bearing supports in fan inlet

Certain fan arrangements require a bearing support in the fan inlet. In a large fan the effect on the fan performance may be negligible, but in a small fan it can be significant.

Drive-guards

Drive guards are used on fans to:

Protect people from moving hazards associated with the motor and drive (WH&S). Protect the fan, drive and motor from external and environmental damage.

These guards must be openable or removable so that the protected equipment can be maintained, and should meet the relevant occupational health and safety design standards where applicable.

Certain fan arrangements require drive-guards close to the fan inlet for health and safety reasons. Depending on fan size, air velocity at the inlet and the degree of ‘openness’ of the



guard, the effects of the guard on the fan performance will vary. In the case of large diameter pulleys, spoked construction is advantageous.

Belt-guards in axial flow fans

Axial flow fans driven by belts from an externally mounted motor usually have a belt guard across the air stream which reduces the free area within the axial casing. Most manufacturers include the effects of such guards in their performance ratings.

2.17.3. Inlet boxesAn inlet box is a device, designed and fitted by the fan manufacturer, to ensure optimum inlet airflow characteristics, particularly where the air stream must be turned sharply through a substantial angle. It may be used to facilitate the motor and bearings being located completely outside an extremely hot or corrosive air stream. These accessories are frequently used in industrial ventilation.

The system effect of inlet boxes can vary considerably. The type of fan impeller also has a considerable effect. If an inlet box is required, this item should be supplied with the fan and to a design proven to have the least effect on the fan performance or to a design such that the manufacturer knows the impact on the fan performance. Inlet boxes are commonly used in industrial ventilation applications.

Figure 2.15 Typical picture required?

2.17.4. Inlet box dampersInlet box dampers may be used to control the airflow volume through the system. Either parallel or opposed blade types may be used.

The parallel blade type is installed with the blades parallel to the fan shaft so that, in a partially closed position, a forced inlet vortex will be generated. The effect on the fan characteristics will be similar to that of inlet vane control. (See below). The opposed blade type is used to control airflow by changing the duct system resistance.

Fitting either parallel or opposed blade dampers will reduce the efficiency of the fan.

Figure 2.16 Typical picture required?



2.17.5. Inlet vanesTo optimise fan efficiency in reduced flow conditions, airflow quantity can be controlled by variable vanes mounted in the fan inlet. These are arranged to generate a forced inlet vortex which rotates in the same direction as the fan impeller (pre-rotation).

Inlet vane arrangements may be of two different basic types:

Integral (built in) Cylindrical (add on)

The system effects of such devices are typically available from the fan manufacturer. It is also necessary to know if any effect is required to be taken into account when they are wide open.

Figure 2.17: Typical picture required?

Note: Providing fan speed control is a more energy efficient method than control by inlet vanes.

2.17.1. EvaséAn evasé is a diffuser fitted at the fan outlet (a passage of gradually increasing area through which the air discharged by a fan must pass) that gradually increases in area to decrease the air velocity, converting kinetic energy to static pressure. This is in conjunction with the change in velocity profile described in Clause 10.6.

Evasés can be used with both axial and centrifugal fans but require appropriate design to be effective, with the ideal slope of transition no more than 30° total included angle. As a guide, the following table demonstrates the range of static pressure recovery based on 3 typical scenarios:

Note: These approximate recovery values assume type “B” or type “D” fan installation (ducted outlet). For very short evasés, the pressure recovery is negative which results in an addition to system pressure. The practice of fitting an inlet cone to the fan discharge is therefore not recommended. For appropriate advice the fan manufacturer should be consulted.

Figure 2.18 Typical static pressure recovery with an evasé


Evasé type

(Figure 2.18)

Pressure recovery range as a % of fan outlet velocity pressure

Short unducted -30 to +15 %

Long unducted +20 to +40 %

Long ducted +40 to +70%


2.18. Other accessoriesOther accessories include:

Flanged inlets and outlets Access doors Shaft, bearing, and belt guards Shaft cooler Shaft/Casing seal Inlet screen Anti-vibration mountings On axial fans – Inlet Cones On axial fans – support Feet Spark resistant construction Extended life bearings Special coatings Silencers and insulation Monitoring sensors

2.19. Standard fan arrangementsStandard fan arrangements and classes are adopted by industry to communicate the operating condition that a fan is capable of, the location of the bearings, and the standard drive configurations. Common fan standards that have been adopted for use in Australia follow the AMCA (Air Movement and Control Association USA) Standard AMCA 99-2404-03.

2.19.1. Axial fansMost axial fans are direct drive arrangement 4 (refer centrifugal arrangement) but also made arrangement 1 (direct drive with coupling) and arrangement 9 (belt drive).

Axial fans can be further differentiated according to the direction of airflow as per the following:

Form A – Airflow over motor first Form B – Airflow over impeller first

External Rotor motor fans are typically described as either:

V flow – Blowing over stator, or A flow – Sucking over stator.

Figure 2.19 External rotor motor airflow designation

2.19.1. Centrifugal fansSingle width single inlet (SWSI) and double width double inlet (DWDI) centrifugal fans are generally fabricated to order to suit various standard configurations. Some of the standard configuration common in the HVAC&R applications are shown in Figure 2.20.



D irection o f Ro ta tion & D ischarge Position

D irec tion o f ro tatio n is d eterm ined from d rive s id e fo r b o th S W S I& D W D I fans

C W.0

C W.45

C W.90

C W.135

C W.180

C W.225

C W.270

A C W.0

A C W.45

A C W.90

A C W.135

A C W.180

A C W.225

A C W.270

O ptiona l M otorPositions, Belt D rive

M o to r p o s itio ns Z & W are s tand ard . A d d itio na l p ric e fo r p o s itio ns Y & X

Y X

Z

D W D IA rrgt. 3

S W S IA rrgt. 9

Z W

W

S W S I A R R G T. 1R oto r o verhang s b earing

p ed es ta l. C an b es up p lied w ith integ ra l

m o to r b as e.

D rive A rrangements - SW & DW Fans

S W S I A R R G T. 8D irec t d rive. A rrg t. 1

w ith extend ed p ed es ta lfo r m o to r and d rive c o up ling .

S W S I A R R G T. 3R oto r s up p o rted b y

b earing lo c ated eithers id e o f the m o to r. N o trec o m m end ed b elo w

s ize 30.

D W D I A R R G T. 3R oto r s up p o rted b y b earing s

in b o th in lets . C an b e sup p liedw ith integ ra l m o to r b ase.

S W S I A R R G T. 4D irec t d rive, ro to r

o verhang s p ed es ta l,and is lo c ated d irec tly

o nto m o to r s haft.

D W D I A R R G T. 7D irec t d rive. A rrg t. 3

D W D I w ith p ed es ta l fo r m o to rand d rive c o up ling .

S W S I A R R G T. 9A rrg t. 1 fan w ith m o to r

lo c ated o n b earingp ed es ta l.

Figure 2.20 Drive arrangements for single width and double width centrifugal fans



3. Fans and energy use

3.1. Section IntroductionThis section provides an overview of all the issues that need to be considered when considering the energy use of fan applications in HVAC&R systems.

3.2. Fans and energyFans consume between 15 -20% of all energy generated worldwide and so their correct selection and application can have a significant impact on overall system efficiency and cost.

There is a strong link between fan selection, system design and system energy efficiency.

Fans are ubiquitous in HVAC&R systems Fans are not always well selected or applied Systems are not always well designed Systems are not always well operated Fans use a considerable amount of power in HVAC&R systems

A fan option with the lowest absorbed power generally has the lowest life cycle cost.

To minimise energy use fans must be:

Applied within an accurately designed distribution system Selected to operate at or near their best efficiency point Installed and commissioned correctly Correctly operated and maintained over the course of their working life.

Designers, installers, operators and maintainers all have a role to play in maximising system efficiency and minimising system energy use.

Fans are the obvious energy user in ventilation systems, and are usually a major contributor to annualised energy consumption in commercial, air conditioned buildings. At the design and installation phase of any project, fan power requirements can be minimised by:

Reducing airflow (q) to the lowest rate required to achieve performance.

Reducing Total Pressure pt required by the duct system to meet airflow performance. Note: Total Pressure pt = Static Pressure pS + Velocity Pressure pV

Static Pressure can be reduced by prudent duct design. Refer to DA03.Velocity pressure can be reduced by selection of larger diameter fans.

Selection of fans with high fan efficiency ηf.

The relationship between these factors and required fan input power is:

Pi = q x (pv + ps) Pi = Fan shaft power input (Watts)

ηf q = System airflow (m3/sec)

pv = Fan velocity pressure (Pa)

ps = System static pressure (Pa)

ηf = Overall fan efficiency (Value between 0 & 1.0)

3.3. Fan motors and energyEfficiency = power in (electricity supplied) / power out (useful work)

The efficiency of the system will depend on the efficiency of the fan (impeller/blade/casing combination) and the efficiency of the motor and drive used to power it. Several phenomena cause inefficiencies (energy loss) in motors and drives including:

Friction at bearings supporting the shaft



Current flow induced through windings causes resistance heating Motors require cooling arrangements to remove heat generated

The efficiency of an electric motor will be dependent on the following:

Efficiency varies with load – motor peak efficiency does not occur at peak load. Efficiency varies with size – larger motors tend to be more efficient that smaller

motors at their optimum loading. Oversized motors are often less efficient than those correctly sized.

Efficiency varies with component quality – Higher quality electrical materials can reduce resistance, heat build-up and improve efficiency

Efficiency varies with power factor – motors with a high power factor (i.e. approaching unity) draw less reactive current and losses due to resistance heating than motors with a lower power factor.

The link between motor efficiency and system energy efficiency is often overlooked by designers and installers. Not all electric motors have the same efficiencies. The annual energy consumption of HVAC&R systems can be significantly reduced by the selection of high efficiency fan motors.

The relationship between motor efficiency and required electrical input power is:

Pe = q x (pv + ps) x 1 Pe = Electrical power input (Watts)ηf ηm ηm = Overall motor efficiency (Value between 0 & 1.0)

3.4. Minimum Energy performance standardsMinimum Energy Performance Standards (MEPS) programs are mandatory in Australia and are enforced by state government legislation and regulations applicable to the relevant Australian Standards. Regulations specify the general requirements for MEPS for appliances and equipment, including offences and penalties if a party does not comply with the requirements. Technical requirements for MEPS are set out in the relevant appliance or equipment standard.

Three phase electric motors are currently regulated under MEPS. Three phase electric motors from 0.73kW up to 185kW manufactured in or imported into Australia must comply with the MEPS requirements set out in AS/NZS 1359.5. The MEPS requirements are set out as minimum efficiency levels. The MEPS standard also defines a voluntary high efficiency level for these motors. These MEPS do not apply to submersible motors, integral motor-gear systems, variable or multi-speed motors or those rated only for short duty cycles. Rewound motors are not required to comply with MEPS.

MEPS are regulated as minimum standards. It is important for designers to understand the difference between a motor that meets the MEPS and a motor that exceeds the MEPS. MEPS are designed to remove very inefficient equipment from the market not drive the market to only use the minimum standard allowed.

Note: At the time of publication there are no MEPS set for fans in Australia. However, the implementation of MEPS for ‘fan-units’ (i.e. fan and motor combinations), based on European Union (EU) regulations is currently under consideration. Since 2012 the EU has implemented minimum efficiency regulations for fan-units driven by electric motors with an input power in the range of 125 Watts to 500 kW. The EU regulations are based on the fan performance test method ISO5801 and the Fan Motor Efficiency Grades set out in ISO12759.

The Greenhouse and Minimum Energy Standards (GEMS) program aims to create a national framework for MEPS, which will replace stated based MEPS regulations.

3.5. BCA Section JBuilding regulations, through the National Construction Code (NCC) Volume One (Building Code of Australia Class 2 to 9 buildings), limit the installed power that may be consumed by



fans in ventilation, air conditioning and miscellaneous systems. Limits are set in Section J of the Code.

For ventilation systems BCA Section J specifies maximum fan motor power (W) to airflow rate (L/s) ratio requirements that need to be achieved by ventilation systems for compliance with building regulations. These W/L/s requirements are designed to reduce the fan energy consumption which is achieved by reducing or optimising the total system pressure drop and by selecting an appropriate fan efficiency. Therefore complying with these targets generally requires duct systems to be designed for low pressure drops and using high efficiency fans.

For air conditioning systems BCA Section J specifies that the total fan motor power of the air-conditioning supply air and return air fans in the building, divided by the floor area served by those fans, must be less than the maximum fan motor power limits specified in the code. Fan motor power is defined as the power delivered to the motor of a fan, including the power needed for any drive and impeller losses

Maximum fan motor power limits are specified in watts (W) per square meter (m2) of the floor area of the air conditioned space. Specified limits are listed dependent on the air conditioning sensible heat load (W/m2) of the conditioned space

Meeting the requirements of the NCC for fan power is dependent on a systems approach including:

The design of the ductwork and air distribution system (ducting, dampers, diffusers) The presence of filters, coils and other air handling components The selection of the fan and its motor The method of fan control

Designers should refer to the latest edition of the code relevant to the authority with jurisdiction over the design to determine the specific requirements that should be applied to a particular installation.

3.6. System design and energy

3.6.1.Size and extentThe system designer must decide on the size and extent of the system. The smaller the duct and fitting size chosen the lower the costs to both purchase and install them. However using smaller duct and fitting sizes results in a higher resistance to flow and therefore a larger fan/motor than might otherwise be required. A larger fan means higher purchase and installation costs and higher operating costs over the life of the system.

Decreasing duct size has the following effects:

Decrease duct and component purchase and installation costs Increase fan procurement costs, including a larger motor and electrical supply

system. Increase operating costs and potentially reduce system life. Potential for higher noise levels with higher fan duty requirements

Similarly with increasing duct size, some costs increase and some decrease. An optimum duct size may be found based on minimising the costs and maximising the benefits over the life of the system, refer Clause 3.14

3.6.2.Flow ratesTo minimise energy consumption it is best to move air at as low a flow rate as the system or process can tolerate. Reducing flow rates reduces friction losses and ultimately reduces the size of fan and motor required. In HVAC&R applications the airflow rate is often a function of the heat load to be transferred which depends on:

The energy released/absorbed by the transfer process The properties of the air



The heat transfer characteristics of the distribution

Some equipment manufacturers (e.g. coils, enthalpy wheels, dampers) will mandate maximum and minimum flow rates to ensure the proper performance of their plant.

3.6.3.Air velocityThe air velocity and flow rate have a direct relationship to the duct sizes selected. In general lower velocity through larger ducts provides a more energy efficient distribution option. There are other design limitations on air velocities including:

Minimum velocity for the application - e.g. throw at a supply grille. Maximum flow velocity – to minimise noise and vibration in distribution system.

Refer to AIRAH DA03 and the AIRAH Technical Handbook for recommendations on air velocity selection when sizing ductwork distribution systems.

3.6.4.Motor power and efficiencyAccurately calculating and specifying the size of motor (power) required for the particular fan and application is an important design step from an energy efficiency point of view. The efficiency of the motor and drive that will be specified with the fan has a significant effect on system energy use. Motors, speed controllers and drive mechanisms should all be specified to maximise the operating efficiency of the ‘system’.

Higher flow rates will occur if the system resistance is lower than anticipated. The operating point of the fan will shift down and to the right on the fan performance curve. For fans with an overloading power characteristic the required power can exceed the motor rated power causing the motor overload protection to trip. Motors should be selected to be non-overloading or a larger motor than required be specified to ensure that the fan will operate at any point on the curve. The larger motor will not run at full capacity and hence there may be a minor efficiency penalty. However the improved efficiency characteristics of larger motors may offset this efficiency penalty somewhat.

3.6.5.Equipment qualityIn many cases the quality of the fan and system components specified or purchased will have an impact on the energy performance of the system. Fan manufacturers offer a range of optional extras for standard fans and many, for a small increase in initial capital cost, can have a significant effect on the energy consumed by the fan. Some of the issues to be considered when specifying a particular fan include:

Quality of manufacture and materials Wear rates for bearing or seals Impeller and casing coatings to improve performance and reduce corrosion Extent of embedded controls and monitors (e.g., EC fans)

3.6.6.Single, parallel or series operationDesigners need to decide the most efficient configuration to use for the system. Options include:

A single fan (with variable or multiple speed control) Equal fans operating in parallel Unequal fans operating in parallel Equal fans operating in series, Unequal fans operating in series.

Section 7 explores many of these design options in detail, including their energy implications.



3.6.7.Shut-off pressureWhen the damper at the fan discharge is fully closed, a condition known as ‘shut-off’ exists. The pressure at ‘shut-off’ produced by a centrifugal fan is only slightly above or below the pressure at maximum efficiency. Closure of the fan discharge damper while the unit is operating should be avoided, or only done with care and only for a very short time.

When operating in shut-off the fan will still consume energy which will cause heating in the casing. As the impeller will be stalling; noise, vibration and severe radial loads on the shaft may occur. With larger fans these effects can be severe and temperature rise can be rapid. The advice of the manufacturer should be sought to ascertain whether, and for how long the fan may be operated at shut off.

Designers should also verify that the peak pressure that could be developed by the fan at shut-off is less than the rated pressure of all components located between the fan discharge and the shut-off damper.

3.6.8.Equipment speedLow speed equipment is generally the most efficient however slower fan impeller speed leads to the selection of larger equipment.

3.6.9.System connectionsThe configuration of the connections between the fan and the duct network are also crucial in achieving optimum fan performance and system efficiency. Poorly configured connections will impose additional resistance to flow resulting in a larger or higher powered fan than would otherwise have been required, see Section 10 for more information. Where connections cannot be configured optimally, due to site or installation limitations, fittings are available to help mitigate the effects.

3.6.10. Optional featuresMany manufacturers have optional features that allow the designer to influence the fan performance. Features like seals, wearing rings, couplings and internal coatings can all be specified by the designer when appropriate to the project to ensure long term efficiency and operability.

3.7. Selecting fans for optimum energy useFan efficiency is largely a factor of the energy losses inherent in the design which include:

Mechanical losses – resulting from friction of the shaft bearings Leakage losses – air short circuiting within the fan or leaking at the shaft represents

an energy loss Hydraulic losses – air friction, velocity changes and churning/turbulence within the

impeller and casing all represent energy losses

For a given fan there will only be one operating point associated with peak operating efficiency, called best efficiency point. Where possible, fans should be selected so that they are operating at their best efficiency point for the largest amount of time.

The key to specifying an efficient fan is to do so in terms of fundamentals including:

Fan type, impeller design, fan diameter Required flow rate and pressure Minimum acceptable fan and motor efficiency (including power factor) Maximum acceptable fan power and speed. Specified fan/system components including inlet guide vanes, wearing rings and air

dampers (balancing, non-return.

The performance of the fan is defined by the fan performance curve. The fan performance curve is matched to the system resistance curve to determine the point at which the fan and



system will operate. Both the fan and system curves can be manipulated to ensure that the operating point will be at optimal efficiency. Refer to section 6.

3.8. Fan control and energyEnergy management in HVAC&R is of growing interest and importance. Fans are at the centre of many systems and provide an opportunity to reduce costs and improve reliability by the application of design and operational solutions. Enhanced controls are at the centre of many of these solutions which utilise speed control enhanced by intelligent monitoring and management capabilities. Fan control is discussed in detail in section 7.

3.9. Right sizingCorrectly sizing the fan for the application ensures that the fan is operating at its best efficiency point and is using the minimum energy required.

Oversized fans are generally either heavily throttled or do not operate at their best efficiency point. Noisy fans generally indicate heavy throttling or excessive flow. Noise regenerated at dampers and other components of the air distribution system generally indicate high pressure drops which represent wasted energy. Oversized fans waste energy because higher flows and pressures are provided than is needed by the system. Oversized fans lead to higher initial capital costs and higher life cycle costs.

Applying excessive or multiple safety factors to fan and motor size is a common way for fans to become oversized for the application. This is particularly relevant in the selection of electric motors because motors operating well below design load are inefficient.

Under-capacity fans generally require excessive maintenance due to high operating temperatures and stresses and increased wearing in bearings.

Fan sizing is discussed in detail in section 6.

3.10. Fan EfficiencyThere are numerous separate efficiency factors that combine to make up an overall ‘Fan efficiency’, some are controlled in manufacture and design and some are controlled in fan application. Some of the separate efficiency factors that need to be considered include:

The fan impeller/housing efficiency The fan bearing efficiency The transmission efficiency The motor efficiency The control efficiency

All of these separate efficiencies need to be considered when determining the efficiency of the fan unit.

3.11. Estimating fan energy useEstimating the energy use for different ventilation solutions can provide useful criteria for assessing different proposals.

Energy use is often the largest cost element over the full working life of the fan. Fan energy use can be estimated if the system operation or output pattern is known, or can be accurately predicted.

The air power (Pu) is given by multiplying the volume flow rate by the system pressure loss, qv x pt. However, the electrical power input Pe, is expressed in AS ISO 5801as

Pe = qv·pt

ηr·ηb·ηT·ηm·ηc

Equation 3.11a

Where:

Pe = the electrical input power, (W)



qv = the flow rate, (m3/s)pt = fan total pressure, (Pa)ηr = fan impeller efficiency, expressed as a decimal between 0 and 1.0ηb = fan bearing efficiency, expressed as a decimal between 0 and 1.0ηT = transmission efficiency, expressed as a decimal between 0 and 1.0ηm = motor efficiency, expressed as a decimal between 0 and 1.0ηc = control efficiency, expressed as a decimal between 0 and 1.0.

All of these separate factors influence the power consumption of the fan and all require consideration during the energy assessment of the whole fan assembly. Fan motor power means the power delivered to a motor of a fan, including the power needed for any drive and impeller losses.

If the system flow qv is constant then the calculation of power consumption is relatively simple.

If the system flow qv varies over time then a time-based usage pattern needs to be established before the input power required can be calculated. For instance, if a system incorporates a variable speed motor then the fan will consume different levels of energy at different efficiencies at different operating points. The efficiency or level of energy used should be plotted on the same time base as the usage values. The area under the curve then represents the total energy used by the system in kilowatt hours (kWh) for the selected operating cycle. If there are differential power costs at different times of day or at different power usage levels then these must be included in the analysis. The total cost of input energy can then be calculated for each system or option under review and normalised to a common time period.

Due to the complexity of these calculations computer software is commonly used to estimate system energy use in variable flow systems. Where variable speed drives (VSD) are used to vary the flow additional energy considerations are needed.

3.12. Calculating energy savings with variable speed drives (VSDs)

Substantial energy savings can often be achieved by using variable speed drives (VSDs) to vary the output of a fan in response to actual system demands. VSDs are not appropriate for all applications, however. When deciding if the installation of a VSD is the right choice, it is important to accurately calculate the potential energy savings. Part of such an analysis involves applying a set of equations known as the fan laws (refer Appendix A). However, other system effects of the variable speed drive also need to be considered. The best practice approach is to carefully consider part-load efficiencies of the VSD, the motor, and the fan itself, as well as drive losses.

Efficiency reductions at part-load are often not considered. Performance changes of the fan generally represent the biggest loss in efficiency. This can be determined from the manufacturer’s performance curve for the particular fan. Motor efficiency may also reduce rapidly at loads less than 40%-50% of the rated full load. VSD efficiencies can be as low as 11% for small and very lightly loaded motors, and even at full load may range from 89%-97% depending on motor size. Drive losses should also be considered and may vary from 2%-5% for direct drives to as high as 10% for belt drives on small motors.

Of equal importance in deciding whether a VSD is an appropriate choice is an evaluation of the required loads. If the loads do not vary substantially and the existing fan is simply oversized (overcapacity), it is often more cost effective to replace the fan with a properly sized unit rather than to install a VSD.

The best practice in calculating energy savings associated with VSDs is to apply the fan laws and to carefully account for all losses in efficiency at part-loads.

3.13. Calculating return on investmentFor any investment option there is often a need to calculate the return on the investment (ROI) in monetary terms, so that the economic outcomes of the proposal can be adequately



considered. There are many ways to calculate the return on investment for a particular strategy, ranging from the very simple to the very detailed; the following brief explanations are provided as an introduction to the topic.

3.13.1. Simple payback periodCalculating a simple payback period is the most basic of economic analysis tools and the simplest to apply. It is most applicable in situations where a reduction in operating costs relative to business as usual (or some other alternative) will be achieved. Simple payback roughly calculates the number of years before capital is recovered but does not include savings beyond that time, and therefore does not calculate return on investment (ROI).

Simple payback period can be calculated using the following equation:

Payback Period (Years) = Total Investment ($) / Savings per year ($)

The advantages of this simple payback analysis is that it is intuitive and easily understood, does not rely on discounting and does not require a specified equipment or system life span.

3.13.2. Net present value analysisNet Present Value (NPV) analysis calculates the net value of an alternative in today’s dollars terms so that direct comparisons can be made. It is the recommended tool for identifying the optimal outcome among a number of options

The major benefit of NPV is that it acknowledges the time value of money; that is $1 today is worth more than $1 in the future. The time value of money is represented in the calculations by a ‘Discount Rate’ which reduces the value of money in future years by a certain rate per year (usually in the range of 5-10% depending on the application).

The ability to include discount and inflation rates (as well as other factors as required) results in the generation of a good indication of the economic outcome of an alternative, however as these rates are assumptions of future trends they can also introduce a degree of inaccuracy.

3.13.3. Internal rate of returnInternal Rate of Return (IRR) analysis is similar to NPV however rather than attempting to calculate a monetary value as the output it identifies the discount rate at which the NPV is zero. This eliminates one of the assumptions required for NPV calculations. IRR has benefits over NPV but it does require some understanding of the underlying economics for the output to be meaningful and is therefore not always effective when persuading others.

3.13.4. Life cycle costingLife Cycle Costing (LCC) is a systematic methodology for assessing all the significant costs of ownerships over a selected period expressed in equivalent monetary terms. It recognises that the various operational elements within a HVAC&R system are inter-related over time. A decision made today will not only affect present functioning but will also have an impact over the working life of the system.

Apart from purchase and installation or capital costs, the ongoing life cycle costs are formally titled "Cost-in-use" and comprise operating, maintenance, cleaning, alteration and replacement costs. These costs often far exceed the initial capital cost when taken over the useful life of a system. In addition choices may have other long term impacts (noise, air quality, thermal comfort) than may be immediately apparent. There is an obvious incentive towards the concept of life cycle costing for an owner-occupier whose interests are best served by ensuring economics for the life of the plant as compared with a developer with motivation towards selling or leasing. An application guide to life cycle costing is provided by Australian Standard AS/NZS 4536.

LCC is an appropriate method of comparing the financial implications of various technical alternatives. Life Cycle Analysis (LCA) goes one step further; to compare financial and non-financial aspects.



3.14. Life Cycle Analysis (LCA)Life Cycle Analysis (LCA) is a detailed analysis technique that aims to quantify all benefits and costs, past, present and future, attributable to an action or product whether they are direct or indirect. LCA goes beyond simply maximising economic returns, it also aims to minimise environmental costs and quantify and value other long term system characteristics such as noise, air quality or thermal comfort.

Any life cycle analysis needs to consider the total costs of ownership and operation over the expected life of the system (or some defined calculation period) including:

Initial costs – Purchase costs for fan, ducts, components including transportation, storage, insurance and the like.

Installation costs – Labour and material costs associated with installation and commissioning.

Energy costs – The cost of purchasing/providing energy to operate the system, present and future cost.

Operating costs – Any costs of system supervision and management Maintenance costs – Labour and materials associated with maintenance. Failure costs – Costs associated with fan failure. Environmental costs – Any environmental costs incurred. Decommissioning costs – the labour, transport and disposal costs associated

with decommissioning, removing and disposing of the system at end of its useful life.

Many of these costs can be influenced by choices made by the system designer and installer. For example maintenance costs will be a function of the time and frequency of service and the materials required. The designer can influence these costs through the materials of construction, quality of plant and components, and ease of access and facilities provided for service.

It is rare that the selection based of lowest first cost provides optimal life cycle costing, and the designer should remain aware of this when evaluating alternative options.

Figure 3.1 Typical life cycle costs of a fan



4. Fan performance

4.1. Section IntroductionThis section discusses the performance rating of fans, the tests used to rate performance, how test data is turned into performance information, the limitations of the test methods and the data produced. The section also discusses fan and system efficiency and the overall impact of fans on system energy use.

4.2. Fan testingIn order that the performance of various products can be compared fan manufacturers must rate the performance of their equipment in accordance with a recognised Code or Standard. The following are the main fan test methods and standards used by fan manufacturers:

AS ISO 5801 deals with the determination of the performance of fans of all types except those designed solely for air circulation e.g. ceiling fans and table fans. Estimates of uncertainty of measurement are provided and rules for the conversion, within specified limits, of test results for changes in speed, gas handled and, in the case of model tests, size, are given. This standard allows the use of a star type straightener for ducted tests. AS ISO 5801 superseded AS 2936.

AS 4429 classifies smoke-spill fans and describes laboratory test methods and procedures used to rate their performance (and that of their motors). Fans are rated in terms of their suitability to operate continuously without significant loss of performance for a specified time at a specified air temperature. This Standard deals only with laboratory type testing and does not consider the testing of smoke-spill fans after they have been installed in a building. Performance ratings are specified in AS/NZS 1668.1.

ANSI/AMCA 210 / ANSI/ASHRAE 51 Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating defines uniform methods for conducting laboratory tests on housed fans to determine airflow rate, pressure, power and efficiency, at a given speed of rotation. The standard also includes requirements for checking effectiveness of the airflow settling means and testing for chamber leakage. This standard and test method(s) is equivalent to but not identical with AS ISO 5801.

ISO 12759 specifies requirements for classification of fan efficiency for all fan types driven by motors with an electrical input power range from 0.125 kW to 500 kW. It is applicable to (bare shaft and driven) fans, as well as fans integrated into products. Fans integrated into products are measured as stand-alone fans. It is not applicable to fans for smoke and emergency smoke extraction; fans for industrial processes; fans for automotive application, trains, aircraft, etc.; fans for potentially explosive atmospheres; box fans, powered roof ventilators and air curtains or jet fans for use in car parks and tunnel ventilation.

ISO 5802 deals with the determination of the performance of fans as they are installed within a system, i.e. an in-situ performance test method.

ISO 13347 deals with the determination of the acoustic performance of industrial fans. In addition, it may be used to determine the acoustic performance of fans combined with an ancillary device such as a roof cowl or damper or, where the fan is fitted with a silencer, the sound power resulting from the fan and silencer combination

ISO 13350 deals with the determination of the performance of jet fans.

ISO 14695 describes a method of measuring the vibration characteristics of fans and ISO 14694 gives specifications for vibration and balance limits of fans of all types, except those designed solely for air circulation.

ISO 1940 specifies balance tolerances, the necessary number of correction planes, and methods for verifying the residual unbalance for rotors in a constant (rigid) state



Recommendations are given concerning the balance quality requirements for rotors in a constant (rigid) state, according to their machinery type and maximum service speed. A balance quality grade of G6.3 is appropriate to most fans and a grade of less than G2.5 is usually only achievable on very special equipment. ISO 1940.1 states acceptance criteria for the verification of residual unbalances. Detailed consideration of errors associated with balancing and verification of residual unbalance are given in ISO 1940.2.

4.3. Test configurationsFan performance curves are produced by the manufacturer by testing a fan in standardised conditions as prescribed by the relevant standard such as AS ISO 5801.

There are four standard test configurations that attempt to represent the range of basic fan applications as shown in Figure 4.1. Roof ventilator fans are represented by Type A, roof discharge fans by Type C. Centrifugal fans in air handling units or plenums are likely to be represented by manufacturers as Type B. Type D is the one most likely to be closest to the representation of both axial and centrifugal fans in many ducted ventilation and air conditioning applications. Many heat rejection fan applications are represented by Type A.

Drafting note: change ‘Category’ to ‘Type’

Figure 4.1 Fan test configuration ‘Types”

Centrifugal fan performances have usually been derived from measurements for fans with free inlets and ducted outlets, but this depends on the size and type of fan. For axial fans, ducted inlets and ducted outlets have usually been used. These methods have been adopted for convenience since for double width centrifugal fans flow measurement at the inlets would be difficult and for axial fans the presence of swirl at the outlet causes complications. Flow straighteners are used to remove the swirl in AS ISO 5801.

4.4. Fan performancePerformance data may be presented either graphically (in a fan curve) or in tabular form (in a rating table). Performance data is either listed for standard air temperature and pressure, or the air temperature, density and pressure at which the tests were carried out are listed so that appropriate adjustments to expe3cted performance can be made.



Note: standard (air) temperature and pressure (STP) is defined as clean, dry air with a density of 1.2 kg/m³, a sea level barometric pressure of 101.325 kPa and a temperature of 21 °C.

It should be remembered that catalogued fan performance data is the result of testing generally without any obstructions in the fan inlet or outlet and without any “optional” accessories in place. Unless careful design of inlets, outlets and ductwork has been undertaken, a fan will not perform in practice as per the catalogued performance data. Appropriate pressure drop corrections should be applied when obstructions and accessories exist and to account for the effect of the system connections. This is discussed in detail in Section 10.

4.5. Fan performance curvesThe fan performance or characteristic curve is a graphical representation of fan performance and is one of the most useful tools for optimising fan selections. A series of performance curves for a particular fan type is usually presented as a graph of flow versus pressure and flow versus power with a separate curve for each particular speed.

Fan performance curves are developed based on standard tests measuring the output of a fan, its volume flow rate and pressure, for a range of conditions. This concept is shown in Figure 4.2, with tests ranging from the flow being fully closed off to when the air path is completely open, all measured at a constant fan speed (although fan speeds do vary when testing). At the same time, the power input to the motor is recorded.

Figure 4.2 The creation of a fan performance curve

Drafting note: X axis is static pressure. Change SP to ps and VP to pv

The fan performance graph is generally composed of a series of separate performance curves including:

Static pressure Vs Volume curve – Called the fan performance or fan characteristic curve, this is a plot of static pressure against volume at a constant speed/gas density.

Fan total pressure (pt) and velocity pressures (pv) are also plotted against volume.

Note: pt = ps + pv, therefore pt can never be less than pv, so the fan performance curve doesn’t reach zero pressure, but rather pv. When volume flow is zero pt = ps and pv = 0

Power Vs Volume curve – plot of the fan power drawn for any point on the performance curve.

Efficiency Vs Volume curve – plot of fan efficiency for any point on the performance curve.

The efficiency curve is produced by dividing air power (air power = pressure in Pa x volume flow rate in m3/s) by the motor shaft power. This can be static efficiency (using Ps) or total efficiency (pt).



Total Efficiency % = airflow (m 3 /s) x Total Pressure (Pa)

10 x Power absorbed or shaft input Power, in kW

Static efficiency % = airflow (m 3 /s) x Static Pressure (Pa)

10 x Power absorbed or shaft input power, in kW

Note: ISO12759 allows for motor input power / air power.

Using the test data, a complete set of fan performance or fan performance curves is produced as illustrated in Figure 4.3.

Fan performance curves offer a convenient method of fan selection as well as additional information such as the amount of reserve pressure that exists between the design pressure and peak available pressure, the maximum power the fan may draw and the likely efficiency of operation.

Figure 4.3 Fan performance curves showing recommended selection range

Typical ‘generic’ fan performance curves for common fan types are shown in Figure 4.4

Figure 4.4 Typical ‘generic’ fan performance curves

Drafting note: add radial bladed fans, decrease vane axial performance to below backward curved aerofoil


Optimum selection range


Note: None of these curves would ‘hunt’ as the system resistance curve would need to intersect the fan curve at 2 points. However, a steeper vane axial fan curve to the left of peak pressure, would lead to instability for certain specific system curves, hence the warning “Possibly Unstable”.

NOTE: Some designers prefer to select at 10-15% below peak pressure.

These ‘typical’ curves are exaggerated and idealised indicative performance curves. Individual (real) fans will perform differently from this, although the attributes will be similar. This includes the areas of instability shown where the fan can flip between two possible flow rates at the same pressure (hunting) or instability as a consequence of the fan stalling (refer to section 7). Some axial flow fans have adjustable pitch blades of which the first 10-20 degrees have a non-stalling characteristic. Manufacturers will generally identify recommended working ranges for their products within their technical literature.

4.6. Published and certified performance curvesThe fan performance curves generated under test become the basis of the catalogue curves and selection tables used by manufacturers to market their products. The manufacturing process and associated tolerances are designed to ensure that a fan will match the catalogued performance.

When purchasing or specifying a fan designers can request its certified performance curve to ensure compliance with the published data. Unlike the published curve which represents a general curve, or set of curves, for a fan model and size, the certified performance curve reflects the actual test results for a particular fan.

4.7. Fan selection aids

4.7.1.Selection chartsA selection chart shows the performance map for a family of similar fans. They are often formatted on semi-log or log-log scales to display a wide range of flow and pressure on a single chart. The chart shows the various fan sizes/designs available and a selection is made by evaluating the fans with a best efficiency point near the specified operating points.

Once the fan size has been selected the individual fan performance curve should be consulted for full details of the fan performance, capability and characteristics.

4.7.2.Fan rating tablesSimilar to fan selection charts multi-rating tables have traditionally been used for centrifugal fans. Usually flow, pressure and power are tabulated, for equal increments of outlet velocity for a given size of fan.

These tables can be used for fan selection although some interpolation may be required.

4.7.3.Computer selection programmesMore frequently used than traditional charts or tables, computerised data selection allows for the rapid selection of many possible fans at the click of a button. The most appropriate choice will still depend on the many factors described in this manual. Specifiers and designers should review choices in detail rather than rely on a choice made from a brief comparison summary table.

4.8. Interpreting fan manufacturer dataWith a basic understanding of the fan performance curve, designers can predict the way the fan performance would change if the fan characteristics were changed or if combinations of fans (series and parallel) are used in a system (refer Section 5). However, designers need to be aware of the following uses when interpreting performance curves:

Fan performance curves are developed under controlled test conditions with the fan installed with favourable inlet and discharge connections. These connection conditions are often not able to be replicated in the field.



Fan performance curves are developed under a specified air condition (temperature, pressure, density), the air conditions prevalent during the test. Check at what actual conditions the fans have been tested at, do not rely on the term “Standard” to identify this as this does vary between locations of the fan test centre.

Fan performance curves are generally developed without any of the optional accessories that may be available. Some accessories may alter the aerodynamic performance of the fan and hence will vary from the standard performance curve.

Fan noise is a function of the fan design, volume flow rate, total pressure and efficiency. The sound power generation of a given fan performing a given duty is best obtained from the fan manufacturer’s actual test data taken under standardised test conditions. However test conditions vary and some manufacturers display actual measured data without manipulation while others manipulate data to provide example in-duct noise levels which changes for each different installation. The true measured sound power data is the only way to compare how each fan will perform in the specific installation. Manufacturers generally have available descriptions of how the fans are tested and how the data is presented.

Different manufacturers may use different test standards to test their product e.g. ISO, AS, EN, AMCA test standards etc. These standardised test methods are all similar but not identical. When comparing fan performance it is important to understand the basis of the fan performance curves.

It must also be remembered that any field testing (e.g. during commissioning) will produce a different result to the laboratory testing carried out by the manufacturer. All appropriate corrections must be made for all deviations from the ideal laboratory test configuration before a valid comparison between test data can be made.

4.9. Derating manufacturers dataApart from fan inlet or outlet obstructions or “optional” accessories there are other reasons why a fans performance data may need to be derated for a particular application.

Ratings found in performance tables and curves are based on a nominated air temperature and pressure. Selecting a fan to operate at conditions other than the nominated conditions requires performance data to be adjusted.

Other reasons why a fans performance might need to be derated for a particular application include:

Fan speed – Operating the fan at a speed not indicated on the performance curves Gases other than air – Most fans are tested with standard air and if the application

involves a gas other than air corrections to performance need to be made. Contamination of air stream – fans are tested with clean air and if the application

involves air contaminated with dust or moisture corrections need to be made.

Axial fans performance data is generally catalogued as Type D but there are manufacturers who show the impact on the fan performance in Types A, B and C installations. It is important to determine in what Type of installation configuration the performance data was defined.

4.10. Fan Laws

4.10.1. About the fan lawsIt is not practicable to test the performance of every size of fan in a manufacturer’s range at all speeds at which it may be required to run, and with every gas density it may be required to handle.

Fortunately, by use of the Fan Laws, the performance of geometrically similar fans of different sizes or speeds can be predicted sufficiently accurately for practical purposes.



Total accuracy would require that the effects of, surface roughness of the fan, the viscosity of the gas and scale effect to be taken into account for example. For the vast majority of fan calculations in HVAC&R applications this level of accuracy is not necessary.

It is important to note, however, that the Fan Laws apply to a given point of operation on the fan characteristic. They cannot be used to predict other points on the fan performance curve.

4.10.2. Applying the fan lawsThe fan laws are most often used to calculate changes in flow rate, pressure and power of a fan when the size, rotational speed or gas density is changed. In the following Laws the suffix “1” has been used for initial known values and the suffix “2” for the changed values and the resulting calculated value:

q2=q1×( n2

n1)×( d2

d1)

3

Equation 4.11.1

p2=p1×( n2

n1)2

×( d2

d1)2

× δδ1 Equation 4.11.2

P2=P1×( n2

n1)3

×( d2

d1)5

× δδ1 Equation 4.11.3

Where:

q = volume flow of air, m3/s

p = pressure developed by fan, Pa

δ = density of air, kg/m3

n = fan rotational speed, m/s

d = diameter of impeller, m

P = power absorbed by fan, kW

When a significant change of density occurs between the fan inlet and discharge, the arithmetic mean of the density and volume is used. For fans operating at pressures below 2.5 kPa the above fan laws may be taken to apply when using inlet volume and inlet density.

These laws are simplified when one or more of the variables remain unchanged. For example when the gas density is constant, the ratio d2/d1 equals 1 and can be omitted from the equation.

Similarly, if the diameter is also constant as with an existing fan, D2/D1 is 1 and this too can be omitted. Only the speed variation laws then apply, as follows:

q2=q1×(n2 )(n1 ) Equation 4.11.4

p2=p1×(n2)2

(n1)2 Equation 4.11.5

P2=P1×(n2)3

(n1)3 Equation 4.11.6

A summary of the fan laws is provided in Appendix A.



5. System design and specification

5.1. Section introductionThis section discusses the theory behind fan and air distribution system design. The system resistance curve is explained and how the fan performance curve is used with the system resistance curve to define fan operation. As well as discussing the performance and design aspects of single fan systems the application and performance of fans operating in parallel as well as fans operating in series is also explained.

5.2. Constant air volumeA constant air volume system will deliver an unchanging air flow. In HVAC&R applications constant volume systems provide either, a consistent rate of ventilation or, with a varying supply air temperature, air conditioning of an area with varying load demand can be achieved.

5.3. Variable air volumeA variable air volume system will deliver a changing air flow in response to the system demand. Supply air fans on variable air volume (VAV) systems are typically controlled to maintain static pressure in the duct system at a given set point. Fans can also be controlled on temperature or manual feedback.

5.4. The systems approach

5.4.1.System pressure requirementsFans cannot be designed in isolation from the air distribution system and designers and fan suppliers need to take a holistic ‘systems’ approach.

As air is moved through a ducted system, the energy (pressure) given to the air by the fan is progressively lost by friction of the air against the duct walls, by turbulence at bends, dampers and changes of duct section and by pressure losses through heaters, coils, filters, terminal units, diffusers and grilles or other items of equipment in the system.

The loss of pressure due to all these sources, known as the system resistance, is for practical purposes proportional to the square of the velocity at the point of loss.

It should be noted that the assessment of system resistance is the sum of the ‘total pressure’ losses throughout the system. However, the value obtained is generally called static pressure as the velocity pressure at the end of the system is generally a very low value.

5.4.2.System resistance calculationsAccurate system resistance calculations are necessary if the fan is to perform in accordance with the required system design.

It is recommended that calculation of the system resistance be carried out by estimating changes in total pressure throughout the system. Pressure losses in both the supply and return/exhaust networks are additive and hence the total pressure always decreases from the discharge of the fan through to the inlet. Static pressure, on the other hand, may change in either a positive or negative sense depending upon changes in velocity in the system. Figure 5.1 is a diagrammatic representation of a typical ductwork system and shows in graphical form the changes in both static and total pressure (below and above atmospheric pressure) which take place. The steep rise in both pressures near the centre of the diagram represents the pressure rise through the fan.

For detailed information on calculating ductwork system resistance refer to the AIRAH DA03, and for calculating the system effect refer to Section 10.



5.4.3.HEPA filter resistanceA frequently encountered variation to the square of the velocity rule occurs where high efficiency particulate air (HEPA) filters are included in the system. For HEPA filters the flow/resistance relationship is approximately linear. This is because:

The pressure drop over the filter is small when clean and high when dirty! The filter media velocity is small at all times which flattens the relationship profile The pressure drop represented on filter resistance curves is time related hence the

linear relationship HEPA filters exhibit a low Reynolds number through filter medium

In a system where the pressure loss across HEPA filters represents a significant proportion of the total system loss, care should be taken to account for this linear relationship.

Figure 5.1 Graphical representation of pressure gradients through a typical fan system

Drafting note: Terms like TSP, FVP, FSP, SP, TP to be changed to the ISO Standard.

Figure 5.2 Fan and duct system curves showing ‘design’ operation point

Drafting note: ‘Design Static Pressure’



5.4.4.Effects of errors in estimating system resistanceSince fans are seldom installed in a manner identical to standard test conditions, the utmost care must be exercised in designing the system, particularly that part close to the fan, so that design performance can be achieved.

When system pressure losses and the system resistance curve have been inaccurately estimated, or when undesirable fan inlet and discharge conditions (termed ‘system effect’) exist, design performance may not be attained.

These situations are illustrated in Figures 5.3 and 5.4. Note that the interaction of the actual system resistance curve and the fan performance curve determines the actual volume flow rate.

Figure 5.3 Fan and duct system curves showing ‘off design’ points

Drafting note: ‘Design Static Pressure’

Figure 5.3, Curve ‘B’ shows a situation where an actual duct system has more resistance to flow than was expected. The fan is operating as tested. This condition is generally the result of practical variations from the designer’s estimate of system resistance to flow. This can be a problem if the initial design estimation calculation of system resistance was inaccurate or if the installation of the system has varied from the design. All losses must be considered when calculating system pressure losses or the final system may impose a greater resistance on the fan and actual flow rate will be deficient (Point 2).

If the actual system pressure loss is greater than design, as in System B, Figure 5.3, an increase in fan speed may be necessary to achieve the design volume flow rate at Point 5. Before attempting to increase fan speed, a check should be made with the fan manufacturer to determine if the speed can be safely increased and also to determine the expected increase in power and noise level. The connected motor may not be able to handle the required increase in fan power.

Note: Fans are products that are manufactured repeatedly and so are basically similar within size and model ranges. On the other hand, no two duct systems are the same. As a result, assuming a reputable manufacturer has supplied the fan; problems are usually caused by incorrect system resistance calculations or installation factors.

5.5. The ‘System Effect’Very few duct-connected on-site fan installations are consistent with the manner in which the fan performance was tested by the manufacturer. Losses due to duct, fittings and accessories are known and can be calculated. The effect of less-than-ideal aerodynamic connections on the fan’s performance (known as the “System Effect”) must also be allowed.

Point 1 in Figure 5.4 depicts the calculated design point with the system pressure losses accurately determined and a suitable fan selected for operation at that point. If, however, no allowance has been made for the effect of the system connections on the fan’s performance, the actual system resistance curve may cut the fan performance curve at Point 4. To obtain



the design airflow the fan should then be selected to operate at Point 2. To compensate for this ‘system effect’ it will be necessary to include additional losses in the calculated system pressure loss to determine the total system resistance curve. The ‘system effect factor’ is a factor which, when multiplied by the velocity pressure, gives an estimate of the extra system effect.

The system effect factor and ways to account for it in the system design process is described in detail in Section 10.

Figure 5.4 Deficient system performance when System Effect is ignored

5.6. Safety factorsSystem designers sometimes apply “Safety Factors” to their estimate of the system resistance to safeguard against inaccurate evaluation and design uncertainties. Design uncertainties are associated with predicted airflows and pressure requirements, allowance for future expansion, performance degradation over time, fouling effects and the like.

On occasion these “Safety Factors” may compensate for resistance losses that were overlooked and the actual system will deliver design flow (Point 1, Figure 5.3). The usual result, however, is that the estimated system resistance including the “Safety Factors” is in excess of actual system resistance. Since the fan has been selected to design conditions (Point 1), it will deliver more air (Point 3) because the actual system resistance at the design flow rate is less than design (Point 4). This result may not necessarily be an advantage because the fan may be operating at a less efficient point on the performance curve and may require more power than at design flow. It may also result in much higher noise levels.

Under these conditions it may be necessary to reduce the fan speed, adjust a damper to increase the actual system resistance (Curve C) to the value determined in the design calculations (Curve A) or, if an axial fan, adjust the pitch angle of the impeller.

Note: Varying fan speed is preferred over varying system resistance (damper) for energy reasons and specifying variable speed drives can significantly reduce or remove the need for additional ‘ safety factors’.

5.7. Deficient fan/system performance

5.7.1.Causes of deficient performanceThe three most common causes of deficient performance of the fan/system combination are:

Improper outlet connections Non-uniform inlet flow Swirl at the fan inlet

These conditions alter the aerodynamic characteristics of the fan so that its full flow potential is not realised. They will occur if the fan inlet and/or outlet connections are not properly



designed or installed. One bad connection can reduce the fan performance far below the catalogue rating, refer to Section 10.

Other major causes of deficient performance are:

Design or installation of less than optimal air distribution ductwork and duct fittings. The air performance characteristics of the installed system are significantly different

from the system design engineer’s intent (see Figure 5.3). The system design calculations do not include adequate allowances for the effect of

accessories and fittings in the system or the fan selection was made without due allowance for fan accessories.

The “performance” of the system is determined by inappropriate or inaccurate field measurement techniques.

The maintenance of filters, coils etc. is neglected. Dirty filters, dirty ducts, and dirty coils will increase the system resistance and consequently reduce the airflow, often significantly.

The system performance has changed due to malfunction, adjustment or changes of control elements used in the system.

Incomplete sealing of ducts allowing air leakage into/out of the system between fan and point of measurement.

5.7.2.Preventing deficient performanceThe following design precautions should be made to prevent deficient performance:

Design the connections between the fan and the system to provide, as nearly as possible, uniform straight flow conditions at the fan outlet and inlet. (See Section 10).

Use appropriate allowances in the design calculations when space or other factors dictate the use of less than optimum arrangement of the fan outlet and inlet connections.

Include adequate allowances for the effect of all accessories and fittings on the performance of the system and fan. If possible, obtain fan manufacturer data on the effect of accessories on the fan’s performance.

Use field measurement techniques which can be applied effectively on the particular system. Be aware of the probable accuracy of measurement and the conditions which affect this.

Include fan operating and maintenance information in the system documentation. Document the design, function and interaction of control elements used in the

system.

5.8. Fans in series

5.8.1.General principlesTwo or more fans may be connected together in series so that the flow passes through each fan in turn. In this arrangement the flow is constant but the pressure is increased by each successive fan. The series arrangement can be achieved either using separate machines or a number of impellers on a common shaft.

Where separate machines are installed, these can have all impellers rotating in the same direction or successively rotating in opposite directions.

The effect of adding a second stage to an existing fan is therefore given by moving up the system resistance line from “A” to “A1” in Figure 5.5. The relative increase in flow depends on the point of operation on the characteristic as shown by other typical system resistance lines “B” and “C”. Series operation can be used as a method of controlling the flow through a system by shutting down fans as appropriate, but the resistance to flow of those fans not



being driven should be allowed for in the calculations and reference should be made to the fan manufacturers.

Figure 5.5 Characteristics of Two Fans in Series

5.8.2.Axial fans in seriesFor axial fans where the separate fan impellers rotate in the same direction, inter-stage guide vanes must be present. This also applies to more than one impeller on the same shaft. The guide vanes ensure that each impeller receives its flow with little or no pre-swirl, and that each impeller absorbs approximately the same power. In practice this arrangement results in each fan producing approximately the same static pressure rise. Thus the static pressure rise for the complete machine approaches the sum of the static pressure rises of each stage, less any interstage losses in connecting channels or ductwork.

Where the impellers rotate in the opposite direction, as is quite common on axial flow fans, the static pressure rise for a pair of impellers can be as much as 2.5 to 3 times that for the single impeller running without guide vanes. Such an arrangement permits relatively high pressures and efficiency being achieved from a compact assembly. The air leaves the assembly in an axial direction and without swirl.

Contra-rotating axial flow fans tend to have a higher noise level than a larger, single-stage axial fan handling the same duty. They generally take up less space. Where required, more than two stages can be assembled to develop even higher pressures. Again reference should be made to the fan manufacturers for more information.

5.9. Fans in parallel

5.9.1.General principlesWhere two or more fans receive air from and deliver into a common system they are said to operate in parallel.

While it is fairly obvious that two identical fans designed to run in parallel in a system will each handle half the air quantity being delivered, the addition of a second identical fan in parallel to one in an existing system will not double the airflow through it because the system resistance rises.

The actual effect is shown in Figure 5.6 where the air volume Qa handled by a single fan operating at Point “A” is shown to increase to Qa1, when a second identical fan is introduced in parallel to it. The operating point moves up the system resistance line from “A” to “A1”.

Relative increase in flow is governed by the point of operation on the characteristic as shown by reference to two other typical system resistance lines “B” to “B1” and “C” to “C1”.

Furthermore, if the actual operating point of a single fan had been “D” there would be no increase in flow at all if a second fan were added in parallel.



Figure 5.6 Characteristics of Two Fans in Parallel

NOTE: Most fan characteristics have a "positive" slope to the left of the peak pressure point and parallel operation on this portion of the curve should be avoided since it can lead to unstable operation. In the case of a forward-curved centrifugal fan such an unstable zone is shown to the left of “E” in Figure 5.6.

Point “D” falls in this zone. The closed loop from point E is the result of plotting all possible combinations of volume flow at each pressure point. Since the system resistance curve intersects the fan performance pressure curve in the area enclosed by the loop, more than one point of operation is possible. The unbalanced, or unstable, flow conditions reverse readily with the result that the fans will intermittently load and unload. This phenomenon is known as "hunting" with the result that pulsing occurs which generates noise and vibrations that may damage fans and ductwork.

This problem gets worse as more fans are coupled in parallel. A way to avoid this is to select a fan or a pitch angle where there is no ‘stall dip’ and then combining these. Sometimes this is not possible and then operation should be avoided in the looped area.

A similar type of instability or “hunting” can also occur when the system resistance curve and the fan performance curve are almost parallel at the working point of the system.

Since the load is changing on the fans, motor power will also fluctuate and may cause overload problems. Fans operated in parallel should be of the same type, size, speed and with identical inlet and discharge flow conditions, otherwise undesirable performance complications may result. It is strongly advised that the advice of the fan manufacturer be sought when considering the use of fans in parallel.

Advantages:

Can be beneficial where space (e.g. height) is restricted and the appropriate fan will not fit.

Allows for partial standby in the event of one fan failure. Volume capacity control. Switching on and off fans depending on volumes required. Stand-by capacity possible. Generally cheaper than one large unit.

Disadvantages:

Additional installation cost including more complex ductwork and electrical needs. Noise generation may be excessive Non-return or motorised damper control required on fans designated for on/off

operation so that back draft through non-operating fan is not occurring.

For fans in parallel adequate distance between fans and walls must be provided to ensure proper intake conditions.



5.9.2.Control of parallel fansWith several, independently driven, fans working in parallel, some control over the total flow can be obtained by switching off a suitable number of fans. If this form of control is used, it is essential to provide isolating dampers or non-return valves on the inlet or outlet of all fans to prevent short-circuiting of air through the stationary fans. Dampers are also required when the parallel arrangement is used to allow a stand-by fan to be brought into action quickly when, in the event of a failure of one fan, the remaining fan(s) can continue to supply into the system.

5.9.3.Noise considerationsA noise problem often encountered with fans operating in parallel is beating. This is caused by a slight difference in speed of rotation of the two theoretically identical fans. The resulting low frequency beating noise can be very annoying and difficult to eliminate. The problem can be likened to the stroboscopic effect of a fluorescent light illuminating a rotating wheel with a slight difference between the frequencies of rotation of the wheel and the AC supply to the light.

5.9.4.Axial fans in parallelThe use of axial flow fans in parallel presents very real potential noise problems unless special measures are taken at the design stage; add-on noise control is not normally possible.

5.10. Fan stallFans, like aircraft, follow basic laws of aerodynamics. If a fan is incapable of delivering the pressure required by the system, flow separation may occur around the blade, resulting in unpredictable performance, unstable operation and increasing noise levels.

The point on the fan performance curve where the pressure being generated stops increasing and falls off is called the stall point (refer to figure 5.7). The tendency to stall is largely dependent on blade design and some fan types are less prone to stall (or can operate in partial stall) than others. Many axial fans have a stall region on their fan performance curve which makes them unsuitable for systems with widely varying operating points.

A fan operating at or near the stall point can have:

Significant mechanical damage due to aerodynamic shock forces (particularly on the blades).

Varying flow over time. Severe increases in noise generation. Poor operating efficiency.

Centrifugal fans are less prone to damage from stall than axial fans.

5.11. Fan surgeSurge occurs within a fan when the energy imparted to the air alternates between creating kinetic energy (air velocity) and potential energy (air pressure) resulting in an oscillating effect that is audible. Surge can occur when the following conditions are met:

High volume of pressurised air High velocity air in ductwork Fan operating at a point to the left of the peak pressure

5.12. System huntingThe term hunting applies to an under-damped control circuit. Where sensors are used to control dampers, vanes or motor speeds, and the control system responds too quickly it will



overcorrect and have to readjust in the other direction. Hunting refers to the condition where the system is continually moving back and forth without finding a stable control point.

5.13. System stabilitySystem stability refers to the ability of the system to return to its normal operating condition after it has been temporarily displaced from that condition. Some fans are not stable at all operating ranges and the fan will continue to operate at a displaced condition even though the cause of the displacement has been removed. This is sometimes referred to as bi-stable flow where the fan can operate at two distinctly different conditions in the same system.

Figure 5.7 Fan/System curve showing potential bi-stable flow points

5.14. Optimising system designsSystems can be optimised for a variety of goals including energy efficiency, life cycle costs, reliability and redundancy etc. Where energy optimisation is a key goal the following should be considered:

Reducing system resistance – Index run (size, bends, routing, and components), low pressure drop filters, coils, components, duct sizes and air velocities.

Fan location – Locate fans away from bends, transitions etc. Reducing air leakage – Fan casing leakage, duct sealing, building sealing Control – Controlling for energy efficiency outcomes, see Section 7. Commissioning – Commissioning for energy efficiency outcomes, see Section 8. Maintenance and management – Filter maintenance, duct cleaning, automatic and

remote monitoring, see Section 9.



6. Fan selection

6.1. Section Introduction

6.2. Fan selectionFan selection is a complex process that starts with a basic definition of the system operating requirements and conditions such as airflows, pressures, temperatures, properties of air stream, system layout and system operating profile. The primary factor driving fan selection is performance and any fan selected will need to match the performance required by the system. The fan selection is based on calculating the airflow and pressure requirement(s) and then matching these to a fan of the appropriate design and materials.

Fans selections are then refined on the basis of a variety of criteria depending on the application and required outcomes from the system. Competing selection criteria can include

First costs/Ongoing costs/Life cycle assessment Efficiency/Energy performance Range of operating conditions (temperature) Air/gas type, moisture content, contamination level Geometry, space constraints (e.g. drive arrangements) and structural constraints Maintenance characteristics, operating life Reliability, quality of materials, quality of components Power supply – AC, DC, single-phase, three-phase

Often a fan is selected for non-technical reasons such as price, availability (lead times) or familiarity. In HVAC&R applications fans are usually selected from a range of available models and sizes and not specifically designed for the application.

6.3. Fans and systemsFans cannot be designed in isolation from the air distribution system and designers and fan suppliers need to take a holistic ‘systems’ approach, refer to Section 5.

6.4. Fan performanceFor an explanation of the Fan Laws refer to Section 4 and Appendix A.

For a fixed system, the Fan Laws state that the pressure required to pass a given volume of air through the system will vary in proportion to the volume squared i.e. P Q2. Therefore, to double the airflow, a pressure four times as great is required from the fan.

This is true only for a constant system and a constant air density. Should the system be altered, by closure of a damper for instance, then this relationship does not directly apply. Similarly, for a fixed system, the pressure loss or system resistance will vary directly with air density.

Fan performance is defined by the fan performance curve, see Clause 4.5.

6.5. The system resistance curveFor a fixed air distribution network there will be a specific relationship between the airflow through the network and the pressure required to produce the flow, independent of the fan used. The first step in the design of any fan system should be the construction of this pressure-capacity curve for the system, called the system resistance curve.

The plot of pressure loss versus volume flow for a given system is known as the system resistance curve or system pressure loss curve. If the volume flow rate in the ductwork is varied the pressure loss will be related to the square of the volume flow rate. This may be simplified to Δp = RQ2 where Δp is the system pressure drop (Pa), Q is the volume flow



(m3/s) and R is a constant for the system relating to its resistance to airflow (the term resistance, should not be confused with system pressure drop).

Using a calculated pressure drop at any particular flow rate, the value of R may be determined and then a curve drawn for a range of volume flow rates against pressure drop, as in the system resistance curve shown in Figure 6.1.

Figure 6.1 Fan performance and system resistance curves

Drafting note: delete ‘required flow rate’ from this graph, fan efficiency is fan ‘total’ efficiency?

The fan performance curve is a series of points at which the fan can operate at a constant speed. The system resistance curve is the series of points at which the system can operate. The operating point for the fan-system combination is where these two curves intersect. This provides the flow rate for this particular fan running at a particular speed within this system.

Note: Selecting fans using fan total efficiency will not necessarily provide the fan that uses least energy because of the influence of the velocity pressure.

6.6. Operating pointWhen a fan is connected to a system the flow will stabilise at the point where the fan performance and system resistance curves intersect. This is represented by point “A” in Figure 6.2, where the system resistance curve is seen to cross the fan pressure/volume curve. Point “A” is called the operating point.

A change in the system resistance curve such as the dashed curves shown in Figure 6.2 will result in different operating points “B” or “C”. This might be caused by changes of damper position or variations in practice from the theoretical system resistance calculations.

An operating point that differs greatly from the design may lead to reduced or excessive fan power depending on the type of fan.



Figure 6.2 Effect of change in system resistance

6.7. Best efficiency point (BEP)Ensuring that the design operating point occurs near the peak fan efficiency or best efficiency point (BEP) will reduce the risk of performance problems and contribute to an energy efficient installation. The assessment and selection of these criteria is termed the fan/system best efficiency point. In order to select the best efficiency point the fan will most likely need to be matched to the system duty.

Figure 6.3 Illustration of fan Best efficiency point

6.8. Matching fans to system duty

6.8.1.Change in Fan SpeedIn a fan system a percentage change in fan speed will result in an equal percentage change in air volume handled. The pressure will vary in proportion to the square of the speed change and the power absorbed by the fan will vary in proportion to the cube of the speed change. Thus, if it is desired to increase the volume of the flow rate by 10%, this can be



done by increasing the fan speed by 10% (where facilities for speed change exist). The pressure against the fan will increase by 21% and the power absorbed by the fan will increase by 33%. The full and broken lines in Figure 6.4 illustrate such a change.

Figure 6.4 Variation in performance with 10% increase in fan speed

6.8.2.Change in Fan SizeIf an increase in flow rate is achieved by replacing the fan with a larger one of the same type, it is no longer possible to calculate the precise performance by referring to the fan and system laws only. If the larger fan is geometrically identical, (or of the same homologous series), the Fan Laws can be used to determine the volume/pressure, efficiency and power curves. The intersection of the fan performance curve with the system resistance curve will be at a different operating point and a new determination of both the operating point and the power absorbed will have to be made. This is illustrated in Figure 6.5.

Figure 6.5 Effect of 10% Increase in fan size (Speed Constant)

6.8.3.Change in Air DensityA change in air density will change both the fan performance curve and the system resistance curve in accordance with the fan laws as follows:

For a given volume flow rate pressure is proportional to the air density System pressure loss is proportional to the air density

A change of air density from standard (1.2 kg/m3) to 20% below standard is illustrated in Figure 6.6, where both the fan pressure and system resistance are reduced by 20% while the volume flow rate remains constant. In accordance with the fan laws, the fan power will vary directly as the air density. Refer Equation 4.11.3 and appendix A.

Note: Although the volume of flow is unchanged, the mass flow is changed (being proportional to density). It is important to consider this in heat exchange calculations (air density changes as a result of temperature changes) and for fans at high altitudes. Given the low altitudes in Australia altitude adjustments generally doesn’t need to be considered in most designs/locations.



Figure 6.6 Variation in Performance at Constant Speed with Change in Density (20% reduction)

6.9. Selection for smoke-spill applicationsSmoke-spill fans are type tested in accordance with AS 4429 to the conditions specified in AS/NZS 1668.1. Fans are selected to handle the design volumetric flow rate (calculated at the smoke spill air temperature) at the installed system resistance under ambient temperature conditions. Motors are selected so that they will not overload during testing at ambient conditions. All safety devices apart from fuses and circuit breakers are overridden during fire mode operation.

An appropriate allowance is made in axial flow fan impellers to allow for thermal expansion of the blades under high temperature reducing the tip clearance and affecting performance.

6.10. Fan noiseFans should be selected for quiet operation; ductwork should be sized to prevent excessive air velocities, dampers and grilles should be selected to prevent noise regeneration. In this application manual only the noise generated by the fans is discussed. The propagation, distribution and attenuation of noise in the ductwork system is discussed in AIRAH DA03. Noise propagation from the fan to the surrounding plant room and adjacent areas is discussed in the AIRAH DA02.

Tonal noise has a prominent frequency and is characterised by a definite pitch. These characteristics can make the noise more annoying than its noise level alone would suggest. Tonal noise is generated by every fan but the impeller speed and number of blades will vary the frequency and the effect on the installation.

6.10.1. Fan selection for noiseIf the typical noise spectra for different types of fans are compared (see Figure 6.7), it can be seen that centrifugal designs produce most of their noise at low frequencies, whereas axial designs generate higher frequency noise. Most people will accept higher levels of low frequency noise and this is one of the reasons why centrifugal fans are generally used if noise is an important consideration.



Figure 6.7 Comparison of typical centrifugal and axial fan noise spectra

It must be realised however, that the higher frequency tones can be more easily suppressed using simple attenuator devices, whereas reducing the lower frequency noise usually requires larger, more expensive solutions. It is sometimes possible to install a high speed, small diameter axial flow fan fitted with an attenuator, less expensively than a slower speed centrifugal fan generating similar noise levels and giving the same aerodynamic performance.

Figure 6.8 shows how fan generated noise varies as the fan duty varies and emphasises that fans are at their quietest when operating near their peak efficiency, and noisiest when running at, or near, the stalled condition.

Figure 6.8 Fan generated noise versus fan duty

Care must be taken to ensure that the airflow into the fan impeller itself is uniform, otherwise the fan will produce more noise than specified. Figure 6.9 shows arrangements which will produce highly turbulent flow into the fan. Ways of correcting the problem are also shown.



Figure 6.9 Factors Affecting Turbulent Flow in Axial Fans

Drafting note: Figure to be redrawn. Regarding bends the air will tend to hold to the inside of the bend resulting in only part of the impeller operating and the other part being partly starved of air. Also, the above are concentrated on the inlet side whilst the outlet is also important.

6.10.2. AttenuationIf the sound power level of a fan is too high, and no other selection is possible, attenuation must be introduced at appropriate locations in the system to prevent unacceptable noise being transmitted to the occupied spaces.

Attenuation can be provided by a variety of means including inserting proprietary attenuator units, changing the layout, using a plenum or by lining the ducts with absorptive material. Duct lining, especially at bends, is often adequate, providing sufficient length of duct is available. Bends are particularly useful for reducing high frequency noise, but are not very effective at low frequencies, particularly if the duct dimensions are small. Acoustic lining materials should not impart any particulate or gaseous contaminants to the airstream which could adversely impact indoor air quality.

Specifically engineered duct mounted attenuators are also available to address specific frequencies of in-duct sound. Fan noise and vibration can also be addressed by fan mounting methods or installing sound baffles around the fan (while maintaining ventilation) to absorb the sound energy.

6.10.3. System design for noise minimisationNoise generation within an air distribution system is caused by aerodynamic turbulence. If the system conforms to recommended design practice, with special attention to those areas where turbulence is likely to occur, both aerodynamic efficiency and acoustic performance will improve.



7. Controlling fans

7.1. Section IntroductionThere are several means by which the performance of a fan may be controlled. They divide conveniently into those which are continuously variable and those which are adjusted occasionally. When optimising fan systems for energy efficiency the method of control and the effect that control has on system power consumption is a significant design issue.

7.2. The control imperativeIt is frequently necessary to control the rate at which air is moved through a system. This may be a one-off adjustment to suit actual operating conditions (commissioning or fine tuning), an occasional adjustment to give, for example, a summer and winter condition, or a continuously variable adjustment to maintain an environmental condition using variation in airflow for control or to satisfy a process.

7.3. Methods of controlling fansAs described in Section 5, the rate of flow of air through a system is determined at the intersection of the system resistance curve and the fan performance curve. Control may be achieved either by changing the effective resistance of the system, or by altering the performance of the fan. The method chosen will depend largely upon the changed running costs at the changed flow rates, weighed against the capital cost of the changed system or fan and drive. In some situations noise may also be a factor.

Methods of control discussed in the section include:

Variable speed control (most efficient) Multiple speed control On-Off control Variable pitch control (no longer common) Inlet vane control (inefficient) Changing fan characteristic Varying system resistance (inefficient) Bypass control (inefficient)

7.4. Factors affecting choice of control methodThe choice of method is one of assessing the change in power costs over the life of the fan against the initial capital and ongoing maintenance costs, bearing in mind the degree of control required and the frequency of its operation.

The following are some of the factors which can influence the choice: Power costs. Initial manufacturing and installation costs. Payback period on initial investment. Maintenance and replacement costs. Degree of control required, stepped or continuous. Accuracy and repeatability of control settings. Range of flow over which control is required. Temperature, toxicity or corrosiveness of gas handled. Period of time over which each setting is effective. The control system (if automatic operation is necessary). Noise levels.

The assessment of these factors is often complex, and it is suggested that the advice of the fan manufacturer should be sought.



7.5. Speed controlOne of the most efficient methods of continuously controlling the performance of a fan is by varying its rotational speed. When working in a constant volume duct system, the point of operation will move down the system resistance curve as the speed is reduced. This has the advantage of maintaining the fan's operating efficiency, resulting in a corresponding drop in maximum power consumption and noise level as the speed is reduced. See Figure 7.1, where the pressure, volume and power curves for three different speeds are illustrated.

Figure 7.1 Flow control by speed regulation

Controlling the speed of the fan may be achieved either by varying the speed of the motor or by changing the ratio of the drive.

When a fan, fitted with an AC motor, has its speed reduced in a constant volume system the impeller efficiency remains the same but the motor efficiency generally drops.

Examples of speed control methods include:

Continuously variable speed electric motors. Multi-speed fan motors Diesel or petrol engine drive. Variable speed gearbox. Fluid coupling (not common in HVAC&R). Magnetic coupling (not common in HVAC&R). Variable ratio pulleys and belt-drive.

The majority of fan applications in HVAC&R are driven by electric motors.

Speed control methods for electric motors used for fans would include:

On/off switches 2 – speed switches 3 – speed switches Capacitor control Electronic speed controllers Auto-transformer speed controllers Star/Delta switches Frequency Inverters Electronic commutation for DC motors

When assessing the power saving using these methods, due account must be taken of the change in efficiency of the motor which may vary with speed or load. The benefits of speed reduction are not limited to energy benefits as reduced speed also reduces wear on bearings and shafts, noise and vibration.

Table 7.1 Advantages and disadvantages of variable speed control



Advantages DisadvantagesEnergy savings Resonant frequenciesImproved control Current ripple, parasitic torques, additional motor losses and

output waveform harmonicsImproved reliability of fans and bearings

Increased system complexity with corresponding reduction in reliability

Reduced noise and vibration Ventilation of electronicsIncreased sensitivity to installed environment (temperature, moisture and dust)Additional costAdditional maintenance requirements

7.6. Variable speed electric motorsVariable frequency drives (VFD) are the most common form of variable speed drive (VSD) used in HVAC&R fan applications however alternative VSD technologies like variable pitch/diameter belt drive systems, hydraulic clutches and electric clutches have also been used in the past. When properly applied VSD technologies can improve the operating efficiency of the fan and therefore the entire system.

Where electrical, magnetic or mechanical slip is involved (e.g. slipring motors, magnetic or hydraulic couplings), the reduction in input power to the motor is roughly proportional to the square of the speed (depending on type of motor), while motor output to the fan impeller varies as the cube of the speed. Hence the efficiency of this type of speed conversion is equal to the ratio of output and input speeds.

AC Variable Speed Drives (VSD) are a common means of fan speed control. This has occurred due to the declining cost of such equipment and the enormous degree of flexibility offered through direct digital control and integration with supervisory electronic control systems. They do however have the potential to create new problems which, if not addressed, may impact on the overall effectiveness of a fan installation.

An important consideration is the starting torque of larger heavy duty fans, particularly centrifugal fans. The fan impeller acts as a fly wheel and can demand a considerable torque to overcome starting inertia. Starting fans at reduced speeds through a VSD may not deliver sufficient torque to achieve the operating speed within acceptable run-up times. This can lead to overload failure. Careful matching of the load and motor size with the VSD will overcome this difficulty. Reference should be made to each of the equipment suppliers.

Electronic VSDs control power by electronic switching of voltage and current. A by-product of this type of control is the generation of voltage and current harmonics in both the input and output of the drive. They affect both the mains supply and the driven motor. These harmonics are superimposed on the normal supply output waveforms, and may adversely affect both the motor and other users of the supply.

In AC drives, harmonics applied to the motor cause current ripple, parasitic torques and additional losses in the motor. It is beyond the scope of this manual to explore in depth the characteristics and behaviours of VSDs, however a user should be aware of motor derating factors which may be applied dependent on the make and type of VSD being employed. Whilst VSD technology is continuously improving, it is recommended that derating factors be checked with the drive manufacturer.

Operating rotating machinery under a variable speed control may also cause certain vibrations to occur at set operating points in the speed range. These vibrations occur within narrow frequency bands and are known as resonant frequencies. VSD units today commonly offer selectable skip frequencies that can be programmed into the VSD so that the offending frequencies are by-passed during operation. This feature and the potential problem should both be considered in conjunction with the fan manufacturer.

Designers should require coordination between drive and motor manufacturers and suppliers to ensure compatibility between equipment and minimise the application problems discussed above.



7.7. Multi-speed controlMultiple speed motors are typically applied with two or more fixed speed options and so the control profile is more stepped than the continuously variable speed option. Multiple speed motors are less efficient and less effective than variable speed motors. Multiple speed motors are wound differently and are consequently more expensive and less efficient than single speed motors. Multiple speed motors may require complex switchgear to function, which must be remembered when comparing costs of relative control methods.

7.8. On-off controlFor simple systems on-off control may be appropriate. When the fan runs it does so at the chosen best efficiency point and when it is off no energy is consumed. The frequency of the stop-start cycle should be within the motor capability so that overheating does not occur.

7.9. Variable pitch bladesMechanisms that permit continuous adjustment of the blade pitch angle of axial flow fans offer a wide range of flow adjustment, with consequent reduction in energy consumption. Under this method of flow control, the fan will not remain operating at the same efficiency as selected for full flow operation, and while the motor remains operating at the same speed, its efficiency will drop off significantly, especially below 50% of the full load.

Variable pitch fans are expensive and the energy savings are not as good as with speed variation, so they are now rarely used in HVAC&R applications.

7.10. Inlet vane controlA second method of continuous control of fan performance is by the introduction of specially designed adjustable vanes into the airstream entering the fan inlet so as to generate a swirl of air in the direction of the impeller rotation. This produces a reduction in the performance capability of the fan as indicated in Figure 7.2, which shows progressively reduced pressure/volume and power curves as the vanes are closed moving the operating point to positions 2, 3, 4 and 5 down the system resistance curve. Note however, that there is an angle of the blades beyond which swirl will become ineffective and throttling will occur with a resultant uneven change to the systems performance.

Inlet control vanes have many forms, but are usually part of the overall fan design and should be supplied by the fan manufacturer.

When optimising fan systems speed control is the preferred option, because the power reduction with inlet vane control is significantly less than that achieved with fan speed control. It is for this reason that inlet vane control is no longer widely used in the fan industry.

Figure 7.2 Flow Control by Inlet Vanes. (Fan at constant speed)

Drafting note: Static pressure on X axis.



7.11. Multi-staged fan operationInstalling two or more fans in parallel is another energy efficient control option. Variation of flow is achieved by switching fans on and off to meet system demand. Parallel fan applications are used to achieve higher pressure and by plotting the fan performance curves onto the same graph as the system resistance curve it is possible to determine the flow and pressure achieved when running one, two, three or more fans in parallel. The combined fan performance curve is obtained by adding the flow rates at a specified pressure. Variation of flow is achieved by turning on and off the fans to meet system demand.

It is possible to run fans of different sizes in parallel. By arranging different combinations of fans running together a larger number of system operating points can be met.

Picture here?

7.12. Control by changing fan characteristicsWhere the adjustment of performance is required once only, or at infrequent intervals, this can be achieved by an alteration to the fan (or drive) itself. This is particularly useful as a means of adjusting the performance of the fan at the installation (commissioning or fine tuning) stage to suit actual on-site operating conditions.

In belt-driven fans the speed of the fan can be adjusted by changing one or both of the drive pulleys (very often belt-driven fans are chosen just for this facility).

Most axial fans have impellers which allow adjustment of the impeller blade angle and the complete impeller can sometimes be changed on centrifugal fans.

With all these methods it is important to note that a reduction in performance can be achieved with little difficulty. An increase in performance can only be made within the mechanical and electrical capabilities of the fan and motor. Increased noise levels may also occur. It is essential that the advice of the manufacturer be sought in these cases.

7.13. Control by varying system resistanceThe simplest means of flow adjustment is by use of a valve or damper at a suitable point in the ducting system.

Closing the damper will increase the resistance to flow and the quantity of air will fall as dictated by the fan characteristic, see Figure 7.3. Dampers can be operated manually or by an automatic control system.

Although cheap to install and a traditional control method, the inherent pressure loss across a damper is a waste of energy and may create noise. A more efficient form of control is achieved by adjusting the performance of the fan itself.



Figure 7.3 Flow Control by System Damper Regulation for a Backward-curved Centrifugal Fan. (Fan at constant speed)

7.14. Control using a bypassIn the bypass control method the fan operates continuously at the peak duty and the system or load is controlled by bypassing air from the fan discharge to the fan suction. This control method is energy inefficient because there is no reduction in fan power consumption with reduced system demand.

7.15. Measurement for controlAll controllers need an input on which to base the control decision. Monitoring flow and pressure and using them to control a system are both common.

7.15.1. Placement of flow sensorsFlow should be sensed in ducts where airflow is constant and stable to allow for accurate measurement. This can prove difficult to achieve on a standard installation and a fixed calibrated orifice plate can be used. Some fan designs offer fixed calibrated orifice plates as a standard feature.

7.15.2. Placement of pressure differential sensorsAnother common requirement is to control the pressure across either upstream or downstream equipment. An important consideration in the design of the control system is the placement of pressure differential sensors.

Pressure tappings should be connected at the point where it is desired to control the pressure.

7.16. Intelligent fansBeyond using basic control strategies such as variable speed drives, adding intelligence to the fan control solutions can provide additional benefits including:

Linkages to building management and control systems to provide performance and operational feedback in real time to assist identifying optimisation opportunities

Monitoring fan operating conditions such as temperature, vibration, current draw, pressure fluctuations and linking this data to a predictive maintenance program.

Management of multi-fan systems to ensure optimised operation Enhanced fan protection, improving reliability and equipment life.

Options for intelligent fans include a VFD with embedded intelligence to control an individual fan or a separate programmable logic controller to control a series of fans or an entire system.



7.17. Monitoring fansFans are monitored for a variety of reasons and in a number of ways. The primary reasons for monitoring a fan include for:

Fan performance assessment – continuous assessment of the operating performance of the system against its expected optimised performance criteria.

Fan condition assessment – as part of a condition monitoring maintenance program, fan characteristics can be monitored to aid in the prediction and prevention of mechanical failure.

Monitoring implies establishing and quantifying a characteristic of interest and comparing it against a defined standard. Monitoring can be carried out visually or by measurement of key performance indicators and comparing the result against expected benchmarks, goals or predicted outcomes. Key performance indicators that can be monitored for fans include flow, pressure, temperature, power, speed, vibration

7.17.1. Monitoring flowMonitoring of flow is essential for fan performance assessment. Flow rate can be measured using flow meters. The duct configuration immediately before and after the flow meter is important for measurement accuracy and manufacturer instructions should be followed.

7.17.2. Monitoring pressureMonitoring of pressure is essential for fan performance assessment and also useful in condition monitoring. Pressure can be measured using pressure gauges or through pressure transmitters. To adequately assess operating performance pressure tappings should be installed at the fan suction and discharge. Pressure measurement is also used for system control.

7.17.3. Monitoring temperatureMonitoring of air temperature is essential for fan/system performance assessment. Temperature measurement using thermometers, thermocouples or resistance temperature detectors is simple and will often be used for system control purposes. Measurement of fan temperature is useful in condition monitoring and the operating temperature of bearings, motor windings and casings are often monitored by thermocouples.

7.17.4. Monitoring powerMonitoring of power is used for fan performance assessment and in condition monitoring. Absorbed power can be calculated from the electrical parameters of amperage, voltage and power factor which are measured directly on the electrical supply to the motor. Mechanical power can also be directly measured using torque meters or strain gauges installed between the fan and drive.

7.17.5. Monitoring speedFan speed is monitored in systems which provide a variable airflow for system control purposes and also to avoid operation near a critical speed (see Clause 7.6). Fan speed is also monitored for condition monitoring purposes to check for speed degradation as an indication of bearing or motor failure or a system resistance increase. Speed is measured using fixed digital tachometers or portable measurement instrumentation.

7.17.6. Monitoring vibrationVibration is monitored for condition monitoring purposes. Many different fan failure modes can cause an increase in vibration and bearings, shaft and casing can all be monitored. Vibrations are measured by accelerometers or velocity transducers and are generally measured in the horizontal, vertical and axial directions.



8. Installation and commissioning

8.1. Section IntroductionThis section provides a brief overview of the fan and associated system installation and commissioning process.

8.2. General installation requirementsInstallation should be performed by competent personnel with the appropriate skills, tools and equipment required to complete the work safely and in compliance with work rules governing the site. Reference should be made to the installation instructions provided by the fan manufacturer or supplier. Local regulations should also be complied with.

Installers need to coordinate site supervision with the equipment supplier. A complete installation specification should be provided to the installer.

8.3. Installation specificationThe system designer should document the system design and operating pressures and temperatures; piping materials; pipe wall thickness or schedules; types of fittings to be used, (e.g. butt weld, socket weld, or screwed) and the valve and flange pressure rating and insulation requirements. In addition, the installation specification defines the fabrication, examination, testing, inspection, and installation requirements, including the requirements for system commissioning, inspection and documentation.

8.4. Fan installation

8.4.1.System connectionsThe fan inlet and outlet connections should be installed as per the designer’s instructions and in accordance with the manufacturer’s recommendations. If, due to on-site limitations the inlet and outlet connections are varied from the designed solution the designer should be informed so that the effect on overall system performance can be determined and managed, (see Section 10).

8.4.2.IsolationFans should be isolated from the building structure to prevent possible noise or vibration issues. The fan should be adequately isolated from the building and the air distribution system at all connection points. Primary connection points include the fan inlet, the fan outlet, and the fan base. Secondary connection points include electrical and control wiring and hydraulic connections.

8.4.3.Flexible connectorsFlexible connectors should be used to:

Isolate any transfer of vibration or resonance between the fan and the duct system. Isolate the fan from the structural loads of the duct system. Compensate for small deviations in alignment between the fan and duct connection Compensate for expansion and contraction of the duct or fan due to temperature

changes

Flexible connections can be designed with acoustical properties to assist in managing fan noise. Ideally flexible connections should not be installed with any slack, and should allow concentric alignment of the fan and duct connection.



8.4.4.Base mounted fansThe fan should be correctly levelled before securing to a stable base. Fans should be well secured to the base in accordance with the manufacturer’s installation instructions so that transmission of vibration is reduced. Fan weight, speed and size usually determine the base requirements. Common installation methods used include:

Grouting the fan to a concrete foundation of suitable mass Using a flexible pad (neoprene, silicone or similar) between the full contact surface of

the fan and the foundation Using a base isolation system such as rubber pads or springs

In all cases the method of isolation should be appropriate for the environmental conditions in service, including temperature, humidity and chemical degradation.

8.4.5.Duct mounted fansDuct mounted fans need to be independently supported from the ductwork.

8.4.6.Belt drivesBelts must be orientated correctly to the preferred direction of rotation, tensioned and aligned correctly. There should be no slack on the drive side of the belt when operating. Incorrect alignment will cause uneven wear and stress distribution causing slipping or premature failure.

8.4.7.WiringAll fans and associated electrical equipment should be wired in accordance with AS/NZS 3000. Control and monitoring instrumentation should be wired in accordance with the manufacturer instructions and all relevant regulations.

Note: Refer AIRAH DA 27 for further information on the installation of control wiring.

8.4.8.GroundingFans installed in flammable environments must be properly electrically grounded (including rotating components) to minimise sparking due to static electricity discharge.

8.4.9.AccessThe provision of adequate access to the fan and its accessories for maintenance and service is essential and is a requirement of AS/NZS 3666.1 which is a regulated requirement in Australia through building and health regulations.

Large fans are often supplied with access points. If access panels or doors are being added during installation the correct type should be used for the system operating pressure. In the case of direct-driven axial flow fans, an access panel may be required in the fan casing, particularly in larger fans.

8.5. CommissioningSystem commissioning is an integrated process that is carried out progressively to a schedule. The commissioning schedule is structured so that attention builds from the simple to the complex following a testing hierarchy.

Early functional tests focus on components, such as the fans and connections, and can be carried out in parallel with other component functional tests. Once functional tests are completed, system testing and balancing (TAB) can be carried out. TAB can be carried out in parallel with the TAB and functional testing of other systems. Systems integration tests are carried out after functional and TAB tests confirm the readiness of each individual system. Whole building tests and tuning tests follow, leading to ongoing monitoring, ongoing tuning and eventual recommissioning tests.



8.5.1.Pre-commissioningPre-commissioning refers to the work that needs to be done or checked prior to the systems being tested, adjusted and balanced. Pre-commissioning work on air distribution systems can include things like duct inspections and cleaning, duct leakage testing and ensuring that the necessary facilities (power, water drainage) are available for the fan and system commissioning.

8.5.2.Pre-functional checklistsPre-functional checklists should be completed throughout construction during normal commissioning site visits as installation of the various components and systems are completed. Sensor and actuator calibration is typically considered to be part of the pre-functional checklist.

8.5.3.Fan Functional testingPrior to starting a newly installed fan the following preliminary checks should be made:

Check the impeller clearances and that the impeller is firmly attached to the drive shaft.

Ensure that the bearings are lubricated with an appropriate lubricant. Ensure that impeller is free to rotate and that the direction of rotation is correct.

The fan will be supplied with manufacturer’s information to assist with commissioning and the following recommendations should be followed:

Check fan data plate against design requirements and electricity supply. Check that fan casing, impeller and duct system have been cleaned prior to start-up Ensure that fan impeller rotates in the correct direction and fan is installed in the

correct configuration. Check operation of rotor/impeller brake if installed. Check for vibration and isolate if any vibration is present, rebalance the fan as

necessary

8.5.4.Fan VSD testingThe fan should be run-in or exercised while under observation. Ramp the fan speed up and down if control is by VSD or modulate the motorised dampers to see how the fan and system responds.

8.5.5.Testing, Adjusting, Balancing (TAB)Testing, adjusting and balancing (TAB) is the term applied to setting the air distribution system up to deliver the design airflow rates. It is a dynamic test where the system is measured and adjusted to deliver the specified measureable performance parameters, such as flow, pressure or temperature.

TAB is an appropriate time for system resistance to be minimised on the index run. Reducing the system resistance at this stage provides benefits over the life of the system. If significant differences between the installed system resistance and the calculated design resistance occur the fan selection and control strategy may need to be revisited.

8.5.1.System TestingSuccessful execution of system tests is dependent on the operation of all related system equipment including air handling units, heat pumps, process loads, chillers, boilers, cooling towers, etc. At a minimum, the pre-functional checklists should be completed on the components/systems served by the air system which should all be capable of safe operation.

Any reset strategies within control algorithms should be disabled and only one control parameter should be varied at a time so that the basic system operation can be verified. Re-



establish the resets for other control parameters progressively and verify system operation remains stable.

Verify proper fan staging and VFD control (if applicable) in accordance with the system designer’s sequence of operations.

System performance testing is intended to observe the entire system under normal operating conditions. The plant sequencing, control set points and resets, control accuracy and stability should all be verified during tests.

8.5.2.Integrated systems testingSystem integration tests are carried out to ensure systems can interact with each other appropriately. Typical system integration tests would address system performance during:

System start-up and shut down. System power loss. Fire alarm or smoke management mode. System interlocks and control responses (response curves). All system control strategies.

8.5.3.Fine tuningSystem tuning forms an important part of final commissioning and should be completed to a documented tuning plan. System tuning typically comprises:

Monitoring and analysis of system results with respect to the predicted performance and performance benchmarks *energy, flow, pressure etc).

System adjustments to suit the actual operational characteristics.

Setting up BMCS trend logs and exception reporting.

Tuning of control loops.

In the first few months of operation it is common to require a significant amount of system tuning as the plant beds down.

System tuning reports should include a review of the tuning activities completed, system performance observations, and recommendations for improving the system design, installation or operation.

8.6. Commissioning records

8.6.1.Commissioning dataA commissioning checklist should be used for fan and system commissioning to ensure that the fan and system is operating within the specified parameters. All of the data should be recorded during the commissioning tests.

The final commissioning data should be recorded, offered for approval and signed off.

8.6.2.Fan dataRecord final commissioning data such as:

Fan data – manufacturer, type, size, model, fan speed and blade pitch angle setting. Electrical data – Motor power, amp draw, operating voltage, efficiency. Drive data – belt type, belt size, centreline distances, tension rating, or coupling size,

type and rating. Bearing data – manufacturer, type, size, lubrication requirements. Operating data –system final flow rate, pressure, discharge velocity and fan motor

amperage, voltage draw and speed.



8.6.3.Vibration dataFans should be tested in accordance with ISO 1940.1 to a balance quality grade of G6.3 or better. After installation, the vibration levels should be checked by personnel experienced with vibration analysis and vibration analysis equipment.

8.6.4.VFD critical frequenciesFans operating with VFD controllers may be susceptible to excessive vibration at particular system ‘critical frequencies’. Fans have critical frequencies and the manufacturer should have this data available for any impeller/ diameter combination. Fans should be manually run from the minimum to the maximum design speed to check for any frequencies that result in excessive vibration or resonance. Problem frequencies should be noted and the controller should be programmed to bypass these frequencies.

The controller should also be locked to prevent the fan from operating beyond the manufacturer’s stated maximum speed or current draw.

8.6.5.Commissioning adjustmentsAny fan adjustments made during the commissioning process such as fan speed, impeller trim, blade pitch and the like should be recorded for future information.

8.7. Designers role in commissioningA primary commissioning focus for designers is the documentation of the design intent and system functionality. Designers need to provide a system design narrative and operational sequences for other stakeholders to facilitate system integration. They need to allow for commissioning in their designs, in their specifications, and in their fee structures.

Designers are largely responsible for the commissionability of their designs, the quality of components, system documentation, and system performance requirements. They need to facilitate the peer review of their designs and fully engage in discussions for modifications or improvements. Documenting design changes and resolving design conflicts is also an important commissioning role for system designers who are often solution orientated.

Designers review installation documentation and site work and advise the commissioning manager of any defects. Designers also assist with the detailing of requirements for the development and review of operating and maintenance manuals, as installed drawings and training materials.

8.8. Operating and maintenance manualsDetailed operation and maintenance manuals should be prepared by the installer, approved by the designer and supplied to the owner or operator. The provision, content and format of operating and maintenance manuals is discussed in AIRAH DA19 and these are mandatory for systems that are required to comply with AS/NZS 3666.1.

Every system should be provided with comprehensive system information in the form of operating and maintenance (O&M) manuals and include:

System designer’s contact details.

System installer’s contact details.

Installation team. Scope and system description. Design intent and functional descriptions of the systems. Design and performance criteria. Control strategy descriptions. Controls, power and wiring diagrams. Operation protocols. Manufacturer’s literature and service contact details.



Certification details. Recommended maintenance plan. Trouble shooting and fault finding instructions. Emergency procedures. Recommended system tuning plan. System commissioning records. As-installed documentation.

Preparation of the operating and maintenance manual by the system installer should be integrated within the overall project management process and commence in the early phases of the construction program, allowing it to be gradually completed as information becomes available. The O&M manuals are finalised at the end of the building tuning period.

Comprehensive information on the benefits, content, and format of the operating and maintenance manuals is provided in AIRAH Application Manual DA 19 HVAC&R Maintenance.

A recommissioning plan (refer clause 9.9) should be developed and included within the operation and maintenance manual.



9. Operation and Maintenance

9.1. Section IntroductionThis section provides a brief overview of the fan and associated system operation and maintenance.

9.2. Transition from construction to operationDuring the transition from construction to operation the system designer and installer need to hand over the system to the operator or owner. One of the most important (and often neglected) aspects of handover is knowledge transfer. Training and system documentation must be sufficient to transfer the system knowledge from the designers/installers to the system owners/operators.

9.2.1.TrainingTraining is a critical aspect of the hand over process. The intended operation and control of the fan and system must be explained to the operators. Operating and maintenance manuals can usefully form the basis of the training. Training sessions can be recorded and training materials retained for reference by future operators.

9.2.2.System documentationDetailed operation and maintenance manuals should be supplied to the operator, see Clause 8.8.

9.2.1.Defects liabilityThe defects liability period, is the period stated in the contract immediately following the date of practical completion, during which the contractor is required to complete any minor outstanding works and to remedy any defects or faults. The contract sets out how and when the contractor must remedy defective work which becomes apparent during the defects liability period. System fine tuning activities typically run concurrent with the building defects liability period.

Care should be taken not to void the warranties or contractor’s responsibility during the defects or warranty period, for example by using another subcontractor to undertake repair activities on works or equipment associated with the main contract. For smaller projects, a defects liability period of 6 months is often used while for larger projects a period of 12 months is common.

9.3. OperationA fan system should be operated using established procedures to minimise maintenance, failures and unexpected downtime.

9.3.1.Start upA checklist should be included in the operating and maintenance manual detailing all the safety precautions, equipment and damper settings, manufacturer recommendations and instrumentation connections that should be made prior to starting a fan.

9.3.2.Shut downIt is important to follow an established shutdown sequence for safety and system control and to prevent flow related problems, pressurisation or depressurisation or the tripping of other equipment within the system,



9.4. Monitoring operations

9.4.1.Why monitor?The way that a fan system is operated is critical to its energy use and the daily/weekly operating cycle within HVAC&R applications generally varies widely. Monitoring fan operation is an effective tool in system energy management. In order for a system to be effectively monitored and managed there must be a method of metering key inputs and outputs and a method of comparing the monitoring results with some pre-defined goal or acceptability data.

9.4.2.Metering fansA metering system is composed of one or more discrete meters installed to monitor the performance of a system or piece of plant. Prior to the design of a metering system, key performance indicators (KPIs) need to be determined so that the results of the system monitoring can be compared over time.

Fan KPIs – Can include system temperatures, energy use, speed, noise System KPIs – Can include system energy use, operational trend logs, etc. Building KPIs – Building rating systems such as NABERS or energy benchmarking

within a portfolio.

9.4.3.BenchmarkingBenchmarking of systems establishes the actual performance in operation of a fan or fan system and trending this information is useful for monitoring system performance over the long term.

Benchmarking of systems can also create a feedback loop to designers and installers, enhancing knowledge transfer and lessons learned and driving a system of continual improvement in the system design and delivery process.

9.4.4.Measurement verificationAccurately measuring performance parameters is an essential tool if the current performance is to be established. Only then will the ability to accurately measure the results of any system fine tuning or equipment upgrades be available.

The accuracy of measurement depends on the quality and capability of the monitoring equipment being used, the configuration of the sensor installation, the frequency of the measurement cycles and the calibration and maintenance of the sensors.

9.4.5.Performance reportingOnce a metering and monitoring system is in place a formalised reporting system should be established to ensure that the data collected is turned into useable information and that the information is readily available for use.

9.5. Intelligent fan/system diagnosticsIntelligent diagnostic systems are the next step on from metering and monitoring systems. These systems use flow, temperature, pressure, voltage, current draw and vibration sensors to collect data on the operating system. The values of monitored parameters are tracked over time and any unexpected (or out of range) changes are highlighted.

System assessment programs use this information to assess the current state of the fan. Predictive maintenance systems use this data to diagnose or predict fan or component failures. Preventative maintenance programs can use this information to reschedule preventative activities and assess the effectiveness of the maintenance program.



9.6. Maintenance

9.6.1.The maintenance imperativeIt is essential that fans are maintained throughout their service life. Fan manufacturers supply maintenance instructions and these should be readily accessible to service personnel.

Most fan maintenance centres around checking drives and belts for wear, performing preventative or predictive maintenance activities on bearings, ensuring correct alignment and proper motor condition and function.

However, maintenance regimes also need to extend beyond the fan itself and for many HVAC&R applications ‘system maintenance’ is crucial for ensuring the energy efficient operation of the fans. For example cleaning or replacing the filters in an air conditioning system reduces system resistance and reduces fan energy use.

9.6.2.Mandatory maintenance (BCA)Maintenance of fans in some applications is a mandatory requirement including fans covered by NCC Volume One (BCA Class 2 to 9 Buildings) Section J and fans covered by AS/NZS 3666.2. Fans which operate as part of the building’s Essential Fire Safety Measures under the requirements of AS/NZS 1668.1, Section E2.2b of the BCA or Section G3.8 of the BCA are required by state legislation and AS 1851 to be maintained and routinely tested for satisfactory performance.

9.6.3.Access for maintenanceIn order for a fan to be maintained there must be adequate access provided for service personnel and for parts and fan replacement. Where adequate access for maintenance is not provided then maintenance will most likely not be carried out.

9.6.4.Preventative maintenanceMaintenance requirements vary with the type of fan, the type of installation and the system application. Maintenance recommendations specified by the manufacturer should take precedence.

Preventative routine maintenance extends the life of the fan and the performance of the system. Maintenance routines comprise checking and periodically replacing the wearing components.

9.6.5.Predictive maintenancePredictive maintenance goes one step further and is generally applied to critical systems where failure is costly or unacceptable. Predictive maintenance includes continuously or periodically monitoring the fan key performance indicators such as flow, temperature, pressure, current draw and vibration and using that data to predict future failure or reduction in performance. Fan problems are detected and resolved early, prior to any critical failures.

9.6.6.Scheduled maintenanceMandatory and preventative maintenance routines are generally carried out to a scheduled frequency. The frequency required for a particular fan will vary by application, i.e. duty, location, corrosiveness of environment etc.

Fan manufacturers have developed comprehensive maintenance procedures which maintenance personnel should follow, in the interest of the owner and the continued reliable operation of the equipment. As many fans run for extended periods without being switched off it is essential that the critical components are checked in accordance with the manufacturer’s schedule or the recommendations from AIRAH DA19.

It is often necessary to install a stand-by unit so that the regular maintenance can be carried out without losing use of the system.



The following recommendations for scheduled fan maintenance are reproduced from Schedule A22 Fans from AIRAH DA19:

This section covers all types of fans. Only those action items applicable should be used.

Schedule A22 Fans (reproduced from AIRAH DA19)

Action Interval

(Months)

Explanation

1. Adjust belt tension as necessary, check for wear.

1 See schedule A17 (DA19) for the steps to be taken.

2. Check drive and drive shaft guard firmly in place.

1 All drives should be checked in accordance with schedule A17 (DA19).

3. Check fan operates. 1

4. Check for vibration, bearing noise or overheating.

1 Vibration can be due to out of balance of the fan rotor or failure of one of the bearings. Heat or noise from the bearing will confirm that this is the source of the problem and appropriate steps can be taken to replace the offending bearing. It is frequently necessary to replace both bearings as vibration from one can cause damage to the second.

5. Check mounts and holding down bolts for security.

1

6. Lightly lubricate bearings to manufacturers’ recommendation where possible.

6

7. Spray or coat belts, where required, with commercial compound to reduce pulley slip.

6

8. Check access panels for air leakage and seal.

12

9. Check drive alignment. 12

10. Check that impeller and drive are tight on shafts.

12 This is carried out by physical examination of keys, keyways and locking bolts. Any movement in these components can lead to wear on the shafts with resultant expensive replacement of the component becoming necessary.

11. If accessible, check cleanliness of fan blades and scroll or casing and record/report if cleaning is required.

12 Where possible, inspect the internal surfaces of the fan casing and the runner for any build up of dirt grime grease etc. Steam cleaning or high pressure water jets can be used to restore the surfaces to an as new condition. The surfaces should then be examined for corrosion and if necessary and possible they should be repainted.

12. Inspect for evidence of corrosion, wear on flexible connections and other deterioration, clean and repair minor corrosion and report where repairs are necessary

12



Action Interval

(Months)

Explanation

13. Replace flexible drive components. 36 Replace with new matched sets. This could refer to belts, in belt drives, buffers, in direct drives, or any other item which is provided for flexibility in the drive. If replacement becomes necessary in less than 36 months, due to normal wear, then the maximum replacement period restarts from the time of replacement.

9.6.7.Maintenance recordsA comprehensive and progressive record of all maintenance activities should be kept for each fan detailing maintenance interval, components checked, preventative maintenance performed, and any operational issues and future maintenance recommendations. Maintenance records should be kept in a building log book and made available for future review.

9.6.8.Maintenance procurementThe selection of maintenance service provider is the key to satisfactory maintenance, which will result in reliable plant performance, good plant life and reasonable expenditure. Lowest tender price is the least appropriate way to select a service provider. Value for money should be the determining factor. The ideal situation is where the customer and service provider establish a partnering relationship, recognizing that the service provider needs to make a profit and the customer needs to contain the costs.

Thus a potential maintenance service provider should have the following attributes:

Competent, committed and well trained technicians.

Appropriate licenses, insurances and accreditation.

Appropriate level of resources.

Efficient and accurate maintenance management system.

Informative reporting system.

Accurate and timely invoicing.

Economical and reliable after hours service.

Quality, environmental and safety management systems.

The assessment of maintenance contractors should include an evaluation of their sustainability practices. It is important to incentivise maintenance contractors to consider the energy efficiency of the system during maintenance inspections. Refer to AIRAH DA 19 for detailed information on HVAC&R system maintenance.

9.7. System tuningIn a typical HVAC&R system chillers, pumps, valves, fans, and the like are all required to operate together in coordination to achieve a space temperature which is within specification. System tuning and the maintenance of controls are crucial to achieving this. Prior to any tuning taking place, key performance indicators for equipment and systems and condition responses need to be established.

9.8. System managementThere should also be some procedures or protocols put in place to manage the system over time. Consideration should be given to how the following issues are managed:



System access – The persons who have access to the system plant or controls should be limited to the nominated individuals so that changes cannot be made to the system without being properly documented and approved.

Documenting changes – any changes made to the system should be documented; the as-installed drawings and the operating and maintenance manuals should be updated to reflect the changes made.

Verifying improvements – any changes made to the system should be verified against the stated goals or objectives of the change. Simply assuming that the changes made have achieved the required objectives is insufficient and a positive feedback should be encouraged to verify the performance of any implemented improvements.

9.9. RecommissioningSystems change over time, components wear, set points are altered, control calibrations drift, often resulting in a deterioration in system performance. Recommissioning is intended to bring a system back to its original performance and operating efficiency and is carried out periodically (every 3 to 5 years) or in response to operating problems. Recommissioning activities include tuning, calibrating, testing and verification and generally follows the tests and methodology developed for the original commissioning program.

Recommissioning begins with a review of the system operating requirements to determine what, if any, changes in requirements have occurred. The system operating requirements need to be updated or confirmed prior to any recommissioning activities commencing.

If changes have occurred, systems are reviewed to establish if corresponding changes to equipment, controls or operation procedures are required. Systems are then fully surveyed and a list of findings or issues compiled. System trend logs or functional performance tests may be used to determine if the system meets the performance defined in the reviewed operating requirements.

Where changes to operating requirements or installed plant are extensive system retrocommissioning may be required.

Refer to AIRAH DA 27 for full details on recommissioning and retrocommissioning protocols.

9.10. UpgradesFan or plant replacement can occur for a number of reasons including due to failure, degraded performance, and changed system goals. Fan replacement could even be considered at initial commissioning if due to excessive margins the selected fans are so oversized the system needs to be excessively throttled.

When upgrading or replacing a fan the system requirements should be revisited and a fan selection process entered into. Do not simply replace like for like.

A facility upgrade strategy might schedule the replacement of inefficient fans and associated equipment with modern high efficiency alternatives However, the load/system requirements should always be reviewed for changes.

9.11. Optimising existing fan systemsMany existing fan systems operate sub optimally, i.e. their performance outcomes can be improved. Many system problems arise from incorrect fan selection and operation. The indicators of a sub optimal fan system can include:

Highly throttled dampers in use. Frequent on/off cycling of a fan in a constant flow application. Presence of excessive noise or vibration. Multiple fan systems where all fans are continuously running. No means for measuring system flow, pressure or fan power. Fan systems that have been modified or extended over time.



The first step in the optimisation process is to assess the current system for deficiencies. Next the system pressure and flow rate requirements and the installed fan capabilities are quantified. Part of this process is to collect system performance data over time; logging data such as flow rate, discharge pressure and energy consumption is essential in diagnosing for optimum system performance.

Comparing the system requirements with the fans performance characteristic it is possible to determine if the fan is over or under sized for the application. In many cases the fan performance can be better tailored to the system requirements. Maximum efficiency and minimum power consumption will be achieved by ensuring that the flow and pressure at the fan best efficiency point closely match the system operating point.

Modelling the system using analytical or CFD models is useful when designing and evaluating potential system improvements. Modelling can help evaluate the impact of proposed changes to the fan, distribution systems or controls on a common platform.

To evaluate an existing fan system you must be able to:

Audit the system installation for inappropriate flow and pressure characteristics. Understand the existing operation and control of the system or process. Identify potential system issues over a range of operating conditions. Use and interpret historical data available for the system or plant. Capture field data and analyse and interpret that data.

Some of the solutions to sub-optimal fan systems include

Oversized fan – trim impeller, smaller impeller, variable speed drive, two speed drive, lower rpm.

Undersized fan – Replace fan or reduce system resistance (optimise flows). Multiple fans operating continuously – review and update control system. High maintenance costs – Match fan capacity with system requirements. High flow rates – adjust system operating temperatures to maximise temperature

differentials and reduce airflow rates. Over throttled system – Modify fan performance to reduce the need for throttling High power use – Re-balance system to minimise flows and remove throttling. Provide instrumentation – To measure pressure, flow and power use. Replace old fans – with modern energy efficient replacements. High pressure drop – Reduce system resistance by upsizing ducts and fittings and

installing low pressure drop plant.



10.The Fan Duty and System Effect

10.1. Section introductionCatalogue ratings of fans are generally based on idealised laboratory conditions particularly in regard to outlet and inlet duct connections. These idealised conditions are rarely achieved in practice and an additional pressure loss is thus imposed on the fan. If this additional loss is not allowed for in system calculations, the fan will not be capable of handling the design air quantity.

The additional pressure loss due to the actual inlet and outlet configuration of the fan is known as the ‘System Effect’. A method of evaluating this effect and allowing for it within the system design calculations and fan selection is discussed in this section.

10.2. The System EffectA fan seldom operates under the ideal conditions prevailing in the laboratory when its performance is determined. The most common causes of deficient performance of the fan/system combination are:

swirling of the air at the fan inlet

non-uniform inlet flow

improper outlet connections

badly fitting flexible connections

misaligned ductwork on both the inlet and discharge

swirl at the discharge of axial flow fans, especially close to bends

bends close to the fan intake or discharge

fans mounted too close to obstructions such as walls

If insufficient straight duct is provided at the fan outlet the velocity profile in the duct will not be equalised and stabilisation of the outlet velocity profile will not be achieved, (see Figure. 10.1). In addition, interaction will occur with the duct fittings downstream resulting in higher pressure losses.

The difference between the fan performance under ideal conditions and its performance in an actual installation is known as the system effect psyst, and is proportional to the other system resistances.

10.3. Fan instabilityIn addition to the system effect, certain inlet configurations will cause a discontinuity in the pressure characteristic of the fan which will result in unstable performance at particular operating conditions. The fan performance becomes unpredictable and the pressure fluctuations cause objectionable duct rumbling noises and vibration. With axial flow fans, blade stall can occur at considerably lower system pressures.

In general, round and rectangular mitred bends (without turning vanes or splitters) on the inlet to either centrifugal or axial flow fans causes this instability.

10.4. System Effect FactorThe system effect is expressed in terms of a system effect factor as follows:—

Psyst = ζ x pv Equation 10.4.1

Where ζ = system effect factor

pv = the velocity pressure at the nominal inlet or outlet of the fan



In the following clauses the system effect factor is tabulated for various inlet and outlet configurations. The values quoted are intended as guidelines only. Some have been obtained previously by individual fan manufacturers, and many represent the consensus of engineers with considerable experience in the application of fans.

Fans of different types and even fans of the same type, but supplied by different manufacturers, will not necessarily react with the system in exactly the same way. It is therefore necessary to apply judgement, based on actual experience, in applying the system effect factors.

Figure 10.2 is a chart of system effect against various velocities for a range of system effect factors. By entering the chart at the appropriate air velocity the system effect in Pascals may be read off for the appropriate system effect factor for the fan configuration. This figure must then be added to the total system pressure when determining the fan duty.

The velocity figure used in entering the chart will be either the inlet or the outlet velocity of the fan. Most catalogue ratings include outlet velocity figures but, for centrifugal fans, it may be necessary to calculate the inlet velocity. The necessary dimensioned drawings are usually included in the fan catalogue.

The System Effect chart is for standard air at a density 1.2 kg/m3. Since the System effect is directly proportional to density, values for other densities can be calculated thus:

Figure 10.2 System effect for various system effect factors

10.5. System Effect for ducts at the fan inletFan inlet swirl and non-uniform inlet flow can often be corrected by inlet straightening vanes or guide vanes. Restricted fan inlets located too close to walls or obstructions, or restrictions caused by a plenum or cabinet will decrease the useable performance of a fan.

Non-uniform flow into the inlet is the most common cause of deficient fan performance. An elbow or a 90° duct turn located at the fan inlet will not allow the air to enter uniformly and will result in turbulent and uneven flow distribution at the fan impeller. Air has weight and a moving air stream has momentum and, therefore, the air stream resists a change in direction within an elbow as illustrated in Figures 10.5 and 10.6.



Figure 10.3

Figure 10.4

The system effect factor for various inlet bend configurations for centrifugal fans is given in Fig 10.3 through 10.6.

For the square 90° bends in Figure 10.6 the maximum permissible angle of any element in the transition is 15° convergent and 7.5° divergent.

Figure 10.5 Figure 10.6



Another major cause of reduced performance is an inlet duct condition that produces a vortex or spin in the air stream entering the fan inlet. An example of this condition is illustrated in Figure 10.7.

Figure 10.7

The ideal inlet condition is one which allows the air to enter axially and uniformly without spin in either direction. Swirling of the air in the same direction as the rotation of the fan reduces the fan performance. Uncontrolled swirling of the air in the opposite direction of the fan inlet may cause instability and pulsation. Proprietary inlet guide vanes supplied by the fan manufacturer are sometimes used to increase or control fan performance, but all types of system-generated swirl should be avoided.

Inlet spin may arise from a great variety of approach conditions and sometimes the cause is not obvious. Some common duct connections which cause inlet spin are illustrated in Figure 10.8, but since the variations are many, no System Effect Factors are tabulated. It is recommended that these types of duct connections be avoided, but if this is not possible, inlet conditions can usually be improved by the use of turning vanes as illustrated in Figure 10.9 and splitter sheets to break the spinning vortex.

Figure 10.8



Figure 10.9

10.6. System Effects at fan outletFans intended primarily for use with duct systems are usually tested with an outlet duct in place. In most cases it is not practical for the fan manufacturer to supply this duct as part of the fan but the rated performance will not be achieved unless a comparable duct is included in the system design. The system design engineer should examine catalogue ratings carefully for statements defining whether the published ratings are based on tests made with outlet ducts, inlet ducts, both, or no ducts.

Figure 10.1 shows the changes in velocity profiles at various distances from the fan outlet. For 100% recovery of uniform velocity profile the duct, including the transition, should extend at least two and one half equivalent duct diameters and will need to be as long as six equivalent duct diameters at outlet velocities of 30 m/s and higher.

If it is not possible to use a full length outlet duct, this must be accounted for when determining the system effect to be added to the system total pressure loss. Values of system effect factor for outlet ducts are given in 10.1, applicable to centrifugal fans.

For axial fan installations, system effect factors will vary depending on the sophistication of the axial fan manufacture. It is now common that axial fan manufacturers supply correction data for various outlet and inlet conditions, i.e. AS ISO 5801 Standard tests which requires data to be presented in Types A, B, C and D



Figure 10.1

Blast AreaOutlet Area

NoDuct

12%Effective

Duct

25%Effective

Duct

50%Effective

Duct

100%Effective

Duct0.40.50.60.70.80.91.0

2.02.01.00.80.50.25 -

1.01.00.70.40.250.15-

0.40.40.350.150.1

--

0.20.20.15----

----

--

Table 10.1 System Effect Factors for outlet ducts for centrifugal fans (effective duct length is as defined in Figure 10.1.)

The ratio of blast area to outlet area is not usually included in fan catalogue data and it will be necessary to obtain this from the fan manufacturer. Refer Figure 10.1 for definition of blast and outlet area.

Fans are often connected to ducts with a cross sectional area AK which is larger than the nominal outlet area AN, e.g. a fan discharging into a plenum or air handling unit. The system effect factors for this configuration are as indicated in Table 10.2

Table 10.2 System Effect Factors for Fan Discharge into a Plenum


AK

AN

1 1.5 2.0 2.5 3.00.50.60.70.80.91.0

------

0.80.60.40.30.20.1

1.30.90.70.50.40.25

1.61.20.90.70.50.4

1.81.41.00.80.60.5

The velocity profile at the outlet of a fan is not uniform and a bend located at or near the fan outlet will, therefore, develop a pressure loss greater than its ‘handbook’ value.

The amount of this increased loss will depend upon the location and orientation of the bend relative to the fan outlet. In some cases the effect of the bend will be to further distort the



outlet velocity profile of the fan. This will increase the losses and may result in such uneven flow in the duct that branch take-offs near the elbow will not deliver their desired airflow.

Wherever possible a length of straight duct should be installed at the fan outlet to permit diffusion and development of a uniform flow profile before a bend is inserted in the duct. If a bend must be located near the fan outlet then it should have a minimum radius to duct diameter ratio of 1.5 and should be arranged to give the most uniform airflow possible.

Table 10.3 gives System Effect Factors which can be used to estimate the effect of a bend at the outlet of an SWSI centrifugal fan. It also shows the reduction in losses resulting from the use of a straight outlet duct.

Table 10.3 System Effect Factors for bends at fan outlet for SWSI fans


OutletElbow

Position

NoOutletDuct

12%Effective

Duct

25%Effective

Duct

50%Effective

Duct

100%Effective

Duct0.4 A

BCD

3.04.55.55.5

2.53.84.54.5

1.82.53.03.0

0.81.21.61.6

System Effect Factor is zero

0.5 ABCD

2.02.83.83.8

1.62.32.82.8

1.21.82.32.3

0.60.81.01.0

0.6 ABCD

1.62.02.82.5

1.41.62.32.0

1.01.21.81.4

0.40.60.80.7

0.7 ABCD

0.71.01.41.2

0.60.81.21.0

0.40.60.80.7

0.20.30.350.35

0.8 ABCD

0.81.21.61.4

0.71.01.41.2

0.50.71.00.8

0.250.350.40.35

0.9 ABCD

0.71.01.21.0

0.60.81.00.8

0.40.60.70.6

0.20.30.350.3

1.0 ABCD

1.00.71.01.0

0.80.60.80.8

0.60.40.60.6

0.30.20.30.3

For DWDI Fans, determine System Effect Factor using the above tabulation for SWSI Fans. Next determine System Effect (Δp) from Figure 10.2, and then apply appropriate multiplier from tabulation below:

Bend Position B = Δp x 1.25

Bend Position D = Δp x 0.85

Bend Position A and C = Δp x 1.00

Refer to Figure 10.10 for bend position designations



Figure 10.10

Dampers are often furnished as accessory equipment by the fan manufacturer, but in many systems a volume control damper will be located in the ductwork near the fan outlet.

Volume control dampers are manufactured with either ‘opposed’ blades or ‘parallel’ blades. When partially closed, the parallel bladed damper diverts the airstream to the side of the duct. This results in a non-uniform velocity profile beyond the damper and flow to branch ducts close to the downstream side may be seriously affected.

The use of an opposed blade damper is recommended when volume control is required at the fan outlet and there are other system components, such as coils or branch takeoffs, downstream of the fan. When the fan discharges into a larger plenum or to free space, a parallel blade damper may be satisfactory.

For a centrifugal fan, the best air performance will usually be achieved by installing the damper with its blades perpendicular to the fan shaft. Published pressure losses for control dampers are based upon the uniform approach velocity profiles. When a damper is installed close to the outlet of a fan, the approach velocity profile is non-uniform and much higher pressure losses through the damper can result. Figure 10.11 lists multipliers which should be applied to the damper manufacturer’s catalogued pressure loss when the damper is installed at the outlet of a centrifugal fan.


StaticPressureMultiplier

0.40.50.60.7

7.54.83.32.4



0.80.91.0

1.91.51.2

Figure 10.11 Pressure loss multipliers for volume control dampers mounted at fan discharge

10.7. System Effect of plenums or enclosuresFans within plenums or next to walls should be located so that air may flow unobstructed into the inlets. Fan performance is reduced if the space between the fan inlet and the enclosures is too restrictive. It is common practice to allow at least one impeller diameter between an enclosure wall and the fan inlet. 1 impeller diameter is the minimum for axial fans and should be the target for centrifugal fans too.

The inlets of multiple fans located in a common enclosure should be at least one impeller diameter apart if optimum performance is to be expected. Figures 10.12, 10.13 and 10.14 illustrate fans located in an enclosure and the System Effect Factors for restricted inlets are listed in Table 10.4.

The manner in which the air stream enters an enclosure in relation to the fan inlets also affects fan performance. Plenum or enclosure inlets or walls which are not symmetrical with the fan inlets will cause uneven flow and/or inlet spin. Figure 12-60D illustrates this condition which must be avoided to achieve maximum performance from a centrifugal fan. If this is not possible, inlet conditions can usually be improved with a splitter sheet to break up the inlet vortex as illustrated in Figure 12-60E.

A reduction in fan performance can be expected when an obstruction to airflow is located in the plane of the fan inlet. Structural members, columns, butterfly valves, blast gates and pipes are examples of more common inlet obstructions. Some accessories such as inlet boxes, fan bearings, bearing pedestals, inlet vanes, inlet dampers, drive guards and motors may also cause inlet obstruction, if their size or location differs from the manufacturer’s standard designs. It is desirable that a drive guard located in a fan inlet be furnished with as much opening as possible to allow maximum flow to the fan inlet.

Obstruction at the fan inlet may be classified conveniently in terms of the unobstructed percentage of the inlet area. Because of the shape of inlet cones of many fans it is sometimes difficult to establish the area of the fan inlet. Figure 12-60F illustrates the convention adopted for this purpose. Where an inlet collar is provided, the inlet area is calculated from the inside diameter of this collar. Where no collar is provided, the inlet plane is defined by the points of tangent of the housing with the inlet cone radius.

The unobstructed percentage of the inlet area is calculated by projecting the profile of the obstruction onto the profile of the inlet. The adjusted inlet velocity obtained is then used to enter the System Effect chart (Figure 10.2) and the System Effect determined from the factor listed for that unobstructed percentage of the inlet area in Table 10.4.

To maintain fan efficiency at reduced flow conditions, airflow quantity is often controlled by variable vanes mounted in the fan inlet.

These are arranged to generate a forced inlet vortex which rotates in the same direction as the fan impeller (pre-rotation).

Inlet vanes may be of two different basic types:

Integral (built in) Cylindrical (add on)

The ‘System Effect’ of wide open inlet vane must be accounted for in the original fan selection. This data should be available from the fan manufacturer. If not, the following System Effect Factors may be applied in making the fan selection:



Table 10.4 System Effect Factors for fans located in plenums for various wall to inlet dimensions

L = distance between the inlet and the wall ζsyst

0.75 x D

0.5 x D

0.4 x D

0.3 x D

0.2 x D

0.25

0.4

0.6

0.8

1.2

Figures 10.12, 10.13 and 10.14



Figure 10.15

Table 10.5 – System Effect Factors for Obstructions at the Fan Inlet

Percentage of Unobstructed Inlet Area

System Effect Factor

100959085755025

NO LOSS0.30.40.530.81.62.0



Figure 10.16 and 10.17

10.8. Example calculation of System EffectA centrifugal fan is to be connected to a ducting system with, on the supply side a square outlet duct, dimension a x a, of length ‘a’ leading into a 90° bend with position B (Figure 12-70B). On the fan inlet, a circular duct is connected with a radiused bend R/D = 1 located two diameters away from the fan inlet.

On both sides, the fan is connected to ducts of the same cross-sections as the terminal flanges of the fan. Determine the resulting system effect.

Given:

The outlet velocity VN1 based on the nominal outlet area AN, is 17 m/s. Inlet velocity VN2 = 10 m/s. The ratio of blast area (AB) to outlet area (AN) is 0.7.

Solution:

INLET SIDE

(a) Bend upstream of the fan inlet.

The connection conditions correspond to Figure 12-50A



R/D = 1 (given)

Duct length L = 2D (given)

From the table in Figure 10.5ζsyst = 0.7

From Figure 10.2, at 10 m/s and ζsyst = 0.7, the system effect Δpsyst is 42 Pa

OUTLET SIDE

(b) Duct downstream of the fan.

Figure 10.1 illustrates how the effective duct length LE is defined.

LE100 at 17 m/s =(2. 5 + 1)×√4a2

π=7 a

√πActual duct length L = a

Actual effective duct length LE = L/LE100

=a√ π7a

×100=25 .3 %

From Table10.1, ζsyst = 0.15 at LE = 25% and AB/AN = 0.7

From Figure 10.2 at VN = 17 m/s and ζsyst = 0.15, the system effect Δpsyst is 25 Pa.

(c) Bend downstream of the fan outlet.

The connection conditions correspond to bend orientation B (Given)

AB/AN = 0.7

Actual effective duct length = 25% (see above)

From Table 12-70C, ζsyst = 0.6

From Figure 10.1 at 17 m/s and ζsyst = 0.6, the system effect Δpsyst is 105 Pa

The resulting system effect which is to be added to other system resistances will then be:

(a) + (b) + (c) = 42 + 25 + 105 = 172 Pa



Appendices



Appendix A Fan Laws

A1 Introduction

This Appendix provides a summary of the fan law equations.

When changing a single fan characteristic the fan laws can be used to predict the changes in performance in accordance with the following summary:

Variable Constants Law FormulaRotational speed

Air density, impeller diameter, distribution system

1. Volume flow is directly proportional to the rotational speed

2. Pressure developed is directly proportional to the square of the rotational speed (or flow)

3. Power absorbed is directly proportional to the cube of the rotational speed (or flow)

q1/q2 = n1/n2

p1/p2 = (n1/n2)²

P1/P2 = (n1/n2)³

Impeller diameter

Air density, distribution system

4. Volume flow and Power absorbed are directly proportional to the square of the impeller diameter

5. Rotational speed is inversely proportional to the impeller diameter

6. Pressure developed remains constant

q1/q2 = P1/P2 = (d1/d2)²

n1/n2 = d2/d1

p1 = p2

Impeller diameter

Air density, rotational speed, distribution system

7. Volume flow is directly proportional to the cube of the impeller diameter

8. Pressure developed is directly proportional to the square of the impeller diameter

9. Power absorbed is directly proportional to the fifth power of the impeller diameter

q1/q2 = (d1/d2)³

p1/p2 = (d1/d2)²

P1/P2 = (d1/d2)5

Air density Pressure developed, impeller diameter, distribution system

10. Rotational speed, volume flow and power absorbed are inversely proportional to the square root of air density

n1/n2 = q1/q2 = P1/P2

= √ (ρ 2 /ρ 1)

Air density Rotational speed, impeller diameter, distribution system

11. Pressure developed and power absorbed are directly proportional to the air density

12. Volume flow remains constant

p1/p2 = P1/P2 = ρ 1/ρ

2

q1 = q2

Where:q = Volume flow (m³/s); n= rotational speed of fan (rev/s); p= pressure developed (Pa)

P = power absorbed (W); d= Impeller diameter (m); ρ = Air density (kg/m³)

Notes:

1. Total pressure (pt) = Static pressure (ps) + Velocity pressure (pv)2. P = p x q3. Fan Laws apply to geometrically similar fans operating at the same point on the fan

performance curve.4. Characteristics of fans with aerofoil blades are likely to be Reynolds number

dependent.5. System resistance varies nearly as the air velocity squared.



Appendix B Measuring pressure and flow

B1 Measuring pressure

Static pressure in a stream of moving air can only be determined accurately by measuring it in a manner such that the velocity of the air has no influence on the measurement at all. This is done by measuring it through a small hole or series of holes arranged at right angles to the flow in a surface lying parallel with the lines of flow. The surface must not cause any disturbance to the flow apart from friction. A measurement of static pressure is made by connecting a tube from a static tapping on the measuring device to one side of a manometer, with the other side open to ambient atmosphere.

Total pressure is measured by connecting a manometer to a tube with its open end facing directly into the flow. Again, for this measurement, the other side of the manometer is open to ambient atmosphere.

Velocity pressure cannot be conveniently measured directly, but can very easily be measured as the difference between total pressure and static pressure by joining the total pressure connection to one side of a manometer and the static pressure connection to the other. This is sometimes referred to as a differential pressure and it is nearly always measured, in fan applications, by an inclined tube manometer.

The Pitot-static tube, often referred to simply as a Pitot Tube, is a convenient form of probe for inserting into a duct to provide, in a single instrument, both static pressure holes and a forward facing (total pressure) tube so that static pressure and velocity pressure may be measured simultaneously on two separate manometers suitably connected, refer Figure B1.

Other methods of static pressure measurements are available.

Figure B1 A Measurement of Air Pressure by Pitot Tube and Inclined Manometer

B2 Measuring flow



B2.1 Flow rates and their measurement

The quantities of air passing through the various sections in a ductwork system may be measured at the entrance to, exits from, or at locations within the system.

B2.2 Measurement by calibrated intake device

The inlet nozzle is the most satisfactory calibrated intake device, but it must be made accurately to proven proportions. A proven inlet as per AS ISO 5801 is comparatively easy to manufacture and has a well proven entry co-efficient. The flow rate can be calculated from a single static pressure measurement taken at a specified distance downstream of the nozzle. Another alternative is the orifice plate, also specified in AS ISO 5801.

B2.3 Measurement by static pressure measurement at the entry to a duct system

If a lower order of accuracy is acceptable, a meaningful measurement of airflow within approximately ± 10% can be made by measuring the static pressure or suction just downstream of the entry to a duct system which is exhausting from a space provided the area of the wall in which the duct entry is located is much larger than the duct entry.

A considerable amount of reliable information is available for entry coefficients of many alternative types of entry and using this data together with a static pressure or suction measurement the flow can be calculated.

Q=AKT−√P s Equation B2.1

for air with a density of 1.2 kg/m3

Where:

Q = airflow, L/sA = cross sectional area of duct, m2

KT = co-efficient of entryPs = static pressure, PaPv = velocity pressure, Pa

The entry co-efficient is

KT=√ PvP s Equation B2.2

A variety of entry configurations are shown in Figure B2 together with their appropriate entry coefficients.

For values of KT for a number of other intake devices refer to AIRAH DA03.

Various information has been published on K factors for calculating losses of various ductwork system components. The K factor is the total pressure loss in terms of the number of mean velocity heads at the section considered. If a particular shaped entry has a known K factor, the entry co-efficient can be derived as follows:

KT=√ 1K+1 Equation B2.3

Plain end of pipeRectangular or circular

KT 0.72

Flanged end of pipeRectangular or circular

KT 0.82

Plain end of pipePlus small radiusElbow bend

KT 0.62



Flanged end of pipePlus small radiusElbow bend

KT 0.74

Exhaust Booth KT 0.82

Sharp edged orifice KT 0.60

Tapered cone orRectangular to Round

KT 0.90(approx)

HOODS

(A) Where

Hood Face AreaPipe Area = 2 or more

Included Angle in ° ¿10 °−100 ° ¿100 °−140 ° ¿

180 ° (Flanged opening ) ¿¿¿¿ Entry KT

Circular ¿ 0 . 95 ¿0 . 90 ¿

0 . 82 ¿ Rectangular ¿ 0. 90 ¿

0. 85 ¿0 . 80 ¿¿¿¿¿¿¿

(B) Where

Hood Face AreaPipe Area = 1.2 to 2

Short Taper < ½ Face Diameter KT 0.95

Long Taper > ½ Face Diameter KT 0.85

Figure B2 Entry Coefficients for various entry Configurations

Drafting note: CIBSE has very comprehensive data on fitting losses and maybe worth looking at. They do, however, go much deeper into the subject but that isn’t a bad thing

B2.4 Measurement by Pitot-Static Tube

B2.4.1 In Duct

Where there is a portion of ductwork system that has a straight parallel section for at least six duct diameters or six duct widths downstream at any bend, obstruction or abrupt change of section, an accurate measure of airflow is possible by traversing the section using a Pitot-static tube in conjunction with a sensitive sloping manometer. The total pressure and static pressure connections are made to the opposite ends of the manometer, which will then indicate velocity pressure.

The air velocity at the point of measurement can be calculated from:

v=1. 291√ pv (m/s) Equation B2.4

For standard air of density1.2 kg/m3 (Standard air is 21°C, 101.325 kPa barometric pressure, 65% relative humidity).

For non standard conditions

v=1.291√ δ s×Pvδt (m/s) Equation B2.5

Where:

v = air velocity (m/s)pv = velocity pressure (Pa)



δ s = standard air density = 1.2 kg/m3

δ t = air density in duct (kg/m3)

The Pitot-static traverse pattern for circular ducts is shown in Figure B3.

Figure B3 Location of Positions for Transverse Measurements in Standardised Airways

At each testing point of the traverse pattern, the velocity pressure is read after allowing sufficient time for the manometer fluid to steady. The mean air velocity at the test section is obtained by averaging the air velocities at each point.

The flow rate is derived by multiplying the mean velocity by the cross sectional area.

B2.4.2 At Duct Discharge

Measuring by means of a Pitot-static tube at the air discharge point is relatively easy if the flow is uniform and straight but if any outlet louvers or other obstructions are fitted, which is the normal situation, reliable readings are very difficult to obtain.

B2.4.3 Measurement by Anemometer

It is possible to use an anemometer at a duct discharge, but significant experience is necessary to obtain meaningful results. Unless the air being discharged is substantially of uniform velocity and parallel to the duct axis, the anemometer readings will require extensive corrections and interpretation. As a result this method is not very accurate and multiple readings need to be taken and the average recorded to improve accuracy results.

It is also essential than an anemometer is re-calibrated regularly as it loses its accuracy quite quickly

B3 Other methods

Other specialised air velocity instruments are available, but they are outside the scope of this manual.

Drafting note: What about direct reading manometers?

Accurate airflow measurements other than in long straight lengths of ductwork, or with calibrated inlet nozzles, are extremely difficult to obtain.



Appendix C Specifying fans

C1 Introduction

Certain essential information is required for a fan manufacturer to be able to supply equipment that best meets the function for which it is intended.

In addition, further information, though not essential, may prevent an unsuitable machine being supplied or will ensure that the best selection from a number of alternatives is made. It is clearly in the interest of the fan user to provide all the information set out below.

C2 Essential Information

C2.1. Flow rate

The volume flow requirement (the actual volume of air/gas per unit time entering the fan inlet) and any possible future increases.

Units: litres per second (L/s) (preferred unit), cubic metres per second (m3/s)

For a fan that is to be controlled for reduced output, the lower duty operating points should also be nominated.

C2.2 Pressure

Fan total pressure

Fan static pressure

Units: kilopascals (kPa) (preferred unit), pascals (Pa)

C2.3 Discharge velocity

Fan discharge velocity.

Units: metres per second (m/s)

C2.4 Inlet gas density

Density of air/gas entering the fan inlet in mass per unit volume.

Units: kilogram per cubic metre (kg/m3)

C2.5 Altitude of fan installation/site

Units: metres (m)

C2.6 Nature of gas

Composition (if not air), temperature at which flow rate, pressure and discharge velocity apply.

Units: degrees Celsius (°C)

Whether gas is toxic, explosive, corrosive or has entrained solids.

C2.7 Noise

The maximum noise level that can be tolerated from the fan. Preferably it should be the in-duct sound power level in each octave band. Often the fan casing radiated sound power level is an important consideration, but unfortunately very little data on this is readily available from manufacturers.

Units: (dB re 10-12 Watts)

Note: In duct measurements are usually calculated numbers based on true measured data. A better design solution may be to have the raw sound pressure ratings for the fan available so acoustic engineers can simply add this data to full system assessments.

C2.8 Fan type and arrangement

Details on inlet and discharge positions, preferred bearing arrangement, size of inlet and outlet ducts to which the fan is to be connected.



C2.9 Drive

Particulars of the type of drive on the fan, whether horizontal or vertical shaft, details of electrical supply, etc., whether a vibration isolating base is required, life and type of bearings, type of bearing housing.

In belt-drive fans the position of the motor should be indicated, left or right, inside or outside.

It is assumed, unless otherwise advised, that the above details are the actual conditions under which the fan will operate, i.e. that all corrections for temperature, density, etc. have been made by the user. If there is doubt about any requirements, then the designer should advise the fan manufacturer.

C3 Additional Information

Additional information may include:

Brief details on the fan’s application, e.g. induced draft, paint spray exhaust. If a fan is to handle hot gasses, information on the ambient conditions to which the

bearings will be subjected should be stated. Whether the fan or drive is to be weather proofed (e.g. IP rating). Is allowance to be made for future increases in speed? Is the fan application extra arduous on the drive, necessitating additional safety

factors in the design?

C4 Fan Selection Considerations

Consideration to the type of fan required to perform a particular duty based upon a given set of selection criteria provides the starting point for good fan selection. Table C1 below provides a guide to fan type, which may be used to assess the options and best fan type.

Table C1 Guide to fan selection criteria

Criteria Fan SelectionLow first cost Propeller / Axial Fan.High efficiency Centrifugal fan with backward-inclined blades and preferably with

aerofoil blade design, or premium efficiency plug fan.Low noise level For low system pressures – Axial or plate mounted fans.

For medium or high system pressures – Backward-inclined centrifugal fans.

Space constraints Axial type, forward-curved centrifugal or plug fan.Flexibility in volume capacity Adjustable pitch axial fan or incorporate means of speed

adjustment i.e. belt-drive or variable speed drive, plug fan with VFD or EC motor.

High pressure systems Backward-inclined centrifugal fan, plug fan or contra-rotating axial fans.

Medium pressure systems Backward or forward-inclined centrifugal, plug or axial fans.Low pressure systems Plate mounted or axial fans.Non-stall characteristics Mixed-flow, centrifugal or low pitch angle axial.Reversible flow Axial fan – truly reversible impeller.

Note: In the case of axial flow fans in particular, because of the relatively high discharge air velocity, the total efficiency result is distorted. Selections made using static efficiency, or air kW will, always give a more efficient selection.

Having selected the right fan type, choosing the right fan size will optimise performance. Selection data may be presented in a tabulated format or by computer printout. For the optimum selection, reference should always be made to the fan performance curve. This acts as a visual check on the operating point and by ensuring the operating point occurs near the peak fan efficiency (best efficiency point) it will reduce the risk of performance problems and contribute to an energy efficient installation.

Often confusing criteria are offered as a basis of comparison. It is important for comparative purposes that the data is presented in its most fundamental form. Operating parameters such as fan speed, outlet velocity or unqualified sound pressure levels do not provide a true comparison between fan selections, makes and models. These characteristics may be



peculiar to a fan design or open to broad interpretation. Outlet velocity does not allow for truly efficient fan selections.

The best comparative information, (before price and physical size are considered), are the parameters of efficiency and sound power level. These two criteria will have the greatest effect on installation operating costs and environmental impact. Scroll fan efficiency data often only relates to impeller efficiency, making true comparison of published efficiency levels difficult. Consumed energy for the fan at the duty is the only true comparison on operating costs of the installed system.

C4 Worked Example of Typical Fan Selection

The example (Figure C1) is a system where the fan supplies filtered heated air to a conditioned space.

Following are the pressure loss calculations for the system (based on total pressure) for a volume flow of 1500 L/s. Fan discharge velocity is 20 m/s and its velocity at the inlet is 15 m/s. Figures, fittings and tables referred to below are taken from AIRAH DA03.

Inlet Losses (Pa)

Filter -50

Contraction 60°, Fitting No. 309 – (0.6 x 0.07 x 152) -10

Straight duct into elbow -70

Elbow 4 piece mitred, R/D = 1, Figure6-30A – (0.6 x 0.34 x 152) -46

Inlet System Effect and fan inlet, Figure 7-50C – (0.6 x 1.2 x 152) -162

Total Inlet Loss = Total fan pressure at inlet -338

Outlet Losses

Abrupt expansion fan discharge to plenum, Figure 6-30B – (0.6 x 1 x 202) 240

Outlet system effect for no fan outlet ductBlast Area/Outlet Area = 0.8: Plenum Area/Outlet Area = 3: Table 7-70B – (0.6 x 0.04 x 202) 192

Perforated Plate 40

Heater 63

Contraction 45°, Fitting No. 307 – (0.6 x 0.04 x 152) 5

Supply ductwork from heater to outlet 150

Velocity pressure loss at outlet – (0.6 x 152) 135

Total outlet loss = Total pressure at fan outlet 825

Fan Total Pressure pt = 825 – (-338) =1163 PaFan Static Pressure ps = 1163 – 0.6 x 202 = 923 Pa

Select fan manufacturer’s catalogue for 1500 L/s at 923 Pa ps and use recommended speed and power.

Note: Because fan static pressure is a function of the velocity pressure at its outlet, a fan with a different outlet velocity connected to the same system will have a fan static pressure different to that calculated above.

If the fan arrangement could be designed to have a straight run of ductwork to the fan inlet and a length of 4 duct diameters (Figure 7-70A) between fan outlet and heater, and the perforated plate excluded, there would be a reduction in pressure loss of approximately:



Elbow 46

Elbow system effect 162

Outlet system effect 192

Abrupt outlet expansion 240

Perforated plate 40

680

This means the fan could easily be operated at a reduced speed to deliver the same volume flow rate and consequently there would be a reduction in absorbed power of 73%. The revised selection point at the reduced speed would result in a quieter installation.

Figure C1 Pressure characteristics of a simple system



Appendix D Fan Performance Trouble Shooting

Fans are often accused of underperforming and not achieving the specified duty. However, it must be understood that the fan is a mechanical machine, which if correctly designed, built and tested will unfailingly deliver the catalogued performance data. It must be further understood that very few site installations reflect the standard test design. Every duct installation is different. Site conditions must be taken into consideration when assessing fan performance.

Given that all else is in reasonable order the fan may be inspected for defects or improper operation. However, before checking the common fan faults listed below it would be wise to ensure that no debris or other obstructions occur within the fan or duct system and that the fan size supplied and installed is correct and as per design requirements. A confirmation of fan diameters and discharge sizes is a good preliminary exercise. Otherwise the following points could be considered:

Axial Fans

1. Excessive tip clearance. Axial fans develop pressure through tight clearance between the case and blade tip. Check with the manufacturer for the recommended clearance for the tested fan design.

2. Impeller installed backwards. In effect this will run the impeller in the incorrect direction. This will reduce the volume flow rates dramatically. Check that the leading edge of the impeller makes the first contact with the incoming air stream and in the direction of rotation.

3. Fan running backward. The effect will be as for item 2 above. Check the direction of rotation and that the leading edge of the fan blade makes the first contact with the incoming air stream.

4. Incorrect pitch angle. The pitch angle is normally set on a jig. If the pitch angle is suspect contact the manufacturer for checking and re-setting if required.

5. Motor support too close to impeller. This causes separated flow through the fan and reduces the volume flow. Check with the manufacturer for their recommendations on tested design parameters.

6. Wrong fan speed. With direct-drive fans, check that the motor speed is in accordance with the selected and ordered fan details. Should the fan be indirect-drive, check the fan and motor pulley combinations and motor speed are all correct to deliver the right fan speed.

Centrifugal Fans

For both single width, single inlet (SWSI) and double width, double inlet (DWDI) fans, check the following:

1. Wrong fan speed through incorrect pulley combinations on belt-drive fans or incorrect motor selections. Check the fan speed at the fan shaft and confirm the fan and motor pulley combinations and motor speed are all correct to deliver the desired fan speed.

2. Insufficient belt tension causing belt slippage.

3. Fan running backward. Check that the leading edge of the impeller with respect to rotation makes the first contact with the incoming air stream. Fans running backward still induce an airflow in the required direction, however the volume flow rate is substantially reduced and power consumption may increase dramatically.



4. Incorrectly fitted inlet cone allowing excessive gap between impeller eye and the cone trailing edge. Figure D1 is a guide to typical limits and variances which may impact on fan performance.

<<INSERT FIGURE D1 Drafting note figure known/available??

For double width, double inlet fans, the following points should also be checked.

5. Check the fan impeller is central to the fan case. A non-centric impeller will cause uneven loading on the fan impeller and affect the fan performance results.

6. Check that the drive arrangement does not excessively decrease the fan inlet area, i.e. drive guards are sufficiently aerated or couplings and bearings allow adequate inlet clearance.

7. The inlets of a DWDI fan may also be obstructed by close proximity of walls or other machinery if installed on an open plenum arrangement. The important criteria is a balanced or equal restriction on both sides of the fan and uneven conditions may arise if an obstruction is within two impeller diameters of either inlet without treatment of the opposing inlet. Also conditions of airflow into the fan may induce a pre-swirl, which will derate the fan performance. Refer to Section 10 for the treatment of these conditions.



Appendix E Glossary and acronyms

Drafting note: To be completed at publication

E1 Glossary of termsIn this Appendix some of the more common terms relating to fans are described with cross references to relevant text in the manual.

Drafting note: What additional terms need to be defined?

Altitude the difference above (or below) sea level.

Attenuation Absorption of sound pressure by reducing amplitude of sound wave leaving the frequency unchanged.

Axial fan A fan design where air is discharged predominately parallel to the impeller rotational axis.

Best efficiency point (BEP) The operating condition at which the fan transfers energy to the air stream most efficiently.

Blast area The fan outlet area less the projected area of the cut-off.

Centrifugal fan A fan design where air is discharged predominately perpendicular to the impeller rotational axis.

Evasé A diffuser at the fan outlet that increases in area to decrease air velocity, converting kinetic energy to static pressure.

Fan performance curve A graphical representation of the fan pressure/flow performance characteristics which may also indicate fan efficiency and power input, (also called fan characteristic curve or simply fan curve).

Input power

Output power The power delivered by a motor shaft to a driven device (motor size in kW).

Fan motor power means the power delivered to a motor of a fan, including the power needed for any drive and impeller losses.

Impeller efficiency

Index run

Fan efficiency

Motor efficiency

Friction loss resistance to airflow through ducts, fittings and components, expressed as a static pressure loss.

Impeller The rotating bladed wheel within the fan that imparts energy to the air stream.

Impeller diameter The maximum diameter measured across the impeller blades.

Inclined manometer A metering device used to measure pressure.

Instability Refers to a condition where the fan will hunt or pulse providing a variable and unpredictable performance.

Make-up air Air that is replaced because of exhaust air requirements.

Pressure definitions

Fan Total Pressure The algebraic difference between the mean total pressure at the fan outlet and the mean total pressure at the fan inlet.

Fan Static Pressure The fan static pressure is a defined quantity used in rating fans and cannot be measured directly. It is the fan total pressure minus the velocity pressure corresponding to the mean air velocity at the fan outlet. Note that it is not the difference between the static pressure at the outlet and the static pressure at the inlet i.e.: it is not the external system static pressure.



Gauge pressure The pressure differential between atmospheric pressure and that measured within the system.

Heat slinger A metal rotor that is bolted to a high temperature fan shaft, designed to dissipate heat conducted along the shaft and induce air movement around the bearings.

Oversized A fan or motor that has a higher capacity than required.

Static Pressure The difference between the absolute pressure at a point in an airstream or a plenum chamber and the absolute pressure of ambient atmosphere, being positive when the pressure at the point is above the ambient pressure and negative when below. It acts equally in all directions, is independent of velocity and is a measure of the potential energy available in an airstream.

Shroud The fan casing or housing.

Sound pressure is a pressure disturbance in the atmosphere whose intensity is influenced not only by the strength of the source, but also by the surroundings and the distance from the source to the receiver, usually expressed in newtons per square meter.

Sound power The total sound energy radiated by a source per unit time, usually expressed in watts.

Stall Describes unpredictable performance, unstable operation and higher noise due to flow separation occurring around the blade of the impeller, caused because the fan is incapable of delivering the pressure required by the system.

System resistance curve A graphical representation of the pressure/volume characteristics of an air distribution system, (also called system curve).

Total Pressure The algebraic sum of static and velocity pressure. It is a measure of the total energy available in an airstream.

Variable speed drive

Variable frequency drive

Velocity Pressure Is a measure of the kinetic energy available in an airstream and is always positive.

Tonal Noise

E2 AcronymsOther key terms that needs to be defined?

AC Alternating currentAHU Air Handling UnitASHRAE American Society of Heating, Refrigerating and Air Conditioning EngineersBCA Building Code of AustraliaBMCS Building Management and Control System (also BMS, BAS, BACS)COP Coefficient of PerformanceDDC Direct Digital ControlDWDI Double width double inletDC Direct currentHEPA High Efficiency Particulate Air filterHVAC&R Heating, Ventilation, Air Conditioning and Refrigeration

IAQ Indoor Air QualityIEQ Indoor Environment QualityKPI Key Performance IndicatorM&V Measurement and VerificationNCC National Construction CodeO&M Operation and MaintenanceWHS Work Health and SafetyROI Return on InvestmentRTS Room Temperature SensorSAT Supply Air TemperatureSWSI Single width single inletTAB Testing, Adjusting, BalancingVAV Variable Air VolumeVFD Variable Frequency DriveVSD Variable Speed Drive



Appendix F Ingress protection and impact resistance rating

F1 The Ingress Protection (IP) CodeThe IP Code (or Ingress Protection Rating, sometimes also referred to as International Protection Rating) consists of the letters IP followed by two digits. As defined in international standard IEC 60529), the IP Code classifies and rates the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water.

The standard aims to provide users more detailed information than vague marketing terms such as waterproof. The digits (characteristic numerals) indicate conformity with the conditions summarized in the Tables below. The first digit indicates the enclosure’s degree of protection against solid objects while the second digit indicates a degree of protection against liquids. Where there is no protection rating with regard to one of the criteria, the digit is replaced with the letter X.

Table F1 Summary of IP Code

First IP Digit

Degree of Protection (Contact hazard and foreign object penetration)

Second IP Digit

Degree of Protection (Water hazard and penetration)

X Not tested for this criterion. X Not tested for this criterion.

0 No special protection. 0 No special protection.

1 Protected against penetration of solid objects larger than 50mm diameter, (e.g. accidental contact with the hand). No protection against intentional access.

1 Protected against drops of water falling vertically (dripping water, 1mm rainfall per minute).

2 Protected against entry of solid objects larger than 12mm diameter, (eg. accidental contact with finger).

2 Protected against drops of water falling at up to 15° from the vertical (dripping water, 3mm rainfall per minute).

3 Protected against entry of solid objects larger than 2.5mm diameter, (eg. tools and wires).

3 Protected against drops of water falling at up to 60° from the vertical, (indirect spraying water, 0.7 litres per minute at 80–100 kN/m²).

4 Protected against entry of solid objects larger than 1mm. (eg. fine tools and wires).

4 Protected against splashing water from all directions, (direct spraying water, 10 litres per minute at 80–100 kN/m²).

5 Protected against quantities of dust that could interfere with satisfactory operation. Ingress of dust is not totally prevented.

5 Protected against jets of water from all directions, (water jets, 6.3mm nozzle, 12.5 litres per minute at 30 kN/m² and 3m).

6 Completely protected against dust. Dust tight and full contact protection.

6 Protected against jets of water of similar force to heavy seas, (flooding, water jets, 12.5mm nozzle, 100 litres per minute at 100 kN/m² and 3m).

7 Protected against the effects of immersion, (up to 1 m of submersion for 30 mins).



8 Protected against the effects of submersion, (continuous submersion, depth specified by manufacturer).

F2 Mechanical impact resistance/’IK’ numberA separate IK number specified in EN 62262 is used to specify the resistance of equipment to mechanical impact. This mechanical impact is identified by the energy needed to qualify a specified resistance level, which is measured in joules (J).

Table F2 Summary of IK Number

IK number Impact energy (joules)

Equivalent impact

00 Unprotected No test

01 0.15 Drop of 200 g object from 7.5 cm height

02 0.2 Drop of 200 g object from 10 cm height

03 0.35 Drop of 200 g object from 17.5 cm height



06 1 Drop of 500 g object from 20 cm height

07 2 Drop of 500 g object from 40 cm height

08 5 Drop of 1.7 kg object from 29.5 cm height

09 10 Drop of 5 kg object from 20 cm height

10 20 Drop of 5 kg object from 40 cm height



Appendix G Resources

Drafting note: To be completed at publication

G1 Referenced documents

AIRAHDA02 Noise Control in and around buildings

DA03 Ductwork for air conditioning

DA 19 HVAC&R Maintenance

DA 27 Building commissioning

DA28 Building Management and Control Systems

AIRAH Technical Handbook

StandardsAS 1851 Routine service of fire protection systems and equipment

AS/NZS 3000 Electrical installations - (Known as the Wiring rules)

AS/NZS 3666

AS 4429 Methods of test and rating requirements for smoke-spill fans

AS ISO 5801 Industrial fans - Performance testing using standardized airways

ISO 5802 Industrial fans -- Performance testing in situ

ISO 12759 Fans - Efficiency classification for fans specifies

ISO 13347 Industrial fans -- Determination of fan sound power levels under standardized laboratory conditions

ISO 13350 Industrial fans -- Performance testing of jet fans

ISO 14694

ISO 14695

EN 62262

IEC 60529

ANSI/AMCA 210 Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating (also designated ANSI/ASHRAE 51)

NCC

G2 Additional resources

Resource documents

CIBSE (2006) TM42 – Fan application guide, Chartered Institute of Building Services Engineers, London

BSRIA

ASHRAE (2007) Fundamentals Handbook, American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc, Atlanta

ASHRAE (2009) Heating Ventilating and Air-Conditioning Applications Handbook, American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc, Atlanta

AMCA Publication 201 Fans and Systems

G. McMahon Selection Criteria for AC Variable Speed Drives AIRAH Journal, Feb 1994

Phoenix Fan Manual Introduction to Fans

Buffalo Forge Company: Fan Engineering



ACGIH Industrial Ventilation: A Manual of Recommended Practice for Design

ACGIH Industrial Ventilation: A Manual of Recommended Practice for Operation and Maintenance

Woods of Colchester – Woods Practical Guide to Fan Engineering

Websites


http://www.ashrae.org/

http://www.cibse.org.au/

http://www.fmaanz.com.au

End of Draft


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http://www.ashrae.org/


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