Cairo University

Faculty of Engineering

Mechanical Power Department

BSc. Graduation Project

2009-2010

AIR CONDITIONING

&HEATING SYSTEM

DESIGN& CONTROL

Under Supervision of :

Prof. Dr. Essam E. Khalil

Dr. Gamal El-Hariry

Presented By: Group (12)

Ahmed Mohammed Salah El din Esmail

Ahmed Monir Twfik

Alaa Abd alhamid Atia abo- Mera

Omar fathy Mohammed Mohammed

Mohammed saad Ewas

Acknowledgment

We would like to express our deep thanks and gratefulness for the support

and care of Prof. Dr. Essam E. Khalil and Dr. Gamal- ElHariry and their

guidance to complete our graduation project.

Finally, we would like to dedicate our deepest gratitude to our families

for their care, encouragement, and support.

And thanks to the team spirit,

Salah

Monir

Mohammed

Allaa

Omar

Preface

This thesis is a Graduation project for the degree of Bachelor of Science

in the Mechanical Power Engineering.

It presents, in details, the components, the design procedures, calculations

and the different types of:

Domestic water Heat exchangers

Fire tube Boilers

Air Handling Units

Fan coil Units

We tried to show, in our thesis, a general view of the various types,

Arrangements, constructions and used materials of the whole air

conditioning system components.

Also we included a detailed design for the all components, in which

We based our design parameters on real values from standards and

references, trying to achieve actual manufacturer dimensions.

Concerning the Air-handling Unit and Fan-coil Unit cooling coils, we

based our design procedures as we studied in the air-conditioning and

heat transfer courses, also by using computer calculation software, as

(Carrier block load E20-II (HAP), Engineering Equation Solver (EES)).

We included, in this project, an overview for the HVAC control

Systems, explaining the control procedures and systems used. Also, we

explained what is meant by BMS (Building Management System) and its

application.

Table of Contents

Chapter1 Basic Air-Conditioning Fundamentals,

Design and Methodology.

Chapter 2 Fire-tube Boilers

Chapter 3 Domestic Water Heat Exchangers

Chapter 4 Air Handling Units

Chapter 5 Fan-coil Units

Chapter 6 HVAC in Health Care Facilities

Chapter 7 Air conditioning system, Development in hospitals

Chapter8 Building Management Systems

Appendix A Distributable Programs

Appendix B Used Tables and Charts

Appendix C References

CHAPTER 1

Basic Air Conditioning Design

Methodology, Development, Materials

And Controls

CHAPTER 1

Basic Air Conditioning Design

Methodology, Development, Materials

And Controls

Air Conditioning:

Air conditioning is a combined process that performs many functions Simultaneously.

It conditions the air, transports it, and introduces it to the conditioned space. It

provides heating and cooling from its central plant or rooftop units. It also controls

and maintains the temperature, humidity, air movement, air cleanliness, sound level,

and pressure differential in a space within predetermined limits for the comfort and

health of the occupants of the conditioned space or for the purpose of product

processing

.

The term HVAC is an abbreviation of heating, ventilating, and air conditioning.

The combination of processes in this commonly adopted term is equivalent to the

current definition of air conditioning because all these individual component

processes were developed prior to the more complete concept of air conditioning.

Air Conditioning Systems:

An air conditioning, or HVAC, system is composed of components and equipment

arranged in sequence to condition the air, to transport it to the conditioned space, and

to control the indoor environmental parameters of a specific space within required

limits.

Most air conditioning systems perform the following functions:

1. Provide the cooling and heating energy required

2. Condition the supply air, that is, heat or cool, humidify or dehumidify, clean and

purify, and attenuate any objectionable noise produced by the HVAC equipment.

3. Distribute the conditioned air, containing sufficient outdoor air, to the conditioned

space.

4. Control and maintain the indoor environmental parameters–such as temperature,

humidity, cleanliness, air movement, sound level, and pressure differential between

the conditioned space and surroundings within predetermined limits.

Parameters such as the size and the occupancy of the conditioned space, the indoor

Environmental parameters to be controlled, the quality and the effectiveness of

Control , and the cost involved determine the various types and arrangements of

components used to provide appropriate characteristics.

Air conditioning systems can be classified according to their applications as

(1) comfort air conditioning systems and

(2) Process air conditioning systems.

Comfort Air Conditioning Systems:

Comfort air conditioning systems provide occupants with a comfortable and healthy

indoor environment in which to carry out their activities. The various sectors of the

economy using comfort air conditioning systems are as follows:

1. The commercial sector includes office buildings, supermarkets, department

stores, shopping centers, restaurants, and others. Many high-rise office

buildings use complicated air conditioning systems to satisfy multi pletenant

requirements. In light commercial buildings, the air conditioning system

serves the conditioned space of only a single-zone or comparatively smaller

area. For shopping malls and restaurants, air conditioning is necessary to

attract customers.

2. The institutional sector includes such applications as schools, colleges,

universities, libraries, museums, indoor stadiums, cinemas, theaters, concert

halls, and recreation centers.

3. The residential and lodging sector consists of hotels, motels, apartment

houses, and private homes. Many systems serving the lodging industry and

apartment houses are operated continuously, on a 24-hour, 7-day-a-week

schedule, since they can be occupied at any time.

4. The health care sector encompasses hospitals, nursing homes, and convalescent

care facilities. Special air filters are generally used in hospitals to remove bacteria and

particulates of sub micrometer size from areas such as operating rooms, nurseries, and

intensive care units.

5. The transportation sector includes aircraft, automobiles, railroad cars, buses, and

cruising ships. Passengers increasingly demand ease and environmental comfort,

especially for long distance travel. Modern airplanes flying at high altitudes may

require a pressure differential of about 5 psi between the cabin and the outside

atmosphere.

Process Air Conditioning Systems:

Process air conditioning systems provide needed indoor environmental control for

manufacturing, product storage, or other research and development processes. The

following areas are examples of process air conditioning systems:

1. In textile mills, natural fibers and manufactured fibers are hygroscopic. Proper

control of humidity increases the strength of the yarn and fabric during

processing. For many textile manufacturing processes, too high a value for the

space relative humidity can cause problems in the spinning process. On the

other hand, a lower relative humidity may induce static electricity that is

harmful for the production processes.

2. Many electronic products require clean rooms for manufacturing such things

as integrated circuits, since their quality is adversely affected by airborne

particles. Relative-humidity control is also needed to prevent corrosion and

condensation and to eliminate static electricity. Temperature control maintains

materials and instruments at stable condition and is also required for workers

who wear dust-free garments.

3. Precision manufacturers always need precise temperature control during

production of precision instruments, tools, and equipment.

4. Pharmaceutical products require temperature, humidity, and air cleanliness

control. For instance, liver extracts require a temperature of 75°F (23.9°C) and

a relative humidity of 35 percent. If the temperature exceeds 80°F (26.7°C),

the extracts tend to deteriorate. High-efficiency air filters must be installed for

most of the areas in pharmaceutical factories to prevent contamination.

5. Modern refrigerated warehouses not only store commodities in coolers at

temperatures of 27 to 32°F (-2.8 to 0°C) and frozen foods at -10 to -20°F (-23

to -29°C), but also provide relative-humidity control for perishable foods

between 90 and 100 percent. Refrigerated storage is used to prevent

deterioration. Temperature control can be performed by refrigeration systems

only, but the simultaneous control of both temperature and relative humidity in

the space can only be performed by process air conditioning systems.

Classification of Air Conditioning Systems according to Construction

and Operating Characteristic:

Individual Room Air Conditioning Systems

Individual Room or simply individual air conditioning systems employ a single, self-

contained room air conditioner, a packaged terminal, a separated indoor outdoor

split unit, or a heat pump. A heat pump extracts heat from a heat source and rejects

heat to air or water at a higher temperature for heating. Unlike other systems, these

systems normally use a totally independent unit or units in each room.

Individual air conditioning systems can be classified into two categories:

− Room air conditioner (window-mounted)

− Packaged terminal air conditioner (PTAC), installed in a sleeve through the outside

wall.

The major components in a factory-assembled and ready-for-use room air conditioner

include the following: An evaporator fan pressurizes and supplies the conditioned air

to the space. In tube and fin coil, the refrigerant evaporates, expands directly inside

the tubes, and absorbs the heat energy from the ambient air during the cooling season;

it is called a direct expansion (DX) coil. When the hot refrigerant releases heat energy

to the conditioned space during the heating season, it acts as a heat pump. An air filter

removes airborne particulates. A compressor compresses the refrigerant from a lower

evaporating pressure to a higher condensing pressure. A condenser liquefies

refrigerant from hot gas to liquid and rejects heat through a coil and a condenser fan.

A temperature control system senses the space air temperature (sensor) and starts or

stops the compressor to control its cooling and heating capacity through a thermostat.

The difference between a room air conditioner and a room heat pump, and a packaged

terminal air conditioner and a packaged terminal heat pump, is that a four-way

reversing valve is added to all room heat pumps. Sometimes room air conditioners are

separated into two split units: an outdoor condensing unit with compressor and

condenser, and an indoor air handler in order to have the air handler in a more

advantageous location and to reduce the compressor noise indoors.

Individual air conditioning systems are characterized by the use of a DX coil for a

single room.

This is the simplest and most direct way of cooling the air. Most of the individual

systems do not employ connecting ductwork. Outdoor air is introduced through an

opening or through a small air damper. Individual systems are usually used only for

the perimeter zone of the building.

Evaporative-Cooling Air Conditioning Systems

Evaporative-cooling air conditioning systems use the cooling effect of the evaporation

of liquid water to cool an air stream directly or indirectly. It could be a factory-

assembled packaged unit or a field-built system. When an evaporative cooler provides

only a portion of the cooling effect, then it becomes a component of a central

hydronic or a packaged unit system.

An evaporative-cooling system consists of an intake chamber, filter(s), supply fan,

direct-contact or indirect-contact heat exchanger, exhaust fan, water sprays,

recirculating water pump, and water sump. Evaporative-cooling systems are

characterized by low energy use compared with refrigeration cooling. They produce

cool and humid air.

Desiccant-Based Air Conditioning Systems

A desiccant-based air conditioning system is a system in which latent cooling

is performed by desiccant dehumidification and sensible cooling by evaporative

cooling or refrigeration. Thus, a considerable part of expensive vapor compression

refrigeration is replaced by inexpensive evaporative cooling. A desiccant-based air

conditioning system is usually a hybrid system of dehumidification, evaporative

cooling, refrigeration, and regeneration of desiccant.

There are two air streams in a desiccant-based air conditioning system: a process air

stream and a regenerative air stream. Process air can be all outdoor air or a mixture of

outdoor and re-circulating air. Process air is also conditioned air supplied directly to

the conditioned space or enclosed manufacturing process, or to the air-handling unit

(AHU), packaged unit (PU), or terminal for further treatment. Regenerative air stream

is a high-temperature air stream used to reactivate the desiccant.

A desiccant-based air conditioned system consists of the following components:

rotary desiccant dehumidifiers, heat pipe heat exchangers, direct or indirect

evaporative coolers, DX coils and vapor compression unit or water cooling coils and

chillers, fans, pumps, filters, controls, ducts, and piping.

Thermal Storage Air Conditioning Systems

In a thermal storage air conditioning system or simply thermal storage system, the

electricity-driven refrigeration compressors are operated during off-peak hours.

Stored chilled water or stored ice in tanks is used to provide cooling in buildings

during peak hours when high electric demand charges and electric energy rates are in

effect. A thermal storage system reduces high electric demand for HVAC and

partially or fully shifts the high electric energy rates from peak hours to off-peak

hours.

A thermal storage air conditioning system is always a central air conditioning system

using chilled water as the cooling medium. In addition to the air, water, and

refrigeration control systems, there are chilled-water tanks or ice storage tanks,

storage circulating pumps, and controls.

Clean-Room Air Conditioning Systems

Clean-room or clean-space air conditioning systems serve spaces where there is a

need for critical control of particulates, temperature, relative humidity, ventilation,

noise, vibration, and space pressurization.

In a clean-space air conditioning system, the quality of indoor environmental control

directly affects the quality of the products produced in the clean space.

A clean-space air conditioning system consists of a re-circulating air unit and a

makeup air unit both include dampers, pre-filters, coils, fans, high-efficiency

particulate air (HEPA) filters, ductwork, piping work, pumps, refrigeration systems,

and related controls except for a humidifier in the makeup unit.

Space Conditioning Air Conditioning Systems

They have cooling, dehumidification, heating, and filtration performed predominately

by fan coils, water source heat pumps, or other devices within or above the

conditioned space, or very near it. A fan coil consists of a small fan and a coil. A

water source heat pump usually consists of a fan, a finned coil to condition the air,

and a water coil to reject heat to a water loop during cooling, or to extract heat from

the same water loop during heating. Single or multiple fan coils are always used to

serve a single conditioned room.

Usually, a small console water-source heat pump is used for each control zone in the

perimeter zone of a building, and a large water-source heat pump may serve several

rooms with ducts in the core of the building.

Space air conditioning systems normally have only short supply ducts within the

conditioned space, and there are no return ducts except the large core water-source

heat pumps. The pressure drop required for the recirculation of conditioned space air

is often equal to or less than 0.6 in. water column (WC) (150 Pa). Most of the energy

needed to transport return and re-circulating air is saved in a space air conditioning

system, compared to a unitary packaged or a central hydronic air conditioning

system.

Space air conditioning systems are usually employed with a dedicated (separate)

outdoor ventilation air system to provide outdoor air for the occupants in the

conditioned space.

Space air conditioning systems often have comparatively higher noise level and need

more periodic maintenance inside the conditioned space.

Unitary Packaged Air Conditioning Systems

Unitary packaged air conditioning systems can be called, in brief, packaged air

conditioning systems or packaged systems. These systems employ either a single,

self-contained packaged unit or two split units. A single packaged unit contains fans,

filters, DX coils, compressors, condensers, and other accessories. In the split system,

the indoor air handler comprises controls and the air system, containing mainly fans,

filters, and DX coils; and the outdoor condensing unit is the refrigeration system,

composed of compressors and condensers. Rooftop packaged systems are most

widely used.

Packaged air conditioning systems can be used to serve either a single room or

multiple rooms.

A supply duct is often installed for the distribution of conditioned air, and a DX coil

is used to cool it. Other components can be added to these systems for operation of a

heat pump system; i.e., a centralized system is used to reject heat during the cooling

season and to condense heat for heating during the heating season.

Sometimes perimeter baseboard heaters or unit heaters are added as a part of a unitary

packaged system to provide heating required in the perimeter zone.

Packaged air conditioning systems that employ large unitary packaged units are

central systems by nature because of the centralized air distributing ductwork or

centralized heat rejection systems.

Packaged air conditioning systems are characterized by the use of integrated, factory-

assembled, and ready-to-use packaged units as the primary equipment as well as DX

coils for cooling, compared to chilled water in central hydronic air conditioning

systems. Modern large rooftop packaged units have many complicated components

and controls which can perform similar functions to the central hydronic systems in

many applications.

Classification of Air Conditioning Systems according to

Heat Transport media:

Air System

An air system is sometimes called the air-handling system. The function of an air

system is to condition, to transport, to distribute the conditioned, re-circulating,

outdoor, and exhaust air, and to control the indoor environment according to

requirements. The major components of an air system are the air-handling units,

supply/return ductwork, fan-powered boxes, space diffusion devices, and exhaust

systems.

An air-handling unit (AHU) usually consists of supply fan(s), filter(s), a cooling coil,

a heating coil, a mixing box, and other accessories. It is the primary equipment of the

air system. An AHU conditions the outdoor/ re-circulating air, supplies the

conditioned air to the conditioned space, and extracts the returned air from the space

through ductwork and space diffusion devices.

A fan-powered variable-air-volume (VAV) box, often abbreviated as fan powered

box, employs a small fan with or without a heating coil. It draws the return air from

the ceiling plenum, mixes it with the conditioned air from the air-handling unit, and

supplies the mixture to the conditioned space.

Space diffusion devices include slot diffusers mounted in the suspended ceiling; their

purpose is to distribute the conditioned air evenly over the entire space according to

requirements. The return air enters the ceiling plenum through many scattered return

slots.

Exhaust systems have exhaust fan(s) and ductwork to exhaust air from the lavatories,

mechanical rooms, and electrical rooms.

Water System

The water system includes chilled and hot water systems, chilled and hot water

pumps, condenser water system, and condenser water pumps. The purpose of the

water system is:

(1) To transport chilled water and hot water from the central plant to the air-handling

units, fan-coil units, and fan powered boxes.

(2) To transport the condenser water from the cooling tower, well water, or other

sources to the condenser inside the central plant.

After the condenser water has been cooled in the cooling tower, it flows back to the

condenser of the centrifugal chillers on lower level 3. The temperature of the

condenser water again rises owing to the absorption of the condensing heat from the

refrigerant in the condenser. After that, the condenser water is pumped to the cooling

towers by the condenser water pumps.

Air, Water, Refrigeration, and Heating Systems

Air, water, refrigeration, heating, and control systems are the subsystems of an

air conditioning or HVAC system. Air systems are often called secondary systems.

Heating and refrigeration systems are sometimes called primary systems.

Central hydronic and space conditioning air conditioning systems both have air,

water, and refrigeration, heating, and control systems. The water system in a space

conditioning system may be a chilled /hot water system. It also could be a centralized

water system to absorb heat from the condenser during cooling, or provide heat for

the evaporator during heating.

For a unitary packaged system, it consists of mainly air, refrigeration, and control

systems. The heating system is usually one of the components in the air system.

Sometimes a separate baseboard hot water heating system is employed in the

perimeter zone.

An evaporative-cooling system always has an air system, a water system, and a

control system. A separate heating system is often employed for winter heating.

In an individual room air conditioning system, air and refrigeration systems are

installed in indoor and outdoor compartments with their own control systems. The

heating system is often a component of the supply air chamber in the room air

conditioner. It can be also a centralized hot water heating system in a PTAC system.

Air conditioning or HVAC systems are therefore often first described and analyzed

through their subsystems and main components: such as air, water, heating, cooling/

refrigeration, and control systems.

Air conditioning system classification, system operating characteristics, and system

selection must take into account the whole system.

Among the air, water, and refrigeration systems, the air system conditions the air,

controls and maintains the required indoor environment, and has direct contact with

the occupants and the manufacturing processes. These are the reasons why the

operating characteristics of an air conditioning system are essentially represented by

its air system.

Water Systems

Types of Water System:

Water systems that are part of an air conditioning system and that link the central

plant, chiller / boiler, air-handling units (AHU s), and terminals may be classified

into the following categories according to their use:

Chilled Water System:

In a chilled water system, water is first cooled in the water chiller the evaporator of a

reciprocating, screw, or centrifugal refrigeration system located in a centralized plant

to a temperature of 40 to 50°F (4.4 to 10.0°C). It is then pumped to the water cooling

coils in AHU s and terminals in which air is cooled and dehumidified. After flowing

through the coils, the chilled water increases in temperature up to 60 to 65°F (15.6 to

18.3°C) and then returns to the chiller.

Chilled water is widely used as a cooling medium in central hydronic air conditioning

systems.

When the operating temperature is below 38°F (3.3°C), inhibited glycols, such as

ethylene glycol or propylene glycol, may be added to water to create an aqueous

solution with a lower freezing point.

Evaporative-Cooled Water System:

Evaporative cooled water is often produced by an evaporative cooler to cool the air.

Hot Water System:

These systems use hot water at temperatures between 450 and 150°F (232 and 66°C)

for space and process heating purposes.

Dual-Temperature Water System:

In a dual-temperature water system, chilled water or hot water is supplied to the coils

in AHU s and terminals and is returned to the water chiller or boiler mainly through

the following two distribution systems:

Use supply and return main and branch pipes separately.

Use the common supply and return mains, branch pipe, and coil for hot and

chilled water supply and return.

The changeover from chilled water to hot water and vice versa in a building or a

system depends mainly on the space requirements and the temperature of outdoor air.

Hot water is often produced by a boiler; sometimes it comes from a heat recovery

system.

Condenser Water System:

In a condenser water or cooling water system, the latent heat of condensation is

removed from the refrigerant in the condenser by the condenser water. This condenser

water either is from the cooling tower or is surface water taken from a lake, river, sea,

or well. For an absorption refrigeration system, heat is also removed from the solution

by cooling water in the absorber. The temperature of the condenser water depends

mainly on the local climate.

Water systems also can be classified according to their operating characteristics into

the following categories:

i. Closed System:

In a closed system, chilled or hot water flowing through the coils, heaters, chillers,

boilers, or other heat exchangers forms a closed re-circulating loop.

In a closed system, water is not exposed to the atmosphere during its flowing process.

The purpose of recirculation is to save water and energy.

Closed Water System

ii. Open System:

In an open system, the water is exposed to the atmosphere.

For example, chilled water comes directly into contact with the cooled and

dehumidified air in the air washer, and condenser water is exposed to atmosphere air

in the cooling tower. Recirculation of water is used to save water and energy.

Open systems need more water treatments than closed systems because dust and

impurities in the air may be transmitted to the water in open systems. A greater

quantity of makeup water is required in open systems to compensate for evaporation,

drift carryover, or blow-down operation.

Open Water System

Once-Through System:

In a once-through system, water flows through the heat exchanger only once and does

not re-circulate. Lake, river, well, or seawater used as condenser cooling water

represents a once-through system. Although the water cannot re-circulate to the

condenser because of its rise in temperature after absorbing the heat of condensation,

it can still be used for other purposes, such as flushing water in a plumbing system

after the necessary water treatments, to conserve water. In many locations, the law

requires that well water be pumped back into the ground.

Once-Through Water System

Water Piping:

Piping Material:

For water systems, the piping materials most widely used are steel, both black (plain)

and galvanized (zinc-coated), in the form of either welded-seam steel pipe or seamless

steel pipe; ductile iron and cast iron; hard copper; and polyvinylchloride (PVC). The

piping materials for various services are shown below:

− Chilled water Black and galvanized steel

− Hot water Black steel, hard copper

− Cooling water and drains Black steel, galvanized ductile iron, PVC

Copper, galvanized steel, galvanized ductile iron and PVC pipes have better corrosion

resistance than black steel pipes. Technical requirements, as well as local customs,

determine the selection of piping materials.

Pipe Joints:

Steel pipes of small diameter (2 in. or 50 mm less) threaded through cast-iron fittings

are the most widely used type of pipe joint. For steel pipes of diameter 2 in. (50 mm)

and more, welded joints, bolted flanges, and grooved ductile iron joined fittings are

often used. Galvanized steel pipes are threaded together by galvanized cast iron or

ductile iron fittings.

Copper pipes are usually joined by soldering and brazing socket end fittings. Plastic

pipes are often joined by solvent welding, fusion welding, screw joints, or bolted

flanges.

Vibrations from pumps, chillers, or cooling towers can be isolated or dampened by

means of flexible pipe couplings. Arch connectors are usually constructed of nylon or

polyester.

They can accommodate deflections or dampen vibrations in all directions. Restraining

rods and plates are required to prevent excessive stretching. A flexible metal hose

connector includes a corrugated inner core with a braided cover. It is available with

flanged or grooved end joints.

Expansion and Contraction:

During temperature changes, all pipes expand and contract. The design of water pipes

must take into consideration this expansion and contraction. Both the temperature

change during the operating period and the possible temperature change between the

operating and shutdown periods should also be considered. For chilled and condenser

water, which has a possible temperature change of 40 to 100°F (4.4 to 37.8°C),

expansion and contraction cause considerable movement in a long run of piping.

Unexpected expansion and contraction cause excess stress and possible failure of the

pipe, pipe support, pipe joints, and fittings.

Expansion and contraction of hot and chilled water pipes can be better accommodated

by using loops and bends. The commonly used bends are U bends, Z bends, and L

bends.

Loops and bends used in piping

If there is no room to accommodate U, Z, or L bends (such as in high-rise buildings or

tunnels), mechanical expansion joints are used to compensate for movement during

expansion. Packed expansion joints allow the pipe to slide to accommodate movement

during expansion. Various types of packing are used to seal the sliding surfaces in

order to prevent leakage. Another type of mechanical joint uses bellows or flexible

metal hose to accommodate movement. These types of joints should be carefully

installed to avoid distortion.

Expansion Tank

Open Expansion Tank:

An expansion tank is a device that allows for the expansion and contraction of water

contained in a closed water system when the water temperature changes between two

predetermined limits. Another function of an expansion tank is to provide a point of

known pressure in a water system.

An open expansion tank is vented to the atmosphere and is located at least 3 ft (0.91

m) above the highest point of the water system. Makeup water is supplied through a

float valve, and an internal overflow drain is always installed. A float valve is a globe

or ball valve connected with a float ball to regulate the makeup water flow according

to the liquid level in the tank.

An open expansion tank is often connected to the suction side of the water pump to

prevent the water pressure in the system from dropping below the atmospheric

pressure. The pressure of the liquid level in the open tank is equal to the atmospheric

pressure, which thus provides a reference point of known pressure to determine the

water pressure at any point in the water system.

The minimum tank volume should be at least 6 percent of the volume of water in the

system Vs, ft3 (m3). An open expansion tank is simple, more stable in terms of system

pressure characteristics, and low in cost. If it is installed indoors, it often needs a high

ceiling. If it is installed outdoors, water must be prevented from freezing in the tank,

air vent, or pipes connected to the tank when the outdoor temperature is below 32°F

(0°C). Because the water surface in the tank is exposed to the atmosphere, oxygen is

more easily absorbed into the water, which makes the tank less resistant to corrosion

than a diaphragm tank (to be described later). Because of these disadvantages, an

open expansion tank has only limited applications.

Open Expansion Tank in a

Closed Water System

Closed Expansion Tank:

A closed expansion tank is an airtight tank filled with air or other gases, as shown in

Figure. When the temperature of the water increases, the water volume expands.

Excess water then enters the tank. The air in the tank is compressed, which raises the

system pressure. When the water temperature drops, the water volume contracts,

resulting in a reduction of the system pressure.

To reduce the amount of air dissolved in the water so as to prevent corrosion and

prevent air noise, diaphragm, or a bladder, is often installed in the closed expansion

tank to separate the filled air and the water permanently.

Such an expansion tank is called a diaphragm, or bladder, expansion tank.

Thus, a closed expansion tank is either a plain closed expansion tank, which does not

have a diaphragm to separate air and water, or a diaphragm tank.

For a water system with only one air-filled space, the junction between the closed

expansion tank and the water system is a point of fixed pressure.

At this point, water pressure remains constant whether or not the pump is operating

because the filled air pressure depends on only the volume of water in the system. The

pressure at this point can be determined according to the ideal gas law.

The pressure in a closed expansion tank during the initial filling process or at the

minimum operating pressure is called the fill pressure (psia). The fill pressure is often

used as the reference pressure to determine the pressure characteristics of a water

system.

Closed Expansion Tank in a

Closed Water System

Penalties due to Presence of Air and Gas:

The presence of air and gas in a water system causes the following penalties for a

closed water system with a plain closed expansion tank:

1- Presence of air in the terminal and heat exchanger, which reduces the heat transfer

surface.

2- Corrosion due to the oxygen reacting with the pipes.

3- Water logging in plain closed expansion tanks.

4- Unstable system pressure.

5- Poor pump performance due to gas bubbles.

6- Noise problems.

There are two sources of air and gas in a water system. One is the air-water interface

in a plain closed expansion tank or in an open expansion tank, and the other is the

dissolved air in a city water supply.

Air Systems

Air systems and their controls directly affect the indoor environment and indoor air

quality (IAQ).

In a broad sense, air systems are a group of subsystems in an air conditioning system.

Air systems include supply and return air systems (space re-circulating systems),

mechanical ventilation systems, air distribution systems, regenerative systems, smoke

control systems, and terminals. The main functions of air systems are as follows:

1-Conditioning the supply air including heating or cooling, humidification or

dehumidification, cleaning and purifying, and attenuation of objection noise produced

by fans, compressors, and pumps.

2-Distributing the conditioned supply air with adequate outdoor air to the conditioned

space, extracting space air for re-circulating, and exhausting or relieving unwanted

space air to the outdoors.

3-Providing space pressurization, toxic gas exhaust, and smoke control for occupants‟

safety and fire protection.

4- Controlling and maintaining required space temperature, humidity, cleanliness, air

movement, sound level, and pressure differential within predetermined limits at

optimum energy consumption and cost.

5- Using high-temperature air stream to reactivate the desiccant, if any.

Classification of Air Systems:

Air systems, in a narrower sense, can be classified into the following

Categories according to their system characteristics:

⇒ Air-handling systems, air handlers, and air distribution systems.

⇒ Supply air systems, return air systems, re-circulating air systems, and exhaust air

systems. A supply air system may supply conditioned air, outdoor ventilation air,

makeup air (either conditioned air or non-conditioned air), or re-circulating air. A

return air system often returns the conditioned space air to the fan room or machinery

room. A re-circulating air system transports the conditioned space air to the AHU,

PU, fan-coil unit, or water-source heat pump for conditioning or mixing with outdoor

air again. An exhaust system exhausts the contaminated air or space air to the outside

atmosphere.

⇒ Single-zone or multi-zone systems, In a single-zone system, there is no terminal.

Space temperature, relative humidity, and volume flow rate are controlled directly by

the coils, humidifiers, and inlet vanes or ac inverter in the air-handling unit or

packaged unit. In a multi-zone system, zone temperature or zone supply volume flow

rate is controlled by terminals.

⇒ Fan combination systems, Three fan combination systems are often used: supply

and exhaust fan combination, supply and relief fan combination, and supply and

return fan combination systems.

There is another classification according to the air flow control:

⇒ Single -duct or dual-duct systems. In a single-duct system, conditioned air is

supplied to the conditioned space by a single supply duct. In a dual-duct system,

conditioned air is supplied to the conditioned space in the perimeter zone through two

supply ducts: a warm air duct and a cold air duct. In the interior zone, only a cold air

duct is needed.

⇒ Constant-volume (CV) or variable-air-volume systems. In a constant-volume

system, the temperature of supply air is modulated to match the variation of space

load during part-load operation. In a VAV system, the supply volume flow rate is

modulated to maintain a predetermined space temperature as space load varies.

⇒ Dedicated ventilation and space recirculating system. In a dedicated ventilation

and space re-circulating system, a required amount of outdoor ventilation air is

supplied by a separate ventilation air system; at the same time, there is a parallel space

re-circulating system to condition the space recirculating air to offset the space

heating or cooling load. Outdoor ventilation air is either mixed with the space

recirculating air first or directly supplied to the conditioned space. When the outdoor

and recirculating air are mixed in the mixing box (mixed plenum) first; the mixture is

then conditioned and supplied to the conditioned space.

Different Types of Air Systems

Constant-Air-Volume systems:

A constant-volume system means that there is a constant volume of supply air

throughout the operating period. Supply air temperature is varied when the space load

reduces in part-load operation. Single-zone states indicates that the system serves a

conditioned space which is controlled to maintain a unique indoor temperature,

relative humidity, cleanliness, and pressure differential.

Variable-Air-Volume Systems:

A variable-air-volume (VAV) system is an air system that varies its supply air volume

flow rate to match the reduction of space load during part-load operation to maintain a

predetermined space parameter, usually air temperature, and to conserve fan power at

reduced volume flow. A constant volume system varies its supply air temperature to

match the reduction of space load during part load operation to maintain a

predetermined space air temperature.

Compared with a constant-volume system, a VAV system has mainly the following

advantages:

⇒ Reduced fan energy use during part-load operation when the supply volume flow

rate is reduced.

⇒ A slightly lower or nearly the same zone relative humidity when the supply volume

flow rate is reduced during summer cooling mode part-load operation.

⇒ More individual control zones.

⇒ Reduction of the construction cost because of taking into consideration of the

supply air volume flow diversity factor instead of the sum of zone peak loads.

⇒ Capability of self- balancing of zone supply volume flow rates.

⇒ Convenience during the relocation of the terminals and space diffusion devices

during future expansion.

Compared with a constant-volume system, the primary disadvantages of a VAV

system are:

⇒ inadequate outdoor ventilation air when the supply volume flow rate is reduced.

⇒ A more complicated system structure and controls, which need more demanding

design, installation, operation, and maintenance.

VAV systems are applicable to air systems whose space load varies significantly so

that there are fan energy savings.

Recently, another VAV system has been developed called the variable diffuser VAV

system. In variable diffuser systems, the aperture of each diffuser can be varied so that

the discharge velocity is relatively constant while the supply volume flow is reduced,

and the throw from the variable diffuser may also be maintained above a certain limit.

Variable diffuser VAV systems provide more individual control zones as well as a

more complicated diffuser construction and controls. More field performance data and

experience are needed to make an appropriate selection.

Types of Variable-Air-Volume Systems:

Most medium-size and large buildings need multi-zone air systems. However, many

indoor stadiums, convention centers, factories, residential buildings, and small retail

stores employ single-zone air systems. Currently used variable-air-volume systems

can be mainly classified into the following types:

⇒ Single -zone VAV systems.

⇒ VAV cooling systems.

⇒ VAV- reheat systems.

⇒ Dual- duct VAV systems.

⇒ Fan- powered VAV systems.

Chapter 2

Fire tube boiler

Fire-tube boiler

Introduction:

Fire-tube boilers are those device in which hot gases, which originates from the fire

passes through one or more tubes within the boiler. They are important boilers that are

available in both horizontal and vertical configurations. They are also some times

referred as smoke-tube boiler.

Operation

Schematic diagram of a "locomotive" type fire-tube boiler

In the locomotive-type boiler, fuel is burnt in a firebox to produce hot combustion

gases. The firebox is surrounded by a cooling jacket of water connected to the long,

cylindrical boiler shell. The hot gases are directed along a series of fire tubes, or flues,

that penetrate the boiler and heat the water thereby generating saturated ("wet") steam.

The steam rises to the highest point of the boiler, the steam dome, where it is

collected. The dome is the site of the regulator that controls the exit of steam from the

boiler.

In the locomotive boiler, the saturated steam is very often passed into a superheater,

back through the larger flues at the top of the boiler, to dry the steam and heat it to

superheated steam. The superheated steam is directed to the steam engine's cylinders

or very rarely to a turbine to produce mechanical work. Exhaust gases are fed out

through a chimney, and may be used to pre-heat the feed water to increase the

efficiency of the boiler.

Draught for firetube boilers, particularly in marine applications, is usually provided

by a tall smokestack. In all steam locomotives, since Stephenson's Rocket, additional

draught is supplied by directing exhaust steam from the cylinders into the smokestack

through a blastpipe, to provide a partial vacuum. Modern industrial boilers use fans to

provide forced or induced draughting of the boiler.

Another major advance in the Rocket was large numbers of small-diameter firetubes

(a multi-tubular boiler) instead of a single large flue. This greatly increased the

surface area for heat transfer, allowing steam to be produced at a much higher rate.

Without this, steam locomotives could never have developed effectively as powerful

prime movers.

Materials

The pressure vessel in a boiler is usually made of steel, stainless steel, or wrought

iron. In live steam models, copper or brass is often usedTemplate:Why. Historically,

copper was often used for fireboxes (particularly for steam locomotives), because of

its better thermal conductivity; however, in more recent times, the high price of

copper often makes this an uneconomic choice and cheaper substitutes (such as steel)

are used instead.

For much of the Victorian "age of steam", the only material used for boiler making

was the highest grade of wrought iron, with assembly by rivetting. This iron was often

obtained from specialist ironworks, such as at Cleator Moor (UK), noted for the high

quality of their rolled plate and its suitability for high-reliability use in critical

applications, such as high-pressure boilers. In the 20th century, design practice instead

moved towards the use of steel, which is cheaper, and welded construction, which is

quicker and requires less labour.

Cast iron may be used for the heating vessel of domestic water heaters. Although such

heaters are usually termed "boilers", their purpose is to produce hot water, not steam,

and so they run at low pressure and try to avoid actual boiling. The brittleness of cast

iron makes it impractical for steam pressure vessels.

Fuel

The source of heat for a boiler is combustion of any of several fuels, such as wood,

coal, oil, or natural gas. Electric steam boilers use resistance- or immersion-type

heating elements. Nuclear fission is also used as a heat source for generating steam.

Heat recovery steam generators (HRSGs) use the heat rejected from other processes

such as gas turbines.

Types of fire-tube boiler

Cornish boiler

The earliest form of fire-tube boiler was Richard Trevithick's "high-pressure" Cornish

boiler. This is a long horizontal cylinder with a single large flue containing the fire.

The fire itself was on an iron grating placed across this flue, with a shallow ashpan

beneath to collect the non-combustible residue. Although considered as low-pressure

(perhaps 25 psi) today, the use of a cylindrical boiler shell permitted a higher pressure

than the earlier "haystack" boilers of Newcomen's day. As the furnace relied on

natural draught (air flow), a tall chimney was required at the far end of the flue to

encourage a good supply of air (oxygen) to the fire.

For efficiency, the boiler was commonly encased beneath by a brick-built chamber.

Flue gases were routed through this, outside the iron boiler shell, after passing

through the fire-tube and so to a chimney that was now placed at the front face of the

boiler.

Lancashire boiler

Lancashire boiler in Germany

The Lancashire boiler is similar to the Cornish, but has two large flues containing the

fires. It was the invention of William Fairbairn in 1844, from a theoretical

consideration of the thermodynamics of more efficient boilers that led him to increase

the furnace grate area relative to the volume of water.

Later developments added Galloway tubes (after their inventor, patented in 1848),

crosswise water tubes across the flue, thus increasing the heated surface area. As these

are short tubes of large diameter and the boiler continues to use a relatively low

pressure, this is still not considered to be a water-tube boiler. The tubes are tapered,

simply to make their installation through the flue easier.

Scotch marine boiler

Side-section of a Scotch marine boiler: the arrows show direction of flue gas flow; the combustion

chamber is on the right, the smoke box on the left.

The Scotch marine boiler differs dramatically from its predecessors in using a large

number of small-diameter tubes. This gives a far greater heating surface area for the

volume and weight. The furnace remains a single large-diameter tube with the many

small tubes arranged above it. They are connected together through a combustion

chamber – an enclosed volume contained entirely within the boiler shell – so that the

flow of flue gas through the fire tubes is from back to front. An enclosed smoke box

covering the front of these tubes leads upwards to the chimney or funnel. Typical

Scotch boilers had a pair of furnaces, larger ones had three. Above this size, such as

for large steam ships, it was more usual to install multiple boilers.[3]

.

Locomotive boiler

A locomotive boiler has three main components: a double-walled firebox; a

horizontal, cylindrical "boiler barrel" containing a large number of small flue-tubes;

and a smokebox with chimney, for the exhaust gases. The boiler barrel contains larger

flue-tubes to carry the superheater elements, where present. Forced draught is

provided in the locomotive boiler by injecting exhausted steam back into the exhaust

via a blast pipe in the smokebox.

Locomotive-type boilers are also used in traction engines, steam rollers, portable

engines and some other steam road vehicles. The inherent strength of the boiler means

it is used as the basis for the vehicle: all the other components, including the wheels,

are mounted on brackets attached to the boiler. It is rare to find superheaters designed

into this type of boiler, and they are generally much smaller (and simpler) than

railway locomotive types.

The locomotive-type boiler is also a characteristic of the overtype steam wagon, the

steam-powered fore-runner of the truck. In this case, however, heavy girder frames

make up the load-bearing chassis of the vehicle, and the boiler is attached to this.

Taper boiler

Certain railway locomotive boilers are tapered from a larger diameter at the firebox

end to a smaller diameter at the smokebox end. This reduces weight and improves

water circulation. Many later Great Western Railway and London, Midland and

Scottish Railway locomotives were designed or modified to take taper boilers.

Vertical Fire-Tube boiler

A Vertical Fire-Tube boiler (VFT), colloquially known as the "vertical boiler", has a

vertical cylindrical shell, containing several vertical flue tubes.

Horizontal Return Tubular boiler

Horizontal Return Tubular boilers

Horizontal Return Tubular boiler (HRT) has a horizontal cylindrical shell, containing

several horizontal flue tubes, with the fire located directly below the boiler's shell,

usually within a brickwork setting

Boiler energy balance

This image shows a typical boiler energy balance for a boiler in good running

condition with no energy efficiency measures added. By first identifying the areas of

energy loss and roughly quantifying it, it is easier to estimate the overall savings

potential by taking efficiency action in that area. For example, if the blowdown loss is

3% of total input energy, it is not possible to expect a 5% savings of input energy by

installing a blowdown heat recovery system.

Water Treatment

Introduction

Untreated water contains dissolved minerals, gases and particulates. The removal or

otherwise 'treatment' of each of these is critical to efficient boiler operation for

different reasons. Minerals lead to scaling that acts as in insulator reducing boiler

efficiency; gases can be corrosive and particulates can contribute to both problems.

Water treatment is dynamic and varies from boiler to boiler and can vary month to

month with the same boiler.

Water quality is primarily an issue with steam boilers that use a lot of make-up water.

Closed-system hot water boilers are the least effected by water quality because they

use the least amount of make-up water and operate at lower temperatures.

The common minerals in water that lead to scaling problems are iron, calcium,

magnesium and silica. When water containing these dissolved minerals are heated, it

looses its ability to hold the minerals in solution. When they come in contact with

metal boiler parts, scale forms. In addition to reduced efficiency, scale can lead to

boiler tube failure if the tubes are over-heated.

Oxygen and certain other gases in water are corrosive. Deaerators and chemicals that

remove oxygen can reduce the corrosiveness of the water.

Primary indicators of boiler water treatment are pH, TDS (Total Dissolved Solids),

TSS (Total Suspended Solids) and hardness

Water Treatment Schematic

Typical water flow schematic for a large boiler system:

Water pH

Water pH is a measure of its relative acidic or alkalinity. A neutral level is pH = 7. A

number lower than 7 is acidic and higher than 7 is alkalinic (caustic). Both extremes

are corrosive to boiler metal.

Methods to Remove Water Impurities

The best way to remove impurities is before they enter the boiler. Small amounts of

impurities can be effectively treated inside the boiler to keep them in solution or allow

them to be discharged via blowdown.

1-External Treatment

External treatment refers to the chemical and mechanical treatment of the water

source. The goal is to improve the quality of this source prior to its use as boiler feed

water, external to the operating boiler itself. Such external treatment may include:

1-Clarification (removes solids, very large boiler systems)

2-Filtration (removes solids)

3-Softening and Demineralization (removes dissolved minerals)

4-Dealkalization

5-Deaeration and Heating (removes oxygen and other corrosive gases)

2-Internal Treatment

Even after the best and most appropriate external treatment of the water source, boiler

feed water (including return condensate) still contains impurities that could adversely

affect boiler operation. Internal boiler water treatment is then applied to minimize the

potential problems and to avoid any catastrophic failure, regardless of external

treatment malfunction.

1-Addition of chemicals (pH Control, Oxygen Removal, other)

2-Blowdown (removes accumulated solids from boiler water)

Monitoring Water Quality

Water quality monitoring varies from weekly litmus test strips to continuous

electronic instrumentation and automated chemical treatment. The size of the boiler,

the importance of water quality and the skills of the boiler operators are all factors in

deciding how best to monitor boiler water quality.

Economizers

Introduction

Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover

some of this heat for pre-heating water. The water is most often used for boiler make-

up water or some other need that coincides with boiler operation. Stack Economizers

should be considered as an efficiency measure when large amounts of make-up water

are used (ie: not all condensate is returned to the boiler or large amounts of live steam

are used in the process so there is no condensate to return) or there is a simultaneous

need for large quantities of hot water for some other use.

The savings potential is based on the existing stack temperature, the volume of make-

up water needed, and the hours of operation. Economizers are available in a wide

range of sizes, from small coil-like units to very large waste heat recovery boilers.

How They Work

Boiler stack economizers are simply heat exchangers with hot flue gas on one side

and water on the other. Or, in direct contact condensing units, the make-up water is in

direct contact with the flue gases.

Economizers must be sized for the volume of flue gas, its temperature, the maximum

pressure drop allowed through the stack, what kind of fuel is used in the boiler, and

how much energy needs to be recovered. Economizers designed for natural gas only,

would likely plug-up if installed on a coal boiler and would face increased risk of

corrosion if installed on an oil-fired boiler. Some units are designed to keep the flue

gases above condensation temperature, and others are made of materials that resist the

corrosive effect of condensed flue gases.

Economics

The savings potential is a function of how much heat can be recovered, which is a

function of how much cold water needs to be heated. A generally accepted "rule of

thumb" is that about 5% of boiler input capacity can be recovered with a properly

sized economizer. A higher percentage can be recovered with a Flue Gas Condenser,

assuming there is enough cold water to condense all of the flue gas that is available.

Therefore, for 'ball parking' purposes, start by comparing boiler input capacity with

the need to heat water.

For example: consider a 500 hp boiler with a gas input of 20 million BTUs per Hour.

20,000,000 BTUs x 5% = 1,000,000 BTUs (100% Load Factor)

1,000,000 BTUs / (1,200 BTUs per Gallon of 200F water) = 833 Gallons per Hour

(1,000,000 BTUs / 80% efficiency) = ~1.2 MCF x $7.00 per MCF Natural Gas =

$8.40 per Hour Value

Savings is reduced by 50% for a 50% Load Factor, etc.

If there is a need for that much hot water, the savings potential of $8.40 per hour

would be multiplied by the number of boiler run hours, or the number of hours that

the hot water can be used. In each application, be sure to consider the boiler Load

Factor, the efficiency that the hot water is otherwise produced at, the cost of natural

gas, and the installation cost of the equipment.

If the economizer would be used to heat boiler make-up water, it is necessary to

determine the volume and temperature at the inlet of the economizer. The lower the

amount of condensate return, the higher the volume of make-up water and the higher

savings potential.

An economizer that recovers 5% of boiler input should easily have a 2 year payback

in a year-round application.

Flue Gas Condensers Introduction

Flue gases from large boilers are typically 450 - 650°F. Stack Economizers recover

some of this heat for pre-heating water. The water is most often used for boiler make-

up water or some other need that coincides with boiler operation. There is a class of

economizers that are designed to condense the flue gases and/or have the water in

direct contact with flue gases. I have called them 'Flue Gas Condensers'. Stack

economizers and Condensers should be considered as an efficiency measure when

large amounts of make-up water are used (ie: not all condensate is returned to the

boiler or large amounts of live steam is used in the process so there is no condensate

to return) or there is a simultaneous need for large volumes of hot water.

The application difference between an economizer and condenser is that economizers

are primarily used to heat a smaller volume of water to a high temperature for boiler

feed water, and condenser units heat a larger volume of water to a lower temperature.

Condensers can be more efficient because they can have a lower outlet exhaust

temperature and take advantage of the energy in condensed flue gasses (the Latent

Heat of Vaporization).

The savings potential is based on the existing stack temperature, the volume of make-

up or hot water needed, and the hours of operation. Economizers are available in a

wide range of sizes, from small coil-like units to very large waste heat recovery

boilers. Condensers are available as small as 50 hp and a single condenser can be used

on multiple boilers.

Some condensers have water in direct contact with the flue gases and others use heat

exchangers. In some applications the water that has been in direct contact with the

flue gases can be directly used; in other applications, the water must be passed

through a heat exchanger before it can be used.

The key to the successful application of heat recovery is the ability to put the

recovered heat to use. Uses include industrial process water heating, clean-up/wash-

down water heating, laundry wash water, domestic water heating, space heating, snow

melt and district heating systems. Potential Applications include: Greenhouses,

Hospitals and Health Centers, Food processing, Schools and Universities, Laundries,

Breweries, Hotels, Wineries, Government Buildings, and Swimming pools.

Operation

In a direct contact unit, water is sprayed in contact with the flue gases, causing

condensation and extracting most all of the heat. In units that have a heat exchanger,

condensation is likely when there is enough water flow -or- at a cold enough inlet

temperature to remove enough heat to cause condensation on the flue gas side of the

heat exchanger. See the Manufacturer's descriptions below for more details.

Economics

The savings potential is a function of how much heat can be recovered, which is a

function of how much cold water needs to be heated. A generally accepted "rule of

thumb" is that about 10% of boiler input capacity can be recovered with a properly

sized condenser. This is a higher percentage than what can be recovered with an

economizer because the water temperature is lower. However, there is also a lot more

volume of water involved, assuming there is a need for enough cold water to

condense all of the flue gas that is available. Therefore, for 'ball parking' purposes,

start by comparing boiler input capacity with the need to heat water.

Insulate Steam Pipes

Uninsulated steam distribution and condensate return lines are a constant source of

wasted energy. Insulation can typically reduce energy losses by 90% and help ensure

proper steam pressure at plant equipment. Any surface over 120°F should be

insulated, including boiler surfaces, steam and condensate return piping, and fittings.

Insulation frequently becomes damaged or is removed and never replaced during

steam system repair. Damaged or wet insulation should be repaired or immediately

replaced to avoid compromising the insulating value. Eliminate sources of moisture

prior to insulation replacement. Causes of wet insulation include leaking valves,

external pipe leaks, tube leaks, or leaks from adjacent equipment.

Operation

Cracking in Fire-tube Boilers

1. SCOPE

This Note provides information on cracking in welded fire-tube boilers, including

location of cracks, failure modes, causes, detection, repair and prevention. The

necessary actions to be undertaken when cracking is suspected or confirmed are

provided. The information provided is based on global experience.

2. BACKGROUND

Cracking in fire-tube boilers at welded joints is a frequent, costly and potentially

dangerous occurrence. The shortest recorded time for serious cracking to leak is 3

years, representing less than 20,000 cycles, and occurred on a laundry boiler subjected

to frequent and rapid firing.

A number of cracked boilers have exploded resulting in major damage and fatalities.

Fortunately,recent improvements in materials, welding and non-destructive testing

(NDT) together with a greater awareness of the potential for cracking have greatly

reduced the incidence of failures. As current boilers age, more cracking is likely

tooccur.

Cracking Occurrence

Virtually all cracks occur at welded joints or at openings. The root cause is corrosion

fatigue with the fatigue cycling being thermally driven. Over 100 boilers in Australia

suffered this type of cracking in the 1950 – 1975 period. The change to natural gas

firing initially accelerated the rate, but it has since fallen. UK inspection data from

2001 showed that 2 % of fire-tube boilers inspected had service defects – mainly

cracks

.

Figure 1 shows a schematic representation of the side and end elevation of a fire-tube

boiler. The front and rear closure plates and reversal chambers have been omitted for

clarity.

Figure 1. Fire-tube boiler showing eight potential cracking locations

Crack Location Crack Description

1- Furnace tube circumferential cracking at tube plate weld

2- Shell circumferential cracking at tube plate and shell weld

3- Tube end cracking

4- Tube plate ligament cracking between boiler tubes

5- Tube plate cracking at or between reversal chamber support lugs

6 -Furnace tube cracking at stiffening ring

7 -Shell cracking at gusset stay welds

8 -Shell cracking in longitudinal seam weld

Of the eight potential crack locations shown, the major occurrence is furnace tube

cracking adjacent to the tube plate weld identified as number 1 in Figures 1 and 2.

Other locations of the boiler also exhibit cracking particularly cracking associated

with fire-tubes identified as numbers 3 and 4 in Figures 1

4.2 Furnace Tube Cracking (location 1)

Cracking occurs in a highly localised area in the furnace tube on the water-side of the

boiler. The cracks originate at the root of the furnace tube to tube-plate weld.

Cracking can occur at both front and rear ends at any position around the furnace tube

plate but cracking is most common at the bottom of the tube plates. Cracking

generally occurs in the furnace tubes as they are thinner, and hence more highly

stressed than the tube plate

The failure mode is corrosion fatigue. Slight corrosion occurs as a result of contact

with the water.

Fatigue arises from thermal cycling and pressure cycling. The primary causes of

furnace tube cracking are a combination of:

• High thermal stress generated by large temperature or material thickness differences;

• Bending stresses due to pressure;

• Poor weld shape, particularly at the weld root in the lower part of the furnace;

• High number (over 10,000) of pressure and temperature cycles;

• Fracture of the protective magnetite layer due to cyclic stresses. Magnetite forms on

the furnace tubes and acts as a protective layer but it is brittle and subject to spalling

under cyclic stresses. Its fracture exposes unprotected surfaces to further corrosion;

• Un-removed slag from furnace tube to tube plate welds providing corrosion

initiation sites.

The secondary (or service) causes of cracking include:

• Rapid firing from cold resulting in high thermal stresses;

• Over firing, typically when changing to gas firing, resulting in severe cracking at the

rear tube plate due to higher temperature differentials;

• Insulation effect of scale deposits on both surfaces giving increased temperature

gradients;

• Increased boiler pressure and decreased water return temperatures;

• Untreated feed water leaving deposits that accelerate local corrosion;

• Incorrect pH of feed water or excessive O2 levels;

• Reduced circulation and increased temperature differentials due to poor feed water

entry;

• Boilers with low slung furnaces or made from higher strength steels operating at

higher stress. For short cracks, the most common type, the resulting failure has

generally been leakage. For longer cracks, the result can be large scale fracture with a

dangerous explosion.

4.3 Shell Cracking (location 2)

A rare but dangerous occurrence is circumferential shell cracking at the tube plate

weld shown at

location 2. Extensive cracking at this location can cause the tube plate to tear away

from the shell in a

catastrophic manner. This type of cracking is generally limited to highly stressed shell

boilers

constructed of high strength materials and consequently operating at higher relative

stress range.

4.4 Tube End Cracking (location 3)

This longitudinal cracking of tube ends is sometimes encountered in ERW tubes or

tubes with poor ends.

4.5 Tube Plate Ligament Cracking (location 4)

Ligament cracking has been reported in boilers with high operating temperature

differentials up ton 400°C. Tube plate cracking typically starts at toes of boiler tube

fillet welds and grows across the tube plate ligament from one boiler tube to another.

Cracking has also occurred from centre-pop marks forming a small notch in the edge

of the tube hole with expanded tubes. Ligament cracking is serious.

Depending on the age and fracture toughness of the tube plate, material crack

extension can occur suddenly by brittle fracture when the boiler cools down to

ambient temperature. High local residual stresses can trigger brittle fracture in heavily

cold worked and aged steel. This occurred with a unique case at location 5 from a 6

mm deep fatigue crack.

4.6 Other cracking locations (locations 5 to 8)

Cracking has been reported at all locations depicted in locations 5 through 8 in

Figures 1 mainly at attachments. Although cracking in these locations is relatively

rare they also should be subject to examination by the boiler inspector.

5. CRACK DETECTION

Good access is required to visually detect cracks and surfaces should be clean for 50

mm each side of the weld where cracking initiates.

of the weld where cracking initiates.

Visual examination with the aid of lights can detect cracks over 5 mm in length and

over 1 mm deep depending on adequate surface cleanliness. Endoscopes and digital

cameras can be used to aid detection (particularly with low slung boilers), with

computers to record information.

Magnetic particle testing (MT) and penetrant testing (PT) are more sensitive than

visual inspection if the suspected crack area is accessible for examination. Ultrasonic

testing (UT) is probably the best method to detect serious cracking.

6. INSPECTION INTERVAL AND MONITORING.

The annual intervals specified in AS/NZS 3788 should be applied in normal

circumstances for visual inspection. If the operational circumstances are such that

none of the primary and secondary causes mentioned above are applicable the

inspection limits can be extended. Conversely frequent rapid firing under harsh

conditions requires more frequent NDT especially as boilers age.

Ultrasonic testing should be carried out within 10 years from the construction date in

normal circumstances or more frequently under harsh conditions. Similarly if there

are significant changes in operating temperature or pressure, ultrasonic testing should

be carried out more frequently e.g. after initial 10,000 cycles. The ultrasonic testing

program should include a reasonable length of weld at both ends of the furnace and at

the top, bottom and sides of the weld circumference at locations 1and 2. Extra care

should be taken with tubes near to stay tubes or near the shell.

Increased inspection frequency should also be implemented if the furnace was

manufactured from steel with Rm>460 MPa, or if the design strength value used is

above 110 MPa.

7. OPERATING OPTIONS FOLLOWING CRACK

DETECTION

7.1 General

Once cracking has been detected, confirmed and sized, an informed decision is

needed on whether to continue operation, repair or scrap. This decision depends on

the estimated remaining SAFE life of the cracked part and the desired remaining life

of the boiler.

7.2 Fracture Mechanics Analysis

In order to determine the estimated cycles to failure and the nature of the failure (leak

or break) a fracture mechanics assessment may be used. A number of options are

available, but the methods described in AS/NZS 3788 provide instruction on how to

carry out the analysis. The accuracy of the following data is critical:

• Crack position, depth, and length around the weld circumference;

• Physical properties of parent plate – fracture toughness, yield and tensile strength;

• Parent plate inclusions, laminations and any banding and direction of rolling;

• Number of anticipated cycles.

• Developed stress range which is often very difficult to quantify particularly at

location 1;

Only personnel with proven expertise and experience should undertake a fracture

mechanics assessment.

7.3 Remaining life assessment

Practically, a better method of assessment is to use world experience, coupled with

the basis of fracture mechanics.

Experience with early ductile, low strength steels indicates that furnace tube cracking

can be tolerated up to the lower of 2 mm and 30% of the furnace tube wall thickness.

Operation changes should be implemented to eliminate some of the primary or

secondary causes of cracking and de-rating the boiler output may be required. If crack

depths are 50% or more through the furnace wall, the boiler should be isolated for

repair or replacement.

8. REPAIR OPTIONS FOR FURNACE TUBE CRACKS

8.1 Local Weld Repair of Furnace Tube

Local weld repairs have been widely used for the repair of cracks with limited length.

Low hydrogen welding processes such as GTAW, MMAW (with EXX16/EXX18

electrodes designed for single sided complete penetration V butt welding) or GMAW.

A relatively high preheat should be used, and then no post weld heat treatment is

required. The method involves:

• Removal of crack and associated damaged material from the inside of the furnace

tube;

• Weld with a AS 3992 qualified welding procedure using low yield strength weld

metal;

• Ultrasonic testing using angle probes to establish quality of repair weld;

• Dressing the bore of the furnace tube flush by grinding;

• Hydrostatic pressure testing using warm water (at least 20°C) to full the test

pressure, ie. 1.5 times the design pressure.

Successful repairs rely on competent welders, good weld shape, low hardness,

negligible defects and competent NDT technicians and importantly, proof by tests or

previous work that the inside root profile is as shown in Figure 4.

Figure 4. Local repair technique for furnace tube cracks located at toe of original

installation weld

8.2 Replacement of One End of Furnace Tube This option should be considered where there is extensive cracking at one end and

there is good access from inside the furnace. The repair will involve using procedures,

inspection and testing practices similar to the original construction.

8.3 Removal and Replacement the Complete Furnace Tube

This option is only practical when both ends have extensive cracking and there are no

stiffening rings to impede removal of the tube.

8.4 Repair of Other Cracks Such repairs should be made using the principles in 8.1

.

9. MEASURES TO PREVENT OR CONTROLCRACKING

9.1 Prevention Measures

Boiler life is proportional to the number of thermal cycles experienced during

operation. With continuous uniform firing and negligible cycling boiler lives 50 or

more years are achievable. Thus to prevent cracking it is necessary to establish

operating conditions that reduce the severity of cycling as far as possible. The

following recommendations apply to all modes of cracking depicted in Figure 1.

However the emphasis is on furnace tube cracking.

9.2 Control Measures

Whilst it may not be feasible to run a boiler continuously to avoid thermal cycling the

following control measures will maximize boiler life for the applied operating

conditions:

• Reduce the risk of low water conditions with reliable low water controls;

• Do not exceed manufacturer's recommended firing rates and metal temperatures;

• Reduce risk of excess pressure by checking and correctly maintaining safety valves;

• Minimize cycling of pressure and temperature;

• Minimize shock loading - avoid rapid heating and cooling particularly below 800C -

preferably use modulated burners and mixing of feed water;

• Review water treatment to ensure appropriate de-aeration and pH control;

• Review blow-down procedures and ensure water sediments are flushed out

regularly.

10. REPORTING AND DOCUMENTATION

It is necessary to maintain appropriate operating, inspection and maintenance records

for boilers so they can be operated, inspected and maintained in a pro-active manner.

Documenting the number of operating cycles the boiler undergoes together with the

severity of those cycles provides the baseline that will ultimately dictate the frequency

of inspection and remaining life of the boiler.

The service records should include:

• Inspection history listing the dates and type of inspections undertaken and results

received;

• All repairs including observations, actions taken and the basis for those actions;

• Correspondence with Regulatory Authorities (where required);

• An inspection and NDT plan based on operating history and inspection results;

Fire tube boiler calculation:

1- for Natural gas

- Natural gas component :(volume basis)

CH4 90.666%

C2H6 5.593%

C3H8 0.539%

C4H10 0.015%

CO2 2.693 %

N2 0.49%

C5H12 0.046%

C6 H14 0.029%

- Assume we have 100 Kmol of fuel

-

- Assume excess air =5% , complete combustion

fuel + X1(1.05) (O2+3.76N2) X CO2 + X2 H2O

+( X1 * 0. 05 O2)+ ((X1 * 1.05 * 3.76)+ 0.419)N2

By using mass balance

X1 = 204.34 X = 106.626 X2 = 200.821

A/F= 16.6 Kg air / Kg fuel

ma /mf = A / F

mg /mf = ( 1+ (A / F)) = 17.6

(m H2o / mf) = (3614.8 / 1779.06 )= 2.03

-Calculation of losses:

1- Losses in fuel gases (dry)

% dry losses = mg *cpg (Tgo –Tcomb) /( mf * c.v)

Assume T go = 160 °c Tambient= 30 °c

Cp g = ∑(Ni *Mi * Cpi) / Mtot

= 1.15 kj/ kg

% dry losses = 5.38 %

C .V =48947.2 Kj /Kg

2-Losses due to H2O from combustion (wet):

% wet losses =(mH2o * hfg ) / (mf * c.v f)

YH2o = (204 .41 /1140.725 ) = 0.1785

PH2o = (YH2o * P atm) = 0. 181 bar

hfg = 2363.9 kj/ kg

losses % = (2.1443 *2363)/49546

= 9.8%

3-Un accounted losses (radiation losses, ……) =2%

ήboiler = 100 - ∑ Losses = 82.82%

mf= 0.025 kg/s

mg= 0.43 kg /s

Calculation of Adiabatic flam temperature :-

Hp = HR ,

∑p Np {hf + (h –h0)}= ∑R NR {hf + (h-h0)}

HR= 90.666(-74873) + 5.593 (-84740) + 0.539(-103900) + 0.015(-126200)+

0.046(-146500)+ 0.029(167300) +

2.693(-393522)

HR = - 8391626.8 Kj

Hp=106.31(-393520+Cp(T-To))co2

+ 200.821 ( -241827+Cp(T-To))H2o

+807.15 (Cp (T-To))N2 + 10.217 Cp (T –To)O2

by trail and error

First trail Ta.f =2400 k

HR < Hp

Assume T a.f = 2200 k

Hp < HR Assume T a.f = 2250 k

Calculation of furnace dimensions :-

Assume heat release of N.G = 450 kW/m3

Qa = Qgain/η

=1000/0.8282

=1207.43 kw

Therefore the volume (V)=2.68 m3

Assume Lf/Df = 4

2.6 = π/4*4 Df* (Df)2

Df = 0.95 m

Lf = 3.795 m

Q 1 pass = µ (mf * c.v ) = 548.4 Kw

Q other passes = (η -µ) (mf * c.v ) = 456.65 Kw

Calculation of inlet temp to 2 nd pass (T1)

µ (mf * c.v ) = Cpg * mg ( T a.f – T1)

T1 = T a.f – 548.4 / (Cpg* mg)

By trail & error

Cpg at T1 +Ta.f /2 M = (mt /Nt) = 27.77

Cpg ( Kj /Kg k ) T1(K)

1.15 1141

1.4 1339

1.45 1370

Assume T1 = 1400 K

Calculation of number of tube

mg = ρg V A

assumptions

1 ) tubes materials is carbon steel

2) Do = 2.5 in Di = 2.282 in

3) V (velocity of gases ) = 15 m/s

ρg = P *M / R Tav = 0.364 Kg /m3

N = mg /( π/4)Di2 * V * ρg =30 tube /pass

Assume the properties of gas as air

At Tav = 916.5 K

Pr = 0.72099 K = 62.759 *10-3 W/m .k

µ = 402.456 * 10 -7

N .s /m2

Cp = 1.1243 *103 J / kg .k

Re = 7948.46 < 2300

hi Di/ K = 0.023 (Re)0.8

( Pr) 0.3

hi = 29.8 W/m2 .k

out side tube

Twall = Tav + T sat/ 2

= 670.675 K

∆ T = Twall - T sat = 245. 83 K

Film boiling

Tf = Twall + T sat / 2

= 547.76 K

At Tf and P = 5 bar

µ = 18.87 * 10 -6

N .s /m

ρv = 2 Kg /m3

Kv = 0.0426 W /m.K

Cpv = 1.039 Kj /Kg

At T sat & P = 5bar from steam table

ρL= 914. 9 Kg /m3

hfg = 2107 .4 Kj /Kg

ho = 0.62 {(Kv3 g ρv (ρL – ρv ) (hfg + 0.4 Cpv ∆T) / (µv do ∆T)}

0.25

ho = 188.5 W / m2 .K

(1/Uo) =(Do/(hi Di)) + Do ln (Do/Di)/(2k)+ 1/(ho)

K @Twall = 45.4 W /m.K

Uo = 23.67 W / m2 .K

Uo S θLMTD = (η -µ) (mf * c.v ) where θLMTD = 202

S = 92.5 m2 = π Do L N Z T1

Assume Z= 2 pass

Tgo

N = 61.01 tube / pass Tsat

Therefore Z = 4 ... N = 24 tube /pass

Dshell = [0.95/2+0.2]*3= 2.025 m

Lshell = 3.79+0.5=4.29 m

2- for Light fuel oil

Assume it is C12H26

Assume 1 mole of fuel is burning and complete comb

Take 7% excess air

C12H26+1.07(12+26/4)(O2+3.76N2)→12CO2+13H2o+1.295O2+

74.4292N2

Assume temp of gas is 177 C

A/F th= 19.795(32+(3.76*28))/((12*12)+26)=

= 15.985 kgair/kg fuel

Cp gas = (mCO2/mg)Cpco2 + (mH2o/mg)CpH2o + (mO2/mg)CpO2 +(mN2/mg)CpN2

={(12*44*0.8905)+(13*18*1.887)+(1.295*32*.931)+(74.4292*28*1.043)}/2887.457

=1.082 kJ/kg k

PH2O=(N H2O/Ng)*Ptotal =(13*1)/100.7242

= 0.129 bar

hfg H2O =2380.68 kJ/ kg

Losses from boiler "dry and wet and uncounted"

1-Dry gas

Qd% ={(mg/mf)Cpg(177-36)}/c.v

mg =mf +ma

16.985= mg/mf =(1+ A/f )

Qd%=16.985*1.082*147/44000 =0.0614

2-Wet gas

Qw% = mH2o hfgH2o / (mf *c.v)

= (234/170)*2380.68/44000

=0.07448

ηb%= Qgain /(mf *c.v)

= (mf *c.v) –Qlosses /(mf * c.v)

= 1-0.07448-0.0614-0.02 =0.844

ηb = 84.4 %

84.4% = 1000/(mf*44000)

m f =.027 kg/s

m a=0.43 m g=0.457kg/s

flame tube volume:-

1- for first pass

Let H.R.R = 450 kw/m3 , L/D =4

Q add = mf *c.v =1184.84 kW

V =1184.83/450 = 2.6 m3

2.6 = (3.14 *D2*L )/4 =(3.14* 3*D

3)/4

D= 0.94 m L=3.76 m

2- for other pass

Q = (η - µ ) *mf * c.v

1/µ 1+ { [(A/f) *(Q /s)0.5

] /5300}

S = 3.14*D*L =10.1612 m2

Q =1019158.194 k cal/hr

µ=0.51

Q2pass = µ *mf* c.v =604.265 kw

= mg * Cpg (T a.f - T1)

We must get adiabatic flame temp

HR=Hp

- for get adiabatic flame temp

1(-291010+0) + 19.795(0+0) +74.4292(0+0)

= 12(-393520+(∆h))CO2 +13(-241820+∆h)H2O +1.295 (0+ ∆h)O2 +74.4292 ( 0+ ∆h)N2

-291010 = -7865900 +12 ∆hCO2 +13 ∆hH2O + 1.295 ∆h O2+ 74.4292 ∆hN2

7574890 =12 ∆hCO2 +13 ∆hH2O +1.295∆O2 +74.4292∆hN2

By trail and error

First trail - assume gas temp is 1900 k

L.H.S > R.H.S

Second trail Tg =2000 K

L.H.S > R.H.S

Adiabatic flame temp = 2100 K

µ * mf * c.v = mg* Cpg ( T a.f –T1)

T1 = T a.f + {( -µ *mf *c.v)/(mg*Cpg)}

By trail and error

Initial guess Cpg =1.06 kj/kg k

Cpg2 = (T a.f + T1)/2

Cpg T1 ( K )

1.06 828.6

1.4 1155.5

1.383 1143.9

1.382 1143.2

T1 =1143 K ,Tsat @ 5 bar = 151.85 ˚C

Өi =718.15 Өo=25.15

Q =S U ӨLMTD = (η - µ ) *mf * c.v

=395.7 kw

ӨLMTD = 206.75 K

1/µ = ∑ (Xi / Mi)=0.0349

Rg = (R¯ / Mg)=0.29

ρg = P/ (Rg *T1) = 100/ (0.29 *(1143+273))

= 0.24 kg /m3

Mg = 0.457=0.24*(π/4)*(di2)*V* n

Take di=2.282 in , do=2.5 in

V = 18 m/s

n ≈ 33 tube / pass

For inside tube

Assume the properties of gas as air

At Tm = 796.5 K

ρ = 0.4374 kg /m3

Cp = 1.09816 *103 J / kg .k

µ = 368.736 * 10 -7

N .s /m2

Pr = 0.70851 K = 75.132 *10-3 W/m .k

mg= mg tot/ N tube/pass = 0.457 /33 = 0.0138 Kg/s

Re = 8381 < 2300

Nu =hi Di/ K = 0.023 (Re)0.8

( Pr) 0.3

hi = 28.6 W/m2 .k

out side tube

Tm= 796.5 K

Twall = (Tm + T sat )/ 2 = (796.5 + 424.85 )/ 2

= 610. 7 K

Properties @ Tf = (Twall + T sat) / 2

Tf = 517. 8 & P = 5bar

µv = 17.85 * 10 -6 N .s /m

ρv = 2.045 Kg /m3

Kv = 0.0414 W /m.K

Cpv = 2.08 Kj /Kg

At T sat & P = 5bar ρL= 915. 3 Kg /m3

hfg = 2108 Kj /Kg

ho = 0.62 {(Kv3 g ρv (ρL – ρv ) (hfg + 0.4 Cpv ∆T) / (µv d ∆T)}

0.25

ho =176.2 W /m2 .K

(1/Uo) =(Do/(hi Di)) + Do ln (Do/Di)/(2k)+ 1/(ho)

Assume pipe is made of carbon steel at T wall

K = 48 .3 W / m .k

Uo =22. 7 W / m2 .k

Q 2nd , 3rd = Uo S θLMTD

S = 84.3 m2 = π Do L per pass N Z

Assume we have 2 pass

N = 69.02 tube /pass

There for Z =4 pass

N =33 tube / pass

Dshell = [0.94/2+0.2]*3 = 2.01 m

Lshell = 3.76+0.5= 4.26 m

Chapter 3

Domestic Water Heat Exchangers

Heat exchanger

A heat exchanger is a device built for efficient heat

transfer from one medium to another, whether the media

are separated by a solid wall so that they never mix, or

the media are in direct contact.[1]

They are widely used

in space heating, refrigeration, air conditioning, power

plants, chemical plants, petrochemical plants, petroleum

refineries, and natural gas processing. One common

example of a heat exchanger is the radiator in a car, in

which the heat source, being a hot engine-cooling fluid,

water, transfers heat to air flowing through the radiator

General Description

Heat Exchanger

The heat exchanger uses steam

from the campus boiler to heat

water for use in various heating

coils throughout the building.

The heating water is circulated

by heating water pumps to

heating coils in the cabinet unit

heaters, fintube radiators and

reheat coils in the zone variable

air volume boxes.

On cold days, room temperatures

(especially those rooms with

windows and outside walls) drop.

The room thermostats send this information to the main control system. If the room

temperature cannot be brought back up by reducing the cool air supply from the duct, then the

hot water flow to the heating coil in the VAV box is increased.

As the duct supply air flows) past the coil, the room is heated, and the hot water is cooled.

The temperature of the water exiting the heat exchanger drops, and a thermocouple sensing

this change signals a valve to automatically increase the steam flow until the temperature of

water leaving the heat exchanger rises to a preset value

Flow arrangement

Countercurrent (A) and parallel (B) flows

Fig. 1: Shell and tube

heat exchanger, single

pass (1-1 parallel flow)

Fig. 2: Shell and tube heat

exchanger, 2-pass tube

side (1-2 crossflow)

Fig. 3: Shell and tube heat

exchanger, 2-pass shell side, 2-

pass tube side (2-2

countercurrent)

Heat exchangers may be classified according to their flow arrangement. In parallel-

flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in

parallel to one another to the other side. In counter-flow heat exchangers the fluids

enter the exchanger from opposite ends. The counter current design is most efficient,

in that it can transfer the most heat from the heat (transfer) medium. See

countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly

perpendicular to one another through the exchanger.

For efficiency, heat exchangers are designed to maximize the surface area of the wall

between the two fluids, while minimizing resistance to fluid flow through the

exchanger. The exchanger's performance can also be affected by the addition of fins

or corrugations in one or both directions, which increase surface area and may

channel fluid flow or induce turbulence.

The driving temperature across the heat transfer surface varies with position, but an

appropriate mean temperature can be defined. In most simple systems this is the log

mean temperature difference (LMTD). Sometimes direct knowledge of the LMTD is

not available and the NTU method is used

Types of heat exchangers

Shell and tube heat exchanger

A Shell and Tube heat exchanger

Main article: Shell and tube heat exchanger

Shell and tube heat exchangers consist of a series of tubes. One set of these tubes

contains the fluid that must be either heated or cooled. The second fluid runs over the

tubes that are being heated or cooled so that it can either provide the heat or absorb

the heat required. A set of tubes is called the tube bundle and can be made up of

several types of tubes: plain, longitudinally finned, etc. Shell and Tube heat

exchangers are typically used for high pressure applications (with pressures greater

than 30 bar and temperatures greater than 260°C. This is because the shell and tube

heat exchangers are robust due to their shape.

There are several thermal design features that are to be taken into account when

designing the tubes in the shell and tube heat exchangers. These include:

Tube diameter: Using a small tube diameter makes the heat exchanger both

economical and compact. However, it is more likely for the heat exchanger to foul up

faster and the small size makes mechanical cleaning of the fouling difficult. To

prevail over the fouling and cleaning problems, larger tube diameters can be used.

Thus to determine the tube diameter, the available space, cost and the fouling nature

of the fluids must be considered.

Tube thickness: The thickness of the wall of the tubes is usually determined to

ensure:

o There is enough room for corrosion

o That flow-induced vibration has resistance

o Axial strength

o Ability to easily stock spare parts cost

Sometimes the wall thickness is determined by the maximum pressure

differential across the wall.

Tube length: heat exchangers are usually cheaper when they have a smaller shell

diameter and a long tube length. Thus, typically there is an aim to make the heat

exchanger as long as physically possible whilst not exceeding production capabilities.

However, there are many limitations for this, including the space available at the site

where it is going to be used and the need to ensure that there are tubes available in

lengths that are twice the required length (so that the tubes can be withdrawn and

replaced). Also, it has to be remembered that long, thin tubes are difficult to take out

and replace.

Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch (i.e.,

the centre-centre distance of adjoining tubes) is not less than 1.25 times the tubes'

outside diameter.A larger tube pitch leads to a larger overall shell diameter which

leads to a more expensive heat exchanger.

Tube corrugation: this type of tubes, mainly used for the inner tubes, increases the

turbulence of the fluids and the effect is very important in the heat transfer giving a

better performance.

Tube Layout: refers to how tubes are positioned within the shell. There are four main

types of tube layout, which are, triangular (30°), rotated triangular (60°), square (90°)

and rotated square (45°). The triangular patterns are employed to give greater heat

transfer as they force the fluid to flow in a more turbulent fashion around the piping.

Square patterns are employed where high fouling is experienced and cleaning is more

regular.

Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across

the tube bundle. They run perpendicularly to the shell and hold the bundle, preventing

the tubes from sagging over a long length. They can also prevent the tubes from

vibrating. The most common type of baffle is the segmental baffle. The semicircular

segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid

to flow upward and downwards between the tube bundle. Baffle spacing is of large

thermodynamic concern when designing shell and tube heat exchangers. Baffles must

be spaced with consideration for the conversion of pressure drop and heat transfer.

For thermo economic optimization it is suggested that the baffles be spaced no closer

than 20% of the shell‟s inner diameter. Having baffles spaced too closely causes a

greater pressure drop because of flow redirection. Consequently having the baffles

spaced too far apart means that there may be cooler spots in the corners between

baffles. It is also important to ensure the baffles are spaced close enough that the

tubes do not sag. The other main type of baffle is the disc and donut baffle which

consists of two concentric baffles, the outer wider baffle looks like a donut, whilst the

inner baffle is shaped as a disk. This type of baffle forces the fluid to pass around

each side of the disk then through the donut baffle generating a different type of fluid

flow.

Conceptual diagram of a plate and frame heat exchanger.

A single plate heat exchanger

Plate heat exchanger

Another type of heat exchanger is the plate heat exchanger. One is composed of

multiple, thin, slightly-separated plates that have very large surface areas and fluid

flow passages for heat transfer. This stacked-plate arrangement can be more effective,

in a given space, than the shell and tube heat exchanger. Advances in gasket and

brazing technology have made the plate-type heat exchanger increasingly practical. In

HVAC applications, large heat exchangers of this type are called plate-and-frame;

when used in open loops, these heat exchangers are normally of the gasketed type to

allow periodic disassembly, cleaning, and inspection. There are many types of

permanently-bonded plate heat exchangers, such as dip-brazed and vacuum-brazed

plate varieties, and they are often specified for closed-loop applications such as

refrigeration. Plate heat exchangers also differ in the types of plates that are used, and

in the configurations of those plates. Some plates may be stamped with "chevron" or

other patterns, where others may have machined fins and/or grooves.

Regenerative heat exchanger

A third type of heat exchanger is the regenerative heat exchanger. In this, the heat

(heat medium) from a process is used to warm the fluids to be used in the process, and

the same type of fluid is used either side of the heat exchanger (these heat exchangers

can be either plate-and-frame or shell-and-tube construction). These exchangers are

used only for gases and not for liquids. The major factor for this is the heat capacity of

the heat transfer matrix. Also see: Countercurrent exchange, Regenerator, Economizer

Adiabatic wheel heat exchanger

A fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat,

which is then moved to the other side of the heat exchanger to be released. Two

examples of this are adiabatic wheels, which consist of a large wheel with fine threads

rotating through the hot and cold fluids, and fluid heat exchangers. This type is used

when it is acceptable for a small amount of mixing to occur between the two streams.

See also: Air preheater.

Plate fin heat exchanger

This type of heat exchanger uses "sandwiched" passages containing fins to increase

the effectivity of the unit. The designs include crossflow and counterflow coupled

with various fin configurations such as straight fins, offset fins and wavy fins.

Plate and fin heat exchangers are usually made of aluminium alloys which provide

higher heat transfer efficiency. The material enables the system to operate at a lower

temperature and reduce the weight of the equipment. Plate and fin heat exchangers are

mostly used for low temperature services such as natural gas, helium and oxygen

liquefaction plants, air separation plants and transport industries such as motor and

aircraft engines.

Advantages of plate and fin heat exchangers:

High heat transfer efficiency especially in gas treatment

Larger heat transfer area

Approximately 5 times lighter in weight than that of shell and tube heat exchanger

Able to withstand high pressure

Disadvantages of plate and fin heat exchangers:

Might cause clogging as the pathways are very narrow

Difficult to clean the pathways

Fluid heat exchangers

This is a heat exchanger with a gas passing upwards through a shower of fluid (often

water), and the fluid is then taken elsewhere before being cooled. This is commonly

used for cooling gases whilst also removing certain impurities, thus solving two

problems at once. It is widely used in espresso machines as an energy-saving method

of cooling super-heated water to be used in the extraction of espresso.

Waste heat recovery units

A Waste Heat Recovery Unit (WHRU) is a heat exchanger that recovers heat from a

hot gas stream while transferring it to a working medium, typically water or oils. The

hot gas stream can be the exhaust gas from a gas turbine or a diesel engine or a waste

gas from industry or refinery.

Dynamic scraped surface heat exchanger

Another type of heat exchanger is called "(dynamic) scraped surface heat exchanger".

This is mainly used for heating or cooling with high-viscosity products, crystallization

processes, evaporation and high-fouling applications. Long running times are

achieved due to the continuous scraping of the surface, thus avoiding fouling and

achieving a sustainable heat transfer rate during the process.

The formula used for this will be Q=A*U*LMTD, whereby Q= heat transfer rate.

Phase-change heat exchangers

Typical kettle reboiler used for industrial distillation towers

Typical water-cooled surface condenser

In addition to heating up or cooling down fluids in just a single phase, heat

exchangers can be used either to heat a liquid to evaporate (or boil) it or used as

condensers to cool a vapor and condense it to a liquid. In chemical plants and

refineries, reboilers used to heat incoming feed for distillation towers are often heat

exchangers.[3][4]

Distillation set-ups typically use condensers to condense distillate vapors back into

liquid.

Power plants which have steam-driven turbines commonly use heat exchangers to boil

water into steam. Heat exchangers or similar units for producing steam from water are

often called boilers or steam generators.

In the nuclear power plants called pressurized water reactors, special large heat

exchangers which pass heat from the primary (reactor plant) system to the secondary

(steam plant) system, producing steam from water in the process, are called steam

generators. All fossil-fueled and nuclear power plants using steam-driven turbines

have surface condensers to convert the exhaust steam from the turbines into

condensate (water) for re-use.[5][6]

To conserve energy and cooling capacity in chemical and other plants, regenerative

heat exchangers can be used to transfer heat from one stream that needs to be cooled

to another stream that needs to be heated, such as distillate cooling and reboiler feed

pre-heating.

This term can also refer to heat exchangers that contain a material within their

structure that has a change of phase. This is usually a solid to liquid phase due to the

small volume difference between these states. This change of phase effectively acts as

a buffer because it occurs at a constant temperature but still allows for the heat

exchanger to accept additional heat. One example where this has been investigated is

for use in high power aircraft electronics.

Flow Arrangements

There are three main types of flows in a spiral heat exchanger:

1. Countercurrent Flow: Both fluids flow in opposite directions, and are used for liquid-

liquid, condensing and gas cooling applications. Units are usually mounted vertically

when condensing vapour and mounted horizontally when handling high

concentrations of solids.

2. Spiral Flow/Cross Flow: One fluid is in spiral flow and the other in a cross flow.

Spiral flow passages are welded at each side for this type of spiral heat exchanger.

This type of flow is suitable for handling low density gases which passes through the

cross flow, avoiding pressure loss. It can be used for liquid-liquid applications if one

liquid has a considerably greater flow rate than the other.

3. Distributed Vapour/Spiral flow: This design is a condenser, and is usually mounted

vertically. It is designed to cater for the sub-cooling of both condensate and non-

condensables. The coolant moves in a spiral and leaves via the top. Hot gases that

enter leave as condensate via the bottom outlet

Selection

Due to the many variables involved, selecting optimal heat exchangers is challenging.

Hand calculations are possible, but many iterations are typically needed. As such, heat

exchangers are most often selected via computer programs, either by system

designers, who are typically engineers, or by equipment vendors.

In order to select an appropriate heat exchanger, the system designers (or equipment

vendors) would firstly consider the design limitations for each heat exchanger type.

Although cost is often the first criterion evaluated, there are several other important

selection criteria which include:

High/ Low pressure limits

Thermal Performance

Temperature ranges

Product Mix (liquid/liquid, particulates or high-solids liquid)

Pressure Drops across the exchanger

Fluid flow capacity

Cleanability, maintenance and repair

Materials required for construction

Ability and ease of future expansion

Choosing the right heat exchanger (HX) requires some knowledge of the different

heat exchanger types, as well as the environment in which the unit must operate.

Typically in the manufacturing industry, several differing types of heat exchangers are

used for just the one process or system to derive the final product. For example, a

kettle HX for pre-heating, a double pipe HX for the „carrier‟ fluid and a plate and

frame HX for final cooling. With sufficient knowledge of heat exchanger types and

operating requirements, an appropriate selection can be made to optimise the

process.[16]

Temperature controlled applications

In a temperature control application, the inlet temperature of the secondary fluid to the

heat exchanger may change with time. This means that in order to maintain a

consistent secondary fluid outlet temperature, the heat supplied to the heat exchanger

must also vary. This can be achieved by using a control valve on the inlet to the

primary side of the heat exchanger, as shown in Figure 13.2.1.

Fig. 13.2.1 Typical temperature control of a steam/water shell and tube heat exchanger

A control valve is used to vary the flowrate and pressure of the steam so that the heat

input to the heat exchanger can be controlled. Modulating the position of the control

valve then controls the outlet temperature of the secondary fluid. A sensor on the

secondary fluid outlet monitors its temperature, and provides a signal for the

controller. The controller compares the actual temperature with the set temperature

and, as a result, signals the actuator to adjust the position of the control valve.

For a constant heating area and heat transfer coefficient, the rate at which heat is

transferred from the steam to the secondary fluid for a particular heat exchanger is

determined by the mean temperature difference between the two fluids. A larger

difference in mean temperatures will create a large heat transfer rate and vice versa.

On partially closing the control valve, the steam pressure and the temperature

difference fall. Conversely, if the control valve is opened so that the steam mass flow

and hence pressure in the heat exchanger rise, the mean temperature difference

between the two fluids increases.

Shell and tube heat exchanger design

There can be many variations on the shell and tube design. Typically, the ends of each

tube are connected to plenums (sometimes called water boxes) through holes in

tubesheets. The tubes may be straight or bent in the shape of a U, called U-tubes.

In nuclear power plants called pressurized water reactors, large heat exchangers called

steam generators are two-phase, shell-and-tube heat exchangers which typically have

U-tubes. They are used to boil water recycled from a surface condenser into steam to

drive a turbine to produce power. Most shell-and-tube heat exchangers are either 1, 2,

or 4 pass designs on the tube side. This refers to the number of times the fluid in the

tubes passes through the fluid in the shell. In a single pass heat exchanger, the fluid

goes in one end of each tube and out the other.

Surface condensers in power plants are often 1-pass straight-tube heat exchangers (see

Surface condenser for diagram). Two and four pass designs are common because the

fluid can enter and exit on the same side. This makes construction much simpler.

There are often baffles directing flow through the shell side so the fluid does not take

a short cut through the shell side leaving ineffective low flow volumes.

Counter current heat exchangers are most efficient because they allow the highest log

mean temperature difference between the hot and cold streams. Many companies

however do not use single pass heat exchangers because they can break easily in

addition to being more expensive to build. Often multiple heat exchangers can be used

to simulate the counter current flow of a single large exchanger.

Selection of tube material

To be able to transfer heat well, the tube material should have good thermal

conductivity. Because heat is transferred from a hot to a cold side through the tubes,

there is a temperature difference through the width of the tubes. Because of the

tendency of the tube material to thermally expand differently at various temperatures,

thermal stresses occur during operation. This is in addition to any stress from high

pressures from the fluids themselves. The tube material also should be compatible

with both the shell and tube side fluids for long periods under the operating conditions

(temperatures, pressures, pH, etc.) to minimize deterioration such as corrosion. All of

these requirements call for careful selection of strong, thermally-conductive,

corrosion-resistant, high quality tube materials, typically metals, including copper

alloy, stainless steel, carbon steel, non-ferrous copper alloy, Inconel, nickel, Hastelloy

and titanium[3]

. Poor choice of tube material could result in a leak through a tube

between the shell and tube sides causing fluid cross-contamination and possibly loss

of pressure

CLEANING OF HEAT EXCHANGER

Cleaning Techniques

In general, the techniques used to remove the foulants from the heat exchanger

surfaces, both

on the shell side and on the tube side, can be broadly classified into two categories:

mechanical and chemical. The cleaning process may be employed while the plant is

still

operating, that is, on line, but in most situations it will be necessary to shutdown the

plant to

clean the heat exchangers, known as 08-line cleaning. In some instances combinations

of

these cleaning methods may be necessary. Each method of cleaning has advantages

and

disadvantages with specific equipment types and materials of construction.

• HIGH COST OF TRADITIONAL MECHANICAL CLEANING

Large shell-and-tube heat exchangers (Figure 20) usually require disassembly of both

ends

and internals, removal of the tube bundle, transportation to a cleaning facility and

cleaning,

reassembly, and leak testing. This process can take between 3-14 days, depending on

several

factors like exchanger size and weight, severity of fouling, whether specialty

equipment is

required to extract the tube bundle etc. In the worst cases the cost for the mechanical

work is

as high as 40-50k$ per exchanger. A penalty of up to ten times that cost could also be

incurred, depending on the duration of outage and if production is affected while the

cleaning

takes place. As a result there is an obviously large incentive to develop cleaning

methods

which minimize or eliminate the mechanical costs and which can be carried out in

short

periods of time (one day or less).

shell-and-tube heat exchangers

• The Cooler Cleaning Process

The heat exchangers are placed in a high temperature chemical solution for several

hours:

The heat exchanger would then be pulled from the cleaning vat and sprayed with a

high pressure

washer to remove loose debris and excess chemicals.

Each individual tube is then rodded out with a pneumatic drill brush.

Each individual tube is also blasted out with high pressure water

Tube integrity is also tested. Tubes are tested for leaks and if necessary, plugs may be

installed on site. Other repairs (if required) would have to be completed at our shop

facilities.

I.e.; Tube Replacement, ceramic cap repair, etc...

After cleaning & testing is complete, each tube bundle is individually wrapped in

plastic to

maintain the integrity of the cleaning

• Chemical Cleaning

The usual practice is to resort to chemical cleaning of heat exchangers only when

other

methods are not satisfactory. Chemical cleaning involves the use of chemicals to

dissolve or

loosen deposits. The chemical cleaning methods are mostly off-line. Choosing a

Chemical

Cleaning Method Chemical cleaning methods must take into account a number of

factors

such as:

1. Compatibility of the system components with the chemical cleaning solutions. If

required,

inhibitors are added to the cleaning solutions.

2. Information relating to the deposit must be known beforehand.

3. Chemical cleaning solvents must be assessed by a corrosion test before beginning

cleaning

operation.

4. Adequate protection of personnel employed in the cleaning of the equipment must

be

provided.

5. Chemical cleaning poses the real possibility of equipment damage from corrosion.

Precautions may be taken to reduce the corrosion rate to acceptable levels. On-line

corrosion

monitoring during cleaning is necessary. Post cleaning inspection is extremely

important to

check for corrosion damage due to cleaning solvents and to gauge the cleaning

effectiveness.

6. Disposal of the spent solution.

CONTROLING HEAT EXCHANGER

INTRODUCTION

Shell and tube heat exchangers are among the more confusing pieces of equipment for

the

process control engineer. The principle of operation is simple enough: Two fluids of

different

temperatures are brought into close contact but are prevented from mixing by a

physical

barrier. The temperature of the two fluids will tend to equalize. By arranging counter-

current

flow it is possible for the temperature at the outlet of each fluid to approach the

temperature

at the inlet of the other. The heat contents are simply exchanged from one fluid to the

other

and vice versa. No energy is added or removed.

Since the heat demands of the process are not constant, and the heat content of the

two fluids

is not constant either, the heat exchanger must be designed for the worst case and

must be

controlled to make it operate at the particular rate required by the process at every

moment in

time. The heat exchanger itself is not constant. Its characteristic changes with time.

The most

common change is a reduction in the heat transfer rate due to fouling of the surfaces.

Exchangers are initially oversized to allow for the fouling which gradually builds up

during

use until the exchanger is no longer capable of performing its duty. Once it has been

cleaned

it is again oversized.

• WHERE DO WE MEASURE?

At the fundamental level, there is only one variable that can be controlled -- the

amount of

heat being exchanged. In practical situations it is not possible to measure heat flux. It

is

always the temperature of one fluid or the other which is being measured and

controlled. It is

not possible to control both since the heat added from one is taken from the other.

Therefore

the first consideration is to specify the place at which the temperature is to be kept

constant.

This is usually within a piece of equipment somewhere downstream of the outlet of

one of

the fluids. Assuming there is not much temperature change along the piping, the

measurement may be anywhere between the outlet itself and the point of interest,

perhaps at

the base of a distillation tower. In cases where the measurement is being made down

stream

of a bypass valve, the further downstream, the better the mixing will be, and the more

representative the measurement. On the other hand, too far down-stream may result in

process dead time that can make control difficult. In cases where the "other" fluid is

the one

being manipulated, it is often quite sufficient to make the measurement directly

downstream

of the outlet nozzle of the exchanger.

• WHICH STREAM DO WE MANIPULATE?

The second consideration is which stream to manipulate. The complications arise

from the

fact that exchangers have four ports and involve two different fluids, either of which

may

change phase. The former feature alone allows eight different valve arrangements.

Figure

allows the reader to figure them all out. The diagram assumes that it is the fluid on the

shell

side whose temperature is being controlled. As likely as not, it is the one on the tube

side. It

doesn't really make any difference to the control strategy. The real issue is which fluid

is to

be manipulated by the valves. For the sake of discussion we will term the two streams

the

"process" side and the "heat exchange medium" side. A complete tabulation of all the

possibilities is:

SHELL AND TUBE HEAT EXCHANGER

a - Process side, outlet throttling.

b - Process side, inlet throttling.

c - Process side, bypass with outlet restriction.

d - Process side, bypass with inlet restriction.

e - Medium side, outlet throttling.

f - Medium side, inlet throttling.

g - Medium side, bypass with outlet restriction.

h - Medium side, bypass with inlet restriction.

Among this profusion of alternatives, some must be better than others. The preferred

choice

depends, as always, on the particular situation.

There are a number of varieties of the basic shell and tube exchanger that can be

controlled

along similar lines. Plate exchangers consist of thin sheets of corrugated metal. The

corrugations are formed to produce passages so that the two fluids pass in opposite

directions

on opposite sides of each sheet. The "shell" side and the "tube" side are essentially

interchangeable.

Aerial coolers, sometimes called fin fan coolers, are similar to shell and tube

exchangers

except that they are all tube. The air blowing past the tubes can be considered to be in

an

extremely large shell.

THROTTLING THE PROCESS FLUID.

It is quite meaningless to attempt to control the process temperature by throttling

either the

inlet or the outlet of the process fluid. The desired process flow rate is set by other

requirements and these would be interfered with by manipulating the process flow.

Temperature will change somewhat since flow reduction increases the residence time

of the

fluid and the outlet temperature will more closely approach the inlet temperature of

the

medium.

On the other hand, variations in process flow, caused by some external influence, is

one of

the major causes of temperature variation. It is often the reason why we must

manipulate

some other parameter to maintain constant temperature.

BYPASSING THE PROCESS FLUID.

Process temperature can be controlled by manipulating process flow if a bypass is

installed.

As the outlet temperature rises (assume this is a heater), more fluid is bypassed

around the

ex-changer without being heated. As the two streams are blended together again, the

correct

temperature is achieved.

PROCESS SIDE BYPASS WITH RESTRICTION ON THE OUTLET

Chapter 4

Air Handling Units

Air handler

Fig1

An air handling unit: air flow is from the right to left in this case. Some AHU components

shown are:

1 - Supply duct

2 - Fan compartment

3 - Vibration isolator ('flex joint')

4 - Heating and/or cooling coil

5 - Filter compartment

6 - Mixed (recirculated + outside) air duct

An air handler, or air handling unit (often abbreviated to AHU), is a device used to

condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC)

system. Usually, an air handler is a large metal box containing a blower, heating and/or

cooling elements , filter racks or chambers, sound attenuators, and dampers. Air handlers

usually connect to ductwork that distributes the conditioned air through the building, and

returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to

and from the space served, without ductwork.

Small air handlers, for local use, are called terminal units, and may only include an air filter,

coil, and blower; these simple terminal units are called blower coils or fan coil units. A larger

air handler that conditions 100% outside air, and no recirculated air, is known as a makeup

air unit (MAU). An air handler designed for outdoor use, typically on roofs, is known as a

packaged unit (PU) or rooftop unit (RTU).

Air handler components:

1-Blower/fan

Fig2

Air handlers typically employ a large squirrel cage blower driven by an AC induction electric

motor to move the air. The blower may operate at a single speed, offer a variety of pre-set

speeds, or be driven by a Variable Frequency Drive so as to allow a wide range of air flow

rates. Flow rate may also be controlled by inlet vanes or outlet dampers on the fan. Some

residential air handlers (central 'furnaces' or 'air conditioners') use a brushless DC electric

motor that has variable speed capabilities.

In large commercial air handling units, multiple blowers may be present, typically placed at

the end of the AHU and the beginning of the supply ductwork (therefore also called "supply

fans"). They are often augmented by fans in the return air duct ("return fans"), pushing the air

into the AHU.

2-Heating and/or cooling elements

Fig 3

Depending on the location and the application, air handlers may need to provide heating, or

cooling, or both to change the supply air temperature.

Smaller air handlers may contain a fuel-burning heater or a refrigeration evaporator, placed

directly in the air stream. Electric resistance and heat pumps are used too. Evaporative

cooling is possible in dry climates too.

Large commercial air handling units contain coils that circulate hot water or steam for

heating, and chilled water for cooling. The hot water or steam is provided by a central boiler,

and the chilled water is provided by a central chiller.

3-Filters

Air filtration is almost always present in order to provide clean dust-free air to the building

occupants. It may be via simple low-MERV pleated media, HEPA, electrostatic, or a

combination of techniques. Gas-phase and ultraviolet air treatments may be employed as well.

It is typically placed first in the AHU in order to keep all its components clean.

4-Humidifier

Humidification is often necessary in colder climates where continuous heating will make the

air drier, resulting in uncomfortable air quality and increased static electricity. Various types

of humidification may be used:

Evaporative: dry air blown over a reservoir will evaporate some of the water. The rate

of evaporation can be increased by spraying the water onto baffles in the air stream.

Vaporizer: steam or vapour from a boiler is blown directly into the air stream.

Spray mist: water is diffused either by a nozzle or other mechanical means into fine

droplets and carried by the air.

5-Mixing chamber

In order to maintain indoor air quality, air handlers commonly have provisions to allow the

introduction of outside air into, and the exhausting of air from the building. In temperate

climates, mixing the right amount of cooler outside air with warmer return air can be used to

approach the desired supply air temperature. A mixing chamber is therefore used which has

dampers controlling the ratio between the return, outside, and exhaust air.

A heat recovery heat exchanger, of many types, may be fitted to the air handler for energy

savings and increasing capacity.

6-Controls

Controls are necessary to regulate every aspect of an air handler, such as: flow rate of air,

supply air temperature, mixed air temperature, humidity, air quality. They may be as simple

as an off/on thermostat or as complex as a building automation system using BAC net or Lon

Works, for example.

Common control components include temperature sensors, humidity sensors, sail switches,

actuators, motors, and controllers.

7-Vibration isolators

The blowers in an air handler can create substantial vibration and the large area of the duct

system would transmit this noise and vibration to the occupants of the building. To avoid this,

vibration isolators (flexible sections) are normally inserted into the duct immediately before

and after the air handler and often also between the fan compartment and the rest of the AHU.

The rubberized canvas-like material of these sections allow the air handler to vibrate without

transmitting much vibration to the attached ducts.

The fan compartment can be further isolated by placing it on a spring suspension, which will

mitigate the transfer of vibration through the floor.

Duct Cleaning

Duct cleaning generally refers to the cleaning of various heating and cooling system

components of forced air systems, including the supply and return air ducts and

registers, grilles and diffusers ,heat exchangers heating and cooling coils, condensate

drain pans (drip pans), fan motor and fan housing, and the air handling unit housing .

If not properly installed, maintained, and operated, these components may become

contaminated with particles of dust, pollen or other debris. If moisture is present, the

potential for microbiological growth (e.g., mold) is increased and spores from such

growth may be released into the home's living space. Some of these contaminants

may cause allergic reactions or other symptoms in people if they are exposed to them.

We use specialized tools to dislodge dirt and other debris in ducts, then vacuum them

out with a high-powered vacuum cleaner.

You should consider having the air ducts in your home cleaned if:

There is substantial visible mold growth inside hard surface (e.g., sheet metal) ducts

or on other components of your system.

Ducts are clogged with excessive amounts of dust and debris and/or particles are

actually released into the home from your supply registers.

Ducts are infested with vermin, e.g. (rodents or insects); or

If any of the conditions identified above exists, it usually suggests one or more

underlying causes. Prior to any cleaning, retrofitting, or replacing of your ducts, the

cause or causes must be corrected or else the problem will likely recur.

Some research suggests that cleaning heating and cooling system components (e.g.,

cooling coils, fans and heat exchangers) may improve the efficiency of your system,

resulting in a longer operating life, as well as some energy and maintenance cost

savings.

How to Prevent Duct Contamination

Whether or not you decide to have the air ducts in your home cleaned, committing to

a good preventive maintenance program is essential to minimize duct contamination.

To prevent dirt from entering the system:

Use the highest efficiency air filter recommended by the manufacturer of your

system.

Change filters regularly.

If your filters become clogged, change them more frequently.

Be sure you do not have any missing filters and that air cannot bypass filters through

gaps around the filter holder.

When having your heating and cooling system maintained or checked for other

reasons, be sure to ask the service provider to clean cooling coils and drain pans.

During construction/renovation work that produces dust in your home, seal off supply

and return registers and do not operate the heating and cooling system until after

cleaning up the dust.

Remove dust and vacuum your home regularly. (Use a high efficiency vacuum

(HEPA) cleaner or the highest efficiency filter bags your vacuum cleaner can take.

Vacuuming can increase the amount of dust in the air during and after vacuuming as

well as in your ducts).

If your heating system includes in-duct humidification equipment, be sure to operate

and maintain the humidifier strictly as recommended by the manufacturer.

To prevent ducts from becoming wet:

Moisture should not be present in ducts. Controlling moisture is the most effective

way to prevent biological growth in air ducts.

Moisture can enter the duct system through leaks or if the system has been improperly

installed or serviced. Research suggests that condensation on or near cooling coils of

air conditioning units is a major factor in moisture contamination of the system. The

presence of condensation or high relative humidity is an important indicator of the

potential for mold growth on any type of duct. Controlling moisture can often be

difficult, but here are some steps you can take:

Promptly and properly repair any leaks or water damage.

Pay particular attention to cooling coils, which are designed to remove water from the

air and can be a major source of moisture contamination of the system that can lead to

mold growth. Make sure the condensate pan drains properly. The presence of

substantial standing water and/or debris indicates a problem requiring immediate

attention. Check any insulation near cooling coils for wet spots.

Make sure ducts are properly sealed and insulated in all non-air-conditioned spaces

(e.g., attics and crawl spaces). This will help to prevent moisture due to condensation

from entering the system and is important to make the system work as intended. To

prevent water condensation, the heating and cooling system must be properly

insulated.

If you are replacing your air conditioning system, make sure that the unit is the proper

size for your needs and that all ducts are sealed at the joints. A unit that is too big will

cycle on and off frequently, resulting in poor moisture removal, particularly in areas

with high humidity. Also make sure that your new system is designed to manage

condensation effectively.

Controller

Controllers are essentially small, purpose-built computers with input and output

capabilities. These controllers come in a range of sizes and capabilities to control

devices commonly found in buildings, and to control sub-networks of controllers.

Inputs allow a controller to read temperatures, humidity, pressure, current flow, air

flow, and other essential factors. The outputs allow the controller to send command

and control signals to slave devices, and to other parts of the system. Inputs and

outputs can be either digital or analog.

Fig 4

Figure- 4 presents the schematic diagram of the two main air-handling units. The supply air

fan was controlled to maintain the duct static pressure set point between 1.5 inches H2O and

2.5 inches H2O depending on the maximum terminal box damper position. If the maximum

damper position was less than 94 percent open, the static pressure set point would be

decreased to open the damper more. If the static pressure reached the minimum value (1.5

inches H2O), the damper was closed more to maintain the room air temperature.

The return fan was controlled by relief damper position according to the following

criteria:

1-When relief damper was less than 25 percent open, the relief chamber static pressure set

point was controlled at -0.02 inches H2O;

2-When the relief damper was higher than 96 percent open, the relief chamber static

pressure was controlled at 0.1 inches H2O;

3-When the relief damper was less than 50 percent and 75 percent open, the relief

chamber static pressure was controlled at 0.0 and 0.01 respectively; and

4-The relief damper position was controlled by the building static pressure sensor.

The supply air temperature was reset based on the outside air temperature. When the

outside air temperature was lower than 50°F, the supply air temperature was maintained at

63°F. When the outside air temperature was higher than 75°, the supply air temperature was

maintained at 53°F. The supply air temperature was reset linearly from 63°F to 53°F when the

outside air temperature increased from 50°F to 75°F.

The enthalpy economizer was implemented. When the outside air enthalpy was lower

than 17Btu/lbm, the economizer was activated. When economizer was disabled, the minimum

outside air was measured using a flow station and controlled at the design value by adjusting

the outside air damper during occupied hours. During unoccupied hours, the outside air

damper was completely closed.

The original control schedules have the following disadvantages: (1) excessive minimum

static pressure set point, (2) outside air backflow from the relief damper due to negative

pressure set point at the mixing chamber, (3) high humidity during mild weather conditions

due to relatively high supply air temperature set point, (4) excessive minimum outside air

intake during occupied hours, (5) negative building pressure during unoccupied hours due to

zero outside air intake, and (6) excessive mechanical cooling consumption due to

inappropriate enthalpy economizer set point.

Air handlers

Most air handlers mix return and outside air so less temperature change is needed.

This can save money by using less chilled or heated water (not all AHUs use

chilled/hot water circuits). Some external air is needed to keep the building's air

healthy.

Analog or digital temperature sensors may be placed in the space or room, the return

and supply air ducts, and sometimes the external air. Actuators are placed on the hot

and chilled water valves, the outside air and return air dampers. The supply fan (and

return if applicable) is started and stopped based on either time of day, temperatures,

building pressures or a combination.

Constant Volume Air-Handling Units

The less efficient type of air-handler is a "Constant Volume Air Handling Unit," or

CAV. The fans in CAVs do not have variable-speed controls. Instead, CAVs open and

close dampers and water-supply valves to maintain temperatures in the building's

spaces. They heat or cool the spaces by opening or closing chilled or hot water valves

that feed their internal heat exchangers. Generally one CAV serves several spaces, but

large buildings may have many CAVs.

Variable Volume Air-Handling Units

A more efficient unit is a "Variable air volume (VAV) Air-Handling Unit," or VAV.

VAVs supply pressurized air to VAV boxes, usually one box per room or area. A

VAV air handler can change the pressure to the VAV boxes by changing the speed of

a fan or blower with a variable frequency drive or (less efficiently) by moving inlet

guide vanes to a fixed-speed fan. The amount of air is determined by the needs of the

spaces served by the VAV boxes.

Each VAV box supply air to a small space, like an office. Each box has a damper that

is opened or closed based on how much heating or cooling is required in its space.

The more boxes are open, the more air is required, and a greater amount of air is

supplied by the VAV air-handling unit.

Some VAV boxes also have hot water valves and an internal heat exchanger. The

valves for hot and cold water are opened or closed based on the heat demand for the

spaces it is supplying. These heated VAV boxes are sometimes used on the perimeter

only and the interior zones are cooling only.

A minimum and maximum CFM must be set on VAV boxes to assure adequate

ventilation and proper air balance.

VAV Hybrid Systems

Another variation is a hybrid between VAV and CAV systems. In this system, the

interior zones operate as in a VAV system. The outer zones differ in that the heating

is supplied by a heating fan in a central location usually with a heating coil fed by the

building boiler. The heated air is ducted to the exterior dual duct mixing boxes and

dampers controlled by the zone thermostat calling for either cooled or heated air as

needed.

Central plant

A central plant is needed to supply the air-handling units with water. It may supply a

chilled water system, hot water system and a condenser water system, as well as

transformers and auxiliary power unit for emergency power. If well managed, these

can often help each other. For example, some plants generate electric power at periods

with peak demand, using a gas turbine, and then use the turbine's hot exhaust to heat

water or power an absorptive chiller.

Chilled water system

Chilled water is often used to cool a building's air and equipment. The chilled water

system will have chiller(s) and pumps. Analog temperature sensors measure the

chilled water supply and return lines. The chiller(s) are sequenced on and off to chill

the chilled water supply.

Condenser water system

Cooling tower(s) and pumps are used to supply cool condenser water to the chillers.

The condenser water supply to the chillers has to be constant so, speed drives are

commonly used on the cooling tower fans to control temperature. Proper cooling

tower temperature assures the proper refrigerant head pressure in the chiller. The

cooling tower set point used depends upon the refrigerant being used. Analog

temperature sensors measure the condenser water supply and return lines.

Hot water system

The hot water system supplies heat to the building's air-handling unit or VAV box

heating coils, along with the domestic hot water heating coils (Calorifier) . The hot

water system will have a boiler(s) and pumps. Analog temperature sensors are placed

in the hot water supply and return lines. Some type of mixing valve is usually used to

control the heating water loop temperature. The boiler(s) and pumps are sequenced on

and off to maintain supply.

Alarms and security

Many building automation systems have alarm capabilities. If an alarm is detected, it

can be programmed to notify someone. Notification can be through a computer,

pager, cellular phone, or audible alarm.

Common temperature alarms are Space, Supply Air, Chilled Water Supply and Hot

Water Supply.

Differential pressure switches can be placed on the filter to determine if it is dirty.

Status alarms are common. If a mechanical device like a pump is requested to start,

and the status input indicates it is off. This can indicate a mechanical failure.

Some valve actuators have end switches to indicate if the valve has opened or not.

Carbon monoxide and carbon dioxide sensors can be used to alarm if levels are too

high.

Refrigerant sensors can be used to indicate a possible refrigerant leak.

Current sensors can be used to detect low current conditions caused by slipping fan

belts, or clogging strainers at pumps.

Design of cooling coil :

Calculation of load:-

Assume 6 persons

Qs Persons = 6* 0.177 =1.062 KW

QL persons = 6* 0.248 = 1.488 KW

Q light = 2 KW

Q instruments = 3KW

Qs tot =2+3+1.062= 6.062 KW

QL tot =1.488 KW

SHF = Qs / (Qs + QL) = 0.8

instrument Heat gain [W]

Electro surgery 147

X-ray system 534

Ultra-sonic system 1063

Laser sonics 256

Pulse oximeter 21

Vacuum suction 337

Endoscope 605

monitoring 80

Total [ Kw] 3.043

40

12

8.6

6

θi= dbt ao – tw i =8.6 – 6 =2.6 °c

θo =dbt ai – tw o =40 -12 =28 °c

θLMTD =( θi – θo) / ln (θi/ θo)

= 10.687

Assume air recirculation = 20 time / hour

m• air = (7*7*3 *1.23*20)/3600

=1.1 Kg /s

Q ref = U S θ LMTD

Q ref = m•a *{( ho – hi) - 4.187(ψ0- ψi)Tadp}

=1.1{ (100.78- 26.04) - 4.187 ( 0.02362 – 0.00693)* 8.478}

=81.56 KW

Q reheat= m•a (hc –h1)

=1.1(30.21 – 26 .04 )

=4.587 KW

Q ref = m•w Cw (two –twi)

81.56= m•w *4.18 (12 -6)

m•w =3.25 Kg/s

= ( π/4) di2 *ρ * v * ntube/pass

3.25 =( π/4)(0.014097)2 *1000 * 1.3 * ntube/pass

n =16 tube /pass

Evaluate heat transfer coefficient

for water side

at Pw =2 bar

Tw avg = (6 +12)/2

= 9 °C

Re do = ρw *Do * Vmax /µw

Nu do =0.0243* C1*( Re m) *

Prw

(0.4)

= hin * Di / kw

h in=6675 W/m2 .k

Given data :

Do = (5/8 )" =17.1704 mm

Di =14.097 mm

K=52 W /m .k

F= 0.89

ήf =0.95

fin pitch =7.75 mm

Dh =0.01268 ft =3.86 mm

Thickness = t =0.016 in =0.04064 mm

σ =0.497

α = 157 ft2/ft

3 =515.09 m

2/m

3

Af / Atot =0.905

Tube materiaL:

Properties at T=300K P=Patm

K= 52 W/m.K

Air properties at Tavg =(40 +12.7)/2 =26.35 °C =300 K , P =P atm

Cp = 1.007 KJ/Kg .K

µ = 184.6 *10-7

N.sec /m2

Pr =0.707

Water Properties at Tavg = (6+12)/2 = 9 °C= 282 k

Cp =4.193 KJ /Kg .k

(1/Uo) =( 1/(hi(Ai/Ao))) + ln (Do/Di)/(2πkL/Ao)+ 1/(ho*ή)

Ao / Ai =19.31

m•a= ρa V Afr

1.1 = 1.23 *2.5* Afr

Afr = 0.36 m2

G = m•a/ (σ * Afr)

=1.1 /(0.497 *0.36) = 6.15

Re = G Dh / µ

= 6.15 *0.00386 /(184.6 *10-7

) = 1285.55

From fig (101) kays & London

JH = 0.0075 f =0.0195

ho = (JH* G*Cp) / Pr^(2/3)

= ( 0.0075 * 6.15 *1.007*1000)/(0.707 (2/3)

) = 60 W/m2.K

ή0,0 = 1 – (Af *(1-ήf)/A)

= 0.955

(1/Uo) =( 1/(hi(Ai/Ao))) + Di ln (Do/Di)/(2kAi/Ao)+ 1/(ho*ή)

Uo= 50.72 W/m2 .k

Q ref = Uo Ao θLMTD

81.56 *103 = 50.72 * Ao *10.687

Ao = 150.467 m2

Ao /Ai = 19.31

Ai =7.792 m2 = 3.14* Di * L * N tot

L * N tot = 175.95

L * N per pass = 21.99 1

Assume aspect ratio = 2

L / St(Nper row +1) = 2

L / (Nper row+ 1) = 0.0762 2

From 1& 2

N PER ROW = 18

N PER pass = 16

Npass = 9

L = 1.22 m

H = 0.61 m

W = 0.4 m

N fin =L pass / fin space

= 1.22 /( 0.129 *25.4 * 10-3

)

= 372 fin

Taking max number of rows

N rows = 8

W = SL ( n row+ 1)

= 1.75 * 25.4 *10-3

*( 8+1) = 0.4 m

Final result:

Qs tot =6.062 KW

QL tot = 1.488 KW

SHF = 0.8

Qref = 81.56 KW

Qreheat = 4.587 KW

n = 16 tube /pass

hi =6675 W/m2 . k

ho =60 W/m2 .k

Uo = 50.72 W/m2 .k

L = 1.22 m

H = 0.61 m

W = 0.4 m

N PER ROW = 18

N PER pass = 16

Npass = 9

Chapter 5

Fan Coil Unit

Fan coil unit

A fan coil unit (FCU) is a simple device consisting of a heating or cooling coil and

fan. It is part of an HVAC system found in residential, commercial, and industrial

buildings. Typically a fan coil unit is not connected to ductwork, and is used to

control the temperature in the space where it is installed, or serve multiple spaces. It is

controlled either by a manual on/off switch or by thermostat.

Due to their simplicity, fan coil units are more economic to install than ducted or

central heating systems with air handling units. However, they can be noisy because

the fan is within the same space. Unit configurations are numerous including

horizontal (ceiling mounted) or vertical (floor mounted).

Design and operation

The coil receives hot or cold water from a central plant, and removes or adds heat

from the air through heat transfer. Fan coil units can contain their own internal

thermostat, or can be wired to operate with a remote thermostat.

Fan coil units circulate hot or cold water through a coil in order to condition a space.

The unit gets its hot or cold water from a central plant, or mechanical room containing

equipment for removing heat from the central building's closed-loop. The equipment

used can consist of machines used to remove heat such as a chiller or a cooling tower

and equipment for adding heat to the building's water such as a boiler or a commercial

water heater.

Fan coil units are divided into two types: Two (2) pipe fan coil units or Four (4) pipe

fan coil units. Two pipe fan coil units have one (1) supply and one (1) return pipe.

The supply pipe supplies either cold or hot water to the unit depending on the time of

year. Four (4) pipe fan coil units have two (2) supply pipes and two (2) return pipes.

This allows either hot or cold water to enter the unit at any given time.

Fan coil units may be connected to piping networks using various topology designs,

such as "direct return", "reverse return", or "series decoupled". See ASHRAE

Handbook "2008 Systems & Equipment", Chapter 12.

Examples of fan coil units:

IEC - International Environmental Corporation

Areas of use

Fan coil units are typically used in spaces where economic installations are preferred

such as unoccupied storage rooms, corridors, loading docks.

In high-rise buildings, fan coils may be stacked, located one above the other from

floor to floor and all interconnected by the same piping loop.

Fan coil units are an excellent delivery mechanism for hydronic chiller boiler systems

in large residential and light commercial applications. In these applications the fan

coil units are mounted in bathroom ceilings and can be used to provide unlimited

comfort zones - with the ability to turn off unused areas of the structure to save

energy.

Fan Coil Systems: Type FC

Barcol-Air manufacture low noise, high efficiency fan coil units for today's modern

buildings.

All control types can be fitted with in-house pipework, wiring etc. carried out in the factory.

Our comprehensive selection catalogue is available for Consultants use at design stage

complete with all sound power levels, pressures, volumes and outputs.

FAN COIL UNITS Design Recommendations

In order to make a proper fancoil unit selection, the whole air conditioning system

must be looked at because sizing a fancoil unit is not just matching the room load.

Other criteria which must be considered during selection are; the minimum room

load, fresh air requirements, with or without reheat, 2 or 4-pipe system, zone size,

flexibility and maximum noise level in the room, etc.

The cooling capacity which is supplied to the room is the sum of cooling energy

available in the primary air and the cooling capacity of the fancoil unit. The way the

primary air is supplied to the room determines a great part of the required fancoil

cooling capacity. The fancoil capacity is defined by the entering and leaving air

conditions (P = m x Cp x T). The leaving air condition is fixed (to offset the room

load) but the entering air condition is dependent upon the way primary air is supplied

The most common methods to supply primary air are shown in the figures below

System-1: This is the most energy

efficient system. Primary air is supplied

directly into the room and the

recirculation diffuser is ducted to the inlet

of the fancoil unit. For this case the

cooling energy available in the primary

air can be deducted from the room load.

An additional benefit with this

configuration is the fancoil unit can be

switched off in situations where primary

air only is sufficient to maintain the

required room conditions or when

ventilation only is required.

System-1

System-2: Primary air is supplied directly

into the room and recirculation air is

taken from the ceiling void. This is

basically the same as system-1, however

the cooling capacity must be higher

because the temperature in the ceiling

void is normally higher than in the room.

System-2

System-3: Primary air and recirculation

air are both ducted to the intake of the

fancoil unit. For this case, the entering air

for the heat exchanger (M) is lower in

temperature and less humid than at

system-1. The required cooling capacity

from the fancoil unit is equal to system-1,

however the air volume must be higher to

supply both the primary and fancoil

capacities of system-1.

System-3

System-4: Primary air is ducted to the

intake of the fancoil unit and recirculation

air is taken from the ceiling void. This is

basically the same as system-3, however

the cooling capacity must be higher

because the temperature in the ceiling

void is normally higher than in the room.

System-4

When primary air is supplied near the intake of the fancoil unit, part of the primary air

will be lost directly into the exhaust system wasting conditioned air energy.This is

wasting energy and should be avoided.

To demonstrate the difference in energy consumption, we have made an energy

analysis of the 4 systems. See the diagram below.

These systems usually have Fan Cooler Units which have a internal fan which can

draw the hot moist air (that may be present during postulated accidents) across

radiator type coils that are cooled by some external source, e.g. the Essential Service

Water System. The cooled exhaust from these units is usually routed through a Duct

to the top of containment where the air would be hotter. Separate Fans in the exhaust

duct, sometimes called Dome Recirculation Fans, direct the flow to the containment

dome.

Ventilation duct and Airlock

in Containment

Control Rod Drive Cooling Ventilatio above

Reactor

Fan Coil Unit (close up)

Fans (e.g. Standby Gas Treatment)

Filtration Systems

These systems usually consist of Fans that draw the air from the potentially

contaminated areas through PAC Filter Units. The PAC unit consists of 3 filter units

-

P - Particulate filter that removes large particles (sometimes called roughing

filters)

A - Absolute filter that removes over 99.5 % of particles

C - Charcoal filter that removes radioactive iodine (and to a limited extent

radioactive gases)

After passing through the PAC unit, the exhaust may be routed to an exhaust stack.

Such systems will normally be actuated by radiation monitoring sensors mounted in

the exhaust ducts. In addition, they will automatically start any time the emergency

core cooling systems start or containment isolation is required.

In conjunction with these "special" or recirculation fans starting, the normal

ventilation system equipment will shutdown with appropriate fans tripping and duct

dampers closing or opening so that the filtration system is the only one operating.

Shield Building Vent Filter and Fan Control Room Filter Unit

Pressure Differential Systems

Pressure differential systems depend on the flow rates of the various buildings' supply

and exhaust fans. Such systems also take into account certain sizes of openings in the

buildings. Because of this operators may be required to keep a log of all building

openings and their size. The supply and exhaust fans are sized to create pressure

differentials between the various buildings.

Turbine Building > Auxiliary or Reactor Building

Cooling Systems

Cooling systems usually consist of one of the following:

Unit Coolers, locally mounted by emergency equipment, that have internal

fans that draw local air across cooling coils and direct the cool exhaust

toward the motor, circuit breaker, or electrical supply panel of concern.

Air Conditioning Units as may be used for the Control Room or locally

mounted to cool electrical panels or equipment

Fans which direct air from outside or specially designated areas to cool

motors, diesels, or other equipment needing cooling. This air may be cooled

by passing across Radiators which are in turn cooled by other systems.

Fan Coil Units

The Fan coil unit Compact option simulates a 4 pipe fan coil unit with hot water

heating coil, chilled water cooling coil, and an outside air mixer. The fan coil units are

zone equipment units which are assembled from other components. Fan coils contain

an outdoor air mixer, a fan, a simple heating coil and a cooling coil. The fan coil unit

is connected to a hot water loop (demand side) through its hot water coil and to a

chilled water loop (demand side) through its cooling coil. The unit is controlled to

meet the zone (remaining) heating or cooling demand. If there is a heating demand,

the cooling coil is off and the hot water flow through the heating coil is throttled to

meet the demand. The hot water control node must be specified (same as the hot water

coil inlet node) as well as maximum and minimum possible hot water volumetric flow

rates. If there is a cooling demand from the zone, the hot water coil is off and the

chilled water flow through the cooling coil is throttled to meet the load.

You can model Fan coil unit systems with or without outside air. If you include

Mechanical ventilation with your Fan coil unit system then heating and cooling will

only operate when the Mechanical ventilation operation schedule is on.

If you do not want to include outside air in your system, you should uncheck the

Mechanical ventilation 'On' check box. In this case heating/cooling availability is

determined entirely from the heating/cooling operation schedules under the Heating

and Cooling headers.

Unlike the Unitary multizone and CAV and VAV Compact HVAC types, Fan coil

unit zone systems take all their data from the zone level.

Note 1: Fan coil supply fans run continuously at full speed whenever the availability

schedules are > 0 so fan coil outside air flow can be 'fully on' or 'fully off' but cannot

reduce to fractional values in between. You may therefore get higher outside air

delivery rates than with other systems if you are using Schedules and your

Mechanical ventilation operation schedule has fractional values.

Limitations

1. Fan coil units cannot be used in the same simulation as Unitary multizone

Compact HVAC type.

2. Outside air flow rate is either off, or on at a fixed flow rate depending on the

value of the Fan operation schedule..

3. Fan coil units cannot incorporate economisers and variable speed fans.

Technical EnergyPlus

EnergyPlus needs both the heating coil and cooling coil to be defined so even if

heating or cooling is not selected in the input, DesignBuilder will schedule the

appropriate coil to be off to mimic a 2-pipe system.

Main Component:

− Supply fan(s).

− Fan motor(s).

− Piping system.

− Control panel.

− Throwaway filter.

− Coil (cooling & heating ).

− Drain pan.

− Casing.

− Outside/return air damper.

Advantages and Disadvantages of fan coil unit:

1) Advantages:

1- Individual room temperature control allows each thermostat to be adjusted for a different

temperature at relatively low cost.

2- Separate heating and cooling sources in the primary air and secondary water give

occupants a choice of heating or cooling.

3- Less space is required for the distribution system when the air supply is reduced by using

secondary water for cooling and high-velocity primary air supply. The return air duct is

smaller and can sometimes be eliminated or combined with the return air system for other

areas, such as the interior spaces.

4- The central air-handling apparatus is smaller than that of an all-airsystem because less air

must be conditioned at that location.

5- Dehumidification, filtration, and humidification are performed in acentral location remote

from conditioned spaces.

6- Ventilation air is positively supplied and can accommodate constant recommended outside

air quantities.

7- Space can be heated without operating the air system, via the secondary water system.

Nighttimes fan operation is avoided in an unoccupied building. Emergency power for heating,

if required, is much lower than for most all-air systems.

2) Disadvantages :

1- For many buildings, in-room terminals are limited to perimeter space; separate systems are

required for other areas.

2- More controls are needed than for many all-air systems.

3- Primary-air supply usually is constant with no provision for shut-off.

This is a disadvantage in residential applications, where tenants or hotel room guests may

prefer to turn off the air conditioning, or where management may desire to do so to reduce

operating expense.

4- Low primary chilled-water temperature and/or deep chilled-water coils are needed to

control space humidity adequately. The system is not appropriate for spaces with high exhaust

requirements (e.g., research laboratories) unless supplementary ventilation air is provided.

5 -Central dehumidification eliminates condensation on the secondary water heat transfer

surface under maximum design latent load, but abnormal moisture sources (e.g., open

windows, cooking, or people congregating) can cause annoying or damaging condensation.

Therefore,

a condensate pan should be provided as for other systems.

6- Low primary-air temperatures require heavily insulated ducts. Energy consumption for

induction systems is higher than for most other systems because of the increased power

needed to deliver primary air against the pressure drop in the terminal units. Initial cost for a

four-pipe induction

System is greater than for most all-air systems.

Installation

In high-rise residential construction, typically each fan coil unit requires a rectangular

through-penetration in the concrete slab on top of which it sits. Usually, there are

either 2 or 4 copper pipes that go through the floor. The pipes are usually insulated

with refrigeration insulation, such as acrylonitrile butadiene/polyvinyl chloride

(AB/PVC) flexible foam (Rubatex or Armaflex brands) on all pipes or at least the

cool lines.

Unit Ventilator

A unit ventilator is a fan coil unit that is used mainly in classrooms, hotels, apartments

and condominium applications. A unit ventilator can be a wall mounted or ceiling

hung cabinet, and is designed to use a fan to blow air across a coil, thus conditioning

the space which it is serving.

Examples of unit ventilators:

FAN-COIL UNITS

PART 1 GENERAL

1.1 SUMMARY

A. Section Includes: Fan-coil units and accessories.

1.2 SUBMITTALS

A. General: Submit in accordance with Section 01330.

B. Product Data: Include specialties and accessories for each unit type and configuration.

C. Shop Drawings: Submit the following for each fan-coil unit type and configuration:

1. Plans, elevations, sections, and details.

2. Details of anchorages and attachments to structure and to supported equipment.

3. Power, signal, and control wiring diagrams. Differentiate between manufacturer-installed

and field-installed wiring.

4. Equipment schedules to include rated capacities; shipping, installed, and operating weights;

furnished specialties; and accessories.

D. Samples for Initial Selection: Manufacturer's color charts showing the full range of colors

available for

units with factory-applied color finishes.

E. Field Test Reports: Written reports of tests specified in Part 3 of this Section.

F. Maintenance Data: For fan-coil units to include in maintenance manuals specified in

Division 1.

Include the following:

1. Maintenance schedules and repair parts lists for motors, coils, integral controls, and

filters.

1.3 QUALITY ASSURANCE

A. Electrical Components, Devices, and Accessories: Listed and labeled as defined in NFPA

70 (1996),

Article 100, by a testing agency acceptable to authorities having jurisdiction, and marked for

intended use.

1.4 COORDINATION

A. Coordinate layout and installation of fan-coil units and suspension system

components with other construction that penetrates ceilings or is supported by them,

including light fixtures, HVAC equipment, fire-suppression-system components, and

partition assemblies.

1.5 EXTRA MATERIALS

A. Furnish extra materials described below that match products installed and that are

packaged with protective covering for storage and identified with labels describing contents.

1. Fan-Coil Unit Filters: Furnish spare filter for each filter installed.

2. Fan Belts: Furnish spare fan belt for each unit installed.

PART 2 PRODUCTS

2.1 MANUFACTURERS

A. Available Manufacturers: Subject to compliance with requirements, manufacturers

offering products that may be incorporated into the Work include, but are not limited to, the

following:

B. Manufacturers: Subject to compliance with requirements, provide products by one of the

following:

1. Airtherm Manufacturing Company.

2. Dunham-Bush, Inc.

3. Lennox Industries Inc.

4. Accepted Substitute in accordance with Section 01600.

2.2 CONFIGURATION

A. Vertical Units: An assembly for floor-to-floor mounting, including cabinet, filter, chassis,

coil, drain pan, fan, and motor in blow-through configuration with hydronic cooling coil and

hydronic heating coil.

B. Horizontal Units: An assembly including cabinet, filter, chassis, coil, drain pan, fan, and

motor in blowthrough configuration with hydronic cooling coil and hydronic heating coil.

2.3 MATERIALS

A. Chassis: Galvanized steel, with flanged edges.

B. Coil Section Insulation: 1 inch duct liner complying with ASTM C 1071 and attached with

adhesive complying with ASTM C 916.

1. Fire-Hazard Classification: Duct liner and adhesive shall have a maximum flame-spread

rating of 25 and smoke-developed rating of 50 when tested according to ASTM E 84.

C. Drain Pans: Galvanized steel, with connection for drain. Drain pan shall have a removable

plastic liner and be insulated with polystyrene or polyurethane insulation. Drain pan shall be

formed to slope from all directions to drain connection.

D. Cabinet: Galvanized steel, with removable panels.

1. Vertical Unit Front Panels: Removable, galvanized steel, with integral galvanized steel

discharge grilles and channel-formed edges and with insulation on back of panel.

2. Horizontal Unit Bottom Panels: Fastened to unit with cam fasteners and hinge and attached

with safety chain; with integral stamped grilles.

E. Cabinet Finish: Bonderize, phosphatize, and flow-coat with baked-on primer with

manufacturer's standard paint, in color selected by Architect, applied to factory-assembled

and -tested fan-coil unit before shipping

.

2.4 WATER COILS

A. Primary Coil: Copper tube, with mechanically bonded aluminum fins spaced no closer

than 0.1 inch

and with manual air vent. Coils shall be rated for a minimum working pressure of 300 psig

and a maximum entering water temperature of 275 deg F.

B. Auxiliary Heating Coil: One row, copper tube, with mechanically bonded aluminum

fins spaced no closer than 0.1 inch and with manual air vent. Coils shall be rated for a

minimum working pressure of 200 psig and a maximum entering water temperature

of 220 deg F.

2.5 FAN

A. Centrifugal, with forward-curved, double-width wheels and fan scrolls made of

galvanized steel or thermoplastic material; directly connected to or V-belt driven

from motor.

2.6 FAN MOTORS

A. Motors for Direct-Drive Units: Permanent-split capacitor, multispeed motor with integral

thermaloverload

protection and resilient mounts.

B. Motors for Belt-Drive Units: Open dripproof with hinged mount and adjustable motor

pulley.

C. Wiring Terminations: Match conductor materials and sizes of connecting power circuit.

Connect motor to chassis wiring with plug connection.

2.7 ACCESSORIES

A. Aluminum wall boxes with integral eliminators and insect screen.

B. Steel sub base , height as indicated.

C. Plastic motor-oiler tubes extending to beneath top of discharge grille.

D. Steel recessing flanges for recessing fan-coil units into ceiling or wall.

E. Filters: 1 inch thick, throwaway filters in fiberboard frames.

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10-01053.00/01-15-03/Revised: 10-27-03 15763-3 FAN-COIL UNITS

F. Dampers: Steel damper blades with polyurethane stop across entire blade length and

having factory mounted electric operators for 25 percent open cycle.

G. Disconnect Switch: Provide disconnect switch.

2.8 CONTROL SYSTEMS

A. Four-Pipe, Valve Cycle: Wall-mounted thermostat, with dead band and manual fan-

speed switch, cycles valves with DDC electronic actuator.

2.9 SOURCE QUALITY CONTROL

A. Test and rate units according to ARI 440.

B. Test unit coils according to ASHRAE 33.

PART 3 EXECUTION

3.1 EXAMINATION

A. Examine areas to receive fan-coil units for compliance with requirements for installation

tolerances and other conditions affecting performance.

B. Examine roughing-in for piping and electrical connections to verify actual locations before

fan-coil unit installation.

C. Proceed with installation only after unsatisfactory conditions have been corrected.

3.2 INSTALLATION

A. Install fan-coil units level and plumb.

B. Install fan-coil units to comply with NFPA 90A.

C. Suspend fan-coil units from structure with rubber-in-shear vibration isolators (rubber

hangers).

Vibration isolators are specified in Section 15071 - Mechanical Vibration Controls and

Seismic Restraints.

C. Install wall-mounting thermostats and switch controls in electrical outlet boxes at

heights to match lighting controls.

3.3 CONNECTIONS

A. Piping installation requirements are specified in other Division 15 Sections. Drawings

indicate general arrangement of piping, fittings, and specialties.

B. Unless otherwise indicated, install shutoff valve and union or flange at each connection.

C. Install piping adjacent to machine to allow service and maintenance.

D. Ground equipment.

E. Tighten electrical connectors and terminals according to manufacturer's published torque-

tightening values. If manufacturer's torque values are not indicated, use those specified in UL

486A and UL 486B.

3.4 FIELD QUALITY CONTROL

A. Testing: Perform the following field quality-control testing and report results in writing:

1. After electrical circuitry has been energized, start units to confirm proper motor rotation

and unit operation.

2. Test and adjust controls and safeties.

B. Repair or replace malfunctioning units. Retest as specified above after repairs or

replacements are made

.

3.5 CLEANING

A. After installing units, inspect unit cabinet for damage to finish. Remove paint splatters and

other spots, dirt, and debris. Repair damaged finish to match original finish.

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10-01053.00/01-15-03/Revised: 10-27-03 15763-4 FAN-COIL UNITS

B. After installing units, clean fan-coil units internally according to manufacturer's written

instructions.

C. Install new filters in each fan-coil unit within two weeks after Substantial Completion.

3.6 DEMONSTRATION

A. Engage a factory-authorized service representative to train Owner's maintenance personnel

to adjust, operate, and maintain fan-coil units.

1. Train Owner's maintenance personnel on procedures and schedules for starting and

stopping, troubleshooting, servicing, and maintaining equipment.

2. Review data in maintenance manuals. Refer to Section 01770 - Closeout Procedures.

3. Review data in maintenance manuals.

4. Schedule training with Owner, through Architect, with at least seven days' advance notice.

1 Introduction

This document presents an implementation example for a typical 3-speed fan coil unit using

Lonix technologies. The controls are done using Lonix Modules, and system design and

configuration utilizes the Lonix Project Creation Tool (PCT).

2 FCU example

This chapter introduces the control diagram and the functional description of a typical 3-speed

fan coil unit.

2.1 CONTROL DIAGRAM

This example diagram shows a typical Fan Coil Unit. Different speeds can be achieved by

controlling the supply to the electrical coil by using relays. The fan speed and cooling

actuator is controlled according to a temperature set point and a local temperature

measurement.

Figure . Control diagram of a typical 3-speed fan coil unit

2.2 FUNCTIONAL DESCRIPTION

Fan coil units are used for attaining a desired temperature in a small area e.g. a small room.

FCUs are supplied with pre-cooled air coming from fresh air handling units. To further cool

the supplied air fan coil units usually use chilled water coming either from chillers or a heat

exchanger. The important mechanical parts involved in the operation of FCUs are the

following:

Control valve (modulating type)

Fan (usually three speeds)

Filters for the purification of the supplied air

Strainers for the filtration of chilled water

Cooling coil

The desired temperature in the serving area is achieved by the simultaneous control of the

control valve and the fan. The control valve regulates the flow of cold water inside the

cooling coil. The fan blows the supplied air through the cooling coil further decreasing its

temperature before it comes to the serving area. When further cooling is not required the

control valve is closed preventing the cold water from flowing through the cooling coil. The

fan is often designed in such a way that it operates in more than one speed.

The temperature of the serving area is controlled according to a set point and a temperature

measurement. The controller regulates both the fan speed and the control valve according to

the deviation of the current room temperature and the set point.

Figure. Fan speed and valve position

The fan can be operated either with manually or automatically. In manual mode the fan speed can

be set to operate always in one of the three speeds. In automatic mode the fan speed is determined

by the valve position, as can be seen in figure.

212 Design of Fan cooling unit

Load estimation

Person, s

Qs =84, QL = 48 (Egypt code)

For 3 persons

Qs = 84*3 =252 Watt

QL = 48*3 = 144Watt

Lighting

Qs = 40 W/m2

= 40 * 20 = 800 Watt

Appliance Q =78 Watt

Qs tot =1130 Watt , QL tot =144 watt

SHF = 0.89

For 3 persons V•fresh air = min no of air change * room volume

=2*3*4*5 = 120 m3/hr

V• tot = 15*60 = 900 m

3 /hr

m•o / m

•tot = 0.133

m•o= 120 /(0.925*3600) = 0.036 kg/sec

m•tot = 0.27 kg/s

Ts = TR – 𝑇𝑅−𝑇𝑎𝑑𝑝 ,𝑓𝑐𝑢

1−𝐵𝐹𝑓𝑐𝑢

= 21.97 – 21.97−11

1−0.1 = 9.78

Fan coil unit

Q ref = (m•tot –m

•o) *{( ho – hi) - 4.187(ψ0- ψi)Tadp fco}

= ( 0.27 – 0.036 ) {( 43.04 – 32.73) – 4.18 *(0.00829 –

0.00818)*10.88 }

= 3.411 KW

= m•w Cw ΔTw

= m•w *4.1944 *(12 – 6)

m•w = 0.136 Kg /S

=𝜋

4 Di

2 ρw Vw n tube /pass

=𝜋

4 (0.008523)

2 1000* 1.5 * n tube /pass

n tube /pass = 1.6

= 2 tube /pass

To get hi

Nu i =0.023* ( Re 0.8

) * Prw

(0.4)

Re = ρ V Dh / µ

= 1000*2*5.523*10-3

/(1343.2*10-6

) = =12690.59

Nu i =0.023*(12690.59)0.8

* 9.68 0.4

hi = 7509 W /m2k

To get ho , Uo

( m•tot – m

•o ) = ρa V Afr

(0.27 – 0.036) = 1.1719 * 2.5 * Afr

A fr = 0.08m2

G = 𝑚 •𝑎

𝜎 ∗𝐴𝑓𝑟 =

0.234

0.08 ∗0.534 = 5.478

Re = 𝐺∗ 𝐷ℎ

µ =

5.478∗ 3.6286∗10−3

183.475∗10−7

= 1083.4

From fig (100) kays & London

JH = 0.01 , f =0.028

ho = 𝐽𝐻 𝐺 𝐶𝑃

Pr 2/3 = 0.01∗5.478∗ 1007

0.7076 2/3 = 69.5 W/ Kg . K

ή o = 1-{ (A f /A)* (1- ή f)}

=1-{0.839( 1-0.95) }

= 0.96

(1/U o) =( 1/(hi(Ai/A o))) + Di ln (Do/Di)/(2kAi/A o)+ 1/(ho*ή)

A o/ Ai =12.27 air 21.97

U o = 59.47 W/m2.k 12.1

Q ref = U o So θ LMTD water 12

3.411*103 = 59.47 *So*7.9 6 { θ LMTD =7.9 }

So = 7.26 m2

Si = 0.592 m2

= π di L N tot

= π * 0.008523* 1 * N tot

N tot =24

N tot = ( Nt /row +1 ) St

24 = ( Nt /row +1 ) 25.4*10-3

Nt /row = 6

N rows = 4 rows

From catalogue:

L = 1 m

H = 0.177 m

W = 0.11 m

Ntot = Nt/pass * N pass

24 = 2 * N pass

N pass = 12 pass

Chapter 6

HAVC

CHAPTER EIGHT (HVAC)

Heating, Ventilating and Air Conditioning (HVAC)

1. Introduction

It is an initialism or acronym that stands for "heating, ventilating, and

airconditioning".

HVAC is sometimes referred to as climate control and is particularly important in the

design of medium to large industrial and office buildings such as skyscrapers and in

marine environments such as aquariums, where humidity and temperature must all be

closely regulated whilst maintaining safe and healthy conditions within. In certain

regions (e.g., UK) the term "Building Services" is also used, but may also include

plumbing and electrical systems. Refrigeration is sometimes added to the field's

abbreviation as HVAC&R or HVACR, or ventilating is dropped as HACR (such as

the designation of HACR-rated circuit breakers).

Heating, ventilating, and air conditioning is based on the basic principles of

thermodynamics, fluid mechanics, and heat transfer, and two inventions and

discoveries made by Michael Faraday, Willis Carrier, Reuben Trane, James Joule,

William Rankine, Sadi Carnot, and many others. The invention of the components of

HVAC systems goes hand-in-hand with the industrial revolution, and new methods of

modernization, higher efficiency, and system control are constantly introduced by

companies and inventors all over the world.

Fig (8.1) Outlet vent

HVAC systems use ventilation air ducts installed throughout a building that supply

conditioned

air to a room through rectangular or round outlet vents, called "diffusers"; and ducts

that remove air through return-air "grilles"

Fig (8.2) Fire-resistance rated mechanical shaft with HVAC sheet metal ducting

Fire-resistance rated mechanical shaft with HVAC sheet metal ducting and copper

piping, as well as "HOW" (Head-Of-Wall) joint between top of concrete block wall

and underside of concrete slab, fire stopped with ceramic fibre-based fire stop

caulking on top of rock wool. The three functions of heating, ventilating, and air-

conditioning are closely interrelated. All seek to provide

I. Thermal comfort

II. acceptable indoor air quality

III. Reasonable installation, operation, and maintenance costs

HVAC systems can provide ventilation, reduce air infiltration, and maintain pressure

relationships between spaces. How air is delivered to, and removed from spaces is

known as Room Air Distribution

In modern buildings the design, installation, and control systems of these functions

are integrated into one or more HVAC systems. For very small buildings, contractors

normally "size" and select HVAC systems and equipment, For larger buildings where

required by law, "building services" designers and engineers, such as mechanical,

architectural, or building services engineers analyze, design, and specify the HVAC

systems, and specialty mechanical contractors build and commission them. In all

buildings, building permits and code-compliance inspections of the installations are

the norm.

The HVAC industry is a worldwide enterprise, with career opportunities including

operation and maintenance, system design and construction, equipment manufacturing

and sales, and in education and research. The HVAC industry had been historically

regulated by the manufacturers of HVAC equipment, but Regulating and Standards

organizations such as ASHRAE, SMACNA, ACCA, Uniform Mechanical Code,

International Mechanical Code, and AMCA have been established to support the

industry and encourage high standards and achievement.

2. Heating:

Heating systems may be classified as central or local. Central heating is often used in

cold climates to heat private houses and public buildings. Such a system contains a

boiler, furnace, or heat pump to heat water, steam, or air, all in a central location such

as a furnace room in a home or a mechanical room in a large building. The system

also contains either ductwork, for forced air systems, or piping to distribute a heated

fluid and radiators to transfer this heat to the air. The term radiator in this context is

misleading since most heat transfer from the heat exchanger is by convection, not

radiation. The radiators may be mounted on walls or buried in the floor to give under-

floor heat.

In boiler fed or radiant heating systems, all but the simplest systems have a pump to

circulate the water and ensure an equal supply of heat to all the radiators. The heated

water can also be fed through another (secondary) heat exchanger inside a storage

cylinder to provide hot running water.

Forced air systems send heated air through ductwork. During warm weather the same

ductwork can be used for air conditioning. The forced air can also be filtered or put

through air cleaners.

Heating can also be provided from electric, or resistance heating using a filament that

becomes hot when electricity is caused to pass through it. This type of heat can be

found in electric baseboard heaters, portable electric heaters, and as backup or

supplemental heating for heat pump (or reverse heating) system.

The heating elements (radiators or vents) should be located in the coldest part of the

room, typically next to the windows to minimize condensation and offset the

convective air current formed in the room due to the air next to the window becoming

negatively buoyant due to the cold glass. Devices that direct vents away from

windows to prevent "wasted" heat defeat this design intent. Cold air drafts can

contribute significantly to subjectively feeling colder than the average room

temperature. Therefore, it is important to control the air leaks from outside in addition

to proper design of the heating system.

The invention of central heating is often credited to the ancient Romans, who installed

a system of air ducts called "hypocaust" in the walls and floors of public baths and

private villas.

2. Ventilating:

Ventilating is the process of "changing" or replacing air in any space to control

temperature or remove moisture, odors, smoke, heat, dust and airborne bacteria.

Ventilation includes both the exchange of air to the outside as well as circulation of

air within the building. It is one of the most important factors for maintaining

acceptable indoor air quality in buildings. Methods for ventilating a building may be

divided into mechanical/forced and natural types. Ventilation is used to remove

unpleasant smells and excessive moisture, introduce outside air, and to keep interior

building air circulating, to prevent stagnation of the interior air.

Fig (8.3) an air handling unit is used for the heating and cooling of air in a

central location

2.1 Mechanical or forced ventilation:

"Mechanical" or "forced" ventilation is used to control indoor air quality. Excess

humidity, odors, and contaminants can often be controlled via dilution or replacement

with outside air. However, in humid climates much energy is required to remove

excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhaust to control odors and

sometimes humidity. Factors in the design of such systems include the flow rate

(which is a function of the fan speed and exhaust vent size) and noise level. If the

ducting for the fans traverse unheated space, the ducting should be insulated as well to

prevent condensation on the ducting, direct drive fans are available for many

applications, and can reduce maintenance needs.

3.2 Natural ventilation:

Natural ventilation is the ventilation of a building with outside air without the use of a

fan or other mechanical system. It can be achieved with operable windows when the

spaces to ventilate are small and the architecture permits. In more complex systems

warm air in the building can be allowed to rise and flow out upper openings to the

outside (stack effect) thus forcing cool outside air to be drawn into the building

naturally through openings in the lower areas. These systems use very little energy but

care must be taken to ensure the occupants' comfort. In warm or humid months, in

many climates, maintaining thermal comfort via solely natural ventilation may not be

possible so conventional air conditioning systems are used as backups. Air-side

economizers perform the same function as natural ventilation, but use mechanical

systems' fans, ducts, dampers, and control systems to introduce and distribute cool

outdoor air when appropriate.

3. Air-conditioning:

Air Conditioning and refrigeration are provided through the removal of heat. The

definition of cold is the absence of heat and all air conditioning systems work on this

basic principle. Heat can be removed through the process of radiation, convection,

and conduction using mediums such as water, air, ice, and chemicals referred to as

refrigerants. In order to remove heat from something, you simply need to provide a

medium that is colder -- this is how all air conditioning and refrigeration systems

work.

An air conditioning system, or a standalone air conditioner, provides cooling,

ventilation, and humidity control for all or part of a house or building. The Freon or

other refrigerant provides cooling through a process called the refrigeration cycle. The

refrigeration cycle consists of four essential elements to create a cooling effect. A

compressor provides compression for the system. This compression causes the

cooling vapor to heat up. The compressed vapor is then cooled by heat exchange with

the outside air, so that the vapor condenses to a fluid, in the condenser. The fluid is

then pumped to the inside of the building, where it enters an evaporator. In this

evaporator, small spray nozzles spray the cooling fluid into a chamber, where the

pressure drops and the fluid evaporates. Since the evaporation absorbs heat from the

surroundings, the surroundings cool off, and thus the evaporator absorbs or adds heat

to the system. The vapor is then returned to the compressor. A metering device acts as

a restriction in the system at the evaporator to ensure that the heat being absorbed by

the system is absorbed at the proper rate.

Central, 'all-air' air conditioning systems are often installed in modern residences,

offices, and public buildings, but are difficult to retrofit (install in a building that was

not designed to receiveit) because of the bulky air ducts required. A duct system must

be carefully maintained to prevent the growth of pathogenic bacteria in the ducts. An

alternative to large ducts to carry the needed air to heat or cool an area is the use of

remote fan coils or split systems. These systems, although most often seen in

residential applications, are gaining popularity in small commercial buildings. The

coil is connected to a remote condenser unit using piping instead of ducts.

Dehumidification in an air conditioning system is provided by the evaporator. Since

the evaporator operates at a temperature below dew point, moisture is collected at the

evaporator. This moisture is collected at the bottom of the evaporator in a condensate

pan and removed by piping it to a central drain or onto the ground outside. A

dehumidifier is an air-conditioner-like device that controls the humidity of a room or

building. They are often employed in basements which have a higher relative

humidity because of their lower temperature (and propensity for damp floors and

walls). In food retailing establishments, large open chiller cabinets are highly

effective at dehumidifying the internal air. Conversely, a humidifier increases the

humidity of a building.

Air-conditioned buildings often have sealed windows, because open windows would

disrupt the attempts of the HVAC system to maintain constant indoor air conditions.

5. Energy efficiency:

For the last 20-30 years, manufacturers of HVAC equipment have been making an

effort to make the systems they manufacture more efficient. This was originally

driven by rising energy costs, and has more recently been driven by increased

awareness over environmental issues. There are several methods for making HVAC

systems more efficient.

5.1 Heating energy

Water heating is more efficient for heating buildings and was the standard many years

ago.

Today forced air systems can double for air conditioning and are more popular. The

most efficient central heating method is geothermal heating.

Energy efficiency can be improved even more in central heating systems by

introducing zoned heating. This allows a more granular application of heat, similar to

non-central heating systems.

Zones are controlled by multiple thermostats. In water heating systems the

thermostats control zone valves, and in forced air systems they control zone dampers

inside the vents which selectively block the flow of air.

5.2 Ventilation Energy recovery:

Energy recovery systems sometimes utilize heat recovery ventilation or energy

recovery ventilation systems that employ heat exchangers or enthalpy wheels to

recover sensible or latent heat from exhausted air. This is done by transfer of energy

to the incoming outside fresh air.

5.3 Air conditioning energy:

The performance of vapor compression refrigeration cycles is limited by

thermodynamics. These AC and heat pump devices move heat rather than convert it

from one form to another, so thermal efficiencies do not appropriately describe the

performance of these devices. The Coefficient-of- Performance (COP) measures

performance, but this dimensionless measure has not been adopted, but rather the

Energy Efficiency Ratio (EER). To more accurately describe the performance of air

conditioning equipment over a typical cooling season a modified version of the EER

is used, and is the Seasonal Energy Efficiency Ratio (SEER). The SEER article

describes it further, and presents some economic comparisons using this useful

performance measure.

6. Major terms of HVAC:-

6.1 Air Change per Hour (ACH):

The number of times per hour that the volume of a specific room or building is

supplied or removed from that space by mechanical and natural ventilation

6.2 Air handler, or air handling unit (AHU):

Central unit consisting of a blower, heating and cooling elements, filter racks or

chamber, dampers, humidifier, and other central equipment in direct contact with the

airflow. This does not include the ductwork through the building

.

6.3 Chiller :

A device that removes heat from a liquid via vapor-compression or absorption

refrigeration cycle, This cooled liquid flows through pipes in a building and passes

through coils in air handlers, fan-coil units, or other systems, cooling and usually

dehumidifying the air in the

building. Chillers are of two types; air-cooled or water-cooled. Air-cooled chillers are

usually outside and consist of condenser coils cooled by fan-driven air. Water-cooled

chillers are usually inside a building, and heat from these chillers is carried by

recirculating water to outdoor cooling towers.

6.4 Coil:

Equipment that performs heat transfer when mounted inside an Air Handling unit or

ductwork

It is heated or cooled by electrical means or by circulating liquid or steam within it.

Air flowing across it is heated or cooled.

6.5 Condenser :

A component in the basic refrigeration cycle that ejects or removes heat from the

system, the condenser is the hot side of an air conditioner or heat pump. Condensers

are heat exchangers, and can transfer heat to air or to an intermediate fluid to carry

heat to a distant sink, such as ground, a body of water, or air (as with cooling towers).

6.6 Constant air volume (CAV):

A system designed to provide a constant air volume per unit time. This term is applied

to HVAC systems that have variable supply-air temperature but constant air flow

rates. Most residential forced-air systems are small CAV systems with on/off control.

6.7 Controller

A device that controls the operation of part or all of a system, It may simply turn a

device on and off, or it may more subtly modulate burners, compressors, pumps,

valves, fans, dampers, and the like. Most controllers are automatic but have user input

such as temperature set points, e.g. a thermostat. Controls may be analog, or digital, or

pneumatic, or a combination of these.

6.8 Damper :

A plate or gate placed in a duct to control air flow by introducing a constriction in the

duct.

6.9 Evaporator:

A component in the basic refrigeration cycle that absorbs or adds heat to the system,

Evaporators can be used to absorb heat from air or from a liquid. The evaporator is

the cold side of an air conditioner or heat pump.

6.10 Fan coil unit (FCU):

A small terminal unit that is often composed of only a blower and a heating and/or

cooling coil (heat exchanger), as is often used in hotels, condominiums, or

apartments. One type of fan coil unit is a unit ventilator.

6.11 Fresh air intake (FAI):

An opening through which outside air is drawn into the building, this may be to

replace air in the building that has been exhausted by the ventilation system, or to

provide fresh air for combustion of fuel.

6.12 Furnace:

A component of an HVAC system that adds heat to air or an intermediate fluid by

burning fuel (natural gas, oil, propane, butane, or other flammable substances) in a

heat exchanger.

6.13 Grille:

A facing across a duct opening, usually rectangular is shape, containing multiple

parallel slots through which air may be delivered or withdrawn from a ventilated

space.

6.14 Heat load, heat loss, or heat gain:

Terms for the amount of heating (heat loss) or cooling (heat gain) needed to maintain

desired temperature and humidity in controlled air. Regardless of how well-insulated

and sealed a building is, buildings gain heat from warm air or sunlight or lose heat to

cold air and by radiation. Engineers use a heat load calculation to determine the

HVAC needs of the space being cooled or heated.

6.15 Louvers:

Blades, sometimes adjustable, placed in ducts or duct entries to control the volume of

air flow. The term may also refer to blades in a rectangular frame placed in doors or

walls to permit the movement of air.

6.16 Makeup air unit (MAU):

An air handler that conditions 100% outside air, MAUs are typically used in industrial

or commercial settings, or in "once-through" (blower sections that only blow air one-

way into the building), "low flow" (air handling systems that blow air at a low flow

rate), or "primary secondary" (air handling systems that have an air handler or rooftop

unit connected to an add-on makeup unit or hood) commercial HVAC systems.

6.17 Packaged terminal air conditioner (PTAC):

An air conditioner and heater combined into a single, electrically-powered unit,

typically installed through a wall and often found in hotels.

6.18 Packaged unit or rooftop unit (RTU):

An air-handling unit, defined as either "recirculating" or "once-through" design, made

specifically for outdoor installation, they most often include, internally, their own

heating and cooling devices. RTUs are very common in some regions, particularly in

single-story

Commercial buildings.

6.19 Thermal zone

A single or group of neighboring indoor spaces that the HVAC designer expects will

have similar thermal loads. Building codes may require zoning to save energy in

commercial buildings. Zones are defined in the building to reduce the number of

HVAC subsystems, and thus initial cost. For example, for perimeter offices, rather

than one zone for each office, all offices facing west can be combined into one zone.

Small residences typically have only one conditioned thermal zone, plus

unconditioned spaces such as unconditioned garages, attics, and crawlspaces, and

unconditioned basements.

6.20 Variable air volume (VAV) system:

An HVAC system that has a stable supply-air temperature, and varies the air flow rate

to meet the temperature requirements, Compared to CAV systems, these systems

waste less energy through unnecessarily-high fan speeds. Most new commercial

buildings have VAV systems.

6.21 Other HVAC equipment:

I. Air conditioner

II. Air filter

III. Boiler

IV. Cooling tower

V. Chilled beam

VI. Diffuser

VII. Duct

VIII. Economizer

IX. Evaporative cooler

X. Fan (mechanical)

XI. Heat exchanger, including 'coils'

XII. Humidifier / Dehumidifier

XIII. HVAC control system

XIV. Piping

XV. Pump

XVI. unit ventilator

XVII. Valve

XVIII. Variable-frequency drive, for fine control of pumps

Chapter 7

AIR-CONDITIONING

SYSTEMS,

DEVELOPMENTS IN

HOSPITALS

CHAPTER NINE (A/C Systems, Developments In Hospitals)

AIR-CONDITIONING SYSTEMS, DEVELOPMENTS IN HOSPITALS

(COMFORT, AIR QUALITY, AND ENERGY UTILIZATION)

1. Abstract

The balance between thermal comfort and air quality in healthcare facilities to

optimize the Indoor Air Quality (IAQ) is the main aim of this chapter. The present

chapter will present this Balance from the viewpoint of the air conditioning design. It

was found that the design of the A HVAC airside system plays an important role for

achieving the optimum air quality beside the optimum comfort level. This chapter

highlights the importance of the proper airside design on the IAQ. The present chapter

introduces some recommendations for airside designs to facilitate the development of

optimum HVAC systems. This chapter also stresses on the Factors that improve the

thermal comfort and air quality for the already existed systems (for maintenance

procedure).

2. Introduction

To design an optimum HVAC airside system that provides comfort and air quality in

the air-conditioned spaces with efficient energy consumption is a great challenge. The

present chapter defines the current status, future requirements, and expectations.

Based on this analysis and the vast progress of computers and associated software, the

artificial intelligent technique will be a competitor candidate to the experimental and

numerical techniques. Finally, the researches that relate between the different designs

of the HVAC systems and energy consumption should concern with the optimization

of airside design as the expected target to enhance the indoor environment.

Health considerations and hygiene requirements necessitate the following:

i. To restrict air movement in and between the various departments

ii. To use appropriate ventilation and filtration to dilute and reduce contamination in

the form of odor, air-borne micro organisms, viruses and, hazardous chemicals.

iii. To regulate different temperature and humidity requirements for various medical

areas.

iv. To maintain accurate control of environmental conditions.

3. Environmental Control

3.1 Temperature & Relative Humidity Control

Codes and guidelines specify temperature range criteria in some hospital areas as a

measure for infection control as well as comfort. Local temperature distributions

greatly affect occupant comfort and perception of the environment. Temperature

should be controlled by change of supply temperature without any airflow control; the

temperature difference between warm and cool regions should be minimized to

decrease airflow drift. Efficient air distribution is needed to create homogenous

domain without large difference in the temperature distribution. The laminar airflow

concept developed for industrial clean room use has attracted the interest of some

medical authorities. There are advocates of both vertical and horizontal laminar

airflow systems. For high-contaminated areas, the local velocity should be greater

than or at least equal to 0.2 m/s. For patient rooms 0.1 m/s is sufficient in the occupied

area. The unidirectional laminar airflow pattern is commonly attained at a velocity of

0.45 ± 0.10 m/s.

3.2 Air Change and Filtration

Three basic filtration stages are usually incorporated namely: Primary filter, second

stage filter (the high efficiency particulate bag filter) and a third stage filter which is

the high efficiency particulate filter located at the air supply outlets. Air Change per

Hour (ACH) plays An important role to provide a free contamination

place. The patient rooms are served by (2 ACH – 6 ACH) in usual. Some critical

rooms could be served by value up to 12 ACH. The critical rooms, such as the

surgical operating theatres, are supplied by (15 ACH – 25 ACH) in usual. There are

some guidelines, which advise the value of 60 ACH for the critical areas

Fig (9.1) Airflow Movement in Rooms

The negative pressure is obtained by supplying less air to the area than is exhausted

from it.

This induces a flow of air into the area around the perimeters of doors and prevents an

outward airflow. The operating room offers an example of an opposite condition. This

room, which requires air that is free of contamination, must be positively pressurized

relative to adjoining rooms or corridors to prevent any airflow from these relatively

highly contaminated areas. In general, outlets supplying air to sensitive ultraclean

areas and highly contaminated areas should be located on the ceiling or on sidewalls

closing to ceiling, figure (9.1), with perimeter or several exhaust inlets near the floor.

The bottoms of return or exhaust openings should be at least 0.075 m above the floor.

4. Design Specification

• Hospital Facilities

As, perfect air conditioning system is helpful in the prevention and treatment of

disease, the construction of air conditioning system for health facilities presents many

precautions not encountered in the usual comfort air conditioning systems.

i) Critical Care and Isolation Rooms

In the isolation rooms for infectious patients, the patient bed should be located close

to the extract ports. The infectious isolation rooms should be maintained at negative

pressure. The immunosuppressed patient‟s bed should be located in the side of

supplied air, or close to the supply outlets, figure (9.2). Previous predictions of local

velocity profiles, air temperatures, relative humidity distributions were reported by

Kameel and Khalil,(2002,2003), using a finite difference computer package , Khalil

(1994,2000), that solves the governing equations of mass, three momentum, energy,

relative humidity and age equations in three dimensional configuration of rooms as

indicated by (Khalil ,2004).

ii) Protective Isolation Units

Immunosuppressed patients are highly susceptible to diseases. An air distribution of

15 air changes per hour supplied through a nonaspirating diffuser is recommended.

When the patient is immunosuppressed but not contagious, a positive pressure should

be maintained between the patient room and adjacent area. Figure (9.3) shows the

velocity, air temperatures and relative humidity contours in an immunosuppressed

patient room

.

Fig (9.2) Airflow Configurations for Critical Areas

Fig (9.3.a) Predicted Velocity Contours immunosuppressed patient room

Fig (9.3.b) Air Temperature Contours In immunosuppressed patient room

Fig (9.3.c) Relative Humidity Contours immunosuppressed patient room

iii) Surgical Operating Rooms

Operating room air distribution systems that deliver air from the ceiling, with a

downward movement to several exhaust inlets located on opposite walls, is probably

the most effective air movement pattern, figure (9.4).

Fig (9.4.a) Air Flow Distributions in Operating Theatre Open Heart Surgery

Fig (9.4.b) Temperature Distributions in Operating Theatre Open Heart Surgery

Based on the above analyses, the following design conditions are recommended for

operating, catheterization, cystoscopic, and fracture rooms, figure (9.5):

1. There should be a variable range temperature capability of 20 °C to 24°C.

2. Relative humidity should be kept between 50% and 60%.

3. Positive air pressure should be maintained by supplying about 15% excess air.

4. Differential pressure indicating device should be installed.

5. Humidity indicator and thermometers should be located for easy observation.

6. Filter efficiencies should be in accordance with codes_

7. Entire installation should conform to NFPA Standard 99, Health Care facilities.

8. All air should be supplied at the ceiling and exhausted from at least two locations

near the floor.

9. Control centers that monitor and permit adjustment of temperature, humidity, and

air pressure may be located at the surgical supervisor‟s desk.

Fig (9.5) Different Configurations of Surgical Operating Theatres

The surgical operating suite should be located in complete floor in the hospital, to be

separated from the other suites and patient rooms. The above design features were

strongly supported by the predicted air flow pattern, temperature contours and relative

humidity as obtained in different operating theatres as discussed by Kameel and

Khalil (2003) and Khalil (2004).

5. CONCLUSIONS AND RECOMMENDATIONS

The air is not just a medium but it can be regarded as a guard in the critical health

applications. The proper direction of the airflow increases the possibilities of

successful pollutant scavenging from healthcare applications. The numerical tool,

used here, was found to be so effective to predict the airflow pattern in the healthcare

facilities at reasonable costs and acceptable accuracy. Good architectural design

allows the HVAC system designers to properly locate the supply outlets and

extraction ports in the optimum locations.

Chapter 8

Building Management

Systems

CHAPTER TEN (Building Management Systems)

Building Management Systems

1. Definition

Building Management System (BMS): is a high technology system installed on

buildings that controls and monitors the building‟s mechanical and electrical

equipment

such as:

i. Building automation (cooling/heating control, ventilation control, pumps, etc.)

ii. Lighting and curtain control

iii. Consumption measurements of water, electricity and cooling (heating) energy

iv. Emergency lighting

v. Access control system (time attendance and info options)

vi. Video monitoring system

vii. Fire alarms

viii. Burglar alarms

ix. Leakage/moisture alarms

Fig (10.1) overview of BMS

• BMS consists on software and hardware.

Software program, usually configured in a hierarchical manner, canbe:

i. Proprietary using such protocols as C-bus, Profibus, etc.

ii. That integrates using Internet protocols and open standards like SOAP, & XML,

BacNet, Lon, Modbus.

Why do we need a Building Management System?

All Buildings have some form of mechanical and electrical services in order to

provide the facilities necessary for maintaining a comfortable working environment.

These services have to be controlled by some means to ensure, for example, that there

is adequate hot water for sinks, that the hot water in the radiators is sufficient to keep

an occupied space warm, that heating with ventilation and possibly cooling is

provided to ensure comfort conditions wherever, irrespective of the number of

occupants or individual preferences. Basic controls take the form of manual

switching, time clocks or temperature switches that provide the on and off signals for

enabling pumps, fans or valves etc. The purpose of a Building Management System

(BMS) is to automate and take control of these operations in the most efficient way

possible for the occupiers/business, within the constraints of the installed plant.

What is a Building Management System and how does it work?

The BMS is a “stand alone” computer system that can calculate the pre-set

requirements of the building and control the connected plant to meet those needs.

Its inputs, such as temperature sensors and outputs, such as on/off signals are

connected into outstations around the building.

Programs within these outstations use this information to decide the necessary level of

applied control.

The outstations are linked together and information can be passed from one to

another. In addition a modem is also connected to the system to allow remote access.

2. The purpose of a Building Management System (BMS)

is to automate and take control of these operations in the most efficient way possible

for the occupiers/business, within the constraints of the installed plant.

3. Functional Integration of Systems

All systems are integrated functionally, utilizing pre-defined situations in the building

or Part of the building.

• RESIDENCES: For example, situations of a residence are as follows:

1. Home (present): When arriving home, the following takes place automatically:

Burglary alarm system is turned off, doors are opened, ventilation becomes need

based instead of minimum level, set point of cooling is at the optimum, and basic

lighting is automatically switched on when needed.

2. Away: When leaving the residence, the following takes place automatically, with

one single button touch: Doors are locked, burglary alarm system is turned on,

ventilation is turned down, set point of cooling is allowed to be higher, all lights are

automatically switched off.

3. Away for a long time: When leaving the residence for a longer time, the following

takes place automatically, with one single button touch: Doors are locked, burglary

alarm system is turned on, ventilation is turned down, set point of cooling is allowed

to be much higher than normally, (respectively, set point of heating is allowed to be

lower than normally,) all lights are automatically switched off.

During the absence lighting can be turned randomly on/off; to look like somebody is

at home.

4. Night: With one single button touch from the master bedroom the house is set to

night mode. Doors are locked and cover protection system is activated. Adequate

cooling and ventilation are ensured. Only selected lights stay on as night lights, all

others are turned off.

5. Party: Fresh air is produced more efficiently than normally. Specially selected

party lighting scenes are applied.

• OFFICES: In offices relevant situations are Present, Away and Away for long time.

4. System Architecture

Intelligent Integrated Building Management System must be implemented as an open

and clearly layered solution as presented in the following figure.

Fig (10.2) A symbolic schematic of BMS

The solution layers include the following:

4.1 Service Layer

4.2 Management Layer

4.3 Control Layer

4.4 Field Layer

Different functionalities (systems) are implemented using distributed control

techniques and standard open communication networks.

4.1 Service Layer

All systems can be connected without additional software to Service Center (provider

of maintenance, facility management and security services), which remotely accesses

the systems through a standard COBA interface as defined in COBA standardization.

Service Center is capable of providing maintenance and security services as follows:

i) Security alarm monitoring

ii) Maintenance alarm monitoring

iii) Main user service, including remote control and optimization of all systems

iv) Technical help desk and training

v) Hardware maintenance

vi) Software upgrades

vii) System documentation

In addition to the mentioned basic services, Service Center is capable of providing

value adding services, such as generic peak load management of electricity as

described in Management Layer. The service takes automatically into account the

mode/situation of the

building (such as home/away), prevailing circumstances in the building and effect

areas of each system.

4.2 Management Layer

To ensure extremely fault-tolerant system functionality, the Management Layer of the

solution is not responsible for any controls. The role of the Management Layer is to

provide a uniform view to all systems. The Control Layer must function

independently, even without the Management Layer.

The Management Layer complies with client-server architecture and must consist of

two clearly separate parts: the Building Operating System (BOS) and client

applications, such as the Graphical User Interface (GUI). The Building Operating

System is the COBA compliant server software that handles the following tasks:

i) Conveying dynamic data from all systems to any application

ii) Conveying alarms to the desired media and application/user

iii) Trending of history data from all systems

iv) Management of user rights based on predefined user roles

BOS must be able to run on Linux and Microsoft operating systems. Controls of

heating, cooling, ventilation and lighting, consumption measurements, access

controls, intruder alarms, fire alarms and CCTV systems are all integrated into BOS.

The Building Operating System includes a structured COBA XML object model of

the building, its parts and spaces, its connected systems, system parts and effect areas

of each system. The model enables generic peak load management of electricity,

which automatically takes into account the mode/situation of the building (such as

home/away), prevailing circumstances in the building and effect areas of the systems.

The Building Operating System includes an open structured XML interface for other

applications to interact with the connected systems. This XML interface has to

comply fully with COBA XML schema. Communication method between BOS and

Client applications has to include at least Open Java Messaging Service (JMS). No

other primary interfaces are accepted.

Graphical User Interface (GUI) is client software, which includes an automatically

adapting tree structure of the building, building‟s parts, individual spaces, different

systems and parts of systems. The tree structure can be used for navigation through

the system.

The client application has to have following views: process view, floor plan view,

trend view, alarm view and event log view per building and system layer. Any alarm

must be shown in red color in both graphical views and tree structure. Each alarm

message must include shortcut button to relevant graphical system and floor plan

view. The client must be launchable with an internet browser. Only HTML based user

interfaces are not acceptable.

4.3 Control Layer

The intelligence of the integrated solution must be distributed into smart control nodes

in the Control Layer. Each node should have about 10 I/O points to achieve maximum

reliability and flexibility.

The systems must be easy to configure using the graphical system/project

configuration tool, which must be fully compatible with COBA definitions and the

Building Operating System. Tool has to produce COBA compatible XML document

about all integrated systems which is used as such to run the BOS.

Communication between control nodes must be done via a Free Topology (FTT-10)

Local Operating Network (LON) with the Standard Network Variables Types

(SNVT). All communication is event-based. No other method of data transmission in

LON is accepted. All systems must be able to react to alarms on the Control Layer

without interference from the Management Layer.

System/Project Configuration Tool has to have following features:

i) Building and System modeler to enable creation and modification of COBA data

model of buildings and systems.

ii) I/O-object view (list and graphical) which enables object configuration and

graphical binding of SNVTs of I/O-objects. This feature must be compatible with

standard LNS binding tool like NL220 or Lon Maker for Windows.

iii) Node view for node configurations and management.

iv) Automatic creation of cable lists between modules and field devices per location.

v) Testing tool to help project management and commissioning.

To minimize the amount of cabling, Control Layer devices are placed to the nearest

electric Panel, side of air-handling and fan coil units or in separate cabins when

adequate. All systems use the same control network cabling, which uses free topology

to maximize flexibility for future modifications and to minimize the need for cables.

Electrical design utilizes free or star topology cabling to maximize flexibility for

changes and to minimize the use of cables.

4.4 FIELD LAYER

To guarantee openness and flexibility of the integrated systems, the Field Layer must

not include any intelligence. Field devices comply with industry standards, such as

PT-1000 for temperature, 0-10 V for other sensors and actuators, potential free

contacts for ON/OFF

indications and control buttons and 24 V relays for ON/OFF controls.

5. Applications:

Fig (10.3) BMS applications

5.1 Building Automation

All mechanical and electrical systems are monitored and controlled by smart control

nodes.

Cooling (heating) control system keeps the temperature at set point, taking into

account the mode of the building (such as home/away/etc) and occupancy

information, thus changing the set points accordingly.

Air handling control brings fresh air into residence when so needed, taking into

account the mode of the building (such as home/away/etc) and prevailing conditions,

such as CO2 level and occupancy.

5.2 Lightning and Curtain Controls

Lighting groups and curtains are on/off controlled and lights dimmed as follows:

i. Using local push buttons (on/off, on/off/up/down, lighting scenes),

ii. On movement detection,

iii. Based on illumination level (dusk),

iv. Time schedules,

v. In connection with situations/modes of the building.

5.3 Consumption Measurements

Consumptions of water, electricity and cooling energy are measured per building, per

area and per system. Meters are connected directly to control network or they can be

equipped with pulse outputs which are connected to counter modules which are

connected to control network.

Consumptions are trended into BOS‟s SQL database.

5.4 Access Control

Access control is implemented with proximity readers, control nodes, electronic keys

and electronic locks. Users can be classified so that they have access only to the

spaces they are allowed to enter according to programmed time zones. The access

control system is connected to BOS for full control and reporting, and integrated into

GUI As option, access control can also have time attendance and info applications.

5.5 Video Monitoring

Camera surveillance is implemented with conventional digital and new IP-cameras.

Camera surveillance can be equipped with Digital Video Recording (DVR) server.

System shall be integrated to BOS server. Usage can happen both via DVR systems

own User Interface Client and the integrated GUI. When equipped with DVR, the

system shall record digital images of events caused by intruder alarm system, access

control, CCTV or any other facility management system.

5.6 Fire Alarms

Fire alarming system is implemented either as 1.) Separate system (towers, offices,

etc.) in accordance with the civil defense requirements or as 2.) Integrated solution

(villas) where detectors are connected directly to control nodes (in Control Layer). In

both cases alarms are relayed to BOS and shown in the integrated graphical user

interfaces. Ventilation is shut down in the area concerned and its location is indicated.

5.7 Intruder Alarms

Intruder alarms are an essential part of the intelligent integrated building management

system. Intruder alarm is seamlessly integrated on software level to access control,

CCTV/DVR, lighting control and building automation. Granted access disarms the

alarm zones automatically. Arming the zones change automatically the mode of the

building into away mode.

Intruder alarm system includes cover protection and indoor surveillance. Doors are

monitored with magnetic contacts. Movement detection with presence indicators are

used for indoor surveillance. In case of burglary the system gives an alarm, which is

relayed through BOS to Service Center and to specified mobile phones.

5.8 Leakage Alarms

In case of leakage or moisture the system gives an alarm, which is relayed through

BOS to Service Center and to specified mobile phones. Service Center checks the

alarm and forwards a request to Maintenance Company, if necessary.

5.9 Energy Savings

The integrated solution optimizes energy consumption through the following features:

i. Need based control of all systems (occupancy, CO2 level, humidity…)

ii. Situation based control of all systems (Home/present, away, night…)

iii. Schedule based control of all systems

iv. System / device monitoring, consumption measurement and trending

v. Electricity consumptions per building / building part

vi. Water consumptions per building / building part

vii. Cooling (heating) energy consumptions per building / building part

6. Benefits of a BMS

The common Benefits of BMS will be listed and classified according to different

User‟s point of view as follows.

These benefits will only be obtained if the system is properly specified, installed,

commissioned, operated and maintained.

6.1 Facilities manager

i) Central or remote control and monitoring of building operations

ii) Low operating cost

iii) Efficient use of building resources and services

iv) High productivity

v) Rapid alarm indication and fault diagnosis

vi) Good plant schematics and documentation

6.2 Building owner

i) Higher rental value

ii) Flexibility on change of building use

iii) Individual tenant billing for services

6.3 Building tenant/occupants

i) Effective monitoring and targeting of energy consumption.

ii) Good control of internal comfort conditions

iii) Possibility of individual room control

iv) Increased staff productivity

v) Improved plant reliability and life

vi) Effective response to HVAC-related complaints

6.4 Maintenance Companies

i) Ease of information availability problem diagnostics.

ii) Computerized maintenance scheduling

iii) Effective use of maintenance staff

iv) Early detection of problems

v) More satisfied occupants

7. Selecting the right BMS

Buying and installing a BMS is a significant investment. Systems are complex and

expensive, and installation can cause disruptions to operations. Facility managers can

take several steps to ensure that the BMS they buy is the best system for their facility

needs. These considerations are discussed briefly below.

7.1 BMS Capabilities

The ability of BMS to control energy cost and to modify the operation of equipment

from remote locations reduces energy waste and labors costs, while improving tenant

comfort.

Also, integrating building functions and operations in one system is one of the most

important features of today‟s automation systems

7.2 Selecting a system

The selection process of a BMS should be considered in view of the following factors:

i) Supplier reputation in similar projects,

ii) How long the system has been on the market

iii) Training package provided by the supplier to the operation and maintenance staff

iv) Supplier after sale technical support and supplier guarantee of spare parts

availability for a reasonable future period.

7.3 System limitations

BMS are not the cure-all for operations and maintenance problems. While they can

help make operations more efficient, they cannot overcome operational shortcomings,

such as lack of preventive and planned maintenance.

7.4 Identifying automation needs

BMS can identify the shortcomings of the existing operations. Typical deficiencies

that motivate facility managers to consider installing a new building automation

system include:

i) High energy use

ii) Low maintenance productivity

iii) Unorganized maintenance activities

iv) Inability to adapt building systems to changing occupant requirements

v) Lack of coordination among various building systems

7.5 System ability to adopt future trends

Selected BMS should be capable of accommodating future trends in the industry

easily, so that facility managers in the future can adopt new features into their systems

without facing huge bill.

It is simply the ability of upgrading systems.

8. Why do some BMS projects fail?

Unfortunately, too many building automation upgrade projects never achieve their full

potential.

Here are some mistakes in project planning that can ruin the project before it gets

started

i) Choosing inappropriate BMS system

ii) Incorrect connections or conflictions between orders

iii) Ignoring the real world and dealing the BMS with complete trust which in some

case can be wrong

9. BMS Future Trends

There are several trends that significantly affect the present revolution or rapid

evolution

of large buildings automation as explained over the page.

10. World Wide Web:

The internet allows BMS to become integrated with enterprise functions, eliminating

geographic restrictions, easing access to all data from any site and, accordingly

making it easier to use and support building systems operation.

11. Wireless Revolution:

There is a great potential in the wireless technology e.g. wireless sensors, wireless

monitoring. Field service technicians will be able to take advantage of this technology

through handheld computers wirelessly connected to the Internet. Moreover, a

wireless approach has the advantages of allowing the comfort system to follow

occupants through the building and to automatically adjust occupancy, ventilation,

lighting and thermal levels to meet personal

preferences wherever the occupant travels through the building.

12. Componentization of the Control of the HVAC Industry:

For building HVAC systems, field devices that were traditionally supplied by the

control vendor are now appearing as component controllers as part of each HVAC

device. The lower cost and increased functionality of combining powerful DDC

microprocessors with standard communication protocols are resulting in the

componentizations of controls for the HVAC industry.