hvac design i - class 8

8/13/2019 HVAC Design I - Class 8

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NewYorkUniversitySchoolofContinuingandProfessionalStudies(SCPS) 11/28/20

HVACSystemsDesignIInstructor:JuanC.Toro,PE

NYU SCPS Fall 2012 (AEHV1-CE9517)

HVAC Systems Design I - Instructor: Juan C. Toro,PE

HVACSystemsDesignI

CLASS 8

AIR SIDE EQUIPMENT, SELECTION

AND COMPONENTS. AIR

BALANCING OF HVAC SYSTEMS



HVACDESIGNIPROGRAMCLASS #1: INTRODUCTION TO HEAT TRANSFER,

REFRIGERANT CYCLE & BUILDING ENVELOPE

CLASS #2: OVERVIEW OF COMMERCIAL HVAC SYSTEMS

AND EQUIPMENT

CLASS #3: DESIGN CONDITIONS & EXTERNAL LOADS

CLASS #4: INTERNAL LOADS AND TOTAL COOLING

LOADS

CLASS #5: PSYCHROMETRIC CHART & PROCESSES

CLASS #6: MIDTERM EXAM

CLASS #7: AIR DISTRIBUTION, DUCTWORK DESIGN &

PRESSURE DROP CALCULATIONS

CLASS #8: AIR SIDE EQUIPMENT, SELECTION AND

COMPONENTS.

CLASS #9: HVAC EQUIPMENT SELECTION

CLASS #10: NYC ENERGY CODE AND ASHRAE STANDARDS

CLASS #11: FINAL EXAM

CLASS #12: HIGH EFFICIENCY SUSTAINABLE BUILDINGS

& FINAL REVIEW



FANSINHVAC

The fan is an air pump

that causes airflow by

creating a pressure

difference.

Fans produce pressure

and/or flow by rotating

blades of the impeller,

imparting kinetic energy

to the air by changing

its velocity.



FANOBJECTIVETo supply the necessary static pressure to

move a specific amount of airin a ventilation

or exhaust system.



FANTYPESFan types are generally classif ied by the

direction of air flow through the impeller.

The two main types are:

2. Centrifugal1. Axial



AXIALFANS In an axial fan the

airflow passes straight

through t he fan, parallel

to the shaft.

Axial fans have less

rotating mass and aremore compact than

centrifugal fans of

comparable capacity

Axial f ans are used for

moving large quantities

of air against a lower

static pressure.

Axial Fan


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AXIALFANSCategorized by blade shapes.

Propeller BladeDisc Blade



TYPEOFAXIALFANS

Propeller fans usually run

at low speeds and

moderate temperatures.

They experience a largechange in airflow with small

changes in static pr essure.

They handle large volumes

of air at low pressure or

free delivery (less than 1

w.c.).

Efficiency is low

approximately 50% or less.



TYPEOFAXIALFANS

Tubeaxial fans are

essentially a propeller fan

placed inside a cylinder,

with close clearance

between blade and housi ng

to improve airflow

efficiency.

The wheel turn faster than

propeller fans, enabling

operation under higher

pressures (less than 2

w.c.).

The efficiency is up to 65%.



TYPEOFAXIALFANS

Vaneaxial fans are similar to

tubeaxials, but wit h addition of

guide vanes that improve

efficiency by directing and

straightening the flow.

As a r esul t, they have a higher

static pressure with less

dependence on the duct static

pressure (up to 8 w.c.).

Vaneaxials are typically the

most energy-efficient fans

available and should be used

whenever possible.



CENTRIFUGALFANS In a centrifugal fan the

airflow follow s a radial

path through the fan

wheel.

Rotating impeller

increases air velocity

Air speed is converted

to pressure.

Centrifugal fans are

able to produce high

pressures. Centrifugal Fan



CENTRIFUGALFANSCategorized by blade shapes.


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TYPEOFCENTRIFUGALFANS

Radial fans are industrial

workhorses because of

their high static

pressures (up to 5 WC)and ability to handle

heavily contaminated

airstreams.

Because of their simple

design, radial fans are

well suited for high

temperatures and

medium blade tip sp eeds.



TYPEOFCENTRIFUGALFANS Forward-curved fans

are used in clean

environments and

operate at lowertemperatures.

They are well suit ed for

low tip speed and high-

airflow work.

They are best suited for

moving large volumes

of air against r elatively

low pressures.



TYPEOFCENTRIFUGALFANS Backward-inclined fans are

more efficient than forward-

curved fans.

These fans reach their peak

power consumption and

then power demand drops

off well wit hin their useable

airflow range.

Backward-inclined fans are

known as "non-overloading"

because changes in static

pressure do not overload the

motor.NYU SCPS Fall 2012 (AEHV1-CE9517)


TYPEOFCENTRIFUGALFANS Air foi l B lade, although not a

a "Basic Type", t his is an

important refinement of the

Backward Inclined w heel

design. It has the highest

efficiency and runs at a

slightly higher speed than

the standard flat blade to

move a given amount of air.

Most efficient of all centrifugal fans. Usually used

in both larger HVAC system and clean air

industrial applications where the energy savings

are significant. Can be made with special

construction for dusty air.



MIXEDFLOWFANS A mixed flow wheel is a hybrid

between an axial propeller and a

centrifu gal wheel. The result is a

design that combines the best axial

and centrifug al properti es: Highly

efficient air movement, increased

pressure capabilities, extremely lowsound l evels, and a steep fan

performance curve

To furt her enhance the performance of the mixed flow

fan, straightening vanes are incorpo rated in the fan

housin g. These serve to convert swirling air flow into a

straight axial flow with a resulting static pressure rise

and energy savingsNYU SCPS Fall 2012 (AEHV1-CE9517)


MIXEDFLOWFANS

Axial Fans : Straight through nearly linear airflow.

Centrifugal Fans: Two 90 deflections, before airflow

exits the fan.

Mixed Flow Fans: Slight airflow deflection from

straight through.


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FANTYPETYPICALAPPLICATIONS



FANTYPETYPICALAPPLICATIONS



FANEFFICIENCY



FANDRIVEARRAGEMENTS Direct drive:

o Offers more compact

assembly and assures

constant fan speed.

o Fan speeds are limited to

available motor speeds.

Belt drive:

o Offers flexibility in

changing the fan speed.

o Important in applications

where changes i n system

capacity or pressure

requirements are needed.



FANROTATIONANDDISCHARGE



FANROTATIONANDDISCHARGE


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MOTORPOSITIONS UTILITYFAN



MOTORPOSITIONS INLINEFANS



FANISOLATION



FANLAWS The fans operate under a predictable set of laws

concerning speed, power and pressure. A change in

speed (RPM) of any fan will predictably change the

pressure rise and power necessary to operate it at

the new RPM.



FANLAWS



FANLAWS


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HVACFANS



HVACFANS

Fan Wall



FANCONTROLControl the Fan Air flow :

Pulley change

Dampers

Variable speed dri ves (VSD)

Inlet guide vanes

Operating f ans in p arallel

Operating f ans in s eries



FANSELECTION

Various factors effecting fan selection are:

Volume required (cfm)

Fan static pressure

Type of material handled

Direct driven vs Belt driven

Noise

Operating temperature

Efficiency

Space limitations

Corrosive applications

Explosive or inflammable

material



TYPICALFANCURVE



AIRBALANCINGOFHVACSYSTEMSPRESSURIZATION CRITERIA

VFR Criteria (Volumetric Flow Rate)

RDP Criteria (Room Differential Pressure)


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VOLUMETRICFLOWRATE(VRF)



ROOMDIFFERENTIALPRESSURE(RDF)



JuanC.Toro,PE,HBDP,CPMP,LEEDAPBD+C

email:[email protected]

hvac design i - class 8

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