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!upply systems are used or two purposes"

# $o create a comortable environment and.

# $o replace air ehausted rom a building.

$he pressure in a building will be lower than atmosphericpressure %case o &negative pressure'( i the amount o

replacement air supplied to the building is lower than theamount o air ehausted.

Introduction

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$he amount o air entering a building is equal to the thefow rate o ehaust air.

Replacement air is necessary to" Ensure that ehaust hoods operate properly.

Insu)cient replacement air and a &negative pressure'

condition cause an increase in the static pressure.

Eliminate high#velocity cross#drats through windows anddoors.

Cross#drats can interere with the unction o ehausthoods and can also disperse contaminated air rom one

section o the building to another* besides a+ecting other

processes* unsettling dust and li,e materials to cause

recontamination.

Replacement Air

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Ensure operation o natural drat stac,s such as combustion fues. -egative pressures can cause bac,drating o fues* and hence health

haards. /or e.0. Combustible products release carbon monoide.

!econdary e+ects include di)culty in maintaining fames in burners*poor operation o air controls* corrosion damage in stac,s and heatechangers due to condensation o water vapor in fue gases.

Eliminate cold drats on wor,ers.

1iscomort is not caused* overall ambient temperature and hence

wor,ing e)ciency is not reduced.

Replacement Air

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Replacement air distribution is critical especially in processindustries li,e pharmaceuticals* electronics* paints and acilities

li,e indoor 4ring ranges* particularly non#turbulent air#fow.

5hen turbulence is caused due to miing e+ect caused by

high#throw di+users* local ehaust hoods are redesigned to

draw in more air to overcome it and hence prevent the upset ocontaminant control. $hus energy costs rise.

$o get rid o turbulence* air may be provided through a supply

air plenum* or a perorated duct with the ace o the plenumcovered with perorations to di+use air.

Critical attention must be given to the eeding o air into the

plenum and avoid high#velocity.

Replacement Air 1istribution

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Replacement Air /low Rate$he replacement air fow rate should be approimately

equal to the total air fow rate removed rom the building.

/actors considered in determination o actual removedfow rate are"

6uantity o air removed.

1etermination o air ehaust locations.

$esting.

-ecessity or a particular piece o equipment.

Reasonable pro7ections or uture requirements* etc.

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&-egative pressure' is desirable* when contaminants are to beprevented rom escaping into the surrounding areas.

/or a clean environment to eist* positive pressure conditionsare maintained.

Either o the conditions are achieved by obtaining a ratio o

the ehaust # supply fow di+erential.

Room Pressure

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It involves the control o ollowing actors" $oic contaminants. 3eat load in the wor, space. 3igh horsepower demand o machines. 3igh light levels in the plant and corresponding greater heat

release and indoor temperature. 1epletion in e)ciency levels and healthul wor,ing

conditions. And increase in tolerance limit o products.

$he control is achieved by various methods adhering to process

speci4cations* using technologies li,e automated buildingcontrol and direct digital control %11C(.

Environmental Control

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$he design supply air fow rate depends on several actors besideshealth and comort requirements. $hey can be enlisted as" !atisactory dilution o contaminants assuming perect distribution o air

and solvent vapors %the miing actor &,' is also included(.

$he location o air supply and ehaust outlets such that the air passes.

$hrough the one o contamination %so that spot ventilation can beconsidered(. &-egative pressure' is desirable* when contaminants are to

be prevented rom escaping into the surrounding areas.

Environmental Control Air /low

Rate

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Environmental Control Air /low

Rate$he location o air supply and ehaust outlets such thatthe air passes through the one o contamination.

$o attain optimum utiliation o air supply it is distributedin the &living one' o the space i.E. 8elow 9#:; eet level

%where ma7ority o people and processes are located(.

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&-umber o air changes per minute or per hour' is the ratio oventilation rate %per minute or per hour( to the room volume.

$he required ventilation depends upon the intensity o aproblem and not the sie o a room and hence no. = air

changes per unit time is a poor criteria or control and haslimited applicability.

Air Changes

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Air !upply >s. Plant 3eating

Costs Even i supply air were drawn into the building* there is an additionalloading on heating systems and the uel costs will rise. /or e)cient heat transer and independence o operation* the same

fow rate o outdoor air can be introduced through separatereplacement air heaters* without eceeding the overall uel costs.

In order or an equilibrium to be established* the heat outfow rom

the building must balance the heat infow.

1esign the supply system to provide su)cient heating to counter airentering the building through in4ltration* to prevent reeing so as toobtain additional energy saving during downtime.

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$he basic requirements o air heater are" Continuous operation capability

Constant pre#selected discharge temperature under varyingconditions o temperature

Air heaters are classi4ed by property o source o heat as" !team heaters %single coil* multiple coil and bypass(

3ot water units

Indirect 4red gas and oil units

1irect 4red natural gas and 2P0 units

Replacement Air 3eating

Equipment

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COST OF HEATING REPLACEMENT AIR

Equations or estimating replacement air heating costs onhourly and yearly basis"

where"

6 ? air fow rate in cm

- ? required heat in 8$@hr:;;;cm

$ ? operating time in hours or wee,

q ? available heat per unit o uel

dg ? annual degree days

c ? cost o uel in B unit.

( ) ( ) ( ) ( )

q

cTdgQ

Cq

QN

154.0

)(Ccostearl!

001.0)(Ccost"ourl!

2

1

=

=

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Air Conservation /our methods to reduce heating and cooling costs"

Reduction in the total fow o air handled.

1elivery o untempered outdoor air to the space.

Recovery o energy rom the ehaust air and.

Recovery o warm* uncontaminated air rom processes.

Reduced fow rate. It is achieved by ta,ing stoc, o all ehaust and supply systems in

the plant and mar,ing them as necessary* replaceable and obsolete*and handling the airfow rate by implementing the changes.

@ntempered air supply. Cold outdoor air can be supplied untempered or moderately

tempered to dissipate sensible heat loads on the wor,ers andprovide e+ective temperature relie rom radiant heat loads.

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Energy recovery Involves use o heat echange equipment to etract heat rom

the air stream beore ehaust by using any o the ollowingequipment "

3eat echangers* heat wheel* 4ed plate echanger* heat pipe* runaround coil echangers* etc

/actors o consideration or selection o a heat echanger are" -ature o ehaust system

Isolation o contaminated ehaust stream

$emperature o ehaust system

!pace requirements

-ature o air stream

-eed or a bypass

Involves recirculation %return( o air rom industrial ehaustsystems

Air Conservation

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Air Conservation!election o monitors

/our basic components o a complete monitoring system" !ignal transer

1etector transducer

!ignal conditioner

Inormation processor

$he choice o detection method depends on whether thecontaminants are particulates or non# particulates

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Evaluation = Employee Eposure

2evels

5here"

CR? air cleaner discharge concentration ater recirculation in mg m

D? ractional air cleaner e)ciency

CE ? local ehaust duct concentration beore recirculation in mg m

R? raction o recirculated ehaust stream that is

composed o the recirculation return air %; to :.;(

C

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Evaluation = Employee Eposure

2evels

5here"

C8? 9 # hr $5A wor,er breathing one concentration

Ater recirculation* mgm

68? total ventilation air fow beore recirculation

6A? total ventilation air fow ater recirculation

C0? general room concentration beore recirculation* mgm

/ ? raction o time wor,ers spend at wor,#station

Co? 9 # hr $5A breathing one concentration at wor, station

beoreRecirculation

8? raction o wor,er's breathing one air that is composed orecirculation

% ; to :.;(

( )( ) ( ) ( )( )MBRBMoMGA

BB CKCKfCCfCC

Q

QC +++= 11

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!ystems should be designed to bypass to the outdoorsand not to recirculate.

3umid air rom wet collectors can cause high humidityand hence auiliary ventilation may be required.

!ince eit concentration o collectors varies with time*

design o data and testing programs should consider alloperational time periods.

2ayout and design o recirculation duct should provideadequate miing with other supply air and avoiduncomortable drats on wor,ers.

1esign o Recirculated Air

!ystems

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In lieu o a monitoring system* a secondary air cleaningsystem is more reliable and is easy to maintain.

=dor and nuisance value o contaminants should becompared to o)cial $2> values.

Records should be maintained or routine tests*maintenance procedures and recirculating systems.

Periodic testing o wor,room should be done.

Appropriate signs should be displayed in prominent places.

1esign = Recirculated Air

!ystems