Cooling Tower TDP

8/12/2019 Cooling Tower TDP

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Fall 2002

Technical Development

Program

Cooling Tower

Applications


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Heat Rejection How do cooling towers fit into an air

conditioning system

A cooling tower is a heat transfer device! A cooling tower will reject heat from water

that is circ"lated thro"gh a chillers shell #t"$e condenser!

A shell # t"$e condenser is the refrigerant towater heat e%changer "sed in an open watercirc"it li&e a cooling tower!


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How Cooling Towers 'or&


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How Cooling Towers 'or& 'arm water leaving the condenser is p"mped to the

top of the tower! This water is then distri$"ted thro"gh spray no((les

or tro"ghs thro"gh the wet dec& s"rface )fill media*so that it may $e $ro"ght in contact with o"tdoor air!

This ca"ses a small portion of the water to $eevaporated! This evaporation removes heat from the

remaining water! The cooled water collect is a s"mp at the $ottom of

the tower where it is ret"rned to the condenser topic& "p additional load and repeat the cycle!


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Definitions +ntering 'et ,"l$

Temperat"re-

The lowest temperat"re thatwater theoretically can reach

$y evaporation!

+ntering 'et.,"l$

temperat"re is an e%tremely

important parameter in towerselection and sho"ld

selected for yo"r specific

climate (one in yo"r e%act

location!

Entering Wet Bulb

Temperature


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Definitions Approach- The difference $etween the

temperat"re of the entering

wet. $"l$ temperat"re of theair and the cold waterleaving the tower!

+sta$lishment of theapproach fi%es the operatingtemperat"re of the tower andis an important parameter indetermining $oth tower si(eand cost!

/ approach is common inH1AC!

Approach

Approach


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Definitions Cooling Range-

The difference intemperat"re $etween the hot

water entering the tower and

the cold water leaving the

tower!

0 is Cooling Range is

common in H1AC!

Cooling Range

Cooling Range


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Definitions Heat 3oad- The amo"nt of heat to $e

removed from the circ"lating

water within the tower! 4t is of primary importance

that an acc"rate heat loaddetermination $e made!

4f the heat load calc"lations

are low the cooling tower will$e "ndersi(ed! 4f the calc"lations are high5

oversi(ed more e%pensivee6"ipment will res"lt!


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Definitions P"mping Head- The press"re re6"ired to

p"mp the water from the

tower $asin5 thro"gh theentire system and ret"rn$ac& to the top of the tower!

78P9 per Ton of

Refrigeration:r

;08P9 < appro%imately 70ton tower


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Definitions 9a&e."p- 4s the amo"nt of water

re6"ired to replace normal

losses ca"sed $y drift

evaporation and $leed off!

Make-up Water


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Definitions Drift- 'ater that is entrained in the

airflow and discharged to the

atmosphere appro%imately

2=!

Drift loss does not incl"de

water lost $y evaporation!

Drift


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Definitions +vaporation- For each po"nd of water that

a cooling tower evaporates5

it removes somewhere near

000,T>?s from the water

that remains!

The more evaporation that

ta&es place5 the more heat

that is removed!

Evaporation


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Definitions ,leed :ff- 'ater contains imp"rities5 when

water is evaporated these

imp"rities are left $ehind! 4f nothing is done a$o"t it5 the

concentration of imp"rities inwo"ld $"ild "p rapidly!

,leed off of some of the water iscontin"o"sly re6"ired to limit

this $"ild "p! The $leed off rate re6"ired is$est determined $y a watertreatment specialist who isprepared to ma&e the necessarytests and recommendations!

Bleed Off


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Cooling Tower Design

'hen air circ"lation is provided $y a fan or

$lower the tower is called a mechanical drafttower!

4nd"ced draft- Draws air thro"gh the tower

Force draft- ,lows air thro"gh the tower!


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4nd"ced Draft

Co"nterflow CoolingTower

Air goes "p 'ater goes down


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Cooling Tower Design 4nd"ced Draft

Crossflow Cooling

Tower

Air goes across

'ater goes down


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Hyper$olic @at"ral

Draft Co"nterflow Cooling

Tower


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Cooling Tower Design Atmospheric pray

Tower


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Cooling Tower Design Forced Draft

Co"nterflow Cooling

Tower


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Application of Cooling Towers ! 'hen selecting the

location5 s"fficientclearance sho"ld $e

allowed for the free flowof air to the inlet of thetower and for itsdischarge from thetower!

:$str"ctions will red"ceairflow ca"sing ared"ction in capacity!

Wind


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Application of Cooling Towers 2! Cooling towers sho"ld $e

located so that noise

created $y air or water is not

a so"rce of annoyance! 7! Cooling tower location

sho"ld $e s"ch that the air

discharge will not ca"se

condensation on near$y

s"rfaces or wetting $eca"seof drift!

Wind Water oi!e


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Application of Cooling Towers B! The tower sho"ld $e

located away from

so"rce of e%ha"st heat

and contamination!


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Application of Cooling Towers ! +ach cooling tower sho"ld $e

located and positioned to

prevent the introd"ction of the

warm discharge air and theassociated drift! This drift may

contain chemical or $iological

contaminants incl"ding

3egionella5 which may get intothe ventilation systems of the

$"ilding on which the tower is

located or those of adjacent

$"ildings!


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To select a cooling tower5

the following m"st$e &nown Wet Bulb Temperature)this is the year ro"nd

environmental temperat"re for yo"r e%act location*!

Cold Water Temperature)this is the desired watertemperat"re to ret"rn to yo"r condenser* "ot Water Temperature)the water temperat"re leaving

yo"r system*

The #allon! $er Minute re%uirement! of&our !&!tem'


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the following m"st $e &nown election of de!ign

wet.$"l$ temperat"rem"st $e made on the

$asis of conditionse%isting at the siteproposed for a coolingtower5 and sho"ld $ethat which will res"lt in

the optim"m cold watertemperat"re at5 or near5the time of pea& loaddemand!


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Cooling Tower Ratings

Conden!erEntering

Water Temp

CA$AC(T)

TO*

+W

($,T

-.'. //.'- 0/'1

-2'. /.1'3 01'.

4.'. /./'1 -.'5

42'. 40'/ -1'2,ased on 70HDC20E crew Chiller5 R27BA

BF 3eaving Chilled 'ater Temperat"re


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the following m"st $e &nown A wet $"l$ chart is arranged to show the s"mmertime fre6"ency

of occ"rrence! Anaheim wo"ld have a E degree wet $"l$ that is e%ceeded !=

of s"mmertime ho"rs

8enerally5 the designer engineer wo"ld select the design wet$"l$ for a specific installation5 $"t some installations aren?tcritical allowing the "se of a red"ced design val"es and smallercooling towers! :ther installations may wor& only in the winter or

at night when the wet $"l$ temperat"re is low! The designer m"st select the design wet $"l$ for hisGher project!

'hen in do"$t5 select the highest anticipated wet $"l$temperat"re to ins"re satisfactory year aro"nd operation!


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Cooling Tower i(ing

4nformation Entering Water Temperature )the

hot water temperat"re leaving yo"r shell and t"$e

condenser and entering the cooling tower*

6eaving Water Temperature)this is

the desired cold water temperat"re to ret"rn toyo"r shell and t"$e condenser*

Entering Wet Bulb)this is the yearro"nd environmental temperat"re for yo"r e%act

location*!

The gallon! per minute

re%uirement! of &our !&!tem' )7gallons per ton*

Cooling To7er Model

EWT

6WT

EWB

#$M

1

*T/..

/2.

02

2

0

2

42

/2.

*T.


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Cooling Tower i(ing

4nformation pending a little

more for a tower

with a 1FD and lasta little longer is

almost always the

wisest decision than

selecting a towerthat is too small!


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Condenser Temperat"re

Control Three way valve

For condenser temperat"re control on ICarrier crew

ChillersJ a three way valve sho"ld $e specified to

maintain temperat"res a$ove Carriers minim"m /0K

water temperat"re for the condenser!

The water loop $etween condenser and valve sho"ld

$e &ept as small as possi$le so the water will heat "p

6"ic&ly!


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Condenser Temperat"re

Control


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4n concl"sionApplication checkli!t !hould include8

Correct selection "sing act"al Entering Wet Bulb Accepta$le location on site 'et dec& compati$ility Piping )inlet5 o"tlet5 drain5 ma&e."p5 overflow5

s"pport5 e6"ali(er* Capacity control Pan water free(e protection o"nd

Cooling Tower TDP

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