formulas coolers

8/10/2019 Formulas Coolers

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FORMULAS, DEFINITIONS and TABLES

Additional information about rigid media:

Virtually all formulas and tables presented here have to do with how the mediaperforms. It's cooling efficiency, static pressure drop across the media relative tothe face velocity and cubic feet per minute of air flow is the measuring rod to whichwe apply all other calculations and determinations. In simpler terms, the rigidmedia is the heart and soul of evaporative cooling. Without an understanding ofit's operation, it is difficult to design a cooling system or size cooling equipment fora building.

The part about applications and design are covered in the section !pplicationsand "esign which can be reached from the Technical Data section which isavailable from our home page. To #eep a surprisingly comple$ sub%ect simple, only

the formulas and tables that relate to this media are covered in this section.

Abbreviations and Definitions:

&et's start with some abbreviations we use in our formulas

AC ( !ir )hanges. * +sually e$pressed in changes per hour or per minute. !irchange is the number of times the air within a structure is e$hausted and replacedduring a specified period such as hour or minute.

BTUH (-ritish Thermal +nits per our. ! measure of heat or the absence of

heat *cold can be defined as the absence of heat in a volume of air or space.-T+ is not commonly used in evaporative cooling terminology but necessary tocalculate heating and mechanical refrigeration. *It is most often used as heat ofvaporization ( /012 -T+3lb in the formula for calculating evaporation rate andstandard )45.

(S)CFM (*6tandard )ubic 4eet per 5inute. +sually referred to as simply)45. This is a necessary ingredient in any formula involving evaporativecooling. It is a measure of air volume movement in one minute.

Fv (or) FV (4ace Velocity. 4ace velocity or air velocity is the measure

e$pressed in feet per minute *475 the air is moving at the entry side *face of thecooling media. This is another necessaryingredient in any formula in evaporativecooling to determine efficiency.

FM (4eet 7er 5inute. The measure of speed *velocity of the air .


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!S " 8$ternal 6tatic 7ressure. 8$pressed in inches, water column. Thepressure against which the air flow must move. The pressure e$ternal to thecooling unit opposing air flow *i.e. restrictive ductwor#, etc.

SD " 6tatic 7ressure "rop. 8$pressed in inches, water column. The amount

of pressure required to push the air through the media as measured with amagnehelic gage. The difference between the pressure of the air flow at the inta#eof the media and the discharge side of the media. The measure of pressure forany component through which air flow is measured at the inta#e and discharge.This is an important consideration in some evaporative cooling applications.

#$ or %&g& or #C or %&'. ( Water gauge or water column in inches. This is ameasure of static pressure. ! 7itot Tube is used to ta#e this measurement. The7itot Tube is a curved *+9shaped glass tube with a prescribed amount of waterand a scale. The tube is hollow. When air is blown into one end the water columnwill be forced up the other side to some level. The level to which the column of

water rises is a measure, in inches, of the pressure of the force required.

$H (:allons per hour. ! measure of liquid *usually water moving during onehour.

$M (:allons per minute. ! measure of liquid *usually water moving in oneminute.

(f) or (F) " 4ahrenheit. Temperature conforming to a thermometric scale onwhich water boils at ;/; degrees and freezes at 2; degrees.


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=0 degrees *f Wet -ulb, the Wbd would be 20 degrees *f. If the actualtemperature drop measured at the discharge side of the media was =2 degrees *f,the percent of saturation efficiency would be @0?. This means that the air passingthrough the media has been saturated with water vapor *moisture to @0? of itsma$imum. )ooling 8fficiency is the same as 6aturation 8fficiency and is most

often used to define the performance level of the media. !lso called %ustefficiency.

Design( This term is used in many ways to define the parameters of anapplication or specifications. 6ome common uses are as follows IDb = IndoorDry Bulb. ODb = Outdoor Dry Bulb. IWb = Indoor Wet Bulb. OWb =Outdoor Wet Bulb. EDb = Entering Dry Bulb. LDb = Leaving Dry Bulb. EWb= Entering Wet Bulb. LWb = Leaving Wet Bulb.This term is often used incon%unction with conditions such as )limate "esign )onditions. In evaporativecooling, climate data is considered to be "ry -ulb and Wet -ulb levels. It wouldrequire a 7sychrometric )hart to locate the %uncture of the "ry -ulb and Wet

-ulb lines to find the grains or pounds of moisture per pound of dry air or relativehumidity *A. Aefer to Table / for a psychrometric chart digitalized for easyreading of relational elements of "b, Wb and A.

H( Aelative umidity. 8$pressed in percent. The percent of water vapor inthe air compared to the amount of water vapor the same air could contain. *i.e./B? A indicates the air is /B? saturated with water vapor

Formulas:

eaving Dr* Bulb ( CD"b 9 *68 $ *Ddb9DWbE

eaving #et Bulb(


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Densit* atio ( /.2;B $ -arometric 7ressure 3 *"b*f

#ater %eig.t (US gallon) ( F.22 pounds per gallon *based on distilled water

#ater volume (US gallon) ( =.1F/ gallons per cubic foot

#ater %eig.t (US gallon 'ubi' foot) ( =.1F/ $ F.22 ( weight of cubic foot ofwater *>;.;FFH

Fa'e Area ( Width $ eight of open face area through which air will flow*e$pressed in square feet.

Fa'e Velo'it* ( )45 3 4ace !rea *6q 4t *e$pressed in 4eet per minute *475.

Tables:

Table / 7sychrometric )hart

#H20 per

#Dry Air

Temperature (Dry Bulb degrees f)

40 50 60 70 80 0 !00 !!0 !20

"b H$ "b H$ "b H$ "b H$ "b H$ "b H$ "b H$ "b H$ "b H$

%00! 27 20 &4 !2 4! !0 46 8 5! 5 54 & 57 2 62 2 65 !

%002 &2 40 &6 28 4& ! 47 !2 5& !0 57 7 60 5 6& 4 66 2

%00& &5 58 4! 40 45 28 50 ! 54 !5 58 !0 62 7 65 6 67 &

%004 &6 75 4& 5! 47 &8 52 26 56 ! 5 !& 6& !0 66 8 6 5%005 & 5 45 65 50 47 54 &2 57 2& 6! !7 64 !2 67 7! 7

%006 ' ' 46 78 5! 55 55 & 5 27 6& 20 66 !5 6 !0 72

%007 ' ' 4 ! 5& 64 57 45 6! &! 65 24 67 !8 70 !2 7& !0

%008 ' ' ' ' 55 7& 5 5! 6& &6 66 28 68 20 7! !4 74 !!

%00 ' ' ' ' 56 82 60 57 64 4! 67 &0 70 22 72 !6 75 !&

%0!0 ' ' ' ' 57 0 62 6& 65 46 68 && 72 25 74 !8 76 !4

%0!! ' ' ' ' 60 64 70 66 50 70 &6 7& 27 76 20 77 !5

%0!2 ' ' ' ' ' ' 65 76 67 55 7! 40 74 2 77 22 78 !7

%0!& ' ' ' ' ' ' 66 8& 6 5 72 44 75 &! 78 24 80 !

%0!4 ' ' ' ' ' ' 67 0 70 6& 74 47 76 && 78 26 8! 20

%0!5 ' ' ' ' ' ' 6 5 72 68 75 50 77 &6 7 27 82 2!

%0!6 ' ' ' ' ' ' 70 7& 72 76 5& 78 & 8! 2 8& 22

%0!7 ' ' ' ' ' ' ' ' 74 76 77 57 7 42 82 &! 8& 2&


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%0!8 ' ' ' ' ' ' ' ' 75 80 77 5 80 45 82 && 84 24

%0! ' ' ' ' ' ' ' ' 76 85 78 62 8! 47 8& &5 85 25

%020 ' ' ' ' ' ' ' ' 77 0 80 65 82 4 84 &7 86 27

%02! ' ' ' ' ' ' ' ' 78 5 8! 6 8& 5! 85 & 87 28

%022 ' ' ' ' ' ' ' ' 7 82 72 84 5& 86 40 87 2

%02& ' ' ' ' ' ' ' ' ' ' 8& 75 85 55 87 4! 88 &!

%024 ' ' ' ' ' ' ' ' ' ' 84 78 86 58 88 42 0 &&

%025 ' ' ' ' ' ' ' ' ' ' 85 8! 87 60 8 4& ! &4

%026 ' ' ' ' ' ' ' ' ' ' 86 85 88 62 0 44 2 &5

%027 ' ' ' ' ' ' ' ' ' ' 87 88 8 65 ! 46 & &6

%028 ' ' ' ' ' ' ' ' ' ' 88 ! 0 67 2 47 4 &7

%02 ' ' ' ' ' ' ' ' ' ' 8 5 ! 6 & 4 5 &

%0&0 ' ' ' ' ' ' ' ' ' ' 0 2 7! 4 5! 5 40


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0%80 0%82 0%84 0%86 0%88 0%0 %02 0%4 0%6 0%8

5 0%50 0%5! 0%52 0%5& 0%55 0%56 0%57 0%58 0%60 0%6!

!0 0% !%02 !%04 !%07 !%0 !%!2 !%!4 !%!7 !%! !%22

!5 !%4 !%5& !%56 !%60 !%64 !%68 !%7! !%75 !%7 !%8&

20 !% 2%04 2%0 2%!4 2%! 2%2& 2%28 2%&& 2%&8 2%4&

25 2%48 2%55 2%6! 2%67 2%7& 2%7 2%86 2%2 2%8 &%04

&0 2%8 &%05 &%!& &%20 &%28 &%&5 &%4& &%50 &%58 &%65

&5 &%48 &%56 &%65 &%74 &%82 &%! 4%00 4%08 4%!7 4%26

40 &%7 4%07 4%!7 4%27 4%&7 4%47 4%57 4%67 4%77 4%87

45 4%47 4%58 4%6 4%80 4%2 5%0& 5%!4 5%25 5%&6 5%48

To determine :allons per 5inute divide by >0. 4ormula to determine evaporationrate is shown in 4ormulas section.

Table 0: Tem+erature dro+ a'ross media (1 233 FM fa'e velo'it*)

"bd(f)

Temperature drp (Dry Bulb) fr /edia T1i*ess f

4 6 8 !2 !8 24

!0%0 5%& 6%8 7% 8% %8 %

!2%5 6%6 8%5 %8 !!%! !2%2 !2%&

!5%0 7% !0%2 !!%8 !&%& !4%6 !4%8

!7%5 %2 !!% !&%8 !5%6 !7%! !7%&

20%0 !0%5 !&%6 !5%8 !7%8 !%5 !%7

22%5 !!%8 !5%& !7%7 20%0 2!% 22%2

25%0 !&%2 !7%0 !%7 22%2 24%4 24%7

27%5 !4%5 !8%7 2!%7 24%4 26%8 27%2

&0%0 !5%8 20%4 2&%6 26%7 2%& 2%6

&2%5 !7%! 22%! 25%6 28% &!%7 &2%!

&5%0 !8%4 2&%8 27%6 &!%! &4%! &4%6

&7%5 !%7 25%5 2%5 &&%& &6%6 &7%040%0 2!%! 27%2 &!%5 &5%6 &%0 &%5


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Table 0: Air Densit* atio: Densit* atio for Various !levations and

Tem+eratures&

Temp% 3le,ati*9*1es Hg

(f)

0

2%2

!000

28%86

2000

27%82

&000

26%82

4000

25%84

5000

24%0

6000

2&%8

7000

2&%0

8000

22%22

000

2!%&

!0000

20%58

68 !%00 0%7 0%& 0%0 0%87 0%84 0%80 0%77 0%75 0%72 0%6

70 !%00 0%6 0%& 0%0 0%86 0%8& 0%80 0%77 0%74 0%7! 0%6

72 !%00 0%6 0%& 0%8 0%86 0%8& 0%80 0%77 0%74 0%7! 0%6

74 0% 0%6 0%2 0%8 0%86 0%8& 0%80 0%77 0%74 0%7! 0%68

76 0% 0%5 0%2 0%8 0%85 0%82 0%7 0%76 0%7& 0%7! 0%68

78 0% 0%5 0%2 0%88 0%85 0%82 0%7 0%76 0%7& 0%70 0%68

80 0%8 0%5 0%! 0%88 0%85 0%82 0%7 0%76 0%7& 0%70 0%68

Table 4: Air C.anges suggested +er .our&

:ea,i*g AirTemp (:Db)

Temperature ,erutside ambie*t

Air -1a*ges+er Hur

;,er 78 (f) 20< &0=60

76f t 78f !5 t 20 20 t 40

74f t 76f !0 t !5 !5 t &0

72f t 74f 5 t !5 !2 t 20

:ess t1a* 72f :ess t1a* !0 !0 t !5


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!E"IE! !I#ID $OOLI%# "EDI& TE$'%I$&LD&T&

7remier )ooling 5edia is a generic term forhigh efficiency fluted evaporative

cooling media. This media is manufactured by several manufacturers in the +nited6tates, )hina, India and 5e$ico among others. The most common configuration ofthis type media is a 1B 3/B degree transverse flute arrangement for typicalevaporative cooling applications.

Des'ri+tion:

This media is a cellulose material impregnated with insoluble anti9rot salts andrigidifying saturants. The media incorporates an internal geometry of transverse 1Bdegree and /B degree alternating flutes. The 1B degree flute carries the water tothe face *inta#e side of the media while the /B degree flute is aligned with the

direction of air flow.

This flute arrangement is self9cleaning and increases cooling efficiency by causingair turbulence while air is traveling through the media. This media providesappro$imately /;2 square feet of evaporative surface area per cubic foot of media.8fficiency of this media is about @0? at 100 to B00 feet per minute face velocity in/; depth. &ife e$pectancy is dependent upon many factors but is usually 2 to Byears when properly maintained and water p is between > and F.

Cooling !ffi'ien'*:

)ooling efficiency is based on saturation efficiency *ability to transfer water vaporinto the air stream. The two ma%or factors to be considered in determining theefficiency of the media are media thic#ness and air flow face velocity . Thefollowing table defines the saturation efficiency by media thic#ness and facevelocity. 8fficiency M 7ressure "rop "ata is based on typical performanceinformation as published by certain manufacturers for their 1B3/B rigid coolingmedia and is appro$imate.

4aceVelocity

7ercent 5edia 8fficiency at 5edia"epth

6tatic 7ressure "rop at 5edia "epth

1 > F /; /> ;1 1 > F /; /> ;1

;00475

=/? F>? @/? @>? @@? @@? 0.0; 0.02 0.01 0.0> 0.0F 0.0@

200475

>=? F/? FF? @1? @F? @@? 0.02 0.0B 0.0= 0./0 0./2 0./@

100475

>;? ==? F1? @;? @>? @@? 0.0B 0.0@ 0.// 0./F 0.;B 0.2/


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B00475

B@? =;? F;? F@? @1? @@? 0.0@ 0./; 0./= 0.;> 0.2> 0.B0

>00475

B=? =0? F0? FF? @;? @@? 0./; 0./F 0.;; 0.2>

00 475 are not recommended. )ontact7remier Industries, Inc., for information regarding methods available to handlehigher velocities. 8$ample !t air velocity of B00 475 and media thic#ness of /;,the saturation efficiency will be @0?. Aecommended design velocity is B00 9 BB0feet per minute. This is the best trade9off between performance and cost.

er'ent effi'ien'* defined:

It is necessary to #now the dry bulb temperature and wet bulb temperature enteringthe media to be able to apply the percent efficiency. The difference between thedry bulb and wet bulb is #now as the wet bulb depression. The wet bulb is thelowest point the dry bulb temperature can be dropped across the media. Thepercent of the wet bulb depression will equal predicted discharge temperature. I.8.at /00 degree dry bulb and =0 degree wet bulb, the wet bulb depression is 20degrees *f. To determine e$pected dry bulb temperature drop across the media,multiply 20 *wet bulb depression G .@0 *@0?. Temperature drop across the mediais ;= degrees *f. To determine e$pected dry bulb discharge temperature, subtractthe temperature drop from the entering dry bulb temperature. I.8. /00 9 ;= ( =2degree *f discharge temperature. Aefer to 4ormulas section for this andadditional information.

Formulas:

The following formulas are provided primarily to determine evaporation rate ofwater from the media into the air stream. The evaporation rate is necessary tocalculate water usage, bleed9off rate and total flow rate of water over the media.The evaporation rate changes with the climate and air flow changes. If desired,the setting of water flow over the media and bleed9off rates can be ad%usted basedon the evaporation rate.

Media effi'ien'*: The first step to determine other data is to establish theactual media efficiency. !ffi'ien'* " (T5 , T/) 6 (T5 , T%) 7 533 #.ere T5 "entering dr* bulb tem+erature8 T/ " leaving dr* bulb tem+erature and T% "entering %et bulb tem+erature&

Dis'.arge Tem+erature: To determine predicted discharge temperature usethe following formula. (9 effi'ien'* 7 (Dr* Bulb , #et Bulb)) " Dis'.argeTem+erature.

Air Velo'it*: in feet per minute *475 Feet +er minute (FM) " Cubi' feet+er minute (CFM) 6 Suare feet of fa'e area (o+en to air flo%)&


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#ater eva+oration rate: in gallons of water per hour *:7. ( (CFM ;(entering Dr* Bulb , leaving Dr* Bulb)) 6 bleed,off rate 7 0 " %ater flo% rate in $H& 0 for gallons perminute.

Media orientation in use:

The media must be installed in a proper orientation to the air flow. The 42 degreeflute must be aligned u+%ards in the direction of the air flow *inta#e side of theflute must be lower than the discharge side and the 52 degreeflute must bealigned do%n%ards with the air flow *inta#e side of the flute must be higher than

the discharge side. If the media is aligned improperly, the water will flow to thedischarge side of the media and can be easily entrained in the air flow.

Media availabilit*:

The media is available in depths up to ;1 as required. 7remier maintains large

inventories of this media in ;1 depths and will cut to size and ship ne$t day in thegreat ma%ority of cases. eight *length is restricted to =; standard, however7remier can supply up to =F lengths. 6tandard width is /;, however 7remier cancut to smaller width if desired. 5edia is usually shipped in individual stic#s*pieces to include sufficient number to provide the total width of the unit into whichthe media is to be installed.


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Aefer to our home page for additional sections of technical data such asinstallation, removal and replacement, cooling season start up, winter shut down,water chemistry and others.

Evaporative Cooler Applications:

"Applications"is a term used in this technology to identify or define thepurposeforwhich the evaporative cooling equipment is selected. It is also sometimes used to definethe method of application or installation.

A simple example would be the need to cool a 40,000 square foot warehouse in theSouthwest. his is usually an application well suited for evaporative cooling,however some additional information is required to fully qualify the application. Some ofthe questions that should be answered are!

1. What is to be cooled? People, Equipment or other? If people, what are they

doing. "ffice, production, warehousing, etc. If #quipment, what type and operation$%oes the #quipment generate high heat loads, etc$

2. What kind of work is going to be performed? &ertain 'inds of operations can bebetter served than others. An example is printing processes. &olor printing cannot dry tooquic'ly or too slowly. (aper cannot be allowed to absorb too much moisture or it becomestoo limp so humidity is very important.

3. What are the cost parameters? &an mechanical refrigeration be afforded even ifit is desired$

. What is the structure capable of supporting? !re there other structuralconsiderations? Is it necessary to locate the equipment on the ground or roof or someother mounting method$

". What are the climate conditions? Is the climate hot and dry or mild conditions$

Qualifyin t! Application#

Answering the above questions will go a long way in the determination of whether ornot evaporative cooling will be the best type cooling system or not. Some of the followingconsiderations will help to provide some answers to these questions!

). (eople in production or warehousing type *obs are prime uses of evaporative cooling.#vaporative cooling not only cools by dropping the %ry +ulb temperature but it also coolsb# the chill factorof air passing over the body. or people in office type wor', it is usuallythe practice to use mechanical refrigeration due to the need to maintain very low humiditylevels. In addition to human comfort it is also important to maintain humidity control andcool equipment -li'e computers. (roduction and/or warehousing type *obs are usually bestserved by evaporative cooling. It is far easier to exhaust heat than it is to recirculate it and


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treat it. (erishable goods usually require mechanical refrigeration. ost mechanicalequipment is best cooled by evaporative cooling due to the need for large volumes of airpassing over the equipment and exhausting the air to the outside.

1. he type of wor' being performed influences the selection of cooling equipment.

he example of printing on paper is a good case in point. "ther types of wor' to beconsidered are those that require large volumes of air flow. Some types of wor' are *ust theopposite. 2igh volumes of air flow may adversely affect the wor' -such as in some plasticfilm manufacturing

3. Acquisition cost of mechanical refrigeration is usually about 3 times that ofevaporative cooling for a similar structure. &osts vary widely due to type of structure,climate and other factors. p'eep and maintenance costs are somewhat lower withevaporative cooling partially due to the technical expertise required. "perating costs areusually much higher for mechanical refrigeration. Sometimes 3 to 5 times higher in energyuse alone.

4. #quipment selection must consider the ability of the structure to support it. It is nottoo unusual to have to locate equipment on the ground or some other mountingmethod because the roof will not support it6s weight. $tructural integrit# is a seriousconsideration in selection and location of equipment.

5. he climate is a ma*or consideration in the selection of cooling equipment.#vaporative cooling is especially effective in hot dry climates. emperature drops of 30 to40 degrees are rather easy to achieve. It is not too unusual to achieve lower temperatureswith evaporative cooling than with mechancial refrigeration during very low humidityperiods due the lowered performance of mechanical refrigeration equipment in theseconditions. In the Southwest, it is a common practice to use both methods. #vaporativecooling can be used during the hot dry periods and mechanical refrigeration during highhumidity periods. ost homes have an evaporative coolerand an air conditioner on theroof. I.#. in (hoenix, A7., the evaporative cooler can be used at a cost of about 830.00 amonth while the air conditioner would cost about 890.00 to 8100.00 a month based on thesi:e of the house and the equipment. ost commercial buildings are cooled withevaporative cooling in the warehouse/production area while refrigeration is used in theoffice area.

E%aporati%e cooling can be successfull# used an#where the wet bulb

temperature is lower than the dr# bulb which is almost e%er#where.

(remier has shipped evaporative cooling to ;ouisiana, lorida, ississippi, Alabama,apan, exico andother countries. he iddle #ast is an excellent example of the ideal climate for evaportivecooling.

Sizing the Evaporative Cooling Equipment:


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he following methods of si:ing evaporative cooling equipment is based on the bestinformation available and some first hand experience. he &realit# of results& rule hasbeen a great teacher. he evaporative cooler technology is still plagued with what I call the&swamp cooler mentalit#&. his mentality views this technology as if it had notprogressed any during the past ?0 or @0 years. he truth is that this technology has changed

enormously during the past )5 to 10 years with the advent of the Bigid edia typecooling medium. &ooling efficiencies have increased from 45C to 50C with the Swamp&ooler to D0C to DDC with the new cooling medium. oday the best answer in selectingcooling equipment is evaporative coolingE

Si$in %apo&ati% coolin 'uip(nt fo& an )istin o& plannd

p&oduction*+a&!ous typ st&uctu

$tep 1' (etermine the )ubic )apacit# of the structure or that portion of the structure to

be e%aporati%el# cooled.

Fo&(ula -idt! . Lnt! . Effcti% /oolin

0i!t1 /apacity in /u2ic Ft3 F G the actual height tobe cooled. I.#. in a 156 tall building, it is the usual practice to cool only to about )?6 to 106based on the highest point the cooling is required. A heat stratification layer will form atthe roof level which will not adversely affect the cooling process provided that space is notused. Bemember cold air drops and hot air rises.

In example of Step ). A structure that is )006 wide x 1006 long with an effectiveheight of )?6 would equal 310,000 cubic feet.

$tep 2' (etermine the number of air changes per hour required to maintain desired

indoor temperatures. his is an extremely important determination. oo many airchanges will result in unnecessary cost while too few air changes will not acheive theindoor conditions desired. he best approach, short of a ma*or engineering study of heatgains, etc., is a common sense approach of using the 'nown conditions inside and outsidethe structure.

It is first necessary to 'now the climate design conditions of %ry +ulb and Het +ulb foryour location. his information is available from AS2BA# publications )C scale -or from(remier6s web site in section x if there is a weather reporting station in your area. I.#.design conditions for (hoenix, A7., is )0D-f %b and ?D-f Hb. his condition is onlyexceeded during )C of the cooling season therefore the conditions are at the high end of therange. hese conditions are concurrent meaning that they are present at the same time.

sing the formula to determine the predicted discharge temperature during theseconditions you can 'now the temperature of the air you have available to use in the coolingof the building. - %ischarge temperature G -#%b #Hb x S# or )0D ?D G 40 x .D G ;%b3?-f temperature drop. %b ;%b G )0D 3? G @3 degrees -f %ry +ulb dischargetemperature. he air temperature of @3 degrees -f is necessary to 'now for the next part ofstep 1. -


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Befer to following table to determine the proper number of air changes.

Suggested air changes per hour

Leaving Air

Temperature

Temperature over

ambient*

Air

Changes/Hr**

Above @9-f 10 degrees -f 30 to ?0

@? -f to @9 -f )5 to 10 -f 10 to 40

@4 -f to @? -f )0 to )5 -f )5 to 30

@1 -f to @4 -f 5 to )0 -f )1 to 10

under @1 degrees -f less than )0 -f )0 to )5

F Average amount indoor temperature exceeds the outdoor temperature when evaporativecooling is not in use at design conditions or interpolation/extrapolation of these conditions. FIt is common practice to coolonly to the height actually used and needs cooling. It is not bad to have a heat layer at theroof level provided the cool air coming into the structure does not flow through this layer.ost cooling installations will extend the discharge duct to the height above the floorwhere cooling is preferred and the capture area of the exhaust ducts li'ewise start at thislevel. his method does not disturb the heat layer.

sing the above table and a leaving discharge temperature -into the building of @3degrees -f and determining that the indoor air temperature -ambient %b and the outdoortemperature -ambient %b is )10 and )0D. he difference is )) degrees -f Beferring to theabove table, we see that we should plan approximately )1 to 10 air changes per hour. hereason for the range of air changes is to allow for other conditions not heretoforeconsidered. Among these other considerations is human comfort cooling as compared toequipment cooing, etc. let6s continue to si:e the equipment needed.

;et6s summari:e what we have determined so far. he cubic capacity to be cooled is310,000 cubic feet. he discharge temperature required is @3 degrees -f. he number of

air changes is between )1 and 10. ;et6s -I hate to say it assume that this structure isheavily populated with people. He should than consider a greater number of air changes toassure the best human comfort level without increasing costs more than absolutelynecessary.

o determine the total &ubic eet per inute of air flow required to cool this structureas indicated, multiple 310,000 -cubic feet by 10/ ?0 G )0?,??? &ubic eet per inute-&. -Bemember to express the requirement in the same unit of measure as the capacity.


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In this instance, that is &ubic eet per minute rather than per hour and that is the reason Iadded the divide by ?0 into the formula. It is alright to round off this amount of & to)0@,000 if you li'e round numbers. In fact if the number of air changes was reduced to, say)9 changes per hour, the amount of & would be D?,000 &. Jou can readily see whythe number of air changes is so important.

It is common practice to refer to air changes as minutes of air change. I.#. in thisinstance, the 10 changes would be expressed as one -) air change every 3 minutes.Another way to prove the process is to multiple the & K air changes -)0@,000 K 3 G31),000 & which is close enough Bemember, we are not si:ing a roc'et ship andafterall, we are dealing with climate conditions that are exceeded only )C of the timeduring the cooling season.


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S& G Indoor Sensible 2eat Lain -+2).09 x -I%+;%+ x %ensity Batio

Hhere I%+ G Indoor -%esign %ry +ulb ;%+ G ;eaving %ry +ulb from&ooler

#xample! An indoor heat gain of )44,000 +2 at an altitude of 4000 feet. An#vaporative &ooler with )1 cooling media M 500 ( velocity is to be used to removethis heat gain. "utside design conditions are D4 %ry +ulb and ?4 Het +ulb with a designindoor temperature of 900-f %ry +ulb.

he discharge temperature -%b must first be determined. sing the formula of "%b -S# x -"%b "Hb, the following result is reached. D4 -.9D x -D4 ?4 G [email protected] -f;%b.

he %ensity Batio is determined from tables available in the formulas and tables section.

At 4000 feet elevation the %ensity Batio is .9@.

o determine S& to offset this indoor heat gain we can now utili:e the formula!

)44,000 +2 G )44,000).09 x -90 [email protected] x .9@ )).D33 G

S& )1,0?@

his result indicates we need at least )1,0?@ &ubic eet per inute of air flow M [email protected] offset the indoor heat gain of )44,000 +2.

"ther types of applications!

n%iron )ooling $#stem 7)$8

A very effective and low cost application of evaporative cooling in a building such as theone described above could be cooled with a system we have named n%iron )ooling&. Init6s simplest form, this type system uses cooling sections mounted in one wall and exhaustfans in the opposite wall. he exhaust fans pull the air through the cooling sections andexhausts the air to the outside. It is somewhat li'e ma'ing the entire structure into anevaporative cooler. Since exhaust fans are required, even with powered air systems, it isnot an extra cost and since there is no expensive blower and motor, the cost is at the lowest

possible.

his type cooling system is presently being used very successfully in several 40,000square foot warehouse/production type buildings in ;as Negas,


17/39

he &onverta(a'-tmA7 is a conversion and upgrade system that consists of a wetsection and blan' panels. It is intended to convert the old, existing Swamp &ooler to thenew high efficient evaporative cooling technology. In the above example of )0D%b and?DHb conditions with a discharge temperature of @3 degrees -f using )1 thic' rigidmedia, the old swamp cooler would have discharged D) degree -- air.

his simple and low cost upgrade/conversion system can also be very effectively usedon Botary Hheel type coolers. hese type coolers are really archaic but many are still inuse. It is a simple process of removing the evaporative wheel and replacing it with aproperly si:ed &onverta(a'. Since the Botary Hheel type unit bloc's almost half the facearea, the conversion also almost doubles the air volume in addition to much lowerdischarge temperatures.

efer to the section on )on%erta*Pak7tm*!58 from our home page for much more

information about this s#stem.

Precooler

he (remier (recooler is a wet section with rigid media, usually 3 to ? thic'. his unit isused to precool the air passing over/through heat exchangers or heat generating equipment.he best example is conventional air conditioners. he precooler is placed over the airinta'e of the condenser coil. he colder air passing over the condenser will increase theheat transfer rate considerably thereby allowing it to operate at a much higher efficiencyand lower cost. It will also extend the useful life of compressors, etc.

he principle is simply to present an air inta'e temperature at the condenser coil that theequipment was designed for. All manufacturers specifications indicate that the hotter the

air across the condenser, during cooling mode, the lower the efficiency. A ?0,000 +2air conditioner at 90 degrees -f ambient, may drop to only 45,000 to 50,000 +2 whenthe ambient temperature rises to the )00 )10 degree -f level. In the Southwest, it iscommon for rooftop temperatures to reach )40 degrees or more during high heat periods.

efer to this section from our home page for more information about Precoolers.

Custom Design/anu!a"ture# Equipment

(remier speciali:es in custom designed and manufactured equipment. he a'ep Airnit or #vaporative &ooling with 2eat type unit is a specialty with us. He can assist in

the initial design of the #quipment and then produce the item to specifications required.his allows the customer to build the equipment to meet the need rather than have tochange the need to accommodate existing equipment.

efer to that section from our home page for more information.

igid edia
http://www.piec.com/precooler.htmhttp://www.piec.com/PREMIER%20COOLING%20MEDIA.htmhttp://www.piec.com/precooler.htmhttp://www.piec.com/PREMIER%20COOLING%20MEDIA.htm


18/39

(remier stoc's large quantities of Bigid edia, . He can cut to si:e and ship next day.)lick here to send e*mail to us for a price quotation or answer questions you may haveabout this media.

efer to this section from our home page for more information about igid edia.

o$ile Coolers

he (remier obileCool-c unit is a portable evaporative cooler with 9 thic' Bigidedia and an. his unit is designed to be moved to the area where spot cooling is needed.A water hose and )10NA& power supply is all it ta'es to be in operation. t also works%er# well as a &through the wall& permanent mount cooler9

-a#ersfield !7 1@B /01 =0 =2

&ittle Aoc# !7 ;B= @@ => F0 99 -arstow !7 ;/1; /0> >F =2

Te$ar#ana !7 2>/ @F => F0 99 -lythe !7 2@0 //; =/ =B

Colorado: 9 9 9 9 99 -urban# !7 >@@ @B >F =/

-oulder B2FB @2 B@ >1 99 )hico ;0B /02 >@ =/

)olorado 6prings !7 >/=2 @/ BF >2 99 8l )entro !7 920 //; =1 F/

"enver !7 B;F2 @2 B@ >1 99 8urea#a !7 ;/= >F >0 >;

7ueblo !7 1>2@ @= >/ >= 99 4resno !7 2;> /0; =0 =;

?da.o: 9 9 9 9 99 &os !ngeles !7 @@ F2 >F =0

-oise !7 ;F1; @> >B >F 99


19/39

E!*O!"&%$E D&T&

I


20/39

1 m/s = 196.85 ft/min

1 m3/s = 3600 m3/h = 1000 dm3(liter)/s = 35.32 ft3/s = 2118.9 ft3/min =

13200 Imp.gal (UK)/min = 15852 gal (U)/min

1 !a = 1 "/m2= 1.#50#$10%#l&/in2= 1$10%5&ar = #.03$10%3in 'ater =

0.336$10%3ft 'ater = 0.102# mm 'ater = 0.295$10%3in merr* =+.55$10%3mm merr* = 0.102# ,g/m2= 0.993$10%5atm


21/39

o% and Medium ressure Du'ts

5a$imum friction rate 0.1 % 0.2 inhes -../100 ft

Velocity 1500 % 2000 ft/min (8 % 10 m/s)

!ir 4low Aate 5a$imum Velocity

(m3/h) () (m/s) (ft/min)

N 200 N /=B ;.B 1@0

N /,000 N B@0 2 B@0

N ;,000 N /,;00 1 =FB

N 1,000 N ;,2B0 B @F0

N /0,000 N B,@00 > /,/F0

O /0,000 O B,@00 = /,2F0


22/39

Hig. ressure Du'ts

5a$imum friction rate less than 0.# inhes -../100 ft

Velocity 2000 % 3500 ft/min (10 % 18 m/s)

(hafts


(m3/h) () (m/s) (ft/min)

N B,000 N ;,@B0 /; ;,2B0

N /0,000 N B,@00 /B ;,@B0

N /=,000 N /0,000 /= 2,2B0

N ;B,000 N /1,=00 ;0 2,@10

N 10,000 N ;2,B00 ;; 1,200

N =0,000 N 1/,000 ;B 1,@00

N /00,000 N B@,000 20 B,F00

It is common to #eep main duct velocity above 20 m/s (39#0 ft/min).

$orridors


(m3/h) () (m/s) (ft/min)

N B,000 N ;,@B0 /0 ;,000

N /0,000 N B,@00 /; ;,2B0

N /=,000 N /0,000 /B ;,@B0

N ;B,000 N /1,=00 /= 2,2B0


23/39

N 10,000 N ;2,B00 ;0 2,@10

,ser &reas Dffices, receptions, lounges and similar


(m3/h) () (m/s) (ft/min)

N B,000 N ;,@B0 /0 ;,000

N /0,000 N B,@00 /; ;,2B0

The duct velocity in air condition and ventilation systems should not e$ceed certain limits to avoidunnecessary noise generation and pressure drop in the duct wor#.

The limits of velocities depends on the actual application. The bac#ground noise in an industrial buildingis significant higher than the noise in a public building and more duct generated noise can be accepted.

)ommonly accepted duct velocities can be found in the table below.

6ervice

Velocity 9

7ublic buildings Industrial plant

(m/s) (ft/min) (m/s) (ft/min)

!ir inta#e from outside ;.B 9 1.B B00 9 @00 B 9 > /000 9 /;00

eater connection to fan 2.B 9 1.B =00 9 @00 B 9 = /000 9 /100


24/39

5ain supply ducts B.0 9 F.0 /000 9 /B00 > 9 /; /;00 9 ;100

-ranch supply ducts ;.B 9 2.0 B00 9 >00 1.B 9 @ @00 9 /F00

6upply registers and grilles /.; 9 ;.2 ;B0 9 1B0 /.B 9 ;.B 2B0 9 B00

&ow level supply registers 0.F 9 /.; /B0 9 ;B0

5ain e$tract ducts 1.B 9 F.0 @00 9 /B00 > 9 /; /;00 9 ;100

-ranch e$tract ducts ;.B 9 2.0 B00 9 >00 1.B 9 @ @00 9 /F00

The design of the ductwor#s in ventilation systems are often done by using the

Velocity 5ethod

)onstant 7ressure &oss 5ethod *or 8qual 4riction 5ethod

6tatic 7ressure Aecovery 5ethod

T.e Velo'it* Met.od

7roper air flow velocities for the application considering the environment are selected. 6izes of ducts are

then given by the continuity equation li#e

4 = / (1)

'here

4 = dt rss setinal area (m2)

= air fl' rate (m3/s)

= air speed (m/s)

! proper velocity will depend on the application and the environment. The table below indicate commonly

used velocity limits

Type of "uct )omfort 6ystems Industrial 6ystemsigh 6peed

6ystems

5ain ducts 1 9 = m3s F 9 /; m3s /0 9 /F m3s
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5ain branch ducts 2 9 B m3s B 9 F m3s > 9 /; m3s

-ranch ducts / 9 2 m3s 2 9 B m3s B 9 F m3s

-e aware that high velocities close to outlets and inlets may generate unacceptable noise.

T.e Constant ressure oss Met.od (or !ual Fri'tion oss Met.od)

! proper speed is selected in the main duct close to the fan. The pressure loss in the main duct are then

used as a template for the rest of the system. The pressure *or friction loss is #ept at a constant level

throughout the system. The method gives an automatic velocity reduction through the system. The

method may add more duct cross sectional changes and can increase the number of components in the

system compared to other methods.

T.e Stati' ressure e'over* Met.od

With the static pressure recovery method the secondary and branch ducts are selected to achieve more

or less the same static pressure in front of all outlets or inlets. The ma%or advantage of the method are

more common conditions for outlets and inlets. +nfortunate the method is complicated to use and

therefore seldom used.

6upport spacing for the ductwor# is typical based upon deflection, stress and cylinder buc#ling analysis.


26/39


27/39

specialties, etc. ! common rule of thumb is to support load of this type with hangers on both sides of theload.


28/39

/F ;F 2= /

;0 20 2@ /9/31

;1 2; 1; /9/31

1 ft (ft) = 0.30#8 m

"uctwor# sheet metal gauges are indicated in the table below

)omments 6heet 5etal :auge6heet Thic#ness

(inhes)

Welded "uctwor# 0 0.2/;

/ 0.;F/0

; 0.;>B0

2 0.;B00

1 0.;210

B 0.;/F=

> 0.;020

= 0./F=B

F 0./=;0

@ 0./B>0

/0 0./100

// 0./;B0

/; 0./0@0

/2 0.0@2=


29/39

/1 0.0=F0

/B 0.0=00

65!)

"uctwor#

/> 0.0>;B

/= 0.0B>0

/F 0.0B00

/@ 0.012=

;0 0.02=B

;/ 0.0212

;; 0.02/;

;2 0.0;F0

;1 0.0;B0

;B 0.0;/F

;> 0.0/F=


30/39

2; 0.0/00

22 0.00@2

21 0.00FB

2B 0.00=F

2> 0.00=0

4riction loss *head loss in standard air ducts are indicated in the diagram below

The diagram is based on standard air 0.0+5 l&/ft3in clean round galvanized metal ducts.

1 inh 'ater = 2#8.8 "/m2 (!a)= 0.0361 l&/in2(psi) = 25.# ,g/m2= 0.0+39

in merr*

1 ft3/min (fm) = 1.+ m3/h = 0.#+ l/s


31/39

1 ft/min = 5.08$10%3m/s

1 inh = 25.# mm = 2.5# m = 0.025# m = 0.08333 ft

4riction loss *head loss in standard air ducts are indicated in the diagram below


32/39

Ai& flo+ < %olu( and %locity < du to stac9 o& flu ffct

causd 2y indoo& !ot and outdoo& cold t(p&atu&

diff&nc

6ponsored &in#s

! temperature difference between the outside and inside air will create a natural draft forcing the air to

flow through the building.

The direction of the flow depends on the temperatures. If inside temperature is higher than outside

temperature, inside air density is less than outside air density, and inside air will flow up and out of the

upper parts of the building. )old outside air will flow into the lower parts of the building.

If outside temperature is higher than inside air temperature 9 the air flow will be in the opposite direction.

@atural Draft Head

The natural draft is caused by the difference in outside and inside air density. The natural draft head can

therefore be e$pressed as

dpmm72= (% r) h (1)

'here

dpmm72= head in millimeter 'ater lmn (mm 72)

= densit* tside air (,g/m3)


33/39

r= densit* inside air (,g/m3)

h = height &et'een tlet and inlet air (m)

@atural Draft ressure

8quation */ can be modified to 6I pressure units li#e

:p = g (% r) h (1&)

'here

:p = pressre (!a "/m2)

g = aeleratin f grait* % 9.81 (m/s2)

Densit* and Tem+erature

With air density of 1.293 ,g/m3 at0, the air density at any temperature can be e$pressed as

= (1.293 ,g/m3) (2+3 K) / (2+3 K ; t) (2)

r

= 353 / (2+3 ; t) (2&)

'here

= densit* f air (,g/m3)

t = the atal temperatre ()

8quation */ above can easily be modified by replacing the densities with equation *;.

@atural Draft ressure Cal'ulator

The calculator below can be used to calculate the natural draft pressure generated by the inside and

outside temperature difference.

9;0tside temperatre ()

;0inside temperatre ()

/0height (m)

Maor and Minor S*stem oss


34/39

The natural draft force will be balanced to the ma%or and minor loss in ducts, inlets and outlets. The ma%or

and minor loss in the system can be e$pressed as

:p = < (l / dh) (r2 / 2) ; > 1/2 r

2 (3)

'here

:p = pressre lss (!a "/m2 l&f/ft2)

< =?@4r*%-eis&ah fritin effiient

l = length f dt r pipe (m ft)

dh=h*drali diameter(m ft)

> =minr lss effiient (smmariAed)

Air Flo% and Air Velo'it*

8quation */ and *2 can be combined to e$press the air velocity through the duct

= B (2 g (% r) h ) / ( < (l r/ dh) ; > r) C1/2 (#)

8quation *1 can also be modified to e$press the air flow volume through the duct

= D dh2 /# B (2 g (% r) h ) / ( < (l r/ dh) ; > r) C

1/2 (5)

'here

= air lme (m3

/s)

@atural Draft Air Flo% and Velo'it* Cal'ulator

The calculator below can be used to calculate the air flow volume and velocity in a duct similar to the

drawing above. The friction coefficient used is 0.019which is appropriate for normal galvanized steel

ducts.

9/0tside temperatre ()

;0inside temperatre ()

Fheight (m)

0.;dt h*drali diameter (m)

2.Bdt length (m)
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/ > minr lss effiient (smmariAed)

!;am+le , @atural Draft

)alculate the air flow caused by natural draft in a normal family house with two floors. The height of the

hot air column from ground floor to outlet air duct above roof is appro$imately 8 m. The outside

temperature is %10 , the inside temperature is 20 .

! duct of diameter 0.2 mgoes from /. floor to the outlet above the roof. The length of the duct is 3.5 m.

!ir lea#ages through the building are neglected. The minor coefficients are summarized to /.

The density of the outside air can be calculated li#e

= (1.293 ,g/m3) (2+3 K) / ((2+3 K) ; (%10 ))

= 1.3#2 ,g/m3

The density of the inside air can be calculated li#e

r= (1.293 ,g/m3) ( 2+3 K) / ((2+3 K) ; (20 ))

= 1.205 ,g/m3

The velocity through the duct can be calculated li#e

= B (2 (9.81m/s2) ((1.3#2 ,g/m3) % (1.205 ,g/m3)) (8 m) ) / ( 0.019 (3.5m)(1.205 ,g/m3)/(0.2 m) ; 1(1.205

,g/m3) ) C1/2

= 3.+ m/s

The air flow can be calculated li#e

= (3.+ m/s) 3.1# (0.2 m)2/ #

= 0.12 m3/s

@ote

that these equations can be used for dry air, not for mass flow and energy loss calculations where air

humidity may have vast effects.

!ir curtains and air screens blows heated air *or cooled air in summertime across door openings and

reduces the ingress of cold air *or hot air in summertime from the outside due to wind forces and natural

draughtthrough the building.
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37/39

4or ware houses, shopping malls and similar buildings with openings up to 2.5 mthe velocity should not

e$ceed 5 % 9 m/s. 4or industrial buildings the velocity can be e$ceeded to 35 % #0 m/s.

Air uantities

The quantities required depends on many variables and an e$act calculation may often be hard to

perform. Values of 2000 % 5000 m3

/h air per m2

door opening are common.

@ote8$posed systems with

lot of wind

low out door temperatures

high buildings

may even double the values.

Air Flo% and otential Differential ressure

The strength of an air curtain is the ma$imum potential differential pressure it can resist. The potential

pressure resistance generated by an airflow through an inlet opening can be e$pressed as

:p = 2.2 2sin(F) / & 73/# (1)

'here

:p = ptential differential pressre er the pening in the 'all (!a "/m2)

= air fl' thrgh disharge nAAle (m3/s per meter pening 'idth in 'all)

F = airfl' angle (nrmall* &et'een 20 % 30)

& = depth f disharge nAAle (m)

7 = height f dr pening (m)

The average air velocity through the discharge nozzle can be e$pressed as

= / & (2)

'here

= aerage elit* (m/s)


38/39

The calculator below can be used to estimate the strength of an air curtain by calculating the pressure

difference and velocity in the air f low. Aeplace the default values with the actual values.

F % lme apait* per meter prt % (m3/s)

;BF % airfl' angle (degrees)

/& % depth f inlet pening (m)

;.B7 % height f prt (m)

The differential pressure shall compensate the differential pressure caused by natural draught and wind

velocity.

)alculate the natural draught force

)alculate dynamic pressure due to wind velocity

!;am+le , Air Curtain

The height of an entrance opening in to a mall is 2.5 m. The depth of the inlet is 1 m. The air flow angle

through the inlet is 25 degreesand the air flowper meterwidth of the opening is 8 m3/s.

The force against natural draught and wind forces can be calculated with */ as

:p = 2.2 (8 m3/s)2sin(25) / 1 (2.5 m)3/#

= 29.9 !a

The velocity through the inlet can be calculated with *; as

= (8 m3/s) / (1 m)

= 8 m/s

Modulating Air Curtains

4orces compensated with air curtains constantly varies with outside temperature and wind velocity and

some control devices modulating the air flow angles and volumes are often required.

with outside temperature close to inside temperature and low wind 9 the curtain air flow is

minimized and the air flow is directed straight through the doorway

with outside temperatures far from inside temperature 9 and a lot of wind 9 the curtain air flow is

ma$imized and the air flow is directed out of the doorway

! modulated control can be achieved with one or more temperature transmitters located as indicated in

the figure above.

Dis'.arge tem+eratures (%inter 'onditions)
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39/39

The air screen discharge temperature should be #ept within certain limits. 4or winter conditions

smaller systems 9 temperature range 35 % 50 (95 % 125)

larger systems 9 temperature range 25 % 35 (80 % 95)

suction temperature 9 temperature range 5 % 15 (#0 % 60)

formulas coolers

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