AIVC 11915

TABLE OF CONTENTS MAIN PAGE

CH-99-9-3

Cooling Loads in Laboratories

Christopher K. Wilkins, P.E. Michael R. Cook MemberASHRAE

ABSTRACT to many of the laboratory spaces over the years. These local cooling systems were usually recirculating type systems. The heating, ventilating, and air-conditioning (HVAC) Recirculating air in a clinical laboratory is contrary to recom­ system for a laboratory must be designed with consideration mended practice (ASHRAE and the multiple units for safety, air cleanliness, and space temperature. The primary 1995), were a maintenance headache. Hospital management wanted safety concern is to ensure proper coordination between fume to provide all ventilation and cooling from the main building hood exhaust and makeup air supply. Air cleanliness is main­ system and eliminate all of the individual cooling units. tained by properly filtering supply air, by delivering adequate Hospital management wanted variable-volume hood controls room air changes, and by ensuring proper pressure relation­ to be evaluated and applied if practical. ships between the laboratory and adjacent spaces. Space temperature is maintained by supplying enough cooling air to VENTILATION RATE ANALYSIS offsetthe amount of heat generated in the room. Each of these factors must be considered, and the one that results in the larg­ The first step for this project was a field survey to deter­ est ventilation rate is used to establish the supply and exhaust mine the number of existing fume hoods and the condition of airflows. The projectdescribed in this paper illustratesa case the existing fume hood exhaust system. The field survey where cooling load is the determining factor in the sizing of the revealed that there were only two fume hoods on the entire air systems. floor. Each fume hood had a dedicated, constant-volume exhaust fan serving it. The fume hood exhaust requirement for 3 DESCRIPTION OF THE PROJECT the entire department was only 1044 ft /min (493 Lis). This made it clear that an elaborate fume hood control package was A medical center hospital is located in Burlington, not going to be practical. It was also clear that fume hood Vermont. The laboratory services department occupies 16,000 requirements were not going to be the governing factor of the 2 2 gross ft (1486 m ) on the second floorof one of the buildings, ventilation rates in the laboratories. 2 2 of which 6,040 ft (561 m ) is active laboratory space. The The next step was to establish a minimum ventilation laboratory department contains ten individual laboratory criteria. The governingbuilding code, as adopted by the state spaces, each with a unique arrangement.The facilitywas built of Vermont, does not dictate a ventilation rate for laboratories. around 1960. The health carecenter has an ongoing program Even if there was a code-mandated minimum, the actual mini­ in the older buildings to install sprinklers and remove asbes­ mum requirement for a specificproject can be greater. For this tos. When it came time to do the facility's second floor,it was project, we referenced industry standards to determine an decided to upgrade the HVAC system as well. appropriate criteria. The existing system was constant volume with steam ASHRAE (1995) recommends a minimum of six air reheat. There was not sufficientcapacity in the main building changes per hour (ACH) in a laboratory for most laboratory system to cool the laboratory spaces. This was evidenced by types. The American Institute of Architects' (AIA 1993) the fact that a number oflocal cooling systems had been added guidelines echo this. This value represents an absolute mini-

Christopher K. Wilkimsa group leader and Michael R. Cooksa seniordesigner, Hallam Associates, South Burlington, Vt.

THIS PREPRINT IS FOR DISCUSSION PURPOSES ONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 1999, V. 105, Pt. 1. Not to be reprinted in whole or in part without written permission of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullis Circle, NE, Atlanta, GA 30329. Opinions, findings, conclusions, or recommendations expressed in this paper are those of the author(s) and do not necessarily reflect the views of ASHRAE. Written questions and comments regarding this paper should be received at ASH RAE no later than February 13, 1999. BACK TO PAGE CHE

mum, and in our experience is below what Wfi.have seen as We recognizeelthe .n�ed t9 perform a thorough analysis of industry practice. One example is the Department, pf Veterans the equipment to obtah1 an accurate load estimate. Our anal­ Affairs' (DVA 1992) requirement of a II],iµimum.9f 10 ACH. ysis included a detailed sur�ey �fall miscellaneous equip- . for laboratories in their health care facilities. This was a prac­ ment. In our,initi\(l su�vey, vr.e_ recoreled the name of the tical referencefor this project since this laboratory is part of a equipn;ien°taridthe name�late rating ( wher� available), and we ' hospital. inle�viewed U1e us¢ s to' detennine how often the equipment � 1 . j ' ' • Th� primary laboratory spaces for this project had been· was rHn.1Nam,e�l�t.e r�tings shown to be misleading _ ha:ve b!!-!!p origina1ly designed for between 10 ACH and 15 ACH: These wl;ler:i used lo de�tt�flil\eair7condjtio;nin?foa�s of office equip-. ventilation rates exceeded all of the established minimum· menl(Wilkins and ¥.cGaffin 1994). We believed that the same values discussed' above but were insufficient to maintain was' lik�ly �f'this laboratory equipme�L We decided lO take comfortable temperature levels in rrlahy of the 'spaces� This· 'measurement� to1verify electric1conslimptioo instead of rely­ . meant that the driving factoP :fordetednining the ventilation; . ing tm nameplate·data. Wherever possible,:the idle and oper­ rate in the laboratory spaces'i.Vas goirikto;benl.e coolin'g load· ating electrical cortsumpti�m,.0f the equipment was measured. in some 6r all cases. We established 10 1ACH as tlie miriirnulli.: Table liis a partial lisrofour findings. ventilatiori i:ati:foi· occupit:'d 'perro�s blit �.:kpt:.btla1fntM �r R11 'Aftei· tht:rluiiling; \�fltill had a number o[items whert:wt: spaces to exceed this based or1 coolirig'lbad relflliier1Ient had to �stimate the'Moling load beca�se the equipment 9ould� not lietested: We based our 'estimate on· a similar item that had· COOLING LOAD ANALYSIS beel\.1tested: 'This gave us measured data:or a solid estimate for· The calculation of cooling load for a laboratory is not the maximum cooling<'load of most ohhe incubators, ovens, different from calculaLing for other \ypes of spaces. Consid­ baths; computers; centrifuges, ·and electronic1:i:nalyzers. ' eration mt.isl be given to solar gain;�iI';ri:J;'ifus ion people, Diversity was assessed by comparing the idle·.consump­ Lights. ao�-equipment. Our \valk·through of tl1is dep:i.rim�ni tion to the:ooeratinc maximum constimotion.Centrifuces had made it apparent that the eqtilipmenl cdmpcmel11 of the l&ad a·significa�t red';Jct�o1,1A n �lecrrical cons�Il)-Ption whiie idle as was going to be very large'.'Tli.'e �arioiis typ� of egu·i�ment co,r3waref'-1PwheP:.operationat: Otqer equipment such as elec-: that were crowding ti1e 'spa�es inclu'ded refrigerators,' frceicirs', tronic an;ilyzersh�p the same cons!-lmptionwhenever the unit incubators ovens, baths, 'corltputer�. centrifuges, a'.hd a'large was po�ered. These data, coupled with our information relat-. mTay of c.lcctronic analyzi:l;·s. The only thing that all the equip­ ing to typical usage patterns, allo:wed us to apply appropriate. ment had in common was Lhal we did not knCJw lhe hea( gener- diversity factors. Ac�ual diversity factors used are discussyd · · ' of of , ation (l'.ooling loa

I• TABLE 1

f LFtborato Equipment H�t .G�neration • fl!• ,. ' cy ... . : . ' .. J ·,, ,: • Nameplate M�asurcil' 1dJ.e' I I Measured Op�r�tlng Dep_wtment . i ; , : Eq�iP.IR.ll-'1t Jt�1n ! - - . . (Bh1/h) (Bh;th)1 ' (Rtj1/h)

I' I -I •.. bator 1024 .. - 0 ' 941 91!��� L�cH ;r I JI " ' IfisLUlugy , I• , .� ., · Tissue Analyzer • Not Available 410 lOM " ' ; "· I . ) 1 ._, · iminun 8assay S yste\:n 2364 ... • 601 60lt

Ektacliem Xn Afyz er 1' ' ' Not Available 6143; ., 7781 ' ! •. I I ··' i 2048 942 f3n cx�,Apl)lY�H ' .• - , '' .. BloodGasSystemlJ.•c:· ._,I,, ., .,. 1638 J1r O' 409 ' , I 853 ,,i,.314 � :; � 628

Chemistry l I , ' - '- , , �' ' T ' Tj f lT ' I'' I ,, • I { . r C.entr.if�ige-1 2048 0 '76l '. .: •, ••1!: :,;I 327p , ,,.; 0 ;1, 2048'

· '" · Polai'fzation.1illalyi�fi ""; - 2048 J\: 248. ·-s,731 ''I Hemoglobin Testiµg 1638 11 1·,cj "I 410 573. ' ,,. J "' • ' \' ·.1 • J '1 r, ,, .1 - \.pnvec.tinn_Tnp1h8tor Not Av8i18hle · o: .. ?,?,l; '

I I Hezyiatqlogy Anal yze� .,, ·n· " , _. 3754 .. 1334;1 .1884 flematology. •J:':/ '.II• I," (Y I 2048;i. �I , . , • l I' ' l' ' q;o·i Micob ogy ' . .' � igl , .. CQ2 Incub�tor ,, 2048 0 ':. 1352

I; '. ·( : : I � c i Ii ;;·'

2 CH-99-9-3 BACK TO PAGE ONE

The cooling load from refrigerators and freezers proved on the other hand, was expected to run nearly all of the time, very difficult to measure; or estitii'ate. t'h�re were 17 units on even when the dcibr was not opened. Hei·e, the manufacturer the floorfrom eight differentmlinufaciurers. Simply measur­ recommended a valuieof 2860 Btu/h (838 W) for the load on ing the idle and operating e1edric consumption does not give the air"conditioning system. · ' ,• enough informationto the ctor. I determfoe load and diversity'� Once all the equipment loads were established, the ca�cu­ Refrigerators heat fro!n the �pa�� i1s we:"ll as �clually remove fation of the overall coolip.gload was straightforward.Wf- used add heat to che spacq. Heaflsn:;n1'6vei:1 ;1roi:·ex�mple, whenever a compiercialload prograll1 that is based on the transfi;:r func­ the door is opened and°Col'if'aJ�·escaj,es e. 0"nto'the'spa Tlieh�t tion method, (TFM) (ASHRAE 1997). The TFM models build­ heat gain must be si�·pty t�jec'teCI: con�id6red,� not -��·heat' i•' ' ::,r-' I � • r , . I ing mass heat dynamic,s and allows a distinction bet.ween condettser. are:the ractiated,and.,convectyq.Jorms pf cooling load. We were not The compress0r and-the _ c0mponents:of; �ble tq deterp1i xadiary� '?nvective spJit for this equip­ the refrigerator that. add .heat to the. space. The a�nount of heat 1�, \�e that the c1Dmpressor adds. directly to;the spacejs small. !he, m�nt.1'Pi, .'?cop�ervativ�1,yte assumed 100% convective load. condenser is the component that is most important ;:fhe heat Building ,en, clop. load cornponent.� were modele.d .based on . F rejection of the condenser will be: gr,i;atei; tl\cw the. ,c;wiling · � M�caJsulaticompressors. All refrig�rators and freez- - Co oling Ca pacity 1600Btu/h 750 Btu/h '" ers are in �se contin��msix, A� ad.ditiorial diversity factor was not appropriate. - Heat Rejection 2000Btu/ h 3000 Btu/h � '�· Tlifs detailed load analysis for our project resulted in Co efficient of Performance 4.00 0.33 . " calculated supply rates bet\Veeri 10 ACH and 20 ACH for the Recommetided Heat Gai)l* 107TBtu/h 2860 Btu/h ten laboratory_ areas. The avetage1for the ten was 13.8 ACH. Insulation Value l4°F·ft�·h/Btu 31 °F ·ft2;h/Btu , The average equipment load is 6.71 W/ft2 (72.2 W/m2) with a 3 3 - inaximuilfof lD.65 W/ni·(n4.6Winh A chemistry l.abora­ Storage Ca pacity l 27.'3ft ,12.0ft . � t0ryhad this largest load, riquiring 2-1.8 ACH. Table 3 gives

• As recommended by unit manufacturer. a summary of some typically referenced air system facts.

CH-99-9-3 3 BACK TO PAGE ONE

160000 . - 1. 1'

140000 "

. \ 10Moo � :c � !! 80000 c

�..J 60000

.. . ' ' 4oobo J' '

- :20000

SOLAR PEOPLE

I OAO r.OMPONFNTR "' Figure 1 Space sensible load comp@nerits.

·- ;\

OVEN INCU MISC .. 2% 4"(o 1%

.1)

42%

•'

..

CENT 22% 5% 0%

Figure 2 Equipment load by type.

SYSTEM SELECTION The 100% outside air AHU include 12-row cooling coils with copper fins, face and bypass steam heating coils, 30% We designed the air distribution system to deliver a mini­ prefilters, 90% final filters, and humidifiers to maintain a mum of 20 ACH to all of the primarylaboratory spaces. This minimum of 30% relative humidity. Copper finswere selected allowed the hospital the flexibility to reconfigure the labora­ to minimize microbial growth on the coils' fins. Copper has tory space in any manner in the future andto have sparecool­ been reported to be of higher toxicity to microorganisms then ing capacity if more equipment is added. All referenced aluminum (Gill and Wozniak 1993). Copper fins also improve minimum ventilation rates were met and sufficientmakeup air heat transfer by up to 5%. was provided to all fume hoods. Two new air-handling units were selected to provide supply to this laboratory area plus The laboratory air-distribution system was designed with some adjacent areas. 11 individual zones. Each zone was provided with an occu-

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TABLE3 CONCLUSIONS Air System Facts- Engineers can encounter many different types of labora­ !tern 1-P SI tory spaces. The project described here is an example of a laboratory that had very high internalheat loads due to a heavy Average Airflow 1.85 (ft.3/min)/ft2 9.39 (Us)/m2 use of electronic equipm1.1nt.A detailed load analysis, includ­ Average Room Air Ch ange 13.8per hour 13.8per hour ing field measurement of actual;equipment power consump­ tion, was performed to determine as accurately as possible the Co il Load Ratio 103ft2/ton 2.72m2/kW actual cooling load of the spaces. Our analysis indicated that Space Sensible Heat Ratio 96% 96% nameplate data will overstate the actual load of electronic Co il Sensible Heat Ratio 59% 59% equipment. This analysis 'also illustrated that in some cases, cooling load can be the detemlining factor in establishing People Density 145ft 2/person 13.5m 2/person room airflow rates and overall air system capacity. Lighting Level 1.50 W/ft2 16.1 W/m2 Average Equipment Load 6.71 W/ft2 71.9 W/ft2 REFERENCES Supply Air Temperature 57.0°F 13.9°C ASHRAE. 1995. 1995 ASHRAE Handbook-HVAC Appli­ cations, Chapter 7. Atlanta: American Society of Heat­ Laboratory Location Burlington, Vermont ing, Refrigeratingand Afr-Conditioning Engineers, Inc. pied-unoccupied switch. A maximum of 20 ACH and a mini­ ASHRAE. 1997. 1997 ASHME Handbook-Fundamen­ tals, mum of 6 ACH were:delivered. Variable-speed drives on the Chapter 26. Atlanta: American Society of Heating, supply and exhaust fans modulated to match the required total Refrigerllting and Afr-Conditioning Engineers, Inc. Guidelines for construction and equipment of airflow of all the individual zones. The fume hoods were AIA. 1993. hospitals and medical facilities. Washington, D.C.: exhausted at a constant volume and with individual fans. The American Institute of Architects Press, · "·· required fume hood exhaust did not exceed the minimum of 6 · DVA. 1992. Design Instructions to Architects and Engineers, ACH (unoccupied ventilation rate) in any of the zones. . Chapter 4.13, HVAC Design Manual for Hospital The laboratories can maintain their pressure relationships Projects. Washington, DC.: Department of Veterans by the action of automatic airflow control devices (VAV ·Affairs. boxes) on the supply and general exhaust to the room. The Gill, K.E., and A.L. Wozniak. 1993. Hospital gets IAQ occupied and unoccupied set points are fixed based on main­ checkup. Heating/Piping/Air Conditioni11;g, August. taining the desired differential airflow. Supply airflow can Simons, C.G., and R. Davoodpour. 1994. De�ign consider­ vary based on room temperature, with general exhaust flow . ations for laboratory facilities using molecular biology tracking to maintain room pressure. Provisions were consid­ techniques. ASHRAE Transactions 100(1): 1266-1274. ered to allow future installation of heat recovery (space Wilkins, C.K., and N. McGaffin. 1994. Measuring computer constraints and location of supply and general exhaust mains equipment loads in office buildings. ASHRAE Journal, make this difficult to impleme11t and service). August. .. ,

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..

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