Trane TRG-TRC016-EN manual

Air Conditioning Clinic Chilled-W ater Systems One of the Systems Se ries TRG-TRC016-EN[...]

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P erforation 5.5 from bottom/top P erforation 0.75 from edge Comment Card We want to ensure that our educational materials meet your ever -changing resource development needs. Please take a moment to comment on the effectiveness of this Air Conditioning Clinic. Chilled-Water Systems Level of detail (circle one) T oo basic Just right T oo diff[...]

Chilled-W ater Systems One of the Systems Se ries A publication of The T rane Company Chilled-W ater Systems[...]

Preface © 2001 American Stand ard In c. All ri ghts res erved TRG-TRC01 6-EN i The T rane Compa ny believe s that i t is incumb ent on manu facturers to serve the industry by regularly dis seminating informa tion gathe red through lab oratory research, tes ting programs, and field experien c e. The T rane Air Conditi oning Clinic s eries is o ne m[...]

TRG-TR C0 16-EN ii Contents period one Types of Water Chille rs ....... ....... ...... ...... ...... ...... 1 Vapor- Compress ion Water Chille rs ..... ...... ......... ...... 3 Air-Co oled o r Water -Cooled Conde nsing ...... ...... ...... 6 Packag ed or Split Compon ents ........... ...... ...... ...... . 11 Abso rpti on Wa ter Chill er s .......[...]

iii TRG- TRC016-EN[...]

TRG-TR C0 16-EN 1 note s peri od o ne T ypes of Water Chille rs W ater chillers are us ed in a varie ty of air cond itioning and p rocess co oling applicati ons. They c ool water tha t is subse quently trans ported by pump s and pipes . The water passes through the tubes of coils to cool air in a n air conditioni ng system, or it c an provide co ol[...]

2 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs W ater chillers us ing the va por -compress ion refrigeration cycle vary by th e type of compres sor used. Re ciproca ting, scroll, helical-rotary , an d centrifugal compress ors are comm on types of com pressors used in vapor -compression water chillers. Absorption water chillers make u[...]

TRG-TR C0 16-EN 3 peri od one T ypes of Water Chille rs note s V apor -Compression Water Chillers In the vap or-com pression refr igeration c ycle, re frigerant en ters the evap orator in the form of a cool, low-pressu re mixture of liq uid and vapo r ( A ). H eat is transferred from the relativel y-warm air or water to the refrige rant, causing th[...]

4 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs The type of com pressor used generally has the greatest impac t on the efficiency and rel iability of a v apor -compression water ch iller . The improvem ent of compress or designs and the deve lopment of new comp ressor technolog ies have led to more-effi cient and -reliabl e water chil[...]

TRG-TR C0 16-EN 5 peri od one T ypes of Water Chille rs note s These various types of compresso rs are discuss ed in deta il in the Refrigeration Compressors Air Co nditioning Clini c. The capa city of a c entrifugal chil ler can be m odulated usi ng inlet guide vanes (IGV) or a combina tion of IGV and a variable-s peed drive (adjus table-frequency[...]

6 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Air -Cooled or W ater -Cooled Cond ensing The heat e xchangers in the water chiller (the c ondenser and ev aporator) ha ve the seco nd greatest i mpact on chiller efficiency and cost. O ne of the m ost distinctiv e differen ces in chille r heat excha ngers continues to be the type of con[...]

TRG-TR C0 16-EN 7 peri od one T ypes of Water Chille rs note s A major adv antage of usi ng an air -cooled chil ler is the el imination of the c ooling tower . Th is elim inates the conc erns and ma intenance requirement s associated with water treat ment, chiller con denser -tube cleaning, tower mechanic al maintenanc e, freeze protection, an d th[...]

8 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Air -cooled chillers are ofte n selected fo r use in system s that requi re year -round cooling requ irements that c annot be met wi th an airside ec onomizer . Air -cooled condens ers have the a bility to operate in below-free zing weather , and can do so without the problems as sociate[...]

TRG-TR C0 16-EN 9 peri od one T ypes of Water Chille rs note s W ater- cooled chil lers are typical ly more ener gy efficie nt than air -cooled chillers. The refrig erant conden sing tempera ture in an air -cooled chiller is dependen t on the ambient dry-bu lb temperature. The con densing temperatu r e in a water -cooled chiller is dependent o n th[...]

10 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Another adva ntage of an a ir -cooled chil ler is its delivery as a “ package d syste m. ” Reduced de sign time, s implified in stallatio n, higher reliab ility , and single-s ource respons ibility are a ll factors tha t make the f actory pa ckaging o f the conde nser , com pressor [...]

TRG-TR C0 16-EN 11 peri od one T ypes of Water Chille rs note s Packaged o r Split Compon ents W ater- cooled chill ers are rarely ins talled with s eparable com ponents. Air -cooled chillers, however , offer the flexibi lity of sepa rating the com ponents in d ifferent physica l locations . This flexib ility allows the sy stem desi gn engineer to [...]

12 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs An altern ative to the packaged a ir -cooled chiller is to us e a packaged condens ing unit (condens er and compre ssor) locat ed outdoors, with a remote evapor ator barrel loca ted in the ind oor equipment ro om. The two components are co nnected with fie ld-installed refrigerant pipin[...]

TRG-TR C0 16-EN 13 peri od one T ypes of Water Chille rs note s Another p opular configu ration is to use an ou tdoor air -cooled condens er connecte d to a pack aged comp ressor and e vaporator u nit (also ca lled a condens erless chiller) th at is loca ted in the indo or equipment roo m. Again, the co mp onen ts ar e con nec ted with fiel d- inst[...]

14 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs The final c onfiguration in cludes a p ackaged compressor -and-evapora tor unit that is loc ated in an i ndoor equi pment room and connected to an indoor , air -cooled condenser . The air used for cond ensing is ducted from ou tdoors, through t he condenser c oil, and rejec ted either o[...]

TRG-TR C0 16-EN 15 peri od one T ypes of Water Chille rs note s Absorption W ater Chille rs So far , we have d iscusse d water chillers that use the vapor -compressi on refrigeration c ycle. Absorp tion water ch illers are a p roven alt ernative to va por - compress ion chillers . The absorpti on refrigeration c ycle uses hea t energy a s the prima[...]

16 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Absorption water chillers generally ha ve a higher first cost than vapor - compression chillers. Th e cost differenc e is due to the additional heat-transfer tubes requi red in the abs orber and gene rator(s), the s olution heat e xchangers, and the c ost of the abs orbent. This initial[...]

TRG-TR C0 16-EN 17 peri od one T ypes of Water Chille rs note s There ar e three basi c types of a bsorption ch illers. They are typicall y available in capac ities ranging from 1 00 to 1,600 tons [350 to 5,600 kW] . Indirect-fired , single-effect absor ption chillers op erate on low-p ressure steam (ap proximately 1 5 psig [205 kPa]) or medi um-te[...]

18 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Equipm ent Rating Standard s The Air -Conditioning & Refrigeratio n Institute (ARI) estab lishes rating st andards for packag ed HV AC equ ipment. ARI also c ertifies and labels equipment throu gh programs tha t involve rand om testing of a manufactu rer ’ s equipm ent to verify p[...]

TRG-TR C0 16-EN 19 peri od one T ypes of Water Chille rs note s The IPL V predicts chiller ef ficiency at the ARI st andard rating c onditions, us ing weighted- average load curves that represen t a broad ra nge of geograp hic locat ions, buildin g types, an d operating-hour scenarios, both wit h and withou t an airside economizer . The NPL V u ses[...]

20 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs The stand ard rating cond itions used for ARI certification r epresent a pa rticular set of desi gn temperatures and flow rates for wh ich water -cooled and ai r-cool ed systems may be de signed. The y are not suggestions fo r good des ign practice for a given system — the y simply de[...]

TRG-TR C0 16-EN 21 peri od one T ypes of Water Chille rs note s The temper ature d ifference ( ∆ T) through the chiller and t he water flow rate are related. Fo r a give n load, as the flow rate is reduced, the ∆ T inc reases, a nd vice vers a. where, n Q = load , Btu/hr [W] n flow rate = water flow rate thro ugh the chill er , gpm [L/s] n ∆ [...]

22 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs In the exampl e system shown in Figure 25, the ch illed water is cooled from 5 7 ° F [13.9 ° C] to 4 1 ° F [5 ° C] for a 16 ° F [ 8.9 ° C] ∆ T . This reduces the w ater flow rate required from 2.4 g pm/ton [0.043 L/s/kW] to 1.5 gpm/ton [0 .027 L/s/k W]. Reducing w ater flow rate[...]

TRG-TR C0 16-EN 23 peri od one T ypes of Water Chille rs note s ASHRAE/IESNA Standard 90.1 – 1999, Ene rgy Standard for Bu ildings, Exc ept Low-Rise Residential Buildings , went into effec t in October 19 99. ASHRAE is the Ameri can Society of He ating, Refrigerati ng and Air -Conditioning Engineers and IESNA is the Illuminating Engi neering Soci[...]

24 TRG-TRC01 6-EN note s peri od one T ypes of Water Chille rs Note: Adde ndum J updat es the minim um IPL V efficiency re quirements in the standard to match the m ethods included in the most current version of the ARI rating stan dard. At the time this bookle t was printed, Ad dendum J had not bee n formally adopted as part of the standard. H owe[...]

TRG-TR C0 16-EN 25 peri od one T ypes of Water Chille rs note s Another s tandard th at is related to chilled-w ater system s, ASHR AE Standard 15 – 1994 , Safety Code for Mechanical R efrigeration , is intended to specify requirements for safe design , constructio n, installati on, and opera tion of refriger ating syst ems. This standard covers [...]

26 TRG-TRC01 6-EN note s Proper desig n of a chille d-water sys tem can gre atly impact the first cos t, operating c osts, and fl exibility of the HV AC system. The purpo se of this p eriod is to dis cuss the d esign of relia ble chilled -water sys tems. The conv entional chi lled-water system c onsists o f combin ations of the following primary co[...]

TRG-TR C0 16-EN 27 period two Chilled-Water System Design note s This period focuses on the c hilled-water side of the sys tem; that is, the water that flows through the chille r evaporator and out through the load termi nals. Specifica lly , we will re view methods o f load-term inal control a nd various multiple-c hiller system config urations. T[...]

28 TRG-TRC01 6-EN note s period two Chilled-Water System Design Load-T erminal Con trol The purpos e of load-termin al control is to modulate th e flow of air or water through t he coil to ma intain buildin g space comfo rt. This i s accomplish ed by measuring the temper ature of the supply air or sp ace. The te mperature t hen converted to an elec[...]

TRG-TR C0 16-EN 29 period two Chilled-Water System Design note s A three-way control valve is one me thod used to regulate the flo w of chille d water through a cooling c oil. As the space coo ling load decrease s, the modulat ing valve d irects less water through the coil, de creasing its capa city . The exce ss water bypasses the coil an d mixes [...]

30 TRG-TRC01 6-EN note s period two Chilled-Water System Design A two-way mod ulating valve is si milar to a three -way valve in that th e water flow through the coil is modulated prop ortionately to the load. The primary differen ce is that th e two-way val ve does no t bypass any unus ed water , it simply thro ttles the amount o f water passing t[...]

TRG-TR C0 16-EN 31 period two Chilled-Water System Design note s The final m ethod of modul ating the coil capa city to match the cooling load is through t he use of face-a nd-bypass dampers. A li nked set of dampers va ries the amount of air flowing through the coil by div erting the exces s air around the coil. As the coolin g load decre ases, th[...]

32 TRG-TRC01 6-EN note s period two Chilled-Water System Design Properly des igned, operat ed, and maintained, a ny of these three methods ca n result in go od space comfort c ontrol. How ever , they have dif ferent effects on the chille d-water system. The use of three-way v alves or face-a nd-bypass dam pers results in variable return-water te mp[...]

TRG-TR C0 16-EN 33 period two Chilled-Water System Design note s effects. System effec ts include pump–sys tem curve in teraction, dyn amic head variations , and vari ation in dist ribution sy stem flow . There are benefits to maintaining a con stant water flow rate through the ch iller evapor ator . Constan t flow provide s more-stable an d-simp[...]

34 TRG-TRC01 6-EN note s period two Chilled-Water System Design Multiple-c hiller syste ms are m ore common than s ingle-chille r systems for the same reas on that mos t commercia l airplanes h ave more tha n one engine — redundancy provides rel iability . Additional ly, because c ooling load s typically vary wide ly , multiple-chiller s ystems c[...]

TRG-TR C0 16-EN 35 period two Chilled-Water System Design note s Parallel Con figuration Parallel pip ing is one c ommon con figuration o f multiple-chi ller systems . Figure 41 show s a system that us es a single pump to deliv er chilled water both to chillers and to the s ystem load terminals. Th is con figuration can be used in systems tha t use[...]

36 TRG-TRC01 6-EN note s period two Chilled-Water System Design If separate , dedicate d pumps are used with each chiller , a pump-and-chil ler pair can be tu rned on an d off together a s the cooli ng load varies . This so lves the temperature m ixing problem that occurred in the prev ious, single-pu mp configuratio n, but it pre sents a new probl[...]

TRG-TR C0 16-EN 37 period two Chilled-Water System Design note s Figure 43 shows an example of th e pump – sy stem curve relationship. When both pumps are operating, the system receiv es 100 pe rcent of desi gn flow . When only o ne pump is operating, the intersection of the pump ’ s performa nce curve wi th the syste m curve resu lts in about [...]

38 TRG-TRC01 6-EN note s period two Chilled-Water System Design Series Configu ration Another way to connect multiple chi llers is to config ure the chille r evaporators in seri es. Series c hilled-wate r syste ms typicall y use three-w ay valves at the co ils to ensure c onstant syste m flow . With two chillers in series, both the tempera ture mix[...]

TRG-TR C0 16-EN 39 period two Chilled-Water System Design note s T emperature contro l in a series s ystem can be accomplis hed in several w ays, depending on the desire d operatin g sequence. T he first method , shown in Figure 45, has bot h set points adjusted to the desired s ystem su pply-water temperature. Assuming eq ually-sized chillers, eit[...]

40 TRG-TRC01 6-EN note s period two Chilled-Water System Design An alternativ e method of c ontrolling chil lers in series involves staggering the set points of t he two chillers. This res ults in the dow nstream chiller operati ng first and be ing prefere ntially lo aded. Any porti on of the load that the downstrea m chiller ca nnot meet is handle[...]

TRG-TR C0 16-EN 41 period two Chilled-Water System Design note s Primary-Secondary (Decoupled ) Configuration If the wate r flow through th e chillers ( production) co uld be hydrau lically isolated from the water fl ow through the coils (dis tribution), many of the problems e ncountere d in parallel and seri es configura tions could be eliminated [...]

42 TRG-TRC01 6-EN note s period two Chilled-Water System Design The bypas s pipe is common to bo th production a nd distribution loops. The purpos e of the bypa ss pipe is to hydraulic ally decoup le the produc tion (primary) and distribution (secondary) pu mps. Becau se water can fl ow freely between the supply a nd return pipes for both loops , a[...]

TRG-TR C0 16-EN 43 period two Chilled-Water System Design note s The produc tion pumps c irculate wa ter only from the return tee, throug h a chiller , to the su pply tee, an d through the by pass pipe. Thi s represents a relatively-s mall pressure l oss and, th erefore, relative ly-low pump energy . In addition, e ach pump on ly operates whe n its[...]

44 TRG-TRC01 6-EN note s period two Chilled-Water System Design Alternatively , the production lo op can be c onfigured wi th manifolded pumps and automa tic, two-positio n isolation v alves at e ach chille r . When t urning on a chiller , a pump i s turned on an d the isolati on valve is opened. This manifo lded-pump configuration prov ides greate[...]

TRG-TR C0 16-EN 45 period two Chilled-Water System Design note s The distribu tion pump circulat es water from the supply tee, through the load terminals, an d back to the return tee. Althou gh the same water is pumped twi ce by different pumps, there i s no duplic ation of pumpi ng energy . The prod uction pumps ov ercome only the pressure drop th[...]

46 TRG-TRC01 6-EN note s period two Chilled-Water System Design Obvious ly , in order to achieve va riable flo w at the distr ibution pump, the load termina ls must be config ured to vary the sys tem flow . This requires the use of a modulat ing two-wa y control valve for eac h coil. T ypically , no three-w ay valves or wild co ils need to be used [...]

TRG-TR C0 16-EN 47 period two Chilled-Water System Design note s The distribu tion pump is typical ly equipped with a v ariable-speed dri ve that is controlled t o maintain a certain pressure differe nce between th e supply- a nd return-water p iping. In response to a reduced cooling lo ad, the two-w ay valve modulates closed, re stricting the flow[...]

48 TRG-TRC01 6-EN note s period two Chilled-Water System Design Another advanta ge of the primary-sec ondary syste m is that the productio n loop is not affe cted by the distribution pu mping arran gement. For exampl e, multiple di stribution pumps can be u sed to vary the flow wit hin the distribu tion loop. Provi ding variable flow through th e a[...]

TRG-TR C0 16-EN 49 period two Chilled-Water System Design note s A variation o f the multi ple-pump con figuration is to use separate p umps to deliver w ater to spec ific, dedicate d loads. An example is a chilled-w ater system serving a c ollege cam pus. Separate distribution pum ps supply w ater to the east ( A ), west ( B ), a nd central ( C ) [...]

50 TRG-TRC01 6-EN note s period two Chilled-Water System Design In very larg e systems , a primary-se condary -tertiary pumping configura tion is sometime s used. The primary pumps circulate water through th e chillers. The secondary di stribution pumps circu late the wa ter around the di stribution loop . The individu al load terminals are decoup [...]

TRG-TR C0 16-EN 51 period two Chilled-Water System Design note s Let ’ s summarize: When design ed and operated cor rectly , the dist r ibution loo p of the pr imary-se condary system ha s the foll owing chara cteristics : n V ariable water flow . Only the am ount of water th at is a ctually used at the load termina ls is pump e d througho ut the[...]

52 TRG-TRC01 6-EN note s period two Chilled-Water System Design For simplic ity of system control, a ll of the chil lers in a primar y-secondary system sh ould be selected to oper ate with the same leavin g-water temper ature and with the same temperature diff erence ( ∆ T). This allows all ope rating chill ers to be loade d to equ al percentages[...]

TRG-TR C0 16-EN 53 period two Chilled-Water System Design note s Primary-Secondary System O peration W e have seen that the production and distributi on loops of th e primary- secondary s ystem act independently . T he next con sideration is to match the capacity of the produc tion loop to the load of the d istribution loop. The operatio n of a pri[...]

54 TRG-TRC01 6-EN note s period two Chilled-Water System Design If production supply is inadequate to meet the loa d demand, a “ deficit ” of supply w ater exists . T o make up for this d eficit, the di stribution pump will pull water from th e return pip e of the distrib ution loop throug h the bypass p ipe. This is called deficit flow . In th[...]

TRG-TR C0 16-EN 55 period two Chilled-Water System Design note s When the flow of chilled water from the production loop exceeds the dema nd of the distribu tion loop, the direction of flow in the bypass pipe re verses. Chil led water flow s from the su pply side o f the production loop, through the b ypass pipe, and mixes with warm water re turnin[...]

56 TRG-TRC01 6-EN note s period two Chilled-Water System Design Starting and stoppi ng of pump-a nd-chiller p airs in a primary-seconda ry system depends on the dire ction and qu antity of wat er flow in the bypass pipe. n Whenever t here is deficit flow through the bypass pipe for a spe cified period of time (typi cally 15 to 30 minu tes in a comf[...]

TRG-TR C0 16-EN 57 period two Chilled-Water System Design note s The dire ction and qu antity of fl ow in the bypas s pipe may be determined either directl y by using a flo w meter or indi r ectly by sensing tempe ratures. Direct flow measurement can be ac complishe d using a va riety of flow-m eter technolog ies. These include press ure-based flow[...]

58 TRG-TRC01 6-EN note s period two Chilled-Water System Design The adven t of micro processor -based co ntrols has led to another method for determining flow in the b y pass pipe . T emperature sensors are placed in the supply a nd return pipes of the producti on and distrib ution loops, a nd in the bypass pipe. With these temperatures, a chiller [...]

TRG-TR C0 16-EN 59 note s period th ree System V ari ations Period T wo discussed seve ral standard confi gurations of chil led-water systems. In add ition, there ar e many va riations available to reduce installed c osts, enhance the efficiency o f the system, improve re liability , or increa se opera tional flexibility . These va riations are wor[...]

60 TRG-TRC01 6-EN note s period thre e System V ari ations doubled, a nd even triple d, during periods of high dem and in the firs t summer of deregulat ion. Utility deregulati on will occur di fferently in various loc ations, but the pos sibility of h igh electrici ty costs d uring peak periods ha s building owners a nd operators lo oking for ways[...]

TRG-TR C0 16-EN 61 period thre e System V ari ations note s A third method of using an “alte rnate” fu el is actually to use the s ame fuel (electrici ty) but to use it at a differen t time. The highest el ectricity costs occu r at the time of hig hest demand. For ex ample, a real-time -pricing rate for electricity may be $0 .50/kW h at times o[...]

62 TRG-TRC01 6-EN note s period thre e System V ari ations Realize, however , that the chil ler is only on e componen t of the chille d-water system. Although chill er efficiency is important, overall system effi ciency is more importan t because the building o wner pays to ope rate the e ntire system, not just the chiller . Said another way , “T[...]

TRG-TR C0 16-EN 63 period thre e System V ari ations note s ARI. They are not, ho wever , suggestions for good des ign practice for any giv en system—t hey simply define a co mmon rating point to aid c omparisons . T r ends toward im proved humidi ty control and syste m-level ene rgy effici ency have led many desig n engineers to reduce the flow [...]

64 TRG-TRC01 6-EN note s period thre e System V ari ations V ariable-Primary-Flow Systems One of the reasons th at many chi lled-wa ter systems are installed us ing the primary-sec ondary confi guration is that , in the pas t, chillers coul d not resp ond well to v arying water flow through the eva porator . Therefore, the p roduction loop was d es[...]

TRG-TR C0 16-EN 65 period thre e System V ari ations note s Notice also tha t the VPF sys tem must c ontinue to inc lude a bypa ss. Although a control v alve prevents flow in the by pass for mos t system operat ing conditions , the modula ting valve a nd bypass are required to ens ure that the water flow through the s ystem remains a bove the min i[...]

66 TRG-TRC01 6-EN note s period thre e System V ari ations Preferential Load ing T o ta ke fu ll ad vant age of a h igh -ef fic ienc y , he at -rec ove ry o r alte rnat e- fuel ch ille r , the syst em may need a metho d to prefere ntially l oad these c hillers. The following two system configu rations are va riations of the primary-sec ondary syste[...]

TRG-TR C0 16-EN 67 period thre e System V ari ations note s The second prefere ntial-loading con figuration, sho wn in Figure 75, ensures that the ch iller in the sidestream po sition receives the warmest en tering-water tempera ture, and that i t can be fully lo aded whenever the sys tem load is high enough. Th is arrangemen t is unique because it[...]

68 TRG-TRC01 6-EN note s period thre e System V ari ations n In a sys tem with an alternativ e-fuel chille r , such a s an abso rption chi ller , preferentially loading the alternativ e-fuel chiller durin g times of hig h electr ici ty cos ts mini miz es syst em energ y co st. He at Re co ver y Heat recove ry is the proces s of capturing th e heat [...]

TRG-TR C0 16-EN 69 period thre e System V ari ations note s For water -cooled centrifugal chill ers, there are generally three methods of implementi ng heat recov ery . The dual-condens er , or double-bundle, he at-recovery chiller co ntains a second, full-size condens er that is conne cted to a s eparate hot-w ater loop. It is cap able of mor e he[...]

70 TRG-TRC01 6-EN note s period thre e System V ari ations There i s usually an e fficiency p enalty assoc iated with th e use of hea t recove ry with a chiller . The cost of this efficienc y penalty , howeve r , is typically much les s than the en ergy saved by re covering the “ free ” he at. The energy consumptio n of a heat-recovery c hiller[...]

TRG-TR C0 16-EN 71 period thre e System V ari ations note s The control of a heat-rec overy centrifug al chiller , although seemi ngly simple, is critica l to reliable chiller op eration. T y pically , either th e temperature o r the flow of the water entering the standard conden ser is modul ated to meet the capacity required by th e heat-recov er[...]

72 TRG-TRC01 6-EN note s period thre e System V ari ations Asym me tr ic D esi gn Many sy stem desig n engineers seem to default to us ing chillers of e qual capacity in a multiple -chiller system. Th ere are benefit s to using c hillers of vary ing c apa cit ies to mor e f avor ab ly mat ch t he syste m lo ads . Reme mb er th at when a c hiller is[...]

TRG-TR C0 16-EN 73 period thre e System V ari ations note s Another b enefit of unequ al chiller c apacities is that the s ystem load can be more clos ely matched w ith the operatin g chiller (and ancillary e quipment) capacity , increasing ov erall sy stem e fficienc y . Figure 81 s hows a sys tem that includes two l arge chillers of equal ca paci[...]

74 TRG-TRC01 6-EN note s period thre e System V ari ations The smal ler swing chille r is turned on to handle the low cooling loads eithe r during the ni ght or during unoccupie d periods of ti me. When the b uilding l oad exceeds the capacity of the swing c hiller , it is turned off and a larger chille r is turned on. Th e larger chill er handles [...]

TRG-TR C0 16-EN 75 period thre e System V ari ations note s “Free” Coolin g There ar e a number of methods that use cool o utdoor con ditions to redu ce cooling energy cos ts. They are often referred to a s “ free cool ing ” because t hey reduce or eli m inate the ene rgy consume d by the comp ressor . They are not truly free, but real ly r[...]

76 TRG-TRC01 6-EN note s period thre e System V ari ations A second type of waterside economizer is the plate-and-fram e heat exchanger . In this case, w ater from the coolin g tower is kept separate from the chille d-water loop b y a plate-an d-frame heat e xchanger . This is a p opular configuratio n because it can ac hieve a hi gh heat-transfer [...]

TRG-TR C0 16-EN 77 period thre e System V ari ations note s The final me thod of “ free ” coo ling is to transfe r heat betwee n the cooling tower water and the chilled water inside a centri fugal chille r through the us e of refrigerant migration . When the tempera ture of the water from the cooling tower is cold er than the des ired chille d-[...]

78 TRG-TRC01 6-EN note s period thre e System V ari ations Application Outside the Operating Range of th e Chiller Some pro cess-load app lications i nvolve eithe r temperatu res or flow r ates that are outside the capab ilities of any chiller . This may includ e high return-w ater temperatures , high or low fluid flow rate s, or high or lo w syste[...]

TRG-TR C0 16-EN 79 note s peri od f our Chiller -Plant Control It is importa nt to understa nd that no matter how go od the system design is, adequate controls are n ecessary for all the co mponents to opera te properly as a syste m. It is equa lly impo rtant to understa nd that you c annot “cont rol your way out o f a bad sys tem design .” The[...]

80 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control The larges t change to chillers in t he last dec ade has un doubtedly be en in the area of co ntrols. In the past, chille rs were pneu matically contro lled, and they were protec ted by turning them off if the flow rates or t emperatures c hanged too qui ckly . T oday’ s microp rocessor[...]

TRG-TR C0 16-EN 81 peri od four Chiller -Plant Control note s There ar e primarily five issues to ad dress in a chiller -plant control system. 1 When shou ld a chiller b e turned on or o ff? 2 After we kn ow that a chiller must be turned on or off, which one should it be? 3 If we atte mpt to turn on a chiller , pump, o r cooling tow er , and there [...]

82 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control Chiller Sequ encing Chiller seq uencing refers to m aking dec isions about w hen to turn ch illers on and off, and in what order . T y pically , turning chill ers on and of f is performed with the goal of matching the ca pacity of the ch iller plant to the syst em cooling load. In orde r [...]

TRG-TR C0 16-EN 83 peri od four Chiller -Plant Control note s T oday’ s ch iller con trols can ve ry accuratel y control the chiller’ s l eaving-wate r temperatures over a wide range of loa ds. This is especially tru e of centrifuga l and helica l-rotary chillers. This fact allo ws constant-flow chi lled-water system s, similar to th e system s[...]

84 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control In a prim ary-secondary system , the direction an d quantity of flow in the bypass pipe is an excelle nt indicator of when to turn a chiller on or off . As discu ssed in Period T wo, the wa ter flow in the bypass pi pe can be mea sured directly using a flow meter , or indi r ectly by meas[...]

TRG-TR C0 16-EN 85 peri od four Chiller -Plant Control note s Another method of monito ring system cooling load is to meas ure the system water flow rate and temperatures directly , and then c alculate the load. Alth ough it would appe ar that direct me asurement of the ac tual system load would be an excelle nt way to de termine when to turn chill[...]

86 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control When the s ystem has determined tha t a chiller needs to be turned on or off, the next issue is to determi ne the se quence in which to turn c hillers on and off. It is ass umed that the first chiller in the sequenc e will always be turned on wheneve r cooling is required. When the s yste[...]

TRG-TR C0 16-EN 87 peri od four Chiller -Plant Control note s When the s ystem consis ts of chille rs with differe nt capaciti es, efficienci es, or fuel types , the questi on of which chiller to turn o n or off next becomes more complex. Although e ach syste m requires a comple te analysis , there are some general princ iples that apply to mos t s[...]

88 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control The sys tem might al so benefit fro m having a heat-reco very chille r fully loa ded. As discuss ed in Period Three, to maximize the amount of heat recov ered, it is often d esirable to p referentiall y load that c hiller , se quencing it a s a base chiller —“ first on ” and “ las[...]

TRG-TR C0 16-EN 89 peri od four Chiller -Plant Control note s The variab le-primary-flow system , introduced i n Period Three, is designe d to operate wi th variabl e flow through the chiller evaporators. Seq uencing ch illers in this typ e of syste m cannot be based sole ly on tempe rature, becaus e in a properly -operating system the supply- and [...]

90 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control Failure Recove ry and Contingency Pl anning In addition to normal chiller sequ encing, the chiller -plant control sy stem mu st react whe n a chiller o r another pi ece of ass ociated equipm ent fails. F ailure recovery , or ensurin g the reliable supply of c hilled water , is a very impo[...]

TRG-TR C0 16-EN 91 peri od four Chiller -Plant Control note s In addition to failure recovery , it is w ise for the sys tem design engineer to work with the building owner to dev elop a contin gency plan for chilled wate r in the ca se of an emergency shutdown or a n exten ded breakdown. Many organizati ons have conti ngency plan s for critica l ar[...]

92 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control System T uning In addition to turning chillers on a nd off, there are other function s of the chi ller- plant cont rol system th at help pre vent system fl ow instability from dis rupting chiller ope ration. Flow instability c an often be caused by normal valve and pump oper ation. The f [...]

TRG-TR C0 16-EN 93 peri od four Chiller -Plant Control note s chiller safeties must be capable of shut ting the chiller down to avoi d equipment damage. The next c ontrol function is to partiall y unload the operating chi llers before an addition al chiller an d pump a re turned on. Dep ending on the system configuratio n, there can be very rapid v[...]

94 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control Another control function that is desirabl e is called soft loading . It is typically used wh en the sys tem has bee n off for an ex tended period of time and the chilled-w ater temperature is the sam e as the ambie nt temperature in side the building. Soft loa ding either del ays turning [...]

TRG-TR C0 16-EN 95 peri od four Chiller -Plant Control note s Constant-flow c hilled-wate r systems freque ntly require ind ividual chil ler set- point control . Its purpose is to help m aintain the s ystem sup ply-water temperature b y compensating for the bypas s of return wa ter through non-operating chille rs. The chill er -plant control system[...]

96 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control System Optimi zation The chill er -plant control syst em can al so be used for system optimization . For the purpos es of this discussion, we will de fine optimiz ation as min imizing the energy used by the chiller p lant (includi ng chillers, chilled -water pumps , condens er -water pu m[...]

TRG-TR C0 16-EN 97 peri od four Chiller -Plant Control note s As prev iously sta ted, as the c hilled-wate r temperatu re set point i s reset upward s, the chil ler will use les s energy . In c onstant-flow systems, this chilled-water reset strategy is fairly simple to implement and ca n be controlled b ased on the drop in return-water te mperature[...]

98 TRG-TRC01 6-EN note s peri od four Chiller -Plant Control Low erin g the tem per atu re of the c ond ens er wate r can als o red uce the ener gy consump tion of the ch iller . Depending o n the syste m load and o utdoor conditions , cooling towers typically ha ve the a bility to supply co lder condenser water than at desi gn conditions. T his, h[...]

TRG-TR C0 16-EN 99 peri od four Chiller -Plant Control note s Related to th e issue o f condenser -water -temperature control is the control of condens ing pressure. Every chille r requires a m inimum refrigerant -pressure difference between the evaporator an d the conden ser , in orde r to ensure that refrigeran t and oil circulat e properly insid[...]

100 TRG-TRC016-EN note s peri od four Chiller -Plant Control Operator Interface System-lev el communi cation and c ontrol is ve ry important. T oday , the amoun t of commun ication between the components (chillers, c ooling towe rs, pumps, control val ves, and s o forth) has increase d immensel y , allowing man y chilled- wate r system s to be full[...]

TRG-TR C0 16-EN 101 peri od four Chiller -Plant Control note s There is a n amazing amount of inform ation available with in a chilled -water system. Often the prob lem is not a lack of informati on, but ho w to interpret that inf ormation. T herefore, a clear and c oncise in terface b etween the control system and the syst em operator is extreme l[...]

102 TRG-TRC016-EN note s peri od four Chiller -Plant Control ASHRAE Guideline 3, Reduci ng Emission of Haloge nated Refrigeran ts in Refrigerat ion and Air Condit ioning Equipme nt and Syste ms , includes a list of recommend ed data point s to be logged daily for each chi ller . Much of thi s data may be av ailable from the disp lay on the c hiller[...]

TRG-TR C0 16-EN 103 note s W e will now review the main conc epts that w ere covered in thi s clinic o n chilled-w ater systems. In Period O ne, we lea rned abou t the different ty pes of vap or-c ompressio n and absorp tion water c hillers. V apo r- compress ion chillers are differentia ted primarily by the type of compressor us ed and whe ther th[...]

104 TRG-TRC016-EN note s period five Review ARI Standard s 550/590 and 56 0 are common industry sta ndards used for rating water chi ller performance . ASHRAE/IESNA Stand ard 90.1–1999, the energy standard, c ontains min imum full-load and part-load chiller efficiency requirements , as well as requirements for the design and operation of chilled-[...]

TRG-TR C0 16-EN 105 period five Review note s Period Three revie wed severa l variations in the desig n of chilled- water system s. These varia tions may allow the system design engineer to provid e added value to the build ing owner and operator in the areas of imp roved relia bility , greater flexibility , redu ced instal led costs, and lower op [...]

106 TRG-TRC016-EN note s period five Review Period Four d iscusse d the issues re lated to chil ler -plant control, includi ng chiller sequenc ing, failure reco very , contingency planning , system tuning, and sy stem- level optim ization. Remember tha t you canno t “control you r way ou t of” a poor s ystem des ign. Although the control system[...]

TRG-TR C0 16-EN 107 period five Review note s For more information , refer to the following re ferences: n Multipl e-Chiller -System Design and Control Applicat ions Engi neering M anual (T rane literature o rder numbe r SYS-APM001-EN) n Refrige ration Cyc le Air Condi tioning Cli nic (T rane literatu re order nu mber TRG-TRC003-EN) n Refrige ratio[...]

108 TRG-TRC016-EN Questions for Period 1 1 What are the four types of c ompressors commo nly used in vapor- compress ion water chillers? 2 List o ne advantag e of an ai r -cooled chiller a nd one adva ntage of a water -cooled chiller . 3 T r ue or False: T he IPL V equation i ncluded in th e ARI standards for rating chillers w as derived to p rovid[...]

TRG-TR C0 16-EN 109 Quiz Questions for Period 3 9 Why does a variable-primar y-flow (VPF) s ystem requ ire a bypa ss in the syst em? 10 Identify one scenario where pre ferential l oading is beneficia l to a chilled-w ater system. 11 What is the benefit of us ing a smal ler -capacity “swing ” chiller in a multipl e-chiller syste m? Questions for[...]

110 TRG-TRC016-EN 1 Centrifugal, h elical-rotary , reci procating, an d scroll 2 Air -cooled chille r advantages include lo wer maintena nce costs , a pre- package d system for easier des ign and ins tallation, an d better low-a mbient operatio n. W a ter -cooled chiller advantages include grea ter energy e fficiency (at least at design c onditions[...]

TRG-TR C0 16-EN 111 Answers 12 Sequencin g 13 Decr eases; i ncreases 14 Fouling ins ide the tube s of the condenser , possibly ind icating a problem with water treat ment in th e cooling tower[...]

112 TRG-TRC016-EN absor be nt A substance use d to absorb refri gerant and transport it from the low-pressure t o the high-pressure si de of the abs orption refrigeratio n cycle. In absorptio n water chi llers, the absorbe nt is commonly lithium bromide. absor be r A component of the absorpt ion refrigeration c ycle in whic h refrigeran t vapor is [...]

TRG-TR C0 16-EN 113 Glossary chilled-w ater system Uses water as the c ooling media. The refrigerant insi de the evapo rator absorbs h eat from the w ater , and thi s water is pump ed to coils in order to ab sorb hea t from the air us ed for space conditionin g. coefficient of p erformance (COP) A dimension less ratio us ed to express the efficienc[...]

114 TRG-TRC016-EN Glossary expansio n tank A compo nent of a clo sed piping system tha t accommod ates the e xpa nsi on and con tra ctio n of the wa te r as te mp erat ure a nd, t her efo re, density , change s. fouling Minerals in the wate r that form scaling on the internal surface s of the heat exc hanger tubes . generator A co mponent of the ab[...]

TRG-TR C0 16-EN 115 Glossary note s swing chille r A smaller -capaci ty chiller used i n a multiple-chiller s ystem. It is altern ated on and o ff between th e larger chill ers' operation to serve as a smalle r , incre mental step of loadin g. variable-prim ary-flow (VPF) sys tem A type of chille d-water system that is designed to vary the flo[...]

The T ran e Compa ny An American Standard C ompany www .trane.com For mo re info rmatio n conta ct your local distict office or e-mail us at comfort@tran e.com Literature Or der Number TRG-TRC 016-EN File Number E/A V -FND-TRG-T RC016-0201-E N Supe rsedes CWS-CLC -1, CWS- CLC-2, CWS-CLC- 3, and CWS-CLC- 4 Stocking Location La Crosse Since T he T ra[...]