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THETECHNOLOCY KEEPS IMPROVINC

Supermarkets exPerience utn dramaticenerg!sauings incorporating f (LPA)'" and suppression. the latestin liquid presureamplifcation

B Y J O H N T O M C Z Y K prcssurcs tcnrpcratufes, densilrg and This lypc of subcooling, oflcn callcd has bccn pracanbient subcooling. liccd lor ycars and has alwals bccn thoughtof as a "ffec nrcthodolsubcooling.This is simpl) not the casc. Arnbinrsubcoolins usuallyaccomis plishedat rhc cost ol incrcascd hcad pressures. hasbccnuscdin rcliigcr' It ation systcms a liquid scal in lhc as condensef bo(on and to pfcvcnt liqu;d linc flash gas.by kccp;Dg solid a colunrn olliquid supplicd thc mctcrto ing dcvicc. Ambicnr subcoolingcannot bc maintained a givcn levcl wilh air at presside controlsonly. Condensing surcs difectlyrelated the teDrpcrare to aturcof {hecondenser coolingmediuDr and the usefulcondDsing in thc arca condenser. Useful.ol cffcctivc,condensingarea is thc lotal condcnsing aleamiius lhc arcauscdfor dcsupcr hcating and thc arcauscdfor subcooling. In othcrwods, the fomula is: Total condenser area - Condenser usedfor area desuperheating subcooling and = Usfulor effeclive condensing area Themoredesuperheating liquid and subcooiing that ;s done by the con' densel,the lessusefulcondenscr arca therevill be. This wiu misc condcnsing pressurcs ralios and compression with highel and causeinefticiencies

This Liquid prssure amplilicalion the boltonl of the coDderrser. sen' ( LPA)rt!technolosy boosted ig- sibleheal rcduclionwill prevenlllashhas refr efalion syslenlcapacilywhile saving ing lrom liquid lirrepressurc drops. The duwbackto thh nrclhod rhal is eleot cal encrgy. liquidon thc bollon will UsingLPA, liquid rcffigerant entcr- thc subcoolcd inglhe liquidlincis prcssuizcd a lakcup valuablc wilh condcnscf volunrc. This pump (Figurcl). Thc will causehishcr hcad prcssurcs and smallccntdlugal mtios, rrsulling in lower amolnt is cqual to thc prcssurcloss comprcssion thc outlcl and thc cfficicncies. we consider ll onlythc subberwccn condcnser TXV inlct on rcccivcrlcss slstems, or coolingol thc liquid without rcgardto and thc recciver thc TXV inlct on TXV and rcceivcrsystcms. LPA syslem Thc is shownin Figurc2, alongwith a normal system, FigurcL By incrcasing prcssurc thc liqthc of uid reiiigeranl.the associalcd saturation lempcralufcis raiscdbccausc ol whilc thc actual the pressure incrcasc, liquid tempcmturcfcmainsthc samc. subcooled will The liqu;dbccomes and not llash if exposed prcssurc to drcps in the liquid line. pumpmotoris Theliquidcenlrifugal extemaltothe refrigemlion syslem, and the impellris drivn by a revolving it magnetic field.The nolor addsnegligi- F I G U R E 1 : A s m a l l c e nu g ap l m p p r 6 s . liqu rfgenlenronng d $e pfes' surizs @uttosy ol Hy Saw,lnc.,lquidIn. bleenergtandheatlo the syslem, (A ligutas [email protected] surizing liquid.Because the drereis no drive shaft protrudingfrom thc moror is condenser surface aLea, we throughrhepumpcasing, systcm decrcasing rhc Thc for completely sealed. LPA ccntifugal will seea sain of lolo of capacity pump can increasc pressure the very thc of d$eeof liquidsubcoolins. liquidby approximarelyto 20 psi. 8 In addition, of ambient 7'F subcool' (bhp) ing cosls.167brakehorsepower per lon because elevated AMBIENT SUBCOOLING of headpres' Subcoolins exists in any liquid sures, However,if we considerthe belowits saturation tmperalure a rcductionof condenser for surlaceareadue given pressure. One nethod of sub- to the liquid subcool;ng, ihereis a net concoolingis to sensibly cool the liquid in lossin capacity due to increased

T r c H N o L o c Y K E E P s l M P R o v r N c

ALTERNATE METHOD of rh highrspecific volOF SUBCOOLING une of the flashed vapo$. A nofe efficient vay lo subcool 1iq- The TXV will bsin to uid is to increase prtssurcof the hunt, stawe the evapomthe liquid without nis;ng dre lemperature. rol. ano systemcapacrty This will causcthc liquid to be at a highcrprcssurc, with a highcrassociat ed satumtion tcmpcraturcihowcvcr', AN EXAMPLE theactualtmperaturc willnot changc. Consider the ourvefor This liquid is subcoolcd an amount an I ICFC refiigerart in equal lo the diifrcncebetwcenthc (Figurc5)- As the prcssure associated saturation tempefaturc, and in thc liquid line drops, the aclual tempemturlr the liquid. morc liquid will flashinlo of Liquidis now belowits satumtion tem- vapor to cool thc rcmainpemturcfor that new pressure. ingliquidto thcsatumtion lly iDcreasing pressure lhe lemperaturc,corrcspondthe oi liquid to overcome pres- ing to the progressivcly subcooled aDy surclosses occur;lr liquidlinc, that rhc prcssufcs be allowed condcnsing can to With an 8 psi prssulc prcssurcs. drop, the llash sas. by lalllo thcir lowcsr allainable Anothcr tcrm fof allainingthc lowcsl weighl,will be 27o wilh a TXV possiblc hcad prcssurc ,4o(ri?g//r? I 00'F condeDsiDg is lenlpcmhead prcssutc.Condcnsingtcmpcra- ture(214psig). vapor FIGUBE 2: ThoLPAsyslem. The lurcs ot 20"F arc not uncomnon in bubblcsin thc liquid hrc Iowtempcraturc systcDrs incorpor"ling will bccome conrpfcsscd liquidprcssurc alnplilicarion. and occupyonly 20./. of llowcvcr. ny lo lloat thc hcadprcs- thc voluDrcin thc liquid surc wilh thc aDrbicnl, and thc lowcr linc. llowcvcr',fcduccthc hcad prcssurcs rcquirc nrorcsub- prcssurc 97 psig(501'F), will ro prcssurc lor coolirrg thc sanrc dropsil] and thc llashins vaporwill thc liquid linc to prcvcnlllashing. This occupyi8% of thc liquid phcnonrcnon fcflcclslhc prcssura/lcDr- line volunre. This vapol pcralurcgraphof rufuigcmnls which is will rcducc thc flow nonlincal it is Druch flaltcr al thc thfough lhc cxpansion lowcr prcssurcs. This nrcansthat thc valvc,havc littlc rcirigel?samcaDrountof liquid subcooling is tion cffcot,and nccd1()bc pfcssufc rccomprcsscd nccded ovcrconre snraller to a aftcr doing drop al thcsclowcf pfcssures lenr- work.Again, and systcncapac, (figurc4). pcmtures ily will sulfcr,thc cvapon, This is onc oi rhe fcasons why LPA tor will stawc, and thc is incorporatcd thc sysrcnwhenlhe TXV will beginto hunt. in hcadprcssufc floatedwirh rheaDrbi' is This is the primary cnt. lt subcools Uqu;d incrcasing valueol the LPA sysle thc by its prssurc and forccs thc liquid to to ensure solid liquid to TXV have a new higher associatcd satura, thc TXV, so drc TXV can lion lemperalurc. Thus, flash gas is supply adequate liquid 10 FIGIJRE 3: A normal syst6m wilhoutLPA. prcventedwhen head prcssurcsafc allowedto float. because LPA ensurcs reached, would only last for a fcw it (andasso- A BETTER WAY thal the liquid Iin pressure hourc.The selection thc condcnscr of ciated saturalion temperaturc)is TO DESIGN A SYSTEM was usuallymade.howevr, bascdon alwayshigher than the aclual liquid In the past, air conditioning and thisseldom-rcached condition. pickcdan rcldgeration system designcrs l\4anyyearsago when energywas Whcn hcadprcssurcis reduced!4i1h: outdoordesign condition thesystcnr. nruohcheaper, for desisners would selecr tlre This outdoordesign condirion typically condensiDg lenrpemlufesat 20' lo e$ LPA, thc liquid experiences sameprssurc drop throughthe liquid was a lemperatur would not bc lo"F above ambienl. that lhe Thiswasdone line as it did at thc highcrcondensing reached morethan2% of the time bccause was droughlthe higherconany it pressuLes. flash gas will occupy dutingdt lifeofthe system. The And.when densing tcmperatures and pressures morevolumin the liquid line because the design condition wouldactually be would enhanccthe flow through the

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and lower efficiency. Today, however, part inefficiency an unacceptable ofa is company'soverhead.LPA allows a lower head pressure and reduced powerconsumption alongwith higher With this new knowl- efficiencies. pressures The advantages an LPA system edge, condensing of ano temperatures were include: . Elimination liquid line flashing allowed Io "floaC' downof ward with rhe ambienr by overcoming prcssure line lossesi . Reduction in energy costs, tempemture, In fact, a majority of the outdoor because pumpingliquid refrigemntis Iemperatures the USA up to 40 times more efficient than in are below70"Fmosl of the usingheadpressure from the comprestime. The compressor sor to do lhe same worki . Increesed capacity increasesabout evapomtor capaoity along 6a/olor eyety lo"F drop in with the nel refrigeration effect;and . Lower compressionratios and conoensrnS rempemture. pressure less strcsson comprcssols, However, meaning dropsacross cxpansion longercompressor the life. valve of less than 30 psi Like it or not, rhe daysof the lixed should be avoided for elevated headpressurcs fading.No are proper evaporator feeding longer consumers are willingto payfor of liquid. For an evapola- inefficiencies. Today\ customers arc tof to operate Peakeffi- lookingat life cyclecosls(equipment al crency,|l musr operale costsplus the operational coslsfor the with as high a percenlage life of the equipment). of liquid to vapor ratio as possible entering evap- SUPERHEAT SUPPRESSION thc orator.To accomplish this, Superhal suppression be used can the expansion valve must in conjuncrionwith liquid pressufe allow liquid relrigerantto amplificarion. The supcrhear suppresenterth evaporalor ttre sion process al injectsliquid refdgerant same rate that it evapo- inlo lhe conrpressort discharge or linc (Figure6). This inlet of the condenser Wilh an LPA pump, liquidusuallycomes thesame from censubcooling liquid was supplied to them. The balancedport TXV designtoday is noted for its low-pressure drop

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FIGURE 4: [email protected] cuoe.

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prossJr FIGURE 5: Eri6ds condensng gas ol 01,asr"

metedng dcviceto outweigh ineffi- can be maintaincd lhe any al cienciesfrom the high compression metering device. Overralios. This would force condensing feedingand underfeeding 6 te'nperaturesand prcssureshigher, by the expansionvalve, causinghigh compression ratios,and which dramatically afect the efficiency the evapof Wilh (odayt escalating eneryy costs, orator,will be minimized. designers are spcifyinglarger con" Historically, high head densers with condensing temperatures pressuresand tempeml0'to | 5"Fabove ambient. sig- tures were artilicially the The nificant energysavings from lower com- maintained a refrigerain pnssion ratiosand possibly increased tion system,so it would subcooling liquid negates higher function well at low ou! of the costs the larger of condenser, door temperatules. These higher pressures were METERING DEVICES considercdnecessaryin After muchrsearch, metering valve order for the TXV to feed suppliers foundthatTXVSwouldwork theevaporator adequately. TXV with a much lower pressuredrop than This resuhed in a large - as long as pure consumption of energy FIGURE 6: Sysrem LPAandslpoihgal expectedin the past wth supprssion.

T E c H N o L o c y K E E P s l M P R o v t N c

trifugalpurnpusedin the LPA prccess. ent subcooling; The air is said to bc less denseper . HiCher overall condenserheat cubic fbot, or have a higher specilic The liquid flashes a vaporwhile to coolingthe superheated gas ttanslerbecause the increased discharge of liq- volume.The tick is to reheatthe air closer its condensing to temperature. uid/vapor mixture heat transferand efficiently to an acceptable As delivery a result, Iesssurfaceis requiredfor increased effectivecondensing area; Ievel with the proper amount of desupefteating. leaves moreeffi- and This a warmth and relative humidity. . Lessfoulingof evaporative cientondenser because ofthe increase con- Accomplishing bo(hof these funcrions in uselul condensing sudacearea.A denserpiping bause the reduced greatly of enhances desircd the opralion. more efficientcondenser increases the heat intensityof dkchargeand conFigure 7 shovs a system that ovemll performanceof the system. densrng gases, reheats air beingdischarged the the by Savings fiom 6010 l27o can be real, to evapomtortair handler. The air actuizedwith superheat supprcssion. SUBCOOLING/HEHEAT COIL ally coms conlactwith a liquidsubin Superheatsuppressionprccesses In an air conditioning system, thc coolingcoilconnected the discharge to have been used in large ammonia evaporator removes moisture fr.omthe of an LPA pump.The liquid subcoolplantsior yearsihowever, pr.ocess air. ThereioLe. would seemr.eason- ing coil is locateddownstream rhe the it of was nol generally feasible smallel ablethat if the tficiency the evapo- liquid receiver. liquid line is modon of The systems. This spurredthe useof LPA fatot werc increascd, more moisture ified to allov liquid ilow throughthis and superhat suppression the samc couldbe removed. appafatus in Thc dew- custom coil and then to the air (ADP) is acrrially conditioning system. smallportionof the pressur- point lenrperatur A direct expansion coil. ized liquid rcffigcnnt providedby the lowered,which increases cooling Rememberthat liquid line prcssure lhe LPA'S centifugal pump can be divert- coils moisture removalability. air is dfop is not a rcal concernwhcn an As ed to the cornprcssor's discharge line passcdthlough an air conditioner's LPA pump is employed. The subcoolto cool the supcrhcatcd vapors coming evapomtor,it reaches dewpoinl and ing /reheat coil can be cuslom buill from the conrpressor. Reduced supeF condnscs a liquid. The liquid is and only employs into one pass with aboul heatof the gasenrering condenser thn removcd as condensate. thc This 4 fins per in., so lan powerdoesnol mcans higher condenscrcfficiency, process callcddehumidification. (Figure8). is haveto be increased lower condensingtemperaturc.and Another pa of the condilioning Depending thc size of the coil, on greatcr compressor efficicncy, process rheating air as it conrs th liquid can be subcoolcd wilhin is the to Allhoughsomecfficiency gainswill be out of the evapo'ator, causing air 8"F of the air temperarurc the lcavingthe seen low ambients, greatest at gain to bccomewarmr' the and expand.This evaportor. Wirh 60'F leaving tcm, air with superhcat suppression rcalized warmer.expanded now has nrore pemture. lhe liquid should bc sub, is ai' at the higherambienttempemlu'.es. abilityto holdmoislu'e and thuswill coold to approximately 68'F. Thc One ol the lessobviousadvantages havea lowcr rclalivehumidity(o/o fh). moresubcooling thereis,lhe closer the of superhcal suppfcssion throughliquid injectionis lessfoulingofevapom, live condenser coilson the watcr side. As the discharge condensing and Ienrpcmturcs decreas, abilityol warer the to hold minerals solutionincfeases. in Because lhis quality,wateris saidlo of have rcveNe solubility. Evapomtivc condenser coilsremainolean and scale tie becauseol the decrcased heat intensityfrom superhcat supprssion. This leads less 1o chemical trearment in mostapplications. The nain advantages suppression of ol cooljngof superheated vaporcin a rclrigcration system are: . Reductionin the heat intensity (temperature) superheated of vapor; pressuLe and volume of (hesesuperheated vapors will decreasei . Fastersaturation superhated of vapors. rsulting quicker in condensingi I . CondensinC the vapors will I of I occur closerto the inlct of the condenser, resullingin lower condensing tempemtures possibly and moreambi- FIGURE 7: [email protected] theairbei.q discharsed bylhe evaporator's airhandef.

T E c H N o L o c Y K E r P s l M P R o v t N c

tioningequipmen(. ActualLPA installalions haveprcven energy savings asmuchas I 5olo energy of of used. High hurnidity supermarkets in causes excessive frost on evaporator coilsin the refr;geration cases. This frosl buildupredrceshcat h'ansfeland the effic;ency lhe of system. only doesthc frcst buildupconsume Not ene,' gy,it takes energy getrid of the frcst by longer to defrost periods. Whenused conjunction in with a dcwpoint con troller, mullion heaterloadscan be reduced with lowered relative humidity in the supermarket. Mullion heaterssimply keep the su'facesof lhe ref gcration casesabove dewpoint so condensate will not folm. (onrrol been Fquipm(nt lhi. n)oisrure lor ha' expensi!c to buy and to mainlain,bur this systenwill reducethc cncrgy lsageon both the air conditioning rcfrigeraand

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Oneol thc keybcnefits is oflhis system the useol the internalnerg] of thc systemlo acconrplish feheating liquid tempefature comesto lhe evaporating lemperaturc. the air. No extemalheat,ncithcrgasnor liquid, is usedfo| This increases net rcfrigeralion the effeot(NRE). reheat. Subcooling alsoaccomplishcd is without any cxtcrThis subcooling allowsliquid in drecoil to be furlher nal energy coil source. subcoolcd the coldcfair beingdischaryed the evapoby by mtort ai' handler. whilc at the sametime p''oviding reheat SUMMARY to lhe flir leaving vapomtor. the Thus,the pefcent Wirh the rapid transi(ion al(ernalivc gemnrs rclative lo rcf and hunidity (o/o of the discharged is lowercd, liquid escalating rh) aif thc energy cosrsfacinglhe rcfligeration and air conin lhe subcooling is beingsubcooled coil iurther.andthc aif ditioningindustrytoday,nore atrentionis being paid lo is beingreheated an acceptable to levelior the occupants. opcrting costsand system efficiencies. Ina(enlion to sysThe subcooling/reheat can subcoollhe reliigefanl lern prcssurs coil and thc amount of liquid subcooling can entering coolingcoil by as muchas 50oF, the resulting a make syslems ;n vcry incfficicnl, Ilccause this, it is vcry of 5070 increase evaporator in capacity, This can allow the important lhal evcry cnginccr and/or lcchnicianundcrevaporator wring out up to 75olo lo mofe moisture lionl the sknds the p nciplesbchind subcooling and sys(cmprcsair. A lowerrelativehumidityof dischafge is thenexpe- surcs. today's air In compctitivc scrvice nrarkct, who canafford rienced This abates build- nol to payaltnlionlo system throughthe ductworksystem. the cfficincics? Es ing of airbomemoldsand bacteria that causcthc undesirable"sick buildinssyndro'ne." 'lbilcrykiNaptolcslat htat ut Iinis stutc ol Uritusit!, ltis taurkls. SUPEFMARKET SAVINGS Lll. a4l is authotoJllk book. tioublcNltaotnryaidsfl,ititry Malcnt Reducing humidityin suprrnarkets rcducethe An Co litioritry ar.l Rchsctario, Srs/cra." ,rrbliyrc./ b) ,!at'?sr the will latentheatloadson the sbre's reliiserarion and air condi- Nc\rsPublishii( Ca. Ib oalq. call I-t'1N.857-1057, FIGUBE A: The subcoolino/rheat b6c!$om coilcan blil.

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. . Reprinted from Ergireereal Systems Ma9azineP.O. Box4270. Troy,MI 48099 Copyright1997

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