The analysis of the adsorption cooling subsystem used in a MCCHP system with Stirling engine like prime mover

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1 The nlysis of the sorption ooling susystem use in MCCHP system with Stirling engine like prime mover V. Pop, C. Pop, A. Şern, L. Costiu Astrt The pper presents n nlysis of the ooling susystem use in trigenertion system with Stirling engine like prime mover. The vntges n isvntges of the sorption ooling re presente, relte to sorption ooling system. The shemti therml igrm of the trigenertion system is presente. Beuse the low effiieny of the Stirling engine, thermlly tivte ooling susystem is use. A theoretil thermoynmi nlysis of the sorption ooling system is presente. The influene of the operting onitions on performne of the sorption ooling is presente. Keywors thermlly tivte hiller, sorption ooling, Stirling engine, trigenertion, thermoynmi nlysis T I. INTRODUCTION RIGENERATION n e onsiere s speil se of the pplition of ogenertion systems where frtion of the shft work or resiul het is use for running refrigertion system. Although the si theories n tehnologies for the power genertion, het exhnge, n sorption refrigertion re not new, omining them together is quite new ie. The onept of trigenertion omes to use is only t the mi-1990s. Some investigtions hve een onute y numer of reserhers, whih showe n enourging effet on rising the energy effiieny n reuing greenhouse gses emissions. The results from the investigtions show tht trigenertion hve the vntges over single eletriity genertions n ogenertions (Comine het n power): the totl energy effiieny is higher; the emissions of CO 2 n the other wste gses re lower; n it hs more hoies for useful energy outputs, i.e., eletriity, het n ooling/refrigertion. The results show tht trigenertion hs oth of the eonomi n environmentl merits. Trigenertion systems ten to eome goo solution for energeti nees for uiling, espeilly if the generl gri is iffiult to e ese. In our university projet for guest house with trigenertion system is evelope. The prime mover is Stirling engine with pellets. Beuse the eletil efiieny of Stirling engine with soli fuels is very low (out 20 %), we eie to use thermlly tivte hiller like ooling system. Mximum therml los of the uiling re lulte. All the omponents system re omerilly ville. II. TRIGENERATION SYSTEM PRESENTATION In figure 1 shemti igrm of the system is presente. The pper refers only to therml los. The Stirling engine n the entrl heting oiler re tivte y pellets urning. To supply the totl heting lo of the uiling in the ol perio, the system ontins entrl heting oiler whih use pellets like omustile too. The system ontins some solr olletors, euse in GlŃi re the solr energy hve goo potentil n the insultion is mximum when the ooling lo of the uiling is mximum. Beuse the return ooling iruit of the Stirling engine must e less then 40 C n the wter in the uffer must hve t lest 65 C for goo effiieny of the sorer ooling hiller, there is suplementry ir ooler in the ooling iruit of the Stirling engine (omponent 8 in Fig.1). In the wrm perio the heting lo is neessry to otin the omesti hot wter n the hot wter whih represents the het soure to tivte the sorption ooling system. In the ol perio, the heting lo is neessry to otin the omesti hot wter n to supply the het lo of the uiling. The trigenertion system struture ontins uffer with two oils. Tht therml uffering hs rmti effet on the ehviour of the trigenertion evie performne. The evie effiieny is improve, while on/off yling is signifintly reue. The ooling omponent is n sorption hiller. It is environmentlly frienly euse it emply nturl refrigernt. In ition, the sorption hiller n enhne the effiieny of energy system if it is riven y wste het or y renewle energy. Beuse of the inrese ttention to the ozon lyer epletion n the glol wrming, the sorption refrigertion hs een intensively stuie for the lst time. The sorentsorte pir for ir onitioning purpose re zeolite-wter, tivte ron-mmoni, siligel-wter. Siligel-wter is suitle n useful pir for most pplitions uner 100 C. In our projet we will use n sorption hiller proue y Sorteh, hving ooling pity of 15 kw. 1

2 Figure 1. Shemti rwing of the trigenertion system. 1. Pellet ox; 2. Stirling engine; 3. Hot wter oiler; 4. Solr pnnels; 5. Asorption hiller; 6. Col wter tnk; 7. Air ooler; 8. Air ooler; 9. Therml uffer; 10. Fnoils. III. ADSORPTION COOLING SYSTEMS A. Comprtive Anlysis of Thermlly Ativte Chillers Beuse Stirling engine hs poor eletril effiieny, in miro omine ooling-heting-power system (mcchp) it is neessry to use thermlly tivte hiller. Sili-gel wter sorption systems, LiBr wter sorption systems re mjor thermlly tivte ir onitioning systems uner onsiertion. Compre to the vpor ompression refrigertion yle, they hve the vntge of eing le to e riven y inustril wste het n other low gre het suh s solr energy, n they lso use environmentlly frienly refrigernts like wter. The mjor rwks ssoite with het tivte ooling systems re their low COP n low speifi ooling power (SCP). However, the reent rise in oil n gs pries n the inresing vilility of inustril wste het n inexpensive flt plte solr olletors is mking these systems more n more ompetitive when ompre to onventionl vpor ompression refrigertion systems. Both thermlly tivte ooling system hs vntges n isvntges. Although extensive experimentl n simultion work hs een one to nlyze eh thermlly tivte system iniviully or to ompre its performne with tht of the vpor ompression system, few ttempts hve een me to ompre their reltive quntittive n qulittive performnes. The reson ehin this is the istintive nture of ll these systems, whih mkes it reltively iffiult to ompre their performne. The istintion is minly in the type of sorent, i.e. generlly soli in sorption n liqui in sorption systems, n the type of sorption proess hemisorption in sorption systems n physisorption in sorption systems Lithium-romie tehnology hs more experiene from ifferent soures n goo numer of instlltions. But ue to its si Li-Br hemistry in generl it hs gine muh less thn positive pereption y opertors, with mny experiene stories of rystlliztion ville within the mrketple. Alterntively, with the stte vntges of siligel sorption, filities will enjoy signifint operting n energy ost vntges - using siligel sorption to elipse Li-Br sorption s the preferre metho for relile low temperture wste het wste reovery. Thermlly riven sorption hillers hve een effetive, ut hve een urene with signifint mintenne n upkeep. Asorption hiller systems often epen on orrosive solution of lithium romie slt tht tens to orroe the internl opper tuing n steel shell of the unit. Aitionlly, sorption hillers proue hyrogen gs s y-prout, requiring n expensive pllium ell insie the hiller unit to remove the hyrogen. The lithium romie solution in sorption hillers lso hs phse stte hllenges n hs teneny to soliify within the system while operting. If the regenertion temperture eomes too hot or too ol, or the onitions hnge too rpily for the system to pt, the liqui slt will soliify n rystllize insie the hiller unit. Mny instlltions of sorption units require eite retker to mintin. Conversely, sorption hillers use muniipl wter s the refrigernt n soli sili gel s the esint. There re no CFCs or freons, no lithium romie, n no mmoni. Not using these hemils equtes to no potentil for hzrous mteril leks, no ggressive orrosion, no hemil testing require, n no mge to upper-level tmospheri ozone. An sorption hiller signifintly reues the mintenne n 2

3 upkeep osts y sustituting the orrosive slt esint with enign sili gel. Reliility n mhine vilility re signifintly improve. Asorption hillers hve very few moving prts n o not require the mintenne n ttention tht the sorption hiller systems require. The het extrte from the hille wter n the het onsume from the hot wter is irete into ooling wter system use to issipte this energy. This het issiption my our in wter system; wter het exhnger, ry wter tower or n evportive (wet) wter tower. Very little eletri power is onsume running the hiller, generlly out the sme mount of eletriity s hnful of ol-fshione innesent light uls. The eletri power use rives the internl proess omputer, PLC (progrmmle logi ontroller), n the intermittent running of frtionl horsepower vuum pump. In Tle 1 omprison sorption hiller versus sorption hiller is presente. Tle 1. Asorption hiller vs sorption hiller Asorption ooling tehnology is reltively new, len n whih n use het soures of low het potentil. An sorption ooling system is similr to the ooling system with mehnil vpor ompression, exept tht the energy neee y the ompression proess is provie y het inste of mehnil work. Unlike the lssi mehnil ompression ooling, whih requires mehnil ompressor, the sorption ooling system uses stti thermlly tivte 3

4 sorent lyer. In this wy the ompression energy requirement rops to 90% over the energy neee to rive the mehnil ompressor. The si operting yle of n sorption ooling system onsists of four thermoynmi trnsformtions. A thermoynmi yle of si sorption ooling system on n isoster of n sorent-sort pir is presente in Fig.2 [3]. An isoster of n sorent-sorte pir inites the hnge of the onstnt mount of sorte pressure with respet to temperture. This thermoynmi proess is pressuristion t onstnt volume. oth from the evportor n onenser. This is epressuriztion proess t onstnt volume. The pressure insie the sorer ereses until rehing the evportion pressure. The temperture e is erese from T (whih is the mximum temperture of the yle) to T. The mount of het whih must e evute from the sorent e is otine from the eqution: ( m m C m ) T = s ps s prw m p, m T, t (3) - Isori sorption -, uring whih the sorer is onnete to the evportor n isolte from the onenser. This is n sorption-evportion proess t onstnt pressure. During the sorption proess, het is relese ue to het of sorption. This generte het is remove from the sorent e to n the temperture will erese T, whih is the oolnt temperture: Figure 2. Thermoynmi yle for the sorption ooling system The min steps of the yle re: - Isosteri heting -, uring whih the sorer is isolte oth from the evportor n onenser. This is pressuristion proess t onstnt volume. The pressure insie the sorer inreses until rehing the onenstion pressure y tking het from n externl soure. This is sensile heting proess. The temperture e is inrese from T (whih is the oolnt temperture) to T (whih is the onensing temperture): ( m m C m ) T = s ps s prw m p, m T t, (1) - Isori esorption -, uring whih the sorer is onnete to the onenser, llowing the refrigernt vpor to flow from the sorer to the onenser, where onenses while the heting proess ontinues. This is esorptiononenstion proess t onstnt pressure. The onenstion het is sore y the ooling flui. The het trnsferre y het soure prtly inrese the temperture of sortesorent pir, prtly uses the esorption proess. = T ( ms ps ms prwc m, m p, m ) T m H x t (2) = T ( ms ps ms prwc m, m p, m ) T m H x t The het of evportion, whih uses ooling effet, is otine from the reltion: evportion Tevp Ton ( C ) T m C = e = m C p, w ( C ) H The het of onenstion is otine from the reltion: onenstion ( C ) H v v (4) (5) = = m C (6) The ooling effet ours uring the isori sorption proess -, when the refrigernt (hille wter) is evporte from the siligel e. The system hs the vntge of sorent mteril store in the sorer eing le to sok reltively lrge mount of refrigernt vpor t low temperture n pressure. The heting power onsume y the sorption hiller, h, is given y : h = τ o yle mɺ hw ( T T ) hw, in τ yle hw, out t (7) -Isosteri ooling -, uring whih the sorer is isolte 4

5 where τ yle is the refrigertion yle perio of the sorption hiller. y: The ooling pity of the sorption hiller, = τ o yle mɺ hw ( T T ) hw, in τ yle hw, out t, is given (8) hnge the proesses, the swithing proess is usully rrie out to mke the pressure in the sorent es loser to the onnetion trgets. During the swithing proess, sensile heting n ooling of the sorent es re rrie out [10]. The ontinuous sorption ooling yle is presente in Fig.3 n Fig.4. As is seen in Fig.4, the sorent e 1, whih suport the esorption proess, is oole own y the ooling wter. In the men time, the sorent e 2, whih support the sorption proess, is hete up y the hot wter [8]. The speifi ooling pity, SCC, is efine s the ooling pity per unit mss of the sorent: SCC = (9) m N s where m s is siligel mss n N is numer of sorent es. The COP of the ooling yle is: COP = e ref = (10) h Figure 3. Asorent e 1 in esorption proess, sorent e 2 in sorption proess The ooling effet my e vrie y justing the temperture of the het soure. In the ove equtions, the signifition of the terms is: m - sorent mss, kg; s - speifi het of the sorent, J/kgK; ps prw - speifi het of the liqui refrigertion flui, J/kgK; C - wter ontent of the sorption e in esorption proess, kg/kg; C - wter ontent of the sorption e in sorption proess, kg/kg; mɺ - hot wter mss flow, kg/s; h - speifi het of the hot wter, J/kgK; pw T h - hot wter temperture, K; H ev - ltent het of the ooling flui, J/kg; H - sorption het, J/kg. Figure 4. The swithing proess So, there is no ooling effet uring the swithing proess. Therefore, the exess swithing time reues the verge ooling pity of the yle. The time hrt of the sorption hiller opertion is presente in figure 5 [5]. B. Asorption Cooling System Improvement. B.1. Multie Asorption Cooling If there is one sorent e, the ooling effet is not ontinuous. A first step in improving this soption ooling proess is to otin ontinuous ooling y using minimum two sorent es. These two sorent es lterntely exeute the sorption proess. Before the sorent es Figure 5. The time hrt llotion of the siorption hiller opertion The yle onsists in four opertionl moes. The sorption time is forme of the time length of the moes M1 5

6 n M3, while the swithing time is forme y the time length of the moes M2 n M4. The sum of the time lengths of the four opertionl moes n e lle the yle time. The sorption time ffets the ooling performnes of the hiller, euse in this time the ooling effet is otine [6].. B.2. Uniform Temperture Asorer Proess These systems onsist of two or more sorers, operting with the sme refrigernt, single evportor n single onenser. A generl view of the uniform temperture sorer yle is shown in Fig. 6. In this system, one of the sorers is prehete with rejetion het of nother sorer whih is uner the ooling proess. The trnsfer of het etween the sorers is performe y het trnsfer flui. The proess ontinues until oth sorers reh to the sme temperture (e n f). After this perio of het reovery, one sorer is hete y the externl het soure (e) while the other one is oole y the externl het sink (f) [12]. Although eh sorer follows extly the sme yle s the si sorption het pump yle, the het whih is supplie to the totl system ereses. This type of vne yle results in enhnement of the COP up to 50% [3]. Dous n Meunier [11] hve propose n me nother lterntive sorption yle. The propose sorption yle onsists of two yles, zeolite wter yle for high temperture stge n n tive ron methnol yle for low-temperture stge. The het whih shoul e trnsferre to the tive ron methnol yle for isosteri heting n isori esorption proesses is ompletely otine from the zeolite wter yle. The riving energy for zeolite wter yle is supplie from n externl het soure. The experimentl COP for ooling ws foun s Figure 6. Thermoynmi yle for the sorption ooling system. B.3. Therml Wve Proess The system is ompose of two or more sorers, onenser n n evportor. The working priniple of therml wve proess is shown in Fig. 7. The yle onsists of two sorers whih re lle s sorer 1 n 2. A het trnsfer flui is irulte etween the two sorers. While sorer 1 is uner ooling, the sorer 2 is uner heting proess n vie vers. For the se shown in Fig. 6, the het whih is reovere from the sorent 1 is trnsferre to the het trnsfer flui. The heting of flui is ontinue to esorption temperture y heting system n then it is fe to sorer 2 for the isori esorption proess. After leving of het trnsfer flui from sorer 2, it is oole y ooler to e fe into the sorer 1. Hene, the het trnsfer flui ompletes yle in the system. A reversile pump is use to hnge flow iretion of het trnsfer flui for the reverse proess, when the sorer 2 is uner ooling n sorer 1 is uner heting stge [3]. Figure 7. Working priniple of n sorption system with wve proess IV. THE INFLUENCE OF OPERATION CONDITIONS ON ADSORPTION CHILLER PERFORMANCE To evlute the sorption hiller performnes, we onsier the hrteristis of sorption hiller mnufture y germn ompny Sorteh, with nominl ooling pity of 15 kw. The min vrile hve n mjor importne in performne hrteristis of the sorption hiller re onsiere: mss flow rte of working flui, hot wter temperture whih tivtes the sorption hiller n time sorption yle. When the mss flow rte of refrigernt is vrie, the NTU of 6

7 sorent e is hnge, so the UA vlue of sorent es kept onstnt. In figure 8 optimum hlf yle time with the vrition of mss flow rte is presente. The optimum swithing time is out 10 % of the hlf time yle for n optimum solution. When the mss flow rte will inrese, the optimum hlf time yle will erese, euse higher mss flow rte proue higher ooling pity of the sorption hiller. If the hot wter temperture is inrese, the ooling pity will inrese. Figure 10. Chrteristi igrm 1 for n sorption ooling system Figure 8. The influene of the mss flow rte on the optimum hlf yle time In figure 9 re presente the vritions of SCC n COP in funtion mss flow rte, for ifferent vlues for hot wter temperture. Figure 11. Chrteristi igrm 2 for n sorption ooling system Figure 9. The influene of the mss flow rte on the SCC n COP We n see tht the SCC will inrese when the mss flow rte n hot wter temperture will inrese, euse of the inrese ooling pity of sorption hiller. In the sme time, COP will erese, euse of shorter hlf yle time t the lrger mss flow rte [7]. In Fig.10, Fig.11 n Fig.12 re presente hrteristi igrms for n sorption hiller with ooling pity of 15 kw, when the ol wter is irulte through fn oils, for two vlues of riving temperture. The ol wter inlet/outlet tempertures re: 10 C/15 C. The following igrms re ment to help estimte the sorption ooling system performne tht is to e expete for ifferent operting onitions (re-ooling temperture, riving temperture) [1]. Figure 12. Chrteristi igrm 3 for n sorption ooling system Power moe urve epits the working point of mximum ooling power/pek ooling lo t orresponingly low COP. This performne is usully the sis for imensioning. ECO moe urve epits the working point of reue 7

8 ooling power/prtil ooling lo t signifintly inrese COP. This is extly the performne use for prtil lo or nnul energy inspetions. V. CONCLUSION The pper presents the sorption ooling susystem whih is prt of trigenertion system with Stirling engine like prime mover. Asorption ooling systems re serious lterntive for vpor ompresion ooling systems sine they o not ontin ny hzrous mterils for environment. One of the vntges of sorption ooling systems is opertion with therml het soure n prtiulrly wste het. On the other hn, sorption hiller n e powere y solr hot wter. For ontinuous ooling effet, n sorption system must hve minimum two sorption es, whih work lterntively: one e is on sorption proess, while the seon e is on esorption proess. The swithing time is very importnt to otin goo performnes for sorption ooling systems. The optimum hlf yle time is shortene y the lrger mss flow rte n higher hot wter temperture euse of inrese ooling pity. It hs to e note tht the smller the COP, the more het input is require n the more het hs to e remove y the ooling tower. Vie vers, high COP vlue is of vntge in reuing het input for the sorption hiller in the re-ooling yle. This is preliminry nlysis of the sorption ooling susystem. After the trigenertion system will e monte on the uiling, we will mke experimentl mesurements n we will ompre with theoretil results otine using mthemtil se on lumpe prmeters. [6] S. Li, J.Y. Wu., Theoretil reserh of sili gel wter sorption hiller in miro omine ooling, heting n power (CCHP) system, Applie Energy 86 (2009), pp [7] Sorteh AG. Sorteh Asorption Chiller Design Mnul. [8] Tkhiko Miyzki, Atsushi Akisw, The influene of het exhnger prmeters on the optimum yle time of sorption hillers, Applie Therml Engineering 29 (2009), pp [9] Wng DC, Xi ZZ, Wu JY, Wng RZ, Zhi H, Dou WD., Stuy of novel sili gel wter sorption hiller, Prt I: esign n performne preition, Int J Refrig 2005;28(7), pp [10] Wng DC, Wu JY, Xi ZZ, Zhi H, Wng RZ, Dou WD., Stuy of novel sili gel wter sorption hiller, Prt II: Experimentl stuy, Int J Refrig 2005; 28(7), pp [11] Dous N, Meunier F., Experimentl stuy of sing sorption yles, Chem Eng Si 1989;44, pp [12] Chhni MH, Lii J, Pris J., Effet of mss trnsfer kinetis on the performne of sorptive het pump system, Appl Therm Eng 2002;22, pp [13] Pospisil J., Fieler J., Appliility of Tri-genertion Energy Proution for Air-onitioning Systems in Czeh Repuli, in Proeeings of the 5th IASME/WSEAS Int. Conferene on Het Trnsfer, Therml Engineering n Environment, Athens, Greee, August 25-27, [14] Mnrell P, Chio G., Energy n CO2 emission ssessment of ooling genertion lterntives: omprehensive pproh se on lk-ox moels, in WSEAS TRANSACTIONS ON POWER SYSTEMS Vol.3, No.4, April 2008, pp , ISSN: [15] Alghoul, M.A., Sulimn, M.Y., Sopin, K., Prmetri nlysis of multipurpose solr sorption system- ooling n heting, in Proeeings of the 3r IASME/WSEAS Interntionl Conferene on Energy & Environment, Cmrige, UK, 2008, pp , ISBN ~ ISSN: , [16] Hw L.C, Sopin K, Suleimn Y., An Overview of Solr Assiste Air- Conitioning System Applition in Smll Offie Builings in Mlysi, in Proeeings of the 4th IASME / WSEAS Interntionl Conferene on ENERGY & ENVIRONMENT (EE'09), ACKNOWLEDGMENT The uthors woul like to knowlege to EEA Finnil Mehnism for finning the reserh on Integrte miro CCHP Stirling Engine se on renewle energy soures for the isolte resientil onsumers from South-Est region of Romni (m-cchp-se), uner the ontrt No. RO- 0054/2009. REFERENCES [1] B.B. Sh, S. Koym, J.B. Lee, K. Kuwhr, K.C.A. Alm, Y. Hmmoto, A. Akisw, T. Kshiwgi, Performne evlution of low-temperture wste het riven multi-e sorption hiller, Int. J. Multiphse Flow 29 (2003), pp [2] Di J, Wu JY, Xi ZZ, Wng RZ., Theoretil n experimentl stuy on hrteristis of novel sili gel wter hiller uner the onitions of vrile het soure temperture, Int J Refrig 2007;30: pp [3] Hsn Demir, Moght Moei, Semr Ülkü., A review on sorption het pump: Prolems n solutions, Renewle n Sustinle Energy Reviews 12 (2008), pp [4] Henning HM, Wiemken E., Solr ssiste ir onitioning of uilings overview on tehnologies n stte of the rt, in: Proeeings of ISES Solr Worl Congress, Gothenurg, Sween, [5] K.C.A. Alm, Y.T. Kng, B.B. Sh, A. Akisw, T. Kshiwgi, A novel pproh to etermine optimum swithing frequeny of onventionl sorption hiller, Energy 28 (2003), pp