Optimization and Analysis of a Vertical Ground- Coupled Heat Pump

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1 INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, 2012 Optmzatn and Analyss f a Vertcal Grund- Cupled Heat Pump Al Savsh Krd*, Seyed Al Jazayer* *K.N.Ts Unversty f Technlgy, Department f Mechancal Engneerng; Crrespndng Authr; Al Savsh Krd,K.N.Ts Unversty f Technlgy,Tehran-Iran, , asavsh@gmal.cm, sajazayer@htmal.cm Receved: Accepted: Abstract- In ths study a grund-cupled heat pump (GCHP system th sngle U-bend grund heat exchanger has been used fr heatng applcatns. The mass, energy, entrpy and exergy balance relatns are derved and appled t GSHP system. The perfrmance characterstcs f ths GSHP system are evaluated n terms f exergetc aspects fr cty f kerman and the ptmum sze fr grund heat exchanger s calculated. The effect f dfferent rck r sl and ater-antfreeze nlet temperature n ptmum length has been shn. Results sh that there s an ptmum length and mass fr vertcal grund heat exchanger Keyrds- Gethermal energy; Grund-cupled heat pump; Energy; Optmzatn. 1. Intrductn Grund-cupled heat pump (GCHP systems play a key rle n develpment f usng clean and l cst energy. These systems cllect and transfer heat frm the earth thrugh a seres f bured ppes cntanng a rkng flud, hch s typcally cmpsed f a mxture f ater and antfreeze slutns such as methanl, ethanl r glycl. GCHP are n ncreasngly used fr space heatng, clng and t prvde dmestc heat ater [1]. Lund and Freestn [2, 3] have reveed the rldde applcatn f gethermal energy fr drect utlzatn. They cncluded that GCHP have had the largest grth snce 1995, almst 59%, representng 9.7% annually. Mst f ths grth ccurred n the Unted States and Eurpe, thugh nterest s develpng n ther cuntres, such as Japan and Turkey. In recent years, nvestgatns have been cnducted by varus researchers n desgn, mdelng and expermental perfrmance evaluatn f GSHP systems (e.g. Kavanaugh, 1992; Kavanaugh and Rafferty, 1997; Healy and Ugursal, 1997; Hepbasl, 2002; Hepbasl et al., 2003; Sanner et al., 2003; Hepbasl and Akdemr, 2004; B et al., 2004; Yumrutas and Kaska, 2004; Ozgener and Hepbasl, 2004, In Iran, n spte f very gd pprtunty, nly a fe effrts have been dne fr usng these systems lke BTU/hr ar-t-ar heat pump hch as desgned and nstalled n Tabrz Engneerng Research Center [4]. In ths study a smulatn prgram has been used fr determnng the ptmzed dmensns f a (GCHP th sngle U-bend grund heat exchanger as ell as estmatng exergy perfrmance f a typcal heat pump n cty f Kerman n dfferent heatng seasn. The frst la f thermdynamcs as used t balance the energy f the system and btan the ceffcent f perfrmance (COP, and the secnd la as used t btan the exergy and exegretc effcency f heat pump als ptmum length and dameter f the heat exchanger [5]. ergy r avalablty analyss s a perful tl n the desgn, ptmzatn and perfrmance evaluatn f energy systems. Ths analyss culd be used t dentfy the man surces f rreversblty that s exergy lss and t mnmze the generatn f entrpy n a gven prcess here the transfer f energy and materal take place [6, 7]. 2. System Descrptn The schematc f a vertcal GCHP system s llustrated n Fg.1. The man cmpnents f GCHP systems are cmpressr, cndenser, expansn valve, and an evapratr. The cmpnents are cnnected t a U-bend grund heat exchanger, as shn n Fgure 1. Grund heat fls frm

2 INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, 2012 the crculatng flud thrugh the grund U-bend t an evapratr that uses heat t ncrease the temperature f a refrgerant, causng t t evaprate. The evaprated refrgerant mves nt the cmpressr, and refrgerant s cmpressed t a hr pressure and temperature. The refrgerant then fls nt the cndenser here t cndenses and gves useful heat. The expansn valve reduces the refrgerant's pressure, subsequently reducng ts temperature. The refrgerant fls back t the evapratr and the prcess repeats agan. Fllng assumptns has been made n ths research: A safety margn f 5 C superheat t prevent lqud drplets enterng the cmpressr The refrgerant n evapratr s subcled 5 C Cndenser and evapratr have a 5% pressure drp Table 1. Specfcatn f the system Heat pump Average cmpressr adabatc 0.96 kw per nput Cmpressr adabatc effcency 0.85 Refrgerant type R134a Refrgerant mass fl rate kg/s Cndenser mass fl rate kg/s Grund heat exchanger Cnfguratn type Water-antfreeze type Water-antfreeze mass fl rate Rck type Vertcal Prpylene glycl slutn kg/s sandstne L pt 2n D pt 3. Thermdynamc Analyss 3.1. Energy and exergy balances The gvernng equatns f mass, energy and exergy cnservatn fr a steady state fl rate are; (2 m m (3 The frst la f thermdynamc can be expressed as; E E The general exergy balance can be expressed n the rate frm as; Or d - + -E. heat rk mass, xmass, d (4 (5a (5b Usng Equatn (5b, the rate frm f the general exergy balance can als be rtten as; T (1 k W m Tr m d, (6a Wth PH x ( h h T ( s s (6b 3.2. Reference envrnment Fg.1. Schematc dagram f the system Determnng the length and dameter f a grund heat exchanger s an mprtant aspect f grund-cupled heat pump desgn [8]. The equatn f determnng the ptmum Reynlds number s gven by Al Sharfzadegan et al [9], the ptmum length and dameter culd be derved as: D pt 4m Re pt (1 ergy s alays evaluated th respect t a reference envrnment. The reference envrnment s n stable equlbrum, acts an nfntve system, s a snk r surce fr heat and materals, and experences nly nternally reversble prcesses n hch ts ntensve prpertes remans cnstant. In the calculatns, the temperature T and pressure P f the envrnment are ften taken as standard-state values. If the system uses atmspherc ar, T mght be specfed as the average ar temperature. If bth ar and ater frm the natural surrundngs ere used, T uld be specfed as the ler values f the average temperatures fr ar and ater [10]. Sme mprtant nfrmatns lke average ar temperature, ar temperature annual ampltude, and heatng desgn day, sl r rck temperatures and types are essental fr ur calculatn. kerman has been chsen as typcal regn and relevant specfcatns are taken frm Iranan meterlgcal rganzatn [11]. The daly sl temperature s calculated usng equatn [12]; 34

3 INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, ( tt0 T (0, t Ta Asn 365 ( Energy and exergy effcences The energy (r frst la effcency s smply a rat f useful utput energy t ttal nput energy and s referred t as a ceffcent f perfrmance (COP fr refrgeratn systems. cndenser COP Wcmpressr On the prduct/fuels (P/F bass, exergy effcency can be rtten as the rat f ttal exergy utput t ttal exergy nput: 3.4. ergy analyss f the system studed (9 (10 The mass and energy balance equatns as ell as the exergy destructns btaned usng the entrpy and exergy balance equatns fr each f the GCHP cmpnents llustrated n Fg. 1 are lsted as flls, respectvely. Fr cmpressr: m m m 1 2 r W m ( h h cmp r 2a 1 T m ( s s dest, cmp, ent 0 r 1 2a m ( W dest, cmp r 1 2a cmp (11a (11b (11c (11d here the heat transfer versus the envrnment as neglected. Fr cndenser:, a m1 m2 mr m5 m6 m (h -h ; cnd r 2a 3 (12a cnd = C p,(t5 -T 6 (12b Fr thrttlng valve; m m m h 3 4 r h 3 4 T m ( s s dest, tv, ent 0 r 4 3 m ( dest, tv r 3 4 Fr evapratr; m m m 4 1 r m ( h h ; eva eva r 1 4 T [ m ( s s dest, eva 0 r 1 4 m ( s s ] 7 8 m ( dest, eva r 4 1 m ( 8 7 Fr cndenser fan; (13a (13b (13c (13d (14a (14b (14c (14d m ar, ar, ar (15a ac p,a (T,a -T,a (15b = cnd; sph =cnd (15c dest,, e T0[ ma ( s6 s5 ], T m ( dest, a 5 6 T 1. a, (15d T a, (15e Fr grund heat exchanger; m m m 7 8 (16a C p, (T8 -T 7, (16b T [ m ( s s dest, cnd, ent 0 r 3 2 m ( s s ] 5 6 dest, cnd r 2a 3 m ( 6 5 m ( (12c (12d dest,, e T0[ m ( s8 s7 ], T m ( dest, 7 8 grund (16c T 1. T grund (16d 35

INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, 2012 4. Result and dscussn The effect f sme rck r sl type n heat exchanger s length s shn n Fg.2. As can be seen fr sandstne type th mre thermal cnductvty [13], the less length s requred.

4 INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, Result and dscussn The effect f sme rck r sl type n heat exchanger s length s shn n Fg.2. As can be seen fr sandstne type th mre thermal cnductvty [13], the less length s requred. The effect f grund temperature hch s functn f clmate and rck r sl type and the ater-antfreeze nlet temperature t the grund heat exchanger n the ptmum length has been shn respectvely n fg.3. The last plt shs that there s an ptmum mass fr decreasng heat exchanger s sze and ptmum length can t be reduced by ncreasng mass after a specfed value. Results f exergy destructn f system cmpnents s gven n n table 2. exergy analyss fr selected system are shn table 3, and shs that the hst lst rk ccurs n cndenser fan unt. ergy effcency f system studed s calculated t be and COP s derved as Fg.3. Parameters affectng the ptmum length Table 2. System exergy destructn N. Descrptn ergy destructn(kw 5 Cndenser fan nlet Ar Gas Evapratr Cmpressr Fg.2. System exergy destructn 3 Cndenser thrttlng valve Cndenser fan Grund Heat changer Table 3. System exergy analyss N. Descrptn Flud Phase Temp. Pressure Specfc Specfc ergy 0 enthalpy ergy rate T( c ( KPa h( KJ / Kg ( KJ / Kg. K m ( KW 0 - R-134a Dead state Ar Dead state Waterantfreeze 2 Dead state Evapratr utlet R-134a Sup.heated vapr Cmpressr utlet R-134a Sup.heated vapr Cndenser utlet R-134a Lqud thrttlng valve R-134a Mxture Cndenser fan utlet Ar Gas ater-antfreeze Waterantfreeze 7 Lqud utlet Waterantfreeze 8 ater-antfreeze nlet Lqud

5 INTERNATIONAL JOURNAL f RENEWABLE ENERGY RESEARCH Al Savsh Krd et al., Vl.2, N.1, Cnclusns The ptmzatn and analyss f a vertcal grundcupled heat pump system n kerman prvnce as nvestgated and ptmum length fr a grund heat exchanger as calculated. The effects f dfferent parameters such as rck and sl type, ater-antfreeze nlet temperature and ater-antfreeze mass fl rate n length f grund heat exchanger have been studed. Results shs that decreasng ater-antfreeze nlet temperature can decrease requred length f a heat exchanger. In addtn the exergy lsses f each cmpnent and exergy effcency tgether th ceffcent f perfrmance f the system culd be calculated. Nmenclature C specfc heat ( KJ / Kg. K ceffcent f perfrmance f heat COP pump (dmensnless exergy rate (kw h specfc enthalpy ( KJ / Kg m mass fl rate ( Kg / S p pressure (kpa heat transfer rate (kw S entrpy ( KJ / Kg. K S entrpy rate ( KW / K T temperature ( 0 c r K W rk rate r per (kw Greek letters exergy (secnd la effcency (dmensnless effcency (dmensnless specfc exergy ( KJ / Kg Subscrpts pt act cmp cnd dest ent eva fc tv r ptmum actual cmpressr cndenser destructn entrpy evapratr fan-cl grund heat exchanger cndenser fan thrttlng valve nlet ater utlet refrgerant References [1] Chassn, A. D., 1999, Advances n Mdelng f Grund Surce Heat Pump Systems, Master f Scence Theses, Graduate Cllege f Oklahma State Unversty. [2] Lund JW, Freestn DH Wrld-de drect uses f gethermal energy Prceedngs Wrld Gethermal Cngress 2000, Kyushu-Thku, Japan, 28 May-10 June; [3] Lund JW, Freestn DH Wrld-de drect uses f gethermal energy Gethermcs 30:29-68.Mran MJ Avalablty Analyss: A Gude t Effcency Energy Use. Prentce-Hall: Engled Clffs, NJ. [4] Mrtaza Yar, Nader Javan. Perfrmance assessment f a hrzntal-cl gethermal heat pump.internatnal Jurnal f Energy Research. 2006(31, P [5] Bejan, A., 1988, Advanced Engneerng Thermdynamcs, Jhn Wley & Sns, Ne Yrk. [6] Ktas TJ The ergy Methd f Thermal Plant Analyss. Anchr Brendn Ltd.: Tptree, Essex. [7] Esen H., Inall M., Esen M., Phtl K., Energy and exergy analyss f a grund-cupled heat pump system th t hrzntal grund heat exchangers, Buldng and Envrnment, 42(10, , [8] Yavuzturk, C., Mdelng f vertcal grund lp heat exchangers fr grund surce heat pump systems1999, Oklahma State Unversty. [9] J. Marzbanrad, A. Sharfzadegan and A. Kahrbaean, Thermdynamc Optmzatn f GSHPS Heat changers, Int. Jurnal f Thermdynamcs, Vl. 10 (N. 3, pp , [10] Hepbasl A.Thermdynamc analyss f grundsurce heat pump systems fr dstrct heatng. Internatnal Jurnal f Energy Research, 2005; 29: [11] Iranan meterlgcal rganzatn (IMO, Data prcessng center. [12] devres, D. A Heat Transfer n Sls. In D.A. de Vres and N.H. Afgan (ed. Heat and Mass Transfer n the Bsphere. pp Scrpta Bk C., Washngtn, DC. [13] Incrpera, F.P. and DeWtt, D. P., Fundamentals f Heat and Mass Transfer, 4th Ed., Jhn Wley and Sns, NY,

Approach: (Equilibrium) TD analysis, i.e., conservation eqns., state equations Issues: how to deal with

Approach: (Equilibrium) TD analysis, i.e., conservation eqns., state equations Issues: how to deal with Schl f Aerspace Chemcal D: Mtvatn Prevus D Analyss cnsdered systems where cmpstn f flud was frzen fxed chemcal cmpstn Chemcally eactng Flw but there are numerus stuatns n prpulsn systems where chemcal