ENERGY AND EXERGY EFFICIENCY OF A HEAT STORAGE UNIT FOR BUILDING HEATING

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1 ENERGY AND EXERGY EFFIIENY OF A HEAT TORAGE UNIT FOR BUILDING HEATING Mejdi. Hzmi 1, *, mi. Kooli 1, Meriem. Lzâr 1, Abdelhmid. Frht 1, Ali. Belghith 2 1 Lbortoire de Mîtrie et de Technologie de l Energie, Technopole de Borj edri, LP 95 Hmmm-Lif, e-mil Hzmdi321@yhoo.fr 2 Fcultée de cience de Tuni, univerité cmpu, Belvédère, Tuni ABTRAT. Thi pper del with numericl nd experimentl invetigtion of dily olr torge ytem conceived nd built in Lbortoire de Mitrie de Technologie de l Energie (LMTE, Borj edri). Thi ytem conit minly of the torge unit connected to olr collector unit. The torge unit conit of wooden ce with dimenion of 5 m 3 (5m x 1m x 1m) filed with fin nd. Inide the wooden ce w buried network of polypropylene cpillry het exchnger with n perture re equl to 5 m². The het collection unit conited of 5 m 2 of outh-fcing olr collector mounted t 37 tilt ngle. In order to evlute the ytem efficiency during the chrging period (during the dy) nd dichrging period (during the night) n energy nd exergy nlye were pplied. Outdoor experiment were lo crried out under vried environmentl condition for everl conecutive dy. Reult howed tht during the chrging period, the verge dily rte of therml energy nd exergy tored in the het torge unit were 400 nd 2.6 W, repectively. It w found tht the net energy nd exergy efficiencie in the chrging period were 32 % nd 22 %, repectively. During the dichrging period, the verge dily rte of the therml energy nd exergy recovered from the het torge unit were 2 kw nd 2.5 kw, repectively. The recovered het from the het torge unit w ued for the ir-heting of teted room (4m x 3m x 3m). The reult howed tht 30 % of the totl heting requirement of the teted room w obtined from the het torge ytem during the whole night in cold eon. NOMENLATURE A c the urfce re of the collector, m 2 A d the urfce re of door, m 2 A g the urfce re of gle of window, m 2 A the urfce re of the olr torge unit, m 2 A w the urfce re of wll, m 2 A g the urfce re of gl, m 2 A Ri Internl roof urfce, m 2 p, pecific het of ir t contnt preure, kj/kg K p,c the pecific het of concrete borber, J/(kg K) p the wter pecific het, J. kg -1.K -1 the wter pecific het, J. kg -1.K -1 D diffuive intenity of rdition d dimeter of the cpillry het exchnger, m F lighting coefficient (F =1.2 for florecent lmp nd 1 for other) H i the olr irrdition t the collector perture, W.m -2 h i het trnfer coefficient, W/m 2. h ir het trnfer coefficient of the ir under the roof, W/m 2. L Length of the cpillry tube, m

2 M c m oncrete m, kg Air m flow rte, kg/ m w Flow rte of the chrging wter, m P Power conumption for lighting ytem, W hrging Rte of het upplied from the collector, W Dichrging Rte of het upplied from the ccumultor, W d Rte of het recovery from the het ccumultor, W Lo Rte of het lo from the ccumultor, W torge the rte of het tored into the ccumultor, W Accumultor urfce re, m² T Ambient ir temperture, T Ab,v Averge concrete temperture, T,v Averge mbient ir temperture, T e,v Averge cold-wter inlet temperture, T F Finl temperture of the wter t the olr torge exit fter 12 h, T I Initil temperture of the wter in the tnk, T i Wter inlet temperture, T m oil temperture inide the ccumultor, T o Wter outlet temperture, T Ri Temperture of the internl roof urfce, T oil temperture inide the greenhoue, T wi Temperture of the interior urfce of the wll, t Time, V Volumetric flow rte of ir, kg. -1 η hrging Net energy efficiency for chrging period, % Greek letter α Aborption coefficient ρ Wter denity, kg.m -3 τ Trnmittnce for olr rdition. λ the equivlent het conduction coefficient, W.m -1 K -1 ν the kinemtic fluid vicoity τ G trnmiion coefficient of gl for direct olr rdition trnmiion coefficient of gl for diffue olr rdition τ D 1. INTRODUTION. Energy contitute the min element of economicl production (in indutry nd trnporttion) nd improving life qulity in the reidence ector. In fct, pproximtely 50% of the nnul energy conumption of primry energy reource throughout the world i detined to houehold irconditioning. Furthermore, the over-ue of primry energy i leding to environmentl degrdtion in hevily populted re. Thu, ctully wide effort hve been undertken to llevite globl wrming of erth cued by the emiion of crbon dioxide in tmophere generted by intenive burning of foil fuel. Due to thee problem, tendency towrd renewble energy reource, prticulrly olr energy, with rther inignificnt environmentl influence, offer wide rnge of exceptionl benefit for ir-houe heting. Indeed, olr energy, which i n bundnt, clen nd fe ource, i n ttrctive ubtitute for conventionl fuel for pive nd ctive heting. However, the mngement of the olr energy in ir-heting ector i uully not economiclly feible compred with the trditionl

3 crrier. In fct, it intermittent chrcter contitute the min impediment of olr energy ue. To reduce the time or rte mimtch between energy upply nd energy demnd it i necery to tore the exce of olr het for hort-or long-term torge. The hort-or long-term torge of the enitive het in oil eem to be pluible from technicl nd economic view point. Indeed, different technique of torge of the enitive het in oil hve been ued (OOzt.urk et l., 2002). The performnce of thee technique re influenced by the trnfer of the het, of the humidity in oil nd the therml efficiency of the het exchnger ued for toring olr het in oil. T. Boulrd nd A. Bille (1986) nlyzed the influence of ome prmeter on the performnce of therml energy torge ytem. Thi ytem conit of 10 cm-dimeter PV het exchnger tube buried in oil t 30 cm-depth connected to n ir-ventiltion ytem plced inide greenhoue. Reult howed tht the torge of het by through the buried ir/oil het exchnger w n intereting method tht cn be ued for the dily olr het torge. In fct, the therml efficiency of the olr het torge ytem w evluted t 50%. In 1997, Guthier et l., propoed three-dimenionl numeric model, uing the FLUENT progrm, to tudy the performnce of wter/oil het exchnger ued to tore het collected from greenhoue. The het torge ytem conit minly of two connected tubulr het exchnger. The firt het exchnger i plced inide the greenhoue. The econd het exchnger i buried within the underground of the me greenhoue. The het collected from the firt het exchnger i trnferred to the econd het exchnger buried in the underground. The reult howed tht the therml trnfer in the ground due to the preure grdient of humidity in oil i inignificnt when compred to the het trnfer due to the temperture of grdient. Reult howed tht the torge of het by through the buried ir/oil het exchnger w n intereting method tht cn be ued for the dily olr het torge. Guthier nd l. etblihed tht the therml efficiency of the het torge ytem i bout 60%. In thi context, we hve built in our lbortory (LMTE, Borj edri), prototype for enible olr energy torge (Figure 1). The experimentl ytem conit minly of (i) olr torge unit which conit of wooden cing whit dimenion of 5 m 3 filed with fin nd. Inide the olr torge unit w buried network of polypropylene cpillry het exchnger with n perture re equl to 5 m² nd (ii) olr collector unit with n perture re of 5 m² connected to buried het exchnger. An experimentl tudy w crried out in order to evlute the therml performnce of the torge ytem. Performnce of the het torge ytem w evluted by theoreticl nlyze bed on firt nd econd lw of thermodynmic. Figure 1: Photo of the olr het torge unit From firt lw perpective, the efficiency of therml energy torge ytem w eed in term of how much therml energy the ytem cn tore. Thi pproch produce workble deign, but not

4 necerily thoe with the highet poible thermodynmic efficiencie. It h been hown in recent yer tht the deign of thermodynmiclly efficient het trnfer equipment mut be bed on the econd lw of thermodynmic in ddition to the firt lw (Krne, 1987). Exergy nlyi, derived from both the firt nd econd lw of thermodynmic, provide greter inight to cot effective deign nd mngement of complex procee (Lron & ortez, 1995). Unfortuntely, there re only few publiction relted to exergetic efficiency of the lrge-cle het torge ppliction. The endevor of thi pper i to pprie the performnce of thi low cot torge ytem tudied under vriou Tuniin climtic condition uing energy nd exergy nlyze. The energy nd the exergy nlyze etblihed in thi pper llowed the etimtion of the mximl vlue of het tored inide the het torge unit. 2. EXPERIMENTAL INVETIGATION 2.1. Experimentl device Figure 2 illutrte chemtic digrm of the olr het tored ytem. The ytem conit of three unit: (i) het collection unit, (ii) het torge unit nd (iii) dt cquiition unit. Figure 2: olr het torge ytem Het collection unit The het collection unit i compoed of olr collector with n perture re of 5 m² mounted t 37 towrd the outh. The borber of the olr collector w mde with 40-cm thick concrete lb pinted blck. The concrete mtrix w ued to incree the torge cpcity of the het collection unit. The thermophyicl nd geometricl proprietie of the borber re given in tble 1. A cpillry polypropylene het exchnger (Figure 3) with n perture re equl to 5 m² w being integrted inide the borber mtrix to crry the het trnfer fluid inide the olr torge collector. The thermophyicl nd geometricl proprietie of the het exchnger re given in tble 2.

5 Figure 3: pillry het exchnger Tble 1 Phyicl nd geometricl proprietie of the het collection unit Prmeter Dimenion ollector price Aborber mteril oncrete m oncrete denity oncrete therml conductivity oncrete pecific het Toxic effect Vlue (1 m x 5 m) 90 ($/1m) oncrete 200 kg 2800 kg.m W.m -1.K J.kg -1.K -1 No Tble 2 Phyicl nd geometricl proprietie of the cpillry het exchnger Prmeter Vlue Dimenion (1 m x 5 m) Inner cpillry 3 mm Outer dimeter 4.2 mm Het exchnger price 20 ($/1m) Het exchnger mteril Polypropylene Polypropylene denity 950 kg.m -3 Polypropylene therml conductivity 0.22 W.m -1.K -1 Toxic effect No Het torge unit A wooden ce of 5m length, 1m width nd 1 m depth, field with fin nd, w ued het torge unit. The nd chrcterized by high torge cpcity per unit volume w ued het torge mteril. The whole urfce of the het torge unit w inulted with 30-mm of polyurethne fom. A network of polypropylene cpillry het exchnger with 5 m² perture re i buried within the nd inide the ce t 40 cm-depth. In fct, preliminry experiment w crried out on the torge unit in order to determine the optiml depth in which the het exchnger will be buried. The tet conited of following the vrition of the nd temperture t different depth v time. By nlyzing the reult we noticed tht the uperior lyer of nd undergoe eily with the externl climtic vrition. Beyond certin depth, the nd temperture doe not vry between the dy nd the night. Thu nd inide the torge unit cn be divided into two zone (upper nd lower). The thickne of the upper zone i bout 20 cm. In thi zone, the nd temperture fluctute eriouly with externl climtic condition. Under thi depth

6 the nd temperture doe not ocillte with externl climtic condition. Thu, le thn 20 cmdepth i conidered to be long-term therml torge ection Dt cquiition unit Meurement mde during the experimentl tudie re divided into to group: -The firt group meurement re relted with the het collection unit. Both the collector outlet temperture T co nd collector inlet temperture T ci hve been meured by T-type thermocouple. -econd group meurement re concerned with the nd in the wooden ce nd the temperture vlue of the urrounding ground. Thu, copper-contntn T-type thermocouple were plced t different depth inide the nd t 10, 20, 30, 40, 50, 60, 70, 80, 90 nd 100 cm depth on the centrl line. The inlet temperture T o nd the outlet temperture T i of the cpillry het exchnger integrted inide the nd hve been meured. The mbient ir temperture w meured by nother thermocouple plced out of the ytem. A pyrometer h been ued to meure the globl rdition coming towrd the horizontl urfce. All the thermocouple ued were new nd of high ccurcy. The dt meured were recorded every 15 mm with totl ccurcy umed to be bout 5% by HP dt logger nd then trnferred to P for further evlution Experimentl protocol An experimentl invetigtion were conduced in Borj edri (North of Tunii): Ltitude N, Longitude E. The experimentl tudy w elborted in two complementry tge: (i) Firt tge (A torge phe) The experiment were crried out t the me time period between 9.00 nd of the dy for m flow rte mintined equl to kg. -1 by uing the liding vlve integrted t the experimentl loop. During thi phe the heted wter (t the temperture rng of ) upplied by the het collection unit, i conduced thought the polypropylene het exchnger buried t 40 cm depth inide the nd. The hot wter inide the het exchnger diipte it therml energy to the nd inide the ce by conduction. (ii) econd tge (A retortion period) The het tored in the ccumultor during the chrging period w recovered during the night (20:00 03:00 h). During the dichrging phe cold wter, t temperture nd me flow equl to 20 nd to kg. -1 repectively, replenih thought the het exchnger buried in the nd. The hot nd inide the ce diipte the tored olr energy to the buried het exchnger. 3. NUMERIAL TUDY 3.1. olr collector unit According to the INPUT/OUTPUT tndrd (Hikmet (2008)), the energy gin (dily het output) of the olr collector, u (W), cn be repreented by the following empiricl eqution: u = α 1 H + α 2 (T,v Te, v ) + α 3 (1) α 1, α 2 nd α 3 re contnt for ytem, determined from the tet reult (Tble.1). The overnight het lo coefficient, U c (W/K.m²), of the hot wter torge ytem i determined by meuring the temperture lo of the wter during 12 h nocturnl period (oulioti et l. (2004)). The formul ued i:

7 U M c p, c I, v = ln (2) A t c T T F T T Ab, v The dily therml efficiency of the olr collector, η j, i given by the expreion: t 2 u ( t ) dt η (3) t1 j = t 2 t1 A.H ( t )dt c The olr collector prmeter were determined during n experimentlly invetigtion. Reult re hown in Tble 3. Tble 3 ollector prmetric dt Prmeter ollector overll energy lo coefficient, U (W/m².K) The opticl yield, η 0 α 1 (m -2 ) α 2 (W.K -1 ) α 3 η (%) j Vlue Het torge unit Energy nlyi for chrging nd dichrging period The rte of het trnfer hrging (t) from the olr collector unit into the het torge ccumultor w clculted during the chrging period by uing the following eqution: h rg ing ( t ) = m w p (T ( t ) T ( t )) i O (4) The rte of het tored in the het torge unit torge (t) w determined with repect to the het trnfer rte into the torge unit nd het loe for the chrging period: torge = rg (5) h ing Loe (t) repreent the rte of het looed from the whole urfce re of the het torge unit. It i given by the reltion: Loe Loe = λ A ( T T ) (6) The evlution of the nd temperture T (t) during the chrging nd the dichrging period, i obtined by the reolution of the eqution of the het conduction: m

8 T T T ρ c = ( λ ) + ( λ ) (7) t y y The nd temperture, T (t), w determined by the het conduction eqution (. V. Ptnkr, 1980). To reolve the het conduction eqution, the following implifying umption were tking into ccount; (i) The ground w regrded being homogeneou nd (ii) The convective coefficient, h, w uppoed to be contnt throughout the het exchnger embedded inide the nd. The integrtion of the het conduction eqution (Between t t t+ t) gived the eqution: T = T + T + T + T + T (8) P P E E W W N N 0 P 0 P Where: λ ) e y E =, nd P e E W W λ ) W = N W y, = P N λ ) n y =, n λ ) = y, λ ) = y, 0 P c x y = ρ t The correponding boundry condition re: T T T T λ / x= 0 = 0 ; λ / x=l = 0 ; λ / y= 0 = 0 ; λ / y=l = 0 T λ / x= k = h (Twter Tm ) ; k i the poition of the het exchnger within nd nd h repreent the het trnfer coefficient between the nd prticle nd the wter in the het exchnger. The form of the correltion ued for the evlution of the het trnfer coefficient h w developed by R. Kübler, 1987: Nu = Pr Re The energy efficiency for the chrging period w defined the rtio of the het tored in the het torge unit to the het trnfer from the olr het collector. Then, the totl energy efficiency during the chrging period η hrging (t) in % w formulted follow: torge η h rg ing =.100 (9) h rg ing The rte of het recovered from the het ccumultor during the dichrging period: Dichrging (t) w clculted by: Dich rg ing d L 0. 7 ( t ) = m (T ( t ) T ( t )) (10) w p O Exergy nlyi for the chrging nd dichrging period The rte of therml exergy trnfer from the het collection unit into the het torge unit X (t) in W w clculted during the chrging period from the following eqution (Öztûrk H H; 1997) : i

9 X Ti t) = h ing T m ex w p Ln (11) T ( rg where T ex i the reference outide temperture. It i importnt to mention tht the rte of therml exergy trnfer i uully clculted on the bi of the rte of therml energy trnfer. The ymbol X (t) refer to the rte of exergy trnfer in the literture of thermodynmic. The rte of the therml exergy tored in the het torge unit X (t) w determined in reltion to the exergy trnfer rte into the het torge unit nd the exergy looed from the het torge unit for the chrging period: X = X X (12) where X l (t) i the rte of therml exergy looed from the het torge unit. During the chrging period, the rte of the therml exergy loe w evluted follow: T X l = h rg ing [1 ] T (13) imilrly energy efficiency, the totl exergy efficiency during the chrging period w determined by the following eqution: l m X ψ c =.100 (14) X l The rte of therml exergy recovered from the het torge unit for the dichrging period X R ( t ) w clculted on the bi of the rte of het recovered from the het torge unit follow: X R T0 = Dich rg ing T m ex w p Ln (15) T O i Dich rg ing Het requirement of the teted room The totl heting lod cn be clculted by conidering into ccount the effect of vriou prmeter ccording (T. Hong, Y. Jing., 1997 et M.. Htmipour et l., 2007): P Trnmiion+ olr + Internl+ Airflow = (16) p repreent the totl het trnferred to the room ir when wter flowing through the polypropylene het exchnger integrted inide the ir-cupbord. It w clculted from the temperture difference between the entrnce nd the exit of the cpillry het exchnger: p = m T T ) (17) p ( w, o w, i Trnmiion repreent the het trnfer from exterior wll, window, door nd envelope (A. hrin et l., 1998) :

10 Trnmiion = h Nw i j= 1 A w j ( T T ) + A ( T T ) + A ( T T ) + h A ( T T ) (18) w i j g j g j d j d j NR i R j= 1 R j R i j olr repreent the het due to un rdition trnmitted from window. Therml het due to thi phenomenon i clculted by uing: olr = τ H + τ D (19) G D Internl repreent internl het generted by lighting ytem, peron in the building nd home pplince cn be clculted by uing (Y. Jing, 1981) : Het generted by lighting ytem w clculted by: Internl Lihting + Peron + Applince = (20) Lighting = P. F (21) Het generted by peron nd pplince were chieved from pproprite tble. Airflow i the het due to irflow into the building (enible nd ltent het). Het lod due to outide ir flow infiltrtion cn be clculted by (E. hviv et l., 2001): = + (22) Airflow L Where: = V ρ c T T ) = m c ( T T ) (enible het by entering ir) p, (, 0, i p,, 0, i L = V ρ W W )λ (Ltent het by entering ir) ( i 0 4. REULT AND DIUION The efficiency of the het torge ytem depend on therml nd phyicl propertie of the het torge mteril (nd), het torge temperture nd performnce of the het exchnger embedded inide the nd. In view of evluting efficiency of the het torge ytem, n energetic nd n exergetic nlye were evluted for the following chrging/dichrging proce hrging proce Figure 4 repreent the numericl nd experimentl vrition of the nd temperture t 50 cm-depth during the torge phe (between 9:00 nd 17:00). It i found tht the temperture of the nd, T,à inide the ce increed grdully with the increed of wter temperture upplied by the olr collector. At the end of the chrging proce the nd temperture, t 50 cm-depth, reched mximum vlue bout 40. Figure 4 how lo good greement between numericl nd experimentl reult. The rte of het nd therml exergy tored in the het torge unit during the chrging period were clculted by uing Eqn (4), (5) nd (6), repectively. The reult of energy nd exergy nlyze during the chrging period re hown in Figure 5. Figure 5 how tht the verge hourly rte of therml energy nd therml exergy chnged with time. In fct, the rte of the het tored in the het torge unit rnged from 400 W to 2.8 kw, where the rte of the therml exergy tored in the het torge unit w in the rnge of 300 W nd 830 W. The

11 mximum vlue of energy nd exergy rte (2.6 kw nd 830 W repectively) were obtined t 13:30. During the chrging period the verge dily rte of the het nd therml exergy tored in the het torge unit were 515 W nd 1.5 kw, repectively. We noted tht the therml energy tored in the het torge unit w higher compred with the therml exergy during the chrging period. The energy nd exergy efficiencie of the het torge ytem during the chrging period were clculted by uing Eq (9) nd (14), repectively. The chnge of the verge hourly energy nd exergy efficiencie during the chrging period re hown function of time in Figure 6. The energy nd exergy efficiencie increed with the temperture increing of the wter upplied by the olr collector. The reult how tht during the chrging period (10:00 h 17:00 h) the energy efficiency rnged from 23 to 41 %, while the net exergy efficiency w in the rnge of 17 nd 28 %. The energy nd exergy efficiencie rech they re mximum vlue (41 % nd 17 % repectively) t 13:30. During the chrging period, it w found tht the verge dily net energy nd exergy efficiencie were 32 nd 22.5 %, repectively. We noted lo tht the energy efficiency i higher thn the exergy efficiency. Figure 4: Evolution of the nd temperture t 50 cm-depth during the chrging phe Figure 5: The rte of het nd therml exergy tored in the het torge unit during the chrging period

12 Figure 6: The chnge of the net energy nd exergy efficiencie for the chrging period:, energy efficiency, O exergy efficiency 4.2. Dichrge proce During the dichrge proce, the temperture ditribution of the nd indicted by the 12 thermocouple fixed t different equl intervl depth inide the ce filed with nd. Figure 7 how tht the temperture of the nd t 50 cm-depth decree grdully. The decree temperture i due to the relee of enible het tored in nd. During the energy dichrging, the nd temperture in the torge het unit decree quickly in the firt two hour. At the end of the dichrging proce the nd temperture t 50 cm-depth reched minimum vlue bout 21. Figure 7 how lo good greement between numericl nd experimentl reult. The rte of het nd therml exergy recovered from the het torge unit during the dichrging period were clculted by uing Eqn (10) nd (15), repectively. The chnge of the verge hourly rte of het nd therml exergy recovered from the het torge unit during the dichrging period re hown function of time in figure 8. The mount of het recovered from the het torge unit w in the rnge of 2 kw nd 2.5 kw during the dichrging period. However, it w found tht the therml exergy recovered from the het torge unit rnged from 600 W to 900 W. During the dichrging period the verge dily het nd therml exergy recovered from the het torge unit were 2.25 kw nd 1500 W, repectively. The reult howed lo tht the difference between energy nd exergy nlyze i ignificnt. ince exergy i meure of the qulity of energy, exergy efficiency i more ignificnt thn energy efficiency, nd tht exergy nlyi hould be conidered in the evlution nd comprion of the therml energy torge ytem. Exergy nlyi clerly tke into ccount the lo of vilbility of het in torge opertion nd, hence, it more correctly reflect the thermodynmic nd economic vlue of the torge opertion. The optimiztion of the deign nd exploittion of the therml energy torge ytem cn be mde by men of the exergy nlyi. When optimizing the efficiency of therml energy torge ytem, both deign nd opertionl prmeter mut be conidered.

13 Figure 7: Evolution of the nd temperture t 40 cm-depth during the dichrging phe Figure 8: The rte of het nd therml exergy recovered from the het torge unit for the dichrging period 4.3. Het requirement of the teted room The totl het requirement of the teted room during the dichrging period were clculted from Eq (16). The chnge of the totl het requirement of the teted room nd the mount of het recovered from the het torge unit during the dichrging period re hown function of time in Figure 9. During the dichrging period, the totl het requirement of the room rnged from 7.2 to 8.2 kw, while the rte of het recovered from the het torge unit to the teted houehold w in the rnge of 2 nd 2.5 W. We etblihed tht bout 30 % of the totl het requirement of the teted room w obtined from the het torge unit.

14 Figure 9: The chnge of the totl het requirement of the tunnel greenhoue nd the rte of het recovered from the het torge unit during the dichrging period ONLUION The performnce of newly deigned het torge ytem been preented. Reult how tht the het torge ytem would be promiing olution for ir-heting building during the night-time. In fct, the het torge ttined coniderble rte of het tored (bout 2.6 kw) with n energy efficiency nd exergy efficiency which reched 41 % nd 28 %, repectively. We noted lo tht the mount of het recovered from the het torge unit w in the rnge of 2 kw nd 2.5 kw during the dichrging period. However, it w found tht the therml exergy recovered from the het torge unit rnged from 300 W to 800 W. The reult howed lo tht the difference between energy nd exergy nlyze i ignificnt. ince exergy nlyi clerly tke into ccount the lo of vilbility of het in torge opertion nd, hence, it more correctly reflect the thermodynmic nd economic vlue of the torge opertion. During the dichrging period, the totl het requirement of the room w bout 8.60 kw, while the rte of het recovered from the het torge unit to the teted houehold evluted by the numericl tudy w bout 2.5 W. We etblihed tht bout 30 % of the totl het requirement of the teted room w obtined from the het torge unit. REFERENE Boulrd, T. nd Bille, A. [1986], imultion nd nlyi of oil het torge ytem for olr Greenhoue. Energy Agric, Vol. 5, pp Guthier,., M. Lcroix nd H. Bernier, [1997], Numericl imultion of oil het exchngertorge ytem for greenhoue, olr Energy, Vol. 60, pp Htmipour. M.., Mhiyr. H. nd Theri. M. [2007], Evlution of exiing cooling utem for reducing cooling power conumption. Energy nd Building. Vol. 39, pp Hikmet, E. [2008], Experimentl energy nd exergy nlyi of double-flow olr ir heter hving different obtcle on borber plte. Building nd Environment. Vol. 43, pp Hong, Y. Jing. [1997], A new multizone model for the imultion of building therml performnce, Building nd Environment. Vol. 32, No. 2, pp

15 Jing, Y. [1981], tte pce method for nlyi of the therml behvior of room nd clcultion of ir-conditioning lod, AHARE Trnction. Vol. 88, pp Krne, R. J. [1987], A econd lw nlyi of the optimum deign nd opertion of therml energy torge ytem, Interntionl Journl of Het M Trnfer, Vol. 30, No. 1, pp Kübler. R., Bierer. M. nd Hhne.E. [1987], Het trnfer from finned nd mooth tube, het exchnger coil in hot wter tore, Het nd M Trnfer, Vol. 30, No. 14. Lron, D. L. nd ortez, L. A. B. [1995], Exergy nlyi: eentil to effective energy mngement. Trnction of AAE, Vol. 38, No. 4, pp Öztûrk, H. H. [1997], The reerch on torge of olr energy in phe chnge mteril (PM) for greenhoue heting, PhD Thei, Deprtment of Agriculturl Mchinery Intitute of Nturl nd Applied cience, Univerity of -ukurov, Turkey Öztûrk. H. H. nd Bçetinçelik. A. [2002], Therml energy torge technique, The Union of Turkih hmber of Agriculture, Publiction Number 230, Ankr Ptnkr.. V. [1980], Numericl het trnfer nd fluid flow. Mc Grw-Hill, New York. hrin, A., hlbi B., Roun A., Thtouh B.. (1998). Effect of the borptnce of externl urfce on heting nd cooling lod of reidentil building in Jordn. Energy onverion & Mngement. 39 (3/4) hviv. E., Yezioro. A. nd I. pelurto, G. [2001], Therml m nd night ventiltion pive cooling deign trtegy. Renewble Energy. Vol. 24, pp oulioti, M. nd Tripngnotopoulo, Y. [2004], Experimentl tudy of P type I olr ytem. olr Energy, Vol. 76, pp