Ecoomic assessmet of a two-stage heat pump with heat exchager to exploit low-temperature geothermal eergy SVEN H. DE CLEYN Faculty of Applied Ecoomics Uiversity of Atwerp Prisstraat 13, BE-2000 Atwerp BELGIUM Sve.decley@ua.ac.be http://www.ua.ac.be/sve.decley AMARYLLIS AUDENAERT Departmet of Applied Egieerig: costructio Artesis Hogeschool Atwerpe Paardemarkt 92, BE-2000 Atwerp BELGIUM Amaryllis.audeaert@artesis.be & Uiversity of Atwerp Prisstraat 13, BE-2000 Atwerp BELGIUM Amaryllis.audeaert@ua.ac.be http://www.ua.ac.be/amaryllis.audeaert Abstract: - Withi the cotext of sustaiable housig, cosiderable research attetio has bee o differet devices ad techiques to lower eergy cosumptio ad alterative, evirometal-friedly alteratives to geerate eergy. Recetly, scholars egage icreasigly i the ecoomic aspects of these devices ad techiques. This study elaborates o the study of Kulcar et al. [1], which have ivestigated the ecoomy of exploitig a two-stage heat pump with heat exchager usig low-temperature geothermal sources for buildig heatig purposes. The results of the aalysis suggest that uder the circumstaces defied i [1], the system is a iterestig ivestmet from a fiacial viewpoit. However, the results tur out to be strogly depedet o the evolutio of the electricity ad heat prices. It turs out that the et preset value of the ivestmet is more sesitive to chages i heat prices tha it is to variatios i electricity prices. Key-Words: Ecoomic aalysis; Payback time; Geothermal eergy; Heat pump Nomeclature a Aual istalmet factor C E Price of electricity (EUR/kWh) C INV Ivestmet costs (EUR/year) C P Icomig cash flow from the extracted heat (EUR/year) C PS Electricity costs for ruig the compressor (EUR/year) C T Price of heat (EUR/kWh) C S Expeses (EUR/year) C TC Total price of a heat pump (EUR) C t Total yearly icomig or outgoig cash flow (EUR/year) C 0 Ivestor s ow resources (EUR) k Required rate of retur (%) Lifespa of a heat pump (years) IRR Iteral Rate of Retur (%) NPV Net Preset Value (EUR) P Power used by a compressor (kw) Q k Heat flow of a codeser (kw) r Discout rate r a Discout rate of aual istalmets r Iflatio rate t 1 Operatioal time of heat pump (h/day) Operatioal time of heat pump (days/year) t 2 1 Itroductio Cosiderable research has bee ad is curretly beig spet o ivestigatig the effects of huma ISSN: 1790-5079 23 Issue 1, Volume 7, Jauary 2011
activities o the emissio of greehouse gases ad the subsequet climate chages. The actual debate o global warmig the craks up the search for evirometal-friedly alteratives to maitai our curret livig stadards ad level of activity. Reductio of eergy use ad evirometal-friedly alteratives to geerate eergy are two pathways that have to be walked simultaeously. For both alteratives, evirometal impact should be assessed together with the ecoomic viability [2], which is however ot yet commo practice. Some of the scarce studies relates to sustaiable housig [3, 4]. Oe of the may alterative eergy sources curretly beig exploited o a larger scale is geothermal eergy [5, 6]. Geothermal eergy gradually becomes a iterestig eergy source from a ecoomic poit of view. As the eergy demad used for space heatig accouts for 78% of EU15 household delivered eergy cosumptio [7], sigificat reductios i eergy demad ca be achieved by promotig sustaiable housig ad evirometal-friedly alteratives [8]. I Japa, 24.5% of total electricity cosumptio of households is used for space heatig [9]. There is thus a curretly largely utapped potetial that offers sigificat opportuities to reach the Kyoto obectives [10]. Withi this framework of sustaiable housig, Kulcar et al. [1] have ivestigated the ecoomic implicatios of a two-stage heat pump usig lowtemperature geothermal eergy for high-temperature heatig of buildigs i the Sloveia cotext. The potetial of this gree techology has bee illustrated by e.g. Gillet [11], statig that he ever ecoutered a situatio where fossil fuel-based techologies caot be replaced by a cleaer techology at a lower total cost. Heat pump techology thus has a sigificat potetial i reducig eergy eeds, amogst other for space heatig purposes [12, 13]. This article will elaborate o the ecoomic aspects of their fidigs, usig idetical techical specificatios of the heat pump. Therefore, the techical sectio of this article will be reduced to its utmost miimum, as more details ca be foud i [1]. The remaider is structured as follows. Firstly, the techical specificatios of the two-stage heat pump uder cosideratio will be highlighted. Afterwards, the ecoomic aalysis will simulate differet scearios, especially cosiderig the impact of eergy ad heat prices ad their effects o the feasibility of exploitig lowtemperature geothermal eergy for high-temperature buildig heatig. 2 Techical characteristics A heat pump is a device which extracts heat from its eviromet ad emits it ito a heatig system at a higher temperature level. The characteristics of a heat pump deped o various desig choices: the coefficiet of performace (gaied heat flow i the compressor divided by the compressor s eergy use), the heat flows of the codeser ad evaporator, the eergy cosumptio of the compressor ad the pressure ratio of the compressor. For more iformatio o these techical characteristics, we refer to the work of Kara ad Yuksel [14], Kulcar et al. [1], Ozgeer ad Hepbasli [15] ad Ozgeer et al. [16]. As buildig heatig requires high-temperature heatig, a two-stage heat pump is ecessary [1]. Therefore, this article exclusively cosiders a two stage heat pump with heat exchager, which is schematically preseted i Figure 1. The heat pump is made up of three compoets: two sigle stage heat pumps coected by a heat exchager. The mai advatage of such cofiguratio is that accordig to the physical chemical characteristics differet refrigerats ca be used at each stage [1]. The heat exchager betwee the two stages represets a codeser for the first stage ad a evaporator for the secod [1]. Geothermal water (T g1 = 62 C) serves as iput for the heat exchager, of which the output (T gm = 42 C) i tur serves as iput for the heat pumps. The priciple of exploitig heat from geothermal water i a idividual facility is show i Figure 1. With such a system it would be possible to exploit the heat of geothermal water to the temperature of 10 C [17]. The best results are obtaied whe combiig refrigerat R407c i the first stage ad refrigerat R600a i the secod [1]. The choice of the refrigerats has bee ispired by the physical chemical characteristics, ecological acceptability, ad the tred of usig refrigerats of well-kow heat pump maufacturers. Refrigerat R407c is a mixture of the followig refrigerats: 23% R32, 25% R125 ad 52% R134a [1, 17]. The mai characteristics of the refrigerats are preseted i Table 1. ISSN: 1790-5079 24 Issue 1, Volume 7, Jauary 2011
Fig. 1. Heatig system usig a two stage heat pump with heat exchager [1]. Table 1. Characteristics of refrigerats [1]. Refrigerat Chemical formula Molecular weight (g/mol) Temperature coditio ( C) Ethalpy of evaporatio (kj/kg) R125 C2HF5 120.00-48.9 159.7 R32 CH2F2 52.02-52.0 382.5 R134a C2H2F4 102.00-26.4 216.1 R600a i-c4h10 58.10-12.3 355.4 3 Ecoomic assessmet The ecoomic assessmet of the heat pump will cosist of two maor sub-parts. I the first place, the period of time i which the ivestmet returs itself will be computed. The most commo ivestmet aalysis ratio, the Net Preset Value (NPV) will guide this aalysis. Withi this aalysis, attetio will be paid to possible variatios i the fiacig of the ivestmet. A wide rage of optios, varyig from etirely fiacig the heat pump with ow resources to borrowig the etire ivestmet will be ivestigated. As the results will prove, the ifluece of this choice o the NPV of the proect is very limited (uder idetical circumstaces as i [1]). Afterwards, a sesitivity aalysis will reveal the most crucial parameters i this computatio. More precisely, the ifluece of the electricity price ad heat price o the ivestmet s NPV will be computed. 3. 1 Net Preset Value Whe cosiderig the Net Preset Value, future cash flows (both icomig ad outgoig) are balaced, takig the devaluatio of moey ito ISSN: 1790-5079 25 Issue 1, Volume 7, Jauary 2011
accout. The NPV the idicates how much value a ivestmet proect creates for a compay or a idividual, as it reflects the moetary value of future cash flows, takig the a priori required retur ad iflatio rate ito accout. The basic formula for the NPV is: NPV = C t t= 0 1+ ( k) t As Kulcar et al. [1] pertietly remark, a ivestmet ca be covered by ow fuds, (bak) loas or a combiatio of both. The aalysis from the ivestor s viewpoit the differs depedig o the combiatio opted for. The preset value of the ivestmet cost C INV is the: C INV = C 0 + = 0 + a C TC ( 1 r) The aual istallmet factor is the determied as: ra( 1+ ra) ( 1+ r ) 1 a (3) = a The yearly maiteace costs C S are estimated at 2% of the iitial purchase price of 24,000, i.e. 480. Uless i situatios where iflatio is higher tha the discout rate (which is irratioal), the discouted maiteace costs will ot exceed 480 (which is i cotradictio to the figures i [1]). Therefore, our results will differ from the results obtaied by Kulcar et al. [1]. The et preset value of the maiteace costs is determied with followig equatio: C S = N CTC( 1+ r) ( + r r) 0.02 = 0 1 + N QkCT t1t 2 1+ r CP = (6) (1) = 0 1+ r + r (1) (4) To operate the heat pumps ad the compressor, a certai amout of electricity is cosumed. The et preset value of this electricity costs C PS is determied with the equatio: C PS = N C Pt1t2( 1+ r) ( 1+ r r) E = 0 + (5) Operatig the heat pumps had the advatage of extractig heat, which provides a icome for the ower of the system. The NPV of the icome from the extracted heat C P is determied with followig equatio: ( ) ( ) 3.2 Ifluece of fiacig mechaism A proect s NPV from the ower s poit of view is partially depedet o the origi of the fiacial meas. If the required ivestmet is etirely fiaced with ow resources, the ivestmet falls etirely at the start of the proect. However, if the eeded resources are (partially) borrowed, the (2) ivestmet from the ower s viewpoit is spread i (2) time. The disadvatage of this spread lies i the fact that borrowed moey carries some additioal costs i the form of iterests o the capital. To which side the balace tips, depeds o the required iterest rates o the borrowed capital, the iflatio rate ad the required rate of retur o the ivestmet. Table 2. Mai figures for the ecoomic aalysis. Variable Symbol Value Uits Price of a heat pump C TC 24,000 EUR system Operatioal life time 20 Years of the heat pump Duratio of the loa 10 Years Discout rate r 0.07 Discout rate of r a 0.07 aual istalmets Iflatio rate r 0.012 Power used by the P 51.79 kw compressor Heat flow of the Q k 187.3 kw codeser Price of electricity C E 0.07 EUR/kWh Price of heat C T 0.0325 EUR/kWh Maiteace costs C S 0.02C TC EUR/year Operatioal time of t 1 18 h/day the heat pump per day Operatioal time of the heat pump per year t 2 120 days/year ISSN: 1790-5079 26 Issue 1, Volume 7, Jauary 2011
Withi the cotext of this study, the basic premises of [1] have iitially bee adopted. The iflatio rate r has bee fixed o 1.2% (which reflects a average sceario compared to the past period of high iflatio followed by the period of low iflatio or eve deflatio recetly), while the discout rate r amouts 7%. With a electricity price of 0.07 /kwh ad a heat price of 0.0325 /kwh, the ifluece of the fiacig mix o the proect s NPV from the ower s perspective has bee ivestigated. The fiacig mix varies betwee 100% of ow ad 100% of borrowed resources. I case of borrowed resources, it has bee assumed that the loa period amouted 10 years with yearly terms. Additioally, the operatioal life of the heat pump is assumed to be 20 years. Table 2 summarises the mai figure used throughout the ecoomic aalyses, uless otherwise idicated. The differece i NPV betwee the two extreme situatios of the fiacial mix (the etire ivestmet borrowed or fiaced with ow resources) is zero. The aual istallmets have bee discouted without accoutig for iflatio (as a bak loa with fixed iterest rate has bee opted for). The results idicate that, uder the basic circumstaces assumed i [1] (C E = 0.07 /kwh ad C T = 0.0325 /kwh), ivestig i a two stage heat pump with heat exchager usig low-temperature geothermal sources for buildig heatig purposes is fiacially iterestig. All fiacial mixes give a sigificatly positive NPV of 27,584.16. The total ivestmet cost of 24,000 is easily recovered by the gais through heat productio. The Iteral Rate of Retur (IRR), which idicates the rate of retur that the ower receives for his ivestmet, amouts almost 20%. This is much higher tha the required 7% (idicated by the discout rate). Thus, uder the give circumstaces, ivestig i the heat pump is fiacially very attractive. This result is i lie with the fidigs of Poberžik et al. [5]. Uder the assumptios of [1], where 8,000 is ivested from ow resources, the NPV is 27,584.16. After a period of 3.64 years, the ivestmet returs itself. This result is cosiderably differet (+14%) from the result obtaied i [1]. As idicated earlier, this is due to a differece i maiteace costs. However, uder the give circumstaces, the ivestmet remais attractive. 3.3 Ifluece of electricity ad heat price Besides the fiacig mix, other variables ca exert sigificat ifluece o the fiacial attractiveess of the ivestmet. I this sectio, it is assumed the etire ivestmet is covered with borrowed resources (ow capital = 0). As discussed earlier, the fiacial mix has o ifluece o the results. The NPV of the proect might be iflueced by the evolutio of the electricity price (eeded to operate the compressors) ad the heat price (icome received from the heat extracted by the codeser). Especially i view of the sharply icreasig eergy prices of the first half of 2008, this aalysis could reveal the sesitivity of the results to the electricity ad heat prices. Fig. 2. Electricity prices for medium size households i Belgium, Sloveia ad EU-15 (EUR/kWh) ISSN: 1790-5079 27 Issue 1, Volume 7, Jauary 2011
Fig. 3. Ifluece of electricity price o NPV. Ifuece of electricity price o NPV (C 0 = 0 ad C T = 0,0325 /kwh) 100.000,00 50.000,00 0,00 NPV (EUR) 50.000,00 0,0400 0,0475 0,0550 0,0625 0,0700 0,0775 0,0850 0,0925 0,1000 0,1075 0,1150 0,1225 0,1300 0,1375 0,1450 0,1525 0,1600 0,1675 0,1750 0,1825 0,1900 0,1975 0,2050 0,2125 0,2200 0,2275 0,2350 0,2425 0,2500 100.000,00 150.000,00 200.000,00 C E (EUR/kWh) The results of the aalysis are preseted i Figures 3 ad 4. Both graphs have bee obtaied through variatio of oe of both parameters (resp. electricity price ad heat price) uder the ceteris paribus hypothesis. The results suggest a liear egative relatioship betwee the electricity price ad the NPV of the ivestmet. For each icrease of the electricity price with 0.0025 /kwh (uder ceteris paribus circumstaces), the NPV decreases with 2,982.00. Uder the give circumstaces (C 0 = 0 ad C T = 0.0325 /kwh), the ivestmet gets a egative NPV if the electricity price surpasses 0.0925. I may Europea coutries, this price is ot urealistic. For example, the average electricity price for household cosumptio i Sloveia i Jauary 2007 was 0.1064 /kwh, while i Belgium this was 0.1581 /kwh [18]. Sice the, electricity prices have bee risig uremittigly i almost all Europea coutries, as is illustrated by Figure 2, util the ed of 2008. Sice the, electricity prices are decreasig a little agai. Therefore, the attractiveess of the proect should be uaced withi the light of these results. I a further stage, the ifluece of the electricity price will be evaluated simultaeously with a evolutio i the heat price. Startig from the basic circumstaces (C 0 = 0 ad C T = 0.0325 /kwh), a icrease of the electricity price to 0.075 /kwh leads to a icrease of the payback period from 3.64 to 4.83 years uder ceteris paribus hypotheses. The results of a similar aalysis to ivestigate the ifluece of the heat price o the NPV are preseted i Figure 4. As expected, the relatioship is positive. Each icrease of the heat price with 0.0025 /kwh uder ceteris paribus circumstaces iduces a icrease of the proect s NPV with 10,784.47. This leads to a NPV of 0 whe the heat prices reaches 0.00261 /kwh, which is low compared to curret prices. The evolutio of the heat price ca be assumed to have a positive effect o the attractiveess of ivestig i a heat pump system. The recet favourable climate however largely depeds o the evolutio of the electricity prices (ad iflatio), as illustrated previously. Additioal to the sesitivity aalysis performed o the idividual variables electricity price ad heat price, it might be iterestig to evaluate simultaeous variaces i both prices. It is ideed atural that both prices, although ot perfectly related, vary i a similar way at the same time, as it ISSN: 1790-5079 28 Issue 1, Volume 7, Jauary 2011
cocers prices of eergy goods. The results of this aalysis are preseted i Figure 5. For the aalysis, variatios of the electricity price betwee 0.04 /kwh ad 0.25 /kwh ad of the heat price betwee 0.01 /kwh ad 0.15 /kwh have bee ivestigated. As the results illustrate, a equal icrease i absolute terms of the electricity ad heat price leads to a amelioratio of the NPV. For example, startig from the origial situatio where C E equals to 0.07 /kwh ad C T equals to 0.0325 /kwh, a rise of both variables with 0.005 /kwh leads to a icrease of the NPV from 27,584.16 to 43,189.11. Similarly, a equal relative rise of both variables leads to a icrease i the NPV. For example, a icrease with 10%, from 0.07 /kwh to 0.077 /kwh for the electricity price ad from 0.0325 /kwh to 0.03575 /kwh for the heat price, leads to a NPV of 33,254.39 istead of 27,584.16. Therefore, it ca be argued that the et preset value of the ivestmet is more sesitive to chages i heat prices tha it is to variatios i electricity prices. 4 Coclusio The results of our study suggest that the ecoomic viability of exploitig low-temperature geothermal eergy for heatig of buildigs usig a two-stage heat pump with heat exchager is guarateed uder may circumstaces. Uder the basic assumptios (idetical to those i [1]), the ivestmet i the heat pump system returs itself i less tha 4 years. However, i view of the recet variatios i eergy costs, this result should be approached with cautio. It turs out that the NPV of the ivestmet is more sesitive to chages i the heat price tha it is to chages i electricity price. Ayhow, the ivestmet i the heat pump system remais iterestig from a ecoomic poit of view uder the maority of the circumstaces. Our results therefore cofirm the results of Kulcar et al. [1]. O the opposite side, the ivestmet should be evaluated carefully, especially i circumstaces where heat prices would icrease at a slower pace tha electricity prices do. The balace could the overtur to result i a egative NPV. Aother iterestig result of our study is the ifluece exerted by the balace betwee ow ad borrowed resources to fiace the ivestmet. Surprisigly, our results suggest that these variables do ot have ay impact o the fial Net Preset Value for the ivestor, uder the circumstaces ivestigated. However, depedig o the specific situatio (other aual istalmet factors, iflatio etc.), this result might ot hold for ay idividual. Fig. 4. Ifluece of the heat price o the NPV. Ifluece of heat price o NPV (C 0 = 0 ad C E = 0,07 /kwh) 600000 500000 400000 300000 200000 100000 0 0,010 0,015 0,020 0,025 0,030 0,035 0,040 0,045 0,050 0,055 0,060 0,065 0,070 0,075 0,080 0,085 0,090 0,095 0,100 NPV (EUR) 0,105 0,110 0,115 0,120 0,125 0,130 0,135 0,140 0,145 0,150 100000 C T (EUR/kWh) ISSN: 1790-5079 29 Issue 1, Volume 7, Jauary 2011
Fig. 5. Ifluece of the simultaeous variatios of electricity ad heat price o NPV. 4.1 Implicatios Our results hold implicatios for differet parties. I the first place, policy makers could use our results i order to further shape geeral ad subsidy policies towards eergy-efficiet ad evirometal-friedly techologies. Our aalysis suggests that the ecoomic appeal of certai ivestmets depeds o some macro- ad meso-ecoomic parameters. I the case of the heat pump exploitig geothermal eergy, the outcome is maily determied by electricity ad heat prices o the local market. Uder chagig market coditios, policy makers might therefore eed to review ad revise the public policies for the stimulatio of gree techologies if they wish to obtai large scale itroductio. Gree techologies will oly fid their way to the large public if they are affordable whether itrisically or after govermet itervetio ad fiacially iterestig. After all, the amout of people willig to make large ivestmets i gree techologies out of ideological belief without fiacial icetive or positive retur is limited. Thus, policy makers should make a aalysis to determie uder which circumstaces various techologies should be promoted. Our study cotributed to this uderstadig by assessig the ecoomic attractiveess of ivestig i a two-stage heat pump with heat exchager to exploit low-temperature geothermal eergy i a residetial applicatio. Secodly, for idividual ivestors, this paper gives a overview of the ifluece of the maor impact factors determiig the fiacial result of a ivestmet decisio. Although the exact parameter values ivestigated i this study might ot be applicable ad relevat for each situatio, the methodology ad lie of reasoig ca be adapted to the specific situatio of the (potetial) ivestor. For example, ivestmets i specific eergyefficiet techologies (icludig solar eergy ad heat pumps) for households ca i Belgium (partially) be deducted from private taxes, especially if the ivestor borrows resources to be able to make the ivestmet. Therefore, the aforemetioed results idicatig that there is o ifluece of the resource origi are ot (etirely) valid i the Belgia cotext. Other (tax) regimes might imply similar differeces. 4.2 Limitatios The teability of aalysis results is rather limited, due to the rapidly chagig ecoomic ISSN: 1790-5079 30 Issue 1, Volume 7, Jauary 2011
circumstaces. I recet years the eergy prices have bee icreasig, although the global ecoomic crisis (temporarily?) slowed dow this process. As eergy prices have a maor impact o this proect s NPV, the results should be carefully aalysed with respect to the chagig circumstaces. A secod limitatio relates to the ifluece of iflatio o the NPV. This ifluece has ot bee ivestigated i this study. As idicated earlier, iflatio has bee fluctuatig quite substatially i Europe lately (i both directios). Therefore, it might become importat to take a closer look at iflatio. However, electricity (ad heat) prices are a compoet of iflatio. Therefore, it ca be argued that variatios of eergy prices reflect the ifluece of iflatio at least partially. Thirdly, techological iovatios are a importat aspect i the idustry sectors of reewable eergy ad sustaiable housig. New products, processes or techologies might ifluece the ecoomics of ivestmets i this sphere. Therefore, the aalyses should be performed for every ew developmet to assess its ecoomic attractiveess, besides a evirometal ad techological evaluatio. I this study however, a status quo situatio o the techological dimesio (compared to [1]) has bee ivestigated ad the evirometal impact of usig low-temperature geothermal eergy for heatig purposes has ot bee evaluated. 5 Ackowledgemets The authors gratefully ackowledge the work performed by B. Kulcar, D. Goricaec ad J. Krope. Their cotributio i Eergy ad Buildigs (Vol. 40, No. 3) iitiated our modest cotributio to the uderstadig of ecoomic aspects related to heat pumps. All credits, especially for the techical details ad cotributios, should be awarded to them. Additioally, the first author wishes to thak the Research Foudatio Fladers (FWO Vlaadere) for fiacially supportig him as PhD Fellow. Lastly, the authors would like to take the opportuity to thak the reviewers for their useful ad costructive commets o earlier versios of our paper. Refereces: [1] B. Kulcar, D. Goricaec, J. Krope, Ecoomy of exploitig heat from low-temperature geothermal sources usig a heat pump, Eergy ad Buildigs, Vol. 40, No. 3, 2008, pp. 323-329. [2] R. Myskova, The developmet ad use supportig of reewable eergy sources i terms of Czech compaies, WSEAS Trasactios o Eviromet ad Developmet, Vol. 6, No. 3, 2010, pp. 176-185. [3] A. Audeaert, S. H. De Cley, B. Vakerckhove, Ecoomic aalysis of passive houses ad low-eergy houses compared to stadard houses, Eergy Policy, Vol. 26, No. 1, 2008, pp. 47-55. [4] A. Audeaert, S. De Cley, Ecoomic viability of passive houses ad low-eergy houses, Proceedigs of the 3rd WSEAS Iteratioal Coferece o Urba Rehabilitatio ad Sustaiability (URES'10), Faro, 2010, pp. 29-35. [5] S. Poberžik, D. Goricaec, J. Krope, Ecoomic Aalysis of Geothermal Heat Source for Residetial Area Proect, Iteratioal Joural of Eergy, Vol. 1, No. 1, 2007, pp. 28-32. [6] G. W. Huttrer, Geothermal heat pumps: A icreasigly successful techology, Reewable Eergy, Vol. 10, 1997, pp. 481-488. [7] Eurostat, Eergy cosumptio i households: 1996 survey, Europea Commissio, 1999. [8] W. Feist, J. Schieders, V. Dorer, A. Haas, Reivetig air heatig: Coveiet ad comfortable withi the frame of the Passive House cocept, Eergy ad Buildigs, Vol. 37, 2005, pp. 1186-1203. [9] V. R. Tarawski, W. H. Leog, T. Momose, Y. Hamada, Aalysis of groud source heat pumps with horizotal groud heat exchagers for orther Japa, Reewable Eergy, Vol. 34, 2009, pp. 127-134. [10] M. Jakob, Margial costs ad co-beefits of eergy efficiecy ivestmets. The case of the Swiss residetial sector, Eergy Policy, Vol. 34, 2006, pp. 172-187. [11] A. C. Gillet, The use of heat pumps i solar heatig i Belgium, Reewable Eergy, Vol. 16, 1999, pp. 647-651. [12] L. Huag, X. Li, X. Fu, The idustrializatio prospect aalysis of water resource heat pump based o sceario plaig, WSEAS Trasactios o Eviromet ad Developmet, Vol. 5, No. 3, 2009, pp. 240-249. [13] I. Sarbu, C. Sebarchievici, Heat pumps Efficiet heatig ad coolig solutio for buildigs, WSEAS Trasactios o Heat ad Mass Trasfer, Vol. 5, No. 2, 2010, pp. 31-40. [14] Y. A. Kara, B. Yuksel, Evaluatio of low temperature geothermal eergy through the use ISSN: 1790-5079 31 Issue 1, Volume 7, Jauary 2011
of heat pump, Eergy Coversio ad Maagemet 42 (2001) 773-781. [15] O. Ozgeer, A. Hepbasli, Modelig ad performace evaluatio of groud source (geothermal) heat pump systems, Eergy ad Buildigs, Vol. 39, 2007, pp. 66 75. [16] O. Ozgeer, A. Hepbasli, L. Ozgeer, A parametric study o the exergoecoomic assessmet of a vertical groud-coupled (geothermal) heat pump system, Buildig ad Eviromet, Vol. 42, 2007, pp. 1503 1509. [17] E. Torhac, L.L. Crepisek, J. Krope, D. Goricaec, A. Salikov, R. Stipic, D. Kozic, Profitability evaluatio of the heatig system usig borehole heat exchager ad heat pump, IASME Trasactios, Vol. 2, No. 8, 2005, pp. 1381 1388. [18] J. Goerte, E. Clemet, Electricity prices for EU households ad idustrial cosumers o 1 Jauary 2007, Eurostat Statistics i focus, Eviromet ad Eergy, Vol. 80/2007, 2007, pp. 1-8. ISSN: 1790-5079 32 Issue 1, Volume 7, Jauary 2011