Application of geothermal heat pumps in a renovated campus building

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  • INTERNATIONAL JOURNAL OF ENERGY RESEARCHInt. J. Energy Res. 2010; 34:445453Published online 30 November 2009 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/er.1648

    Application of geothermal heat pumps in a renovated campus building

    Jae-Han Lim,y,z

    Department of Architectural Engineering, Faculty of Engineering, CheongJu University, CheongJu, Sangdang-gu 586,360-764, Republic of Korea

    SUMMARY

    Recently, geothermal heat pumps (GHPs), which are normally known as ground-source heat pumps (GSHPs), offermany advantages for heating and cooling of commercial buildings due to the higher energy efciency compared withconventional EHP system. In Korea, a recent requirement for mandatory implementation of the renewable energysystems in public building has been enforced for buildings with oor area exceeding 3000m2. While GHPs may be morecostly to install initially than the regular heat pumps, they can also produce markedly lower energy bills. For thisreason, GHPs are scrutinized as the heating and cooling alternatives in the renovation of the campus buildings inKorea. In this study, we investigate the application methods of GHPs for the renovation of the campus building, andcompare the energy costs of GHPs with that of conventional system. The objective of this study is to present anoperation status of GSHPs in a renovated campus building as an example. In results, when the GHP with water storagehas been operated during the whole year, the coefcient of performance (COP) for heating has reached from 3.12 to5.27 according to the leaving uid temperature and entering uid temperature. The COP for cooling has reached from2.86 to 5.49. In comparison results, the sum of the operating costs of GHP system was about one third of the currentheating and cooling systems. Copyright r 2009 John Wiley & Sons, Ltd.

    KEY WORDS: geothermal heat pumps (GHPs); campus building renovation; energy bills; COP; operating cost

    1. INTRODUCTION

    For many years, ground-source heat pump (GSHP)systems have been widely used in many countries ofthe world, including Turkey, India, North America,and Europe [1, 2]. In Korea, due to the PromotionLaw of the New and Renewable Energy Develop-ment, Use and Dissemination, which was enacted in2004 and imposed an obligatory installation ofspace heating and cooling systems using the newand renewable energy (NRE) sources including the

    geothermal energy for newly constructed publicbuildings, GSHP systems have spread quickly upto about 60% of the total public installation ofthe NRE equipment between 2004 and 2007 [3].Starting with 35.2 kW of two buildings in 2000,the total system capacity has been 127.1MWinstalled in 551 buildings as of August 2008. AGSHP system uses the thermal energy of theground or groundwater as the heat source andheat sink for the space heating and cooling.Typically they cost more to install than the

    zAssistant Professor.

    *Correspondence to: Jae-Han Lim, Department of architectural engineering, CheongJu University, Cheongju, Sangdang-gu 586,360-764, Republic of Korea.

    yE-mail: limit0@cju.ac.kr

    Received 1 October 2009

    Accepted 1 October 2009Copyright r 2009 John Wiley & Sons, Ltd.

  • conventional systems, however, they are expectedvery low energy costs and can also provide reliableand environmentally friendly heating and coolingwith buildings [46]. GSHPs typically were knownto have higher efciencies than air-source heatpumps (ASHP). This is because they extract heatfrom the ground or groundwater, which is about10151C at a relatively constant temperature alltimes of the year. The GSHP system mainlycomprises a heat pump, ground heat exchanger,and an interior heat distribution system. Thesecomponents affect the efciency of a GSHP system,the coefcient of performance (COP). According tothe ASHRAEs classication of GSHP system, theycould be subdivided into ground-coupled heatpumps (GCHPs), groundwater heat pumps(GWHPs) and surface water heat pumps (SWHPs)in relation to ground heat exchanger. GCHP systemis the closed-loop system, and GWHP system is theopen-loop system. GWHP systems in a semi-openloop arrangement are commonly known as stand-ing column well (SCW) systems. SCW systems usegroundwater circulated from wells as a heat sink orsource. The ground heat exchanger in these systemsconsists of a vertical borehole that is lled withgroundwater up to the level of the water table. Andwater is circulated from the well using thesubmersible pump in an open-loop pipe circuit. Alarge proportion of water is returned to the well.Compared with other GSHP systems, shorterborehole depths and more stable water tempera-tures make the SCW system an attractive commer-cial and industrial design approach [7]. Among theinstalled GSHPs between 2000 and August 2008 inKorea, closed-loop system (GCHP) and open-loopsystem (GWHP), including the semi-open loopsystem (SCW) occupy about 68.6 and 30.5%,respectively [3]. Especially, SCW systems haverecently received more attention in Korea becausethe re-injection of pumped groundwater minimizedthe amount of extracted groundwater and there isgenerally competent rock below a few meters ofsubsurface soils. According to the previousresearch, the COP of the GSHP must be greaterthan 3 to get an advantage over natural gas heatingsystem in Turkey [8].

    In Korea, the government established the New &Renewable Energy Center (NREC) under the

    Korea Energy Management Corporation (KEM-CO) and empowered the NREC to take charge ofthe development and deployment of a lot of energytechnologies, such as the geothermal energy, solarenergy, etc. To promote the installation of thegeothermal energy equipment, there are variouspromotion programs such as subsidy program,obligative applications of NRE in public facilities,and full supports for regional energy program. Withthis background, geothermal heat pumps (GHPs)has been scrutinized as the heating and coolingalternatives in the renovation of the campus build-ings. Although there have been a lot of researchesregarding the GHPs, most of the research focus onthe energetic or exergetic aspects of the geothermalenergy and its application [915]. To evaluate theeconomic feasibility of the renovation of the campusbuilding with GHPs, it is necessary to compare theenergy costs with those of the conventional systemafter the long-term operation. In this study, weinvestigate the application methods of GHPs for therenovation of the campus building, and compare theenergy costs of GHPs with that of the conventionalsystem. Also, the objective of this study is to presentan operation status of GSHPs in a renovatedcampus building as an example.

    2. THE ENERGY CONSUMPTION ANDENERGY RATES FOR THE CAMPUS

    BUILDINGS IN KOREA

    2.1. The energy consumption in the campusbuildings

    For the past decades, the energy consumption ofuniversities in Korea has been gradually risingbecause of the severe outdoor temperatures withregard to recent global warming and also suddenexpansion of the campus buildings. Because thefunction of the campus buildings has been compli-cated according to the social needs of not onlyeducation but also research & development, it isinevitable to increase gradually in the energyconsumption of university. According to the recentarticle regarding the energy consumption of uni-versities in Korea, the total energy consumption getsto 397,130 TOE, which is the sum of 75 universitiesamong the whole country (see Figure 1). It is the

    J.-H. LIM446

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

  • same value of 353,000 ton in CO2 emission. Thatwas a remarkable value because 1.3 millions ofKorean pine trees should be planted to absorb theemitted CO2 gas. Furthermore, it was very amazingthat 23 universities were included in 190 energy-guzzling buildings in the whole country. Also it wasa notable issue that the portion of the electricalenergy consumption was very large. Similarly, somany universities in the world have perceived theenergy problems for each campus and tried toreduce the energy consumption.

    Most of the newly-built or renovated buildingsin university have tried to use the most efcientenergy sources, construction materials for walls andwindows, electronic appliances, and electric light-ings. For example, the NRE such as the geothermalenergy and solar PV system have been consideredas an alternative of the conventional energy sour-ces. Also examples include the emphasis on thethermal insulation of interior and exterior walls,and high efcient mechanical and electrical equip-ments. Most buildings have the HVAC systemsoperated by computer over the campus network.

    2.2. The energy rates for the campus buildings in Korea

    In Korea, there are several kinds of main energysources such as oil, gas, electricity, and the thermalenergy. In spite of the surging domestic energyconsumption, Korean government has been ableto maintain a stable supply of energy through thecontinuous expansion of the energy supply facil-ities. As for the energy demand by source, theoverall oil consumption is expected to increase byan annual average of 2% or more by 2010 and the

    oil price is gradually increasing every year, thedemand of oil for heating equipment are decreas-ing in the campus buildings, although the currentheating sources were oil-red boilers. As comparedwith the oil supply, gas supply is a little morestable since it is deposited widely around theworld. For this reason, the consumption of gas isexpected to increase rapidly in the residential andcampus buildings. Electricity demands also con-tinue to grow as people demand high-qualityenergy. As shown in Figure 1, the electricityconsumption in the campus building was enor-mous. Because there are so many equipments forresearch and education in the campus buildings,the demand for electricity will be more increasingcompared with any other energy sources. NRE isalso expected to apply to the HVAC system of thecampus buildings because of the changing attituderegarding fuel economy and the subsidy programof government. Especially the geothermal energyusing GHPs is normally recognized as an alter-native for the current Packaged-type air condi-tioner (PAC) system.

    In the campus buildings, the electricity rates havebeen different from the other facilities like the re-sidential and industrial buildings (Table I). Becauseof the low prices compared with the residentialelectricity, the individual PAC system was normallyused for cooling. As the installation of PAC systemhas been generalized in lecture rooms, the electricityconsumption also rapidly increased. For this rea-son, air-source electric heat pumps (EHPs) wererst considered as the heating and cooling equip-ment. Though the easy installation and a little in-itial cost for applying the air-source EHPs to thecampus buildings, the operation cost was greatcompared with the NRE. As the energy rates (oil,gas, or electricity) have increased consistently andthe university has an accumulated decit for theenergy costs, the common concern has been focusedto the NRE, such as the geothermal energy.

    3. APPLICATION OF THE GHPs IN THERENOVATED CAMPUS BUILDING

    Recently, as the geothermal energy has beenconsidered as the alternative for saving the

    Figure 1. Statistical record of the energy consumptionof university in Korea (referred to the news articleabout the energy consumption of campus in Korea,

    Ohmynews, http://www.ohmynews.com).

    APPLICATION OF GEOTHERMAL HEAT PUMPS 447

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

  • electrical energy consumption, there have been somany researches about GHPs and eld applica-tions in the commercial buildings in Korea. In thisstudy, we investigate the application methods ofGHPs as an example and compare the energy costsof GHPs with that of the conventional system. Forthis purpose, the renovated campus building(Figure 2), which is located in Cheong-Ju city ofKorea, has been investigated and the energy billswere analyzed.

    3.1. The campus building renovation

    The summary of the renovated campus building isthe following Table II. The total oor area is14,167m2 and the conditioned space is 8480m2.There are several types of room, such as lectureroom, professors ofce, departments ofce,seminar room, computer room, etc. For the spaceheating and cooling with domestic hot watersupply, 50 RT (54 kW of heating capacity and43 kW of cooling capacity) three GHPs with waterstorage tank were installed in the basement oor ofthe building. Among the several type of ground

    heat source/sink, the open-loop heat pumps, i.e.SCW method, were applied to the buildingmechanical system.

    GHPs that use groundwater drawn from wellsas a heat source/sink are commonly known asSCW systems. As shown in Figure 3, the GHPssystem in this project was composed of boreholes(SCW), water storage tank and heat exchanger,etc. In this SCW system, the heat exchange rate

    Table I. Comparison of energy rates in Korea (20072008).

    For educational electricity (high-voltage A)Alternatives Basic rate

    (Won/kW)Summer Winter

    (Won/kWh)Other seasons

    Alt. 1 4 340 72.6 52.9 46.7Alt. 2 4 970 69.3 49.3 43.5

    For night-time electricity (B type)Year Basic rate

    (Won/kW)Winter Other seasons

    (Won/kWh)Daytime

    2007 5 890 42.9 33.1 72.82008 4 970 52.1 37.9 70.6

    For residential electricity (low-voltage)Basic rate(Won/kW)

    Energy rates(Won/kWh)

    0100 kWh 370 55.10101200 kWh 820 113.80201300 kWh 1 430 168.30301400 kWh 3 420 248.60401500 kWh 6 410 366.40Above 501 kWh 11 750 643.90

    For oil for boiler (Won/l)Year2007 1 0502008 Rapidly increasing recently

    Figure 2. Photo of renovated building.

    J.-H. LIM448

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

  • could be enhanced by the pumping action, whichpromotes the movement of groundwater and in-duces the advective heat transfer. Compared withthe GHPs system with closed-loop heat exchangers(U-tube), the efciency of SCW system may beimproved because the uid ows through theGHPs are closer to the mean ground temperature.The ground heat exchanger in such a system con-sists of a vertical borehole that is lled withgroundwater up to the level of the water table (i.e.similar construction to a domestic water well).Water is circulated from the well through the heat

    pump in an open-loop pipe circuit to the heat ex-changer (HX). The piping from water storage tankwas connected to each of fan coil units (FCUs)and domestic hot water supply.

    Building the mechanical system have been re-novated and upgraded to improve the energysavings. The university is pursuing thermal storageas an alternative to add the capacity and shiftenergy use at night to reduce the electrical costs.As shown in Figure 4, the night-time electricity(from 22:00 p.m. to 8:00 a.m.), which is nearly halfthe price of the day-time electricity, is used formaking the water of storage tank cool or heat.

    Through the implementation of a central con-trol system for the mechanical equipment using thecampus network, it is possible to allow the severallevel of control over the HVAC system in eachroom of buildings depending on the schedule ofoccupants. Most room temperatures can be mon-itored remotely and fans can be started or stopped.Various informations regarding the operation ofGHPs are available at the Department of Facilitiesin university. Technicians can also access the sys-tem from their desktop computer to look at theproblems during operation. Where conditionsallow, all buildings have scheduled according tothe pre-determined timetables. As almost no wasteheat is discharged to the atmosphere, the use ofthese systems is expected to contribute to a

    Table II. Summary of renovated building.

    Category Description

    Building type Educational facilityFloor space 14 167m2

    Services Space heating/coolingdomestic hot water supply

    Application methods Standing column wellwith water storage tank

    Water storage tank 540 ton (13.5 8 5m3)Domestic hot water 3 tonControl Automatic control systemTerminal unit FCUsConditioned space 8 480m2

    Heat pump 50 RT, 3 EANumbers of borehole 6 holesDepth of borehole 400m

    Figure 3. Conguration of GHPs with SCW system. GHPs, geothermal heat pumps; SCW, standing column well.

    APPLICATION OF GEOTHERMAL HEAT PUMPS 449

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

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  • reduction in the heat island effect. Also it couldlower the demand for electrical peak power duringthe day-time operation.

    3.2. Application of the GHP system

    The rst step for the installation of a GHP systemis to nd the characteristics of the site in terms of ageology and groundwater availability. Normally,the ground-source industry for domestic watersupply has not fully taken a consideration of thegeological information in the past. But in design-ing the HVAC system, it is necessary to know thewater temperature distribution of heat exchangeborehole and the COP according to the leaving orentering water temperature. The temperature inthe well is shown in Figure 5.

    The minimum temperature in the well was 14.81Cat a depth of about 40m and it would be uctuatedbetween the ranges of 711C according to the circu-lation quantity of water ow. As shown in Table III,the COP for heating has reached from 3.12 to 5.27according to the leaving uid temperature (LFT) andentering uid temperature (EFT). Also the COP forcooling has reached from 2.86 to 5.49.

    4. ANALYSIS OF THE ENERGYCONSUMPTION AND OPERATING COSTS

    After the building renovation in 2006, the GHPsystem has been operated during heating andcooling seasons. According to the usual academic

    schedule, GHP system integrated with waterstorage tank was operated. For example, thelecture rooms or seminar rooms were scheduledin the central control system during the 1st and2nd semesters, and the professors ofces ordepartments ofces were operated by using theindividual room controller.

    During the measurement period in winter, theoutdoor temperature was about an average of 01Cand the room temperature was kept at 18201C.This temperature was sufcient in the heating con-dition of Korea. From these measurements, it was

    Usage ofwater

    storagetank

    Nighttimeoperation usingwater storage

    tank

    Figure 4. Operation strategy of GHPs with water storage tank. GHPs, geothermal heat pumps.

    Figure 5. Measurement results of well temperature.

    J.-H. LIM450

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

  • veried that heating by GHP could be used insteadof the conventional oil-boiler in winter in Cheong-Ju, Korea. Moreover, it is possible to decrease thedischarge of carbon dioxide with the GHP system.

    We have rst analyzed the monitoring data of theelectrical energy consumption, which are composed

    of day-time electricity consumption, night-time elec-tricity consumption, and electricity consumption ofwater circulation pumps every month. Based on eachof the electrical energy consumption, the amount ofheat production from the GHP was calculated ac-cording to the assumptions as given in Table IV.

    Table III. COP test results of GHP.

    LFT (1C) EFT (1C) Capacity (mcal/h) Power (kW) COP (heating)

    40 6 133.5 35.95 4.328 141.8 36.27 4.5410 150.5 36.61 4.7812 159.7 36.98 5.0214 169.3 37.36 5.27

    45 6 131.2 39.41 3.878 139.1 39.72 4.0710 147.4 40.05 4.2812 156.2 40.41 4.5014 165.5 40.78 4.72

    50 6 129.2 43.25 3.478 136.7 43.56 3.6510 144.6 43.89 3.8312 153.0 44.24 4.0214 161.9 44.60 4.22

    55 6 127.6 47.51 3.128 134.6 47.82 3.2710 142.1 48.16 3.4312 150.0 48.51 3.6014 158.4 48.87 3.77

    LFT (1C) EFT (1C) Capacity (mcal/h) Power (kW) COP (cooling)

    40 6 119.3 27.93 4.978 114.6 31.07 4.2910 109.8 33.82 3.7712 104.5 36.88 3.3014 99.2 40.32 2.86

    45 6 123.8 28.16 5.118 119.0 31.27 4.4210 113.9 34.01 3.9012 108.5 36.88 3.4214 103.0 40.50 2.96

    50 6 128.4 28.39 5.268 123.4 31.48 4.5610 118.2 34.21 4.0212 112.6 37.26 3.5214 106.9 40.68 3.06

    55 6 133.0 28.64 5.408 127.9 31.70 4.6910 122.6 34.41 4.1412 116.9 37.46 3.6314 110.9 40.87 3.16

    LFT, leaving uid temperature; EFT, entering uid temperature.

    APPLICATION OF GEOTHERMAL HEAT PUMPS 451

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

  • As shown in Figure 6, the electrical energyconsumption in 2007 was maximum 55,210 kWhand in 2008 was maximum 53,601 kWh. Com-pared with the winter season, the energy con-sumption in summer was a smaller quantity. It isbecause the operation time of GHP system inwinter is longer than that in summer.

    To compare the operating costs of GHPsystem with those of the conventional system, asshown in Table V, the capacity of boiler with2 ton and the 12 PAC with 30 hp capacity wereassumed. The oil price was assumed as given inTable I.

    In comparison results, the sum of the operatingcosts of the GHP system was about 34 million(won) in 2007; however, those of oil-red boilerwith PAC system was about 92 million (won).That was nearly 3 times per year (Table VI).

    And the initial cost for GSHP systems dependson where you live and which system you use. If theuse of GHP systems becomes more popular, it willreduce the cost of drilling boreholes for the verticalground heat exchangers, which is the main causeof the high initial cost. If a 50% subsidy is ob-tained from the government to promote the in-troduction of these systems, the initial investment

    Table IV. Assumptions for calculation of the amount ofheat production.

    GHP with water storage system (150 RT)

    ElectricalConsumption(kW)

    Number ofequipment

    COP

    Heating Cooling

    62.0 2 3.0 3.5

    Operating time of circulationpump (h/day)

    Efciency of waterstorage (%)

    15 95

    Figure 6. Monitoring data of the electrical energy consumption and heat production.

    Table V. Assumptions for Comparison of operatingcosts.

    Oil-red boiler (2 ton) with PAC (30 hp 12)

    Heating value(kcal/l)

    Boiler efciency(%)

    Operatingtime (h/day)

    62.0 92 7.5

    Heat extractionrate (kcal/kW)

    Electric power(kW)

    COP

    860 338 2.7

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  • for the installation of the GHP can be recoveredwithin a few years.

    5. CONCLUSION

    In this study, the application of GHPs for theretrotted building and the energy costs of GHPs arecompared with the conventional system. In experi-mental results, when the GHP with water storagehas been operated during the whole year, the COPfor heating has reached from 3.12 to 5.27 accordingto the LFT and EFT. The COP for cooling hasreached from 2.86 to 5.49. When the GHP systemhas been operated during the whole year, it wasveried that heating and cooling by GHP couldreplace the current oil-red boiler with PAC system.Also the operating cost is found to decrease by onethird of the current heating and cooling systems.

    NOMENCLATURE

    C 5 specic heat (kJ/kgK)COP 5 heating coefcient of performance

    (dimensionless)T 5 temperature (K) AbbreviationsASHPs 5 air source heat pumpsEHP 5 electric heat pumpGCHP 5 ground-coupled heat pumpsGHPs 5 geothermal heat pumpsGSPHs 5 ground source heat pumpsGWHP 5 groundwater heat pumpsKEMCO 5Korea Energy Management

    CorporationNRE 5 new & renewable energyNREC 5New & Renewable Energy Center

    PAC 5 packaged-type air conditionerSCW 5 standing column wellSWHP 5 surface water heat pumps

    REFERENCES

    1. Sanner B, Karytsas C, Mendrino D, Rybach L. Currentstatus of ground source heat pumps and undergroundthermal energy storage in Europe. Geothermics 2003;32:579588.

    2. Rybach L, Sanner B. Ground-source Heat Pump Systems,The European Experience. GHC Bulletin. Geo-Heat Center,Oregon Institute of Technology, 2000.

    3. Lee J-Y. Current status of ground source heat pumps inKorea. Renewable and Sustainable Energy Reviews 2009;13:15601568.

    4. Kavanaugh SP. Ground-Source Heat Pumps. ASHRAE.W. Stephen Comstock: Atlanta, GA, 1997.

    5. Cane D, Morrison A, Ireland CJ. Maintenance and servicecosts of commercial building ground-source heat pumpsystems. ASHRAE Transactions 1998; 104(2): 699706.

    6. Esen H, Inalli M, Esen M. Technoeconomic appraisal of aground source heat pump system for a heating season ineastern Turkey. Energy Conversion and Management 2006;47:12811297.

    7. ONeill ZD, Spitler JD, Rees SJ. Performance analysis ofstanding column well ground heat exchanger systems.ASHRAE Transactions 2006; 112(2):633643.

    8. Kara YA. Experimental performance evaluation of a closedloop vertical ground source heat pump in the heating modeusing energy analysis method. International Journal ofEnergy Research 2007; 31:15041516.

    9. Hepbasli A. Thermodynamic analysis of a ground-sourceheat pump system for district heating. International Journalof Energy Research 2005; 29:671687.

    10. Ozgener L, Hepbasli A, Dincer I. Energy and exergyanalysis of Salihli geothermal district heating system inManisa, Turkey. International Journal of Energy Research2005; 29:393408.

    11. Hepbasli A, Akdemir O. Energy and exergy analysis of aground source (geothermal) heat pump system. EnergyConversion and Management 2004; 45:737753.

    12. Inalli M, Esen H. Experimental thermal performanceevaluation of a horizontal ground-source heat pumpsystem. Applied Thermal Engineering 2004; 24:22192232.

    13. Ozgener O, Hepbasli A. Experimental investigation of theperformance of a solar-assisted ground-source heat pumpsystem for greenhouse heating. International Journal ofEnergy Research 2005; 29:217231.

    14. Hwang Y, Lee J-K, Jeong Y-M et al. Cooling performanceof a vertical ground-coupled heat pump system installed ina school building. Renewable Energy 2009; 34:578582.

    15. Kara YA, Yuksel B. Evaluation of low temperaturegeothermal energy through the use of heat pump. EnergyConversion and Management 2001; 42:773781.

    Table VI. Comparison of total sum of operating costs(in 2007).

    GHP with waterstorage system

    Oil-red boilerwith PAC system

    34 155 086 Won 92 536 437 Won

    1 UD$5 1000 Won (in 2007).

    APPLICATION OF GEOTHERMAL HEAT PUMPS 453

    Copyright r 2009 John Wiley & Sons, Ltd. Int. J. Energy Res. 2010; 34:445453

    DOI: 10.1002/er

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