Renewable Energy 35 (2010) 1275–1282Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene Comparison of energy and exergy analysis of fossil plant, ground and air source heat pump building heating system S.P. Lohani a, *, D. Schmidt b a b University of Oldenburg, Oldenburg, Germany Fraunhofer Institute of Building Physics, Kassel group, Germany a r t i c l e i n f o Article history: Received 2 May 2009 Accepted 5 October 2009 Available online 31 October 2009 Keywords: Ground source heat pump system Air source heat pump system Conventional system Energy analysis Exergy analysis a b s t r a c t The energy and exergy flow for a space heating systems of a typical residential building of natural ventilation system with different heat generation plants have been modeled and compared. The aim of this comparison is to demonstrate which system leads to an efficient conversion and supply of energy/ exergy within a building system. The analysis of a fossil plant heating system has been done with a typical building simulation software IDA–ICE. A zone model of a building with natural ventilation is considered and heat is being supplied by condensing boiler. The same zone model is applied for other cases of building heating systems where power generation plants are considered as ground and air source heat pumps at different operating conditions. Since there is no inbuilt simulation model for heat pumps in IDA–ICE, different COP curves of the earlier studies of heat pumps are taken into account for the evaluation of the heat pump input and output energy. The outcome of the energy and exergy flow analysis revealed that the ground source heat pump heating system is better than air source heat pump or conventional heating system. The realistic and efficient system in this study ‘‘ground source heat pump with condenser inlet temperature 30 C and varying evaporator inlet temperature’’ has roughly 25% less demand of absolute primary energy and exergy whereas about 50% high overall primary coefficient of performance and overall primary exergy efficiency than base case (conventional system). The consequence of low absolute energy and exergy demands and high efficiencies lead to a sustainable building heating system. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The use of energy in the building sector for heating and cooling is nearly one third of the total energy consumed in the world [16]. As there is growing concern in the use of fossil fuels that is being depleted soon and because of the sustainability issue, an alternative source of energy must be found to meet energy supply of high energy consumption sector. The building sector is one of the prominent sectors, which could save tremendous amount of fossil fuels if renewable energy source like ground coupled heat pumps (GCHPs) substituted them. The use of GCHPs is growing significantly in commercial and residential sectors and has numerous advantages over air source heat pumps as described by [11]. The increase in interest to the heat pumps is due to their high utilization efficiency over conventional heating and cooling systems. More or less constant temperature over the year is an important feature of the * Corresponding author. Tel.: þ4791004758. E-mail address: [email protected] (S.P. Lohani). 0960-1481/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2009.10.002 ground coupled heat pump over air source heat pump that has extreme low outside temperatures at severe weather conditions and lead to high operational energy consumption. Capital cost of GCHPs is 30–50% more expensive than air source heat pumps, which is a major hurdle in gaining overwhelming demand despite having several advantages. Nevertheless, the annual operation cost is less making the unit justifiable over the life time operation [12]. As heat pumps are advantageous from the energy, environment and sustainability point of view, efforts should focus on to show scientific evidence to the knowledge body of the society. Thermodynamic analysis of the system would produce scientific results that help convince scientific knowledge body to propel the system at large. Thermal analysis of a system focuses on first law and second law of thermodynamics. First law deals with energy balance of a system whereas second law address energy and entropy of a system, it gives in depth of the system operations. Combining first law and second law of thermodynamics is necessary for exergy analysis of the system that gives detail know how of the performance evaluation and optimization of the system. Exergy analysis is the basis 2. [J] Entropy.13].ln Tret þ m. 1 À T0 þm. the exergy demand of the room is therefore low. Thermal analysis This paper focus on the analysis of the energy and exergy flow of the fossil plant and air or ground coupled heat pump building heating systems.ln Tin _ _ _ m. both laws alone cannot investigate quality of energy flow in any systems. combination of both laws which gives the concept of exergy analysis will be imperative for the quality analysis. However.c. which takes into account of basic governing equations of first and second law of thermodynamics for the analysis. 2. All processes are steady state and steady flow. physical exergy is considered as important while dealing with heat and mass interactions of the systems. [W. ðTret À TÞ À T . Few numbers of experimental investigations of ground coupled heat pumps in building application based on exergetic analysis has been published [5–8. Theoretical investigation of similar system has not yet been published to the knowledge of the author. physical exergy ExPH. since the comfort temperature demand of the room is not high. The mathematical formulation depicting the exergy flow in the process can be stated as follows. 4 5 2 zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{ zfflfflfflffl}|fflfflfflffl{ zfflfflfflfflfflfflfflfflfflffl}|fflfflfflfflfflfflfflfflfflffl{ zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{ zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{ ! ! ! Ti _ gen . [J/KgK] Temperature.1276 S. [K] Energy efficiency Exergy efficiency Carbon dioxide out des evp exp aux ret gen env cond Ex En S h Outlet Destruction Evaporator Expansion Auxiliary energy return generation subsystem Envelope subsystem Condenser Exergy flow. for identifying irreversibility of the system and is helpful to minimize entropy generation in a process where heat and work interaction takes place [1]. There is no kinetic and potential energy effects and is no chemical or nuclear reactions. Exergy analysis is an important tool to determine how efficient thermal systems can be designed or in other words it can reveal unavoidable thermal inefficiencies of the system [4]. kWh/a] Specific heat capacity at constant pressure. However. [W. the exergy balance can be expressed as: Exin À Exconsumed ¼ Exout (2) Since this building heating system is a floor heating system this circulating water heats or cools the floor followed by heating or cooling of the room with some response time depending on the heavy or light floor heating systems. all analysis has been performed with steady state condition. Some exergy is consumed in the floor heating system with entropy generation. ðTi À T0 Þ À T0 . However. kWh/a] Energy. Lohani. Balance equation for building system When the abovementioned assumption is observed.T ¼ Q .ln ÀS 0 0 0 in h F T0 Th T0 Tret (4) . Total exergy of a system can be written as following equations. Thus. D.ð1 À h Þ ðT À Tret Þ À T . Reference temperature is taken as dynamic environment temperature and atmospheric pressure.P. kinetic exergy ExKN and potential exergy ExPT [1]. Schmidt / Renewable Energy 35 (2010) 1275–1282 Nomenclature avail 0 D.c. This study intends to carry out dynamic energy analysis and quasi static exergy analysis of the system on theoretical basis. 1 3 Ex ¼ ExPH þ ExKN þ ExPT þ ExCH CH KN (1) Neglecting chemical exergy Ex . [J/K] Floor average temperature h j CO2 Indices in Abbreviation GCHP Ground coupled heat pump GSHP Ground Source Heat Pump ASHP Air source heat pump COP Coefficient of Performance Inlet The environment or system surrounding is considered as large thermal reservoir and has no influence of local activity of source or sink. kinetic exergy Ex and potential exergy ExPT. chemical exergy ExCH.1. While developing model following basic assumption has been made. In the process exergy is transferred to the room air through floor surface. dis electr f FH H irrev p q COP Q cp T Available Reference state Distribution Electricity Fuel Floor Heating Heat Irreversible primary quality Coefficient of Performance Heat flow. the exergy is basically divided into four different subcomponents.c. Moreover analysis has been based on simulation work on IDA-ICE where energy and exergy model has been developed and implemented in to the simulation environment. _ Exghx ¼ ! _ Q ghx Tout ðTout À Tin Þ À T0 ln ðTout À Tin Þ Tin (12) The exergy transferred from flow of stream to the evaporator can be calculated using a following equation.w . However.exp ¼ T0 Sout. Where mass flow rate of the antifreeze water solution.ðTin À Tret Þ (8) À Á Exdes.r À T0 ln Tout.2.floor (5).r ¼ À Tin. It is a loss due to inefficient floor heating system that is expressed as efficiency factor of the floor heating system. Lohani.r À Tin.c.r À Tout. in other words. ground source and air source heat pump system. heat generator of the systems. Exergysupply. specific heat capacity and temperature difference of the water gives an amount of heat taken out by the system. A simple building zone model ‘‘reference zone’’ has been created for the energy and exergy analysis that represents the thermal behavior of the whole multi-family building. The other term Exergyloss. Exergyin.floor (3) _ _ Q ghx ¼ mw .comp (14) Exdemand ¼ Exin À Exret ¼ Exsupply. In addition this analysis is focus on evaluating one representing figure that can be extrapolated for in general all building system with reasonable accuracy and simplicity. represents exergy consumption in a floor heating system solely because of the irreversibility in process of the system.floor ¼ Qh 1 À T0 Th (9) Exergy consumption in a system due to irreversibility can be evaluated with an equation.floor þ Exloss. The zone model is found as a best model to meet all criteria required for this analysis.floor þ Exconsumption _ T Q ðT À Tret Þ À T0 ln in Tret ðTin À Tret Þ in ! (6) It can be referred as total generation energy from ground coupled heat pump is being delivered through condenser. which is nothing but an amount of heat energy delivered by the floor heating system to the floor construction can be expressed as: The working fluid is returned to its original states and enters to the evaporator to complete the cycle.evap.cond.exp À Sin. The exergy demand of the room is. Excond Exdemand ¼ (7) " À Á Qcond Á Tin.cond.floor þ Exergyloss. The simulation results of energy consumption in the north/east and south/west orientation differs Exsupply.P. is selected in the building system.evap. À Á Exdes. In this study we conform to the findings of [9] and adopt the reference zone accordingly.r À T0 ln Tin.floor (1) refers an amount of exergy supplied to the floor heating system.comp À Sout. The reference zone should be considered at a height that has no influenced from the ground and the roof [9]. is also an exergy losses term but it has nothing to do with entropy generation. therefore.cond. an exact and detail simulation of the whole building is not imperative at the moment. the influence of the orientation of the zone has also significant role in evaluating the thermal behavior and performance of the system. subtraction of exergy input to exergy return in the floor heating system. An Exergyconsumption (2).floor À Exergyconsumption ¼ Exergysupply.r À Tin. 3. Hauser further claim that the corner room will likely mimic the thermal behavior of the building.cond.floor (3) stands for transported exergy from the floor heating system to the floor construction. Exconsumption ¼ ! _ T Q .ln in ðTin À Tret Þ Tret (10) T ÀQh 1 À 0 Th 2.r (13) hF ¼ Qh ðQin À Qret Þ (5) The electrical energy supplied to the compressor is taken as energy supplied to the fluid system that is also considered as exergy supplied to the system. hF.r (15) Where the term Q is introduced.r # Tin. since the quality factor of electrical energy is 1.cond.r À Tout.S. _ _ Q ¼ m.evap.ðTout À Tin Þ (11) An amount of exergy extracted by the ground heat exchanger from the ground surface is In the above equation (3).evap.r # Tout. Exergy transfer through a condenser is investigated with this formula.floor þ Exergyret. The exergy destruction in a compressor can be determined using the equation below. The exergy destruction in an expansion device can be evaluated using the following equation. " À Á Qevap Á Tout. Balance equation for heat pump system Heat extracted by the ground heat exchanger from the ground surface is calculated with the general equation 11.r Exevap ¼ À Tout.evap. Schmidt / Renewable Energy 35 (2010) 1275–1282 1277 Exergyin.cond. .exp (16) Exergy supplied to the floor can be represented in terms of heat and temperature.cp.hF ðTin À Tret Þ À T0 .floor (4) is an amount of returned exergy through returned water of the floor heating systems. which eventually transferred to the room air and Exergyret. The efficiency factor of a floor heating system can be calculated with the given equations. System description Since this study is focus on comparing energy and exergy flow in the building system supplied with fossil fuel plant.comp ¼ T0 Sin. D.evap. therefore. The fossil plant or ground source heat pump is responsible to meet the difference. 2. The relation between COP and the temperature of the heat sources is shown in Fig. 1b depicts the exterior walls and windows placed on them. 1. U Value Internal Wall. Therefore. . U Value Floor and Ceiling. The climate data for the analysis of a building is taken from ASHRAE IWEC Weather file for Hamburg. includes long wave radiation calculations. and the location of the zone under investigation. air mass. the model from distribution to building envelope system is used in accordance with Schmidt [14].1278 S. In this analysis. few operating Fig. 1. Brief descriptions of these curves are presented herein. The energy model is simple and has a more conventional precision level and based on a mean radiant temperature. Location of the reference zone and its boundary walls. 1a shows that the whole surface of the building.5 W/m2 K Frame fraction to the total window: 20% Solar heat gain coefficient: 0. 3 shows the COP curve that is used in this analysis. However. D. but input and output from the heat pumps are obtained. an earlier studies of representative heat pumps characteristic curves (COP curves) are used for the purpose of analysis and in this approach of evaluation heat pumps are usually deemed as black box that is to say no detail analysis of component basis has been done. this analysis has been carried out taking consideration of high grade energy sources. Moreover. The energy flow in a system is divided into thermal energy and auxiliary energy flow. 4. occupants are taken as 5 W/m2 year around value according to German standard [3]. which in above figure can also be seen. humidity and energy of the system. Fig. a water source heat pump gives a higher COP than an air source heat pump if both temperatures are the same. The mechanical ventilation system is not considered and the air exchange rate with infiltration is taken as 0. Output of the heat pump is generation energy which then flows through distribution subsystem to finally envelope subsystem.41 (W/m2 K) U-glass: 2 W/m2 K.P. Climate model and Energy model. the size. primary and generation energy is substituted by ground and/or air source heat pump. mean radiant and operative temperatures. Fig. and air source heat pump). The zone model is shown in Fig. IDA-ICE has also provision for two different zone models. Fig. Floor heating system is incorporated here in the simulation of the zone model of the building. primary energy source is taken as renewable energy (ground source heat pump. A characteristics curve from Ito [10] is used in this study. Schmidt / Renewable Energy 35 (2010) 1275–1282 Table 1 Overview of the most important parameters defining the base case building model. Both models evaluate CO2. The value is taken as representing figure for all European buildings analysis.6 hÀ1 that is supposed to represent a typical modern tight German building. Parameters External Wall. The various inputs of the construction details of the building are given in the Table 1. 3. Thermal energy flow at each subsystem provides an information of energy demand at each modules whereas auxiliary energy flow is an amount of electricity required to operate the system. fossil fuels as a source of primary energy. however. The Fig. The internal loads of a building including equipments. the model is slightly changed to incorporate the modification.9 Solar Transmittance: 0. since analysis is being done for heating in this study. The reference zone model is an inbuilt function of IDA-ICE building simulation and has been modeled in detail using the CEDETZONE model. Here.76 Internal emissivity: 0. U Value Windows Value 0. While obtaining the typical characteristics curves.6764 21 C–23 C (Heating Mode) 40 C 0. this study takes in to account of climate model for the simulation of the building system. Storage is not considered in this analysis.2 m and the total height of the building is considered as 13 m so that no ground and roof influence has occurred in the zone model. Table 2 shows different cases that have been studied.48 (W/m2 K) 1. therefore. The reference zone has two outer walls with length of 8 m each and the zone area of 64 m2 (8 m  8 m). Lohani.6 hÀ1 No Ventilation System Tsupp (30 C)–45 C Tsupp (20 C)–22 C ASHRAE IWEC Weather File about 20%. The floor and ceiling of the zone are adjacent to each other. In the figure it has been seen that there is two interior walls that is considered as adiabatic meaning no heat and work transfer through the walls between zone and the surroundings. In this model the long wave and short wave heat interaction are taken in to account using the net radiation method [2]. U-frame: 1.072 (W/m2 K) 0. Since there was not a typical simulation module developed for a heat pump integrating heating or cooling system. Model analysis and simulation procedure Energy analysis model developed by Schmidt [14] is quite explicit and has detail investigation of energy chain from primary Set Point Temperature Maximum supply inlet temperature for floor heating system Infiltration rate Boiler with proportional controller Weather data energy source via building to the sink. Height of the zone is 2.6 m is at height of 5. The climate model is in detail and calculates vertical temperature gradient. and comfort index and daylight level. Generally. which are involved in heat interaction between zone and the surroundings along with two exterior walls. hence the average of both could be of best representative figure to evaluate the energy demand of the system [15]. Selecting climate model in the simulation does not complicate and lengthen the simulation process and time instead it assures better accuracy and precision of the results. from the simulation result of conventional heating systems. we obtained inlet temperature of the generation plant lies in the range of 26–32 C ensuing condenser inlet temperatures constant at 30 C is quite reasonable for our investigations. The simulation is performed dynamically with periodic start up for 1st January. While in the case of heat pumps dynamic values of energy from IDA-ICE is taken from distribution subsystems to envelope subsystems. but in case of ground source heat pump we consider a system with vertical heat exchanger of 50 m depth and took constant temperature of 10 C. Relation between COP and the temperature at the evaporator using air or water as a heat source (Ito et al. COP curves of earlier studies has taken and fit into the analysis of this study.P. However. For the primary energy transformation and generation part. Energy and exergy input output of the Fig. condenser inlet temperature was maintained constant at 30 C and 40 C respectively. Infiltration rate 0.95) and floor heating system. 2007 a representative day for winter climate using ASHRE IWEC climate file for Hamburg. Building system same as base case and Air source heat pump with constant condensation temperature 40 C with varying ambient temperature. Working fluid of the heat pump in all cases was R22. Energy flow at different modules of a building system (Schmidt. 2000). 3.1. constant in this analysis. D.S. therefore. Cases Case 1: Conventional system (base case) Case 2: Ground coupled heat pump integration system Description Building with condensation boiler (hboiler ¼ 0. thus inlet water to evaporator approximates around 8 C. Building system same as base case and ground coupled heat pump with constant condensation temperature 40 C with varying inlet evaporator temperature. Working fluid R22 is quite applicable for low and medium temperature floor heating system that has been used in getting the above curves. . Building system same as base case and ground coupled heat pump with constant condensation temperature 30 C with varying inlet evaporator temperature. 2004). Building system same as base case and Air source heat pump with constant condensation temperature 30 C with varying ambient temperature. Hence there is no need of changing anything in the IDA-ICE building zone model for both systems. Fig. 1279 Case 3: Ground coupled heat pump integration system Case 4: Air source heat pump integration system Case 5: Air source heat pump integration system conditions were imposed during experimentation. COP in ground source heat pump is. The self developed exergy model with steady state exergy equations has used dynamic values of energy from the simulation and calculates quasi steady state exergy for the each subsystem. while varying the evaporator source temperatures. The self developed exergy analysis module that uses dynamic values from IDA-ICE is implemented on each system and starts simulation of the system. 2. 4. The source temperature was varying in air source heat pump as ambient temperature fluctuates with day and time. condenser inlet temperature 40 C is also rational to be examined because in many other cases this situation might occur for low/medium floor heating systems. Similarly. As the building heating system is low temperature floor heating system.. Schmidt / Renewable Energy 35 (2010) 1275–1282 Table 2 Describes the different cases that have been studied during analysis. Simulation procedure As the aim of this study is to compare energy and exergy flow of a system supplied with fossil fuel plant and ground and air source heat pump for the same building zone model. Lohani.6 h–1. This operating condition of the heat pump with air and water source temperature resembles with our analysis for the heat pump integrated building heating system. are about 36.7 2. at the primary sub system reduction of energy demand for cases 2 and 3. While illustrating energy and exergy performance of the system. From above primary exergy efficiency comparison gives that fossil plant need more exergy at primary level than to ground source heat pump whereas air source demand is highest to all to supply the same amount of exergy at an envelope system. D.1 106 Case 3 5.3 2899 2896.7 2.7 2. In case 1. the rest of the energy demand in a building envelope is met with internal loads and solar gains. primary energy and exergy is taken a sum of compressor and evaporator. Since case 1 is conventional fossil plant system the term efficiency is used whereas cases 2–4 are heat pump systems the term coefficient of performance is used to designate overall input/ output energy ratio.: electrical energy/exergy flow. Elec.6%. Elec. the active energy demand is about 32% of the total energy dissipated through the building shell.3 2899 2896.3 2899 Exergy [kWh/a] 265 2 267 264.1 Case 2 7.8% respectively against case 1. This proves that the ground source heat pumps have better performance against fossil plant (conventional system) and air source heat pumps in terms of energetic point of view that lead to reduction of overall primary energy demand following reduction in environmental impacts and uphold sustainability. Lohani. This overall efficiency and/or coefficient of performance indicate the extent of matching of energy/exergy levels of the supply and demand sides in the building. From case 2 to case 6. whereas for cases 4 and 5 energy demand increases at 22.3 267 264. Table 3 Energy and exergy demands for the different subsystems of all cases.6 264. Elec. Elec. which is delivered by active heating system like condensing boiler and ground or air source heat pumps respectively via floor heating system. Results and discussion The considered system has two parts: building part and energy supply part that is fossil plant. the total energy demand is what the total energy dissipated from the building shell to the environment. Moreover.7 2.1280 S. Total Th. In ground source heat pump system overall primary exergy efficiency is higher than that of air source heat pump with same condensation temperature that is obvious and complies with basic heat pump theory.4 81 Case 4 3. 3. 5. Total Th. But. Table 3 presents energy and exergy demand for all cases studied here.7 2. Above table gives energy and exergy demands status in number for each subsystem of different cases analysed in this study. basically energy and exergy demand. where the dashed line at primary energy is energy extracted from evaporator in the case of heat pumps. However.: thermal energy/exergy. The output of the energy and exergy analysis which were presented on the above table are compared graphically and shown in Figs.3 267 264. and 17%. In the envelope sub system. Just to give a bit detail overview total demands are separated in to thermal and electrical parts. Schmidt / Renewable Energy 35 (2010) 1275–1282 Table 4 Overall primary exergy efficiencies for the building in all cases. Primary Energy Energy [kWh/a] Case 1 Th.7 2.6 Case 5 3. . a glimpse of comparison that is followed by energy and exergy efficiency and/or COP in Table 4.3 267 Emission Energy [kWh/a] 2503 0 2503 2503 0 2503 2503 0 2503 2503 0 2503 2503 0 2503 Exergy [kWh/a] 227 0 227 227 0 227 227 0 227 227 0 227 227 0 227 Room-Air Energy [kWh/a] 2292 0 2292 2292 0 2292 2292 0 2292 2292 0 2292 2292 0 2292 Exergy [kWh/a] 200 0 200 200 0 200 200 0 200 200 0 200 200 0 200 Envelope Energy [kWh/a] 7147 0 7147 7174 0 7174 7174 0 7174 7174 0 7174 7174 0 7174 Exergy [kWh/a] 450 0 450 450 0 450 450 0 450 450 0 450 450 0 450 Case 2 Case 3 Case 4 Case 5 Th.3 123.47 51. Elec. The generation sub system in cases 2. ground source and air source heat pump systems.7 2. Description Case 1 5 67.P. The thermal energy and exergy demand of the building envelope subsystem depicts overall losses through the building envelope that is being supplied by active as well as passive heating system of the building.7 55.7 2 2899 2896.7 heat pump are calculated with the help of spread sheet using similar steady state equations of the exergy. Elec. energy and exergy losses and energy and exergy efficiencies of each subsystems and overall system are being derived. an external supplied energy and exergy is only compressor part and evaporator energy/exergy is free but monitored during analysis. Above Table 4 presents overall primary energy efficiency and coefficient of performance. The above graph compares the energy flow from primary subsystem to envelop subsystem. Total Th. Total 3365 51 3415 2175 2166 4341 1952 2832 4784 1521 4127 5648 1418 4436 5854 Exergy [kWh/a] 3028 51 3078 44 2166 2210 33 2832 2865 6 4127 4133 5 4436 4441 Generation Energy [kWh/a] 3059 15 3074 2899 0 2899 2899 0 2899 2899 0 2899 2899 0 2899 Exergy [kWh/a] 2753 15 2768 267 0 267 267 0 267 267 0 267 267 0 267 Distribution Energy [kWh/a] 2896. Total Th.7 2. 4 and 5 have around 6% less energy demand against case 1. and overall primary exergy efficiency for all cases investigated and found quite different values for each case. The term exergy efficiency is used for both systems. which is extracted from ground or air sources. 4 and 5 below.3 2899 2896.6% and 31. The overall primary exergy efficiency is of important to compare total quality of energy required to produce the same amount of exergy that is being supplied at the building envelope. the overall primary exergy efficiency is 5% that means an amount of total exergy needed to produce exergy for building envelope is 20 Overall primary exergy efficiency [%] Overall primary energy efficiency [%] & COP times. Since the energy dissipates from the envelope sub system to the environment is at low temperature between 21 C and 23 C. Schmidt / Renewable Energy 35 (2010) 1275–1282 1281 Fig. 3. Thus. 6. 2. While in cases 2. The reason behind a typical results for cases. the absolute amount of primary exergy needed for maintaining the same temperature level of the zone 21–23 C in the heating mode. D. While generation exergy demand is 91% less for all heat pumps. This clearly substantiate that ground coupled heat pump building heating system is far more sustainable approach than conventional building heating system. and 8% less than that of case 1.P. ranking of the cases Fig. The discrepancy between two analyses substantiates the need of exergy analysis in getting more insight of source energy requirement. all exergy provided to the building envelope is at last consumed. 3. but for cases 4 and 5 exergy demand is 34% and 44% higher as compared to case 1. pro and cons of it with regard of sustainability issue that is utmost important in days to come to keep up balance between energy supply and climate change have been unveiled. 4 and 5. A final conclusion of the system. Comparison of exergy flows in cases 1. Comparison of energy flows in cases 1. and 3. The exergy flow fed to the building envelope is zero when it finally gets to the outside air (reference). Prioritizing the systems from energetic/exergetic viewpoint The performance of the different cases has been presented mostly with energetic/exergetic standpoint. . exergy demand of envelope sub system is very low down despite having the highest energy demand for the same. Lohani. the exergy content of these massive energy flows is then very small and in principle could be supplied through low quality energy sources say low exergy energy. which is the point of high quality energy in the form of fuels or electricity is being fed to the building system. 5. 4. It needs less absolute energy and exergy supply at primary level and it also make clear that high grade energy is not a requirement for the building heating energy supply.S. are 30%. The exergy curve gives completely different picture from the energy curve. 2. As it is evident from the curve that in the fossil plant system (case 1) biggest exergy losses take place at primary and generation sub systems. 4 and 5. Energy and exergy analysis of a ground source (geothermal) heat pump system. [16] Energy conservation in buildings and community systems (ECBCS) [viewed 27/10/2007]. JW & Freeston. A study of modeling and performance assessment of a heat pumps system for utilizing low temperature geothermal resources in buildings. The International Journal of Low Exergy and Sustainable Buildings 2004:1–47. Building and Environment 2007:1126–34. [11] Lund. DTU–Technical University of Denmark. Mehmet E. The comparison of the . Hepbasli A.und des Jahresheizenergiebedarfs.1282 S. Sahlin P. Exergy losses in each subsystem are basically due to intrinsic thermodynamic irreversibility in the processes. course on heating with geothermal energy: conventional and new schemes. The exergy losses in generation subsystem is in the range of 90% while in heat pumps exergy losses in primary subsystems is in the range of 85–95%. Lohani. Copenhagen (2004).org/home. [8] Hepbasli A.htm.P. [10] Ito S. ¨ ¨ [9] Hauser G. Cases Case1 – Base case Case 2 – GSHP @ condenser inlet temperature 30 C Case 3 – GSHP @ condenser inlet temperature 40 C Case 4 – ASHP @ condenser inlet temperature 30 C Case 5 – ASHP @ condenser inlet temperature 40 C Energetic perspective Reference case Better Good Worse Worst Exergetic perspective Reference case Better Good Worse Worst analysis gives case 2 is one of the most realistic systems that have around 50% high overall primary coefficient of performance and overall primary exergy efficiency and about 25% less primary energy and exergy demand than the base case ‘‘case 1’’. Numerical and experimental analysis of a horizontal ground–coupled heat pump system. Akdemir O. however energy demand is not. Design of low exergy building and a pre–design tool. [12] Lund. Energy and exergy analysis of a ground coupled heat pump with two horizontal ground heat exchangers. Kazuno. PhD thesis. Ground-source (geothermal) heat pumps. Models for building indoor climate and energy simulation. Report of IEA SHC Task 22. D. energy losses are negligible in conventional system. Japan. [15] Weitzmann P. International Journal of Green Energy 2004:1–19. Vuolle M. [14] Schmidt D. Subtask B (1999). though overall losses proportion in the system can be determined. by far in the energy conversion process namely: in conventional heating system at generation subsystem and in heat pumps at primary subsystems. [2] Bring A.09 whereas energy efficiency is from 0. pp. Building and Environment 2006:3747–56. Proceedings world geothermal congress. 7.V. DH. (2000) 1–21. Exergy as a driver for achieving sustainability. (2000) p. Advanced engineering thermodynamics. Studies of a heat pump using water and air heat sources in parallel. Modelling building integrated heating and cooling systems. World-wide direct uses of geothermal energy. Warmeschutz und Energie-Einsparung in Gebauden – ¨ Teil 6: Berechnung des Jahresheizwarme. Schmidt / Renewable Energy 35 (2010) 1275–1282 Table 5 Ranking of all cases from best to worst with energetic and exergetic perspective. The biggest exergy losses occur in all cases studied. [7] Hepbasli A. Mehmet E. Dincer I. New York: Wiley Interscience. studied have been presented primarily based on sustainability viewpoint in Table 5 below. Nevertheless. Energy and Building 2006:286–92. Vereinfachte Behandlung des Warmeverhaltens großer Gebaude durch thermische Systeme. 501–14. World Geothermal Congress 2000 Short Courses. Betonwerk und Fertigteil-Technik 1978:266–71. Rosen MA. Heat Transfer Asian Research 2000:473–90. Miura N. 1998. [13] Ozgener L. ¨ German National Standard. 209–36. The energy efficiency exceeds over 1 just because extraction of evaporator energy (which is free) is ignored in the calculation of the efficiency but is monitored. ¨ ¨ [3] DIN 4108-6: 2003–06.ecbcs. The discrepancy over overall primary energy and exergy efficiencies has divulged the fact that exergy demand of a building heating system is very low. References [1] Bejan A. hence absolute energy and exergy demands are crucial to determine heat generation plant. [4] Dincer I. Berlin: Deutsches Institut fur Normung e. [5] Hikmet E. Tolga Balta M. Kyushu-Tohoku. The efficiencies alone do not reveal more insight of the absolute demand. Mustafa I. http://www. Performance investigation of two geothermal district heating systems for building applications: energy analysis.06. Energy Conversion and Management 2004:737–53. [6] Hikmet E. Conclusion The analysis of the several cases under investigations has revealed that exergy analysis is very important to get more insight of the processes than that of sheer energy analysis. Japan.5 to 1. JW. Exergy efficiency is in the range of 0. International Journal of Building and Environment 2007:3606–15. Tohuko District. Kazim P.035–0. Mustafa I.