Geothermal Heat Pump System Research Articles

The effect of borefield geometry and ground thermal load profile on hourly thermal response of geothermal heat pump systems

Vertical BHE (borehole heat exchangers) are a common solution for GCHP applications (ground coupled heat pump). Correct BHE design and sizing are mandatory to either assure long term GCHP performance or reduce the payback period. Most models for performing the time varying analysis of complex borefields are based on the solution of the conduction equation, through the calculation of proper temperature response factors. The DST (Duct Storage Model) is often referred as the benchmark analysis tool, even if it is based on a simplified description of the borefield geometry. In this paper, DST predictions, in terms of hourly fluid temperatures along 20 years, are compared with the corresponding results obtained by implementing the MLAA (Multiple Aggregation Algorithm) approach by Bernier et al. into a model able to employ suitable g-functions generated starting from the Finite Line Source solution. This paper discusses some aspects of the improvements here introduced to the original MLAA method. The study is devoted to the comparison between the predicted fluid temperature values by the DST and MLAA models, with special attention to the influence of the BHE geometry (matrix like vs in line configurations) and to the shape of the yearly hourly load profiles (balanced vs unbalanced ground loads).

New Developments in Geothermal Heat Pumps : with a View to the Swiss Success Story

Global geothermal heat pump (GHP) system growth is exponential, with 20 % annually. Promoting factors are identified and discussed. GHP technology is still developing, now increasingly supplying large building complexes with heating, cooling and domestic hot water. A combination of supporting conditions brought Switzerland to a top international rank in GHP applications.

현장 타설 에너지파일을 적용한 지열 히트펌프 시스템의 성능 예측

ABSTRACT:The aim of this study is to evaluate the performance of the GHP system with 45 cast-in-place energy piles(CEP) for a commercial building. In order to demonstrate the feasibility of a sustainable performance of the system, transient simulations were conducted over 1-year and 20-year periods, respectively. The 1-year simulation results showed that the maximum and minimum temperatures of brine returning from the CEPs were 23.91℃ and 6.66℃, which were in a range of design target temperatures. In addition, after 20 years’ operation, these returning temperatures decreased to 21.24℃ and 3.68℃, and finally reached to stable state. Annual average extraction heat of cast-in-place energy piles was 94.3 MWh and injection heat was 65.7 MWh from the 20 years of simulation results. Finally, it is expected this GHP system can operate with average heating SPF of more than 3.45 for long-term.Keywords:Cast-in-place energy pile(현장 타설 에너지파일), Ground heat exchanger(지중열교환기), Geothermal heat pump system(지열 히트펌프 시스템), Cooling and heating performance(냉난방 성능), Transient simulation(동특성 시뮬레이션)

분자생물학적 방법을 이용한 지열시스템 관정 및 주변지역 미생물종 모니터링

This study was conducted to monitor microbial species dynamics within the aquifer due to long term operation of geothermal heat pump system. The species were identified by molecular biological methods of 16S rDNA. Groundwater sample was collected from both open (S region) and closed geothermal recovery system (J region) along with the control. J measured and control as well as S measured found Ralstonia pickettii as dominant species at year 2010. In contrast, Rhodoferax ferrireducens was dominantly observed for the control of S. In 2011, Sediminibacterium sp. was universely identified as the dominant species regardless of the monitoring places and type of sample, i.e., measured or control. The difference in the dynamics between the measured and the control was not critically observed, but annual variation was more strikingly found. It reveals that possible environmental changes (e.g. ORP and DO) due to the operation of geothermal heat recovery system in aquifer could be more exceedingly preceded to differentiate annual variation of microbial species rather than positional differences.

Methodological approach for evaluating the geo-exchange potential: VIGOR Project

In the framework of VIGOR Project, a national project coordinated by the Institute of Geosciences and Earth Resources (CNR-IGG) and sponsored by the Ministry of Economic Development (MiSE), dedicated to the evaluation of geothermal potential in the regions of the Convergence Objective in Italy (Puglia, Calabria, Campania and Sicily), is expected to evaluate the ability of the territory to heat exchange with the ground for air conditioning of buildings. To identify the conditions for the development of low enthalpy geothermal systems collected and organized on a regional scale geological and stratigraphic data useful for the preparation of a specific thematic mapping, able to represent in a synergistic and simplified way the physical parameters (geological, lithostratigraphic, hydrogeological, thermodynamic) that most influence the subsoil behavior for thermal exchange. The litho-stratigraphic and hydrogeological database created for every region led to the production of different cartographic thematic maps, such as the thermal conductivity (lithological and stratigraphical), the surface geothermal flux, the average annual temperature of air, the climate zoning, the areas of hydrogeological restrictions. To obtain a single representation of the geo-exchange potential of the region, the different thematic maps described must be combined together by means of an algorithm, defined on the basis of the SINTACS methodology. The purpose is to weigh the contributions of the involved parameters and to produce a preliminary synthesis map able to identify the territorial use of geothermal heat pump systems, based on the geological characteristics and in agreement with the existing regulatory constraints.

현지 측정에 의한 남한지역의 지중유효열전도도, 보어홀 전열저항 및 초기온도 분석

Investigation of the effective soil thermal conductivity() is the first step in designing the ground loop heat exchanger(borehole) of a geothermal heat pump system. Another important factor is the borehole thermal resistance(). Thermal response tests offer a good method to determine the ground thermal properties for the total heat transport in the ground. The first step is measured for initial soil temperature. This is done by supplying a only pump power into a borehole heat exchanger. They need to supply into water unload heat power more than 30 minutes. In this study, the initial soil temperature was found to analysis ,the ratio was 68.7% represented. In this case of , was 2.1~3.0 , was 0.11~0.20 . In this work, it is also shown that the distribution of a soil thermal conductivity and borehole thermal resistance were on the influence of initial soil temperature. And soil thermal conductivity was related with factors of equation by linear least square method, borehole thermal resistance was on the influence of composite factors.

New approach to evaluate the seasonal performance of building integrated geothermal heat pump system

This paper is to introduce a dynamic simulation method and a total monitoring method and a new hybrid method combining the simulation and the monitoring to evaluate the building integrated geothermal heat pump (BIGHP) system seasonal performance factor (SPF). SPF is sometimes defined as CSPF(Cooling Seasonal Performance Factor) and HSPF(Heating Season Performance Factor). CSPF is equivalent to COPcs while HSPF is to COPhs in practice. However, the single point based COPc and COPh could not express the annual performance of BIGHP system properly due to the characteristics of the system partial load operation. Therefore, a specially proposed new method with twelve data points indicating twelve months per year from the climate weather data has been proposed to predict the CSPF and HSPF and finally annual performance factor (APF).The purpose of this paper is to evaluate the COPcs(CSPF) and the COPhs(HSPF) and finally the APF for a climate building integrated geothermal heat pump system in Nice and Seoul from a joint collaboration between CSTB and KIER. The results are expected in terms of CSPF, HSPF and APF for the different located buildings of Nice and Seoul. The new hybrid method could predict the CSPF 5.16 while HSPF predicted as 4.55 in Nice. This is the difference of about 3.03% error compared with reference simulation approach. The new hybrid method could apply to evaluate CSPF and HSPF for the same case assumed in Seoul. The results indicated that the new hybrid method could well apply to evaluate the SPF's for the Seoul case within the error range of 2.42%. In future, a more verification study would be required between this hybrid method approach and IPMVP calibration model approach.

에너지슬래브 지중열교환기의 성능 분석

ABSTRACT:Recently, utilization of building foundations as ground-coupled heat exchangers has attracted much attention because they reduce the cost and enhance the heat transfer. The objective of this study is to evaluate the performance of energy-slab ground-coupled heat exchanger installed in a commercial building. In order to demonstrate the energy transfer characteristics of the energy-slab, experiments were conducted from October 2010 to September 2011. The 1-year measurement results showed that the mean EWTs of brine returning from the energy-slab were 9.6℃ in heating season and 24.9℃ in cooling season, which were in a range of design target temperatures. In addition, the geothermal heat pump system with the energy-slab showed on-off operation according to the setting temperatures of secondary fluid in water storage tank. The results also showed that the energy-slab extracted heat of 198.6 kW from the ground and injected heat of 318.9 kW to the ground, respectively.Keywords:Energy-slab(에너지슬래브), Building foundation(건물 기초), Ground-coupled heat exchanger(지중열교환기), Geothermal heat pump(지열 히트펌프), Performance(성능)

Current state of the art of geothermal heat pumps as applied to buildings

This paper summarizes the current state of the art of geothermal heat pumps as applies to buildings. Geothermal or ground source heat pump (GSHP) systems provide heating, cooling as well as domestic hot water, by the use of the underground or bodies of surface water as heat source or sink. More specifically, a GSHP system comprises a heat pump (usually water-to-water) and a ground source system (ground heat exchanger or groundwater well) in order to provide heating and cooling to the building through a low-temperature heating system and domestic hot water as well. The main concept of a GSHP system is the maximization of the heat pump efficiency i.e. minimization of electricity consumption mostly due to underground temperature which is almost invariant throughout the year. So, it is clear that GSHP systems have contribution to the environmental protection and reduction of greenhouse gas emissions. GSHPs are a mature industry, with a continuous trend of development and due to their increasing energy efficiency due to recent advances of the technology (described in the following chapters) are attractive and are more and more considered as an excellent substitute of conventional heating/cooling sources including air source heat pumps and variable refrigerant volume. Due to these advances in several cases the high efficiency of GSHP compared to the initial capital cost minimizes the need for subsidies.

Effect of borehole array geometry and thermal interferences on geothermal heat pump system

Properly sized borehole heat exchanger in geothermal heat pump system (widely known also as ground source heat pump system) needs to minimize long-term ground and working fluid temperature changes. These changes occur due to imbalances of heat extracted from the ground during winter and heat rejected into the ground during summer months, as well as thermal interferences of adjacent boreholes in borehole array. Simple calculations and spreadsheet-based analogical solutions of required borehole length for heat transfer run into difficulties when dealing with such large, complex ground source heat pump heating and cooling systems which use compact borehole array. A number of analytical computer programs are available to simulate how ground loop fluid temperature varies in such complex systems, using so-called ‘g-function’ – a mathematical function dependent on the geometry and shape of the borehole array. The type of calculation involves a type of ‘step-function’, where 24h ‘step’ of peak loading is superimposed on a top of a long-term base load. In analytical simulation models, the base load is typically specified as the heating and cooling load per month of a typical year, and is simulated as the combination of sequential monthly steps. This paper will show, by simulating long-term operation of complex geothermal heat pump system with multiple boreholes in various geometric arrays, how spacing of adjacent boreholes and thermal interferences influence required borehole length for heat transfer.

Geothermal heat pump systems: Status review and comparison with other heating options

Heating is a major requirement in many regions, and growing energy demands and pollutant emissions have allowed unconventional heating technologies to be considered, including geothermal. Geothermal heat pumps are reviewed, including heat pump technology, earth connections, current world status and recent developments. Geothermal heat pump technology and conventional heating systems are compared in terms of costs, CO2 emissions and other parameters. Geothermal heat pump use is economically advantageous when the price of electricity is low. Alternatively geothermal heat pump units have the lowest emissions depending when electricity is produced from a low emitting source.

에너지슬래브 적용 지열원 열펌프 시스템의 성능 특성에 관한 실증 연구

Energy foundations and other thermo-active ground structure, energy wells, energy-slab, and pavement heating and cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. This paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Pipes, energy slabs, filled with a heat carrier fluid are installed under conventional structural elements, forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and a heat sink in summer. The geothermal heat pump system with energy-slab represented very high heating and cooling performance due to the stability of EWT from energy slab. However, the performance of it seemed to be affected by the atmospheric air temperature.

Effect of heating system using a geothermal heat pump on the production performance and housing environment of broiler chickens

A geothermal heat pump (GHP) is a potential heat source for the economic heating of broiler houses with optimum production performance. An investigation was conducted to evaluate the effect of a heating system using a GHP on production performance and housing environment of broiler chickens. A comparative analysis was also performed between the GHP system and a conventional heating system that used diesel for fuel. In total, 34,000 one-day-old straight run broiler chicks were assigned to 2 broiler houses with 5 replicates in each (3,400 birds/replicate pen) for 35 d. Oxygen, CO2, and NH3 concentrations in the broiler house, energy consumption and cost of heating, and production performance of broilers were evaluated. Results showed that the final BW gain significantly (P < 0.05) increased when chicks were reared in the GHP broiler house compared with that of chicks reared in the conventional broiler house (1.73 vs. 1.62 kg/bird). The heating system did not affect the mortality of chicks during the first 4 wk of the experimental period, but the mortality markedly increased in the conventional broiler house during the last wk of the experiment. Oxygen content in the broiler house during the experimental period was not affected by the heating system, but the CO2 and NH3 contents significantly increased (P < 0.05) in the conventional broiler house compared with those in the GHP house. Fuel consumption was significantly reduced (P < 0.05) and electricity consumption significantly increased (P < 0.05) in the GHP house compared with the consumption in the conventional house during the experiment. The total energy cost of heating the GHP house was significantly lower (P < 0.05) compared with that of the conventional house. It is concluded that a GHP system could increase the production performance of broiler chicks due to increased inside air quality of the broiler house. The GHP system had lower CO2 and NH3 emissions with lower energy cost than the conventional heating system for broiler chickens.

Viability analysis of renewable energy systems for commercial buildings: case study of Briarwood Club of Ankeny, Iowa, USA

The viability of implementing renewable heating, cooling and electric systems for commercial buildings at Briarwood Club of Ankeny (BCOA), a golf course located in Ankeny, Iowa, USA, is addressed. A geothermal heat pump system with a horizontal loop field is the most viable renewable solution after incentives with an equity payback of less than 6 years and an internal rate of return (IRR) of 18.4% compared with conventional solutions. Solar thermal heating is not optimal for BCOA. Net metering of a 50 kW wind turbine is the most economical renewable electric solution after incentives with an equity payback of less than 13 years and an IRR of 8.6%; however, it is not attractive enough for BCOA to invest in. Solar photovoltaic systems are not as economically viable as wind turbines. However, zoning, incentives and net metering policy significantly affect the analysis, and the impact of these will be addressed.

「地中熱利用にあたってのガイドライン」の公表に寄せて

「地中熱利用にあたってのガイドライン」の公表に寄せて

Performance Characteristics of Geothermal Heat Pump System by Using an Old Well

Performance Characteristics of Geothermal Heat Pump System by Using an Old Well

地中温度再生型・地中熱利用システムの紹介

地中温度再生型・地中熱利用システムの紹介

Determination of groundwater flow direction in thermal response test analysis for geothermal heat pump systems

A methodology was proposed to determine the groundwater flow direction from a thermal response test analysis using three boreholes. The methodology was verified using sample test data generated from a three-dimensional numerical model for the borehole ground heat exchangers. It was found that the groundwater flow velocity and the borehole separation had significant effects on the correctness of the estimated groundwater flow direction. A smaller borehole separation and a higher groundwater flow helped improve the traveling speed of the heat front and, consequently, the thermal interference effect from adjacent boreholes. This was crucial for the correct prediction of the groundwater flow direction in the analysis. The adoption of a longer test period also strengthened the borehole thermal interference and, hence, the accuracy of the estimated groundwater flow direction. Besides, the minimum groundwater flow velocity capable of being determined with confidence from the analysis could also be decreased. Finally, the use of an unequally spaced borefield could further enhance the effectiveness of the methodology.

Comparing the Energetic and Exergetic Performances of a Building Heated by Solar Energy and Ground-Source (Geothermal) Heat Pump

In this study, we considered a building, which had a volume of 336 m3 and a floor area of 120 m2, with indoor and outdoor air temperatures of 20 oC and 0 oC, respectively. For heating this building, we selected two options, namely (i) a ground-source (geothermal) heat pump system (Case 1), and (ii) a solar collector heating system (Case 2). We employed both energy and exergy analysis methods to assess their performances and compare them through energy and exergy efficiencies and sustainability index. We also investigated energy and exergy flows for this building and illustrated from the primary energy transformation through the heat production system and a distribution system to a heating system, and from there, via the indoor air, across the building envelope to the surrounding air. We calculated that the total exergy efficiencies for Cases 1 and 2 were 4.7%, and 26.1% while sustainability index values for both cases were 1.049 and 1.353 at a reference (dead) state temperature of 0 oC, respectively.

Thermodynamic analysis of a hybrid geothermal heat pump system

A thermodynamic analysis of a hybrid geothermal heat pump system is carried out. Mass, energy, and exergy balances are applied to the system, which has a cooling tower as a heat rejection unit, and system performance is evaluated in terms of coefficient of performance and exergy efficiency. The heating coefficient of performance for the overall system is found to be 5.34, while the corresponding exergy efficiency is 63.4%. The effect of ambient temperature on the exergy destruction and exergy efficiency is investigated for the system components. The results indicate that the performance of hybrid geothermal heat pump systems is superior to air-source heat pumps.