Residential Ground Source Heat Pump Research Articles

Evaluating Long-Term Performance of a Residential Ground-Source Heat Pump System under Climate Change in Cold and Warm Cities of Japan

A residential ground-source heat pump system often requires a long payback time to recover the capital cost. Long-term uncertainty in such a system’s performance increases as the climate changes. This study compares 20-years hourly heating/cooling demands of a typical residence in the present (2000–2020) and in the future (2076–2095) for two locations in Japan. This study also calculated soil temperatures as heat sources through 1D heat-transfer simulation based on the A1B climate scenario in the Intergovernmental Panel on Climate Change’s Special Report. System performance and simple payback times were compared in one cold and one warm city in Japan (Sapporo and Tokyo, respectively). Soil temperatures at a middle depth of a borehole heat exchanger were predicted to increase in the future by ~1 °C, with insignificant effects on a borehole heat exchanger. Seasonal performance factors increased in Sapporo because thermal demands would be kept even in the future, but decreased in Tokyo, which has a higher ratio of the energy used in operating the system in cooling mode compared with its small heating demand. The simple payback time was estimated at 16.2 and >20 years in Sapporo and Tokyo, respectively, both in the present and future, with the constant energy prices. If oil and gas prices doubled, the payback time would be halved in Sapporo to 8.4 years but remain around 20 years or more in Tokyo.

Clustering based on dynamic time warping to extract typical daily patterns from long-term operation data of a ground source heat pump system

While clustering has been commonly used to profile the building electricity consumption data, its application to HVAC system data is relatively less. Based on the operation data of a residential ground source heat pump (GSHP) system, a pre-processing procedure was set up, including acquisition, cleaning, missing-data fill-in, and standardization. Then hierarchical clustering was used, based on the dynamic time warping (DTW) distance calculation method. A new index, the sum of squares of errors based on DTW, was used to determine the best cluster number. The patterns were extracted based on clustering results.The heat exchange on the user-side during one cooling season was processed as a case study. We obtained 5 valid clusters and extracted patterns from each. For the studied case, the result based on the DTW method yields a better homogeneity compared to the Euclidean method. The method is then applied to a five-year operation data, where 9 and 6 patterns were obtained for the cooling and heating seasons, respectively. They mainly differed in shape, and the cooling patterns fluctuate more. Overall, clustering and pattern extraction can reduce the data dimension, and provide a data-driven view of how the system supplies the cooling and heating.

Utilization of on-grid photovoltaic panels to offset electricity consumption of a residential ground source heat pump

Ground source heat pump (GSHP) system is an efficient solution to mitigate energy consumption and environmental emissions in the building sector. Although the GSHP system is categorized among renewable energy technologies, considering the fact that the system's power demand is usually provided by fossil fuel resources, it may not fully meet this classification. One way to offset the GSHP's electricity consumption in a renewable approach is the use of photovoltaic (PV) panels. This paper aims to study the feasibility of a hybrid PV-GSHP system for a residential building in Tehran, Iran. To that end, a numerical model is developed to explore the GSHP system's performance over a 20-year design life, taking several borehole lengths into account. Moreover, the PV modules are simulated by EnergyPlus software. A life cycle cost analysis is also performed to assess the economic viability and optimal design of the PV-GSHP system. The results illustrate that using four PV modules can best cover the system's electricity consumption and the discounted payback period is less than four years. Furthermore, an environmental evaluation reveals that the PV-GSHP system can save 29.2 t of carbon dioxide emissions over the 20-year period compared to the GSHP system.

Life cycle analysis (LCA) of residential ground source heat pump systems: A comparative analysis of energy efficiency in New Jersey

Developing clean energy policy supported by science-based research is essential for mitigating the hazards and risks associated with climate change. This study aims to explore ground source heat pump (GSHP) systems, an underutilized energy efficiency technology, as a means to promote emission reductions in the buildings sector. GSHP systems have the capacity to decrease the environmental impact of building space heating and cooling needs through fossil fuel displacement and higher energy efficiencies than baseline technologies. Although the benefits and engineering applications of this technology are established, it has not been adopted at scale, thus limiting potential emission reductions. Furthermore, energy economics can vary significantly across geographies which makes quantifying benefits of mitigation action challenging in regions with diverse electricity generator types and building heating fuels. This study uses life cycle analysis (LCA) to evaluate mid- and long-term sustainability metric impacts of GSHP systems operating in New Jersey, US, to assess the technology’s effectiveness while operating within the state’s electricity generating fuel mix. Results show that the state is a suitable location for residential GSHP systems, and that an electricity generation fuel mix with increased use of renewable energy sources would enhance the technology’s efficiency and decrease associated emissions even further. In addition, we compared GSHP technology to that of other common space heating/cooling methods and found that use of GSHP systems in conjunction with electric-based heating/cooling provides a substantial improvement in terms of environmental emissions. When compared to oil and gas-based heating, GSHP systems provided some improvement on mid-point impact factors and considerable improvement on end-point impact factors, most notably the economic improvement associated with decreasing dependence on fossil fuels. These findings suggest that GSHP systems should be considered for reducing emissions and end-use energy consumption and support new clean energy policies in the state.

Performance assessment and techno-economic optimization of ground source heat pump for residential heating and cooling: A case study of Nanjing, China

This study implemented the performance assessment and techno-economic optimization of residential ground source heat pump (GSHP). First, a detailed numerical model integrating the ground heat exchanger and heat pump and economic model considering economic indicators were developed to analyze the thermal and economic efficiency of residential GSHP. Then, Taguchi method was proposed to investigate the impacts of five parameters on the thermal and economic performance of GSHP and obtain the optimal parameters set. After that, the sensitivity of optimal parameter to the drilling costs, pipe prices, and interest rate were performed. Lastly, the analysis of variance approach was implemented to find out the relative significance of parameters. Results revealing that the superiority of individual GSHP can be maintained in the vast majority of time and the capital investments are relatively high within the range of 13034.4 to 18199.2 CNY. The optimal parameters combination was of great discrepancies when taking the economic indicators into account. The most economical choice of pipe size remains unchanged, despite the optimization objectives and varying pipe prices. The relative importance of fluid velocity, borehole depth, and pipe material towards the variation of economic efficiency largely depends on the drilling costs, pipe prices, and the interest rate.

Dynamic thermal analysis of a residential ground-source heat pump

We present the dynamic thermal analysis of a residential ground-source heat pump (GSHP) with the following objectives: (1) to present a comprehensive GSHP model accounting for the dynamic behavior of a vapor compression unit, lumped serviced space, and the ground heat exchanger (GHE); (2) to identify a set of GHE temperature, mass flow rate, and evaporator area fraction (α) improving the time-averaged coefficient of performance (COP‾) while retaining thermal comfort in the serviced space; and (3) to propose a GHE design satisfying the desired design and operating conditions determined in (2). For a 4-ton residential GSHP considered herein, we verified the existence of a critical GHE mass flow rate of 1kg/s after which the COP‾ hardly varied. Furthermore, we observed a design trade-off between cooling and heating modes wherein a smaller α was preferred in cooling mode while the heating mode favored a higher α. Cooling COP‾ was sensitivity to both α and GHE temperature (TB), whereas that in heating mode was insensitive to TB as long as both α and Lt were sufficiently high. The optimal α impartial to both modes was 0.29 and the peak COP‾=5.49 and 3.6 in cooling and heating mode, respectively.

In-field performance evaluation and economic analysis of residential ground source heat pumps in heating operation

The objective of this study is to investigate the field performance, economic benefits, and environmental impact of ground source heat pumps (GSHPs) for residential space heating compared with conventional natural gas furnaces in a severely cold climate. A total of 32 residential houses with 16 vertical and 16 horizontal loop GSHPs in Iowa, U.S. were included in this study. The required heating energy in each house was estimated by using the heating degree-day (HDD) method and the building characteristics obtained during the on-site energy audits. The monthly GSHP electricity use in each house was collected over two consecutive heating seasons. Based on the estimated heating energy and the monthly GSHP electricity consumption, the coefficient of performance (COP) was derived for each unit on a monthly basis over the dominant heating period. Results showed that the median values in the calculated COP were 2.8 for both horizontal and vertical loop systems. The calculated COPs were found to be 30%–124% of the nominal values for horizontal systems and 46%–110% for vertical systems, with an average being 80% of the nominal value for both horizontal and vertical systems. In addition, 28 out of 32 GSHPs showed lower calculated COPs compared with the nominal values. The economic analysis showed 44–86% savings in energy expenses as a result of using GSHPs in place of conventional natural gas furnaces, with median savings being 70–77% depending on the electricity rates. The environmental analysis showed 23%–61% CO2 emission reduction with a median of 45% compared with natural gas furnaces. These results quantified the economic and environmental benefits of using GSHPs in Iowa, U.S., which provided essential information for policy making and incentive program development. Also, the developed analytical approach to determining the field performance of GSHPs is suitable for large-scale, long-term GSHP performance evaluation given its minimum requirement on field measurements and readily available utility data.

Lowering greenhouse gas emissions in the built environment by combining ground source heat pumps, photovoltaics and battery storage

Ground source heat pumps (GSHPs) have been suggested to replace gas-based heating in urban environments to reduce greenhouse gas emissions and help to comply with the Paris Agreement. The emission reduction from GSHP depends on the carbon intensity of the electricity generation mix. Moreover, grid capacity may be limiting the introduction of these high-electricity demand GSHP systems. Photovoltaics (PV) systems help to provide additional emission reductions for residential GSHP systems. Battery energy storage systems can reduce the peak demand and allow for more GSHPs within the low voltage grid. We developed a techno-economic and environmental assessment model to quantify this impact of PV and batteries combined with residential GSHP systems. Measured demand data of 16 dwellings with GSHP and PV systems from the Netherlands were used. We show that PV can provide around 19% of the GSHP demand, while batteries enhance this by 53% and reduce the peak demand by 45%. Greenhouse gas emission of a GSHP with PV is reduced on average with 73 tCO2-eq, corresponding to a 80% reduction, over a 30-year lifetime. Dwellings with only a GSHP system have a net present values increase of around € 275 per tCO2-eq of avoided emission. This is reduced to € 230 per tCO2-eq when PV and storage is added to the system. Nevertheless, investment in GSHP systems today is not economically attractive for many dwellings. A sensitivity analysis showed that policies should focus on increasing natural gas tariffs, carbon taxation, investment subsidies or combinations of these routes to encourage sustainable heating.

An empirical analysis on awareness and intention adoption of residential ground source heat pump systems in Greece

Residential heating, cooling and Domestic Hot Water (DHW) production are responsible for a significant part of the residential energy consumption in Greece, which is currently based on the consumption of fossil fuels. A solution for the reduction of fossil fuel use -and all the negative effects that their use implies- is the application of renewable energy technologies, among which Ground Source Heat Pump (GSHP) systems are included. The present study examined awareness and adoption intention issues concerning this technology in Greece, through the conduction of a questionnaire survey. Specifically, it investigated public's knowledge on issues involving this technology, intention of installing it in households, main information sources and installation barriers. Socioeconomic and residence characteristics, as well as consumers’ preferences and attitudes affecting the knowledge and adoption issues were examined. Factors affecting the subjects under investigation are gender, age, education level, environmentally friendly behavior and awareness, as well as having an occupation, studies or interests related to environment, technology or engineering. Additionally, the intention of installing a GSHP system is affected by specific household characteristics, infrastructure and consumers’ preferences on characteristics of heating systems. In order to promote GSHPs, suitable financial incentives, regulatory improvements and awareness activities are required.

Field testing and performance analyses of ground source heat pump systems for residential applications in Hot Summer and Cold Winter area in China

To conserve energy, ground source heat pump (GSHP) system has been used worldwide for cooling and heating buildings, and there is a persistent concern in the performance of the system. In this study, the performances of five residential GSHP systems in Hot Summer and Cold Winter (HSCW) area in China were examined. Data were acquired through field testing, operation record and long-term monitoring. And outdoor climate parameters, water temperature characteristics, cooling load characteristics, system efficiencies and energy consumptions, heat extraction and rejection imbalance were analyzed. Field test data were used to analyze the dynamic cooling load characteristics and the energy efficiency of the heat pump units and systems. Energy consumption was statistically analyzed. The results show that the weighted average Coefficient of Performance (COP) of the heat pumps and system Energy Efficiency Ratio (EER) varied from 3.36 to 5.94 and 1.95 to 4.35, respectively. Positive correlation of high cooling load and high COP was presented. More heat extraction than rejection was found, which was relevant to domestic hot water supply. Furthermore, long-term distributions of ground side water outlet temperature were used, and the skewness and kurtosis were introduced into the quantization evaluation method.

Energy use and carbon reduction potentials from residential ground source heat pumps considering spatial and economic barriers

Ground source heat pump (GSHP) systems are significantly more energy efficient than conventional heating and cooling systems, but they have suffered from low market penetration. This study analyzes the implications of and barriers to nation-wide GSHP retrofits in U.S. single-family houses based on national databases of housing units and home energy use. Our model estimates maximum annual savings of 1.26 quads (1.33EJ) of energy, $7.1 billion in energy costs, and abatement of 64.8 million tons of CO2eq. Economics is the major barrier as typical GSHPs cost $164 less to operate annually but cost $8990 more to install than the conventional alternative HVAC systems. Spatial and economic constraints exclude 7.7% and 89% of homes respectively, leaving only 10% of homes suitable for retrofit. Applying these two constraints, savings reduce to 0.15 quads (0.16EJ), $3.0 billion in energy costs, and abatement of 12.1 million tons of CO2eq. A 30% federal tax credit helps increase the percentage of GSHP-suitable homes from 10% to 30% while reducing the average payback period from 9.1 to 4.8 years among those homes. More effective policies to lower high cost premiums would be needed to promote large-scale GSHP implementations.

Performance of a residential ground source heat pump system in sedimentary rock formation

The use of ground-source heat pump system has been widely adopted over the past decades due to its potentials to provide renewable and low carbon footprint energy source for building’s heating and air-conditioning needs. This paper reports the design and post construction monitoring of a vertical ground-coupled heat pump system installed adjacent to a three-floor residential house located in Cleveland, OH, USA. The system operates under the special geological condition with shallow depth outcrop of sedimentary shale rock formation typical of Northeastern Ohio, USA. A comprehensive monitoring program was installed to collect data on the operation and performance of the ground-coupled heat pump system. The data recording was initialized in Oct. 2012 and has been in place ever since. Overall, the monitoring data shows that the ground heat pump achieved very good performance. The coefficient of performance (COP) of ground coupled heat pump system ranges from 3 to 4. The heat pump satisfies most of the house heating requirements, including severe cold winter, during the monitoring period. This case study demonstrates the feasibility of ground-coupled heat pump system in providing Heating Ventilation and Air Conditioning (HVAC) source for residential building for either heating dominant or cooling dominant conditions under sedimentary rock geological conditions. The possible solutions to decrease the initial investment are proposed in the study.

가정용 지열원 열펌프 시스템의 냉난방 성능 특성 연구

Abstract Ground Source Heat Pump (GSHP) systems utilize geothermal energy as a thermal source or sink, for heating,cooling and domestic hot water. It is well known that GSHP is environmentally friendly, and saves energy dramatically.For this reason, many investigative researches have been conducted on commercial and governmental buildings. However,studies on residential GSHP are few, because of the small capacity and cost. In this study, we experimented with thecharacteristic performance of heating, cooling and seasonal performance factor for a residential GSHP system, which consistedof two 180 m deep u-tube ground heat exchangers, a heat pump and measurement instruments. The installed capacityof the heat pump was 5RT, and the conditioning area was 62.23 m 2 . From the experimental results, the cooling COPof the heat pump was 4.13, and the system COP was 3.51, while the CSPF was 3.32. On the other hand, the heatingCOP of the heat pump was 3.87, and the system COP was 3.39, while the HSPF was 3.39. Also, in-situ cooling COP and capacity were 93.7% and 96.4% compared with the EWT certification data, respectively, and that of heating were98.3% and 95.7%, respectively.

Foundation heat exchangers for residential ground source heat pump systems—Numerical modeling and experimental validation

A new type of ground heat exchanger that utilizes the excavation often made for basements or foundations has been proposed as an alternative to conventional ground heat exchangers. This article describes a numerical model that can be used to size these foundation heat exchanger (FHX) systems. The numerical model is a two-dimensional finite-volume model that considers a wide variety of factors, such as soil freezing and evapotranspiration. The FHX numerical model is validated with one year of experimental data collected at an experimental house located near Oak Ridge, Tennessee. The model shows good agreement with the experimental data—heat pump entering fluid temperatures typically within 1°C (1.8°F)—with minor discrepancies due to approximations, such as constant moisture content throughout the year, uniform evapotranspiration over the seasons, and lack of ground shading in the model.

Calculation algorithm of the temperatures for pipe arrangement of multiple ground heat exchangers

The authors introduce calculation algorithm of the temperatures of the ground and heat carrier fluid in multiple ground heat exchangers for pipe arrangement of ground source heat pump (GSHP) systems. First, the outline is explained. Next, in order to investigate possibility for the operation of the GSHP system with steel foundation piles and validate reproducibility of the value calculated by the design tool including the calculation algorithm, field tests of heating and heat extraction were conducted with a residential GSHP system using 25 steel foundation piles of 8 m long as ground heat exchangers. From a result of comparison between temperatures of the measurement in the test and calculation by using the design tool, it was confirmed that the tool could predict the temperatures with acceptable precision and speed for utilizing as a design tool. In addition, performance of GSHP systems with steel foundation piles in long term is predicted with the design tool. In moderate climate region, since the GSHP systems using multiple ground heat exchangers with short length can operate with high efficiency as well as the GSHP system using a single ground heat exchanger with long length, the GSHP systems with steel foundation piles have possibility to become popular.

Development of a design and performance prediction tool for the ground source heat pump system

This paper introduces a novel design and performance prediction tool for the ground source heat pump (GSHP) system. This tool features, a user-friendly interface for data input and graphical output. First, an outline of this tool was described. Next, the authors validated temperature variation calculated by theoretical method of the developed tool compared with one measured in the thermal response test. The thermal response test was carried out in a house garden in Sapporo. Giving the calculated conditions, the calculated temperature variation almost traced the measured value. The developed tool’s preciseness was proved with the results. In final, performance prediction and feasibility study of a residential GSHP system in Sapporo was performed with this tool as an example. Results of the calculations show that the life cycle CO 2 emission (LCCO 2) of the GSHP system is 2038 kg-CO 2/year and it is less than half compared to conventional oil boiler systems. Also, the GSHP system can reduce life cycle cost (LCC) by 50,000–90,000 Japanese-yen/year. The payback time for increased investment cost of the GSHP system is about 9–14 years in comparison with other conventional systems.