2022 Proceedings of the IGSHPA Research Track


Recent Submissions

  • Publication
    2022 Research Conference Proceedings, International Ground Source Heat Pump Association
    (International Ground Source Heat Pump Association, 2022)
  • Publication
    Impacts of prospective LEED building's energy loads on a borehole heat exchanger: A case study in Central Illinois
    (International Ground Source Heat Pump Association, 2022) Zhao, Zilong; Stumpf, Andrew; Lin, Yu-Feng; Wang, Xinlei
    Assessing the thermal behavior in the subsurface surroundings of a borehole heat exchanger (BHE) is necessary for evaluating the performance of GSHP systems. In this study we undertook a preliminary thermal analysis on a constructed GSHP system that is coupled to a LEED-certified building, the Campus Instructional Facility (CIF), at the University of Illinois at Urbana-Champaign, The building is designed to utilize multiple energy-saving technologies that achieve a building performance of LEED-Gold certification. Energy modeling of the entire building was performed in DesignBuilder software by considering all of the high efficiency thermal-insulated features, and the building energy load was obtained and used in the iterations of the ground thermal response model. An analytical model (Erol & Francois 2018) was applied to evaluate the thermal response from a single BHE within a multilayer geology considering the annual energy extraction/rejection from the building. A parallel scenario was considered for comparison when the GSHP was coupled to a building with a typical heating-dominated load profile in central Illinois. The difference in the development of isotherms around the BHE are simulated to demonstrate the benefits of coupling green buildings and GSHP. This research may facilitate the wider implementations of GSHP systems with energy-efficient buildings.
  • Publication
    Experimental performance analysis of a dual source heat pump integrated with thermal energy storage
    (International Ground Source Heat Pump Association, 2022) Wang, Lingshi; Liu, Xiaobing; Shen, Bo; Liu, Xiaoli; Gehl, Anthony; Shi, Liang; Qu, Ming
    To mitigate disturbances to the electric grid resulting from the growing penetration of intermittent and decentralized renewable generation, a dual-source (air source and ground source) heat pump (DSHP) integrated with thermal energy storage (TES) was developed. The DSHP can use either ambient air or the shallow subsurface of the ground to provide space heating or space cooling to the building as the conventional heat pump and produce hot/cold water for charging TES. Using dual sources (air and ground) can reduce the required size of the expensive ground heat exchangers while retaining high energy efficiency. During the off-peak period, the DSHP cools/heats the TES with low-cost electricity or overproduced renewable power. The stored cooling/heating energy in the TES is released during peak hours of the electric grid to meet the thermal demands of the building without consuming electricity to run the DSHP. A 2-ton (7 kW) prototype DSHP was developed and integrated with a 50-gallon (189 L) TES tank filled with a phase change material. Field tests were conducted to characterize the performance of the integrated system operating in various operation modes.
  • Publication
    Ground heat exchanger performance with variable speed ground-source heat pumps
    (International Ground Source Heat Pump Association, 2022) Viviescas, Geoffrey; Bernier, Michel
    The objective of this paper is to compare the required length and performance of ground heat exchangers as well as heat pump energy consumption for fixed and variable speed ground-source heat pumps. In the first part of the paper, a physics-based model of a water-to-water heat pump is briefly presented. This model is incorporated in TRNSYS simulations using a performance map where variable speed operation is handled through a linear relationship linking the COP to the percentage of the full capacity being used. The ground heat exchanger is modeled using a thermal resistance and capacitance approach to account for borehole thermal capacity. Simulations are performed on a typical residential building located in a cold climate (Montreal, Canada) and equipped with either a fixed or variable speed ground-source heat pump. Results are obtained for eight cases with: variable or fixed speed operation (VSC or FSC), with or without consideration of borehole thermal capacity (TC or NTC), and with annual heating needs covered at 90% or 100% by the heat pump. The differences in the required borehole length between the TC and NTC cases are relatively small. The smallest required borehole length is for the FSC-90%-TC case (180 m) and the longest is for the VSC-100%-TC case (250 m). The VSC-100% case has the largest seasonal Performance factor (SPF) at 4.14 and the FSC-90% case has the lowest at 3.11.
  • Publication
    Control strategy evaluation framework for ground source heat pumps using standing column wells
    (International Ground Source Heat Pump Association, 2022) Tonellato, Giulio; Kummert, Michael; Candanedo, Jose A.; Beaudry, Gabrielle; Pasquier, Philippe
    Standing column wells (SCWs) are efficient ground heat exchangers (GHEs) that have a significant cost saving potential. Recent developments have shown that they can also adapt successfully to cold climates despite previous concerns about operating near the freezing point. Therefore, new research frontiers are now being explored as the integration of this type of GHE to a real case study building model has hardly been analyzed until now. An institutional building has been selected for a SCW demonstration project in Mirabel, Canada. This paper includes in one single model the building, the Heating Ventilation and Air Conditioning (HVAC) system and the SCWs. The objective is to develop a software framework to analyze the impact of building operation strategies on the entire system during winter. Peak loads revealed to be the most critical points to control as the groundwater can freeze if the heat extraction is too high. Night indoor air temperature setbacks can bring significantly high peak loads whenever the building is heated to be occupied during the day. This paper shows that, using a bleed ratio above 20 %, a night setback can be successfully operated ramping up the temperature in around 3 hours.
  • Publication
    Field tests and numerical simulation of a novel thermal response test equipment for water wells
    (International Ground Source Heat Pump Association, 2022) Tanaka, Satoshi; Fujii, Hikari; Kosukegawa, Hiroyuki; Tsuya, Shunsuke
    The objective of this study is to develop a novel thermal response test (TRT) equipment that can be applied to existing water wells instead of borehole heat exchangers (BHEs). Accordingly, field tests were conducted using new and conventional equipment to estimate the vertical distribution of ground thermal conductivity. The result showed that the estimated thermal conductivity profile was higher than the reference profile obtained using conventional equipment. The temperature behavior in the well was considered to be unstable due to natural convection because the heating time was 4 hours, which is not long enough. Next, a numerical model of the water well including the novel equipment was developed, and the model was validated through history matching by using the temperature change in each depth. Finally, the TRT was simulated for two days using the model, and the simulated thermal conductivity profile was similar to the reference profile except near the end of the heated section. This result indicates that a more accurate thermal conductivity profile can be obtained by increasing the heating time until approximately 1.5 days.
  • Publication
    Open library of g-functions for 34,321 configurations
    (International Ground Source Heat Pump Association, 2022) Spitler, Jeffrey D.; West, Timothy; Liu, Xiaobing; Borshon, Ishraque
    Thermal response functions, known as g-functions, are commonly used in ground heat exchanger design tools and whole building energy simulation programs to simulate the ground heat exchanger performance. Calculation of g-functions can be quite computationally time-consuming, particularly as the number of boreholes gets large. However, once the g-function is computed, the actual simulation time can be quite short, particularly if a hybrid time-step (Cullin and Spitler 2011) approach is used. Because of this, pre-computed g-function libraries are commonly used in design tools and building simulation tools. This paper describes development of a new, publicly available library containing g-functions for 34,321 borehole field configurations; for each configuration, gfunctions are provided for 5 depths to allow interpolation between different borehole-to-height ratios. The available configurations include configurations in standard shapes: lines, rectangles, open rectangles, L-shapes, and U-shapes. It also includes new configurations: C-shapes, lopsided-U-shapes, and zoned rectangles, which are rectangular configurations with different interior and perimeter spacing of the boreholes.
  • Publication
    Ground heat exchanger design tool with rowwise placement of boreholes
    (International Ground Source Heat Pump Association, 2022) Spitler, Jeffrey D.; West, Timothy; Liu, Xiaobing
    Simulation-based design tools have been used since the late 1980s for designing ground heat exchangers (GHE) used with ground source heat pump (GSHP) systems. The ground heat exchanger simulations used in these tools rely on thermal response functions known as g-functions. Because of the significant computational burden in computing g-functions for even a single configuration, the design tools have relied on libraries of pre-computed g-functions. These g-functions were available for standard configuration shapes, such as lines, rectangles, open rectangles, L-shapes, and U-shapes. Standard shapes are often sub-optimal. For any building on a site, the available land may preclude use of a standard shape. For large GSHP systems with significantly imbalanced annual heat rejection and extraction loads, large rectangular fields may experience significant heat build-up (or heat draw-down) in the interior of the field. This paper describes a new ground heat exchanger design tool capable of automatically selecting and sizing both standard and irregular configurations. The focus of this paper is a method for creating, selecting and sizing irregular configurations where the available land area and "no-go" zones are described as irregular polygons.
  • Publication
    Long-term GSHP system performance measurement in the USA and Europe
    (International Ground Source Heat Pump Association, 2022) Spitler, Jeffrey D.; Gehlin, Signhild E. A.
    This paper presents an overview of the International Energy Agency (IEA) technology collaboration program Heat Pumping Technologies (HPT) Annex 52, "Long term performance measurement of ground source heat pump (GSHP) systems serving commercial, institutional and multi-family buildings." This project, which ran from 2018 through 2021, focused on measuring the performance of larger GSHP systems, going beyond energy use intensities which commingle the performance of the building envelope, occupancy effects and the system performance. Instead, performance factors were calculated, similar to coefficients of performance, but measured over various time intervals and system boundaries. The primary objectives of the Annex were refining and extending methodologies to better characterize system performance in larger buildings, creating a library of quality long-term measurements in the form of case studies, and providing guidelines for instrumentation, uncertainty analysis, key performance indicators, data management and quality assurance.
  • Publication
    Climate change effects on the energy performance of a residential groundsource heat pump system
    (International Ground Source Heat Pump Association, 2022) Sabbagh, Gabriel; Bernier, Michel
    The objective of this paper is to examine the impact of climate change on the energy performance of a typical residential ground-source heat pump (GSHP) system equipped with a horizontal ground heat exchanger (GHE) and located in a heating dominated climate (Montreal, Canada). Simulations results under future weather conditions (Relative Concentration Pathway – RCP8.5) show a drop in heating and a rise in cooling energy loads over 30 years. The outlet temperature from the GHE increases consistently from year to year and shows a high degree of variability in-line with the general trend of future ambient temperature fluctuations. In terms of electricity consumption, the main conclusion is that the use of current TMY weather files is inadequate to predict the yearly electricity consumption fluctuations.
  • Publication
    Forecasting hydraulic head changes in injection wells using LSTM network
    (International Ground Source Heat Pump Association, 2022) Rose, Christopher; Pasquier, Philippe; Nguyen, Alain; Beaudry, Gabrielle
    Monitoring of well's specific capacity is commonly used to plan maintenance of injection wells in open-loop GSHP and standing column well systems. However, this method does not consider the effect of temperature on hydraulic conductivity. A first step towards an alternative approach that does include the effect of temperature is proposed in this work. We present a long short-term memory network capable of predicting the water level in the injection well of an operating GSHP system. The methodology consists of building a training set using a numerical model. A total of 500 simulations were conducted to evaluate hydraulic head signals under various inlet temperatures and flow rates along with hydraulic and thermal parameters drawn from a uniform distribution. Predictive performance of the artificial neural network is tested on an operational data set. The resulting RMSE between the forecasted and operational data set is 14.8 cm.
  • Publication
    Ground heat exchangers with large diameter pipes: What are the benefits?
    (International Ground Source Heat Pump Association, 2022) Raymond, Jasmin; Gosselin, Jean-Sebastien; Lavoie, Jean-Francois
    The geothermal industry has recently been opting for large high-density polyethylene pipes to design vertical ground heat exchangers of ground-coupled heat pump system. Thus, we hypothesized that large diameter pipes can help improve heat exchange rate with the subsurface and made this study with the objective of quantifying the benefits gained with U-loop configurations. The finite line source equation and the multipole model were used to evaluate the maximum heat exchange rate that can be achieved with increasing pipe diameter. Sizing calculations were then performed for a school building in Boston. Ground heat exchangers with a single U-pipe having a nominal diameter of 1.25, 1.5 and 2 inches, as well as a double U-pipe, having a nominal diameter of 1.5 inches, were considered. Results highlighted that the double loop is by far the most efficient configuration, followed by the single loop with a 2 inches pipe diameter, respectively providing heat exchange rates that were 16% and 6% greater and total borehole length that were 22 and 9% smaller when compared to single loop with a 1.25 inches diameter. The use of large diameter pipes was shown without a doubt to benefit ground heat exchanger performances.
  • Publication
    Transient heat transfer in ground heat exchangers under groundwater flow
    (International Ground Source Heat Pump Association, 2022) Prieto, Carlos; Cimmino, Massimo
    An analytical solution for the transient heat transfer under groundwater flow for ground heat exchangers (GHEs) is presented. The method is an extension of the transient multipole expansion that describes the transient heat transfer as a pure conduction phenomenon inside and around a GHE including arbitrarily positioned pipes in the grout, coupling an irrotational and incompressible potential field in the ground with constant far-field velocity. The method does not rely on the supposition that groundwater flows through the GHE but instead moves around it. The method is validated against a finite element analysis model comparing the borehole wall temperature for two cases considering different single U-tube pipes position. It is shown that the thermal resistances inside the GHE do not respect the general symmetry condition as opposed to the pure conduction problem.
  • Publication
    Accuracy of analytical approaches to thermal response test interpretation
    (International Ground Source Heat Pump Association, 2022) Oh, Hae-Rim; Kim, Seong-Kyun; Park, Byeong-Hak; Baek, Ji-Young; Lee, Kang-Kun
    Thermal conductivity obtained via thermal response test (TRT) is one of the essential parameters for the design of shallow geothermal systems, especially a borehole heat exchanger (BHE). During TRT analysis, several factors (e.g., start time of analysis and test duration) could influence the estimated thermal conductivity. In addition, the influence of the factors may be different depending on the characteristics of the borehole and ground. This study investigated the effects of the start time and test duration through numerically generated TRT data under a diversity of environment and BHE information such as the thermal conductivity of grouting and ground. The generated numerical data were analyzed with three analytical approaches having different assumptions about the heat source to interpret the sensitivity of factors in the TRT analysis. By conducting the analytical sensitivity analysis, the importance of determining the appropriate start time and test duration could be emphasized when designing the test.
  • Publication
    Development of a topology optimization method for the design of ground heat exchangers
    (International Ground Source Heat Pump Association, 2022) Noel, Alexandre; Cimmino, Massimo
    A new method for sizing vertical ground heat exchangers is proposed using topology optimization to reduce the number of boreholes required to fulfill the cooling and heating demand. The ASHRAE sizing equation is adapted to formulate a topology optimization problem to minimize the number of boreholes required in a bore field. The results show that topology optimization can help reduce the number of boreholes required when compared to a sizing performed on a regular grid using conventional sizing methods. These optimized configurations show smaller spacings between the boreholes located on the perimeter and larger spacings between the boreholes located in the center of the bore field.
  • Publication
    Economic optimization and parametric analysis of large hybrid ground source heat pump systems: A case study
    (International Ground Source Heat Pump Association, 2022) Nguyen, Alain; Eslami-Nejad, Parham; Tamasauskas, Justin; Kegel, Martin
    Hybrid ground source heat pump systems offer a solution to reduce initial costs and make systems more economically viable. Their design is however complex and their financial profitability difficult to establish. The design of hybrid system is usually determined by following rough rules and is neither mathematically rigorous nor optimized. In this paper, a methodology recently introduced by the same authors for economic optimization of hybrid ground source heat pump systems is used to carry out a parametric analysis and assess the impact of uncertainty on the optimal design solution. The results show that all the parameters have significant impact on the optimization, and the ground heat exchanger construction costs and ground source heat pump COP had the most impact on the net present value. However trends are difficult to observe because if the non-linear nature of the problem, and thus there is a need for more robust optimization of hybrid GSHP systems under uncertainty.
  • Publication
    Machine-learning-based models for predicting the performance of ground-source heat pumps using experimental data from a residential smart home in California
    (International Ground Source Heat Pump Association, 2022) Najib, Antash; Hussain, Abbas; Krishnamoorthy, Sreenidhi
    Ground-source heat pumps (GSHP) reject (extract) heat to a lower (higher) temperature sink (source) as compared with air-source heat pumps which allows them to operate more efficiently. With the rapid development in the field of artificial intelligence, data-driven based Machine-Learning (ML) models are playing an important role in simulating various building energy systems including GSHP. In this paper, ML models have been applied to predict the performance of a water-water GSHP. The models presented in this paper, require climate data (which is readily available or easily measurable) and the power consumed in the previous time-step for predicting the power consumption for the current time-step. The models were rigorously trained using measured data from a residential technological demonstration home located in Davis, California. Data spanning from October 2018 to April 2019), i.e. heating mode, was used in the study. Eight linear and non-linear ML models were employed and the results show that the linear models namely, multiple linear regression (MLR), elastic net (ELN) and support vector regression (SVR) can predict the power consumption with a very high level of accuracy. Within the linear models, the coefficient of variation of the root mean squared error (CV-RMSE) for the MLR was 4.04062 which was 0.19% and 0.05% less than the ELN and SVR model respectively. Within the five non-linear models, gradient boosting decision tree (GBDT) exhibited the lowest CV-RMSE i.e. 4.26141 (which is 5.46% higher than the MLR model). The CV-RMSE for extreme gradient boosting trees (XGBT) was the highest (i.e. 45.42% higher than the MLR model). Thus MLR model can be used to accurately predict the power consumption of the GSHP system.
  • Publication
    Development of a web-based screening tool for ground source heat pump applications
    (International Ground Source Heat Pump Association, 2022) Liu, Xiaobing; Degraw, Jason; Malhotra, Mini; Forman, Wes; Adams, Mark; Accawi, Gina; Brass, Brett; Kunwar, Niraj; New, Joshua; Guo, Jean
    Ground source heat pump (GSHP) technology has great potential to help the nation meet its energy and decarbonization goals, but several barriers hinder the wide application of GSHP. Important barriers include the lack of a coherent toolset for analyzing the technical feasibility and economic viability of the GSHP application. The current design and analysis methods are ineffective and require significant expertise to apply. Although building energy modeling is increasingly important in designing buildings, the tools for GSHP modeling and simulation are lacking. A web-based free-to-use tool is being developed for quick techno-economic analysis of GSHP applications in nearly any building in the United States. This tool is enabled by improvements in the calculation methodology to allow rapid sizing of borehole configurations that provide significant cost savings. The screening tool currently uses US Department of Energy (DOE) prototype building models and an extended g-function library to size ground heat exchangers and simulate the performance of GSHP systems. The team is integrating with DOE's Oak Ridge National Laboratory's AutoBEM program to automatically create a building model based on user inputs. This paper introduces the structure, components, features, and results of the web-based screening tool for GSHP applications. Future directions for further developing the tool are also discussed.
  • Publication
    Impact analysis of heating electrification in US buildings with geothermal heat pumps
    (International Ground Source Heat Pump Association, 2022) Liu, Xiaobing; Malhotra, Mini; Li, Yanfei; Lian, Jamie; Wang, Xiaofei; Ho, Jonathan
    Few studies have investigated the impacts of large-scale deployment of geothermal heat pumps (GHPs, also called ground source heat pumps) on the electric grid. GHPs utilize the ground as a heat source to warm buildings more efficiently than other space-heating systems. The coupling with the ground offers seasonal thermal storage so that GHPs can also cool buildings in summer more efficiently than other space-cooling systems. This study simulated the performance of GHP systems for various commercial and residential buildings in 15 climate zones in the United States. Combined with the latest End-Use Load Profiles of the US building stock and grid modeling, this study aims to assess the impacts of a national deployment of GHP systems on the US electric grid in terms of energy consumption, emissions, and operational resilience. The preliminary results show that the GHP deployment can save 429 billion kWh of electricity (a 19% reduction from baseline) and reduce carbon emissions by 496 million tons per year (a 31 % reduction from baseline). A geographical view of the results indicates that retrofitting existing HVAC systems with new GHP systems can lead to further reductions in annual electricity consumption and peak electricity demand in the southern regions of the United States than in other parts of the country. On the other hand, GHP retrofits result in higher percentages of site energy savings and carbon emission reduction in the north (cold climates) than in the south (warm climates).
  • Publication
    Technical and economic evaluation of a ground source heat pump with thermal and battery energy storage systems for residential dwellings in Quebec
    (International Ground Source Heat Pump Association, 2022) Kimiaei, Kimiaei; Kazemi-Ranjbar, Sina; Eslami-Nejad, Parham
    Ground source heat pump (GSHP) systems have been identified as promising solutions to help buildings achieve future carbon neutral targets. However, two main barriers decelerate the wide adoption of this technology in every location. One barrier is the high initial cost, which is sometimes justified by high local energy prices. The other potential barrier that always imposes a major bottleneck on a transition to electrification by using GSHP systems is the impact on the electrical grid at peak demand times. In this study, a solution has been proposed to address both issues by integrating thermal and battery energy storage systems into a conventional GSHP system. Numerical simulations are performed to evaluate the technical and economic feasibility of the proposed configuration. In addition, a comparative analysis is performed with other commonly recognized GSHP configurations with and without thermal energy storage. Results show that the new configuration requires a 22% shorter borehole by using the thermal energy storage, and reduces the annual peak electricity demand by almost 500kW cumulatively by using the battery energy storage. These benefits contribute to improving the net present value of the new configuration by 23% compared to the conventional GSHP configuration.