2024 Research Conference Proceedings of the IGSHPA

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  • Publication
    On the interaction between a geothermal borehole and groundwater flows
    (International Ground Source Heat Pump Association, 2024-05-28) Rico, Javier; Hermanns, Miguel
    The presence of aquifers can highly affect the heat exchange between geothermal boreholes and the ground. To optimally design them, theoretical models for the thermal interaction of geothermal boreholes with groundwater flows are required. The present work exploits the presence of large disparities in time and length scales, using matched asymptotic expansion techniques, to build a mathematically rigorous and physically sound model that accounts for the presence of creeping groundwater flows. The derived model not only exhibits great performance compared to detailed numerical simulations but also serves to critically assess the merits and limits of the state of the art.
  • Publication
    Research on design and control methods of medium-depth geothermal heat pump energy storage system for clean electric utilization
    (International Ground Source Heat Pump Association, 2024-05-28) Peng, Chenwei; Deng, Jiewen; Wei, Qingpeng
    Electric-driven heat pump systems, commonly used for space heating and cooling in buildings, have emerged as a crucial component in integrating with the power grid, promoting clean electricity consumption. This paper introduces a high-efficiency space heating and cooling system that combines heat pumps with medium-depth ground heat exchangers and a cooling tower. Additionally, it employs a heat storage system for daily thermal and cooling storage. The system encompasses a design methodology and control strategy optimized for maximizing the use of local photovoltaic power generation and municipal clean power sources. Furthermore, the paper presents a case study of a large public building, including a quantitative analysis to assess its energy-saving capabilities and CO2 emission reduction impacts. Results showed that the proposed system has a payback period of less than six years and reduces carbon dioxide emissions by over 14,900 tons, showcasing substantial energy savings and emission reduction benefits.
  • Publication
    Techno-economic assessment of deep geothermal technologies for district heating systems on the South Shore of Montréal (Québec, Canada)
    (International Ground Source Heat Pump Association, 2024-05-28) Miranda, Mafalda M.; Comeau, Félix-Antoine; Raymond, Jasmin
    Geothermal district heating systems with deep boreholes (1.5 to 3.0 km) can be an interesting alternative to electric heating systems powered by hydroelectricity. The techno-economic potential of deep borehole heat exchangers and geothermal doublets (with and without reservoir stimulation) was assessed, and the results suggest that the latter installed in a permeable medium is more economically attractive than deep borehole heat exchangers. The economic analysis also suggests that the former systems can potentially provide energy at a lower cost than Hydro Québec’s minimum electricity selling price of 0.063 $/kWh (Rate D applied to domestic use for the first 40 kWh/day – 1st tier). However, geothermal doublets are a high-risk technology. Further field tests would be needed to fully assess their technological potential. Nevertheless, despite the risk and uncertainty, utilizing deep geothermal energy for district heating systems offers potential long-term benefits that surpass the challenges related to drilling and resource assessment.
  • Publication
    Extending the ASHRAE method to a 25-year horizon through the Tp8 model for temperature penalty accurate estimation
    (International Ground Source Heat Pump Association, 2024-05-28) Fossa, Marco; Morchio, Stefano; Memme, Samuele; Priarone, Antonella; Parenti, Mattia
    The accurate design of Borehole Heat Exchangers (BHE) fields in ground-coupled heat pump (GCHP) systems is crucial for ensuring long-term performance. Traditional sizing methods, such as the ASHRAE method as modified by ASHRAE-Tp8 version, consider the annual building heating and cooling demand over a 10-year time horizon by applying the temporal superposition of 3 aggregated thermal pulses of different durations. The present paper aims to clarify how the ASHRAE-Tp8 method could be adapted to be employed over a 25-year plant operation horizon. Temperature penalty estimations are compared with "real" precalculated temperature response factors (g-functions) through the minimization of a suitable objective function. Optimized constants for the present new ASHRAE-Tp8 method are derived, enabling its easy adaptation for the 25-year time period. Comparisons with EED and GLHEPRO commercial software results demonstrate the reliability of this improved method, with borefield length estimations accurate within 7% and 6% respectively. The results reported in the present paper lead to easily inferring the error in terms of overall length and borehole depth that would be obtained by employing the design process proper of the 10-year reference period when the 25-year time horizon is considered. The methodology is in general demonstrated to be applicable to different time frames.
  • Publication
    Influence of short-term dynamic effects on geothermal borefield size
    (International Ground Source Heat Pump Association, 2024-05-28) Meertens, L.; Peere, W.; Helsen, L.
    A borefield is often oversized in practice, leading to unnecessary investment costs. This is the result of using a steady-state borefield model to describe the heat transfer inside the borehole, thereby neglecting the dynamic behavior of the fluid, the pipe, and especially the grout. When using a dynamic model (which incorporates transients), the thermal mass of the materials between the fluid and the ground introduces inertia, reducing the heat transfer peak to the ground. Consequently, the borefield size can be reduced while still meeting the predetermined temperature limitations, leading to a significant decrease in investment cost. The aim of this study is to investigate the influence of short-term dynamic effects on the sizing of geothermal borefields. This study starts from the Finite Line Source (FLS) model as baseline. This model is corrected to account for the cylindrical geometry of the boreholes and coupled to an explicit 1-D numerical model of an equivalent borehole, thereby extending the scope of the response factors to short time scales. Validation was based on the dynamic Modelica borefield model of the IDEAS Library and experimental borefield data. Results show that the relevance of using a sizing method based on a dynamic model is highly dependent on the thermal load profile. In case a building has a high variation in peak demand and the sizing is not dominated by imbalance a size reduction up to 34.7% is obtained for the case investigated.
  • Publication
    Assessing coaxial collector performances: Field data and analysis
    (International Ground Source Heat Pump Association, 2024-05-28) Vautrin, Adrien; Pallard, Willem Mazzotti; Acuña, José; Lazzarotto, Alberto
    Since the development of Ground Source Heat Pumps (GSHPs), there have been mostly three types of borehole heat exchangers in use, single and double U-pipes as well as coaxial, the latter being seldom installed. Most earlier work has thereby been focusing on the classic U-tube solutions. This work aims at providing more information on coaxial heat exchangers. Field data from 11 installations having coaxial borehole heat exchangers has been gathered in this work and measured effective borehole resistance as well as pressure drop have been presented and compared to calculated values. The Hellström approach as well as correlations for pressure drop have been implemented. Significant deviation from theory has been observed regarding the pressure drop (75% average absolute relative error) as well as the effective borehole resistance, albeit to a lesser extent (33%). An exploration of the geometrical parameter space (length, brine concentration, fluid temperature and inner diameter) has been carried out, giving insights into potentially better coaxial designs.
  • Publication
    Tools for automated circuiting of large vertical borehole fields – a preliminary investigation
    (International Ground Source Heat Pump Association, 2024-05-28) West, Timothy N.; Spitler, Jeffrey D.
    Recent developments in automated vertical borehole ground heat exchanger design tools can reduce the required engineering time and improve the resulting ground heat exchanger designs by taking full advantage of available property. However, current practice when designing irregularly shaped borefields is to minimize the total drilling rather than the installation cost or life cycle cost of the system. Total drilling can serve as a proxy for total installation cost, but neglecting the cost of horizontal piping and trenching may be misleading in some circumstances. This paper describes the initial development of a tool to estimate the installation cost of a ground heat exchanger corresponding to an arbitrary borefield. To complete this task, the design tool automatically determines the trenching network and pipe network required to connect the boreholes and heat pump of the ground heat exchanger, sizes the pipes in the pipe system to meet given hydraulic constraints, and then estimates the installation cost from the resulting trench and pipe network. The trench and pipe network synthesis consists of a hierarchical k-means clustering algorithm which groups boreholes into individual vaults then circuits. Circuits are separated into groups so that their pipe systems can be routed through a handful of vaults. From this grouping, a trenching network is created with a pathing algorithm, shortest path algorithm, and minimum spanning tree algorithm. Together, these algorithms form a trench network that can stay within irregularly shaped property boundaries, avoid user-defined obstructions, and produce a trench network without a large surplus of extra trenching. The pipe network is created with the trench network, the borehole grouping, and user-given network type (i.e., direct return, reverse return, etc.).
  • Publication
    Numerical characterization of the thermal performance of horizontal geo-exchange pipes
    (International Ground Source Heat Pump Association, 2024-05-28) Ghalayini, Ibrahim; Mwesigye, Aggrey; Dworkin, Seth B.
    Ground source heat pump systems offer efficient and sustainable heating and cooling solutions; however, traditional vertical boreholes involve high capital costs associated with drilling, hindering widespread adoption. Recent research introduces a novel approach by integrating geothermal heat exchangers into steel helical piles within building foundations, known as "Geo-Piles." These devices, extending typically 50 ft to 100 ft into the ground, serve a dual purpose (structural and thermal) and show promise as cost-effective alternatives. Further advancements explore the use of plastic as a casing material, for thermal-only systems, enhancing affordability and enabling standalone system deployment without relying on extensive new construction projects. This paper investigates plastic geo-exchange pipes (PGEPs), designed similarly to Geo-Piles, aiming to reduce costs by implementing a horizontal installation method at depths comparable to other forms of linear utility infrastructure. Numerical modeling was employed to assess the system's performance at three depths—15 ft, 18 ft, and 21 ft and was then compared to a vertical configuration. The results indicate that with every additional 3 feet of depth in the horizontal configuration, there is an enhancement in capacity of 0.5 tons for every 200 feet of PGEP. Moreover, the 18-ft configuration exhibits exceptional thermal performance while simultaneously reducing installation space and potentially meeting permit requirements, showcasing its potential as an economical and efficient solution in the realm of ground source heat pump systems.
  • Publication
    Effect of the geothermal heat flux on vertical ground heat exchanger performance
    (International Ground Source Heat Pump Association, 2024-05-28) Sabbagh, Gabriel; Bernier, Michel
    Ground heat exchangers (GHE) are typically modeled using a simplifying assumption: the mean ground and atmospheric temperatures are assumed to be equal to the ground temperature halfway down the length of the borehole. This paper examines the impact of this assumption on vertical ground heat exchanger performance. A numerical model using a finite volume method is developed to simulate the performance of ground heat exchangers. The model takes into consideration the effect of the geothermal gradient, varying surface temperatures, inlet fluid temperatures or energy extraction loads over long periods of time. Results from the first comparison show that the geothermal heat flux provides more energy to the GHE than the outside environment and that over long periods of operation, the geothermal heat flux establishes itself as the main energy source. Moreover, the existence of a geothermal heat flux diminishes the effect of continuous heat extraction on the natural ground heat flux profile and therefore, infers a more sustainable exploitation of the energy resource. Results from the second comparison show that inadequate GHE dimensioning in both cooling and heating can occur if the geothermal heat flux is not considered. However, using simple approximations to the ground temperature profile that consider the geothermal heat flux can lead to accurate heat exchange calculations.
  • Publication
    Thermal resistance of a CO2 geothermal thermosyphon with an active condenser
    (International Ground Source Heat Pump Association, 2024-05-28) Badache, Messaoud
    In this study, an experimental setup was built and fully instrumented to investigate the thermal resistance of a CO2 geothermal thermosyphon (GT) with an active condenser connected to its upper section. The study explores the effects of CO2 filling ratios, cooling fluid flow rate and temperature on the thermal resistance in different zones of the experimental GT system. The results show that the total thermal resistance of the GT stands out, displaying a notably higher value, up to 12 times that of the active condenser. Furthermore, the thermal resistance of the active condenser is higher than those of the evaporator and condenser sections, being up to 3 and 7 times higher, respectively. Therefore, reducing the thermal resistance of the active condenser and between the evaporator wall and the ground represents the most effective approach to enhance the performance of the GT system. These findings offer valuable insights for the efficient design of GT systems with active condensers, identifying areas where improvements can be made to maximize GT performance.
  • Publication
    Evaluation of short and long-term performance of a dual-source heat pump
    (International Ground Source Heat Pump Association, 2024-05-28) Bordignon, Sara; Pengo, Riccardo; De Carli, Michele; Zarrella, Angelo
    A dual-source heat pump is a heat pump coupled with two heat sources/sinks, such as the ground and the air. Such solutions allow to balance the thermal load to the ground, shifting part of the heating or cooling thermal load to the finned coil heat exchanger and preventing the possible degradation of the long-term ground-source heat pump performance. In addition, a similar configuration can be more economically convenient than a ground source heat pump. Depending on the plant configuration and the boundary conditions (mainly climatic area), the control strategy to switch between the two heat sources and sinks is crucial to ensure good heat pump performance in the short and long-term operation of the system. This work investigates a control strategy to choose the value of switch temperature, which establishes the most favorable heat source or sink to be used by the heat pump. A dynamic model is developed using TRNSYS to study and predict the thermal and electrical behavior of double-source heat pumps, which can be used in the context of retrofitted and new buildings under different weather conditions. The modeled system simulates an existing commercial building, where a dual-source heat pump is installed and whose operation data are monitored.
  • Publication
    Numerical investigation of an energy pile-based solar-assisted ground source heat pump system for space heating and cooling
    (International Ground Source Heat Pump Association, 2024-05-28) Beragama Jathunge, Charaka; Adebayo, Philip; Dworkin, Seth B.; Mwesigye, Aggrey
    While ground source heat pump systems are a sustainable method to climatize buildings, their long-term performance in cold climates may lead to ground overcooling and, thereby, performance deterioration over time, especially when the loads are significantly imbalanced. Solar-assisted ground source heat pump systems are an alternative to mitigate the ground thermal imbalance by injecting solar thermal energy into the ground to balance energy extraction by the heat pump while also improving the heat pump performance. This study numerically evaluates the performance of a solar-assisted ground source heat pump system for three different climate zones and three modes of operation using a thoroughly validated finite volume-based computational model. A 0.139 m diameter helical steel pile installed to a depth of 18.288 m below the ground was used in this study as the ground heat exchanger. Realistic building load profiles were obtained using OpenStudio for residential applications in Calgary, Toronto, and New York and coupled with a computational fluid dynamics solver to evaluate the overall system performance. The results show that the solar-assisted system shows a significant performance improvement of 16.3% over a non-solar enhanced system for the coldest climatic zone studied. Out of the three system operation modes studied (mode 1: solar loop is turned off at low irradiance, mode 2: solar thermal energy is redirected based on the season, mode 3: solar thermal energy is redirected based on the heat pump operating mode), mode 3 yields the best overall heat pump performance for all the locations (COP: 3.72, 3.74, 4.24 for Calgary, Toronto, and New York, respectively). Interestingly, the results indicate the best-suited system operating mode depends on the degree of dominance of the building’s heating load.
  • Publication
    Exploration of a heuristic predictive control strategy for ground source heat pumps coupled to standing column wells
    (International Ground Source Heat Pump Association, 2024-05-28) Tonellato, Giulio; Kummert, Michaël; Candanedo, José; Beaudry, Gabrielle; Pasquier, Philippe
    Standing column wells (SCW) have shown to be a cost-effective hybrid ground heat exchanger (GHE) configuration suitable for high-density urban areas as they benefit from groundwater advection while not requiring particularly productive aquifers. However, operating SCWs in cold climates can represent a control challenge since the groundwater can approach freezing conditions while recirculating; on the other hand, submersible pumps can cause a significant power usage. This article explores the potential of a heuristic predictive pumping control strategy built with an accurately calibrated white-box model of a real case study in Mirabel, Quebec, Canada. Results show that it can be used to both contain pumping power and safely operate the SCWs without using an electric boiler as anti-freezing protection. In an exceptionally cold month, the predictive control strategy effectively prevents the boiler intervention, resulting in a 3.25 times reduction in peak power, with a slight increase in energy use (5.75%). In less extreme winter weather, the energy usage difference will be smaller, but the reactive control will likely use the boiler whenever the weather gets particularly cold. This study provides the basis for the development of predictive control rules that may be easily implemented in similar configurations.
  • Publication
    Reduction of injection flow rate with an underground buffer tank coupled with a standing column well
    (International Ground Source Heat Pump Association, 2024-05-28) Ben Aoun, Mohamed Arbi; Nguyen, Alain; Pasquier, Philippe
    This study proposes a new solution for disposing of bleed water in standing column well systems. A perforated septic tank is used simultaneously as a storage tank for storing large water volumes and as an infiltration basin. By integrating a storage tank with a standing column well, bleed water is stored in the tank and is then drained rather than being returned to an injection well. A 3D coupled thermohydraulic finite element model supports this new bleed method. For this reason, a 30-day simulation examined a case study of a 20 m³ storage tank associated with a standing column well operating in heating mode at an experimental site located in Varennes, Canada. The model considers realistic bleed operation flow rate, temperature, and the geological properties and weather conditions observed at the experimental site. Additionally, the drainage process at the base of the tank was modeled by pairing Navier-Stokes flow with unsaturated and saturated porous media flow. Despite the unfavorable geological conditions of the experimental site, numerical results indicate that infiltration was sufficient for draining the bleed water that accumulated in the storage tank. The latter managed to dispose 121.5 m³ of water throughout the simulation period. Finally, infiltration proved to be a promising alternative to injection wells.
  • Publication
    Investigation of effective bleed strategies for standing column wells using experimental transfer functions
    (International Ground Source Heat Pump Association, 2024-05-28) Jacques, Louis; Pasquier, Philippe; Dion, Gabriel
    Standing column wells are an efficient type of ground heat exchanger that continuously recirculates groundwater in an uncased borehole. To increase heat exchange during peak load periods, a process called "bleed" is used. This process creates groundwater discharges that must be managed in accordance with local regulations and may incur additional costs, for example, if directed to injection wells. Alternatively, inter-well reinjection can be used to reroute the discharged water to other standing column wells. This study presents experimental results of a standing column well system operated during 35 days under four different reinjection modes. A full recirculation mode, basic mode, is compared to two levels of bleed and to the proposed inter-well reinjection mode. The experimental data were used with a robust deconvolution algorithm to extract a transfer function for each mode. These functions represent the thermal response of the system to a unit excitation, allowing for comparison of reinjection modes under the same heat load. Analysis of these transfer functions showed that, at the specific experimental site studied, the inter-well reinjection can be as efficient as a bleed operation. Thus, inter-well reinjection can successfully extend system use during peak load periods, while decreasing groundwater discharge to injection wells.
  • Publication
    Impact of a standing column well on the geochemical and microbiological quality of groundwater
    (International Ground Source Heat Pump Association, 2024-05-28) Ouferroukh, Mosaab Imed Eddine; Courcelles, Benoît; Millette, Denis; Pasquier, Philippe
    Transitioning to renewable energy sources is crucial in the fight against climate change and ensuring sustainable energy security. Geothermal systems emerge as a promising solution, specifically through the utilization of standing column wells (SCW). These wells, integrated into geothermal systems, offer a greater heat exchange efficiency. However, the implementation of SCWs for heat extraction and injection can impact groundwater geochemistry and bacterial communities. This article explores the repercussions of employing a SCW geothermal system on groundwater for a school in Mirabel, Quebec, Canada. Groundwater sampling was conducted from July 2022 to May 2023 to analyze the geochemical and microbiological aspects of the water quality affected by SCWs used for heating and cooling. This comprehensive study, spanning over a year, revealed some changes in the chemical composition of groundwater, and the absence of several bacterial groups responsible for various bio-corrosion issues, such as iron and sulfate-reducing bacteria. The data also unequivocally demonstrate that the system's operation limits the proliferation of pathogenic groups rather than fostering their multiplication. While the initial findings are promising, this work demands longer-term monitoring. Continued observation over an extended period is crucial for a deeper understanding of the trends in biogeochemical developments.
  • Publication
    Drake Landing Solar Community: an analysis of different technology scenarios
    (International Ground Source Heat Pump Association, 2024-05-28) Kosteniuk, Isabelle; Thornton, Jeff; Mesquita, Lucio; Boulter, Raymond
    The present work simulates the Drake Landing Solar Community (DLSC) in Okotoks, Alberta, using calibrated borehole heat exchanger models to evaluate the energy performance of different technology scenarios. Four technology scenarios were compared to the existing design, including an updated DLSC solar thermal system with high efficiency collectors, a photovoltaic plus heat pumps and electric boilers system with high temperature seasonal thermal storage, a conventional ground source heat pump system, and a hybrid solar thermal and photovoltaic system with heat pumps, electric boilers and seasonal thermal storage. The ground source heat pump scenario presents the highest SPFnet (seasonal performance factor net) to solar panel area with one caveat: the operation is dependent on ground temperature, which goes down with time, s, and the heat pump operation would experience interruptions after 30 years of operation without heat injection into the ground. The solar thermal + borehole thermal energy storage systems presented the highest SPFs of the options evaluated.
  • Publication
    Thermal power budget approach to estimate the geothermal potential of closed mines
    (International Ground Source Heat Pump Association, 2024-05-28) Comeau, Félix-Antoine; Lacombe, Samuel; David, Dan; Arsenault, Thierry; Raymond, Jasmin
    Over the past 5 years, research at the Institut National de la Recherche Scientifique (INRS) in Québec City has focused on the concept of thermal power budget to evaluate the geothermal potential of abandoned and flooded mines. The objective of this paper is to describe this new resource assessment concept and show how it was applied to a variety of mine sites, both open pit and underground, at the early stage of geothermal development. This considers not only the volume of water in the mine, as well as initial and final temperatures, but also the volume of rock involved in heat exchange and water inputs, such as precipitation and groundwater. The gigantic open-pit mines in the Thetford Mines area contain geothermal resources with promising potential for cooling data centres. Studies have also been carried out in Yellowknife (Northwest Territories) to assess the amount of thermal energy that could be produced from a world-scale underground mine integrating geothermal heat pumps.
  • Publication
    Study on expansion of air-conditioning area by a hybrid ground source heat pump system for retrofitting an office building to be a net-zero energy building
    (International Ground Source Heat Pump Association, 2024-05-28) Katsura, Takao; Nakamura, Yasushi; Nagano, Katsunori
    In recent years, ground source heat pump (GSHP) systems have become recognized as one of the applications of renewable heat energy utilization and are being installed in buildings to be Zero Energy Buildings in Japan. At an office building in Kitakyushu City, Japan, which has been in operation since 2010, a hybrid GSHP system with 80 m x 50 borehole double U-tube ground heat exchangers and a cooling tower has been installed. The results of more than 8 years of monitoring of the hybrid GSHP system showed that the effective thermal conductivity of the ground was estimated to be 4.5 W/(mK), which was higher than the results of thermal response tests due to the influence of groundwater flow, and that the maximum cooling load was smaller than the design value. In this paper, the authors attempted to expand the air-conditioning area by the hybrid GSHP system for retrofitting the office building to be a net-zero energy building. Specifically, the air-conditioning area that can be covered by the hybrid GSHP system was investigated by using simulation and giving the heating and cooling loads based on the actual measurements. As a result, it was confirmed that the air-conditioning area by the hybrid GSHP system can be increased three times, and that the air-conditioning area that can be covered by the hybrid GSHP system can be expanded from approximately 20% of the present air-conditioning area to approximately 60%. Then compared to the case where all the systems are ASHP, the reduction in electric energy increases as the area of the building is increased, with a reduction of approximately 13% when the area is doubled and an increase of approximately 19% when the area is tripled.
  • Publication
    Sizing equation based on the outlet fluid temperature of closed-loop ground heat exchangers
    (International Ground Source Heat Pump Association, 2024-05-28) Dion, Gabriel; Pasquier, Philippe; Perraudin, Diego
    The ASHRAE sizing equation is widely used to find the length of a ground heat exchanger required to cover a given ground thermal load. Some sizing methods use the concept of g-functions, based on a finite line source model, to compute the thermal resistances required by the equation. Such g-functions are defined at the borehole wall and do not incorporate the short-term features of the boreholes such as fluid residence time and borehole heat capacity, and thus are not readily applicable to simulation of ground heat exchanger outlet temperature. This article proposes an adaptation to the alternative ASHRAE sizing equation of Ahmadfard and Bernier (2018) and defines the transfer function at the outlet of the ground heat exchanger. The proposed approach iterates on the borehole length to identify the borehole outlet transfer function that maintains the fluid within prescribed temperature limits. Verification of the method are performed using test cases described by Ahmadfard and Bernier (2019). It is found that ground heat exchanger length obtained are within 5% of the ones predicted by the alternative ASHRAE sizing equation. The variations are related to the approximate nature of a three-pulse sizing approach. The proposed method also benefits from the use of the short-term transfer function provided by an artificial neural network.