Session: 04-01: Energy Storage Systems and Applications

Paper Number: 152218

152218 - Experimental Characterization of Low Temperature Borehole Thermal Energy Storage System: A Case Study 

Abstract: 

Building decarbonization is gaining momentum as a reliable strategy to meet the 2050 net zero emissions goal. In cold climates, the majority of residential and commercial buildings’ energy use and emissions are attributed to space heating and domestic hot water needs. According to the International Energy Agency, buildings account for 26% of the global CO₂ emissions related to the total energy consumed in the world and about half of the global building’s energy demand was due to space and water heating in 2022. This underpins the need for the development and deployment of reliable and sustainable heating and cooling technologies to transition from conventional heating systems which burn fossil fuels. For this purpose, the use of heat pump to upgrade the stable low-grade ground energy to meet the space heating and cooling and hot water needs efficiently is receiving considerable interest. The energy performance of this system, ground source heat pump (GSHP), is highly dependent on the heat transfer process between the borehole heat exchanger (BHE) and the ground for a given building energy load profile. The circulating fluid within the BHE enables heat transfer between the BHE and the ground.

The major challenge impeding the use of ground source heat pumps is the initial cost associated with longer BHE required in cold climates with heating dominant building energy loads and lack of space in urban areas. Undersized BHE can cause ground thermal imbalance in the neighborhood of the BHE triggered by an unbalanced building cooling and heating loads. Continuous ground temperature drops or increase over long-term use significantly affects system performance. To avoid premature system failure in cold climates, combined use of intermittent solar energy with ground source heat pumps has the potential to reduce BHE length, alleviate ground temperature decline and improve the systems’ coefficient of performance (COP). Although various researchers have studied solar-assisted ground source heat pumps (SAGSHP) with the ground assumed as purely conductive model, the literature is scarce on experimental study of this system in cold climates. In addition, experimental studies on the influence of ground water flow on the BHEs operations have not been widely studied. This paper aims to contribute to the understanding of the heat treat transfer between the BHE of a SAGSHPs and the ground in the presence of ground water flow.  

An experimental test system set up in southwest of Calgary, Alberta, Canada is used to monitor the performance of a SAGSHP. The experimental test platform comprises of a vertical double U-tube close loop BHE with independent heat pump and solar collector circuits. This configuration allows for the storage of available solar energy in the ground while also extracting heat from the ground to meet the heating demand of the experimental room. The closed loop BHE consists of a 32 mm diameter high-density polyethylene (HDPE) U-tube pipe with a borehole diameter of 152 mm drilled to a depth of 150 m. One of the U-tubes is connected to extract and reject heat into the ground, while the other is connected to the solar collector array to recharge the ground to maintain ground thermal balance. The experimental room is a 3.05 m x 14.75 m worksite trailer with R-20 insulation. The borehole is backed filled with a thermally enhanced bentonite grout for a higher effective thermal conductivity. The experimental setup allows for hourly monitoring of the inlet and outlet circulating fluid temperature and flow rate of the U-tubes. The system was operated between March and October 2024 for solar thermal storage. The results show a consistent increase in the solar loop monthly average inlet and outlet temperature up to July and then decrease afterwards because of solar irradiation availability. Ultimately, the results from this research will promote the development of GSHP in extremely cold climates for sustainable space heating and cooling, providing practical insights on the performance of the BHE of a SAGSHP.

Presenting Author: Philip Adebayo University of Calgary

Presenting Author Biography: Philip Adebayo is a promising researcher specializing in clean and renewable energy technologies. Currently pursuing his PhD in the Department of Mechanical Engineering at the University of Calgary, Canada, Philip focuses on optimizing solar-assisted geothermal heat pump systems with thermal storage for sustainable space heating and cooling in cold climates. Philip received the Indigenous and Black Engineering and Technology (IBET) Momentum Fellowship and the prestigious Vanier Canada Graduate Scholarship to support his PhD studies. He earned his master’s degree from the American University of Beirut in Lebanon, fully sponsored by the Mastercard Foundation. Prior to that, he obtained a bachelor’s degree with first-class honors in Mechanical Engineering from the University of Ibadan in Nigeria where he emerged as the best graduating student in his class.