Impact of soil freezing on the thermal performance of geothermal borehole heat exchangers across Canadian climates

• Published in: Building services engineering research & technology Vol. 46; no. 4; pp. 441 - 466
• Main Authors: Keramat, Fatemeh, Zhong, Lexuan
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.07.2025
• Subjects: thermal resistance; coefficient of performance; Borehole heat exchanger; soil freezing; computational fluid dynamics; ground temperature profile
• ISSN: 0143-6244; 1477-0849
• DOI: 10.1177/01436244251339720

This study evaluates the thermal performance of geothermal borehole heat exchangers (BHEs) in various Canadian locations during winter, focusing on soil freezing effects. Using a computational fluid dynamics approach, it examines how soil porosity and thermal conductivity influence BHEs’ thermal performance. Ninety case studies across nine Canadian zones assessed these effects under winter conditions. The RNG k-ɛ turbulent model tracked fluid flow, and the solidification model monitored ice formation. Soil temperature fluctuations along the ground depth were incorporated using user-defined function codes. Coefficients of performance (COP) were calculated for heat pump thermal performance. Results showed substantial soil freezing around the borehole in Saskatchewan and Manitoba. The BHE systems in Alberta and Manitoba had the highest thermal resistance, while those in Saskatchewan and Prince Edward Island had the lowest. Increasing soil porosity from 0.4 to 0.55 and decreasing thermal conductivity from 2.0 to 1.385 W/mK led to up to 40% and 58% increases in ice formation, respectively. The COP of the heat pump in British Columbia was maximized, reflecting the peak temperature of the outlet fluid from the BHE. By incorporating site-specific climatic data and addressing gaps in existing standards, this research enhances geothermal system guidelines with practical design recommendations. Practical application This study provides built environment professionals with valuable insights into optimizing geothermal borehole heat exchangers (BHEs) for cold climates, particularly across various Canadian regions. By incorporating site-specific soil and climatic data, the research identifies key factors, such as soil porosity and thermal conductivity, that influence system performance. The findings will guide professionals in designing more efficient BHE systems, reducing ice formation, and improving heat pump efficiency. These design enhancements ensure that geothermal systems operate effectively in cold climates, contributing to sustainable heating solutions in residential and commercial buildings.