Numerical analysis of the long-term thermal performance of a solar assisted foundation heat exchanger - ground source heat pump system for space heating and cooling in extremely cold climates
Creators: name: Darbandi, Amirhossein
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Heat pumps
subject: Geothermal Energy
subject: Building energy loads
subject: Foundation heat exchangers
subject: Engineering--Mechanical
subject: Engineering--Environmental
subject: Energy

description: In the face of escalating global energy consumption and the environmental challenges posed by continued reliance on fossil fuels, addressing the substantial energy demand of buildings, which contribute 36% of the world's total energy usage and substantial greenhouse gas emissions, is imperative. Swiftly transitioning from conventional heating and cooling systems is crucial to reducing the emissions from the building sector. The heat pump technology is considered a potentially highly efficient alternative to conventional gas furnace heating systems. Owing to the high capital costs associated with the ground source heat pump systems, foundation heat exchangers offer a non-conventional solution by utilizing the building's foundation and the heat capacity of underground soil for efficient space heating and cooling. However, the performance of foundation heat exchangers when coupled with heat pumps, especially in cold climates, is not widely studied. The aim of this research was to investigate the thermal performance of a horizontal foundation heat exchanger integrated beneath the foundation of a single-family residential building coupled with a heat pump. A comprehensive transient computational fluid dynamics model, validated against experimental studies, was developed using a finite volume computational fluid dynamics tool, ANSYS® Fluent. The model incorporates actual building energy loads determined from an energy modelling study, and basement indoor temperature profiles to assess heat transfer rates, heat pump coefficient of performance, and soil temperature changes over the years of operation. This study focuses on cold climatic regions, where the performance of horizontal foundation heat exchangers coupled with heat pumps has not been extensively studied. Furthermore, a novel configuration, incorporating a secondary ground loop connected to a solar collector for thermal recovery, was introduced, and its performance was investigated. This enhanced system is evaluated for a single-family residential house in representative cities in Minnesota, USA. For this recovery system, three enhancement configurations are scrutinized: (1) integrating a secondary solar ground loop with no summer operation, (2) incorporating a secondary solar ground loop with summer operation, and (3) extending underground pipe length with a secondary solar ground loop and summer operation. Results indicate that the combined use of a secondary solar ground loop and backyard extension enhances the heat pump's coefficient of performance in heating mode by up to 40%, reduces soil freezing by up to 35%, and increases the average yearly soil temperature by up to 4.5 °C over a 5-year period.