Long-Term Thermal Performance Evaluation of a Novel Energy Pile for Space Heating and Cooling in a Cold Climate

Abstract

Abstract In cold climates, space heating and domestic hot water production account for a large portion of the building’s energy demand and the related CO2 emissions. To sustainably climatize buildings, renewable energy technologies need to be integrated into building energy systems. The ground source heat pump (GSHP) technology is one such clean energy technologies. The energy pile technology is an excellent alternative to conventional borehole heat exchangers which reduces the cost of GSHP systems substantially. This study numerically investigates the long-term performance of a novel energy pile coupled with a GSHP using realistic building loads for a cold climate. A finite volume-based computational model was developed and thoroughly validated using experimental data from a system in Waterloo, Ontario, Canada. First, three normalized building load profiles were derived using a building energy model for a typical residential house in Calgary, Alberta, Canada. Then a 4-year performance investigation on the performance of the energy pile for the three normalized load profiles was undertaken. In addition, two configurations were considered — one with the pile beneath the basement of the building and another one with the pile at the ground surface level. For the first configuration, results show that the higher heating loads (> 0.4 tons) render the system inoperable for a significant amount of time. Also, the yearly average heating coefficient of performance (COP) decreased over the years while the yearly average cooling COP increased. The average ground temperature decreases for all the load cases, indicating ground thermal imbalance. The decrease in ground temperature was 0.08°C/year, 0.1°C/year, and 0.13°C/year for 0.3, 0.4 and 0.6 tons, respectively. The first configuration yields favorable results compared to the second in terms of system operability and thermal performance due to the reduced influence by low ambient temperatures.