Performance investigation of a solar-assisted ground source heat pump system coupled with novel offset pipe energy piles and solar PVT collectors for cold climate applications
Charaka Beragama Jathunge, Seth B. Dworkin, Carsten Wemhöner, Aggrey Mwesigye
Abstract
• Long-term performance evaluation of a solar-assisted ground source heat pump system. • Optimum system operating mode is subjective to the load and climate conditions. • Solar thermal integration significantly improves the heat pump performance. • Ground thermal imbalance can be avoided by properly sizing the solar collectors. • Properly sized solar photovoltaic/thermal collectors allow system self-sufficiency. Ground source heat pumps are an efficient and environmentally friendly technology for heating and cooling. However, high capital costs and ground thermal imbalance, especially in cold climates, are among the reasons hindering their widespread use. To address these challenges, this study proposes and numerically investigates the long-term performance of a solar-assisted ground source heat pump system using a novel offset pipe energy foundation pile as the ground heat exchanger coupled with solar photovoltaic/thermal collectors. A thoroughly validated computational model that couples a realistic building energy load profile, the solar collector and climate data with the pile heat exchanger was used. Two pile design thermal load settings (peak heating load: 0.4 tons/pile and 0.5 tons/pile) and four normalized solar collector sizes (1.0 m 2 /pile, 2.0 m 2 /pile, 3.0 m 2 /pile, and 3.5 m 2 /pile) were considered. Three system operating modes for the solar-assisted ground source heat pump system were conceptualized and evaluated to determine the most appropriate. Results indicate that the solar-assisted ground source heat pump system performance is best when the system operating mode, which diverts the solar thermal energy based on the heat pump operating mode (heating or cooling) rather than directly sending it to the heat pump, is used. Long-term performance results show that solar thermal integration reduces ground thermal imbalance from −0.27 K/year to a thermally balanced condition (∼0.01 K/year). Moreover, the overall heat pump performance improves by 6.7–19.7%, depending on the system configuration. Furthermore, the system with 3.5 m 2 /pile and a pile design thermal load of 0.4 tons/pile produces all the energy required to run the heat pump and a net energy surplus of 3.7 MWh, equivalent to 9.4% of the heat pump’s energy consumption.