Session: 08-04-02: Sustainable Energy Systems for Heating and Cooling

Paper Number: 112783

112783 - Long-Term Thermal Performance Evaluation of a Novel Energy Pile for Space Heating and Cooling in a Cold Climate 

In Canada, the residential sector contributed 12% of the total national energy consumption in 2019. Space heating alone accounted for 64% of the total residential sector energy consumption while the majority (55%) of the energy requirement for space heating was fulfilled by fossil-fuel derived energy. In this context, there exists an immense potential to improve the energy performance and to reduce emissions of residential space heating systems.

The ground source heat pump (GSHP) technology is a highly efficient renewable energy technology which utilizes geothermal energy for space heating and cooling applications. However, the widespread use of conventional GSHP systems is hindered by the high capital costs, lack of drilling space in densely populated areas and ground thermal imbalance when heating and cooling loads are unbalanced. Energy piles are an alternative for the conventional borehole heat exchangers in which the heat exchanging components are integrated into the building foundation pile to serve dual purposes: bearing the building structural load and provide heat exchange with the ground. Since the heat exchanger is integrated in the building foundation pile, this technology does not require additional drilling space or deep drilling. As such, it has the potential to drastically cut down the upfront cost of implementing the GSHP technology as opposed to the use of conventional borehole heat exchangers. Compared to conventional borehole heat exchangers, the performance of GSHPs coupled with energy piles is still not well understood.

In this study, the long-term performance of a novel energy pile when employed in a cold climate is numerically investigated.  A building energy model implemented in EnergyPlus and OpenStudio was developed for a residential house in Calgary, AB, Canada and  used to evaluate the annual hourly building heating and cooling load profile. Three normalized load profiles with maximum loads of 0.3 ton, 0.4 ton, and 0.6 ton each were derived using the obtained building load profile and used to determine the performance of the energy pile. A finite volume computational fluid dynamics model was developed to establish the long-term performance of the coupled heat pump – pile system. The model was thoroughly verified through domain and grid dependence tests and later thoroughly validated using the existing experimental data in the literature. Moreover, further validation was done using actual data from a field-scale test system located in Waterloo, ON, Canada. The developed numerical model was used to evaluate the performance of the system over a 4-year period. Moreover, the operation of the pile in three different configurations (1 – pile used with the basement, 2 – pile used at the ground level, 3 – pile exposed to the ambient conditions) was considered.

The variation of the pile’s outlet temperature, ground temperature profiles, and the coefficient of performance (COP) of the heat pump over time were obtained. Results show that the heating performance of the heat pump is the best when the maximum energy load is 0.3 tons, while the cooling performance was the best when the maximum energy load 0.6 ton. In addition, the long term results showed the average ground temperature dropped by 0.102^oC/year, 0.183^oC/year, and 0.329^oC/year for the 0.3 ton, 0.4 ton and 0.6 ton cases respectively indicating ground thermal imbalance. Furthermore, the yearly average heating performance of the heat pump was found to deteriorate by 0.005/year, 0.016/year, and 0.034/year for the 0.3 ton, 0.4 ton, and 0.6 ton maximum load cases respectively. The deterioration in heating performance is much higher as the heating loads increase.  The yearly average cooling performance on the other hand improved by 0.014/year, 0.044/year, and 0.098/year for the 0.3 ton, 0.4 ton, and 0.6 ton maximum load cases respectively. This is due to the heating dominant load overcooling the ground, which leads the outlet temperature from the pile (entering water temperature to the heat pump) to decrease over the years.

Presenting Author: Charaka Beragama Jathunge University of Calgary

Presenting Author Biography: Charaka Beragama Jathunge is a graduate student at the University of Calgary specializing in Mechanical and Manufacturing Engineering. His current research area is utilization of geothermal energy piles for space heating and cooling applications using energy piles in cold climates. He holds a bachelor's degree in mechanical and manufacturing engineering from the University of Ruhuna, Sri Lanka. He has worked in the industry and academia for two years prior beginning his postgraduate studies at the University of Calgary.

Authors:

Charaka Beragama Jathunge University of Calgary
Amirhossein Darbandi University of Calgary
Nayoung Kim Toronto Metropolitan University
Sahar Taslimi Taleghani Toronto Metropolitan University
Seth B. Dworkin Toronto Metropolitan University
Aggrey Mwesigye University of Calgary