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

Paper Number: 112353

112353 - A Comparative Study of the Long-Term Performance of Vertical U-Tube Borehole Heat Exchanger and Foundation Piles in a Cold Climate 

Global increase in energy demand and use as well as the greenhouse gas emissions associated with the continued use of fossil fuels has opened up research and development of low energy technologies for heating and cooling of buildings. For cold climates, such as those found in Alberta, Canada, heating makes up 60% of residential buildings’ energy use.  Among the most efficient energy technologies and systems developed to reduce building carbon footprint, the use of ground source heat pumps (GSHP) is gaining traction as a reliable and environmentally friendly solution. The GSHP technology is regarded as one of the oldest, most prevalent, and most flexible types of geothermal energy utilization. GSHPs work with stable deep ground temperatures to provide heating and cooling with much higher efficiencies than conventional air source heat pumps. However, in cold climates, like Canada, heating loads are significantly greater than cooling loads which makes the amount of heat extracted from the ground each year greater than heat injected back. As a result, gradual performance reduction and system failure can occur because of the associated soil temperature decline. Annual building load imbalances have been reported to be the cause of long-term ground temperature changes from heat accumulation or depletion in the ground.

Consequently, thermal imbalance in the ground’s temperature, large capital investment with unfavorable payback period and lack of drilling space in densely populated areas are the major challenges to wider adoption of this technology. To address these challenges , researchers have been focusing on the development and optimization of the vertical u-tube borehole heat exchanger and foundation piles. The installation expenses of foundation piles have been reported to be lower than those of boreholes since they do not need to be installed using an expensive drilling equipment and expertise. Though foundation piles help reduce the cost, but they are not widely studied. In contrast to piles, which are normally constructed between 10 and 25 meters deep, boreholes are typically installed to a depth of roughly 60 - 300 meters below ground.

There is still limited understanding of heat transfer in foundation piles, which are shallower and larger in diameter than boreholes, and borehole heat exchanger, especially in cold climates, to be able to optimally design the system to completely eradicate the problem with thermal imbalance. In addition, to the best of our knowledge, the literature lacks studies that provide technical justification for the choice of foundation piles or borehole heat exchanger, operating under the same conditions. To this end, this study aims to evaluate the long-term thermal performance of the foundation pile and borehole heat exchanger of a ground source heat pump system for space heating and cooling in a residential building in Calgary, Canada. A meticulously validated and verified computational fluid dynamics model was developed using Ansys Fluent and has a good agreement with the literature. The validated model was extended and coupled with transient building energy loads obtained from OpenStudio/EnergyPlus through a developed user defined function. In this study, foundation pile and vertical borehole heat exchanger were examined for a period of 5 years. Ultimately, the results from this analysis will promote research and development on the use of ground source heat pumps. This will provide information on the efficiency of foundation piles and borehole heat exchangers for supplying sustainable thermal energy for space heating and cooling in cold climates.

Presenting Author: Philip Adebayo University of Calgary

Presenting Author Biography: Philip Adebayo is a Ph.D. student in the department of Mechanical and Manufacturing Engineering at the University of Calgary. He obtained his master's degree from the American University of Beirut in Lebanon under the full sponsorship of the MasterCard foundation and a bachelor’s degree (with honors) from the University of Ibadan in Nigeria. He has keen interest in exploring sustainable engineering practices to improve the efficiency of energy systems with less environmental impact to meet increasing energy demand. His Ph.D. research focuses on the modelling and optimization of solar assisted ground source heat pump systems with and without thermal energy storage for cold climates

Authors:

Philip Adebayo University of Calgary
Charaka Beragama Jathunge University of Calgary
Roman Shor University of Calgary
Abdulmajeed Mohamad University of Calgary
Aggrey Mwesigye University of Calgary