Borehole thermal energy storage system for heating applications: Thermodynamic performance assessment

• Exergy analysis of BTES for heating season is carried out.
• Exergy efficiency of BTES is determined to be 41.35% for overall system.
• COPHP is determined to be 2.6 for overall system.
• Increasing evaporator temperature to 6 °C decreases the exergy destruction rate.
• Increasing condenser temperature to 70 °C increases the exergy destruction rate.

A comprehensive thermodynamic assessment of a borehole thermal energy storage system (BTES), which helps in meeting the heating and cooling demands of campus buildings of University of Ontario Institute of Technology (UOIT), is presented for the heating case. The BTES located on UOIT campus in Oshawa, Canada is recognized as the world’s second largest BTES system. Energy and exergy analyses of the heating system are performed through the balance equations, and exergy destruction rates are determined for each system component and the overall BTES. In addition, a comparative system performance assessment is carried out. Based on the conducted research for the studied system, COPHP is calculated to be 2.65 for heating applications. Energy and exergy efficiencies of the boilers are determined to be 83.2% and 35.83%, respectively. The results of the exergy analysis show that the boilers are the major contributor to exergy destruction, followed by condenser and evaporator. The effects of condenser and evaporator temperatures of the heat pump systems on energy and exergy efficiencies are also investigated. The overall exergy efficiency of the whole system is calculated to be 41.35%.