In this study, exergy analysis of a borehole thermal energy storage system (BTES) for cooling season is carried out. A comprehensive case study is conducted based on the system at University of Ontario Institute of Technology in Oshawa, Canada, and actual thermal load data are employed for analysis. The exergy destruction rates of each system component and overall system are calculated and studied for comparison purposes. It is determined from the analysis that the exergy destructions in a system particularly take place in condensers of cooling systems. Also, it is found that condenser and evaporator temperatures have strong effects on the exergetic performance of the system. For system performance analysis and improvement, exergy efficiencies of the overall BTES are investigated and determined to be a maximum of 62%. (C) 2012 Elsevier B.V. All rights reserved.