Cooling-dominated commercial and institutional buildings served by ground-source heat pump (GSHP) systems generally reject more heat to a closed ground-loop heat exchanger (GLHE) than they extract over the annual cycle. This imbalancemay result in a significantly larger GLHEthan would be required for a system with annually balanced heat rejection and extraction. So-called “hybrid GSHP systems” use supplemental heat rejecters (such as cooling towers, fluid coolers, cooling ponds, or pavement heating systems) to reject excess heat on a seasonal or diurnal basis, thereby reducing the required size of the GLHE and, hence, the first cost of the system. The design challenge lies in finding the optimum size of both the GLHE and the supplemental heat rejecter, which directly depends upon the control strategy used to reject the excess heat. This study uses a system simulation approach to investigate various design alternatives with the aim of optimally sizing a GLHE with a cooling pond supplemental heat rejecter. A control strategy is selected based on the results of a previous study, and a life-cycle cost comparison is conducted for various design cases in two different climatic regions. This study demonstrates the usefulness of system simulation as a tool for determining the optimal design of hybrid groundsource heat pump systems.

Units: Dual