Modeling ground source heat pump systems in a buildingenergy simulation program (energyplus)

Despite the low energy and lower maintenance benefits of ground-source heat pump systems, little work has been undertaken in detailed analysis and simulation of such systems. Long-term transient ground heat transfer significantly affects the performance of these systems. Annual and multi-year simulation consequently becomes an invaluable tool in the design of such systems – both in terms of calculating annual building loads and long-term ground thermal response. Models of vertical ground loop heat exchanges and water-to-water heat pumps have been implemented in the EnergyPlus program. The models are described, and techniques for modeling zone-system-plant interactions in the EnergyPlus environment presented. A case study is presented to show how the long-term (multi-year) effect of unbalanced loads on the ground loop, and the propagation of these effects through the system and zone models, can be calculated.