Comparative Study of Operating and Control Strategies for Hybrid Ground-Source Heat Pump Systems Using a Short Time Step Simulation Model

Ground-source heat pumps for cooling-dominated commercial buildings may utilize supplemental heat rejecters such as cooling towers, fluid coolers, or surface heat rejecters to reduce system first cost and to improve system performance. The use of supplemental heat rejecters for cooling-dominated buildings allows the use of smaller borehole fields. Degradation of the heat pump performance is avoided by offsetting the annual load imbalance in the borefield. A comparative study is presented that investigates the advantages and disadvantages of various system operating and control strategies in a hybrid ground-source heat pump application using an hourly system simulation model under different climatic conditions. An actual small office building is used as the example building. The use of a short time step simulation model enables the detailed assessment of the ground heat exchanger’s behavior and the determination of system energy consumption on an hour-by-hour basis. A life-cycle cost analysis is conducted to compare each operating and control strategy to determine the lowest cost alternative for a given climate.