Evaluation of a Building Integrated Ground Source Heat Pump Using System Performance Factors

A mathematical model of a ground source heat pump system has been developed and validated using experimental data from a full system installation. This system includes a heat pumpwith a fixed speed compressor, variable speed internal and external circulation pumps and provides space heating or cooling using fan coil units. In this study,the performance of the system,subject tovaried boundary conditions,is evaluatedusingdifferent SPF (systemperformance factor) definitions. The results show that the auxiliary components can consume a large proportion of the total system energy consumption. Depending on the definition of SPF, different system performances were observed.The internal circulation pump and fan coil units, which remain in constant operation, act to degrade the SPF, particularlyas the building load factor is reduced. This degradation is present in both heating and cooling. In heating mode, the SPF increases for decreasing return water set-point temperature, which is primarily attributed to an improved heat pump COP. However, fordecreasing return water set-point temperature, the fan coil unit heating capacityis reduced, which suggests an optimal return water temperature for maximising SPF, while matching the required building demand is possible. For cooling mode, a higher return water set-point temperature increases the SPF, but again the heat transfer across the fan coils is reduced, leading to a similar conclusion.