Energy analysis of different configurations for a reversible ground source heat pump using a new flexible TRNSYS Type

TRNSYS Software is a flexible tool for dynamic simulation of plants, interconnecting the different components of the system represented as black boxes and called "Types". This paper presents a novel Type for the simulation of a reversible water-to-water heat pump that is freely released. Differently from the previous models available in this environment, the Type is based on the polynomials of the compressors and contains an internal link to REFPROP to easily evaluate the thermodynamic properties of refrigerant fluids. In the present work, the Type was employed for investigating a ground source heat pump providing space heating and cooling to a historic building, where, for architectural limitations, the existing high-temperature terminal units cannot be replaced. Its operation, using different refrigerants, was evaluated under three climates, simulating two heat pump configurations coupled with radiators or fan coils. In the first case, a cascade-cycle configuration was considered to supply high-temperature heat, whereas, with fan coils, a standard single-stage cycle was studied. The results for the cascade-cycle configuration showed a seasonal coefficient of performance ranging from 2.48 for the coldest location (Helsinki) to 2.86 for the warmest one (Athens). These values increased to 3.29 and 4.90, respectively, when considering fan coil terminal units instead of radiators. On the other hand, the seasonal efficiency values were equal to 7.95 in Helsinki and 5.56 in Athens. Moreover, the low incidence of the thermal drift effect on the long-term performance of the cascade ground source heat pump was highlighted, showing for the coldest location a penalisation of 2.5%, compared to 7.3% of the single-stage cycle.