Parallel vs series configurations in combined solar and heat pump systems: A control system analysis

This paper presents the modelling of two Solar Heat Pump systems, one for Domestic Hot Water and other one for Space Heating in two different configurations. Both system’s configurations can commute between parallel and series operation. The Configuration “A” uses a heat pump with two evaporators, allowing to work as an air source Heat Pump or as a water source Heat Pump. The Configuration “B” uses a heat exchanger to preheat the air entering to an air-to-water Heat Pump. These configurations are simulated in TRNSYS 17 for evaluating their performance in three Chilean cities: Santiago, Concepción and Puerto Montt. The control system applies a switching criterion between operation modes based primarily on the available solar irradiation. According to the results, the individual performance figures of the Heat Pump and of the Solar Collectors increase. Nonetheless, the results show that the Seasonal Performance Factor of the overall system decreases when it is switched from parallel to series. In the case of space heating, the Configuration A using evacuated tubes collectors shows a decrease of the Seasonal Performance Factor from 5.85 to 4.78 in Santiago, 5.35 to 4.30 for Concepción and 4.70 to 3.87 for Puerto Montt. In all case studies, unglazed collectors applications show a maximum SPF decrease of 0.04 and a maximum increase of 0.01. The results obtained can be influenced by the applied switching criterion used in this study, which does not force the Solar Collectors to increase their operational time by cooling them with the Heat Pump. Then, for the case studies, the non-inclusion of additional solar collector’s operational time leads to decrease the system performance.