Operating characteristics of photovoltaic/thermal–ground source heat pump system in cold regions

Abstract

To investigate the operating performance of photovoltaic thermal integrated heat pumps in terms of the effects of the control strategy and the component parameters, this paper considers an office building in Zhengzhou city as the research object. A photovoltaic/thermal integrated ground source heat pump system model is established using TRNSYS software. Using this model, a system is developed with four operating modes based on temperature differences and seasonal control. The soil temperature, the unit energy consumption, and the solar energy guarantee rate are used as indicators to study the soil’s thermal balance and the energy consumption characteristics of the model system in the four operating modes. The effects of the control strategy design and the photovoltaic/thermal collector area on the system performance are analyzed, and the annual cost method is used to evaluate the system’s economy. The research results indicate that the tank heating mode’s closing temperature increased from 47 °C to 49 °C, the system energy consumption and power generation were reduced by 1.86 % and 1.24 %, respectively, and the instances of unsatisfied demand for domestic hot water were reduced by 19.05 %. The soil temperature increased gradually with increasing photovoltaic/thermal collector area, but the rate of this increase slowed down at larger areas; when the area increased from 50 m2 to 100 m2, the soil temperature increased by 16.6 %, but when the area increased from 200 m2 to 250 m2, the temperature then only increased by 10.6 %. In addition, there is a specific photovoltaic/thermal collector area that can maintain the soil temperature in equilibrium. When compared with a solar-assisted ground source heat pump heating system, the photovoltaic/thermal integrated ground source heat pump heating system can save 63.2 % in terms of operating costs and can reduce the annual cost by 60.9 % over a 10-year period. The research results show that the law of the photovoltaic/collector area affects the soil heat balance, and also provide data support for promotion of photovoltaic/thermal integrated ground source heat pump systems from both performance and economic perspectives.