The evacuated tube solar collector assisted heat pump for heating greenhouses

Using the solar energy for greenhouse heating can reduce both CO2 emissions and heating costs. Thus, the aim of this study was to investigate the performance and viability of using an evacuated tube solar collector as a solar water heater assisted an electric heat pump for greenhouse heating. The experiment has been conducted in twin experimental greenhouses installed in Kunming, China. The required energy for heating the greenhouse was calculated. Moreover, the microclimatic conditions in greenhouses under different local weather conditions, the produced thermal energy, and electric energy consumption were analyzed. The efficiency of the solar collector was determined and the effectiveness of the evacuated tube solar collector with the electric heat pump was also examined. Results revealed that the internal air temperature in the heated greenhouse exceeds the temperature inside the unheated (control) greenhouse by 2°C-3°C, whereas, the relative humidity decreased by 10% in the heated greenhouse. Furthermore, the thermal efficiency of the solar collector and the payback period were 0.49 and 4.1 years, respectively. In conclusion, this integration could provide more than 35% of the total required heat for greenhouse.