Performance of a Solar Heat Collection and Release System for Improving Night Temperature in a Chinese Solar Greenhouse

Abstract

<abstract> <b><i>Abstract. </i></b> To increase the year-round greenhouse production in North China, a sustainable heating method should be developed to increase the night air temperature during the winter in Chinese Solar Greenhouses (CSGs). Solar heating is an inexpensive and effective way to heat greenhouses, and has been investigated by several previous studies. For the present study, a heat collection-heat release (HCHR) system that was attached to the north wall was developed for CSG night temperature improvement. Two experimental greenhouses were located in Beijing, China, with a floor area of 392 m² each. Environmental parameters (temperature, humidity, heat flux) inside and outside the greenhouse were investigated, including the average solar collection efficiency of the heating system and the pump energy consumption rates. The results showed that the average solar collection efficiency of the system was 52%, which was 1.3 times greater than the reported value of a HCHR system installed in a small CSG. The effective collector absorptivity was 0.59 and heat transfer proved to be by natural convection. The night air temperature in the experimental CSG was increased by 5°C on average compared to the reference CSG. To meet the heating demand of the CSG during cold winter nights the release capacity must be increased by 40%. Pump capacity to circulate the water proved to be crucial for energy efficiency.