Experimental study on effect of an active solar heating soil heat storage system on the thermal environment in Gobi solar greenhouses

The present study proposes an innovative active solar heating soil heat storage system to enhance the thermal environment of Gobi solar greenhouses (GSGs) and address the issue of uneven heat distribution. This system utilizes Gobi gravel soil as a heat storage medium, combining solar flat plate collectors and horizontal buried pipes at a depth of 0.15 m. To validate the system’s practical efficacy, an 80-day field experiment was conducted in Jiuquan City, located in the northwest Gobi region of China. The experiment focused on investigating the impact of soil heat storage on the temporal and spatial distribution of air and soil temperatures within the greenhouse, as well as assessing the system’s environmental and economic benefits. The results demonstrated that the system exhibited outstanding performance, with an average heat collection efficiency exceeding 56.96 % and a daily average heat storage amount of 132.13 kWh. Compared to the contrast greenhouse, the experimental greenhouse showed an increase in nighttime average air temperatures of 4.9 °C, 3.9 °C, and 3.6 °C on typical sunny, cloudy, and snowy days, respectively. The average surface soil temperatures increased correspondingly by 6.5 °C, 4.8 °C, and 4.5 °C. And the effective accumulated temperature increased by 40 %. Furthermore, the system significantly improved the uniformity of indoor temperature distribution. During nighttime heat release, the maximum temperature difference in the air, both span and vertically, did not exceed 0.8 °C; the maximum soil temperature differences in the span and length directions were no greater than 0.3 °C and 1.8 °C, respectively. During the daytime heat storage process, the maximum soil temperature differences in the span and length directions were no more than 0.4 °C and 1.7 °C, respectively. This study of the active solar soil heat storage system demonstrates significant application effects in improving the thermal environment of GSGs, with substantial environmental and economic benefits.