Experiment and analysis on thermal characteristics of cob wall in sunken solar greenhouse

In order to explore temperature distribution and changes regulation, further correctly evaluate thermal insulation performance of cob wall in sunken solar greenhouse, 2a consecutive test monitoring was conducted to study the thermal characteristics and heat preservation capacity from December 2009 to June 2011. The result showed that wall surface temperature was significantly affected by indoor, outdoor air temperature and solar radiation, and had the same diurnal and seasonal variation as indoor and outdoor air temperature variation. Every point of temperature inside the wall was affected by surface temperature of wall. Overall, the wall temperature declined from inner surface to outer surface at thickness direction and the thermal-stable layer existed inside wall whose location and thickness varied with season, and thickness had positive correlation with wall thickness. From January to March, the thermal-stable layer existed in the center area inside the wall, and there was no the thermal-stable layer when the wall thickness was 2 m, while the thickness of thermal-stable layer was 30 cm when the wall thickness was 3m, and the thickness of thermal-stable layer was 70 cm when the wall thickness was 4m. During April or May, the location of the thermal-stable layer moved to 100 cm away from outer surface of the wall, and it was thicker 10~20cm than that from January to March. According to construction costs, heat preservation, land availability and other factors, in Henan area of China, the parameters of soil-made back wall in sunken greenhouse were proposed with top width of 2.5 m, bottom width (the junction of back wall and outside ground) 4.0 m and back wall height from outdoor 2.5 m. This paper provides a reference for construction and development of sunken solar greenhouse.