Energy consumption analysis of simply soft insulated wall-assembled Chinese solar greenhouse

Simply assembled Chinese solar greenhouses (SA-CSG) have been widely used in northern China in recent years, due to their simple construction and better thermal insulation. Among them, the wall of SA-CSG is made of the thermal blanket in a general way, indicating better insulation performance, but a relatively low capacity of thermal storage. The heat load of SA-CSG can be normally higher than that of the traditional Chinese solar greenhouses (CSG). An accurate calculation of heat load and heating requirement in winter can greatly contribute to assessing regional adaptability. In this study, 17 cities in China were selected to analyze the local climate and scale of CSG development. The total solar radiation from October to next February and the lowest air temperature outdoor in winter were extracted using the downloading data from China Meteorological Data Network. The heat balance equations and thermal environment simulation software RGWS-RHJPJ V1.2 were used to calculate the winter solstice heating requirement and the heat load at the lowest outdoor temperature in the coldest month for SA-CSG in 17 cities. The local sensitivity analysis was also carried out to determine the influencing parameters on the heat load of the SA-CSG. Furthermore, the heating requirement was analyzed to select an active heat storage and release system as the heating source for the SA-CSG. The results showed that the minimum heat load of SA-CSG occurred in Nanjing at 56.4 W/m2, whereas, the maximum was found in Altay at 140.9 W/m2, among 17 cities in the CSG production area of China. The city with the minimum SA-CSG heating requirement on the day of the winter solstice was Lhasa with 0.7 MJ/m2, and the maximum heating requirement was in Harbin with 7.7 MJ/m2. The heat load of SA-CSG was in the range of 50~150 W/m2, where the ratio ranging from 50 to 100 W/m2 was more than 50%. The heating requirement of SA-CSG ranging from 0-2 MJ/m2 was about 20% of the regions, 2-4 MJ/m2 was about 50% of the regions, 4-6 MJ/m2 was about 20% of the regions, and only about 10% of the regions were in the heating requirement of more than 6 MJ/m2. As such, the heat load increased with the latitude of the city. The influencing parameters on the heat load of SA-CSG were ranked in the descending order of the integrated heat transfer coefficient of the thermal blanket on the south roof, the number of air changes in the SA-CSG, and the integrated heat transfer coefficient of the thermal blanket as the wall. The active heat storage and release system fully satisfied the heating requirement of the SA-CSG in Lasa and Changdu. At the same time, the active storage and release system satisfied with 50% of the greenhouse heating requirement in Shouguang, Beijing, Hotan, Xi'an, and Xining. By contrast, less than 30% was found in Shenyang, Altay and Harbin. There were large regional disparities in the heat load and heating requirement of the SA-CSG in the CSG production areas. Similar regional disparities were found in the application effect of active heat storage system. The finding can also provide some guidance to constructing the heating design of SA-CSG in China.