New insights on span selection for Chinese solar greenhouses using CFD analyses

Chinese solar greenhouses (CSG), with thin plastic films on the south roof for transmitting the sun's rays during the daytime and a heavy cover at night over the south roof with large thermal masses in the wall, north roof and soil to retain heat, can be used to produce vegetables and flowers year round without auxiliary heating during the winter. CSG spans can be increased to increase the production area; however, although the effect of increasing the span on the inside climate has been investigated experimentally, there is still no good guidance on selecting a suitable span configuration for growers. This investigation analyzed three groups of span configurations with spans of 10 m, 12 m and 14 m. The first set of designs had all the other dimensions varied in proportion to the span width. The second set had the same dimensions for the north roof and north wall with the other dimensions varied to fit the longer spans. The third set had the same south roof with a longer north roof to fit the longer span. The analyses were based on a 12 m span CSG simulation model validated in a former study with the thermal environments predicted using computational fluid dynamics (CFD) analyses. The results show that, for the CSG with all the dimensions varied in the same proportion, the inside air temperature is highest with the 14 m span and lowest with the 10 m span. For CSG with the same north roof and north wall dimensions, the air temperature is the highest with the 12 m span and lowest with the 14 m span. For the configurations using the same south roof size, the 10 m span with the taller north wall has similar air temperatures as the 12 m span, with temperatures inside both spans being higher than the other 10 m span with the shorter north wall height. Analyses of the solar heat gains, heat losses and temperature distributions for each group give good guidance for span selections for the growers.