Simulating thermal environment in a two-span solar greenhouse using CFD

Two-span Chinese solar greenhouses (TSCSG) are commonly used in China, due to the low construction cost and high rate of land utilization. There are two sheds with one back wall in the TSCSG, compared with the traditional solar greenhouses (single-span Chinese solar greenhouses, SSCSG) with one back wall and one shed. The two sheds can be located both on the south side or separately on the north and south sides of the back wall. In terms of the addition of a north shed behind the back wall, there are different significant extreme temperature values and distribution characteristics of the walls, and soil in the TSCSG, compared with the SSCSG. In this study, the thermal environment performance of TSCSG was focused mainly on the heat transfer in the TSCSG. A three-dimensional transient state model was established for temperature environment in the TSCSG and SSCSG using computational Fluid Dynamics (CFD) on the Fluent platform. A series of experiments were carried out to collect the indoor temperature and Heat flux of the enclosure structure in the TSCSG. The ANOVA (analysis of variance) and isoscedasticity t-test method were then employed to analyze the significance of differences between simulated and test data. Consequently, the test verified that there was no significant difference between simulated and measured data. Accordingly, the CFD simulation model was employed to calculate the indoor temperature and heat flow in the TSCSG and SSCSG. Consequently, the following results were obtained after CFD simulation. Under the same external climate conditions, the nighttime indoor temperature, the soil temperature, the inner surface temperature of the wall were 1.7-3.8 ℃, 2.9-3.0 ℃, and 2.9-7.9 ℃ higher in the TSCSG than that in the SSCSG, respectively. The soil and walls of TSCSG released the heat towards the south side shed at night with a stable heat flow continuously, but nothing occurred in the SSCSG. Moreover, the heat flow rates densities of walls and soil in the TSCSG were 7.11-8.59, and 12.65-15.19 W/m², respectively, which were 0.76-2.42, and 9.71-14.36 W/m² higher than the surface heat flux densities of SSCSG, respectively. Consequently, the temperature regulation of TSCSG was stronger than the SSCSG. Additionally, the CFD model cannot consider the impact of crops in the solar greenhouses. The validation experiments were also conducted under no crop cultivation conditions. Actually, there were the crops to affect the heat storage and release of soil, walls, and other heat storage materials in the solar greenhouses, as well as indoor convective heat transfer. Therefore, it is necessary to clarify the impact of these errors for the more accurate thermal environment of TSCSG.