Abstract
This paper clarified the mechanism of the south and north roofs' effect on the thermal environment of the Chinese solar greenhouse (CSG), using a new parameter: ridge position ratio (RPR), which can describe the dynamic dependency relationship between the south and north roofs. A mathematical model was established using a method of combining computational fluid dynamics (CFD) simulation with experiments, then the model was used to further analyse the effect of RPR on the thermal environment of the CSG. The experimental greenhouse was simulated as an empty building to obtain results independently from these factors including crop and ventilation conditions. The results showed that the occurrence time of the maximum air temperature will be delayed when RPR increases to 0.3 during the daytime. As RPR increases, the heat storage layer of the soil gradually becomes thinner, but the north wall remains unchanged. RPR has a relatively small effect on the minimum temperature of each greenhouse part during the night. Mathematical models of the relationships between RPR, the solar energy that entered the greenhouse and the released heat energy of the enclosure structures were established, respectively. This paper can provide theoretical guidance for the structural design of the CSG.
Highlights
By the end of 2018, the area of the solar greenhouses had reached 577 000 hectares in China [1]
Compared with the simulation model CSGHEAT, the model in this study considers the distribution of solar energy in the greenhouse and energy transfer and can accurately calculate threedimensional heat flux distributions for all the enclosure structures including walls and soil by calculating partial differential equations, which makes the calculation results more realistic
The numerical results were lower than the measured values in the daytime due to the thermocouple shell being heated by solar radiation and having a certain heat preservation function
Summary
By the end of 2018, the area of the solar greenhouses had reached 577 000 hectares in China [1]. CSG consists of a north wall, gables, north and south roofs. The thermal environment of the greenhouse is significantly important for crops growth [7]. It is necessary to create a reasonable light and thermal environment, which are the key factors that play an important role in the growth and development of the crops. The commonly used building space parameters of the solar greenhouse mainly include span, height of the roof ridge, horizontal projection length of the north roof and height of the north wall. It should be noted that the horizontal position of the ridge of the solar greenhouse determines the area ratio of the south roof and north roof and affects the thermal environment of the solar greenhouse
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