Evaluation of thermal loss of Chinese solar greenhouse cover under all operating conditions.

• Heat transfer model of greenhouse cover under all operating conditions proposed. • The model can calculate the heat loss on the surface of greenhouse cover. • First study the long wave radiation relationship between crops and greenhouse cover. • First study on the influence of latent heat on the heat loss of the covering layer. • Considering the impact of greenhouse building layout on heat loss. The solar greenhouses in China are composed of gables on the east and west sides, north walls, and north and south roofs. The south roof is the main heat dissipation surface of the greenhouse. To quantitatively and comprehensively analyse the heat transfer characteristics and heat loss pathways of the south roof of a solar greenhouse, based on the actual usage of the greenhouse, the heat transfer of the south roof is classified into two working conditions: heat transfer of the transparent covering material (TCM) and heat transfer of the composite thermal insulation coating (CTIC). A theoretical heat transfer model of the covering layer of the solar greenhouse under all working conditions is constructed by applying the heat transfer theory. The model was tested using field test data from two areas different regions in China: Beijing and Lhasa. The results show good agreement between the simulated and measured values, the relative errors between simulated and measured values were 18.54% and 8.17%, respectively, with root mean square errors of 1.69 and 1.92. The model can comprehensively and accurately reflect the comprehensive heat transfer coefficient and heat loss changes of the south roof of the solar greenhouse. It can be used to analyze the proportion of heat loss caused by radiation, convection, and water vapor condensation. The analysis shows that condensation heat loss cannot be ignored during the winter night period. Measures such as covering the roof with plastic film and controlled irrigation can help reduce condensation heat loss. [ABSTRACT FROM AUTHOR]