Methods for calculation of heating load in gutter-connected glasshouse

Heating load is the most basic parameter in the design of greenhouse heating system. The calculated heating load directly affects the equipment configuration of the heating system. If it is too small, it can not meet the design requirements. If it is too large, it will increase the initial investment and is not conducive to the efficient operation of the system. Climate screens have been widely used in China since the 20th century, and have become the standard configuration of greenhouse. In order to study whether the greenhouse heating load calculated under the current standard system is still applicable with the popularization and application of equipment such as internal climate screens and the improvement of greenhouse air tightness, this study compares the calculation methods of heating heat load in six standards of China and the United States, and takes a multi span glass greenhouse in Beijing as an example quantitative analysis of heating load. It is found that the heat loss of the sill wall accounts for 0.1% of the total heat loss of the enclosure structure, and the ground heat loss accounts for about 1% of the total heat load of the greenhouse, neither of them is the main factor affecting heating load. The results show that the minimum heating load per unit area of greenhouse is 230.10 W/m2 and the maximum is 305.24 W/m2, which is quite different from each other. Moreover, compared with the actual heat capacity of radiator 139.61 W/m2, there is a significant difference between them. Analyze the reasons, the former is due to the fact that the heat loss of cold air infiltration calculated by gap method in civil and industrial buildings in China does not consider the glass splicing gap, which makes the calculation value of heating heat load of greenhouse obviously low; the latter is due to the fact that all the calculation standards of heat load do not consider the influence of climate screens on greenhouse insulation. The minimum heating load per unit area of the greenhouse is 101.56 W/m2 and the maximum is 176.69 W/m2 after considering the effect of internal climate screens. If we get rid of the minimum value of low heat loss of cold air infiltration caused by glass joint in Chinese civil and industrial buildings, the calculation method of heating load in greenhouse special standards basically conform to the actual situation. Therefore, it is suggested that the effect of internal climate screens should be fully considered in the calculation of heating load of greenhouse, and the heat loss of cold air infiltration should be calculated according to the method of ventilation rate rather than the gap method. The results provide a scientific, accurate and standardized basis for heating load calculation of multi span glass greenhouse in China.