Study On Application Effect Of Soil-Air Heat Exchange System In Large Span External Thermal Insulation Plastic Shed

In recent years,large-span external thermal insulation plastic shed has been rapidly popularized in some facilities horticultural production areas in China because of its high land utilization rate,stable environmental performance and suitable for mechanized operation.However,the thermal storage capacity of large-span external thermal insulation plastic shed is limited.Low temperature often occurs in cold seasons and extreme weather conditions,which affects crop growth and yield.Therefore,this experiment designed a soil-air heat exchange system,and observed the application effect of different working conditions in large span external insulation plastic shed,in order to provide theoretical guidance for system optimization and production application.The main research results are as follows :1.From November to December,the application effect of soil-air heat exchange system based on hot air in greenhouse was observed.The results showed that : The diurnal average temperature and maximum temperature in the treatment area were 0.7°C and 0.9°C lower than those in the control area in sunny days,and 0.5°C and 0.7°C lower than those in cloudy days,respectively.The night average temperature and minimum temperature in sunny days were2.5°C and 3.0°C higher than those in the control area,and 1.9°C and 2.4°C higher than those in cloudy days,respectively,and the spatial distribution of temperature was more uniform.The diurnal average ground temperature,night average ground temperature and minimum ground temperature at 15 cm soil depth were 1.4°C,1.5°C and 2.0°C higher than those of the control in sunny days,and 1.1°C,1.1°C and 1.6°C higher in cloudy days,respectively.The horizontal distribution of ground temperature in the treatment area was more uniform.The energy efficiency ratio of the heat exchange system is 16.23 ～ 20.95 in sunny days and 8.43 ～13.20 in cloudy days.2.From December to March of the next year,the application effect of the soil-air heat exchange system coupled with hot air and shallow water source heat pump in the shed was observed.The results show that : The average night temperature and minimum temperature in the treatment area were 4.2°C and 4.9°C higher than those in the control area,and 3.1°C and3.4°C higher than those in the cloudy day,respectively.At the same time,the spatial distribution of temperature in the shed was more uniform.The diurnal average ground temperature,night average ground temperature and minimum ground temperature at 15 cm soil depth were 3.2°C,3.4°C and 3.5°C higher than those of the control in sunny days,and2.1°C,2.0°C and 2.0°C higher in cloudy days,respectively.The horizontal distribution of ground temperature in the treatment area was more uniform.Under the coupled operation mode,the COP of the system is between 2.92 and 6.24,and the heating cost is 35.49% lower than that of the coal-fired boiler,51.12% lower than that of the gas boiler,61.2% lower than that of the electric boiler,and 79.8% lower than that of the oil-fired hot fan.The plant height,stem diameter,leaf area and biomass of tomato in the treatment area increased,and flowering and fruit ripening were earlier.