| The problem of greenhouse cooling in summer has always been one of the directions of research on the regulation of protected horticulture in China.At present,there are many researches on solar greenhouses cooling in daytime,but fewer methods for cooling at night.The traditional method of cooling in solar greenhouse is not suitable for regulating greenhouse crop cultivation environment at night in summer.And studies have shown that the greenhouse indoor temperature at night also determines the quality and yield of crop production.Therefore,it is important to study the solar greenhouse cooling methods in summer night for the cultivation of horticultural crops.In Northeast China,there are a lot of natural cold sources in winter.This topic uses this geographical advantage to store the natural ice in winter,as a cooling source to design the ice storage cooling system for greenhouse cooling in summer according to the summer environment of the test greenhouse.The system is mainly divided into two parts.The first part is the ice storage tank.By analyzing the environment of the greenhouse in summer,the ice storage volume is calculated and the structure of the ice storage tank is determined.The design results are as follows: the volume of the ice storage tank is 6m×6m×2m,the outer layer of the enclosure structure is 15 cm polystyrene board,the inner layer is 24 cm brick wall concrete,the inner part of the brick wall is 2mm waterproof plastic,and the upper layer is sealed with 15 cm polystyrene colour steel board.The second part is the design of heat exchange system,which is mainly divided into the design of heat exchanger in ice storage tank and the indoor air supply pipe.Through the ice melting model of ice storage air conditioning,the relationship between the length of heat exchanger tube is calculated,and the length of heat exchanger tube at outlet temperature of 0 C is selected.The performance of the heat exchanger tube is simulated and analyzed by COMSOL,a commercial CFD software.The results show that the heat exchange system of ice storage tank with 16.2m heat exchange pipe length,0.05 m diameter and 30 pipes meets the design requirements.COMSOL simulates the heat transfer structure of the environmental ice storage tank in summer.The results show that when the inlet temperature is 25 C and the inlet velocity is 13.31m/s,the outlet temperature is 0 C.The heat transfer efficiency is the best one meter before the heat exchange tube.With the increase of the tube length,the heat transfer efficiency decreases.The design of indoor air supply pipes mainly uses COMSOL software to model and analyze the number of different side wall openings of pipes to achieve uniform air supply in greenhouse.Three different ways of opening are analyzed,the number of uniform opening is 100.On the basis of the number of holes 100,the number of holes at the end of the pipeline is increased by 25 and 50,respectively.The model results show that increasing the number of holes at the end of the pipeline can increase the flow rate in the pipeline,increase the gas output at the end of the pipeline,and the outlet temperature at the end of the pipeline with the number of holes 125 is the lowest.This experiment chooses the opening mode with the number of holes 125 and the diameter of holes 0.05 m.Through the above design,the system cooling effect was tested in simulated summer environment.The maximum temperature difference in cultivation area was 6.7℃,and the average temperature difference was 4.4℃.Compared with other cooling systems based on the principle of heat exchanger,the ice storage cooling system with ice as the cold source obtains a larger temperature difference of heat exchange tube on the basis of relatively small fan flow rate than the system with soil and water storage as the cold source,thus increasing the refrigeration capacity of the system.Combined with the initial construction of the system and the analysis of summer operating costs,the system is more suitable for the use of greenhouse structures with better insulation and tightness in natural cold source areas.The greenhouse is suitable for summer high-quality or off-season vegetables and fruits and the cultivation environment requires no light conditions for edible fungi. |
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