The Cooling Effect Of Greenhouse Soil Heat Exchange System Research On Influencing Factors

Solar greenhouses need to be maintained in a suitable temperature and humidity environment for normal agricultural production,and soil heat exchange systems can assist in regulating the temperature and humidity environment of solar greenhouses.In order to improve the cooling performance of soil heat exchange systems,this article investigates the effects of different pipeline diameters,flow rates,lengths,and materials on heat exchange characteristics.By using ANSYS Design Modeler and ANSYS fluent,a three-dimensional model of soil heat exchange system is constructed.By comparing the actual measured values with the simulated results,the RE value is less than 15%,the MBE value is less than 5%,the CV value is less than 30%,and the RMSE value is less than 3.These all meet the engineering requirements,indicating the accuracy and correctness of the model’s prediction.The numerical model was established to simulate and calculate the magnitude of the influence of factors such as pipe length,pipe diameter,air supply speed,and drilling on the heat transfer performance of the system.Taking the soil heat exchange system in a solar greenhouse as the research object,the soil heat exchange in the greenhouse was tested under summer operating conditions,and the temperature changes of the air inside the soil heat exchange system were analyzed under continuous operation conditions of day and night for 6and 72 hours in summer.The following conclusion can be drawn: the heat transfer performance of PVC corrugated pipes and perforated corrugated pipe soil heat exchange systems is significantly better than that of PVC straight pipe soil heat exchange systems;Aluminum alloy straight pipes and stainless iron straight pipes have slightly better heat transfer performance than PVC straight pipe soil heat exchange systems;Extending the length of the pipeline can improve the heat transfer performance of the soil heat exchange system.From this,it can be concluded that the complexity of pipeline shape,drilling of pipelines,and extension of pipeline length can all improve the heat transfer efficiency and energy efficiency ratio of soil heat exchange systems.Increasing the inlet flow rate significantly reduces the COP and heat transfer efficiency of the soil heat exchange system,but the cooling power of the soil heat exchange system increases with the increase of the inlet flow rate.By comparing the results of the model experimental bench with the simulation,it was verified that the shape of the pipeline can effectively affect the heat transfer performance of the soil heat exchange system.Combined with numerical simulation,it is believed that the heat transfer performance index of the soil heat exchange system decreases with the increase of the supply air speed.Excessive wind speed can increase the energy consumption of the fan during operation,and also reduce the effective time for unit air to exchange heat in the soil heat exchange system,thereby reducing the heat exchange performance of the soil heat exchange system.As the thermal conductivity of the pipes continues to increase,the air temperature output by the soil heat exchange system becomes more stable.The thermal conductivity of pipeline materials has a limited impact on the cooling performance of soil heat exchange systems.In actual soil heat exchange system construction,PVC pipes are mainly used to meet the demand,and increasing the length(contact area)is more effective in improving the heat exchange performance of soil heat exchange systems.The complexity of pipeline shape effectively improves the cooling performance of the soil heat exchange system,and its outlet air temperature fluctuation is minimal throughout the day under 72 hours of continuous operation day and night.The air temperature output of the PVC corrugated pipe soil heat exchange system is more stable than that of the straight pipe,and the complexity of the pipeline shape has a significant impact on the stable outlet temperature.Pipe drilling can to some extent enhance the heat exchange capacity of soil heat exchange systems.The main advantage of PVC perforated corrugated pipes is reflected in the continuous operation of day and night,and their heat exchange effect at night is significantly better than other types of pipes.Therefore,they have more cold storage at night and can lower the air temperature during the day.