Study On Soil Heat Storage Characteristics Of Solar Variable Heat Flow In Severe Cold Region

The solar ground-source heat pump system is a new type of energy-saving and environment-friendly heating system.However,in the cold area of northern China,the building heat load is far greater than the cold load.With the long-term operation of the system,the heat is continuously extracted from the soil.In order to solve this problem,the soil temperature is difficult to recover,the cold accumulation of soil is formed over time,and the COP of the system continues to decline.In order to solve this problem,this paper mainly studies the heat storage characteristics of solar energy variable heat flux soil in cold regions.In this paper,the theory of solar radiation and soil heat transfer is introduced briefly,the formula of solar radiation intensity on a inclined plane is given,and the existing heat transfer models of buried pipes are compared and analyzed.The computational simulation method suitable for the research of this subject is selected.According to the geological conditions in Zhangjiakou area,the soil heat storage characteristics of the horizontal buried pipe in the solar energy ground source heat pump system are studied.The solar radiation intensity and the heat storage characteristics of horizontal serpentine tube heat exchanger are collected and the experimental results are analyzed in detail.The heat storage per unit tube length and the soil temperature variation during the whole heat storage period of the ground buried tube heat exchanger are obtained.The mathematical model of solar variable heat flux soil heat storage system is established,and the three-dimensional heat transfer model of ground buried tube heat exchanger composed of multi-layer horizontal snake tube is established by using FLUENT software,and the model program of solar energy collection system is compiled by UDF function.The dynamic simulation of solar variable heat flux soil heat storage is completed by loading it into the model of buried tube heat exchanger.The heat storage characteristics of multi-layer horizontal buried tube heat exchanger in cold region are simulated under experimental conditions.The variation of heat storage per unit pipe length and soil total heat storage per day with storage time is obtained,and the distribution of soil temperature at different depths at the end of heat storage is given.The above simulation results are compared with experimental data to verify the feasibility and correctness of the established solar variable heat flux soil heat storage model.Finally,the effects of soil thermal properties,heat exchanger structure(spacing between buried pipes,diameter of buried pipes)and system operating parameters(inlet flow velocity,starting temperature of soil heat storage)on soil heat storage were analyzed by simulation.The research results in this paper provide a useful reference for the application of multi-layer horizontal serpentine tube in the solar ground-source heat pump system in the cold region,and can be used for reference in the research of solar energy storage in the cold region.