Study On Heat Transfer Characteristics Of Time-sharing And Zonal Buried Pipe Group In The Cross Season Heat Storage System Of The Solar Ground Source Heat Pump

Solar assisted ground source heat pump(SAGSHP)is widely used for its environmentally advantages.As a key component of SAGSHP system,vertical U-shaped ground pipe group has an important impact on its operation efficiency.The connection mode of traditional buried pipe group mainly includes series connection and parallel connection.In series connection mode,the heat exchange temperature difference is large,but the heat exchange efficiency is low;in parallel connection mode,although the heat exchange efficiency is high,the heat exchange temperature difference is low.Therefore,in order to overcome the problems of low efficiency of traditional series connection and low temperature difference of heat exchange in parallel connection,a new type of layout of sub district series parallel ground pipe group is proposed in this study.Under this connection mode,the solar ground source heat pump cross season heat storage system has the characteristics of taking into account high temperature difference and high heat exchange efficiency.In order to study the influence of the two factors of the series number and the distance of the buried pipes on the thermal storage and extraction characteristics,the geometric model and mathematical model of the underground pipes are established firstly,and the model is verified by the measured data.Through the simulation and analysis of two key factors.The series number(two-stage series,three-stage series,four-stage series,five-stage Series)and the distance between buried pipes(L = 3.25 m,l = 4.25 m,l = 5.25 M,l = 6.25m),the operation parameters and soil temperature field changes of the heat storage mode and the heat collection mode are monitored respectively Heat,heat storage efficiency,soil temperature after heat storage,heat storage efficiency ratio and heat collection index: heat collection,heat collection efficiency,heat collection temperature difference,heat collection efficiency ratio,and soil temperature after heat collection are studied theoretically.Secondly,in order to study the optimal combination strategy of heat storage and extraction and the long-term heat storage performance of the solar energy ground source heat pump cross season heat storage system,based on the principle of minimum heat loss to determine the heat storage strategy,four different heat collection strategies(first series and then parallel,first series and then together,first parallel and then series,first parallel and then together)are studied Research,and through the extended function of FLUENT software-user defined function(UDF)to write the solar collector,plate heat exchanger,heat storage tank model and load it into the sub district series parallel buried pipe group model,to realize the dynamic simulation of the sub district series parallel buried pipe group solar ground source heat pump cross season heat storage system.The results show that:(1)The simulation results show that the higher the series number is,the better the heat storage will be,but the higher the series number is,the lower the heat storage efficiency and the energy efficiency ratio of the heat storage will be;the higher the series number is,the larger the heat and the temperature difference of the heat collection will be,but with the increase of the series number,the growth of the two will slow down and the attenuation will increase with time The ratio of heat energy efficiency and the rate of recovery and storage are decreasing.In order to obtain a large heat exchange temperature difference and maintain a large energy efficiency ratio and storage rate,the recommended series stage is four stage series.(2)The simulation results show that the larger the distance is,the better the heat storage is.But when the distance is increased from 5.25 M to 6.25 m,the change of the maximum soil temperature caused by the increase of the heat storage is not significant.When the heat is taken,the larger the distance is,the greater the temperature difference is,but the heat exchange capacity is poor in the later stage.With the increase of the distance between buried pipes,the collection rate increases first and then decreases.In order to obtain a larger heat storage effect with a smaller buried pipe spacing,the recommended buried pipe spacing is 5.25 M.(3)The simulation results show that when the heat transfer strategy is from the parallel area to the series area or from the parallel area to the series area or from the parallel area,the heat transfer rate is higher,and the heat transfer strategy is from the parallel area to the series area or from the parallel area The temperature difference of the heat transfer of the buried pipe group in series and parallel connection in the lower zone is large and the soil temperature field after the heat removal is uniform.Therefore,the recommended heat storage strategy in this study is: first store the heat in the series area,then store the heat in the parallel area when the heat transfer capacity in the series area is insufficient,then take the heat in the series area first,and then take the heat in the series area when the heat transfer capacity in the series area is insufficient Zone and parallel zone take heat together.In this study,a new type of layout of sub district series parallel ground pipe group is proposed.Based on the above theoretical analysis and numerical simulation,the influence law of series series and distance between buried pipes on the heat exchange effect of sub district series parallel ground pipe group is clarified,the heat storage strategy of sub district series parallel ground pipe group is mastered,and the cross season heat storage system of time-sharing sub district solar ground source heat pump is obtained The method of long-term heat storage performance provides a reference for optimizing the performance of vertical U-type buried tube group heat exchanger.