Study On The Experiment Of Vertical Double U Underground Heat Exchanger For Ground-coupled Source Heat Pump System

The research background and significance, the basic characteristics anddevelopment status of heat preservation and thermal insulation double U buried tube insoil source heat pump are expounded. Through experimental testing method, the schemeof the experimental study, the specific process and the setting of experimental systemare introduced roundly. The error analysis of experiment is done. Systematically, thetest of the actual project operation data in winter and summer are focused on dailytemperature of different time, monthly average temperature, seasonal averagetemperature and temperature difference. Besides, the layer heat transfer theory modelsare expounded. Furthermore, the saturation heat exchanger, heat exchanger and withoutheat exchanger of the case are solved respectively combining with experimental results.What’s more, the calculation methods and calculation formulas of heat preservationlength and buried tube depth are also put forward.The measured object is the ground-coupled source heat pump system of ademonstration building engineering in Chongqing. Moreover, the actual operationsituation of ground-source heat pump system in winter and summer are testedcontinuously, which are divided into large flow and small flow conditions.It is suggested that the G80temperature is the maximum value in the depthdirection of buried tube in winter, the G40temperature is the minimum value and theG40temperature value is closed to G80for water supply pipes. Besides, the H100～H80temperature is the maximum value in the depth direction of buried tube in winter,and the H40temperature value is closed to H80, and the H100～H80temperature is theminimum value for return pipes.According to the water supply temperature, the influence of increased insulationresistance for hourly temperature and average temperature are both smaller.Therefore,there is no need to thermal insulation for water supply pipe.Respectively, the return water temperature of same test point is compared hourly inboth winter and summer. In winter, the heat preservation temperature is higher. Themaximum range is2.3%~6.8%, and the minimum range is0.1%~2.1%. What’s more,in summer, the maximum range is3.0%～8.6%, and the minimum range is0.5%～6.5%. Therefore, return pipe insulations have obvious effect in both winter and summer.Moreover, the average temperature difference of day, month and season are all higher in winter and summer. Furthermore, the range of daily average temperature is10.76%～15.40%, the range of monthly average temperature is20.13%～22.81%, and the rangeof heating and cooling season average temperature is41.97%and40.65%respectively.Both return pipe temperature and temperature difference are considered for return pipeheat preservation. Comprehensively, it is proved to be effective. In consequence, it hasgreat value of engineering application.Three factors that are season, flow and heat preservation are used in orthogonal testanalysis. As a result, the better experimental condition is the heat preservation smallflow running in the summer, that is to say, the heat preservation measures is better,small flow is better, and summer operation is better. Moreover, season is the key factor,while the ranges of flow and heat preservation are both smaller. Though the range ofheat preservation is minimal, it is0.83times that of flow. Consequently, the influenceof thermal insulation on heat transfer temperature difference is closed to flow. Inconsequence, the influence of return pipe thermal insulation on heat transfertemperature difference is significant.By experimental data analysis, the soil source heat pump project of demonstrationbuilding in Chongqing is calculated. The L equals to5～10m, L equals to20～30m, and L equals to60m.It is necessary for return pipe water supply pipe to heat preservation. But it isessential for return pipe to heat preservation.Insulation length is the sum of L and L, considering some rich coefficient.L41m is calculated. Furthermore, intermittent operation is conducive to therebound of saturation heat exchange area, and the most reasonable economic insulationlength L equals to L, considering some rich coefficient. L31m iscalculated. What’s more, minimal depth D is the sum of LMAXand LMAX,considering some rich coefficient. Also D52m is also calculated.