Thermal Short Circuiting Analysis Of Heat Exchanger On Ground Source Heat Pump

Due to its high efficiency and energy saving, the benefits of Ground Source Heat Pump(GSHP)is gradually recognized by people. However, the greatest obstacle of promoting the application of GSHP is its high initial investment. Therefore, how to improve the capacity of heat exchanging per meter is an important issue in this field. Short circuiting and thermal interference is one of the factors that impacting the efficiency of the heat exchanger. The numerical simulation is a good way to analyse this problem.The operation of borehole heat exchanger in the ground is a long time unsteady-state process which occurred in a three-dimensional space. It can not be simulated accurately by two-dimensional or equivalent model which are used currently.A numerical simulation is introduced to establish a three-dimensional heat transfer model of GSHP by FLUENT . To measure the impact of short circuiting, changing the depth of borehole, backfill material, fluid flow input for single U-tube boreholes. the author analyses the effects of short circuiting and heat exchanging on depth of borehole in different condition by comparing with the changes of average transect temperature of intake pipe and outtake pipe at different borehole depth,. In the obvious character of short circuiting ,simulated and analysised the effect of part heat preservation, defined the cost of heat exchanger on depth of borehole and power consumption of pump in deferent conditions.The result shows that the phenomenon of short circuiting will be more obvious with the increase of borehole depth and heat coefficient conductivity of backfill. When the velocity of flow increase, the effect of short circuiting will reduce whereas power consumption will increase. So, various factors should be considered while designing the systems. Reserch shows that holding tube or tubular holder around outlet pipe can not be very effective whereas the method of operating intermittently can reduce the effect of short circuiting and increase heat exchange efficiency .But whether operating intermittently can be used is decided by the load of the systems.