Research On Grout Properties Around A Vertical U-tube Heat Exchange Of Ground Source Heat Pump

Ground Source Heat Pump (GSHP) system is wildly used for its low consumption and high efficiency. The ground loop heat exchanger (GLHE) is one of the important parts in GSHP systems. In all types of closed-loop heat exchangers, vertical U-tube heat is the most wildly used one in China. Firstly, finite line source model is used to do the analyses for its simplification comparing to cylindrical source theory and its completeness in vertical temperature distribution comparing with infinite line source theory. Secondly, the influence between grout radius and heat transfer is analyzed. A test bench is established to test and verify the analysis.The results are: the immersion heater, which is instead of the common used U-tube heat exchanger in lab, shortens the stably time by 50%. When the temperature field is near the surface of the ground or the heat source, or the operation time is within 1 hour, the finite line source theory is not reliable. The error between theoretical results and lab data is higher than 30%. Otherwise, the error is within 5%. The grout-inside test shows that the higher the ground thermal conductivity or the grout radius, the better the heat transfer condition will be. However, when the grout is thick enough that the heat resistance will not change obviously, using more grout will not improve heat transfer condition of the borehole heat exchanger. In another hand, it costs more but not effective.