A dynamic simulation method of ground coupled heat pump system based on borehole heat exchange effectiveness

An updated method for the dynamic simulation of ground coupled heap pump (GCHP) system was proposed. The method developed an analytical heat transfer model for the borehole heat exchanger (BHE) with considering the variation of fluid temperature along borehole length and thermal interference between two adjacent legs of U-tube. Based on the BHE model, the borehole heat exchange effectiveness (BHEE) was put forward and defined, and then the influences of borehole thermal resistance, fluid thermal capacity and borehole depth on the BHEE were investigated. By quoting the BHEE in the system simulation, the inlet and outlet fluid temperature of BHE can be calculated directly by the BHEE rather than by the calculation of average fluid temperature of BHE, this can overcome the disadvantage of former model that the average fluid temperature must be calculated previously to determine the inlet and outlet temperature of BHE. Validation of the model was undertaken by comparison with the variable heat flux cylindrical source model validated experimentally and theoretically. The experimental validation was also conducted by a model experimental facility, and the results show that the model developed in this paper has a good predicted precision, and the predicted relative error is less than 3%.