Method of calculation of the ground temperature for multiple ground heat exchangers

In this paper, the authors propose a method of calculation of the ground temperature for heat extraction or injection via multiple ground heat exchangers. First, a high-speed algorithm to calculate the ground temperature is described. Next, a variation of the ground temperature calculated by using this method is compared with the one obtained by applying spatial superposition principle of the temperature responses calculated by the theoretical equations. As a result, the method’s preciseness was proved and the computation time was about 1/135 compared to the method with the theoretical solution. From these, it was shown that the method has appropriate precision and computational speed to use as a design tool. Additionally, if the ground heat exchangers are short such as when foundation piles of a building are used as ground heat exchangers, it is necessary to consider the heat transfer from the edge of the ground heat exchangers. Thus we devised a method, which uses the equivalent radius obtained by multiplying the ideal ground heat exchanger radius by a modification coefficient, to obtain the average surface temperature of the ground heat exchangers influenced by the heat transfer. The temperature calculated with the modification coefficient was compared to the one calculated without the modification coefficient.