Calculation algorithm of the temperatures for pipe arrangement of multiple ground heat exchangers

The authors introduce calculation algorithm of the temperatures of the ground and heat carrier fluid in multiple ground heat exchangers for pipe arrangement of ground source heat pump (GSHP) systems. First, the outline is explained. Next, in order to investigate possibility for the operation of the GSHP system with steel foundation piles and validate reproducibility of the value calculated by the design tool including the calculation algorithm, field tests of heating and heat extraction were conducted with a residential GSHP system using 25 steel foundation piles of 8 m long as ground heat exchangers. From a result of comparison between temperatures of the measurement in the test and calculation by using the design tool, it was confirmed that the tool could predict the temperatures with acceptable precision and speed for utilizing as a design tool. In addition, performance of GSHP systems with steel foundation piles in long term is predicted with the design tool. In moderate climate region, since the GSHP systems using multiple ground heat exchangers with short length can operate with high efficiency as well as the GSHP system using a single ground heat exchanger with long length, the GSHP systems with steel foundation piles have possibility to become popular.