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Experiments on Heat Collection from Soil Using a Steel Pipe Pile and Examinations of the Applicability of the Thermal Performance Calculation Method

by Kimio Morino

In order to confirm the heat exchange characteristics during a long-term operation and to establish a design methodology for a ground source heat pump system(GSHP) employing a steel pipe pile acting as a heat exchanger with the soil, originally designed as a building foundation, we conducted a long-term heat collection experiment for about seven months at Koto-ku, Tokyo. A steel pipe pile with an outer diameter of 600mm, a thickness of 14mm and a length of 22.5m, was driven perpendicularly into the ground.

From the experimental data, we confirmed the heat exchange characteristics between the soil and the steel pipe pile during long-term operation. The quantity of heat collected from the soil with the pile per day was about 23kWh and the coefficient of performance was 3.3 which reflected the high performance of the GSHP in a stationary state. We also confirmed that the calculation method we developed could estimate the fluctuation of the water temperature in the steel pipe pile and the thermal performance of the heat collection system during long-term operation with sufficient accuracy when compared with actual measurement data.

From the information obtained from the experiment and the confirmation of the applicability of the calculation method to a long-term operation, the design methodology for a GSHP employing a steel pipe pile was established.