THERMAL CHARACTERISTICS OF STEEL FOUNDATION PILES AS GROUND HEAT EXCHANGERS
Thermal characteristics are evaluated in the ground thermal energy system with steel foundation piles. Two kinds of field measurements are conducted in different places in cold regions of Japan. In the first one, the use of a double U-tube results in the equivalent heat extraction per unit length of the ground heat exchangers compared to that in a direct circulating heat exchange even in the case with a steel pile of a large diameter of 400 mm. The average effective heat conductivity of the surrounding soil is also estimated to be 1.5 W/m/K. The other measurements using multiple steel piles demonstrate the heating output enough to cover the whole heating demand in the regions.