ANALYSIS OF SOIL TEMPERATURE DISTRIBUTIONS IN A GEOTHERMAL HEAT-PUMP AIR-CONDITIONING SYSTEM

A geothermal heat pump (GHP) heating system is one of the most promising alternative heating systems for cold regions such as Hokkaido, the northernmost is land of Japan. Thermal demand during heating seasons from 2005 was measured and simulated for a residential house installed with a GHP air-conditioning system that had a U-tube with a depth of 91 m. It was demonstrated that heating was fully supplied by the GHP system alone for four years. Soil temperature distributions around the U-tube were measured in order to establish criteria for ground capability as a heat source. The results showed that soil temperature reduction during the entire heating season was limited to within a radius of about 5 m from the U-tube. This means that a U-tube must maintain distance of about 10 m from an adjacent U-tube which gives a similar thermal gain. Accumulative geothermal absorption during heating season did not fully recover during non-heating season even with external thermal input to the ground by free cooling.