A new type of heat extraction tube was devised. It is called a wet film vertical tube with a Freon flushing pump at the bottom. The diameter of the tube is 20 cm, and it is 20 m long. From this tube ground heat extraction of 50 W/m (1 kW total) was possible under continuous operation. Two heat extraction tubes were set in the ground separated by 30 m. One tube(A) was filled with sand and the other (B) with mortar. The evaporation temperatures were kept constant at -4 and -8°C. No direct expansion ground source heat pump system has been commercialized in Japan. The ground source heat pump combined with heat storage system was also discussed. With 8 hours of operation during the night, it was possible to collect ground heat about 2.5 kW.