Geothermal Heating an Cooling System Using Building's Pile of Sanno Junior High School in Akita City

Abstract

The system is mainly composed of the underground heat exchangers using 75 building's piles, four 15HP heat pumps, a 140m³ heat storage tank, piping systems, air-conditioning and heating equipments. Each pile is drilled up to 50m deep by the earth drill technique and equipped with a double U-tube which carries the liquid for the geothermal system. The designed quantity of heat exchanged between the underground heat exchangers and these external formations is 114kW. The heat pumps are driven in the night when electricity cost is low, and the water in the storage tank is heated to 50°C in winter and is cooled to 5°C in summer, which are store in the heat storage tank. In the daytime, the former is used for heating the 970m² floor of the gymnasium and the latter for cooling the control room and the special school room. The operating performance of the heat source equipments meets the evaluation standards : in the heating the inlet temperature of the underground heat exchanger t_in> 0°C, the outlet temperature of the underground heat exchanger t_out>atmospheric temperature t_air, the system power q≥132kW, the storage temperature t_s≥50°C and in the cooling t_out>t_air, q≥120kW, t_s≤5°C. Heat pump heating and cooling coefficients of performance are respectively 3.04 and 4.5. The total quantity of heat given by the heating floor face of the gymnasium is 54kW by estimate from the floor temperature of 21.5°C and the room temperature of 15°C. Additionally the energy consumption of the geothermal system is 68 % that of the kerosene boiler and the carbon dioxide emission of the former is 56% that of the latter.