2010 Volume 32 Issue 3 Pages 169-183
In this paper, the quantitative evaluation of performance and advantages of Geothermal Heat Pump (GeoHP) system in Yumoto District in Fukushima Prefecture, Japan, was studied comparing to other ordinary areas, where the geothermal gradient and the thermal conductivity these values are 3-4 and 1.7 times larger than those in other ordinary areas shown in literatures, respectively. In this study, the GeoHP was operated at Yumoto Nursery School and the numerical simulation has also been carried out to analyze the dynamic behavior of GeoHP system, considering the geothermal gradients and thermal conductivities.
It was revealed that the outgoing fluid temperature of circulation fluid in Yumoto was about 3-4°C higher than that of an ordinary area after the operation for 30 days, and that the thermal conductivity much affect the temperature change. Under a condition of 8 hours continuous operation a day, the electric power consumption of the compressor was 3.1-6.7% lower and the COP of the system was 0.2-0.4 higher in Yumoto than those in ordinary area. The maximum amount of extracted heat for 15 years under this operation condition in Yumoto was estimated to be 1.4-1.7 times larger than that in an ordinary area. It was also revealed that the room temperature recovers in only 30 minutes after an intermission of 8 hours operation a day to the same level as the 24 hours continuous operation. The electric power consumption of the compressor in the intermittent operation exceeded the case of continuous operation only in the first 20 minutes after the heat pump system restarted. It was suggested that these demerits of the intermittent operation, such as room temperature drop and higher electricity consumption after the intermission, are smaller than the demerits of the fall of the ground temperature in the continuous operation, and that the intermittent operations are suitable for the geothermal heat pump system.
