제어 기법에 따른 수직 밀폐형 심부지열 순환 시스템의 난방 성능 분석에 관한 연구

Abstract

Shallow geothermal system uses a water temperature of 15 ℃ through borehole depth of 150 ~ 200 m. The heat pump must be used in order to supply sufficient energy to the heating horticulture of facility. Shallow geothermal system requires the use of heat pump, which results in high maintenance costs. In addition, the heat pump consumes a large amount of power and degrades the system performance. On the other hand, in deep geothermal vertical closing systems, high temperature can be attained in a single borehole and a heat pump is not required this reduces the power consumption and improves the system performance. In this study, the circulation simulator was designed in order to analyze circulation system’s heating performance of deep geothermal facilities for a 2,002 m borehole in Naju-Sanpo-myeon. Temperature variation, flow rate and power consumption of variables that affect the heating coefficient of the system were measured. VVVF control system was applied to the submerged pump and on-off control system to the circulation pump. In addition, the heating performance of system was analyzed. The submerged pump was operated by VVVF control on the simulator. When the submerged pump was operated at 40 Hz, system coefficient of performance recorded 28.95. The circulation pump was operated by on-off control on the simulator. When temperature of water in tank is 55 ℃, system coefficient of performance was 27.32. Demonstration data of heating performance was acquired at 2,002 m borehole. As a result, the coefficient of heating system when the system operated for one month was kept from 7 to 12.5. The experimental results of variable speed control for submerged pump was showed the same trend of experiments in the simulator. The coefficient of heating performance when submerged pump was operated at 45 Hz recorded 18. When the outside temperature of greenhouse was greater than 12 ℃ and the circulation pump was operated by on-off control, coefficient of heating performance recorded from 7 to 8.5.