Feasibility Study of Ground Source Heat Pump System Considering Underground Thermal Properties

: A typical ground source heat pump (GSHP) system in South Korea has a ground heat exchanger (GHX) with a length of 100–150 m, which utilizes annually stable underground temperature to meet the loads of cooling, heating and hot water in buildings. However, most GSHP systems have been introduced in heating dominated areas because the system performance advantage is larger compared with air source heat pump system than that in cooling dominated areas. To effectively provide geothermal energy to the building in the limited urban area, it is necessary to install deep GHXs. Despite its large capacity, there are few studies on GSHP system with deep GHX over 300 m. In this study, to estimate the performance of the GSHP system with deep GHX and evaluate its feasibility, numerical simulation was conducted. To quantitatively analyze heat transfer between soil and GHX, the coupled model with GHX model and ground heat and groundwater transfer model was used. Furthermore, the heat exchange rate and the source temperature were calculated according to the operation modes, the length of GHX, and soil conditions such as geothermal gradient and thermal conductivity. As a result, the total heat exchange rate of GHX with a length of 300 m heat exchanger was 12.62 kW, 173% that of a length of 150 m. Finally, it was found that the GSHP system with deep GHX has realistic possibility in good condition of geothermal gradient.

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