CHARACTERISTICS OF GROUND AND GROUNDWATER TEMPERATURES IN A METROPOLITAN CITY, KOREA: CONSIDERATIONS FOR GEOTHERMAL HEAT PUMPS

Abstract

As a basic feasibility study for geothermal heat pumps, characteristics of ground and groundwater temperatures in a metropolitan city, Seoul, were examined. For the purpose, groundwater data obtained from the subsidiary groundwater monitoring wells of the city and data of ground temperatures at depths of 0.05–5.0 m were analyzed. The annual ground temperature variations decreased exponentially with ground depths and the corresponding phase differences compared with the ambient air temperatures increased linearly with them. The ground temperatures were very stable below 3.0–5.0 m depth with minimal annual variation and they were averagely 15°C. The annual mean groundwater temperatures were 15°C and the groundwaters of most monitoring wells showed the annual variation within 3°C. All these temperature conditions are very promising for the application of the geothermal heat pumps. But the limitation of available space for the buried pipes and the thin unconsolidated soil layer in the metropolitan area would restrict the practical wide application of the closed loop systems. So open systems can be beneficial. A large number of the existing groundwater wells and the shallow water levels may enhance efficiency of the open system maintenance. Some relevant engineering considerations for the groundwater heat pumps were suggested for the metropolitan city.