Characterization of groundwater temperature obtained from the Korean national groundwater monitoring stations: Implications for heat pumps

Groundwater is being now seriously considered as heat sources for space heating and cooling in Korea. This study evaluated groundwater temperature data obtained from 266 Korean national groundwater monitoring stations. Spatial distribution of the groundwater temperatures is mainly affected by geographical latitude, air temperature, and local topographic elevations. The distribution pattern for the groundwater temperatures is most similar to that of the air temperature. Annual variations of the groundwater temperatures were classified into four main patterns. The P (periodic) type representing periodic annual variation was mainly found in shallow groundwaters (62.5%). Most peculiar is F (flat) type, in which the groundwater temperatures showed nearly no variation, and was mostly observed in deep wells (47.9%). Water levels are seemingly related to the classifications. Water levels of P or WP (weak periodic) types were shallowest while those of F type were deepest. Magnitude of annual temperature variation was within 8 °C for 76.6% of the shallow wells while 97.1% account for the variation within 8 °C in the deep wells. The highest groundwater temperatures mostly occurred in the coldest months (November–February) and the lowest temperatures in March–June, immediately before the hottest months (July–August). A simple exponential relationship between the amplitude and the phase difference with respect to the air temperature was found, which indicates propagation of the air temperature mainly due to conduction. Considering stability of groundwater temperatures, F type in bedrock aquifers appeared most suitable for the heat pumps in respect to efficient system design and maintenance. For practical application of the groundwater heat pumps, detailed investigation of hydrogeologic conditions and potential environmental changes is required.