The monthly load factor (LF) and equivalent full load hour (EFLH) were calculated by using the design parameters in the geothermal utilization reports and the reference data for heating and cooling loads according to building types. The difference of EFLHs according to building type using the monitoring data of the ground source heat pump (GSHP) systems was also identified. The amount of heating energy supply for the newly installed GSHP system in 2013 using different EFLHs was 61.6% of the data in the official statistics of Korea while the value according to the method adopted in the World Geothermal Congress was 44.5%. So, it is concluded that the geothermal energy utilization of the official statistics is overestimated. As a result, it is necessary to apply EFLHs of various building types and coefficient of performance (COP) of the GSHP system to the estimation of the accurate statistics of geothermal energy utilization.

The amount of geothermal energy utilization in 2013 was newly calculated by applying the EFLHs of various building types and heating COP of 3.7 and cooling COP of 4.8. The amount of geothermal energy utilization for heating thus calculated is 32,549 toe while the amount of energy saving for cooling is 17,315 toe. If only the heating application of the GSHP was considered as the geothermal energy utilization, which is true in Europe, the result was 37.4% of the official statistics in 2013. When both the heating and cooling are considered as the geothermal energy utilization, the result became 57.3% of the official statistics. Crude oil import substitution effect through the utilization of GSHP in case of the official statistics was calculated as USD 63 million in 2013, while the effect by the newly calculated statistics reduced to USD 36 million. In terms of green house gas (GHG) reduction, the official statistics corresponded to 471 thousand tonnes assuming GSHP system substitutes electricity utilities, while the newly calculated statistics showed only 270 thousand tonnes.

Though the amount of geothermal energy utilization in the official statistics has been calculated based only on the GSHP system capacity until now, it is needed to take into account various geothermal direct use technology including geothermal district heating and hot spring. Furthermore, the cooling effect of the GSHP is not yet considered as the geothermal energy in the international standard, but it should be also included in the geothermal energy utilization.

The verification of the performance and the reliable estimation of geothermal energy utilization using GSHP is needed for the renewable heat obligation (RHO), fostering the private investment and the export business in the future. Therefore in this study, an improved estimation method of the geothermal energy utilization was proposed. Through this, it is expected to get a reliable setup of the national target and policy for the geothermal energy, and also it can offer a good opportunity for Korean companies to expand their business to foreign markets, such as Mongolia and southeast Asian countries.