## 1 Introduction  
The development of alternative energy sources is becoming increasingly necessary in Korea to prepare for an era of hefty oil prices, as Korea faces energy and resource shortages and imports approximately 97% of its fossil fuels. The post-Kyoto Protocol, which is in effect since 2013, limits the rate of emission of greenhouse gases. In 2000, Korea's CO\({}_{2}\) emissions amounted to 480.4 million tons, making Korea the ninth highest CO\({}_{2}\)-emitting country worldwide. Most of the greenhouse gases emitted come from energy consumption [1; 2; 3]. The Korean government initiated a program known as law section 11 to reduce the consumption of fossil fuels. The program promotes the supply of renewable energy by enforcing the use of renewable energy systems for more than 5% of the total construction cost for public buildings whose floor space is more than 3000 m\({}^{2}\). Moreover, the Korean government set up a plan in 2000 for stimulating the consumption of renewable energy in order to increase the renewable energy share of the total energy consumption to 5% by 2018 [4]. Geothermal energy, defined as thermal energy generated and storedin the ground, is considered to be a relatively clean and inexhaustible source of renewable energy. Geothermal energy comes mainly from the breakdown of natural radioactive isotopes of uranium, thorium, and potassium. The average heat flow on the surface of the earth is 82 W/m, and the total heat loss is approximately \(42\times 10^{6}\) MW. The estimated total thermal energy from the surface of the earth to a depth of 10 km is \(1.3\times 10^{27}\) J, which corresponds to burning of \(3\times 10^{17}\) barrels of oil. The heat content of rocks on the Earth's surface is the largest source of geothermal energy. The highest hundreds of meters of crust are not a geothermal reservoir in the classical sense, but the temperature in the area is too low for immediate use. Adjusting only the heat pump gives access to this wide range of resources, which increases the temperature of the heat carrier fluid. The most extensive technique to utilize shallow geothermal resources involves borehole heat exchangers (BHE) with geothermal heat pumps [5; 6]. After inserting the BHE into the drilled hole, the borehole is grouted by mixing sand, cement, and bentonite. An important role of boreholes is that thermal contact is a very important factor to ensure sufficient heat transfer properties between the borehole wall and the water circulation system to prevent vertical movement of water. [7]. A thermal response test (TRT) requires suitable measuring equipment to select the thermal performance of the BHE. This test takes into account the overall heat transfer characteristics including groundwater effects and other disturbance factors. The first approach for the constant heat injection or extraction is provided by [PERSON] [8] and is based on the line source method [9]. Firstly, mobile TRT devices were deployed in Sweden [10] and the United States [11]. After this period, analytical methods were greatly improved in several countries [10; 11; 12]. However, it is more practical than standardized TRT measurements, and it contributes in an easy-to-use way, further reducing TRT costs. The thermal performance characteristics of the ground are measured in a laboratory, but the results are generally inaccurate with some errors. These methods tend to ignore site conditions, such as groundwater effects and grouting materials. [13]. For actual measurement, it is necessary to select a test suitable for local conditions and prepare to compare the thermal performance of various BHE types of underground heat exchangers [14]. The literature allows you to find references to the appropriate number of geothermal system heat pumps (GSHP) and BHEs in the field, design, economic analysis and standard booklets [7; 15; 16; 17; 18; 19]. Various BHE types (single U type, double U type, coaxial type) and grouting materials are used in GSHP systems.