| Title | Interpretation of the first thermal response test in Central Asian countries |
|---|---|
| Authors | H. Fujii, D. Ishiyama, J. Rahmatov, F. Inagaki |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Ground source heat pump, thermal response test, ground heat exchanger, Tajikistan |
| Abstract | Ground Source Heat Pumps (GSHP) systems have been widely distributed in several regions of the world due to the low operation costs and environmentally-friendliness. In Central Asian countries, however, the number of installations is very limited due to the low recognition of the GSHP system and its advantages. Akita University, Japan and the National Science Academy of Tajikistan are currently carrying out a five-years jointproject for the promotion of GSHP systems in the Republic of Tajikistan (hereafter, called as Tajikistan) with the sponsorship by the Japanese government. To demonstrate the applicability of the systems in dry countries like Tajikistan, a closed-loop GSHP system of 10kW cooling and heating capacity will have been installed in the capital city, Dushanbe in Autumn, 2024. For the evaluation of the heat exchange capability of the ground at the location, a Thermal Response Test (TRT) was carried out in September 2023 at a Ground Heat Exchanger (GHE) of 105 m deep near one of the buildings in the Academy. The TRT consists of a heating period of 2 days followed by a temperature recovery period of 2 days. The inlet and outlet temperatures of circulation fluid were measured every 1 minute, while the temperature distributions in the GHE were measured using an optical fiber sensor. The graphical interpretation of the TRT showed that the average thermal conductivity of the ground is around 1.9 W/m/K, which is reasonably high to introduce GSHP systems. The thermal resistance of the GHE, on the other hand, was estimated quite high in the shallow part of the formation due to the low groundwater level which exists 50 m below ground level. Based on the geological information and GHE specifications, an analytical simulation model of the GHE based on the cylindrical source function was constructed and was validated using the TRT results. A case study on the thermal properties of grouting material of the GHE was then carried out using the model for improving the performance of the GSHP system. The simulation indicated that the heat exchange capacity of the GHE could be improved by 20% by improving the thermal conductivity of the grouting material. |