Analysis on thermal response test of soil in desert area and operation scheme of desert source heat pump system

Abstract: The "Thirteenth Five-year Plan for Geothermal Energy Development and Utilization" sets forth the guidelines and targets for the development and utilization of geothermal energy, and that becomes the basis of Chinese geothermal energy development and utilization during the "13th Five-Year" period. Due to the impacts of geological conditions, the use of geothermal energy is limited. Light and heat are abundant in the desert, however, because of its harsh conditions, shallow geothermal energy has not been effectively utilized. At present, China has actively explored the development of modern and sci-tech agriculture in the desert region. The application of shallow geothermal energy provides a better opportunity for the development of desert agriculture, especially the greenhouse. Ground source heat pump technology as an important way to apply shallow geothermal energy in China has been widely used. Geothermal conductivity has a great influence on the determination of the number and depth of boreholes, thus it affects the initial investment of the system. At the same time, inaccuracy of geothermal thermal and physical parameters lead to mismatches between the designed system and the actual load, so that they cannot give full play to their energy-saving advantages. Therefore, determining the geothermal thermal properties of accurately is the basis for the design of ground source heat pump system. In this paper, a desert source heat pump project in Ningxia desert area was used to carry out geothermal thermal response test. There were large sandstorms and no stable water source in the test area. The testing process in this project was designed according to the unique geomorphology and climatic conditions of the desert area. The heat transfer coefficient of ground heat exchanger in this desert area was tested by analyzing the average geothermal coefficient. The testing data were as follow: The soil temperature was 16.52 ℃; The average thermal conductivity of the soil was 1.12 W/(m·℃) by using the theory of linear heat source. In the cooling mode, the ground heat transfer was 40.94 W/m; and the heat transfer of the ground heat exchanger in the heating mode was 25.28 W/m. By comparing with the data of the related tests in the eastern part of China and combining with the operation scheme of the climatic conditions analysis system in the desert area, the operation scheme considers adding heat source in winter to assist heating, and a hybrid energy storage desert source heat pump system suitable for summer operation in the desert area was proposed, which could provide a solution for the limited use of shallow geothermal energy in desert areas. The results can provide a reference for the thermal response experiment in the desert area and the application of desert source heat pump system.