Numerical Simulation On The Temperature Field Of Soil Heat Exchanger Of Ground Source Heat Pump (GSHP) And The Technoeconomic Analysis

The ground source heat pump (GSHP) systems have been used widely in Eastern Europe and North America. In china, however, GSHP is still in its initial stage and experience plays dominant role in the system design. The role of design theories of GSHP is limited since the operating condition of the systems change greatly according to the geologic and climatic condition, system type and materials used in the systems. The rapid development of numerical simulation technique provides a good solution for GSHP system designing and overcomes some of the disadvantages of theory analysis.Most literatures available now pay more attention on the steady operating conditions of GSHP and often take its underground U-tube as thread heat source. The details of fluid-solid coupling (FSC) heat transfer are neglected. So the author thinks that transient heat transfer together with FSC analysis can be used to increase the designing precision of GSHP system and the technoeconomic analysis is also helpful for the system energy saving.In this thesis, the study background and system composition of GSHP are introduced firstly and thermophysical properties of soils and heat transfer model of U-tube are described in the following sections. The 2-D steady and transient temperature distribution of the U-tube underground were studied using Ansys software. Technoeconomic method was used to analyze the energy loss of the whole system. Main works are listed below: (1) Simulation of the temperature field and heat flux of U-tube underground at different operating conditions; (2) to observe the effect of the depth, inlet and outlet water temperature, velocity, U-type diameter and type of backfill soil on the temperature distribution around the U-tube heat exchanger; (3) technoeconomic analysis was conducted to explore the optimal operating mode of the GSHP.Concluding remark: (1) the heat exchange capacity of the U-tube alone the vertical direction and the radial direction decreased with the increasing of the fluid temperature; (2) the velocity of fluid in U-tube shows negligible effect on the heat exchange; (3) the heat exchange intensity improved dramatically with the increasing of the conductivity of tube wall and backfill soil; (4) the irreversible loss of compressor, heat exchanger and circulating pump caused most of the exergy loss. The suppression of flow resistance and temperature difference of heat transfer are effective to lower the irreversible exergy loss.