Study On Scheme Design And Optimization Of Ground Heat Exchanger For Ground Source Heat Pump System

As a renewable energy technology, ground source heat pump system is an important way of the building air conditioning system, it uses the earth as cold and heat source for system efficiency and energy-saving operation. Reasonable and effective design of ground heat exchanger system is a prerequisite for the efficient operation of ground source heat pump systems, then rock-soil thermal response test and optimization of the design is the key process. This paper reviews the development and research status of the ground source heat pump technology and ground source heat exchanger design calculation methods in domestic and foreign, then analyzes some promblems of system design and actual operation at present, and it lays a theoretical foundation for the main research of this paper. In order to solve the problems and improve the heat transfer performance of ground heat exchanger system and the reliability of actual operation, scheme design and optimization of ground heat exchanger for ground source heat pump system were studied in this paper.Firstly, this paper analyzes the heat transfer processes of ground source heat exchanger surrounding soil, combined with the stratification of soil structure and the variability of thermal parameters, then take Layered Thermal Resistance theory as the basis for soil stratification, establishing the single pipe model of vertical double U ground heat exchanger for layered heat transfer. Based on the measured data of a rock-soil thermal response test project in Chongqing, simulate the test conditions by Fluent software, then verify the results of simulation and measurement through the inlet-outlet water temperature at different moments and the wall temperature at different depths in the same time, the average relative error is 0.99% and 0.96% respectively, and the average relative error of temperature difference is 3.26%. Comprehensive error analysis, this paper believe that the model has rather high computational accuracy and reliability.Secondly, according to comparative analysis of example calculation, it points out the applied differences and existing problems between conventional and layered thermal response test method, which is mainly affected by the complexity of the geological structure, further prove the superiority of the layered thermal response test. On this basis, combined with the theory of Layered Thermal Resistance and distributed optical fiber temperature measurement system, this paper puts forward a new thermal response test method which can achieve distributed vertical soil temperature measurement. This method not only improves the reliability and accuracy of thermal response test, but also reduces the difficulty of construction and test.Finally, through the example calculation of ground heat exchanger design, this paper points out that there is a large mismatch when we design ground heat exchanger system by traditional design method. According to analyze the causes and impacts of optimization design, this paper puts forward a ground heat exchanger design optimization method which is suitable for different case of soil heat balance. By using layered heat transfer model of ground heat exchanger to study for optimization design, and take Comprehensive Energy Efficiency Economic Index as evaluation basis, then optimize the design of the original program and analyze the regulation strategies of system operation. Thereby further verify the feasibility of the optimization design method, and provide important application evidence for scheme optimization of ground source heat pump system and modification of existing systems.