Study On Operating Simulation Of Ground-coupled Heat Pump System And Design Optimization Of Ground Heat Exchanger In Its Life Cycle

Ground Coupled Heat Pump System (GCHPs) is one of the most important ways of renewable energy development in Architecture field, which makes soil as heat source or heat sink and realize operating energy-saving. The especial thermal performance and initial cost of Ground Heat Exchangers (GHEs) hinds the application and growth of GCHPs. Therefore, reliability and economical performance of GCHPs become the key of system design and application.In the life cycle of GCHPs, heat (cool) accumulation effects of soil caused by long-term operating of GHEs challenge the reliability of GCHPs. Therefore, accurate operating performance anticipation of GCHPs by use of system dynamic simulation in the life cycle is crucial for engineering design.Firstly, vertical U-type GHE mathematical model is studied so that simulating speed and precision can be ensured. For single bore GHE, Green Function is applied to calculated heat transfer out of the bore and the way increases the calculating speed and precision. At the same time, Duct Storage System (DST) model is introduced to calculate thermal performance of GHE bore group by comparing the Finite Line Source Model (FLSM) of GHE. On the basis of heat pump model, pump model and GHE model, GCHPs model are established. For the system model, the input is dynamic hourly building air-conditioning load in the typical meteorological year, the outputs includes hourly circulating outlet/inlet water temperature in the GHE U-type tubes, average hourly soil temperature and relative hourly energy consumption in its life cycle (20 years) under the boundary conditions that soil thermal parameters are constant.Secondly, the GCHPs model validation is made with the experiment of cooling supply and heating supply of a GCHPs project. By comparing the simulating results and experimental results of the hourly outlet water temperature of U-type tube, the daily energy consumption of circulating pump and heat pump, the mathematical model of GCHPs and every component model are validated. So the operating performance anticipation results of GCHPs are credible.Thirdly, optimized designs of GHE group are made based on GCHPs model. According to the operating performance of GCHPs and building load, the maximum/minimum simulating outlet water temperature of GHE in its life cycle is as optimizing object. By coupling system optimizing software Genopt and GCHPs model, optimizing design of GHE group is made and the optimal GHE group is obtained corresponding to input building load, and influencing performance of building load and maximum inlet water temperature of heat pump on life cycle cost (LCC) is analyzed corresponding to LCC of optimal GCHPs.At last, optimizing design way of GHE is applied in practical project. Selected buildings include teaching building, office building, hotel and residential building which locate in Beijing, Qingdao, Wuhan and Chongqing respectively. Each optimal GHE bore dimension corresponding to single U-type tube and double U-type tubes can be obtained according to different building load. Because of the differences in building functions and climate conditions, double U-type tube GHE is not superior to single U-type tube GHE by comparing LCC of every optimal GHE. The initial cost of most GCHPs schemes in this thesis is about fifty percent of LCC in term of electric power price and interest rate. The selected optimizing project samples give references to reliability and economical performance of GCHPs design, which proves sharp-cut practicability of optimizing design way of GHE by GCHPs simulation in its life cycle. Relative anticipated economical index from LCC calculation insure scheme optimization, control strategy evaluation and investment controlling.Generally, mathematical modeling, experimental validation of GCHPs and optimizing design of GHE are studied in this thesis, which enrich optimizing design method of GCHPs. Relative economical index are analyzed based on LCC, which provides references for popularizing and application of GCHPs as an important renewable energy utilization technology.