On the closed-loop ground source heat pump system model – CRI Tester – china 12P
As Ground Source Heat Pump Ground of many factors influencing heat transfer is difficult to design, basic data, and some of the improper selection of parameters will cause unacceptable project cost, limited the technology, so until the last century until the late 80's in the business, civil Building Of Air conditioning System used. In recent years, a large number of reports reflecting the work carried out abroad, and the results achieved [1] .
Because of its environmental protection and energy saving features, ground source heat pump system in China is being more and more attention, especially in recent years, the country began to have ground source heat pump system actually works. Therefore, the ground source heat pump design details, and match with the traditional building system is little information on ground source heat pump engineering case studies and lessons learned in international research on ground source heat pump is an important aspect.
In ground source heat pump systems, geothermal heat source of the research has been to Heat Pump The difficulties, but also is the core of the technology and application of foundation. Existing geothermal heat exchanger design methods are based on the United States and Europe on geothermal heat exchanger pilot study. Domestic related research focuses on ground source heat pump geothermal heat exchangers are placed on the pilot studies, were also given the relevant experimental results. The absence of a heat exchanger in the complex mechanism of heat transfer in soil-depth research, making conclusions apply only to a specific experimental system, theory is poor, provide basic data and less, thus making it difficult to guide the actual design . Therefore, it is one of the research is to build closer to the actual situation of the ground heat exchanger heat transfer model.
Is well known that the characteristics of ground source heat pump system contains two major decisions: First, the length of geothermal heat exchangers and configuration, and second, matched the performance of heat pump units. Therefore, the ground heat exchanger configurations have been defined circumstances, the performance of ground source heat pump system works how is most concerned about. Therefore, the content of this research is to build another geothermal heat pump heat exchanger and a dynamic model and by experimental verification of the model.
1. Review of the geothermal heat exchanger model
According to the different layout, closed-loop geothermal heat exchanger can be divided into horizontal underground heat pipe heat exchanger with vertical two categories. Vertical Geothermal heat exchanger is set in a number of vertical borehole ground heat exchanger buried in the ground, usually in the form of U-tube ground. U-tube geothermal heat exchanger is a U-tube borehole arrangement, together with backfill material, and the surrounding soil form a whole. A borehole can set one group of U-tube, you can set the two U-tube. Vertical Buried small footprint, heat transfer efficiency, the project has been widely used, this article in order to project the most widely used example a single U-tube. As the geothermal heat exchanger heat transfer process involved in the complex nature of geothermal heat exchanger heat transfer model is still the foreign closed-loop ground source heat pump system focus. The geothermal heat exchanger heat transfer, so far no universally accepted model and specification. Internationally available heat transfer model can be largely divided into two categories. The first category is based on the concept of thermal analytical models, the second method to discrete numerical model based on the numerical solution. The first model uses a line heat source model or Kelvin infinite cylinder model [2] . The concept of semi-empirical methods such simple and easy for engineers to accept, and therefore the application of a certain project. The drawback is that the calculation of the thermal entry done a lot of simplifying assumptions [3] , Model is too simple and limited to the factors considered, in particular, is difficult to consider the cold, heat load with time, hot and cold throughout the year of conversion and load imbalance more complex factors. The second class method to discrete numerical heat transfer model based on, can be considered close to reality, using the finite element or finite difference method for ground temperature response and heat transfer analysis. However, due to geothermal heat exchanger spatial extent of the problem involves a large, complex geometric configuration, and load changes over time, the time span of more than a decade, so if this method by using three-dimensional non-steady-state problem solving practical engineering problems will cost a lot of computer time, the calculation of the current projects under the direct problem solving is almost impossible. This approach is currently only suitable for certain research work carried out under simplified conditions in the parameter analysis, but not for doing large-scale multi-borehole ground heat exchanger heat transfer simulation, much less suitable for engineering design and optimization.
2. Vertical single U-tube ground heat exchanger model
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