To really make the ground source heat pump to replace the traditional air conditioning system, there are many core technical issues to be further resolved. From the system point of view, microscopic to macroscopic view of the following problems need to be resolved:
1 soil heat transfer, mass transfer process
At the bottom of the system is the sub-subsystem of a buried heat exchanger. In this system, the main concern is the heat exchange process between the buried heat exchanger and the surrounding soil. Since soil is a heterogeneous dispersion of solid soil frameworks, liquid and gaseous water, and air, the simple composite unsteady heat conduction used in most studies at present, attributed the effects of moisture and air transport processes to The additional value of thermal conductivity to describe the coupling of heat and mass in the soil apparently results in large errors. As a result, the size of the buried heat exchanger in the ground source heat pump is too large and the initial investment in the heat pump unit increases Buried heat exchangers generally account for the total cost of heat pump system, 20% -30%), can not compete with the traditional air conditioning system.
Therefore, an urgent solution is to use a more complete mathematical model to describe the heat exchange process between the buried heat exchanger and the soil, and fully consider the heat and mass transfer processes. Porous media hydrodynamics methods can be a powerful tool. Some researchers propose to adopt the method of irreversible thermodynamics to study, but also a very innovative and feasible method. Some researchers also proposed the use of fractal method to study the thermal conductivity of soil, it is possible to make the mathematical model is simplified, so that the difficulty of reducing the study.
Another purpose of studying the heat and mass transfer process in soils is to find a new type of filler material that can enhance the heat transfer. Researchers in other countries have done research in this field and have some reports. Of course, the ultimate goal is the same, that is, as far as possible to reduce the groundwater source heat pump buried heat exchanger initial investment costs, but the country has not seen a similar study.
2 and the heat pump device coupling process
The purpose of studying the coupling process with the heat pump device is to optimize the performance of the heat pump device subsystem. Due to the use of soil as a heat source, the operation conditions of the heat pump system (operating point of the outdoor side heat exchanger) are different from those of a conventional air-source heat pump or a general water-source heat pump in either winter or summer, causing the entire Heat pump system operating characteristics are subject to change. Specifically speaking, how to configure the corresponding components of the evaporator, the condenser, the compressor and the entire system under the new outdoor side heat exchange fluid temperature so as to optimize the heat cycle performance of the heat pump and maximize the performance of the soil source heat pump Energy saving potential. Therefore, it is necessary to adopt the thermodynamic method of refrigeration system.
3, ground-source heat pump system, annual economic analysis of energy consumption
It can be seen from the thermodynamic system diagram of the ground-source heat pump that the third level of the problem to be studied is the annual energy consumption analysis of the entire heat pump system. The conclusion that the adoption of ground-source heat pumps is superior to the need for air-conditioning throughout the year should be based on the results of the annual energy consumption analysis.
This is of particular importance when determining solutions for ground-source heat pumps. For different weather conditions and different building functional requirements, the building's heat and cold load in winter and summer may not be the same. Should be given priority to the winter heating, the summer part of the cold load by the traditional air-conditioning system (such as the installation of cooling towers) to be supplemented; or summer cooling load as a benchmark, winter auxiliary heat source mode? Based on the annual energy consumption analysis, the initial investment and operation costs of the system should be fully considered. Finally, the investment recovery period should be used as the basis for judgment.
Therefore, based on the complete knowledge and understanding of the heat exchange process of the underground heat exchanger and the dynamic thermal characteristics of the heat pump system, the advantages of the ground source heat pump can be achieved by combining with the annual dynamic load of the building To fully play to achieve the purpose of energy saving and environmental protection.
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