| The closed-loop ground-coupled heat pump system as a kind of more energy efficient air conditioning form, has been widely used in our country. In a closed-loop ground-coupled heat pump system, the energy consumption of the pump accounts for about 20%～30% of total energy system. Therefore, the energy consumption of the pump is one of the important factors, which affects the energy consumption of closed-loop ground-coupled heat pump system. Currently, the study of variable flow system for closed-loop ground-coupled heat pump is not very good, especially the load-side and the ground source-side variable flow system simultaneously. Therefore, the pump operation energy efficiency remains to be studied in closed-loop ground-coupled heat pump system.Contents and results are as follows:(1) The building load model is built, and the dynamic cooling and heating load of building is calculated by TRNSYS simulation software. In the application of TRNSYS software for calculating the cooling and heating load, in order to improve the accuracy of the calculation, the "start-stop" of load calculation should be synchronized with the "start-stop" of air-conditioning system.(2) A mathematical model of variable frequency pump based on temperature difference control is established, and the variable frequency pump module is developed based on TRNSYS software. The variable frequency pump module can be used not only in multiple pumps system with parallel operation, but also in changed number of operating pumps system with the cooling and heating load change. According to the characteristics of TRNSYS simulation software, two methods were proposed to apply this simulation module. One of the methods is adopted to simulate the load side variable flow system of ground source heat pump, and the test of model is carried out.(3) According to DOE-2 model and multivariate polynomial regression model, the water-water heat pump mathematical model was established for variable flow rate system. The advantages, disadvantages and applications of DOE-2 model and multivariate polynomial regression model were pointed out, respectively. The water-water heat pump module was developed based on TRNSYS software, and the test of model was made for the water-water heat pump model.(4), Depending on the area of building, two design processes of the geothermal heat exchangers were proposed with TRNSYS software. One of the methods was adopted to design the geothermal heat exchangers, and the whole life cycle of heat pump system was simulated dynamically by TRNSYS.(5) The variable flow simulation on the source-side of GSHP system was studied using TRNSYS software,It can be derived that the outlet temperature of geothermal heat exchangers is higher than that of constant flow operation in winter heating condition, and the outlet temperature of geothermal heat exchangers is lower than of constant flow operation in the cooling mode in summer.It can be inferred that the heat transfer capacity of geothermal heat exchangers fully meets the needs of the entire system using variable flow operation on source-side.(6) The feasibility of the ground source-side and load-side simultaneous variable flow of closed-loop ground-coupled heat pump system was studied by schemes comparison There are three schemes:Scheme one:The load-side and ground source-side constant flow operation of closed-loop ground-coupled heat pump system.Scheme two:The load-side variable flow and ground source-side constant flow operation of closed-loop ground-coupled heat pump system.Scheme three:The load-side and ground source-side simultaneous variable flow operation of closed-loop ground-coupled heat pump system.Before the energy consumption comparison, the optimization calculations of the minimum operating frequencies of frequency pumps were carried out by TRNSYS simulation software for scheme two and scheme three in winter and summer condition. Through the analysis of the energy consumption of the three schemes, it is concluded that, in terms of energy saving, scheme three> scheme two> scheme one. Taking the scheme one as a benchmark, the economic analysis of scheme three was finished that the payback period was 2 years. Conclusions:The load-side and ground source-side variable flow operation of closed-loop ground-coupled heat pump system not only is feasible, but also has good energy-saving and economy. |
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