| With the raising of social economy standard, building energy consumption is growing rapidly, so the energy issue and environmental problems are becoming obviously important. Energy-saving and emission reduction policy is raised by government. As a kind of using renewable energy technology, the ground source heat pump has wide application for its environmental-friendly and energy-saving characteristic. But in the practical engineering application, many ground source heat pump systems can not reflect the superiority of its performance, on the contrary, it is always famous for its short service life and larger initial investment. Researchers often consider that the heat transfer performance of the soil and soil thermal balance are key problems, but they tend to neglect the impact of pipe network hydraulic characteristics on system efficiency.This paper argues that the effect of pipe network hydraulic characteristics and soil thermal balance on long-term, stable and efficient running of ground source heat pump system is equally important. In this paper, a ground source heat pump system in south-central hilly region as an example, De ST is applied to simulating all-year dynamic load; TRNSYS16 software is used to establish a simple simulation model, studying the factors which affect soil average temperature, determining the scope of its reasonable design, and then the influence degree of different factors on the soil average temperature will be discussed; At the same time, this paper use Pipe Flow Expert software to build Pipe network model is established, and analyze hydraulic characteristics of the buried Pipe network; Finally TRNSYS16 sofeware is applied again to establish ground source heat pump system model, simulating and analyzing long running characteristics of the system and relationship of the soil thermal balance and buried pipe network resistance, then with the buried pipe network delivery system comprehensive COP in summer as a evaluation index, this paper has optimized drilling depth, drilling spacing, the buried pipe length and form of the buried pipe.The analysis results have shown that:(1) In building load afforded by ground source heat pump system, load rate which is lower than 40% accounted for 41% of the all-time; Buried pipe all-year acumulated load imbalance rate is 67.3%;(2) If considering the system initial investment cost, and not considering the system interval operation, the best design range of drilling depth is 60m-100 m, the best design range of drilling spacing is 4m-5m, the optimum design range of backfill material thermal conductivity coefficient is 1.7 to 2.1 W/(m·K); The degree of influence on soil average temperature from primary to secondary is drilling spacing, drilling depth, drilling amount, thermal conductivity coefficient of the backfill material;(3) resistance of buried vertical pipe is about 80% of the total resistance, so the focus of the pipe network optimization object is buried vertical pipe; decreasing the length from machine to pipe network area can effectively reduce the total resistance;(4)in this system, considering initial investment cost,all-year delivery system comprehend-sive COP and soil thermal balance, the appropriate drilling depth is 60m-90 m, drilling spacing should be 4.0m-5.0m. Ensuring that drilling depth is same, the COP of double U-tube is higher than single U-tube; Ensuring that the buried pipe length is same, there is a critical pipe length. When the buried pipe length is less than 24000 m, single U-tube is appropriate, when the buried pipe length is more than 24000 m, double U-tube is the appropriate.This paper has studied a ground source heat pump system in central hilly region, and provides some theoretical basis and guidance. The conclusion of this paper can be also applied to similar areas. |
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