| With the continuous development of underground space,the subway as the core of the underground transportation system has developed rapidly in China.The development of the subway brings convenience,as the same time,due to the large amount of heat generated by the subway system during the operation such as vehicles,air conditioners,personnel,equipment,piston wind,etc.,it is difficult to effectively exhaust heat only by the subway wind pavilion,so in the subway tunnel a large amount of waste heat is accumulated,and heat is collected in the surrounding rock near the tunnel through the tunnel,causing underground thermal pollution problems.For this part of the subway waste heat has been committed to the use of its resources at domestic and overseas,derived from the soil source heat pump,air source heat pump,but there are construction difficulties,heating instability and other problems.A subway source heat pump system based on capillary network(CN-SSHPS)has received more and more attention as a new idea.In this paper,numerical simulation method based on TRNSYS simulation platform was adopted.CN-SSHPS was taken as the research object to systematically analyze the key factors to its performance,so as to provide design basis and reference for practical engineering.Firstly,based on the theories of heat transfer and fluid mechanics,the mathematical model of CN-SSHPS was established and the simulation TRNSYS model was built.Secondly,taking an actual CN-SSHPS project in Qingdao as the background,the components of the simulation model and the operation strategy of the system were set.Thirdly,the actual CN-SSHPS project was used as an experimental platform to measure its operating parameters under typical working conditions,and the measured results were compared with the simulation results of the simulation model to verify the correctness and reliability of the simulation model.Based on the verified simulation model,orthogonal test method was used to analyze the key factors to CN-SSHPS performance.Multi-factor analysis method was adopted to further analyze the influence of key factors on COP of the system and unit,annual heat transfer,unit area heat transfer of capillary network,etc.Finally,based on the rule of the key factors influencing the system performance,some constructive suggestions and opinions on the design of CN-SSHPS were put forward.Through the above research,the main conclusions obtained in this paper were as follows:(1)The average relative errors of measured and simulated water supply temperature and backwater temperature at the load side were 3.99% and 3.95% respectively;the average relative errors of the measured and simulated water supply temperature and backwater temperature at the load side were 11.95% and 13.84% respectively.The average relative errors of system COP and unit COP were 6.62% and 5.90% respectively,indicating that the simulation system had high accuracy and reliability.(2)Orthogonal test results showed that the influences of cooling and heat load ratio and capillary flow rate on system performance were highly significant,so this paper took the above two factors as the key factors affecting the performance of CN-SSHPS.(3)The results of key factor analysis showed that COP of the system was the highest when the ratio of cooling and heating load was 1:1.5,and the ratio of actual heat transfer to annual load was the highest when the ratio of cooling and heating load was 1:2.When designing CN-SSHPS,the COP of the system,the annual heat transfer,the ratio of heat absorption and emission on the source side and other factors were taken into consideration comprehensively,and the cooling and heat load ratio borne by the CN-SSHPS should be controlled between 1:1.5 and 1:2.5.If the actual cooling and heat load ratio of the building was outside the recommended range,auxiliary cooling and heat sources should be used.(4)The analysis results of key factors showed that,during the change of capillary flow velocity from 0.02m/s to 0.2m/s,both the resistance along the pipe and the local resistance increased with the increase of the flow velocity,but when the tube flow velocity was higher than 0.05m/s,the change of heat transfer between the system and the source side was not obvious with the increase of the flow velocity.For the design of capillary flow velocity,more attention should be paid to the problem of pipeline resistance and increased energy consumption caused by excessive flow velocity,and the capillary flow velocity should be selected between 0.05m/s and 0.09m/s.This study enriched the research on the operation characteristics of CN-SSHPS,and had certain reference value to the actual engineering and the formulation of relevant specifications. |
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