| Along with the rapid development of rail transit in China,the heat generated by the long-term operation of subway,the operation of air conditioning in the station,the opening of lighting equipment and the movement of personnel,causing serious problems overheating in the tunnel.A variety of measures have been adopted to remove or recycle the waste heat of subway by domestic and foreign scholars,including the use of mechanical ventilation devices to reduce the temperature in the tunnel and the application of heat pump technology to recover the waste heat of the tunnel to provide heating for the above-ground buildings.In view of the above problems,this research group proposed the subway source heat pump system based on the related research of capillary network heat exchanger.This system absorbs heat from the surrounding rocks in the winter to cool the tunnel and supply the heat to the ground buildings,thus reducing the temperature of the surrounding rocks in winter.In summer,the heat recovers in the cold rocks through absorbing heat from the air in the tunnel,thus maintaining the annual thermal balance.The surplus capacity,if any,can be used to share the heat release from the air conditioning system of the ground buildings.However,in the actual operation process of the system,due to the different climatic conditions and building load characteristics will be carried out problems of thermal imbalance of tunnel surrounding rock.Therefore,in view of this phenomenon,this paper takes a demonstration project in Qingdao as an example to build a subway source hybrid heat pump system with capillary network as the front-end heat exchanger,established a simulation model in TRNSYS,and proposes three summer operation strategies and dynamics simulation respectively,and the surrounding rock temperature field and COP value under different strategies were analyzed.In this paper,firstly,according to the characteristics of building load,De ST modeling is carried out for the above-ground buildings to obtain the dynamic load that the subway source hybrid heat pump system can be undertake.By using the TRNSYS capillary network front-end heat exchanger module,the measured values obtained from typical daily experiments in winter were compared with the simulated values.The results showed that the relative error of water supply temperature on the user side was within 7%.The relative error of return water temperature is less than 10%.The relative error of COP value of the unit is less than 10%,which proves that the mathematical model of the capillary network front-end heat exchanger module used for TRNSYS simulation in this paper can meet the requirements of engineering analysis.The simulation platform of the subway source hybrid heat pump system was established by TRNSYS,and the variation of the surrounding rock temperature field of the tunnel in Qingdao was studied.The initial temperature of the tunnel surrounding rock was 14.60°C.When the subway source heat pump system was operated for 1 year alone,the average surface temperature of the surrounding rock rose to 21.69°C.After 5 years of operation,the average surface temperature of the surrounding rock rose to 22.45°C.The average temperature of the surrounding rock in the depth of 10 m rose to 15.11°C and 19.31°C respectively.It can be seen that the closer to the surrounding rock surface,the larger the annual temperature fluctuation range,and the hysteresis of the underground building heat transfer,the deeper the surrounding rock increases with the system running time,the temperature rise phenomenon is significant.It shows that the release of heat from the surrounding rock in summer has an adverse effect on the surrounding rock,and the phenomenon of underground thermal imbalance is aggravated.Formulate three control strategies for the subway source heat pump unit to undertake the full load in winter,and undertake 20%,50%,80% of the rated cooling capacity of the unit in summer,and the rest of the cooling capacity is provided by “chiller + cooling tower”.Compared with the subway source heat pump system for 1 year,the temperature analysis of the tunnel surrounding rock temperature and unit COP in four cases is analyzed.When the subway source heat pump system is operated for one year alone,the average surface temperature of the surrounding rock increases by 7.09 °C,while the average surface temperature of the surrounding rock increases by 5.9 °C,6.5 °C and 7.0 °C under the three schemes of the composite system;The mean value is 4.285,and the summer COP mean values of the heat pump units under the three schemes of the composite system are 4.432,4.386,and 4.323,respectively.In summary,it can be explained that after adding a cooling tower with auxiliary cooling on the basis of a single subway source heat pump system,the heat accumulation in the tunnel is relieved to a certain extent and the summer COP value of the unit is slightly increased,which is beneficial to the subway source composite heat pump.The system operates in a long-term,efficient and stable manner. |
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