| The waste heat generated by the subway during operation,such as braking,acceleration,friction,auxiliary equipment,etc.,will accumulate in the underground tunnel after long-term operation.At present,the methods for cooling the tunnel mainly include setting up cooling towers,ground source heat pump technology,setting piston wind shafts and ventilation fans,setting up air conditioning systems,and spray.But the above methods have their drawbacks and limitations.In recent years,the capillary network was tried to absorb the waste heat generated by the subway operation on the surface of the surrounding rock of the subway tunnel.In winter,the waste heat can be transported to the ground through the heat pump unit to heat the building.In summer,the waste heat in the tunnel and the heat in the building are stored together in the rock near the subway tunnel or exhausted by the piston wind.However,there are many aspects including the calculation method of the dynamic heat transfer process of the front end continuous heat exchanger of the capillary network,the actual operation characteristics of the heat pump system of the waste heat source of the subway,the change of the underground temperature field caused by the long-term operation of the system,the setting of the auxiliary cold heat source and the operation strategy of the system.These aspects remain to be further studied.Therefore,this paper studies the operation performance of the subway waste heat source heat pump system.The parameters of the system and surrounding environment are predicted after the subway waste heat source heat pump system is put into operation.And it provides reference for engineering design.This paper first introduces the operation principle of the subway waste heat source heat pump system and the laying of the actual engineering capillary network,and carries out the hourly load calculation according to the above ground construction conditions.The heat transfer model of the front end heat exchanger of the capillary network is simplified,and the heat transfer calculation TRNSYS module of the front end heat exchanger of the capillary network is programmed to realize the dynamic and time-by-time calculation of various parameters of the front end heat exchanger of the capillary network.The calculation results are compared with the field test results of the capillary network front end heat exchanger.The relative error between the simulated calculated value and the experimental value averages-0.25%,and the maximum is 8.79%.The relative error between the simulated and experimental values averages-0.25% and the maximum is 8.79%,which verifies the correctness and reliability of the calculation method.Based on the above content,this paper simulates the operating characteristics of the simulated heat pump system,which includes dynamic operating parameters throughout the subway waste heat source heat pump system,such as water temperature,COP value,tunnel air temperature,surrounding rock surface temperature and capillary flow heat flux.The results show that the temperature difference between the inlet and outlet of the source side and the load side(user side)of the subway waste heat source heat pump system is relatively stable.When the pump is set to fixed frequency,the average temperature difference between the source side of the unit,the load side of the summer unit,the source side of the winter unit and the load side of the winter unit is 4.95 ° C,4.96 ° C,3.46 ° C,5.42 ° C,respectively,during the first year of operation of the system.The average system COP in summer is 3.38,and the average system COP in winter is 3.81.After one year of system operation,the surface temperature of the surrounding rock goes up 4.73 °C.The frequency conversion technology is applied to the load side water pump,and the simulation results show that the variable flow system is more energy efficient.The variable frequency pump technology increases the average COP of the system by 0.11 in summer and 0.13 in winter.After that,various factors affecting the operating performance of the system were further analyzed,such as the capillary network laying area,the lining thickness,the rock type,and the cooling load of the above-ground building.Under the simulated conditions of the constant flow system in this paper,the main analysis includes the relationship between the laying area of capillary network and the annual heat exchange capacity of the user,the effect of different thickness ratios of the first lining and the second lining on heat transfer on the air side and surrounding rock side of capillary network and heating and cooling capacity to users on the ground,the influence of different kinds of rocks in the tunnel on the operation of the system and its fundamental factors,and the influence of different sizes of cooling load on the system operation and temperature variation of surrounding rock.Then this paper simulates and analyzes the variation of the surrounding rock temperature field under long-term operation of the system.It is found that the temperature rise of the surrounding rock is higher after the first year of operation of the system,and then the temperature rise is slow,which can ensure the long-term operation of the subway waste heat source heat pump system and will not cause a serious impact on the thermal environment of the surrounding rock.Finally,the control strategy on the operation of the system is formulated in combination with the actual project. |
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