Study On The Characteristics Of Underground Space Shaft Ventilation System Based On Stack Effect

With the increases of energy shortage and environmental pollution,using natural ventilation technology and the development and application on solar energy and other renewable energy has been heavily promoted by the people,which is the main technical means to realize building energy efficiency,also fit now advocations on sustainable development of our urban the strategic target.In this paper,putting forward“the underground space shaft ventilation system based on stack effect”form combined with the idea of solar chimney,this system is mainly meeting the vigorously developing underground space ventilation requirements,the technology is preheated by solar PV/T collector,dilivering the hot water to the annular channel of the shaft,then the heat exchange will be proceeded within the hot water and air,the air density decreases and after generate upward buoyancy,the ventilation effect is achieved by inducing the dirty air in the underground space to enter the shaft tunnel and discharge from the top.With the help of numerical simulation software FLUENT,this paper established a two-dimensional steady-state heat transfer and flow mathematical model to the shaft ventilation system with single and double channel,and then select Realizable turbulence model and combine with enhanced wall function method to study the induced ventilation rate,temperature field and velocity field distribution characteristics under different structure size and operation parameters.Firstly,based on the calculation method of this paper,the experimental model structure in literature[12]is studied numerically,and then by comparing the simulated data with the experimental data in the literature[12],the results show that the error is within the allowable range,which validates the correctness and the rationality of the method.With shaft diameter D=1 m,shaft high H=30 m,water flow rate Q_w=1 kg/s as design parameters,a simulation study is conducted on the single-channel shaft ventilation system with different inlet water temperature,then the internal air flow field distribution features of different section height along the horizontal direction are analyzed in detail on the system.Secondly,the four influence factors of the shaft height,inlet water temperature,water flow rate and the environment temperature on the shaft ventilation ventilation effects and heat transfer performance of the system 0were simulated based on the single factor analysis method,and analysis the influence factors on the influence degree and the change rules of test index;Then,on the same ventilation rate demands,in this paper,the energy consumption of traditional mechanical ventilation system and the"shaft ventilation system based on stack effect"are compared,and the advantages of the system in this paper are illustrated by energy consumption and induced ventilation rate.Finally,combined with characteristics of the distribution of temperature field and velocity field in single-channel shaft ventilation system,the double-channel shaft ventilation system is proposed because the heat wall only has obvious heating effect on the air near it that there is a large temperature gradient and velocity gradient near the heat wall surface and the air temperature away from the heating wall is very weak.The double-channel shaft structure is on the basis of the original shaft structure of single channel and added a layer of annular water area,and thus the entire circulation channel of air flow split into two channels,its purpose is by increasing the air and water coupling heat transfer area to strengthen the effect of natural ventilation.Firstly,according to the characteristics of double-channel shaft structure,the change rules of the induced ventilation rate on various inner area channel diameter are simulated,and the optimal design size under different design parameters is d=0.35m at all.Then,the double-channel shaft system is simulated with the diameter of the shaft channel D=1m and the inner zone channel diameter d=0.35m?optimal value?and the water flow Q_w=1kg/s as design parameters,compared to the induced ventilation rate with single-channel structure above the same conditions,to calculate the percentage increase of induced ventilation rate towards optimized double-channel shaft ventilation structure,the optimization effect is best when the shaft height H=15 m,inlet water temperature T_w1=50?,which the value can reach 59.43%;Finally,Finally,internal air temperature field,velocity field distribution is analyzed with the best design parameters of single and double-channel shaft,the results show that double-channel shaft internal temperature field,velocity field distribution is more even,moreover,due to the increase of thermal pressure effect in the middle area,the export reflux phenomenon will also decrease.Through the analysis of energy consumption,the energy consumption of the double-channel shaft structure is smaller,which further illustrates the superiority of the optimized double-channel shaft ventilation system.