| The waiting hall of the railway station that is characterized by high height,large volume of space,large heating and cooling load is just one typical kind of tall space buildings.In order to form a uniform and stable temperature field and velocity field in the passenger staying area,Air conditioning design usually adopts the stratified air conditioning system,i.e.,only placing supply and return air in the lower space of building,instead of the upper space;in the winter conditions,the nozzle with adjustable angles is traditionally used for hot air heating for the working area to reduce the vertical temperature gradient.However,in some projects,part of the cold is wasted in the upper,while the air conditioning effect is not good in the lower area.The nozzle air supply speed,air supply temperature and installation height have a great effect on the indoor air conditioning.Therefore,numerical simulation was conducted to study the influence of these three factors on the effect of the air flow organization in this article,and puts forward the improvement measures of airflow distribution scheme.In the winter heating,the floor radiant heating system was introduced to discuss the thermal environment of the improved air conditioning effect.This study aimed at one waiting hall of the train station includes the calculation for stratified air conditioning to determine the speed of supply air in the nozzle,air temperature and installation height.Through reasonable assumptions,a numerical simulation model for the space of the waiting hall is built using standard k-? equation model and SIMPLE algorithm.In the premise of maintaining the same amount of cold air,the distribution of temperature and velocity of the waiting hall were simulated using the software of Airpak in terms of different air velocity,air temperature and nozzle installation height,and for the working condition of hot air heating,the temperature and velocity fields were simulated and analyzed under different air supply angle and hybrid air conditioning.The vertical temperature gradient,average temperature,average air velocity and the index of PMV-PPD and ADPI were analyzed under different working conditions of air conditioning and non-air conditioning area.Under the preliminary design condition,the temperature gradient of air conditioning and non-air conditioning area are-0.26?/m and 1.32?/m,with a significant layered effect.For the working area(Y=1.1m),the average temperature and average wind speed were 26.3? ? 0.263m/s,meeting the basic design requirement.In the premise of supplying the same amount of cold air into the waiting hall,the decreased air supply velocity would lead to the deterioration of the lap effect of the jet and increased air velocity in the working area,while the increased air supply velocity would lead to a higher position of lap and part of cold air moving to non-air conditioning area.If the air temperature difference is 8 ?,the jet heat exchange ability become weak,and the average temperature of the working area increases up to 27.4?,and the PMV-PPD is 1.28 and 30.5%,respectively,indicating a poor thermal comfort condition;if the air temperature difference is 12?,the PMV-PPD is 0.80 and 20.4%,respectively,indicating a satisfying thermal comfort condition.The impact of air temperature on air speed is considerably small.The installation height of nozzle in the working area could affect the distribution of air temperature and velocity significantly.In the nozzle installation height of 7.3 m,the average temperature is 27.1? and the average wind speed is 0.258m/s;when h=5.3m,the jet would appear short circuit,and the average air velocity is high,reaching 0.275m/s.Under the optimization scheme,the average temperature of the work area is 25.7?,the average wind speed is 0.254m/s,and the thermal comfort condition is better than the preliminary design condition.In the winter condition,changing the nozzle outlet angle could improve the hot air accumulation slightly.When the wind angle is 0o?15o?30o,the average temperature of working area is 16.5??16.9??17.4?,respectively,but the air velocity in the working area increases gradually to 0.14m/s,0.19m/s,0.28m/s,respectively.The waiting area uses hybrid mode of hot air heating and radiant floor.When the individual load distribution ratio was 50%,the average temperature and the average wind speed were 18.4? and 0.16 m/s,which meets the design requirement.The study presented in this paper is expected to provide valuable guidance for the air distribution design of the stratified air conditioning for waiting halls and serve as a reference for similar projects... |
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