Study On The Optimization Of The Distance Between The Air Supply Terminals Of The Stratum Ventilation Based On Multi Parallel Non-isothermal Jets

Stratum ventilation can maintain good thermal comfort and air quality under the condition of increasing air conditioning temperature in summer.Since the stratum ventilation was put forward,a lot of thermal comfort and air distribution optimization research has been carried out for the stratum ventilation,among which the air distribution optimization research for the terminals mainly includes the layout of air supply and return terminals and the optimization of air terminals type.When the air terminals of the stratum ventilation room are arranged in the same side wall side by side,the air supply terminals will send multiple jets into the working area horizontally.The unreasonable air gap will worsen the air distribution in the room,and result in the critical difference of thermal environment in different positions in the occupant area.Therefore,it is very important to find a suitable air supply spacing to meet the thermal comfort and air quality requirements of the occupant area.In this paper,the experimental measurement and numerical simulation are used to study the optimization of the spacing of air supply terminals of the stratum ventilation room.Firstly,several measuring points are arranged at different positions in the occupant area of the stratum ventilation environment room.The velocity and temperature of each point under four working conditions(including two kinds of air supply parameters combination and two kinds of air supply terminals spacing of 650 mm and 1300mm)are measured,and the thermal comfort analysis is carried out through the calculated PMV and EDTS.It is found that the thermal environment of the occupant area is very different under different air supply terminals spacing,and there may be great difference in thermal feeling at the same position.At air supply terminals spacing of 650 mm,the air flow near the central air supply terminals is stronger,PMV and EDTS are lower,and the position is cold.However,the air flow at this position is weak and hot at 1300 mm air supply terminals spacing.This is because when the air supply terminals spacing is 650 mm,the distance between the three air supply jets is small,so the confluence between the jets is earlier and more concentrated,and the air flow in the central area is stronger.Compared with 650 mm air supply terminals spacing,the air flow is stronger,PMV and EDTS are lower and cooler at 1300 mm air supply terminals spacing.This is because the location is closer to the left air supply terminals and is easier to be cooled by jet.Secondly,in order to obtain a theoretical formula that can predict the attenuation of axial velocity of multi jet in stratum ventilation,a large number of measuring points are arranged in the jet area to obtain the axial velocity of jet at different downstream positions;the measured data are used to verify the attenuation formula of axial velocity of jet.By comparing the experimental data with the theoretical formula and calculating the root mean square error,it is found that the main jet proposed by Abramovich The improved formula of axial velocity decay and the correction coefficient of velocity coincidence can better predict the axial velocity decay of the main section of the air jet with multiple outlets in the stratum ventilation.Thirdly,in order to study the influence of air supply parameters and air supply terminals spacing on five evaluation indexes(PMV,EDTS(effective ventilation temperature of stratum ventilation),DR(draft),age of air and ε(energy utilization coefficient)),the CFD model verified by experimental data was used to simulate 30 working conditions of 6 kinds of air supply terminals spacing and 5 kinds of air supply temperature and velocity combinations.It is found that when the air supply velocity is constant,PMV and EDTS decrease first and then increase with the increase of air supply temperature,and the overall relationship is quadratic,PMV and EDTS are the lowest when the air supply terminals spacing is 950 mm;the change trend of draft DR is similar with that of air supply terminals spacing,which increases first and then decreases,and reaches the maximum value at 950 mm air supply terminals spacing;the age of air of occupant area is decreasing under different air supply terminals spacing,and the air supply terminals spacing with the lowest age of air is always 950 mm.When the supply air temperature is constant,with the decrease of air supply velocity,the PMV and EDTS under all the air supply terminals spacing are increased;the DR under different air supply terminals spacing decreases,and the difference between DR is gradually reduced;the change curve of PMV,EDTS and DR becomes slow.When the air supply speed is low,the air flow difference between the jet and non jet areas in the occupant area is small,so the difference of each index under different air supply terminals spacing is relatively small.Under all air supply conditions,the energy utilization coefficient ε of 950 mm air supply terminals spacing is the largest;when the air supply temperature is constant,the energy utilization coefficient ε of all air supply terminals spacing increases with the increase of air supply velocity.Then,the entropy weight method is used to determine the weight of the five evaluation indexes,and the relative entropy multi-objective optimization method is used to optimize the air supply terminals spacing.The results show that the optimal air supply terminals spacing is 950 mm under the thermal neutral temperature(i.e.the design condition of the stratum ventilation room)or warm environment.In the cold environment,the optimal air supply terminals spacing is no longer 950 mm.This paper analyzes the rationality of this situation by combining the influence of different air supply parameters on five evaluation indexes under different air supply terminals spacing.Finally,in order to verify whether the optimal air supply terminals spacing is still applicable when the number of people in the occupant area and air supply terminals increases.In this paper,two kinds of room models with four and five air supply terminals arranged at spacing of 950 mm with personnel arrangement in two rows and six columns are simulated.The simulation results show that: when the occupant area people of the room is increased to two rows and six columns,and five air supply terminals are arranged according to the optimal air supply terminals spacing of 950 mm,good thermal comfort and air quality can be ensured in the occupant area.This is because when four air supply terminals are arranged,the radiation range of the four jets cannot cover the people close to the side walls,which may cause the personnel to feel overheated and the air quality can not be guaranteed.When five air supply terminals are used in the room,the five jets can not only converge well,but also radiate to the personnel close to the side walls.There is a relatively uniform thermal environment and a lower age of air in the occupant area.