Study And Optimization Of Flow Field Characteristics And Thermal Comfort Of Typical Convection Terminal Outlets In Office Buildings

Office always has dense staff and people stay indoors most of the time,as a result,people in office buildings expect a more healthy and more comfortable indoor environment.Air conditioners are widely used to improve indoor thermal environment,but except for improving indoor thermal environment,air conditioners also bring a series of problems,such as large vertical temperature difference in winter,uneven flow field distribution,and blowing feeling,which cause discomfort.Therefore,the main purpose of this article is to research indoor flow field characteristics and thermal comfort of typical convective air outlets in office buildings,and to find optimization directions in order to create a more comfortable office environment.First,writer selected an office building to build an experimental platform.Through experimental tests and subjective questionnaire surveys,the characteristics of the indoor flow field and thermal characteristics of the typical convective end air outlets in winter and summer at different air supply angles,air temperatures,and air speeds were studied.The results show that the temperature uniformity of the working area in summer decreased with the increase of the set temperature,and the temperature uniformity of the working area in winter increased with the increase of the set temperature.In summer,the vertical temperature difference was mostly within 1℃.In winter,the maximum vertical temperature difference of the air-conditioned experimental room was close to 10℃,and the PD value under the tuyere was between 80% and 100%,indicating that the large vertical temperature difference in winter can lead to a high local dissatisfaction rate.At the same time,through experimental research,it was found that the air supply angle had a greater impact on the flow field of the room.From the subjective questionnaire analysis results,feeling the blowing sensation under the summer wind was easy.Secondly,the effects of different air supply angles and air supply speeds on indoor flow field characteristics and thermal comfort were studied by CFD numerical simulation.Comparing the simulation results with the experimental results,the temperature deviation was basically within 0.1,and the speed deviation was between 0.04 and 0.5.Considering the influence of the entry and exit of the experimenter and the turbulence disturbance on the wind speed,the model can be considered reasonable.The simulation results showed that: compare the flow field evaluation indexes of the three air supply speeds of 1.2m/s,1.8m/s and 2.5m/s(calculated by using the air flow hood to measure the average air volume at a distance of 0.2m from the air outlet),when the air is supplied by 1.8m/s in summer,the vertical temperature difference in the indoor working area was only 0.7℃and the average wind speed was lower than 0.5m/s.Therefore,1.8m/s can be considered as the optimal air supply speed in summer.In winter,by increasing the air supply speed,DR value and PPD value were significantly reduced,and the overall thermal sensation was warmer at high wind speeds,so it can be considered that 2.5m/s is the optimal air supply speed in winter.By adjusting the angle of the air supply blades,the airflow spread farther on both sides of the room.The temperature uniformity in summer was reduced from 1.34 to 0.372,and the temperature uniformity in winter is reduced from 4.7 to 1.33,comparing the flow field characteristics and thermal comfort evaluation index of the five air supply angles of 0°,15°,30°,45°,60°,it can be seen that the air supply at30°～60° was better in summer,and the air supply at 45° in winter was the best.Finally,based on the previous thermal environment analysis,optimized design of the air outlet at the convection end of the office building air conditioner was carried out,and three optimization schemes were proposed: installing air deflectors,changing the number of blades,and adjusting the blade oblique feeding structure.The results showed that the addition of wind deflectors in winter caused significant changes to the velocity field,but if the wind speed was too low,the buoyancy of the hot air flow cannot be suppressed and the indoor temperature response time was slow.Therefore,this optimization method was not recommended in winter.The speed cloud map in summer showed that the cold air jet range when there are 6 air supply blades was farther than 4blades,making the temperature on both sides of the room 0.5℃ lower;in winter,the temperature uniformity of 6 air supply blades was reduced from 4.73 to 2.27,and the vertical temperature difference was reduced to 4.5 ℃.According to the flow field characteristic index and the thermal comfort evaluation index,it can be considered that the six blades is better than the four blades.The jet flow of the fixed blade oblique air outlet can maintain a long range indoors,the horizontal temperature difference in summer had dropped by two degrees and the temperature uniformity dropped by two degrees 0.5,the DR value dropped by 6%,and the two types of oblique delivery were obviously optimized in summer.In winter,the room temperature and PMV value adjusted by the oblique delivery structure(2cm)of the air outlet were still within a comfortable range and the temperature uniformity was significantly reduced.However,the average temperature of the room with the oblique delivery structure(4cm)of the air outlet was very low and the PMV and PPD were both in uncomfortable range,indicating that the adjustment of the oblique delivery structure(2cm)of the air outlet had a certain optimization effect.This study provided guidance for the subsequent optimization of typical convective end air outlets.