| Reasonable ventilation is helpful to improve indoor air quality,human thermal comfort and promote building energy saving.At present,the common ventilation methods of air conditioning system are mixed ventilation(MV)and displacement ventilation(DV).MV is not limited by season and can be used in cooling and heating conditions,but the ventilation efficiency is low.Compared with MV,DV can improve indoor air quality and save energy,but it can not be used in winter heating because of low air velocity.As an alternative,impinging jet ventilation not only has the advantages of DV,which can improve air quality,increase air exchange efficiency and energy utilization,but also overcomes the limitations of DV which can not be used in winter heating and large space.As a new type of ventilation,impinging jet has its own unique air distribution.It ejects high momentum fresh air vertically from the air supply outlet,and after hitting the ground,the momentum decays,and then diffuses around the floor surface.Due to the high air velocity at the air supply outlet,people are worried about the blowing sensation of human ankles under IJV system.Although the air velocity decreases obviously after the air jet impinges on the ground,and IJV is often used in large spaces and other public places,and people only stay near the air outlet for a short time,the uncomfortable blowing sensation of human body still needs to be paid attention to,which is the key to whether IJV can be widely promoted.At present,there are few researches on human blowing sensation of IJV.Therefore,this study uses numerical simulation,experiment and questionnaire survey to study the air distribution near the air outlet(ankle height)of IJV and the thermal comfort sensation of human body during a short stay(1 ～ 5min).Firstly,through numerical simulation,the air flow pattern of IJV near the ground is analyzed under the conditions of isothermal condition in transition season,cooling condition in summer and heating condition in winter,with different air supply speed and different air supply outlet shape and position.After that,30 subjects participated in three experiments in the transition season,summer and winter to obtain the subjective evaluation parameters of the subjects: the acceptability and preference of air movement,the preference of thermal comfort and temperature,and the thermal sensation.The results show that the air velocity at 0.1M height is not sensitive to the distance of air supply outlet due to the influence of the attached jet formed by IJV impacting the ground.Although the traditional research height of the air blowing sensation at the ankle is 0.1M,in the IJV air supply mode(close to the ground jet),the air velocity close to the ground(0.01 M above the ground)is very high,and the air blowing sensation at the ankle may be affected by the obstruction of shoes.Therefore,it is not enough to study the air distribution at the height of0.1M for IJV rooms.The experimental results of human thermal comfort show that the comfort of IJV ventilated room is worse with the increase of exposure time under the mode of isothermal air supply in transition season and cooling in summer,and more and more subjects expect to reduce the wind speed and increase the temperature.In the winter heating mode,the comfort of the subjects did not change significantly with the increase of exposure time,and the subjects were comfortable at all working conditions. |
