Study On The Influence Of Air Supply Mode On The Affecting Scope Of Outdoor Cold Air During Winter Heating Season

The public places with the larger flow of people have an inevitable phenomenon of opening the outdoors frequently,which will cause the outdoor cold air infiltrating into the room consequentially in heating season.Cold air that infiltrates in to the room goes down by the negative buoyancy effect and then spread along the ground,which lowers the temperature of personnel workspace.Over the last two decades,the principle of impinging jet has been applied to air condition and ventilation,and developed as a new ventilation strategy,i.e.,impinging jet ventilation(IJV),which is considered to have the advantages of displacement ventilation(DV)and mixed ventilation(MV).For the consideration of the principle,the heat airflow of the impinging jet ventilation system streams to the ground directly,which will reduce the influence of cold air that infiltrates into the room on indoor thermal environment.In a heating room with significant outdoor cold air infiltration,conducting a series of experiments that are under different air supply parameters to study the heating effects of IJV and MV in the present investigations.The results indicate that the temperature near the ground of the two air supply modes is obviously decreased due to the intrusion of outdoor cold air,and the phenomenon of temperature stratification is obvious.However,the affecting scope of cold air in the IJV rooms is much smaller than that in the MV rooms.Increasing the supply temperature can not reduce the influence of the cold air on the room’s thermal environment for both the MV and IJV,but increase the temperature gradient of the room and reduce the energy utilization rate of the room.Although increasing the supply velocity can decrease the temperature gradient of MV heating room,and reduce the affecting scope of cold air on indoor thermal environment,the heating effect of IJV with lower supply velocity is better.In addition,the height of supply inlet of IJV affects the mixing degree of hot and cold airflow.Therefore,the aim of present study is to investigate the distributions of indoor air velocity and temperature under different heights of supply inlet.The results indicate that reducing the height of supply inlet increases the temperature near the ground of the room and reduces the functioning range of cold air.Although reducing the height of the supply inlet can increases the energy utilization rate of the room and reduces the airflow velocity above the ground,it increases the velocity of the airflow near the ground.Because the temperature near the ground is higher,which can make up for the deficiency of the higher level of draught sensation caused by the higher velocity,it will not cause people discomfort due to the draught sensation.