Accessibilities And Thermal Environments Of Impinging Jet Ventilation And Displacement Ventilation In Classrooms

In the past two decades, air conditioning systems in urban areas in China havebeen greatly improved in operation control techniques, thus indoor air parameters canbe adjusted or controlled according to the demands of indoor thermal comfort and airquality. Floor-height of a ventilated room may influence air flow pattern and humanthermal comfort. Temperature difference between ankle and neck may also influencehuman comfort indoors. Meanwhile, occupants are becoming more and moreinterested in how to design a ventilation system so that it can supply air to specificzones as soon as possible. Besides, when supply air contain pollutants, the occupantshope to delay the polluted air from getting to the breath zone, with the density ofpollutants as low as possible. So evaluating time-limited performance of theventilation system is necessary.Numerical simulations have been carried out to compare the human thermalcomfort and air flow pattern in classrooms which feature with different floor-heightbetween impinging jet ventilation and displacement ventilation. Meanwhile,accessibilities of supply air and tracer gas distribution in limited period of time arealso studied.The results show that the floor-height of the ventilated classroom can onlyinfluence local air flow and temperature distribution in upper zone of the classrooms.In the lower zone, however, air distribution and human comfort stay the same withoutbe chenged. The temperature gradient in the lower zone of the classroom andtemperature difference between ankle and neck in displacement ventilated rooms ishigher than that in impinging jet ventilated rooms. In both ventilation strategies peakair velocity and peak PD appear close to the ceiling and the floor, the peak PD nearthe floor in impinging jet ventilated rooms are larger than that in the displacementventilated rooms. Thus the thermal comfort is better in a DV than in a IJV when boththe strategies are available.At the early stage impinging jet ventilated rooms have more uniformed fresh airdistribution around the occupants than that in displacement ventilated rooms, but theaccessibility of supply air in an impinging jet ventilated room is slightly lower thanthat in a displacement ventilated room. In displacement ventilated rooms, those occupants who seat back to the outlet enjoy higher accessibility of supply air. As timepassed the differences of the accessibility between these ventilation methods are nolonger distinct. In both the ventilation modes, the accessibility of supply air in thelower zone of the classroom is higher than the accessibility of supply air in the upperzone of the classroom.The simulation results also show that in the both ventilation strategies, tracer gasdistribution near the occupants who sit close to the air supply outlet depends on theoccupants’ locations and their facing direction. In displacement ventilated rooms thetracer gas concentration decay slowly at the leeward side of the occupants. In bothventilation methods, it appears that there is no relation between the highestconcentration moment at the upwind side of the occupants and that at the leeward sideof the occupants.In both ventilation modes, the nearer to the air supply outlet, the higher andearlier peak tracer gas volume fraction could achieve. One can get peak tracer gasvolume fraction at the same location in impinging jet ventilated rooms earlier thanthat in displacement ventilated rooms.