Numerical Simulation Research On Air Distribution In Office Buildings With Cold Dedicated Outdoor Air System

The cold, dedicated outdoor air system (CDOAS) is a new air conditioning system with the combination of the cold air supply system, great temperature difference technique and conventional cold source dedicated air system. CDOAS uses the chilled water to make outdoor air temperature dropped and reduces its relative humidity, then takes the treated outdoor air into the room. The outdoor air system undertake all the indoor latent heat load and part or all sensible heat load and the residual sensible heat is taken by other refrigeration facilities with no return air system and only taking sensible heat load. After heat and moisture transfering, the outdoor air is discharged directly through outlet. By using CDOAS, much energy can be saved and higher indoor air quality, lower noise level can be achieved. More and more attention is paid to CDOAS in recent years. But, because of the great temperature difference and small air supply rate, whether air distribution in the building with CDOAS can reach the requirement or not is still unlear.Based on the Navier-Stokes equation and and RNG k-ε turbulent model, air distribution in office building with CDOAS is researched using finite volume method (FVM) in this thesis. STAR-CD, the commercial computational fluid dynamics (CFD) software is used to simulate the distritution of temperature, velocity and concentration of CO₂ under different air conditioning conditions. By considering the thermal transfer processes such as the heat transfer through the building surroundings, the heat release of persons, equipments and the solar radiation, and etc., a model using low temperature and great temperature difference jet flow was established. Then influence of all kinds of parameters such as presonnel density, heat release of equipments and room size on the room temperature and thermal comfortable was thoroughly studied. Finally, some reasonable proposal on the designing of CDOAS was presented.The studied results show that: if the CDOAS is emploied to office room, the comfortable request may be satisfed when all the sensible heat load is undertaken by the outdoor air system. When the personnel density decreases gradually, temperature in the room would increase if the air supply rate is decided accordingto the hygienic standard with the minimum rate of outdoor air. If the indoor equipment heat release reduces, by enhanceing the air supply temperature (reduce air supply temperature difference) and reduceing the air supply rate, room temperature can be maintained. Although both above two ways can achieve the good distribution in the"personnel zoom", the way that reduceing the air supply rate may cause the value of carbon dioxide density exceeds the permission and and the comfort level of the "personnel zoom" decreaseres. If enlarge the room size in the direction of the jet flow direction, the ability of cold jet attaching, diffusing and rolling will drop, which leads the comfort level dropped.