A general model (semi empirical) to predict temperatue efficiency of displacement ventilation systems.

Temperature efficiency is an important index to estimate the ventilation effectiveness. Usually ,the temperature efficiency is determined through field or model tests such as gas-tracing technology. The heat source structure(location, size, heat emission, etc) has a strong effect on the temperature efficiency. The heat sources present themselves or may be arranged in three basic models:(A)heat sources uniformly distributed in the space; (B) heat sources uniformly distributed on the floor; (C)concentrated heat sources at the bottom of a room. Based on the literature and our previous long time work by experimental and CFD technology on the indoor upward air supply systems, the ventilated space temperature distributions can be classified into several typical patterns according to different indoor heat sources conditions. Then the thermal stratification heights of the displacement ventilation are analyzed and determined. Based on the analysis and experimental data, the temperature efficiency is proven to closely correlate with the thermal stratification height Z, the room radiation transfer factor R, the room volume V as well as the ratio of source to floor area f/F. The semi-empirical equation of temperature efficiency for a ventilated room with a plate heat source is proposed. A general model to predict temperature efficiency of displacement ventilation systems is obtained. Some practical examples agree satisfactorily with experiment results.