Time dependent flows in displacement ventilation considering the volume envelope heat transfers

The displacement ventilation process is studied through analytical time dependent tools. The characteristic times, the interface overshot and the steady state height are analysed step by step considering heat transfers within the volume envelope. In a first step, the influence of heat losses is analysed, followed by the thermal mass (heat storage) on the displacement ventilation process. Finally, the coupling of both is considered. The analyses are done using both dimensional and dimensionless approaches in order to keep physical values for the consideration of thermal transfer in a first part and to give global view of the acting forces in a second part. Results show the great influence of both thermal losses and thermal storage on the ventilation processes. The overshot phenomenon is strongly enhanced by the thermal mass while the thermal losses limit the dynamics of the displacement process. Depending on the values of both, their coupling can result to enhancing the interface height overshot or increasing the global time scale process. Anyway, thermal transfers are important to be considered while designing displacement ventilation strategies.

► Analyses of displacement ventilation including envelope thermal transfers.
► Both dimensional and dimensionless forms are proposed.
► Characteristic times are influenced by envelope heat losses and thermal storage.
► Overshot phenomenon is influenced by envelope heat losses and thermal storage.
► Neglecting envelope thermal transfers lead to strong errors for ventilation design.