Influence of cross-jet temperature and pressure differences on the separation efficiency of air curtains in buildings

Air curtains (ACs) are of interest in building applications to support energy efficiency and air quality by restricting heat and mass transport across continuously open entrances. Environmental conditions to which ACs are generally subjected, such as differences in temperature and pressure, induce loads on ACs that alter their flow pattern, hence can considerably influence their separation efficiency. Therefore, proper design and implementation of ACs demands detailed knowledge of the impact of these parameters both individually and combined. This is addressed here by a systematic evaluation of the AC separation efficiency under moderate environmental temperature (5 °C ≤ ΔT ≤ 25 °C) and pressure (1 Pa ≤ ΔP ≤ 8 Pa) difference conditions. RANS CFD simulations of an AC are conducted on verified computational grids, validated with experimental data and calibrated with field measurements. Results show a strong yet non-linear dependency of AC performance on environmental parameters and indicate there is an optimal separation efficiency (based on total mass transfer) in which competing effects between a given jet momentum flux on the one hand and cross-jet loads caused by temperature or pressure differences on the other hand are counterbalanced. Findings suggest to dynamically control the supplied AC jet momentum as a function of variable environmental conditions in order to continually deliver an optimal performance.