Restriction of Air Infiltration by an Air Curtain Optimized with Secondary Jets: A Numerical Investigation

Infiltration of unconditioned air through access openings and entrance doors with high recurrence can cause detrimental impacts to the energy performance, air quality and thermal comfort of buildings. Air curtains are of strategic importance to attenuate these negative impacts. In addition, air curtains are relevant in specialized HVAC applications for which the impediment of infiltration is also essential (e.g., reduction of smoke propagation in fire events, decrease of contamination hazard in clean rooms, preservation of refrigeration properties in cold rooms). A common performance indicator of an air-curtain system is the separation efficiency, which relates to the rate of heat or mass transfer between the two environments that are separated by the air curtain. The jet parameters have a large influence on the momentum and mixing/entrainment processes that take place in the jet, ultimately affecting the separation efficiency of air curtains. However, to the best of our knowledge, information in the scientific literature is focusing mostly on the analysis of air curtains with single jets. Therefore, this study addresses a preliminary investigation of the implementation of secondary co-flowing jets in air curtains as an approach to modify the jet characteristics to restrict jet entrainment and improve the separation efficiency of air curtains. Reynolds-averaged Navier-Stokes (RANS) simulations are performed to analyze the effect of modifying one of the major parameters of secondary jets (i.e., velocity ratio R) on the air-curtain separation efficiency. The simulation results indicate that reasonable improvements of 4.3% in the air-curtain separation efficiency based on infiltration can be obtained with the incorporation of secondary jets under certain jet discharge conditions.