Numerical investigation of the thermal efficiency of a multi-nozzle air curtain doorway under different wind conditions

Loading gate openings cause thermal inefficiency due to the substitution of indoor-outdoor air in cold seasons, and as a consequence, escalating energy consumption of warehouse buildings or unloading docks. Research findings have demonstrated that air infiltration/exfiltration through open doors results in the loss of a quarter of annual heating loads in buildings. Air curtains have shown a bright and promising future to compensate for the infiltration rate through the door opening, however, the most prior investigations were allocated to the jet planar air curtains and as yet there is a gap in the literature for other modified air curtain devices, including multi-nozzle air curtains (MNAC) with higher induction and resistance against the strong frontal winds, especially for gates higher than 4.27 m of installation height. Hence, in this work, designed MNAC with various configurations (i.e. large nozzles, small nozzles and holes) and installed on a warehouse loading gate was first characterized using the validated numerical turbulence model, SST (k−ω), to solve governing equations. The validate model is then used to evaluate the MNAC thermal efficiency, using the sensible energy gained by the inside zone, under various outside temperatures (−5, −10, −20, and −30∘C), and two wind conditions (i.e. with and without a front wind as recommended by ASHRAE (2010)). While the air curtains demonstrated limitations in fully controlling the infiltration rate during extremely cold and windy conditions, the results indicate that the MNAC systems have obtained thermal efficiency values higher up to 10% when compared to conventional planar air jets.