METHOD FOR IMPROVING THE EFFICIENCY OF AIR CURTAINS INSTALLED AT BUILDING ENTRANCES

Abstract

　The energy consumed by air-conditioning is large in convenience stores that are open 24 h. This is because the air-conditioning load caused by the infiltration of outdoor air through the entrances is particularly large. This study investigates the sealing efficiency of air curtains in reducing the air that infiltrates through doorways in stores by using CFD simulations and experiments. In particular, this study focuses on double air curtains in which two air curtains are installed on both the outdoor and indoor sides, and the sealing efficiency of the double air curtains is compared with that of normal single air curtains.

　If the air curtain is installed at the top of the door, the airflow from the air curtain to the floor affects the efficiency of the air curtain. When the air curtain is installed on the outside, the outdoor air from the air curtain reaches the floor and partially enters the interior. When the air curtain is installed on the inside, the indoor air from the air curtain reaches the floor and partially exits. When air curtains are installed on both sides, the infiltration of outdoor air and the exfiltration of indoor air can be small. The results of this study are as follows:

(1) CFD simulations were conducted using a model comprising an experimental room and its surrounding large space. Summer or winter conditions were set as the initial temperature condition of the experimental room and the surrounding space, and the temperature variation was simulated. Under both summer and winter conditions, the sealing efficiency of the double air curtain was higher than that of the single air curtains.

(2) CFD simulations were performed under various supply air velocity conditions of the double air curtain. The results showed that a high-velocity supply air generated an imping jet in the vicinity of the floor under the air curtain, and the indoor and outdoor air were mixed by turbulence. In contrast, when the supply air velocity was low, the supply air did not reach the floor, and the sealing efficiency was low.

(3) The experiments were conducted under conditions similar to those of the CFD simulations, and the sealing efficiency was calculated using the measured temperature of several points. Under the summer conditions, the sealing efficiency of the double air curtain and the single outside air curtain was high, and the efficiency of the single inside air curtain was low. However, under the winter conditions, the efficiency of the double air curtain and the single inside air curtain was high, and the efficiency of the single outside air curtain was low. The double air curtain had a high efficiency under both summer and winter conditions.

(4) When the human body moves through the entrance, it causes an air disturbance and may decrease the sealing efficiency of the air curtain. In this study, the influence of air disturbance on the air curtain efficiency was investigated using a moving body CFD simulation. The infiltration of outdoor air increased when the panel entered the interior. The exfiltration of indoor air increased when the panel moved outward. In the case of the double air curtain, both the infiltration and exfiltration air volumes were smaller than those in the single air curtain cases.