Evaluation of Horizontal Recirculatory Air Curtain Efficiencies: Cooler to Conditioned Space

Abstract

Air curtains have long been used to reduce losses from high traffic doorways in cold storage facilities. Different varieties of air curtains have been used including vertical (down blast) non-recirculatory, horizontal non-recirculatory and horizontal recirculatory. The effectiveness of air curtains to provide thermal separation between rooms of differing temperatures has long been a matter of debate. Previous experiments have been done to determine the effectiveness using tracer gas decay methods. This paper will evaluate the thermal effectiveness of the horizontal recirculatory air curtain when applied in a typical cooler application using an environmental chamber. This allowed testing of the air curtain’s ability to reduce infiltration on the actual thermal envelope. A vertical non-recirculatory air curtain was also evaluated for comparison purposes. The air curtains were tested in an environmental chamber that was divided into two rooms of differing temperature. The chamber was instrumented to measure all energy transfer into and out of each room. The cold room was maintained at a temperature of 4°C (39°F) and the warm room was maintained at a temperature of 24°C (75°F) and 60% RH throughout all tests. Three phases of testing were conducted for each air curtain to completely evaluate all energy losses — a completely closed doorway test for calibration, a completely open doorway test with no air curtains and an open doorway test with the air curtains adjusted and running. Completion of the testing revealed the horizontal recirculatory air curtain had a thermal efficiency of 71% while the vertical non-recirculatory air curtain had an efficiency of 38%. The results were slightly lower than theoretical calculations which may be attributable to chamber size. Additional tests were conducted using a smaller doorway for comparison. Applying the results from the smaller doorway yields an effectiveness of 76.2%. Using the theoretical open doorway energy loss yields an effectiveness of 80%. Paper published with permission.