Variation of clean air delivery rate and effective air cleaning ratio of room air cleaning devices

Abstract

Air cleaners have been normally used to remove airborne particles from indoor air, and these devices are normally rated according to their clean air delivery rate (CADR), which is a measure of the delivery of contaminant-free air. This study evaluated and compared the performance of room air cleaning devices in removing submicron-sized particles. Most of the CADRs that were experimentally obtained were lower than that stated by the manufacturer. The difference between the experimental measurements and the device specifications gradually increases as the CADR increased. For the same air cleaning device, the experimental CADR decreased as the size of the test chamber increased. The effective air cleaning ratio (EACR) was newly defined to provide an accurate measure of the CADR. The EACR is the ratio of the real CADR to the stated CADR. The experiments and simulations revealed that the EACR of the air cleaning devices was in the range of 0.70–0.83. The ECAR is little changed with respect to the size of the test chamber and the flow rate of the air cleaning devices, unlike the experimental CADR. The real CADR is affected by the filtration efficiency, the flow rate, and the design of the air cleaning device as well as the size of the test particles. The real CADR decreases as the particle size increases. Therefore, the recommended CADR of air cleaning devices for use in facilities with sensitive populations or hospitals must be higher than that for general purpose use.