Not all boxes are equal: Investigation of parameters affecting PM2.5 particle removal by the Corsi-Rosenthal box

Abstract

The Corsi-Rosenthal (C-R) box has gained widespread popularity as an affordable, do-it-yourself air cleaner designed to improve indoor air quality. Despite its rapid adoption, limited studies have evaluated how different operational and experimental variables affect the C-R box's efficiency. This study investigated the Clean Air Delivery Rate (CADR) of the C-R box as a function of filter rating, its electret enhancement, measurement interval, location, and type of measurement devices, and additional air mixing when removing PM_2.5 sodium chloride (NaCl) or Arizona Road Dust (ARD) particles in a 3024 ft³ (∼86 m³) room. Based on measurements by a research-grade MiniWRAS (1371, DURAG Group, Hamburg, Germany), the C-R box with four 2-inch MERV-13 filters achieved a CADR of 358.56 ± 10.58 cubic feet per minute (cfm) at its highest fan speed, outperforming MERV-8 filters (209.93 ± 9.30 cfm) by 71 % despite only a 41 % increase in filter cost. MERV-13 filters with an electret designation did not improve CADR compared to plain MERV-13 filters. When challenged with ARD particles, the C-R box achieved a CADR of 416.60 ± 8.31 cfm: 15 % higher compared to NaCl particles. We also observed that moving the C-R box farther away from the measurement devices (140 inches vs 65 inches) led to a decrease in CADR by ∼8 %. However, using additional mixing fans helped improve CADR in the room's corners by up to 21 %. Comparison of CADR determined by an out-of-the-box consumer-grade AirVisual monitor with MiniWRAS showed that the AirVisual yielded the same trends, albeit at a ∼14 % higher CADR. Our investigation of variables affecting the measured C-R box's CADR will help optimize its performance and improve data comparison across studies. We also demonstrate that consumer-grade monitors are a viable option in investigating the performance of air cleaners, especially their localized performance.