When ASHRAE Standard 52.2-1999 was written, Standard Project Committee 52.2 recognized that the first dust loading step, also called the conditioning step, was not fully adequate for revealing the drop in efficiency that electret filters undergo during actual use. This is pointed out in the standard's foreword: "The initial conditioning step of the dust-loading procedure described in this standard may affect the efficiency of the filter but not as much as would be observed in actual service." To address this issue, and a related issue with high voltage electronic air cleaners, an ASHRAE research project was undertaken, 1190-RP "Develop a New Loading Dust and Dust Loading Procedures for the ASRHAE Filter Test Standards 52.1. and 52.2."
An aerosol-based laboratory method was developed to reproduce the drop in efficiency that electret filters can undergo with use. The method exposes the filter to a high concentration of solid-phase (i.e., dry) submicrometer salt aerosol particles. The approach successfully reveals the drop in efficiency for both low- and high-efficiency electret filters. To address differences seen in an interlaboratory comparison, additional qualification criteria were added to the conditioning procedure; however the adequacy of these additional criteria was not evaluated on the project. The conditioning procedure may also reduce the measured weight gain of some filters relative to the current 52.2 procedures. A draft addendum to ASHRAE Standard 52.2 was prepared. Incorporating this new conditioning procedure into the 52.2 test standard would allow the standard test to better reflect the minimum efficiency performance of electret filters that may be experienced during actual use.