Integration of a thermal aerosol generator into a full-scale HVAC filter test rig for aging filters with representative urban aerosol size distributions (RP-1734)

HVAC filter performance is significantly influenced by the physicochemical properties of the aerosol the filters encounter. HVAC filters play a critical role in maintaining indoor air quality by removing airborne particles, making it essential to accurately simulate real-world filtration conditions during standardized testing. Among aerosol properties, the particle size distribution (PSD) is a key factor governing filter loading behavior and efficiency. However, current standardized protocols rely primarily on coarse-mode loading dusts that poorly represent the submicrometer number and mass PSDs characteristic of urban atmospheric aerosol. The overarching goal of ASHRAE RP-1734 is to develop a novel methodology for rapidly aging HVAC filters by simulating their pressure drop evolution over their service life, enabling more accurate assessments of blower energy consumption and informing optimal filter replacement schedules. As part of this effort, the present study evaluates the integration of a thermal aerosol generator (TAG) with a full-scale HVAC filter test rig and assesses its suitability for filter loading applications. Controlled experiments were conducted to characterize in-duct number and mass PSDs under varying operational conditions, including volumetric airflow rate, relative humidity, and salt stick feed rate. The TAG-generated aerosol exhibited a stable unimodal distribution, with a submicrometer peak near 100 nm in the number PSD and 150 nm in the mass PSD, with only minor shifts in modal diameter across operational conditions. Notably, the number PSDs closely aligned with those observed in urban environments. Although the mass PSDs differed by approximately 100 nm from typical urban aerosol mass PSDs, they still effectively captured the submicrometer fraction, especially when compared to standardized coarse-mode loading dusts. This study demonstrates the TAG’s ability to generate stable, reproducible PSDs across diverse conditions, enabling realistic simulation of urban aerosol properties in a controlled laboratory setting. Incorporating TAG-generated aerosol into standardized HVAC filter testing protocols offers a more representative approach to evaluating filter performance and informs the design of filters that enhance indoor air quality in urban environments.