Evaluation of Long-Term Changes in HVAC Filtration Efficiency and Airflow Resistance: Implications for Indoor Aerosol Concentrations and Building Energy Consumption
Chunxu Huang, Nusrat Jung, BRANDON E. BOOR,
Purdue University Abstract Number: 257
Working Group: Indoor Aerosols
AbstractHVAC filters are an effective strategy for reducing aerosol concentrations in buildings. They can protect building occupants from exposure to aerosols of indoor and outdoor origin. The filtration efficiency and airflow resistance (pressure drop) of HVAC filters can change and evolve during their service life in commercial and residential HVAC systems. However, the performance of HVAC filters is primarily evaluated at their initial, un-aged state. In this study, long-term changes in size-resolved filtration efficiencies and airflow resistances of HVAC filters were evaluated over two years of continuous ageing under 100% outdoor air. A HVAC filter test rig was custom designed and built to age three HVAC filter banks with pre- and final-filters at a constant volumetric airflow rate of 2000 ft
3 min
-1 (3400 m
3 h
-1). Particle number size distributions from 10 nm to 10 µm were measured across each pre- and final-filter using a scanning mobility particle sizer (SMPS) and an optical particle sizer (OPS) connected to an automated valve switching system. The natural filter ageing experiment began in November 2020 and concluded in January 2023. The pre-filters were changed in January 2022. The pre-filters (all MERV8) and final-filters (MERV8, MERV13, MERV14) exhibited unique temporal trends in their performance over the two year ageing process. The pleated MERV8 pre-filters exhibited large increases in pressure drop, whereas all three final-filters exhibited comparatively smaller or negligible increases in airflow resistance. The MERV8 pre-filters became more efficient over time, while the electrostatic bag MERV13 final-filter became less efficient and the V-cell MERV14 final-filter showed no noticeable change in efficiency. The results demonstrate that initial testing of HVAC filter performance may be insufficient to predict long-term changes due to ambient aerosol loading. Temporal changes in HVAC filtration efficiency and airflow resistance over months to years must be considered in modeling indoor aerosol concentrations and HVAC blower energy consumption.