AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Failure (and Promise) of Residential Filtration
JEFFREY SIEGEL, University of Toronto
Abstract Number: 213 Working Group: Indoor Aerosols
Abstract Approximately three quarters of American homes have forced air heating and/or cooling systems. Most of those systems, which primarily recirculate indoor air and serve no ventilation function, employ a filter to remove particulate matter from indoor air. A substantial fraction of homes use filters that are predominantly intended to remove very large particles, largely to protect the HVAC equipment rather than improve health. However, recent years have seen an increased emphasis on higher efficiency filters, which are intended to remove health-relevant particles. However, there is a broader question about whether high efficiency filters can actually protect human health. There are many barriers to filter efficacy including the fundamental limitation that most systems only use their fan when there is need for heating or cooling. In periods of time when the weather is moderate, systems do not operate and air is not filtered. Even in more extreme weather conditions, many systems operate much less than half of the time. A second set of issues arises from system design, installation, and operation. Air volumetric flow rates vary considerably between homes and conditioning modes and, in many homes, there may be insufficient air flow through the filter to result in measurable cleaning. Many American homes also locate ducts outside of the conditioned space and ducts often leak. This results in the entrainment of air from buffer zones such as attics and crawlspaces as well as increased infiltration of outdoor air because of the resulting pressure differences. Even in well-designed and properly installed systems, the filter itself often does not perform as anticipated. Filter bypass (air that goes around the filter) and filter efficiency degradation are ubiquitous. If these challenges are addressed, filtration can offer indoor air quality benefits in residential environments where we spend over 65% of our time. This presentation takes a fundamental view of aerosol removal to filters and a systems view of residential recirculating systems and utilizes data from over 10,0000 North American homes to demonstrate both the current impact of filtration and the potential impact that could be realized if system operation was optimized.