HVAC filter testing

Central HVAC filters are often a dominant mechanism for particle removal in buildings, but little is known about filter performance in real environments, particularly in residential and light-commercial buildings where particle concentrations and compositions can be very different from laboratory test conditions. We continue to advance applied research in HVAC filtration and summarize some of that work here.

New research at IIT

Measurements. We are currently working to build a database of size-resolved single-pass particle removal efficiencies for a large number of commercially available filters for use in residential and light-commercial buildings. The measurements are relatively simple: we elevate particle concentrations in one of our unoccupied apartment units and measure size-resolved particle concentrations from ~10 nm to ~10 µm with both a Scanning Mobility Particle Sizer (SMPS) and an Optical Particle Sizer (OPS). Realistically, we can typically calculate removal efficiencies for particles from 10 nm to about 3 µm, which provides a great dataset for both fine and ultrafine particles. We currently have 16 commercially available filters tested and will continue to update the dataset here.

Download the current version of the dataset here:

Modeling. In 2014, we published a paper in Atmospheric Environment in which we used nearly 200 outdoor particle size distributions (PSDs) from all over the world in the existing literature to estimate single-pass HVAC filter removal efficiencies for both fine particles (i.e., PM2.5 mass) and ultrafine particles (UFPs: <100 nm) of outdoor origin. Results from this work are designed to be used to simplify indoor air quality modeling efforts and inform standards and guidelines.

Acknowledgements for IIT research

This research at IIT has been funded by ASHRAE via Research Project RP-1299, a New Investigator Award to Brent Stephens, and a Graduate Student Grant-in-Aid to PhD student Torkan Fazli.


Previous research from UT-Austin

In two different papers from 2012 and 2013, we worked to explore differences in HVAC filter test protocols and refined a whole-house method for in-situ testing of filters for size-resolved particle removal efficiencies. The test method consisted of (1) artificially elevating indoor particle concentrations and (2) measuring the subsequent concentration decay with and without a filter installed in the operating HVAC system, all while simultaneously measuring the air exchange rate (AER) through the building by tracer gas decay. The total particle deposition rate (to indoor surfaces and HVAC components) was thus measured for each HVAC condition, and particle removal efficiencies were calculated by comparing the differences in deposition rates between conditions. In the first study, removal rates for six different particle sizes from 0.3 to 10 µm generally increased with increasing rated filter efficiency:

Particle loss rates for six different size bins and five different filter/HVAC conditions

Results from the in-situ method were also compared to results from a simple upstream-downstream method for three types of commercially available filters in an unoccupied test house. Results from both field methods were compared to standardized laboratory test results as measured by an independent laboratory and as reported by the manufacturer, again for 0.3 to 10 µm particles:

Filter removal efficiency measured with four different test methods

In general, comparisons between filter efficiency as measured by the refined whole-house method and as measured by the upstream-downstream method resulted in similar values of particle removal efficiency for many particle sizes and compared well with standardized lab tests, although experimental uncertainties were generally greatest for the whole-house method. However, the refined whole-house method has the added benefit of allowing an investigation of more particle interactions in an indoor environment, including deposition to ductwork and other HVAC system components, exfiltration by duct leakage, and bypass airflow around filters. Both field methods can be used to investigate the effects of HVAC system characteristics and dust loading on filter efficiency in real environments.

In the second paper, the same validated test method was applied in the same test house using six different HVAC filters: MERV 4, 6, and 11 (1-inch filters) and MERV 10, 13, and 16 (5-inch filters). This time we focused explicitly on ultrafine particles (particles less than 100 nm in diameter), which are not measured in commonly used HVAC filtration test standards. Size-resolved removal efficiencies for the six filters are shown below:

Size-resolved particle removal efficiency for six residential test filters

Size-resolved particle removal efficiency for six residential test filters

Read the full papers from the UT-Austin work published in (1) Aerosol Science and Technology in 2012 here and (2) Indoor Air in 2013 here.

Acknowledgements for UT-Austin research

This work was performed by Brent Stephens while he was a Ph.D. student under the supervision of Dr. Jeffrey Siegel at the University of Texas at Austin. Portions of this work were funded by the National Science Foundation (IGERT Award DGE 0549428) and by a Continuing Fellowship from the Graduate School at the University of Texas at Austin. We thank Kevin Kinzer at 3M for providing laboratory testing of filters for the first paper and Mark Jackson for providing filters for testing in the second paper.