Modeling the impact of residential HVAC filtration on indoor particles of outdoor origin (RP-1691)

Abstract

Much of human exposure to airborne particles of outdoor origin, including fine particles smaller than 2.5 μm (PM 2.5 ) and ultrafine particles smaller than 0.1 μm (UFPs), occurs in residences. High-efficiency central HVAC filters are increasingly being used in residences, but questions remain about their effectiveness in reducing indoor PM 2.5 and UFPs of outdoor origin in homes operating under realistic conditions (e.g., with HVAC systems operating only to meet heating or cooling demands). Here dynamic building energy and indoor air mass balance modeling are combined to estimate the impacts of 11 HVAC filters (minimum efficiency reporting value [MERV] 5 through high-efficiency particulate air [HEPA]) on indoor concentrations of PM 2.5 and UFPs of outdoor origin in multiple vintages of prototypical single-family residences relying on either infiltration or mechanical ventilation systems in 22 U.S. cities. Results demonstrate that higher-efficiency HVAC filters can meaningfully reduce indoor proportions of outdoor PM 2.5 and UFPs inside residences, but home vintage, climate zone, and ventilation strategy strongly influence the outcomes due to widely varying air exchange rates, HVAC system runtimes, and sources of ventilation air. Higher efficiency filters had a greater impact in older, leakier homes relying on infiltration alone and in new homes relying on supply-only mechanical ventilation systems designed to meet ASHRAE Standard 62.2.

Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions

“…This is a critical distinction to consider that, if not accounted for, can lead to rather large overestimations of ePM 2.5 and ePM 10 for indoor particles of outdoor origin if one uses only the 100% outdoor air assumptions in ISO 16890. It may be more appropriate to first account for transformations that occur during outdoor-to-indoor transport, rather than relying on ePM reported according to ISO 18690, if one is to estimate ePM removal efficiency of a filter for particles of outdoor origin for use in a building that relies on infiltration for ventilation air (which includes the vast majority of residences in the US, for example), as several studies have done recently [45][46][47][48][49]. It is also worth noting that the absolute differences in ePM 2.5 and ePM 10 were smaller for the MERV 14 filter, because the filter has a removal efficiency of almost 100% for particles larger than 3 µm, and over 90% for 1-3 µm particles (Figure 4).…”

Fine and ultrafine particle removal efficiency of new residential HVAC filters

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Central heating, ventilating, and air-conditioning (HVAC) filters are increasingly being recommended to reduce exposure to airborne particulate matter in buildings, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] including in residences where the majority of exposure to particulate matter of both indoor and outdoor origin often occurs. 16 In the United States, the three most common rating systems that manufacturers use to characterize and market their residential particulate air filters include the following: MERV (Minimum Efficiency Reporting Value) from ASHRAE Standard 52.2 17 ; MPR (Microparticle Performance Rating) from 3M; and FPR (Filter Performance Rating), which is exclusively used for filters sold by the retail store, The Home Depot.

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In‐situ effectiveness of residential HVAC filters

“…This is because, generally, most systems cycle on and off to meet conditioning needs and median system on time fractions (runtime) have been reported as 9.6% and 18% in two recent investigations . To mitigate this limitation, some studies (eg,) provide important perspectives on the long‐term performance of residential filters through modeling approaches considering realistic system runtimes. However, most of these modeling studies rely on simple assumptions for most input parameters, such as filter efficiency, even though it is temporally dynamic .…”

“…[1][2][3][4][5][6][7] Particulate matter (PM) reduction impacts of residential filters have been assessed in a series of measurement and modeling investigations in the literature. 4,5,[7][8][9][10][11][12][13][14][15][16][17][18][19][20] In situ field testing is a common measurement approach, which involves measuring the overall particle loss rates in homes with and without a filter installed, or with a filter while HVAC system is on vs. when it is off to calculate filter effectiveness, H, 21 as shown in Equation (1).…”