In situ efficiency of filters in residential central HVAC systems

Abstract

High‐efficiency filtration in residential forced‐air heating, ventilation, and air conditioning (HVAC) systems protects equipment and can reduce exposure to particulate matter. Laboratory tests provide a measure of the nominal efficiency, but they may not accurately reflect the in situ efficiency of the filters because of variations in system conditions and changes in filter performance over time. The primary focus of this paper is to evaluate the effective filtration efficiency, which is inclusive of any loading and system impacts, in 21 occupied residential homes through in‐duct concentration measurements. We considered the role of filter media by testing both electret and non‐electret media, as well as the role of loading by considering new and used filters. The results show that filters with higher nominal efficiency generally had higher effective filtration efficiency in the same home. In terms of performance change, there is no significant difference in efficiency between initial and 3‐month non‐electret filters, but the efficiency of electret filters generally decreased over time. However, both nominal efficiency and performance change were vastly overshadowed by the wide variety in loading and system conditions across homes, making it hard to predict filter efficiency in a given home without in situ measurements.

Quantitative filter forensics: Size distribution and particulate matter concentrations in residential buildings

“…(1). With lower filtration volumes resulting from low system runtimes, 23,27 there are also smaller loss rates of particles from indoor air by filtration causing higher TSP concentrations. Other differences between the two studies were population statuses (ie, a high proportion of low socioeconomic status in Givehchi et al), home floor areas, home ages, filter nominal efficiencies (MERVs 7‐8 in Givehchi et al), and climate (ie, cold and dry in Toronto vs hot and humid in Central Texas).…”

“…k x , the HVAC metadata parameter, is the product of η x and K. η x is the in-situ filter efficiency by size distribution (-) calculated based on upstream and downstream particle concentrations for PM 2.5 and PM 10 which was averaged between new and used filters. 27 We assumed that the efficiency for TSP was 100% for all filters because the volume of most of the recovered particles was greater than 10 µm (see Section 3). K is the filtration volume (m 3 ), the volume of air passing through the filter during its service life.…”

“…( 1). With lower filtration volumes resulting from low system runtimes, 23,27 there are also smaller loss rates of particles from indoor air by filtration causing higher TSP concentrations. Other differences between the two studies were A wide variation in both m TSP and k TSP −1 allowed us to test the predictability of QFF concentrations (C TSP ) by these two first-order parameters according to Eq.…”

Filter evaluation and selection for heating, ventilation, and air conditioning systems during and beyond the COVID ‐19 pandemic

“…3 Filters, such as those rated with a minimum efficiency reporting value (MERV), are commonly used in HVAC systems to capture particles on filtration fibers. [3][4][5][6][7] In addition, electrostatic enhanced air filters (EEAF) can assist particle removal by active ionization. 4,8,9 In January 2021, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommended a MERV of no less than 13 filters for building HVAC systems, 10 to reduce the transmission of indoor infectious airborne viruses in heating, ventilation, and air conditioning (HVAC) systems during the COVID-19 pandemic.…”

“…High-efficiency filtration systems in heating, ventilation, and air conditioning (HVAC) systems play a vital role in controlling indoor air quality by removing various indoor air pollutants, such as particulate matter (PM), microorganisms (e.g., bacteria and viruses), and gaseous pollutants. 3 Filters, such as those rated with a minimum efficiency reporting value (MERV), are commonly used in HVAC systems to capture particles on filtration fibers. [3][4][5][6][7] In addition, electrostatic enhanced air filters (EEAF) can assist particle removal by active ionization.…”