VENTILATION SYSTEMS
Navigating Australia’s new HVAC filter standard
Gregor Riese, director at Australian-based supplier of filtration, UV, and disinfection technologies for the healthcare and pharmaceutical sectors, Opira Group, discusses an important new Australian standard for the classification of filters used in HVAC systems, and advises on how to select the right one.
Standards Australia is in the process of replacing the AS1324 filter series, with the replacement of the existing G1-G4 and F5- F9 filter classifications with the ISO 16890 series (Figure 1). While at first glance, the new filter classification method appears far more complicated to apply, the new rating system is an improvement, as it better reflects the actual filter performance, and will help to ensure adequate protection from airborne particulates for occupants of health facilities. The adoption of the ISO 16890 series does not affect the Australian HEPA filter standard (AS4260) used to filter air for surgeries and areas in the hospital with immunocompromised patients.
Understanding particle size The rationale behind the new filter classification method is to better/more accurately define the particulates arrested by the filter. The old classification scheme, while simple, would give no estimate of particulate arrestance, and users would need to look up the standard to try to understand how effective these filters are. There is nothing intrinsically informative about an F5 filter versus an F9 filter and what a user could expect in terms of cleaning air.
The new filter classification method describes the particulate arrestance of the filter that is specified. An ISOePM2.5 65% has been tested to remove 65% of PM2.5 particulates (i.e. particles smaller than 2.5 microns). The same filter will remove a higher proportion of PM10 particulates, but a lower proportion of PM1 particulates. The selection of this particulate size range by ISO 16890 is deliberate, since these smaller ‘respirable particles’ (10µm or smaller) embed deep in the lungs. Exposure to PM2.5 particulates has been
linked to heart disease, stroke, lung cancer, chronic lung disease, and respiratory infections. The soon-to-be-published ISO/ AS 16890 classification method challenges a filter with 12 different particle sizes in the 0.3 µm to 10 µm size range. For reference, a fine human hair is between 50 and 70 µm in size, while respirable dust is generally so small to be invisible to the naked eye (Figure 2). The smallest particle tested (0.3µm) is in the pathogen size range, and typical of the size of many smaller bacteria, while the largest particle (10 µm) is typical of smaller dust particles, pollen, and mould. For a filter to be classified in accordance with the ISO 16890 method, it needs to capture at least 50% of one of the three
PM2.5
HUMAN HAIR 50-70 µm
(microns) in diameter
Combustion particles, organic compounds, metals etc.
<2.5 µm (microns) in diameter
Figure 1: AS1324 is being replaced by ISO/AS16890.
main particulate classes: ePM1, ePM2.5, or ePM10. The ‘e’ denotes the efficiency of the filter to that size category of particle. The ISO/AS 16890 standard will also have a fourth category called ‘Coarse filters’ – for those which do not meet a minimum ePM10 arrestance of 50%. For example, if a tested filter only captures 40% of the ePM10 particles, then it can be classified as a ‘PM Coarse 45%’ filter. Course filters are not recommended for most HVAC applications. Figure 3 seeks to show a visual
PM10
Dust, pollen, mould etc. <10 µm (microns) in diameter
Influenza 0.1 µm
representation of this filter classification method. Once a filter has achieved the 50% arrestance threshold in that particulate category, it will be specifically classified in terms of its % arrestance of the particle size range (i.e. ePM1, ePM2.5, or ePM10). This is denoted as a % arrestance in 5% increments – for example ‘ePM1 55%’.
90 µm (microns) in diameter FINE BEACH SAND
Figure 2: Particle sizes in the micron range. 34 Health Estate Journal August 2024
Rhinovirus 0.03 µm
Application of the correct ISO filter classification The application of the correct ISO filter classification based on particle arrestance
Source: US EPA
Source: Table 5.1, DA15, AIRAH Guide to Air Filters and Cleaning Devices
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