Recently there have been significant changes in the normally sleepy world of filter test standards and overall building “wellness” ratings.
Greater focus has been placed upon cleaner indoor and outdoor air, driven by increased awareness of air pollution and the negative health impacts of personal exposure to harmful airborne particles.
When it comes to appropriate filter selection for your building, competing standards and suppliers start to create a muddy situation. In this article, we seek to bring a little clarity to what has changed and what remains the same.
At the core of all these standards, guidelines, ratings and methods – are various sized test materials referred to as “dust”. Test material dust is comprised of synthetic particle mixtures or generated liquid and/or solid particles, known as aerosols etc.
These test materials, which are of a known composition and size, are what filters are subjected to within a test rig. Methods of test and ratings vary, but the fundamental of all is the following: an artificial aerosol is blown through a filter at controlled situations, and what is captured or breaks through is measured.
These tests are a valid guide – but they do not assure a perfectly accurate picture of the IAQ (indoor air quality) of your individual site. There are many significant factors beyond the quality of a filter in determining IAQ. This includes the indoor and outdoor environment, air distribution system configuration, amount of fresh air vs recycled air, building occupation levels and activities, site location and the time of the year.
The various test methods and rating systems, do allow a general comparison between various products, and give guidance to general performance expectations. They are useful, as long as the user realizes that they are relevant for valid choices between one level of filter to another within a given filter manufacturers range. However, from manufacturer to manufacturer, they can provide misleading information at times.
The three main standards used globally for commercial building filtration are ASHRAE 52.2, EN779 and the recent ISO 16890   . Additional standards also exist for the measurement of HEPA level filters in specific applications. These are EN1822 and ISO 29463.
Many advocates of a given standard vs. another will suggest that their favoured standard is more “real world” or “more rigorous” or “more detailed” or “easier to interpret”. To some extent, these opinions are all correct. Most of the standards do a pretty good job of measuring standardised performance and relating it to a rating system. However, no one standard or system is perfect, and will not monitor the actual air quality levels of individual buildings or user sites.
The most significant factor to be aware of is that while each of the ASHRAE 52.2 and EN779 standards run one test type to provide a single value rating, the recent ISO 16890 standards provide three percentage results for the three particle sizes to provide a rating.
The method for discharging the initial static charge from a filter to allow fair testing varies from standard to standard. If any static remains, it will allow the filter to initially perform better during testing. It has been argued that the ISO 16890 standard has the most comprehensive and “fair” method for discharging initial static from filters.
The real issue with each standard is more related to attempts by various filter manufacturers to gain competitive advantage, than the standard itself. For the single number rating standards, lower cost products can be optimised to “just” pass the test for a given level. Or perhaps a filter might be tested to a standard with poorer static discharging methods to make it look better.
Whatever the rating system, filters will have some form of rating on them, so that a comparison can be made between the filters within a given manufacturers range. Over time, “translation” tables will inevitably be released by the various filter manufacturers, rating the various filters within their range against each standard.
It is difficult to make a direct comparison between the various standards, as the test measurements and classification criteria for each standard is different – and there is currently no “official” standard table available.
This is one of the initial example translation tables comparing the equivalent ratings of ASHRAE 52.2:2012, to EN779:2012 to ISO 16890:2016. Note: that all figures, descriptions, references and technical data are not binding and may be subject to change.
The quality of the air supplied into any building is ultimately defined by three parameters; the efficiency of the filter, the quality of installation and the condition of the air prior to the filter.
Assuming fair testing and effective installation, a filter of a given rating will remove a given percentage of dust for varying dust sizes. If the installation of the filter is poor and air is allowed to bypass, the filter efficiency will be reduced.
Depending on the application, the relevant standards, and the air conditioning requirements, the air prior to the filter consists of either inside air, outside air or often a combination of both. The ratio of inside air to outside air plays a big role in determining the level of particulate concentration which will challenge the filter.
The concentration of particulates in the outside air will vary due to the season of the year, geographic location of the building and proximity to dust generating environments such as construction sites.
In addition to the filter itself and the quality of installation, indoor air quality is also affected by the building use (e.g. office or workshop), the density of occupation, and the rate in which air is recirculated past a filter.
Realistically, as the condition of the air prior to the filter for any given building is hard to predict, filters are either over designed which consumes excessive energy, or under designed which provides inadequate indoor air quality. The industry is moving towards PM1, PM2.5 and PM10 monitors on filtration units so the level of filtration can be adjusted after the original installation to suit the desired indoor air requirements.
In the end the user needs to ask – what particle size am I really trying to capture? And to what concentration level do I want this particle size reduced?
Particles do naturally fall into some “size categories”, the most common classifications by organisations like EPA (Environmental Protection Agency), WHO (World Health Organisation) and EU (European Union) include, PM2.5 and PM10. The recent ISO standard uses terms of ePM1, ePM2.5 and ePM10. Surprisingly – these terms have different definitions of the materials.
The WHO, EPA, EU classification of PM10 and PM2.5 is defined as particulate matter that passes through a size selective inlet with a 50% efficiency at the cut-off aerodynamic diameter (PM10 – 10um, PM2.5– 2.5um).
The ISO 16890 standard defines ePM, as particles larger than 0.3um and smaller than the rating 
The differences are subtle, but it is important to note – there is not an automatic, direct, 100% correlation with all the health based studies using the WHO definition and the ISO 16890 ePM values.
PM1 particles have gained notoriety, with the recent levels of city exposure to fine diesel particulate production from modern, low emission diesel and the associated fuel blends. The composition of PM1 particles is generally sourced from diesel exhaust residue and/or other sources of industrial fines, often involving metals like lead or similar oxides. Diesel engine exhaust particles are sized below 1.0um in diameter and have a Group 1 IARC (International Agency for Research on Cancer) classification labelling them as carcinogenic to humans.
Filtration systems for commercial or residential buildings that remove these ultra-fine particles are desirable, where likely exposure levels to these PM1 particles are high. Any quality filter of a higher than MERV13, or F7 or ISO ePM1 50%, should provide measureable improvements in this area – when used correctly. It’s not critical what the rating system is – just that the filter is “fit for purpose” to capture these fine particles.
If a particular environment has a lower level of initial PM1 or PM2.5 dust, the efficiency of the filter required to achieve the same indoor air quality decreases.
Coarse dusts greater than PM2.5 are often removed by pre-filters to protect finer filters that are downstream, protecting them from excessive load and premature failure. These course pre-filters are also commonly used as the sole filter in fan coil units where only recirculation air is being filtered; this is because the fine dust levels are expected to be low. Choices could include MERV 6-7, G4, ISO COURSE 90 or MERV 8-9, M5, ISOePM10 50%
PM2.5 is another focus point for ratings. It is more completely studied and documented than PM1, and is primarily caused by combustion / burning fuels (sources include power plants, vehicles, wood burning stoves, wildland fires).
According to ISO 16890, 70-80% of what is regarded as PM2.5 is actually PM1 material. So, as a guide, most of the medical and environmental studies that give well documented results for PM2.5 actually relate to the more recently fashionable PM1. As such, it’s highly likely that most of the injurious effects of these particles – lie in the “finer” levels of material, and its various compositions. There is good evidence that “where” the particle comes from relates to its harm as well – particles of the same size, may be silica, carbon or lead – each has its own severe but different potential health impacts.
For general HVAC applications the total cost of ownership is really not driven by the price of the individual filter, as change out costs and energy costs are often 70-80% of the lifetime cost. As a rule of thumb, changing filters sooner rather than later will be a better cost choice to help save money and energy.
Similarly, one of the common mistakes with selecting a “cheap” filter is that it has less surface area, fewer pockets or lower pleat count. For a given media efficiency, lowering the surface area will increase pressure drop and so increase operational costs, far more than was “saved” on the filter. Low pressure drop filters are generally more expensive as they will simply have more media and therefore surface area.
Dust holding capacity also figures in the total ownership cost, as the more dust a filter can hold whilst maintaining a lower pressure drop will decrease the lifetime energy consumption. Generally, more expensive filters may use a different material for the media which allows a greater dust holding capacity relative to pressure drop.
Various building performance rating systems such as the GBCA (Green Building Council of Australia) Green Star and Federal Government NABERS (National Australian Built Environment Rating System) have addressed the energy consumption of buildings. A new standard by the IWBI (International WELL Building Institute) known as the WELL Building Standard addresses the energy consumption of buildings, as well as simultaneously measuring and rating the practical performance.
The WELL Building Standard – developed by the International Well Building Institute, covers a more complete perspective of the overall building, light, water, air, comfort etc. – which are included in a rating matrix.
The standard has a set of specific minimum goals required for IAQ known as “P – Preconditions” that are required for the building to pass. In addition to this, there is also “O –Optimisation” goals for superior comfort and a higher rating.
Air Concepts for the WELL Standard”
The air sections described within this table are relatively informative group goals for particles and chemical issues that are now partially covered by a variety of codes and standards in Australia – including the regulated BCA (Building Code of Australia).
|Typical (P) preconditions for air quality include:
|Some of the (O) optimisations include:
It remains to be seen what the adoption level of the guideline and certification is, however, it certainly points to the trend to have more complete “whole environment” perspectives to the places where we live and work.
Ultimately, a great deal of well-intentioned effort goes into the establishment and promotion of various test standards. Almost all have their merits and blind spots. For most users, the general trends of “good, better, best” for filters measured by a given standard, allows for ample information to make solid selections. However, when comparisons between standards are done, and a supplier claims to be wildly cheaper, faster or better are included, some healthy scepticism should be applied.
The health of building occupants are genuinely protected by the intelligent application of some basic air filtration design rules. Developments in localised air monitoring will likely be very effective in the future. Further, energy costs and total operational costs may be reduced, by the right selection of change out times, and superior grades of filters, in the right format.
Written by Airepure Australia and published in Hotel Engineer Vol 22, Number 1, April 2017.
 ASHRAE 52.2-2012: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size
 EN 779:2012: Particulate air filters for general ventilation. Determination of the filtration performance
 EN ISO 16890-1:2016: Air filters for general ventilation. Technical specifications, requirements and classification system based upon particulate matter efficiency (ePM)
 EN ISO 16890-2:2016: Air filters for general ventilation. Measurement of fractional efficiency and air flow resistance
 EN ISO 16890-3:2016: Air filters for general ventilation. Determination of the gravimetric efficiency and the air flow resistance versus the mass of test dust captured
 EN ISO 16890-4:2016: Air filters for general ventilation. Conditioning method to determine the minimum fractional test efficiency
 EN 1822-5:2009: High efficiency air filters (EPA, HEPA and ULPA). Determining the efficiency of filter elements
 ISO 29463-1:2011: High-efficiency filters and filter media for removing particles in air – Part 1: Classification, performance testing and marking
 ISO 7708:1995: Air quality — Particle size fraction definitions for health-related sampling
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