By Eamonn Ryan from a presentation by Peter Mostert
The latest SAIRAC Cape Town Centre Tech Talk ‘Introduction to Air Filtration’ was presented by Peter Mostert, managing director of Filta-Matix.
The latest SAIRAC Cape Town Centre Tech Talk ‘Introduction to Air Filtration’ was presented by Peter Mostert, managing director of Filta-Matix. Images supplied by SAIRAC Cape Town Centre.
The presentation delved into both the challenges and advancements in ensuring superior air quality across various applications. It explored key topics including the complexity of filtration systems, the limitations of washable panel filters, and the latest in nano fibre technology.
One major highlight was the South African market preference of washable panel filters versus disposable primary pocket filters which offer higher levels of dirt holding capacity and reduced maintenance. Mostert explained that the fibre diameter together with progressive density technology ultimately determines filter efficiency. Higher efficiency filters such as 85% (MERV 13) and 95% (MERV 14) are required to effectively reduce contamination in general HVAC systems.
The new ISO 16890 standard establishes filter efficiency based on particulate matter (PM) which assists end users to determine filter efficiency by particle size.
Mostert urged the necessity for accurate testing methods and test reports to verify filter performance levels in accordance with ISO standards. The role of airflow and pressure drop testing was underscored, along with the importance of ISO 14644 standards for clean room validation.
One key takeaway was the need for local manufacturers to prove their capability in meeting international quality standards. The speaker invited attendees to conduct audits and assessments of their own manufacturing facilities as well as competing suppliers in order to assess quality management systems and technical capability.
One significant topic was the debate over pocket filter depth. Mostert emphasised the importance of media velocity and differential pressure. For example, a pocket filter designed with a depth of 300mm versus 600mm could impact the filter’s performance and lifespan. At a typical velocity of 2.5m per second, a shorter pocket filter may reach maximum differential pressure prematurely, resulting in high operating costs.
Nano fibre technology allows for high-efficiency secondary filters, up to MERV 14, to be used in constrained spaces of just 50mm deep. Despite the reduced depth compared to pocket filters, nano fibre filters offer a viable solution where space is limited.
Attendees had the opportunity to view and handle samples of nano fibre filters, which have revolutionised filtration by allowing for high-efficiency performance in compact designs. Mostert also covered the balance between media area and fibre diameter, noting that traditional synthetic fibres like polyester could not achieve the same efficiency levels due to the limitations of extruding fine fibres for increased efficiency levels.
These nano fibres, produced through advanced manufacturing techniques, resemble a spiderweb structure with multiple layers to enhance efficiency. This technology has evolved to create fine fibres to improve filter performance.
A critical point addressed was the balance between filter efficiency and lifespan. Nano fibre filters, will not provide the dust holding capacity of traditional filters like pocket filters or compact cassettes. Like all secondary filters, products containing nano fibres have to be protected with primary filtration.
By doing so, a manageable lifespan can be ensured. The audience was reminded that nano fibre technology was a viable solution in areas where space was limited and not necessarily directly equivalent to filters with larger effective media area.
Nano fibre filters are not washable and will require replacement when the final differential pressure has been reached. The specific lifespan will depend on environmental conditions but when used with high quality primary filtration, lifespans of 12-18 months can be achieved.
The presentation delved into both the challenges and advancements in ensuring superior air quality across various applications.
Despite the advancement in technology of primary and secondary filtration, only HEPA filters can provide absolute filtration efficiency levels. For purposes of this presentation, Mostert dealt with the advances in test methods of primary and secondary filtration as depicted in EN ISO 16890-1:2016.
The total cost of ownership of filtration products is not limited to just the initial purchase price but will include dust holding capacity. It was stressed that selecting filters based on the environment’s specific dust load can help optimise both performance and cost-effectiveness.
He highlighted the role of consultants and contractors in implementing effective filtration systems. Contractors are encouraged to specify their needs clearly and to seek guidance from suppliers on selecting the right products. This collaboration ensures that filters meet the required performance criteria and adapt to the unique demands of each facility.
ISO 16890 allows for a detailed breakdown of filter efficiency based on particle size distribution, which can help better match filters to specific environmental conditions. This change addresses previous limitations and provides more actionable data for selecting appropriate filtration solutions.
Measurement and technology advances
The advent of advanced particle counters has revolutionised the way we measure filter performance. Unlike older discolouration tests, modern particle counters provide precise counts of particles within specific size ranges. This allows for a more accurate assessment of a filter’s efficiency across different particle sizes.
While HEPA filters can remove up to 99.999% of particles as small as 0.3 microns, their implementation in standard HVAC systems can be impractical due to high differential pressures and cost considerations. The discussion pointed out that while HEPA filters offer near-total removal of fine particulates, they are not always feasible for every system due to:
- Most HVAC systems not being designed to accommodate the pressure drop associated with HEPA filters.
- The cost of high-efficiency filters that require frequent replacement, which might not be practical for all applications.
For environments where air quality is critical, such as hospitals or laboratories, higher efficiency filters are essential. For general applications, a filter with 95% efficiency may provide a good compromise between protection and practicality.
Design recommendations:
- Use primary filters to capture larger particles and secondary, higher-efficiency filters to address finer particulates.
- Consider nano fibre technology for compact, high-efficiency filtration in space-constrained applications, which offers a practical solution for improving air quality without overwhelming system capacities.
Evolution of filtration standards
ISO 16890 has replaced the old EN 779 standards, marking a significant shift in how we assess filter performance. This new standard introduces a more detailed categorisation of particulate matter (PM), specifically PM1, PM2.5, and PM10, which allows for a more nuanced understanding of filter efficiency across different particle sizes.
- PM1: Particles with diameters less than 1 micron.
- PM2.5: Particles with diameters less than 2.5 microns.
- PM10: Particles with diameters less than 10 microns. This categorisation enables end-users to select filters based on specific particle sizes relevant to their application, which was not possible under the previous standards.
Efficiency ratings:
- For ISO PM1, a minimum efficiency of 50% is required.
- For ISO PM2.5, a minimum efficiency of 50% is also required.
- For PM10 and coarser particles, filters must meet an average efficiency standard.
| Filter Group | Particulate Size (µm) | Classification Criterium |
| ISO ePM₁ | 0,3 ≤ x ≤ 1 | Minimum efficiency ≥ 50% |
| ISO ePM₂‚₅ | 0,3 ≤ x ≤ 2,5 | Minimum efficiency ≥ 50% |
| ISO ePM₁₀ | 0,3 ≤ x ≤ 10 | Average efficiency ≥ 50% |
| ISO Coarse | 0,3 ≤ x ≤ 10 | Average efficiency < 50% |
The test procedures now involve removing electrostatic charges from filters before testing, as these charges can significantly impact efficiency results. This step is crucial for accurate testing and comparison.
The emergence of standards for the removal of microbial contaminants:
Before the pandemic, there was no international standard or independent test method that addressed microbial contaminants in HVAC systems. The outbreak prompted extensive research and investment, with the EPA developing rigorous testing methods involving large-scale test facilities with turbulent airflow designs to assess efficacy under real life conditions.
Anticipate new standards in the future which will mandate effective microorganism removal strategies. These standards will shape how we approach and implement decontamination technologies in HVAC systems.
As we navigate the post-Covid era, the focus must remain on integrating advanced technologies with proven test results. Continuous improvement and adherence to emerging standards will be essential for maintaining high air quality and ensuring healthy environments for the occupants of HVAC spaces.
