www . refrigerationandaircon . co . za RACA Journal I November 2024 43
Technical 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 (µ m ) 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 . RACA
“ For general applications , a filter with 95 % efficiency may provide a good compromise between protection and practicality .”
www . refrigerationandaircon . co . za RACA Journal I November 2024 43