Air filters are a critical component in maintaining the air quality and energy efficiency of your site. This guide will help you select the right filter for your facility’s needs.
Filter Size and Ratings
Nominal filter dimensions can vary by manufacturer, so when dealing with replacement filters, it is essential to know actual filter dimensions and the quantity required before you re-order.
Accepted filter performance rating systems are EN779:2012 (G1 to F9) and ASHRAE 52.2 (MERV 1 to 16). Based on the successful removal of airborne particles by size, these ratings provide a relative measure of filter effectiveness; whereby lower rated filters remove larger sized particles and higher rated filters remove smaller sized particles.
Higher rated filters will remove more airborne particles; however this is almost always at the cost of energy and more frequent filter changes. Similarly, lower rated filters will impact air quality, duct cleanliness, heat exchanger performance and in some cases safety.
Inspection of your current filters will reveal their rating, and you should replace these filters with a comparable rated filter. With large installations, it is worth checking the original filter specifications to confirm the right filters are still installed.
Whilst nominal dust holding capacities obtained from controlled laboratory testing are useful when comparing similar filters within a manufactures range, comparisons between different filters or manufacturers can be misleading due to differences in test conditions, dust ranges and other factors.
Similarly, real world dust, temperature, humidity and other contaminations are difficult to directly relate to this laboratory test data. As such, you should seek advice from suppliers with reputable technical knowledge and experience. Ultimately, with replacement filters, actual historic data will be your best guide.
Finally, all filters have a finite capacity and benefit from a “staged” sequence i.e. pre filters followed by higher efficiency final filters. Filter sequencing allows inexpensive filters to be sacrificed to maximise the life of the more valuable final filter.
Static pressure is the recognised measurement to assure appropriate filter change out times.
For example, if the static pressure across a G4 filter was measured above 175Pa, it is demanding to be changed. While this filter is still providing good air quality, the excess energy used in airflow would cost more than the filter is worth to change.
In general, it’s better to change filters early – rather than late.
Internal air filtration is an increasingly critical component of the energy efficient facility. Accurate tracking of static pressure via a BMS system will be a significant component in any energy assessment.
With older buildings, an overall review of the filter types, fan settings and system construction will reveal valuable opportunities for energy savings that would be comparable to LED lighting conversions.
Buying decisions should start with obtaining the right filter and conducting service changes at the appropriate time. Supplier considerations should include stock availability, breadth of range, credible support, warranty and overall cost. Similarly, local and knowledgeable support is an important factor when changes or upgrades are being considered.
The humble filter is often a forgotten part of the facility – but the people and equipment that it protects are critically important.
Is it time to change your filters?
Written by Dr. Allan Heckenberg (PhD), BDM for Airepure Australia for Facility Perspectives, Vol 9 No 3 September 2015.
Written for Facility Perspectives
by Dr Allan Heckenberg (PhD)
64 Geddes St,
Mulgrave VIC 3170
1300 886 353