Choosing the right air filters for your air handling unit (AHU) will help keep your operation cost-effective, ensure food safety, keep the air your workers breathe clean and contaminant-free, save you money and prolong the lifespan of your HVAC system.
Designed for Efficiency and Durability
Primary filters usually have a pleated panel design. The pleated fibre media is held in place by a wire mesh encased in a cardboard frame. The pleats allow these filters catch more dust (down to 4 or 5 microns), giving them a longer lifespan. This design also helps prevent dust sticking to the cooling coil, fan and motor in the AHU and also to the inside of the ductwork. Dust build-up on these elements can present a fire hazard and can reduce energy efficiency. Having a good primary filter will help protect the other more expensive filters in your AHU, such as the secondary filters.
Secondary filters are typically bag filters made of synthetic material. The bag extends backwards as it inflates, giving it a large surface area to catch pollen, bacteria and smaller particles of dust. Look for synthetic media in these bag filters rather than glass fibre media. Glass fibre media can shed from this type of filter and potentially get into food. Synthetic filter media, on the other hand, is shatter-proof, environmentally harmless and performs equally as well as glass fibre media.
HEPA filters at the final stage of filtration, for those applications that need a higher level of contamination control, are composed of a galvanized steel frame with side handles for ease of handling. The media is a water-repellant randomly-arranged matted micro-fibres. The fibre media, which is folded to calibrated spacing and separated by thermoplastic threads, is capable of trapping very small particulate contaminants from an air stream. Read more about HEPA filters here.
Every filter should be labelled. The label should give details of supplier for reordering purposes, an arrow indicating direction of the airflow and dimensions of the filter.
Suitability for the Application
To maintain good indoor air quality at all times, you have to choose the right filter for your specific application. Each type of production area (low care, high care, high risk) has a different set of requirements. The level of filtration for a high risk area is much greater than for a low care area.
The table below shows which filter application grades are suitable for each type of production area at pre-filter, secondary and final filter stage.
Energy Efficiency and Conformity to ISO 16890
Up until 30th June 2018, BS EN 779:2012 set out the standards that air filters had to meet, including the test methods and the test bench used to measure the performance of a filter. This was replaced by ISO 16890, which represents real-life performance of a filter much more accurately.
While EN 779 was based on a particle size of 0.4 µm, filter efficiency is now measured using three different particle fractions of PM10 (particles up to 10 µm), PM2.5 (particles up to 2.5 µm) and PM1 (particles up to 1 µm). The filter efficiency is reported as a percentage (from 50% – 95% in 5% increments) for each of the ePM ranges.
The new measuring procedure introduced by ISO 16890 makes it possible to select the best filter for a specific local particulate matter concentration in the air.
A new classification for air filter energy efficiency was introduced by Eurovent on 1st January 2019. The Eurovent Energy Rating 2019 is based on ISO 16890:2016. Air filters are graded from A+ (lowest energy consumption) to E (highest energy consumption). The new classification has increased the efficiency performance demands on filter manufacturers. For example, filters previously considered to have an efficiency rating of A+, have been downgraded to A.
As filters pick up dirt, they create a lot of pressure resistance. Pressure is measured in pascals by a magnehelic gauge, and you can tell from the pressure reading when the bag needs to be replaced. (Speak to your air filter supplier to find out what the pressure difference should be across the filters in your AHU.) Filters vary by energy efficiency. Higher efficiency rated filters create a lower pressure drop that means there is less pressure to overcome for the fans. You can save a lot of energy by switching to a more energy efficient filter.
A Good Supplier of AHU Air Filters
A good AHU air filter supplier will offer more than just the product. They will also provide an installation and filter change service. In addition, not only will they advise on what the pressure difference should be across the air filters in your AHU, but they will also put in place a regular filter change schedule for you. This helps relieve the burden on in-house engineers of checking differential pressure at intervals. Reliance on checking pressure drop often results in dirty and worn filters not being picked up soon enough. Having a schedule means that filters are changed in good time without have to check pressure. This preventative approach also means that bacteria does not get chance to build up.
A good supplier will also add value to their service by looking at your air handling system holistically. They will provide additional hygiene and remedial services to keep your AHU clean, contamination free and well-maintained. This will help to ensure it works as energy efficiently as possible. It will also prevent your AHU contributing to the contamination of your product and the air your employees breathe.
HVDS provides a holistic air filtration service from AHU installation to filter changes and from system cleaning to remedials. For more information get in touch with our air filtration experts today.