How Air Filters WorkBefore asking for the right air filter, it is essential to understand how they work and why your units need them. The main job of air filters is to purify the air that passes through HVAC systems. Filters work by capturing air particles and releasing clean air. If you are using an AC, an aircon filter is even more important because it recycles the air in a room. Air filters can trap the following:
- Pet dander
- Mould spores and fungi
- Dust and dirt
- Dust mites
- Bacteria and viruses
Air Filtration MechanicsHVAC systems with air filters use different methods to capture pollutants from the air.
Impaction and InterceptionImpaction happens when the airflow pushes the particles in a single direction with the filter acting as the target point of impact. It is often applied in pre-filtration stages. Interception, on the other hand, is not about having a powerful airflow to push the particle in a straight line but about having enough power to push the particle until it touches the media (fibres, mesh, etc) and becomes attached to it.
StrainingStraining is about trapping particles between the media that has a smaller diameter than the one it needs to capture. The size, spacing and density of the media determine its capacity to filter.
Electrostatic AttractionThis uses static electricity created by fibres or other materials to attract particles similar to how magnets work.
Types of Air FilterThere are several kinds of air filters that are designed for different purposes. They are:
- HEPA filters
- Electrostatic filters
- Fibreglass filters
- Pleated filters
- UV light filters
- Carbon air filters
- Media filters.
Air Filter Selection
Why Having the Right Air Filter Is ImportantAlthough air filters have a similar job, they differ from one another. Choosing the right one is important if you want to get your desired level of protection and prevent your HVAC from damage. If someone in your family has allergies, asthma or other conditions that make them sensitive to pollutants, aircon filters with a low minimum efficiency reporting value (MERV) rating will not be enough. However, incompatible ratings might jeopardise the airflow and could damage the unit.
How Do I Choose an Air Filter?There are several factors that need to be considered to maximise the performance of your system and its filter.
Size and ThicknessGetting the right size is important. Wrong size and thickness significantly reduces the filter’s capability to trap particles.
You will know the size of your filter by checking the nominal size written on the packaging. The nominal size is the rounded up number of the air filter’s actual size.
For example, its nominal size is 20 x 20 x 1 but the actual size is 19.75 x 19.75 x 1.
Manually measuring your air con’s filter is by getting the length, width, and depth and checking the air filter intake as well.
Tip: You’ll know the air filter doesn’t fit when you either force it in or there is a little amount of space left on the frame.
Aircon filters’ efficiency also depends on the thickness rating. Too thin means lesser purifying capacity; too thick means high airflow restriction. The recommended minimum efficiency reporting values or commonly known as MERV ratings are 6 to 8. Consult with an expert to make sure that what you want is suitable for your system.
RatingThe recommended MERV rating will apply only based on your unit’s specs and requirement at home with airflow suitable for sick family members. A family member who has asthma or allergies may need an aircon filter with 10 to 12 MERV rating. Higher than 12 will cause damage to your AC. MERV determines the extent of a filter’s capacity to trap particles (0.3 to 10 microns in size). MERV ratings and particles:
- MERV 1 to 4: pollen, dust mites, spray paint, carpet fibres
- MERV 5 to 8: mould spores, cooking dust, hair spray, furniture polish
- MERV 9 to 12: lead dust, flour, auto fumes, welding fumes
- MERV 13 to 16: bacteria, smoke, sneezes
- Disposable Vs Washable [H4]