"Aaachoo!" Need Air Conditioner Filters

What makes air conditioner filters so important? Because your family and yourself need clean air to live in. You can have cool air from air conditioners, but it won’t be complete if you keep sneezing, or having to live with unwanted smell in your house.

We want to remove unwanted air borne particles using air conditioner filters, especially dust and odour.

Let’s face it. Dust particles, your pets’ fur and carpet fibres, do exist almost everywhere in this world. Some people can live with it, but there is substantial number of people who can’t stand the allergy from inhaling dust.

I am one of them. The feeling is extremely unpleasant, especially when you’re driving.

Therefore, we include air conditioner filters as one of air conditioning part.

The functions:


  • trap air borne particles

  • trap unpleasant odour within the conditioned space

  • protect blowers and other air conditioner parts within the vicinity of blowers, from larger particles

General operation principle of air conditioner filters:

Air filtration in common conditioning units happen in the following ways;

  • mechanically trapping particles, using series of mesh. This principle is similar to refrigerant’s filter dryer. Only air, and particles with smaller size than the mesh will go through

  • using the electrostatic concept to attract charged particles, into oppositely charged filter materials

  • using carbon or charcoal cartridges to remove odour within your conditioned space

Supports of these filters are provided by filter frames and wire mesh.

Mechanical filter may exist on its own, while electrostatic filters are supported by mechanical filters.

Carbon or charcoal cartridges may complement either mechanical, or electrostatic air conditioner filters.

Mechanical partitions:

These air conditioner filters will be constructed using carbon fibre, or foam.

Construction of these filters will either be flat, or pleated. Flat configuration ensures simplicity in design and construction, however, the total effective surface area for filtration is lower, compared to pleated, or corrugated filters.

Pleated filters are more common in air conditioners nowadays. It increases the efficiency or air filtration, and reduces the interval between each cleaning activity.

Foam filters are of washable type, whereas fibre glass ones are disposable.

Electrostatic filters:

Air will have particles that are positively charged and negatively charged. Similarly, a solid matter will also have positively charged, and negatively charged molecules.

Rubbing action between air and the filters will initiate electron transfer between these media. One will have more electron and the other. Hence it is negatively charged. The other material will be positively charged.

Opposites attract, and charged dust will be attracted towards oppositely charged filter material.

However, we have to ensure that,

  • the filtering material is an electrical insulator, so that charge may accumulate easier.

    It MUST also be free from any connection to earth. Otherwise, the filtration system will not work as the charged filter is uncharged almost immediately.

    Polyester and polypropylene are widely used as electrostatic air conditioner filter material

  • the air is dry for better charging. Dry air will charge better than humid air, as it is a better insulator.

    Which is why air conditioner filters are placed before the evaporator and blower. We want to minimise contact of the filter, with condensed water vapour.

    The low cost electrostatic filters depend on rubbing action from air flow, to generate the desired charges.

    There are however, more expensive and more effective filters of this type. But it has to be connected to electrical power, to artificially charge the filter into negative and positive panels.

    Positively charged panel will attract negatively charged particles, and vice versa.

These filters or dust collectors are normally of washable type.

Odour control:

Activated carbon, or charcoal has the ability to adsorb neutralise odour from normal activities within your house. For example, smoking and cooking.

The “activated” phrase is used, as the carbon, will be treated with oxygen in order to create the porous structure.

Carbon cartridge used for this purpose will be very porous, thus increasing the total surface area for adsorption. The adsorption process is a chemical process. It will chemically attract odour contributor molecules, and trap it.

Activated carbon is normally used in conjunction with air conditioner filters, to deliver comfort air to you.

Characteristics of air conditioner filters:

Those are,

  • MERV rating, is the Minimum Efficiency Reporting Value for air conditioner filters. This number is a requirement from ASHRAE. It indicates the dust trapping ability of a filter. The higher the number, the better.

  • atmospheric dust weight arrestance. This is the effectiveness of removing air borne particles down to 0.3 microns. Normal air conditioner filters will have less than 10% atmospheric dust weight arrestance.

    Manufacturers will normally quote dust weight arrestance numbers. Hence the number will be close to 100%, as particles smaller than 1 micron will have small contribution towards the total dust weight.

    The former representation is more stringent, whilst the latter is less stringent for air conditioner filters.

  • dust holding capacity. It is stated by ASHRAE, as the maximum amount of dust weight, a filter can trap before servicing, or replacement.

  • initial resistance value, is the minimum resistance that blower has to overcome, when the filter is first installed.

    It is essentially the value of pressure differential between inlet and outlet of air conditioner filter, and it is measured in inches of water at a given flow rate.

    The resistance number will increase as dust is collected throughout its operation.

    Generally, low initial resistance numbers will permit higher air flows, but lower dust trapping efficiencies.

These filters are normally applied with antimicrobial agents, to prevent formation of allergy causing fungi.

Air conditioner filters are mostly passive equipment, but absence of these will mean a room full of sneezing people. No way we are going to tolerate that, are we?

After all, comfort air is not just about cool air. It has to be clean.

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