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Air Purifiers Explained

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Air purifiers work by having the air drawn through the machine. The various parts of the machine clean the air as it passes through them. There are many different types of air purifiers with many different features. The following is a list of those features and things to consider when choosing.

Things to consider

  1. Air is lazy
  2. Things to remove
  3. Room size and air changes per hour
  4. Noise level
  5. Cost of operation

Filter types and technologies of air purifiers

  1. True HEPA
  2. HEPA-type
  3. Electrostatic
  4. Activated carbon
  5. Ioniser and Ion generators
  6. UV light
  7. Photocatalytic Oxidation
  8. Incinerator

Things to consider

1. Air is lazy

It is important to remember that air is lazy. Whereas water will flow to the lowest point to find a level, air will not. So if you have an air purifier in one room the air quality in an adjacent room may not be significantly affected. So portable air purifiers are room specific.

2. Things to remove

The things that are in the air that you may want to remove fall into the following categories.

Particles such as pollen, dust, dust mite faeces, shed skin, tiny fibre ends from material, smoke particles, mould spores and dust.
Organic compounds including pesticides, herbicides and some solvents.
Odours such as smoke, cooking odours, animals and organic odours from sewers and other rotting material.
VOCs are volatile organic compounds used as solvents in some paints and some cleaning products.
Bacteria and viruses are very tiny and can either be trapped in a filter or killed using specific types of filters.

3. Room size and air changes per hour (ACH)

At The Healthy House we recommend the air in the room be changed at least 3 times an hour. This provides a good level of cleaning and will keep up with the normal flow of air into and out of a room. If the room has high traffic or doors and windows are continuously opened and closed you may need a larger unit.

You may find that the size of room a unit is recommended for on our website is different than the size claimed on the box. This will be due to manufacturers using different multiples of ACH. By standardising them you can compare like for like.

We assume that the standard room height is 2.2 metres. So a 10 sq metre room actually has a volume of 22 cubic metres.

4. Noise level

The following excerpt is taken from the Health and Safety Executive website

“How is noise measured?

Noise is measured in decibels (dB). An ‘A-weighting’ sometimes written as ‘dB(A)’, measures average noise levels, and a ‘C-weighting’ or ‘dB(C)’, measures peak, impact or explosive noises. You might just notice a 3 dB change in noise level, because of the way our ears work. Every 3 dB doubles the noise level. So what might seem like small differences in the numbers can be quite significant.”

The following list shows different common noises in the range from 10 to 70 dB.

 10dB just audible
 40dB lowest level of urban ambient noise
 44dB bird calls
 50dB normal conversation
 60dB an air conditioning unit
 70dB a loud radio

An air purifier of 45dB may seem quiet in a room full of people but will seem loud in a bedroom while you are trying to sleep.

5. Cost of operation

There are 2 main running costs with an air purifier: electricity and replacement filters.

The cost of the electricity will depend on the size and speed of the motor, and over what period of time it is running.

The cost of replacements depends on the amount of pollutants in the air and the cost of a filter.

Technology and filters of air purifiers

True HEPA filtration information

What True HEPA is

HEPA is short for for “High Efficiency Particulate Air” or “High Efficiency Particulate Arrestance.” True HEPA refers to a filter that is manufactured, tested, certified, and labeled in accordance with current True HEPA filter standards.  The True HEPA filter must  capture 99.97% of the particles down to 0.3-micron particles in the air passing through it.

Efficiency is typically greater than 99.97% against larger or smaller particle sizes. Particles larger than 0.3 microns are more easily trapped, or intercepted, by the media. Smaller particles often lack sufficient mass to penetrate the media.

To meet the minimum requirements of a True HEPA filter, the filter must be tested and certified to prove that it will remove at least 99.97% (9,997 out of 10,000) of particles 0.3-micron in diameter from the air passing through the filter. Particles of that size are about 300 times smaller than the diameter of a human hair, and 25 to 50 times smaller than we can see. Manufacturing a filter with HEPA filter media does not mean that the filter itself meets True HEPA efficiency requirements.

What True HEPA removes

With filtration down to 0.3 microns and 99.97% efficiency the True HEPA filter will remove most dust, pollen, pet dander, mould spores, mites, cigarette smoke and even particles as small as bacteria and some viruses.

HEPA-type filtration information

What HEPA-type is

HEPA is an acronym for “High Efficiency Particulate Air” or “High Efficiency Particulate Arrestance.” This acronym refers to a filter that is manufactured, tested, certified, and labeled in accordance with current true HEPA filter standards.  The minimum true HEPA standard requires the filter to capture 99.97% of the 0.3 micron particles in the air passing through the filter.

HEPA-type filters typically remove 99% of particles between 0.3 and 3 microns which will be sufficient to deal with most particle filtration requirements in your home.

What HEPA-type removes

HEPA-type filters remove pollens, dust mite debris, mould spores, pet dander, smoke, odours and some chemicals.

Electrostatic filtration information

What is electrostatic filtration?

An electrostatic filter or precipitator induces an electrostatic charge into the flow of air. Basic filters consist of vertical wires followed by metal plates evenly spaced. Voltage between the plates and wire charge the particles which are then attracted to the plates. The electrostatic process can also be used to improve the performance of HEPA and HEPA-type filters

What electrostatic removes

The process is highly effective for airborne dust and particles such as smoke particles, pollen, mildew and dust mite faeces.

Activated Carbon Filtration Information

What is Activated Carbon?

Activated carbon, also called activated charcoal, carbo activatus or an “AC filter”, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2.

What Activated Carbon filters remove

Because of its super porous texture active carbon is able to attract, adsorb and neutralise smaller particles like organic gases, odours and some chemical compounds. These particles are too small to be trapped by other types of air purifier filters.

Activated carbon is a form of carbon that has been treated to make it extremely porous giving it a very large surface area available for the adsorption of chemical compounds. Activated carbon primarily adsorbs organic chemicals along with some larger molecular weight inorganic compounds. One gram of activated carbon has a surface area about one tenth the size of a football field.

If you would like to remove smells, gases or some chemicals from the air in your home an activated carbon filter is a very effective part of an efficient air purifier.

Ionisation information

What it is

Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions. An air ioniser is a device that uses voltage to ionise air molecules. Airborne particles are positively charged and are attracted to the negative ions in a  similar way that static from your television attracts dust. The negative ions attach to these particles and form larger particles that can be trapped more easily by an air purifier filter or are attracted to surfaces within the room itself.

The ionisation process also has a disinfecting property on viruses and bacteria. This has a beneficial effect on bacteria and viruses trapped within the filter medium that may otherwise reproduce in that environment.

Ionisers are effective by themselves or, when combined with filters, can dramatically improve effectiveness of those filters.

What it removes

Ionisers will have a positive effect on particles such as dust, pollen, cigarette smoke and pet dander.

UV Light information

What it is

UV light treatment is a disinfection method that uses short-wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unable to perform vital cellular functions. UV light is used in a variety of applications, such as food, air, and water purification.

What it removes

UV light has ant-bacterial, antiviral, sterilising and deodorising properties against microorganisms.

Replacing the bulbs

UV bulbs will deteriorate over time and The Healthy House® recommends that they are replaced when they are not functioning,damaged, when no blue light is observed or at least every 12 months. Take a look at our Filter (bulb) Replacement Service tab for peace of mind.

Photocatalytic information

What it is

UV light is often used in conjunction with Titanium dioxide. Titanium dioxide, is a photocatalyst under ultraviolet (UV) light. It has been reported that titanium dioxide is also a photocatalyst under either visible or UV light. The strong oxidative potential oxidizes water to create hydroxyl radicals. The hydroxyl radical can damage virtually all types of macromolecules: carbohydrates, nucleic acids, lipids and amino acids. Hence titanium dioxide in conjunction with UV light  can be added to products for its sterilizing, deodorizing and anti-fouling properties.

Unlike basic UV light which only affects what it is in its light, hydroxyl radicals can permeate a room having a much further reaching effect.

What it removes

Hydroxyl radicals have antibacterial, antiviral, sterilising and deodorising properties against pathogenic and non pathogenic microorganisms. Hydroxyl radicals will eliminate bacteria, mould and fungi, viruses, dust mites, allergens and harmful VOCs giving you clean healthy air.

Incinerator technology information

What is incinerator technology

Incinerator draws in particles which are then incinerated on a ceramic core. Sterilised air is then cooled before being released back into the room. Within fourteen to twenty one days the level of microorganisms and allergens will have been reduced by 85% and from then on are kept to a minimum.

The technology works by eliminating microorganisms and allergens, destroying them in a fraction of a second. Depending on the model, between 14,000 and 20,000 litres of air pass through such devices every hour, treating all the air in the room in a very short space of time.

The process works in much the same way as sterilising water by boiling it. When water is boiled, the microorganisms it contains are eliminated. In similar fashion, incinerators continually draw in air from the room, heating it to over 200 ºC and instantly sterilising it. The purified air is then cooled inside the device before being returned to the room.

The entire process is completely silent and requires no maintenance, not even the occasional replacement of parts. All you have to do is switch the device on and leave it to get on with the job.

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