Air Purifiers Explained
Air purifiers work by having the air drawn through the machine and the various parts of the machine cleaning the air as it passes through them. There are several different types of air purifier with a series of different features. The following is a list of the things to consider when choosing an air purifier, features that may be included in an air purifier and how these features may benefit you.
Things to Consider
Features of Air Purifiers
- Electrostatic Filter
- Activated Carbon
- Ioniser and Ion Generators
- UV Lamp
- Air Sterilisers
- Plasma Air Purifier
- Automatic Setting and Air Quality Sensor
- Filter Change Indicator
1. Air is Lazy
It is important to remember that air is lazy. Whereas water will flow to the lowest level and travel between rooms to reach a level throughout your home, air will not. So if you have an air purifier in one room the air quality in an adjacent room will 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. These include pesticides, herbicides, some solvents.
- Odours such as smoke, cooking odours, animals and organic odours from sewers and other rotting material.
- VOCs. These are volatile organic compounds - chemicals that are used as solvents in some paints as well as some cleaning products.
- Bacteria and viruses. These 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
At The Healthy House we recommend that the air in the room be changed at least 3 times an hour. This gives 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 there are door and windows that are continuously being opened and closed you may decide to have a larger unit or use a higher fan speed during high traffic times.
It is assumed 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)', is used to measure average noise levels, and a 'C-weighting' or 'dB(C)', to measure peak, impact or explosive noises. You might just notice a 3 dB change in noise level, because of the way our ears work. Yet every 3 dB doubles the noise, 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 with a fan that measures 45dB may seem quiet in a room full of people with conversation going on 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 of the motor, the speed that it runs at and over what period of time it is running either continuously or intermittently.
The second expense is the cost of replacement filters. This will depend on the cost of the individual filters as well as the amount of pollutants in the air that the air filter traps in its filter.
Features of Air Purifiers
1. HEPA Filter (High Efficiency Particulate Air Filter)
HEPA stands for High Efficiency Particulate Air which means that it is a highly efficient particle filter. A true HEPA filter will remove 99.97% of airborne particles that are as small as 0.3 microns in diameter. This means that they can trap bacteria, viruses, pollen, dust, dust mite faeces, pet dander, mould spores and cigarette smoke. HEPA filters do not filter out chemicals or smells.
A HEPA filter is made from randomly arranged fibres, typically fibreglass. These fibres are immensely small, with diameters between 0.5 and 2.0 microns. The arrangement of these fibres allows very small openings of less than 0.3 micrometers for air to flow through. This design not only filters particles larger than the openings like a sieve but also smaller particles stick to the fibres of the filter allowing the air purifier to trap much smaller particles and pollutants. Because the fibres are arranged randomly the particles cannot flow along any curving contours forcing them to embed onto a fibre. The design also causes particles to collide together, increasing the probability that they will be trapped by a fibre.
Because of its design and efficiency a HEPA air purifier is one of the best air purifiers available for people who suffer from airborne allergies or anyone who would like a bacteria and mould free environment. It is especially effective for asthma and eczema sufferers whose condition is triggered by airborne allergens. It is also very useful in helping combat a pet allergy.
2. Electrostatic Filter
Electrostatic filters are made from back to back layers of unique polyurethane and polypropylene blends. These layers are charged with alternating negative and positive charges.
An electrostatic filter acts like a magnet attracting particles of all sizes. As dust and other airborne particles pass through a positively charged layer they are given a positive charge. The second layer of the filter is negatively charged. The positively charged particles are attracted to the negatively charged surfaces and stick to it.
Electrostatic filters are very effective at removing dust, dust mite faeces, pet dander, mould spores and pollen. The best quality electrostatic filters can also remove smoke, smog, bacteria and viruses. Electrostatic filters also often have a higher CADR (clean air delivery rate) than other air purifiers. This means that they clean the air in your home faster helping you feel better sooner.
3. Activated Carbon Filter
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.
4. Ionisers and Ion Generators
Airborne particles like dust, pollen, cigarette smoke and pet dander 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. These larger particles also tend to fall to the ground. Ionisers generate negative ions. Negative ions are particles that have one or more extra electron giving them a negative charge.
An ioniser is a great way to increase the efficiency of your air purifier. It does not trap any particles itself but instead increases the ability of other filters to remove airborne particles. It also causes particles to fall to the floor making them easy to vacuum.
5. UV Lamp
A UV lamp kills bacteria, viruses and other germs. The germicidal ultraviolet light deactivates the DNA of bacteria, viruses and other germs stopping their ability to multiply.
A UV lamp uses a specific type of bulb that emits germicidal ultra violet light. Germicidal ultraviolet light has a wavelength shorter that visible light making it invisible to the human eye.
A UV lamp will kill any bacteria, viruses or other germs trapped in the air purifier. This means that their effectiveness is dependent on the air purifier's ability to trap particles. When combined with an efficient filter a UV lamp helps to create a clean, sterile environment.
6. Air Steriliser
Because of its unique design an air steriliser is able to silently destroy 99.9% of microorganisms that pass through its core. An air steriliser destroys viruses, bacteria, ozone, dust, dust mite faeces, pet dander and mould spores. Air steriliser technology is unique to Airfree air purifiers. An Airfree air steriliser silently pulls airborne particles into its chamber through air convection. It then carries these particles into the sterilizing chamber. Inside the chamber the temperature is around 204C incinerating all microorganisms. The sterilised air is then cooled and returned to the room. Its unique design allows an air steriliser to clean the air silently and without the use of a filter. Within 14-21 days the level of microorganisms and allergens will have been reduced by 85%.
7. Plasma Air Purifier
A plasma air purifier destroys bacteria and viruses and sterilises the air helping you to keep healthy. It neutralises chemicals and VOCs including formaldehyde helping to reduce symptoms of MCS. A plasma air purifier also absorbs harmful gases and odours.
The plasma generator produces positive and negative ions to destroy bacteria and viruses and sterilise the air. This combination of negative and positive ions also destroys harmful chemicals including formaldehyde.
8. Automatic Setting and Air Quality Sensor
The automatic setting will sense the contamination in the air and increase the fan speed so that more air passes through the unit and the air in the room is cleaned more quickly. Once the contamination has been removed the machine will reduce the speed of the fan to a low setting. This facility is particularly useful if the unit is to be placed in a bedroom since the unit will run on a quiet setting for most of the time.
9. Filter Change Indicator
Some units have an indicator that tells you when the filter is becoming clogged and the machine is having to work harder to force the air through the filter. By changing the filter the machine will clean the air more efficiently and more effectively.
