How does a Whole House Air Purifier Work?
I am sure that you have noticed that every home has a unique smell. The smell you detect when you enter a home is the result of particulates in the air in the home that have been produced by cooking, the people in the home, chemicals used, pets, and a multitude of other contributors. One of the consequences of making a home more energy efficient is that it is sealed better. As discussed in this review, windows are tighter and leak less air, while walls and doors are better insulated. As a result, the air inside your home cannot easily mix with the outside air and the particulates that are in your home – stay in your home. Whole House Air purifiers use several different processes to remove particulates and the odors they cause from the air in your home.
Probably one of the most common types of Whole House Air Purifier is a simple air filter (these are sometimes called air cleaners). The air filter fits inside the heating or cooling system in your home. It is placed in the system so that the air is filtered after it has been heated (or cooled) and before it is returned to your home. Not only does this remove contaminants from the air, it can also prevent damage to your furnace due to dust and dirt build-up. Filters can also be placed into the air return vents in each room of a house. Filters are made of materials such as foam, fiberglass, cotton and synthetic fibers that are densely woven together. The density of the filter material limits the size of the particles that can pass through. Very dense filters have smaller gaps allowing them to catch very small particles. Pleated filters have an increased surface area for catching particles. All air filters have to be replaced on a regular basis to keep them working properly (some filters are washable). One disadvantage of using a filter is that it restricts air flow through the heating system which can cause a drop in overall efficiency.
HEPA (High Efficiency Particulate Air) filters meet a Department of Energy standard for removing particles from the air. The filter must also allow a specific amount of air to flow through, which varies by the size of the filter. The ULPA (Ultra-Low Penetration Air) standard is even stricter. It is also possible to use substances in a Whole House Air Purifier that trap the particles that cause odors. Adsorption (not absorption) is the process of trapping one substance on the surface of another. A very common adsorbent is activated charcoal. Activated charcoal is extremely porous and has many microscopic “nooks and crannies” to trap passing molecules. Particles get stuck in the pores in the charcoal, and some particles react chemically with the charcoal and bond to it. Regardless of the mechanism the particles are trapped in the charcoal and are removed from the air.
Some Whole House Air Purifiers use ionization to remove particles from the air. In order to understand how these purifiers work let’s review some basic science. Think back to science class when you learned that objects have a charge associated with them. Objects with opposite charges attract objects with the same charge repel, and objects with no charge (neutral) do not attract or repel. Remember the experiment where you would take a comb and run it through your hair and then see if a piece of paper would stick to the comb? What was happening is that when you ran the comb through your hair you placed a charge on the comb. The charge you placed on the comb was the opposite of the charge on the paper. That is why the paper would cling to the comb – because opposite charged items attract.[G1]
An ionizing purifier uses this same technique to remove particles from the air. Most particles in the air have a neutral charge. The ionizing purifier uses a small electrical field that causes the particles in the air to become either positively or negatively charged. There are two metal plates in the ionizing purifier, one with a positive charge and one with a negative charge. The charged particles are attracted to one of the two metal plates and stick to it. Particles that are not captured by the plates become attracted to other (oppositely) charged particles in the air. When enough of the escaped particles stick together they become too heavy to float and fall to the ground.
A third type of Whole House Air Purifier, an ozone generator, turns oxygen particles found in the air into ozone. The idea behind this is not that the particles have to be removed or trapped. Instead, the ozone generated by the purifier reacts with the particles in the air and disinfects and deodorizes them. It is not clear whether ozone actually does what some manufactures of these purifiers claim. Critics claim that ozone is actually harmful instead of helpful and that it can react with other chemicals in the air and with items in your home to create even more harmful chemicals. Others say that it is a perfectly safe way to purify the air in your home. Unfortunately, the jury is still out on this one, even though the technology has been well endorsed [G2] by major cruise lines, restaurant and hotel chains.
Some Whole House Air Purifiers use an ultraviolet light to eliminate harmful airborne bacteria and viruses from the air. It does this by rendering certain micro-organisms sterile (and harmless).
All of the techniques that we have discussed have removed particles from the air. In some cases micro-organisms will be captured by these processes but not killed or sterilized.
Also, see my other review posts for this green living product:
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