WHEELER ON HVACR: Ozone and Air Quality
I was amused by a TV ad that I saw for a well-known portable electric air cleaner the other day. The ad said that they had just added a device to remove “one more source of indoor air pollution - ozone.” What's so funny is that they failed to mention that it is their air cleaner that was adding ozone to the room, since ozone isn't normally found in any measurable quantities inside homes. It's the source of that “clean smell,” which they used to advertise as a feature.
I had wondered about how they were handling the problem, and this new feature shows that they weren't until now.
All high-voltage devices (such as electronic air cleaners and automobile ignition systems) and ultraviolet light sources create some ozone. This is especially serious when the ozone is di-rected straight into the living area where it may be breathed, since ozone is a powerful bleaching agent.
Whole-house electronic air cleaners (and UV lights) create some ozone, but the difference here is that the ozone is blown through the HVAC air return, across a wet evaporator coil (where much of the ozone is removed), then through the discharge ductwork and diffusers, where it does a lot of good by decontaminating the system. And if you can't smell it (that “fresh, clean smell”), there likely isn't a problem. In fact, ozone devices are often added to the intakes of HVAC systems to clean them up and to reduce the presence of mold and bacteria spores (a good thing!).
How do they create ozone? They simply take a high-voltage transformer (such as one that is used for neon signs) and connect it to two metal plates, then place them close enough to create an ionized field, but not so close that arcing will occur. This uses just a slight amount of energy (mostly the inherent losses in the transformer). Of course, recognize that such a thing can also cause fires and elec-trocution, so I'm not really recommending that you try this; I'm just telling you how it is done.
The force from the ionized field breaks down oxygen molecules into loose atoms (in the form of molecules of two oxygen atoms, or O2), giving these loose atoms a charge that draws them together to create O3 molecules, or ozone. Then, when this charged molecule touches anything that it can react with, the charge is lost and one oxygen atom is released, which does the bleaching (or killing). The lone oxygen molecule will bond with anything that it can react with.
It's like taking small amounts of deadly chlorine gas (the first deadly gas used during World War I) and releasing it into the air. If you breathe it, it's hazardous. However, if you're using small amounts to decontaminate an area, and all of it is used in the decontaminating, there's no danger. That's how they decontaminate our drinking water.
Ozone is also used to purify drinking water, swimming pools and even cooling towers, because it's that powerful.
What's the point? Bad advertising gives the public the idea that all ozone is bad. And many in our industry have refused to sell electronic air cleaners because they think they are adding pollutants to the air. So people are buying these portable devices that do little good, and until now, were more hazardous than the devices that our industry sells. So, know and explain the facts!