HEPA Filters: What They Can And Can’t Do!
The air in a room may not be as clean as you think, even if you are using a HEPA filter. Particle concentrations from outside air are on average one million 0.5 microns and larger, or even higher in some parts of the country. These numbers translate into an estimated 35 million particles in a cubic foot, which is more than enough to irritate allergies, and adversely affect overall health. Even with a HEPA filter that is 99.99 percent effective, around 350 of these tiny particles can be left in the air. Since this is the maximum number allowed for a clean room rated Class 100, it is obvious that more is needed to further reduce the concentration of particles in the air.
One method that can help reduce particle concentration, is to mix small amounts of outside and recirculated air. Not only will the air become progressively cleaner, this method is also energy efficient. Another way to improve indoor air quality is to use two sets of HEPA filters. Not only is this effective, it is also recommended by industry experts. With filters in the makeup handler and for the room, larger amounts of particles can be removed for improved air quality. Using double sets also has the advantage of decreasing the number of particles that reach the room filters, which can reduce how often it needs to be changed, along with preventing buildup or drops in pressure.
It is important to avoid using HEPA filters with an efficiency rating of less than 99.99 percent. While it may be tempting to save money on a less expensive and lower rated product, the poor air quality it produces and frequent replacement costs, do not make it worth it in the long run. For example, gross leak measurements show that a filter that is 99.7 percent effective will allow 0.03 percent of the upstream particles to pass through into the room, which can result in poor air quality. Filters that are 99.99 percent effective have almost no leaks, and if any are measurable it is well below the .01 percent limit. This ensures good air quality in the room, which is always beneficial for your health.
What a HEPA Filter Can and Can’t Do?
One of the first things to understand about HEPA filters is what they can and can’t do. While they are effective at removing the majority of particles from air that is flowing into a room from outside, they are not designed to clean any air that is already in the room. This means that a HEPA filter will not be effective at removing downstream contaminates, which is surprising to many people.
The HEPA filter is only a part of an effective and efficient HVAC system. Its main purpose is to remove contaminates from the air that are flowing into the room, and this accounts for 10 percent of the particles. The other 90 percent of the contaminates found in the air are generated by movements and activity in the room, and it is the job of an efficient HVAC system to remove these downstream pollutants. To ensure the HVAC system in the room is functioning efficiently, it is important to take a few minutes to find out where the majority of the contaminates in the air are coming from. For example:
* Someone who is either sitting or standing still, can create an estimated 100,000 tiny particles in a cubic foot, while the movements necessary to sit down and stand up can generate rise the number of contaminates to 2,500,000 for every cubic foot.
* Walking around in a room can generate 10,000,000 particles per cu. ft.
* Active play creates 30,000,000 particles per cu. ft.
Other activities that can add particles to the air after it passes through a HEPA filter include sweeping, welding, general maintenance and construction work, open doors, processing equipment and materials, or two objects rubbing against each other. All of these, and other activities can dramatically reduce air quality in a room, even if a HEPA filter is being used.
Since HEPA filters are not capable of removing particle concentrations that are generated indoors, it is important that the HVAC system is designed to clean downstream air. When this is combined with HEPA filters, air quality can be dramatically improved.