Posted on May 25, 2023
Air filtration in a building serves two primary purposes:
- To keep particles and contaminants like dust out of the air ducts and HVAC equipment.
- To remove particles and pollutants from the air circulating in a building.
Historically air filtration worked to keep ducts and equipment operating smoothly, sort of like oil in your car designed to keep engine parts running smoothly. But COVID-19 and the associated infectious airborne pathogens have flipped these two functions in importance for most building owners.
Viruses and bacteria range in size, but most come in around .005-.30 microns. Some are slightly larger or smaller, but air filters today are rated against their efficiency in removing particulates. For comparison, COVID-19 and the coronavirus it derives from is about 0.12 microns in diameter. A typical N95 mask—which is 95% effective at filtering the virus, hence the name—filters down to 0.1 microns.
Unlike face masks, air filters come in MERV ratings—Minimum Efficiency Reporting Value. The higher the MERV rating, the better the filter removes pathogens, particles, allergens, dust, etc.
- MERV 8 filters particles 3-10 microns in size. Note the lack of a decimal point—these filters do little to remove viruses and are primarily used to collect larger dust and debris.
- MERV 11 filters particles 1-10 microns in size. These filters don’t remove most viruses but may help remove some allergens.
- MERV 13 filters begin to filter viruses, with capabilities in the .3-10 micron size.
- MERV 16 filters remove particles .3-10 microns, which is the same size as MERV 13, but MERV 16 promises a 95% efficiency rate.
MERV 13 filters and higher can be so restrictive that they potentially reduce air flow in existing HVAC systems. This can have an adverse effect on occupant comfort, as well as decrease the functional life of the equipment. It’s important to understand the capabilities of existing systems and select the highest-rated filter they can accommodate.
Reducing airborne transmission through HVAC systems and cycling air
The best way to improve air quality inside your building is by introducing “fresh” outdoor air to the building. This has long been the go-to practice for commercial buildings but comes at a cost to air conditioning and heating. Outdoor air brings heat and humidity during the summer and cold, dry air in the winter. This requires a building to continually operate heating or cooling systems, which means a higher energy impact.
Current design codes call for cycling some fresh air within a building. Most buildings can cycle the air entirely every 2-3 hours, depending on their size. This measure, however, underscores how critical one-to-one interactions are in reducing the spread of viruses. If someone coughs or sneezes in your vicinity, no air filtration or air purifier will remove those airborne contaminants within seconds.
Improving air quality through air purifiers
Many commercial and residential air purifiers come with ionizers. These features, technically called bi-polar ionizers, use positive and negative ions to “zap” themselves onto pathogens. This is why if you’ve ever listened closely to one in a small room you can hear what sounds like static electricity “zapping” particulates.
An ionizer in an air purifier neutralizes viruses that are otherwise too small to be filtered and makes them physically larger, allowing them to be caught in HEPA filters or other high-MERV rating filters.
There are downsides with these ionizers, however.
- Corona discharge ionizers—which get their name not from the virus but from a sort of electrical output—have a high ion output and produce small ozone levels. Corona discharge is common from X-rays and old cathode ray tubes used in TVs. These ionizers are sometimes called tube-type ionizers because of their shape and these ozone discharges can be harmful.
- Needlepoint ionizers last a decade or more and need occasional cleaning every 18 months or so. Still, these units only work when running and work on ionizing and cleaning the air over time.
Needlepoint ionizers can be effective means as an air purifier but generally are reserved as portable air cleaners.
Improving air quality through UV lights
Ultraviolet light (UV) messes with the DNA of microorganisms, similar to radiation. While it can be harmful to people in direct exposure, UV lights are typically located inside air ducts or air filtration systems. When properly located and calibrated for exposure, UV is highly effective, fast, quiet, and has no harm to people or the ozone when installed properly.
Large particles and small particles alike are affected by UV light. When combined with a proper MERV-rated filter, such as a HEPA filter, everything from airborne viruses to tobacco smoke, bacteria, and allergens are zapped, filtered, or cycled out in a single air pass. UV treatment still relies on the air system running, but because UV lights can be compact, they make for sound air purification systems inside buildings and vehicles like buses.
UV lights are also relatively affordable and make for excellent air pollution and air purifiers for rooms in schools, hospitals, ambulatory surgical centers, and on planes, trains, and other public vehicles.
Keep your HVAC systems running
Medical-grade systems used in healthcare facilities will combine multiple techniques to clear up high-efficiency particulate air. HEPA filtration combined with charcoal filters and a constantly running HVAC system is excellent at helping hospital staff and patients breathe easily.
Healthcare facilities—and many other large commercial buildings—keep their systems running continuously. It cycles clean air from outside at optimal levels and also allows the filters to remove particulates from the cycled air. It also reduces wear and tear on the HVAC systems by reducing the number of starts and stops on the system components.
It sounds counter-intuitive, but the hardest, most damaging part of an air conditioner or heater’s job is just cycling on. Spinning up the fans, belts, bearings, and other components from a dead stop is energy-intensive, too. It’s easier for a fan to stay in motion and adjust fan speeds up or down depending on the room’s temperature while it’s already running.
DHP systems for high-demand areas
Some special facilities require extra attention, similar to medical facilities.
- Cafeterias and dining spaces, such as restaurants, higher education dining halls, and K-12 cafeterias
- Administrative or lobby areas in high-traffic government buildings, offices, or schools
- Fitness centers, gyms, and workout studios
- Locker rooms with spas or showers
- Shared housing spaces, such as dorms on college campuses
These facilities need heavier-duty air cleaners; we recommend dry hydrogen peroxide cleaners. These DHP systems disburse hydrogen peroxide as a gas through a ventilation system. Like an application on a skin cut or wound, the peroxide attaches to bacteria and viruses and kills them. The only byproducts are water vapor and oxygen, which can be drained or cycled away.
Unlike UV light, DHP systems can continue working up to an hour after shutting off in a space as large as 1,000 square feet because the DHP is still in the air. Depending on the size of the area, however, a DHP unit may need to be installed in multiple places in a room or building and require additional ventilation.
As air purifiers go, DHP systems are new and come in different sizes for small and large spaces.
Contact us for recommendations about your air cleaning and purification system. We specialize in K-12, government, commercial, and industrial filtration systems.