Coronavirus (SARS-CoV-2) has highlighted the need for us to be flexible as we tackle new challenges. And while the virus may be “novel” (how many times have we heard that word?), most of us are just trying to make it work with what we have. For building owners and managers, that means adapting existing building layouts and HVAC systems to keep occupants as safe as possible. So, what are our options when major upgrades are out of the question?
You have probably heard that increasing ventilation is one way to reduce the risk of SARS-CoV-2 spread. But what exactly does that mean?
Ventilation involves introducing new air—or recirculating filtered air—to flow through a space. You can increase ventilation naturally by opening windows and doors, or by adjusting your HVAC settings. For example, you can adjust your HVAC’s settings to keep the system fan running for longer periods, or you can open your system’s outside air intake to increase the new air that is circulated.
Ventilation is usually measured by the number of air changes per hour (or the number of times all of the air in a space is completely replaced in a time period). The recommended air change rate to keep occupants comfortable is a minimum of 4 air changes per hour. Facilities with high-risk occupants should aim for higher ventilation rates, nearing 15 air changes per hour.
Ventilation can also be employed to remove airborne contaminants (which is the main way it’s believed that SARS-CoV-2 spreads). How long it takes to remove airborne contaminants depends on the number of air changes per hour and filtration efficacy (MERV rating, see below).
The AIA Guidelines for Design and Construction of Hospitals and Health-Care Facilities (2001) outline unique ventilation specifications for different hospital settings depending on disinfection and patient needs. The CDC has made them available for public viewing here.
Capacity and traffic flow are also important factors in determining ventilation needs for your facility. An IAQ specialist or HVAC specialist can help you determine the specific needs of your facility.
The possible downside? You may experience higher energy costs due to running your system fan for longer, or if you’re introducing more outdoor air into the system that needs to be conditioned.
HEPA Air Filters
If you manage buildings, you’ve probably heard of HEPA (High-Efficiency Particulate Air) filters. Why exactly are HEPA filters special?
Every HVAC system (including the one in your home) has air filters that need to be checked and replaced on a regular basis. Air filters are rated on a MERV (Minimum Efficiency Reporting Values) scale from 1-20, which denotes the percentages of particulates of a certain size range that the filter can capture. The lowest rating category (1-4) provides baseline filtration and only removes up to 20% of particulates 3.0-10.0 microns (µm) in size. In contrast, filters rated 16, can remove up to 75% of particles 0.3-1.0 µm in size. You can see a full chart of MERV ratings on the EPA’s website.
HEPA filters (MERV 17-20) offer the highest level of filtration and can remove up to 99.97% of dust, pollen, mold, bacteria, and any airborne particles at a size of 0.3 microns (µm) or greater. However, they might not play nicely with your existing HVAC setup. HEPA filters are so effective, that they can overload HVAC systems by requiring increased pressure to circulate air. This can increase energy usage, and cause damage to your HVAC system if it is not designed for this excess workload. Similarly, increased air flow resistance can impact ventilation and air change rates.
For reference, ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends that commercial buildings be fitted with filters rated 13 or higher. MERV 16 might be used for general healthcare use or high-traffic facilities, whereas MERV 17-20 (HEPA) filters are necessary for high-level air filtration in operating rooms, clean rooms, and the like.
Considerations: HEPA filters
If you’re considering HEPA filters for your facility, make sure that your HVAC system can handle the increased air pressure needs and that the filters are the right size for your system. The proper fit is important to prevent air filter bypass, which occurs when air moves around the filters in your HVAC system instead of through them (and defeats the whole purpose of having an air filter). An HVAC specialist can help you determine the right fit for your system.
Bipolar ionization works with your HVAC system to reintroduce ions (positively or negatively charged molecules) back into indoor air. The ions interact with indoor air particulates like bacteria, mold, gases, VOCs and viruses, giving them a positive or negative charge that encourages them come together; the larger particles are then either easier to filter within the HVAC system or eventually settle out of the air in the conditioned space.
Reducing airborne particulates is important because small particulates (like bacteria and viruses) attach themselves to larger particles (like dust and mold) so they can travel farther.
Considerations: Bipolar ionization
A bipolar ionization system can be fitted to your current HVAC systems without drastic system upgrades. In our experience, this technology has been shown to be effective at removing particulates from indoor air. In addition to cleaner air, you may also experience energy savings because air that has already been conditioned can be recirculated through the space.
However, bipolar ionization has been known to produce ozone as a byproduct; it’s important to thoroughly research the specific technology you’re considering before adding it to your HVAC system. If you choose to install bipolar ionization technology, you can ask an IAQ specialist to monitor ozone levels in your facility to ensure that levels do not reach unhealthy levels.
Ultraviolet light purifiers
Recently you may have heard about ultraviolet (UV) light radiation being used to disinfect indoor air. The theory behind this technology is that submitting airborne particles to UV-C light can potentially damage the DNA of microorganisms in the air and deactivate them. Usually, UV-C light is paired with a forced air system or other air filter (like in your existing HVAC system), and the air is pushed through a chamber with UV lamps after it is filtered.
Considerations: UV air purifiers
Some studies have shown that this process could be effective in deactivating some bacteria and viruses, but has minimal effect against mold, allergens and VOCs. The major sticking points are that these systems oftentimes don’t expose the air at a high enough concentration to UV-C light or for a long enough time period to provide a meaningful reduction in viruses. The greater benefit would most likely come from the air purification systems used in conjunction with the UV-C light technology.
One additional concern is that, like ionizers, UV air purifiers can generate ozone. Specifically, the UV light can break apart oxygen (O2) molecules and result in the creation of ozone (O3) molecules, especially if the UV lamps in the air purifier are uncoated.
Ozone-Generating Air Purifiers
The EPA reviewed a wide assortment of studies about ozone-generating devices that are sold as air purifiers. The theory behind these devices is that ozone, which is composed of 3 atoms of oxygen, can break apart so that one molecule reattaches to molecules of other substances and alters their chemical composition, deactivating them. The main issue with this theory is that ozone can be harmful to human health, whether on its own or mixed with other chemicals. While ozone helps protect us from the sun’s rays way up in the stratosphere (think ozone layer), it can do damage to the respiratory system when it’s found in the atmosphere (the air we breathe).
The EPA review found that these ozone-generating devices can produce ozone at concentrations that exceed health standards, even when operated according to manufacturers’ instructions. Furthermore, it’s been shown that ozone generated at levels allowed by health standards is generally not very effective at controlling indoor air pollution. Instead of removing pollutants, ozone can interact with other compounds and particles in the atmosphere and create additional harmful pollutants.
A more effective (and safer) use for ozone is to purify water, but its effectiveness in purifying air is questionable.
Considerations: Ozone-Generating Air Purifiers
The California Air Resources Board https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/hazardous-ozone-generating-air-purifiers#:~ is firmly against the use of Ozone-Generating Air Purifiers, citing a range of health risks and respiratory symptoms that ozone exposure if known to cause in humans. They’ve even gone so far as to make a list of these products that should be avoided. https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/potentially-hazardous-ozone-generators-sold-air
In sum, we would follow the EPA’s recommendation that ozone-generating air purifiers should not be relied upon for controlling indoor air pollution. Instead, other methods for controlling pollutants should be used, such as ventilation, filtration and pollutant source control.
You may be wondering: how do we know if we need to improve our IAQ? And if we implement one of these mitigation strategies, how will we know if it’s working (other than anecdotally)?
The easiest way to check your indoor air quality is to have baseline particulate monitoring conducted. A baseline study will give you a close look at how polluted your air is, and can even tell you what types of contaminants you’re dealing with.
If you decide to implement any of these methods in your facility, we can conduct a follow-up particulate measurement study to test effectiveness. For example, we used this exact method https://amienvironmental.com/bipolar-ionization-iaq/ to test the effectiveness of a bipolar ionization system that was installed as part of an existing HVAC system for a 3-story, 180,000 square foot community building.
Finally, keep in mind that no air cleaning method is fool proof. After all, even HEPA filters can’t remove the tiniest particles, including some viruses, bacteria and VOCs. In this case, adjusting behavior is sometimes the best solution for keeping people healthy.
Our industrial hygienists are always available to discuss specific needs or concerns for your building. Contact Dan Taylor at 402-981-1000 or firstname.lastname@example.org with questions.
As president and chief executive officer, Dan focuses on the overall direction of the firm, strategic alliances, and business development, while upholding his commitment to clients to ensure their projects’ success. He remains involved in the field, applying his 30 years of experience to resolve the most complicated and high risk environmental hygiene issues encountered in healthcare facilities.