The Connection Between Indoor Air Quality and Outside Air

Robert LoForte · September 2, 2020

The COVID-19 pandemic has elevated Indoor Air Quality (IAQ) on the list of priorities for commercial building owners. What was once a supplemental benefit for occupant comfort has now become a core responsibility that is imperative to the health and safety of tenants. Many property owners are toeing the line between pouring capital into enhancing their IAQ measures through increased ventilation rates, improved filtration, and disinfection technology in an effort to minimize transmission rates for this novel virus.

Incorporating more outside air is recommended but costly, and many aren’t sure where or what exactly to invest in to ensure occupants are safe, while keeping capital expenditures and increased energy costs in check. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) circulated new IAQ guidelines for buildings that are continuing operations during the COVID-19 pandemic, but this is a framework and not a clear-cut solution for addressing the current crisis.

Commercial property owners need to evaluate three things before changing how they operate: They need to understand what types of mitigation measures their existing equipment and infrastructure can support, how much they are willing to invest, and which solutions will be most beneficial to them moving forward as we navigate through the new normal. There are a number of solutions available to optimize IAQ, and by taking these three steps, building owners will be in a much better position to keep occupants safe, happy, and comfortable.

Increase outdoor air ventilation and dilution ventilation

Evidence points to COVID-19 being an airborne virus, spread from person to person through droplets. In commercial buildings, transmission risk can be mitigated by increasing the air change rate for outside air ventilation. Pulling in more outside air can dilute potentially contaminated air so occupants are less likely to be exposed to recirculated infected droplets. By replacing contaminated indoor air with fresh outside air, dilution decreases the potential concentration of infectious particles. Coupling dilution with filtration and disinfection provides a strong, three-pronged approach to minimizing transmission risks.

Many commercial buildings use demand-controlled ventilation (DCV), which adjusts outside ventilation based on occupant demands, as a simple way to save on both energy and costs. The aforementioned  recommendations from ASHRAE, designed specifically to help buildings address the COVID-19 pandemic, advise against this and instead, recommend keeping outdoor air dampers as fully open as possible to maximize the air changes within the space. To do this, existing control sequences and economizer limits will need to be temporarily modified or overridden. Commercial HVAC systems will typically have either air-side or water-side economizers, which are used when there is a cooling demand in the facility—but if ambient conditions are sufficiently cool, then outside air can be used instead of mechanical cooling to save energy. Under normal circumstances, equipment with air-side economizers will only fully open outdoor air dampers if the outdoor air temperature is sufficiently cool.

During the pandemic, the programming of the controllers which handle this action should be modified to make the system operate differently. Since most commercial HVAC equipment is not sized to handle 100 percent outdoor air during peak summer and winter conditions, the programming could be modified so that it will allow the dampers to fully open up to a certain outside air temperature, and then linearly and inversely throttle them closed as the outdoor air temperature rises. As a theoretical example, if the outside air temperature is below 80 F, the outside air damper will remain fully open. Between 80 F and 100 F, the damper will close from 100 percent open down to 50 percent open.

Facility managers will need to consider the thermal capacities of their equipment to ensure the air can be adequately conditioned and adjust ventilation rates down when ambient conditions are at their peak. Extending system schedules both before and after normal occupancy times is also recommended to purge the space.  Unfortunately, drastically increasing outside air ventilation can be very expensive depending on the climate of the facilities location, so coupling some level of dilution ventilation with other mitigation measures might be the best approach for many facilities.

Incorporate UVGI Disinfection

Ultraviolet Germicidal Irradiation (UVGI) is the application of UV energy to irradiate organisms, altering the structure of the organism’s DNA and stopping replication. While the entire UV spectrum is capable of inactivating microorganisms, UV-C energy is most effective in providing a germicidal effect, with 265 mm being the optimum wavelength.

Overall, there are four main types of disinfecting systems that use UV-C energy. First, UV-C lamps installed in the AHU downstream of the cooling coil provide surface disinfection of the coil surface, in addition to some disinfection of the airstream itself. UV-C lamps installed in ductwork use high UV doses to inactivate microorganisms on the fly, as they pass through an irradiance zone. (The distance of the irradiance zone will be determined by the velocity of the air stream.) There is a minimum UV exposure time, meaning the microorganism must be in this treated area for sufficiently long to be inactivated.

UV-C upper air disinfection uses UV fixtures mounted in occupied spaces near the ceiling, which could be considered when there is limited or no mechanical ventilation. When ventilation is insufficient, however, supplemental fans might be required. Portable room decontamination using UV LED lighting is for surface decontamination, which has been used for some time to disinfect patient rooms in hospitals after patients are discharged, and before a new patient moves in. They could also be used to disinfect classrooms, gyms, and other spaces. It’s important to keep in mind that the room should be completely unoccupied during the disinfection process.

Improve Central & Portable Air Filtration

According to the ASHRAE Position Document on Infectious Aerosols , infectious aerosols can pose an exposure risk, regardless of whether or not an infectious disease is defined as an “airborne.” Larger droplets, containing pathogens, can remain airborne longer if the airflow allows for extended suspension, as noted in a paper titled, “Recognition of aerosol transmission of infectious agents: a commentary.” Propagation of these pathogens makes it possible for individuals to be infected, even when they’re at a farther distance from the original source. Increasing central HVAC filtration to the highest level achievable, without compromising system operation, should be considered. MERV, known as Minimum Efficiency Reporting Values, indicates a filter’s ability to capture various size particles. The higher MERV rating the better, as higher MERV ratings remove smaller and more harmful contaminants from the air. To capture the most airborne contaminants, increase the AHU filtration to the highest equivalent MERV level the equipment can handle, with MERV-13 filtration as a minimum. Determining the highest filter efficiency fan systems can handle is best done in collaboration with either a commissioning provider or a testing and balancing firm.

When it comes to air filters, there are two important factors to consider: the size of particles the filter can capture and the efficiency of that filter to capture those particles. High efficiency particulate air (HEPA) filters can capture 99.97 percent of particles down to 0.3 microns in diameter, but they inflict a substantial pressure drop to the air system. While equipment designed for use in healthcare facilities likely accounted for this, HEPA filtration was usually not considered in the design of commercial office HVAC systems. The latest electronic disinfecting filtration systems can exceed the performance of HEPA, both in terms of particulate size and efficiency with a pressure drop closer to standard filtration media. One variation of this disinfecting filtration system is portable self-contained units, which can be used in high-risk or heavily trafficked areas, such as a lobby or conference room. Alternatively, the filtration system of a central air handling unit can be replaced or supplemented by a modular deployment of these filters. These systems work by first, using a standard pre-filter to capture large particles before having the air pass through a high energy grid. This causes an agglomeration of ultrafine particles, making them larger and easier to capture in the final filter. High voltage energy is then applied to this filter to actually disinfect and kill the contaminants. While this is more costly compared to standard passive filters, it’s highly effective.See also

The Universal Appeal of Living In a Connected Community

When central ventilation system filtration is either not possible or feasible, adding portable room air cleaners with HEPA or electronic disinfectant filtration systems can have a similar effect. The visibility of the equipment to the occupants also provides an added layer of comfort. While portable air filtration units make the most sense in specific high traffic areas, their limiting factor is in how much air they can move through them with their internal fan. In commercial spaces, these are often used as add-ons to other methods, such as improving filtration. Compared to other solutions, contaminants do not need to be brought back to the AHU to be captured by filters or neutralized with UV light, as the ions are created in the supply air and perform once in the occupied space.

Bipolar Ionization

Bipolar ionization is an emerging technology that utilizes high voltage electrodes to create reactive ions that react with airborne contaminants, including viruses. Whereas other solutions require contaminants to be recirculated back to the equipment to either be captured or killed by filtration or UV irradiation, this technology compliments those strategies by distributing disinfecting ions directly into the occupied spaces, where they can neutralize volatile organic compounds and other contaminants at the source. While bipolar ionization is still being thoroughly tested, early results have been positive. A recent study indicated that coronavirus was reduced by 99.92 percent within 30 minutes.

In light of the COVID-19 pandemic, this approach has piqued the interest of many property owners who see it as a no-energy solution for occupant safety. In the past, bipolar ionization was deemed an effective solution for fighting outbreaks such as SARS, norovirus, and strains of influenza but it’s efficacy for the novel coronavirus is still being examined. Some facilities, specifically large airports, have shown their faith in this technology and are currently utilizing it, such as Los Angeles World Airport, Chicago’s O’Hare, Fort Lauderdale International, and Tokyo’s Narita Airport.

Glimpse into Future Practices

Overall, building sanitization and indoor air quality will be viewed through a different lens in the future, as we’ve seen and experienced just how critical it is to maintain a safe and comfortable building environment. Certainly, the impact of the COVID-19 pandemic will shift the building industry in several ways. Moving forward, our society will need to thoroughly adapt to mitigate the risk of virus spread and further infection. Creating healthy buildings has already been gaining traction in newer buildings, with programs such as LEED and WELL leading the way. Indoor air quality has been a key component of both, though ultimately only a small fraction of the overall built environment is certified. Buildings that can provide better indoor air quality are going to be at an advantage in attracting high quality tenants. While in the short term, making IAQ investments might be looked at solely as getting through the COVID-19 pandemic. Going forward, tenants will likely demand spaces that provide high levels of indoor air quality as a standard.

It’s imperative to be cautious, aware, and proactive when it comes to halting the spread of COVID-19 and preventing the potential for future outbreaks. When starting to craft your response plan, property owners need to evaluate the types of mitigation measures their infrastructure and equipment can support, determine what their budget is, and identify what available options will be the most beneficial within that budget. There are a variety of IAQ solutions and approaches including UVGI disinfection, bipolar ionization, and HEPA filters that can support ventilation and dilution efforts with outside air. It’s important to evaluate which options exist, the amount of energy they use, and how they fit within the budget and decide what could be the most practical for the building as a whole. By following these steps and ASHRAE’S framework, property owners could more effectively navigate this new normal by keeping occupant safety a priority, while also maintaining compliance and avoiding costly bills.

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