IAQ, COVID-19 and Metal Architecture

Even with the vaccines, COVID-19 remains a concern, especially regarding indoor air quality (IAQ). The airborne transmission of SARS-CoV-2—the official name for the coronavirus responsible for COVID-19—is the subject of multiple ongoing research and studies across the world. These studies are confirming the importance of having the best IAQ possible inside our buildings to minimize COVID-19 transmission as well as other infectious diseases.

IS YOUR IAQ A-OK?

COVID negatively affects IAQ. “IAQ, by definition, is indoor air, including all of the constituents that make up that indoor air,” says Andre’ Lacroix, vice president of EZ Breathe Healthy Home Solutions, Macedonia, Ohio. “COVID-19 is a small, airborne particulate that remains suspended in the air for prolonged periods of time, thus negatively affecting IAQ.”

“Like other airborne pathogens, the SARS-CoV-2 virus is emitted by respiratory activities (breathing, speaking, singing, sneezing, coughing in droplets ranging from about 0.1 micron to more than 100 microns in size,” explains William P. Bahnfleth, Ph.D., PE, professor of architectural engineering, Penn State, University Park, Pa., and chair of the ASHRAE epidemic task force. “Large droplets tend to fall out of the air relatively quickly over a fairly short distance, but most of the viral load is in small droplets 5 micron and smaller that can stay airborne for long periods of time and travel far from the source. Because COVID-19 is airborne and transmission predominantly occurs indoors, ventilation, filtration and air disinfection are important ways to reduce risk. These engineering controls are discussed in detail in ASHRAE’s COVID-19 guidance at ashrae.org/covid19.”

At this site, the ASHRAE Core Recommendations provide a concise summary of recommendations for ventilation, filtration and air disinfection. ASHRAE has published several COVID-19 related guidelines for commercial applications that vary based upon specific building types and are applicable for all types of buildings.

Joshua Thompson, research and development specialist at Hamstra Heating & Cooling Inc., Tucson, Ariz., says, “Improving HVAC system air filtration, when possible, is one excellent method to remove indoor airborne viruses. Research suggests that a Minimum Efficiency Reporting Value (MERV) 13 efficiency is the minimum MERV rating capable of capturing many airborne viruses. [There is] a wide range of filtration options ranging from MERV13 to MERV16 efficiency, and even HEPA filtration for critical environment projects.” The higher the MERV rating, the better the filter is at trapping specific types of particles.

“ASHRAE’s guidance is that buildings have at least code-minimum ventilation, upgrade filtration for recirculated air to MERV 13 if possible, and consider using in-room air cleaners and air disinfection technologies such as germicidal ultraviolet light to provide additional protection,” Bahnfleth says.

DESIGNING FOR IAQ

With respect to COVID-19 risk reduction, buildings should be designed to have outdoor air ventilation that meets the building code, which generally means complying with ASHRAE Standard 62.1 for non-residential/non-healthcare buildings.

However, Bahnfleth cautions this is not sufficient in many cases to provide the level of mitigation many recommend, i.e., four to six equivalent clean air changes per hour from ventilation, filtration and air disinfection.

“Mechanical filters of higher efficiency can greatly reduce airborne particulate matter (PM) 2.5 exposure. Removal of gas phase contaminants by ventilation can be enhanced by use of sorbent air cleaners and other technologies. An overall IAQ plan must be holistic, addressing in appropriate ways all of the main contaminant exposures.”

Valerie Bradt, marketing communications manager for DriSteem, Eden Prairie, Minn., says ASHRAE’s Position Document on Infectious Aerosols contains a wealth of information about design considerations. “This ASHRAE position paper recognizes the role of the built environment in reducing the transmission and impact of the virus and, more importantly, has extended this to commercial buildings that currently lack minimum RH guidelines.”

Lacroix explains architects must understand what makes up the entire building envelope, not just the traditional living spaces. “If a part of the house is not completely sealed off from the living space—attic, crawlspace, etc.—then that is part of the living space, and must be designed as such. When calculating ventilation and loads on the home, this needs to be considered. If a structure is poorly insulated, then the ventilation and filtration rates will not be sized appropriately.”

Can air cleaning devices that use bipolar ionization, including portable air cleaners and in-duct air cleaners used in HVAC systems, protect against COVID-19? Yes, says Lacroix, but he cautions they need to be meticulously maintained, and are one part of a whole building solution, including a ventilation system. “Any air cleaning device has a law of diminishing returns, where the machine will never be as effective as the day the new filter or accessory is installed. For example, if you have to change out a filter every three months, the machine will not be nearly as effective on day 90 of the filter as it was on day one of the filter.”

HUMIDIFICATION

Healthy levels of humidification can help reduce the spread of viruses like COVID-19 in the built environment. Bradt says while this applies to all buildings—hospitals, clinics, senior living facilities, schools and offices are among those that will benefit the most from adding a humidification system or from improving the existing humidification system. “The World Health Organization has called for ‘non-pharmaceutical approaches to mitigate the transmission of COVID-19’; the addition of humidity is a safe, efficient, and easy way to protect staff, patients, residents, teachers and students.”

A key study completed in 1986, titled “Indirect Health Effects of Relative Humidity in Indoor Environments” by the U.S. National Library of Medicine, showed that the optimal conditions to minimize risks to human health occur between 40 to 60% relative humidity (RH), at normal room temperatures. Bradt says this study is still referenced by HVAC professionals today and forms the basis of standards for healthy indoor air quality in built environments set by ASHRAE. “Maintaining RH within this 40-60% range not only decreases the impact of viruses, but also reduces bacteria and allergens found in the environment, while preventing skin dryness and eye irritation.”

Adding humidity is a safe and efficient way to protect building occupants against the transmission of viruses, one that Bradt says is a hands-off approach that offers an additional layer of protection. “For buildings that did not originally have humidification equipment and need to be retrofitted, supplementary humidification systems can be quickly installed on a wall and add moisture to rooms right away. Larger humidification systems can be incorporated into a facility’s HVAC system, in the mechanical room or on the roof, and can keep an entire building humidified.”

IAQ AND THE METAL IMPACTS

Air leakage and condensation are the two main concerns for any building enclosure and they apply to metal buildings as well. “It has been my experience operating a water and mold remediation business for many years, that metal buildings when properly insulated reduce the likelihood of outside water migration through the building envelope,” says Keith Roe, CIC/CMC, founder/CEO, Advanced IAQ Solutions lnc., Bath, Pa. “Also, this type of construction is less likely to have water condensation forming in the wall cavities behind the finish material when insulated with expanding foam insulation. This minimizes the growth of microbials—mold and mildew—inside the building which would increase the release of bioaerosols into the indoor air environment.”

Thompson believes metal buildings have better IAQ benefits when compared to alternative construction. “Uncoated metal should never outgas or release VOCs, termites are not a concern—meaning there’s no need for harsh chemical treatments that could impact IAQ—inorganic steel does not promote or feed mold spores or mildew, and metal contains no respiratory allergens.” But Thompson cautions that certain types of metal construction can also negatively impact indoor air quality. “Depending on the specific materials/finishes involved, there is potential for outgassing and VOC introduction to the space. Care should be taken when selecting construction materials and interior finishes to avoid or minimize potential IAQ hazards, and proper ventilation and IAQ solutions should be implemented to address potential concerns when applicable.”

When metal construction features materials subject to outgassing or VOC emission, Thompson says applying a sealed finish can help prevent or even eliminate the risk factors involved by containing the source and preventing it from coming into contact with indoor air. “Product selection and application are vital because some finishes contain chemicals and compounds that are arguably more hazardous to occupant health than the construction materials being covered.” Bradt believes any finish that reduces heat transfer will help to reduce condensation, which is important because excessive condensation buildup can lead to mold and mildew growth.

A TIGHTER ENVELOPE

Metal envelopes have become tighter. How has this affected IAQ? Lacroix contends tighter metal envelopes may have contributed to an increase in poor IAQ. “A tighter envelope means less air exchanges, which leads to more stagnant air, which means increasingly poor IAQ.”

Roe explains airtight buildings do not allow natural, passive ventilation to occur without opening windows and doors or pumping fresh air in mechanically. “When exhaust fans are operating with no makeup air, they create a negative air condition that can actually pull in outside moisture. A negative air condition will also not allow exhaust systems to effectively dispel odors, gases, VOCs and bioaerosols that are created inside the building envelope. Often elevated carbon dioxide levels increase, contributing more to the stale air condition. Dedicated fresh air ventilation systems with high efficiency filters in addition to heating and cooling HVAC systems can provide a desired level of fresh air and sustain healthier indoor air quality standards.”

Thompson explains that the most important takeaway is to ensure architects, HVAC mechanical design professionals and all involved work closely to review the project, construction materials, health/allergy sensitivities and specific desires for indoor air quality. “While some IAQ solutions can be easily installed at any point post-construction, certain solutions and components—such as filtration and fresh air ventilation—need to be accounted for and specified during the initial design phase.”