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Engineering designs to help keep indoor air clean as we begin the "new normal"

With stay-at home orders being lifted and laxed, most of us are ready to return to some form of normalcy. Part of that is making changes to indoor environments to create safer spaces in which to live; to work, to learn, to shop, to dine… among other things. We believe that one of the key measures for businesses, offices, schools and other buildings to make this safety change is in evaluating their indoor air flow and quality in an effort to mitigate the spread of viruses. Harvard T.H. Chan School of Public Health sites "healthy building environments can play an important role in combating the spread of infectious disease, including coronavirus."

The CDC lists inhalation of airborne particles as one of the basic means of disease transmission for non-bloodborne pathogens. While social distancing and cleanliness can deter part of the spread, airborne transmission can also impact the spread based on the air distribution/ventilation system in businesses where you work, dine and shop.

ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) states: “…Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures. Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air…”

ASHRAE’s recent documentation sets forth “pathogen dissemination through the air occurs through droplets and aerosols typically generated by coughing, sneezing, shouting, breathing, toilet flushing, some medical procedures, singing, and talking.” That is a lot of ways! It also sites three ways to mitigate the spread through airborne particles: filtration, disinfection, or ventilation. In design approaches these usually overlap. The design and method selected and utilized will most likely depend on the HVAC system you have in place or plan on procuring.

To trap airborne particles, (filtration) you want to examine your system, replace filters with higher-rated filters, trying to do so with little or no changes to your existing system. Sometimes minor modifications may be required. These changes should be reviewed with a mechanical engineer. When meeting with the engineer, discuss usage for areas like conference rooms, bathrooms and waiting areas. It may be necessary to add additional air filtration, like a stand-alone portable HEPA unit. The key will be to monitor and replace filters continuously. However, filtration will not eliminate all risk of transmission of airborne particulates because many other factors contribute to disease transmission.

In addition to filtration is disinfection. We want to “clean” the air that is being filtered and conditioned. UV lighting is one of the most common HVAC disinfectant systems to kill viruses in ductwork. Beyond UV disinfectants, one could consider bipolar ionization and photocatalytic oxidation which charge the existing air to kill pathogens. Reliable testing for these systems is still in early stages.

Then there’s ventilation. Sounds easy enough, right? Open a window or door and increase the amount of fresh or outdoor air. Increasing the air change rate is the most common way to reduce unwanted airborne particles. But what if there are no windows or doors to open to outside air? You can try modifying the system to full-air economizer mode, increasing your outdoor air damper positions, and/or adding air changes by night-flushing or running the system continuously; kind of like what you do to filter, clean and chlorinate a pool. Such frequent air exchanges will impact energy use and operating costs. Again, meeting with a mechanical LEED engineer will assist with these changes.

As the infection pathways of COVID-19 are discovered and better understood, guidance is shifting regarding criteria such as the optimal relative humidity levels to maintain in a building and the criteria around air filtration. Relative humidity is an important consideration of any system. Studies have shown that pathogens have a difficulty surviving at higher relative humidity levels. However, indoor relative levels of above 60% humidity can have negative effects in certain environments. They can promote, if not facilitate, the growth of mildew. This requires we keep a tight range of humidity (40-60%) to help control pathogens without other adverse effects.

Finally, it is important to measure and test the quality of the air. Properly designed air filtration systems can be important in mitigation of the spread of airborne pathogens such as COVID 19, improving your indoor air quality and creating safer environments in which to work and live. Well-designed, installed, and monitored mechanical and plumbing systems can produce healthy indoor environments vital to post COVID-19 living. Our mechanical engineers apply fundamentals to design and implement these systems to achieve the goal of healthy, clean air.

DMG can provide business owners and operators guidance on how to improve their indoor environments with readily available technologies sized for any building and budget. DMG utilizes polar ionization to reduce outdoor air energy requirements by 50% in a number of projects.

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