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Responding to Infection in the Built Environment – COVID-19 and future airborne viruses

Image: Henry Ford Hospital West Bloomfield Atrium Space.

As you sit at your makeshift desk chatting with colleagues in a virtual meeting, you begin to wonder, what will life be like when we return to work? Surely, we won’t return to our workspaces unscathed from this pandemic.

While we don’t know the extent to which the COVID-19 virus will live on in the future, we do know that it won’t be eradicated immediately. Once states lift their various shelter-in-place orders, we must find a new normal.

This pandemic will impact each architectural and engineering discipline just as pandemics and epidemics have been a source of design innovations throughout our history. Architectural and Engineering firms are beginning to explore alternative designs to the spaces we interact with daily, and maintaining social distancing of six feet will likely be part of our new normal.

But what about the air we breathe and the environment we live and work in? We need to turn our attention to the building system we feel, but don’t often see. The system that can effectively stop airborne viruses and protect the health of building occupants—mechanical systems are like a building’s lungs; we need to equip them with the technology to expel the infected air rather than simply recirculate it.

Dr. Stephanie Taylor, a trained Doctor and Architect with a specialty in infection control, recently gave a presentation titled, “Humidification, Human Health & the fight against COVID-19,” in which she drew a startling connection between the buildings we construct today and the rise in infectious diseases.

Over the last few decades, as we have been focusing on making our buildings more energy-efficient, the environments inside have become dryer. This dry air is a problem. Culling together data from numerous studies, Taylor concludes, when the relative humidity is less than 40%, the likelihood of viruses transmitted through the air rises, it is harder to keep surfaces clean as pathogens resettle on surfaces, and pathogens have an increased survival rate.

To prevent this, the relative humidity (RH) level or the amount of water vapor in the indoor air at a given temperature needs to be between 40-60%.

Why? When humidity is increased, infected particles get trapped inside water droplets, making them heavier and easier to pull out of the air by mechanical systems. When the air is dry, the infected particles are small enough that they remain in the air longer and can travel greater distances. Smaller pathogens are also more harmful to humans as they can penetrate deeper into the lungs, causing more severe symptoms.

But that’s not all. At 40-60% RH, building occupants are healthier and able to fight off viruses more successfully. This level seems to be the golden ratio. Ask any museum conservator what the best environment for a Van Gogh is, and it’s no surprise that they respond 45-55%. Actually, under 30% RH and some art objects become stiff and brittle. Why then, do we expect to function at peak performance and remain healthy in dry indoor environments?

Of course, this isn’t new information. For decades, ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, has set standards for indoor air quality in all types of buildings, including optimal RH levels for various building occupancy types.

In addition to humidity levels, what else can be done to eradicate and reduce the spread of airborne viruses from within our built environments? After speaking to engineers at Albert Kahn Associates, they offered several suggestions:

  • Air-Change Rate. Increase how many times an hour the filtered conditioned air is supplied to and removed from a room. Ensure the rate that fresh air is brought in from the outside, is maintained during all modes of HVAC system operation to control indoor pollutants.

  • Air Flow Direction. Manage the direction of airflow, supply from the floor and return at the ceiling to get clean air to the breathing zone. The particulates and heat will rise and exit the returns at the ceiling level.

  • Filtration. Select optimum over minimum filtration. Select the appropriate filter MERV rating to capture particulates at the target micron level. Hybrid filters using ionization UV and impingement can attract, capture, and kill bacteria and viruses. Use bag-in/bag-out filter changing to reduce risk to maintenance personnel.

  • UV Treatment. Strategically placed UV lights at cooling coils can kill bacteria before it’s distributed in the duct system.

The Challenge. Using hospitals as an example, RH levels vary by room, though many are typically at 30%. ORs and surgical suites, many of which are placed in the center of the building, achieve a higher RH, partly due to the insulating materials used to construct the space. When RH is increased in other spaces along the exterior of the building, patients and staff notice a buildup of condensation on windows and exterior walls.

The building envelope isn’t performing well enough to accommodate the optimum space humidity. The building envelopes, or layers of building materials that enclose an interior space, need to keep humidity inside without the condensation that occurs.

We can achieve recommended humidity levels in existing buildings if we improve the performance of the exterior envelope or if we construct an interior zone separated from the perimeter using a properly designed partition. The resulting space located between the existing exterior envelope and the new interior zone could be used for circulation.

All of this, of course, costs money. But, it would vastly improve the health of our indoor environments.



Johannes Palm, PE, LEED AP® BD+C is the Director of Mechanical Engineering for Albert Kahn Associates in Detroit, Michigan. With over 30 years in the industry, he engineers mechanical solutions for clients in industrial, healthcare, education, and corporate facilities.

Caitlin Wunderlich is a writer for Albert Kahn Associates and has written on a variety of topics from the built environment and history of design to sustainable business practices and the cultural sector.

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