Designing for Better Infection Control
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Mar 5, 2020

Experts are starting to realize that Covid-19 will be with us for the long term. How do we rethink office space design so that it is more like being in the outdoors? How can we design offices in order to decrease the rate of spread of disease? What is best practice in hospitals and elsewhere in the world? How does this all align with sustainability? And health?

Skye, United Kingdom. Photo by Robert Lukeman on Unsplash

The standard office space is designed with a mixed air ventilation system. There are heating and cooling units, usually on the roof in a mechanical penthouse that preheat and precool the air. VAV boxes are usually found in the plenum space on each floor. Each VAV box pushes the right amount of volume of air to each air diffuser on the floor, above open plan workspaces and in each office.

The air is supplied to the space and it mixes with the air that is already in the space. That’s why it is called “mixed air ventilation”. If someone is coughing at the cubicle next to you the water droplets in the air from their cough go up into the air, mixes with the new supply air and travel a distance in the space. The distance that they travel depends on the air velocity and other factors such as humidity and temperature.

No one likes to share an occupied space with an infectious person. Please stay home when you are not feeling well. I anticipate that due to the increased hygiene practices and cleaning to prevent CoVid-19 will have a positive effect on the number of flu and cold illnesses in the general population. Watch for those numbers to go down in 2020, but back to mechanical systems…

Mixed air ventilation systems not only moves the air back to the mechanical systems it moves it into perpetual recirculation. That means that the air that some breathed out will move into adjacent spaces, being delivered to the space as supposedly “fresh air”.

“Fresh air keeps the doctor poor.”
~ Danish Proverb

This mixed stale air not only can be laden with viruses but also is more saturated with exhaled carbon dioxide. Have you ever gotten groggy in an enclosed meeting room after an hour of meeting? That is the build up of carbon dioxide. As atmospheric carbon dioxide levels go up it will be more challenging to keep these carbon dioxide evels down in indoor spaces—plants and living walls can help.

Back to designing HVAC systems to help minimize the spread of infection…

The best approach is to separate the heating and cooling delivery from the air delivery and provide 100% fresh air ventilation.

In fact, this is best practice HVAC design that used to keep gamblers feeling refreshed and awake in casinos (no kidding). This ventilation system also removes all of the toxins from offgassing finishes and furniture in the space and is healthier for the occupants.

This 100% fresh air ventilation strategy has also been implemented in our award-winning state-of-the-art Humber River Hospital.

But 100% fresh air ventilation is not a green building strategy until you put in heat recovery. In an airtight house that heat recovery is your “HRV”, or better yet, an “ERV”. In a hospital it is a giant enthalpy wheel that transfer the latent heat over to the incoming air without transferring the viruses.

The executive at HRH was hesitant about enthalpy wheels until I took them on a field trip to stand in one at the Earth Rangers building on a -10oC day. They could feel the different between the incoming fresh air and the preheated fresh air.

Perhaps surprisingly, the shift to this type of mechanical systems design also makes the building more efficient to heat and cool. Because water is more dense than air, hydronic systems can delivery heat more effectively. Chilled beams with hydronic pipes can deliver cooling more effectively.

In fact, this is the way that the Europeans have been designing their buildings for years. Isn’t it time we caught up to their best practice?

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