Why Treating Recycled Air in Commercial Buildings is so Important

Did you know that ventilated air in commercial buildings is shared among all spaces?

In fact, the air extracted from all the rooms is mixed together, spreading contaminants from room to room.

Only a small percentage, about 10%, is rejected and replaced with outside air.

What happens to the other 90% of contaminated air? It is recycled and recirculated in all of the rooms...

Sometimes with insufficient filtration, sometimes without any filtration at all.

How Recycled Air Works in Commercial Buildings

Your CO2 detectors will show good readings, because you evacuated 10% of the CO2, four to six times per hour.

This is enough to maintain a healthy level of CO2 for occupants, but what about for airborne viruses?

Ideally, we don't want to recirculate virus particles back into the rooms.

We want to filter and treat the recycled air with the best efficiency possible.

This applies to all commercial buildings including schools, elderly residences and offices.

What if the water coming out of your faucet was recycled from the rest of the building without being filtered and treated?

Would you drink that water?

And yet that's what we do with the air we're breathing.

Knowing this, which of these water filtration systems would you choose to purify the water coming out of your faucet?

Air Filtration Percentages Represented as Water Glasses

As you can see, increasing the percentage of outside air to 20% or even 50% is not much better despite wasting a lot more energy.

89.93% is the "minimum" recommended by ASHRAE, the CDC and other organizations. Most new buildings use these filters called MERV-13. But is it enough? How can we get closer to 100%?

There are only two ways to properly treat recycled air before it enters the room: filters and UV-C light. These technologies instantly clean the air while passing through them.

Room air purifiers clean the air inside the room over a period of time but they do not prevent contaminated air from entering the room.

Air purifiers would be the equivalent of putting a small aquarium filtration system in your glass of dirty water and waiting until the water is clean before you drink it.

Unfortunately, you cannot wait until the air is clean before you breathe it.

That is why we created UV Diffusers. They treat the recycled air at the end of the ventilation system, right before it enters the room. They deactivate airborne viruses with UV-C light and they also catch dust, mold spores and other allergens with their filter.

UV Diffuser treats the air coming from the ventilation system with UV-C light and filter, before distributing the air in the room while improving air mixing

In your building, you can simply replace your old diffusers with UV Diffusers without having to do other upgrades. It's a simple, quick and very efficient solution.

We also believe in setting higher standards for recycled air when it comes to designing new buildings. Filtering or deactivating at least 99% of airborne viruses like SARS-CoV-2 should be the objective.

There are other ways to achieve 99%+, but UV Diffusers are a simple and energy efficient way to do it.

The problem of treating recycled air applies to all types of buildings, including office buildings, schools and elderly residences.

The purpose of this page is to explain why treating recycled air is so important, and why it should be addressed more seriously. Although the most qualified HVAC and air quality experts are already aware of it, it is our observation that the public conversation about air quality in schools and other commercial buildings seems mostly focused on portable air purifiers and CO2 detectors. Addressing ventilation rates without addressing proper treatment of recycled air is only addressing half of the problem. In our mission to bring global awareness to the importance of treating recycled air, we kept this page as simple, yet as accurate as possible to make it accessible to the global audience beyond industry experts. The notes below add precisions and clarifications to previous statements on this page.

(1) We normally use the lowest percentage of outside air required for human health in order to save energy. Buildings account for 1/3 of global consumption and 1/4 of total CO2 emissions. HVAC systems account for 38% of buildings consumption, equivalent to 12% of the world’s total energy consumption.

(2) The percentage of outside air varies from one building to another. It is affected by the cost of energy, pollution, the location and its climate. The more extreme are the temperature and humidity, for instance, the more energy is used to treat and condition outside air.

(3) In most commercial buildings, a minimum of four Air Changes Per Hour (4 ACPH) is recommended. The number of ACPH depends on the room type, occupancy, presence of contaminants, etc. With the pandemic, it has been recommended to increase ventilation rates to 6 ACPH or more, in schools for instance.

(4) Some energy recovery technologies exist which can help reduce the energy cost of outside air. However, energy recovery has its limits, and increasing the percentage of outside air will still have a considerable impact on energy consumption.

(5) 89,93% is the ‘Droplet Nuclei Efficiency’ of MERV-13 filters. It is the average efficiency of the filter at stopping droplets, weighted by the Anticipated Distribution of Virus Particle Sizes. MERV-13 filters are more efficient at catching larger droplets (3 to 10 um), but are much less efficient at catching smaller droplets (0.3 to 1 um). MERV-13 filters’ average efficiency against smaller virus particles is only 66.3%. It has also been demonstrated that the smaller the particle, the further it can travel in the ventilation system and also in human’s respiratory tract, causing more harm than larger particles (source: Airborne transmission of respiratory viruses, Science Magazine).

(6) It is possible to calculate or measure the single-pass efficiency of filters and UV-C inside the ventilation system, meaning the percentage of virus that is neutralized while in contact with the technology. In the case of UV-C, we must know the light intensity and how long the virus is exposed to the light while passing through it. Exposure time is inversely proportional to the air velocity inside the duct or diffuser.

(7) Portable air purifiers and HEPA air purifiers, PCO, bipolar ionization and other progressive air cleaning technologies’ performance depends on the room size and the period of time for which the technology has been treating the air in the room. Be careful when you see a simple number like “efficient at 99.9% against virus X” for these technologies. In order to be accurate in their claim, they should also provide the room size in which they tested their product, and the duration after which they achieved that percentage.