Dilution: A Strategy to Reduce Indoor Air Pollution

Jul 7, 2021DMA Engineering, Steven Forrester - Principal

Data tells us that COVID-19 is an airborne virus, spread from person to person through droplets or what is known as bioaerosols. In a commercial building, we believe dilution is the key to any indoor air quality strategy. 

With dilution, we can proactively replace contaminated indoor air with fresh outside air. This decreases the potential concentration of infectious matter.  If you use a dilution combined with filtration and disinfection, you’ve got a strong approach to minimize COVID-19 transmission.   

In our experience, many commercial buildings use demand-controlled ventilation (DCV), adjusting outside ventilation based on occupant demands. This was great in the past and it was deployed in most large commercial buildings. But times have changed in the face of the pandemic. ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, advises against the use of DCV technology because we want to keep outside air dampers as fully open as we can to maximize air changes in interior spaces. So, we’ve got a nation full of buildings using DCV and none of them are optimized for your (and your occupants) safety. 

So how do we tackle this and how do we leverage dilution as a tool in our arsenal? 

To do it right, you’ll need a trusted HVAC engineer to help. DMA can come in, look at your existing control sequences and economizer limitsImproving indoor air quality during a pandemic is not as simple as adding a few HEPA filters or air monitors and calling it a day. It requires looking at the available systems holistically and determining what is the best fit for your building. The approach for your building needs to be tempered with budget and what the plan for the building is both short and long term. 

For the short-term, we want your building to remain open and keep your occupants safer than they would be without any evaluation. We can do a Building Readiness analysis to make that happen. For long-term, we can look at energy efficiency, occupant wellness, potential disasters (hurricanes, fires, etc) and how that impacts the standing of your building from an HVAC perspective — and from a climate change perspective as well.  

Why would you want a long-term strategy for your building? To preserve and protect the valuation of your building. To reduce operating expense. To be compliant with future environmental regulations.  For the health and well-being of yourself and your valuable tenants.  

In summary, the key to reducing indoor air pollution is dilution. Whether by higher filtration, higher outdoor air rates or both. Collectively, we need to be wary of adding charged particles to the air and be mindful of the long-term effects of breathing these particles. If you need help navigating this brave new world, let’s talk. We’re here to help. 


Propmodo, September 2020 

HPAC Engineering, August 2020 

** Figure 1 shows that MERV 13 filters are 95% efficient at removing those aerosol sized (2 µm) particles.