Dear Partners,

HVAC systems have limitations; however, there may be some things you can do to increase the “health” of your building air:

FILTERING – Why spending money to improve your filters is not necessarily a good value:

1. The coronavirus is very small and capable of making it through virtually all filter media. With that said, the higher the efficiency the more it will capture. The sticking point is that most AHU’s cannot handle the increased static pressure drop of higher efficiency filters
2. We believe what coronavirus that finds its way into the return air will die before it makes it back to the air handling unit, let alone be recirculated to the occupied space. This is due to most buildings having a plenum return, which has low velocity allowing the virus to settle out and die. This “social distancing” is large.

UV LIGHTING IN AHU’s – Why spending money in this area might be a better value:

1. UV lighting does kill the virus. However, most UV lights are not sized to assure that EVERY virus that goes by them is destroyed. Many of the UV lights are sized to destroy molds that grow on AHU coils at night while the AHU’s are shut down.

AIR CHANGES IN YOUR BUILDING – Spending money here can provide value:1.   Increasing the percentage of outside air being delivered to your building by the AHU is one thing that you can do that does improve the health of your building and reduce the likelihood of spreading the virus. The good thing is we are at the time of the year where your building naturally increases the amount of outside air because of air-side economizers.

• In some buildings, the amount of outside air can be temporarily modified through the BAS to increase the percentage of outside air delivered to your building.
• If your building does not have an-air side economizer this logic does not apply.

HUMIDIFICATION – Something to think about if it is part of your HVAC system:1.   Studies show that viruses do not survive as well if the relative humidity is between 40 and 60%. If your building has a humidification system, it typically operates at set points below these levels. With the weather being mild, your humidification system may be able to increase the humidity to these levels, reducing the virus spread.

If you want to dig deeper, we have provided a number of resources from ASHRAE for your reference.

• ASHRAE's Position Document on Airborne Infectious Diseases
• Guidance for Building Operations During the COVID-19 Pandemic
• ASHRAE Letter to the World Health Organization

Jim Cooper, PE
VP Engineering