During COVID times, we have to look at all available – and viable – options for occupant safety.
To help slow the spread of the coronavirus, ASHRAE (Guidance for Building Operations During the COVID-19 Pandemic) , CDC and WHO recommends running HVAC systems for a minimum of 4 hours (but preferably more) on a daily basis with 100% outside air (OA) to “flush out” the virus. But I slightly beg to differ from this recommendation.
While the virus might be “flushed out” during that time, it doesn’t mean the germs are flushed off from surfaces. And the results only last as long as 100% OA continues. When the next new person enters that space, they can introduce the virus all over again. Not to mention, Relative Humidity (RH) guidelines combined with increasingly extreme temperatures in summer and winter make it impossible.
If you bring in 100% OA during the hot summer months, here’s what going to happen:
- The HVAC system brings in 5-6x the amount of OA it’s typically designed for
- The A-C system works harder to get the temperature of that OA down so the inside temperature can be a comfortable one at a more reasonable RH – but it cannot do this.
- It will cost you more money on utilities
- Due to the higher RH, chance of developing mold increases
- Occupants complain about higher indoor temperatures and humidity
However we do support the other recommendations provided by ASHRAE (Position Document on Infections Aerosols) to prevent coronavirus in your building:
- Change building operations, including HVAC systems, to reduce airborne exposures
- Increase Ventilation and Filtration
- Maintain humidity between 40 – 60% RH
- Use higher MERV rated filters
- Run Systems Longer
- Use UV Germicidal Irradiation, in any form (duct, in-room, portable)