A majority of the coronavirus COVID-19 exposure human clusters reported globally are in air-conditioned indoor environments, such as nursing homes, cruise ships, places of worship, hospitals, etc. Why? There are two potential explanations. Clearly, people prefer comfortable air-conditioned indoor environments. Being more comfortable makes occupants spend more time in the space and be more social than if they were less comfortable. At the same time, keeping the air temperature and relative humidity in these comfortable ranges also prolongs the viability of viruses. Such an environment allows COVID-19 and other viruses to live for several days on indoor surfaces and in the air, increasing the likelihood of transfer by human to human contact.

Activities such as touching, coughing, sneezing, and talking generate large quantities of viruses to pass through the air and deposit, not only on other people, but also on indoor surfaces which others can touch and be exposed to. One study showed that viral particles expelled from people are small enough, 0.3 µm or less, to linger in room air for several days. Research shows that both indoor air temperatures and a low relative humidity that people favor also lead to long periods of their viability on surfaces and indoor air. This, therefore, increases the risk of infection with a virus like COVID-19.

This corresponds to “well” air-conditioned spaces, such as the typical, comfortable temperature range of 71⁰F to 75⁰F and a relative humidity range of 60-70%. Research suggests that infectious viruses would lose much of their viability if the temperature of a space is raised to 90⁰F or more and a relative humidity of 90% or more. However, such conditions would lead to the growth of other biologicals, such as mold, and would volatilize chemicals, such as VOCs, in indoor areas, which have their own health impacts, not to mention such conditions are not safe for humans, particularly the elderly.

Of course, the most pragmatic solution, as public health experts have told us, is behavioral. Thorough hand washing water and soap and regular face washing are effective in reducing the risk of getting infected with a virus, social distancing, and staying home if one has any infectious symptoms.

If a building is shut down because of the possibility of COVID-19 presence, a thorough cleaning with disinfectant is useful, but may not be the complete answer. While major areas which people contact (door knobs, bannisters, chairs, etc.) should be thoroughly cleaned, missing one spot could still lead to spreading exposure given COVID-19 can survive for days. Building management may wish to consider, in addition to a thorough cleaning, the temporary raising of the temperature and relative humidity to the levels listed above to aid in reducing the viability of viruses. This may not be the complete solution either, as it depends how effective the HVAC is and whether that temperature and relative humidity can be reached in every affected area of the building where people may be occupying. However, this is something to consider.

CCES has the experts to help you in designing and operating a good, effective, safe HVAC system and can work with public health experts to assess COVID-19 or other potential health impacts. Contact us today at 914-584-6720 or karell@CCESworld.com. Please act and be safe these days!