Air Purifier for Small Office/Home
Any recommendations for air purifiers/filters that are effective in ‘vacuuming’ the coronavirus? Aware that it may only be a small percent if any at all in filtering out a room. But friends and family are returning to work, and anything would be considered if it helps. Any experience with these?
Jesse Smith - July 13, 2020
Harvard is publishing guidelines around school reopening that’s pretty good: https://schools.forhealth.org/wp-content/uploads/sites/19/2020/06/Harvard-Healthy-Buildings-Program-Schools-For-Health-Reopening-Covid19-June2020.pdf
Basically, increasing the rate of ventilation is of primary importance. This is not ventilation as laypeople understand it! Ventilation in this context is the providing fresh air from outdoors, usually regulated by fan motors, and integrated into the HVAC design. Do the buildings have a ventilation system already? If so, verify rates of airflow and modify as needed. Most buildings either don’t have ventilation systems at all, and the remainder have super f’ed up ventilation systems. In a few weeks systemic HVAC failures are probably going to have some very dire consequences for the whole country.
An easy way to add mechanical ventilation is to install bathroom fans in occupied rooms. Ensure that these fans are ducted to outdoors. Standard ventilation rates are 15 cubic feet of air per minute (cfm) per building occupant. So in a room with 4 occupants you would require a minimum of 60 cfm. More is better! Intensive care units are ventilated at a rate of 2 air changes per hour (ACH), with an additional 2 filtered air changes. I have a pretty strong preference for Panasonic bathroom fans. I’ve tested airflow at hundreds of bathroom fans, and Panasonic tend to hit pretty close to rated airflow, are virtually inaudible, and have the best ratio of watt:cfm of any fan on the market. Note: air out = air in, so by definition you’re replacing air at the same rate that it’s being exhausted via the fan.
The problem with ventilation is that you may overwhelm heating and cooling equipment which will cause comfort issues. If this occurs you may need to modify building heating and cooling settings to boost heating or cooling prior to occupancy. Ex. Ventilation rate never goes below 20% of max. Program tstats to boost heating overnight to 73F. Once workers arrive ventilation goes to 100% and the building floats down to 66 throughout the day. An individual late leaving worker turns the ventilation system back down to 20% as they leave. At most this should only be required near peak heating or cooling – basically a few scattered days throughout the year.
System-based filtration is the next line of defense. In most cases the most effective way to provide this is via heating and cooling system. Add a MERV 13 (or higher) filter to the system and set system fan to “ON”. However, this may require technical supervision. Low particulate filters are slightly more restrictive than standard filters, so this can cause problems. IMO, this is being way overblown in tech circles right now by unsophisticated naysayers who enjoy the power rush of acting as a gatekeeper, ymmv.
I’m really not certain on the risks associated with changing filters, but would want whoever was performing this task to behave like they’re handling an object that is potentially very hazardous. Ideally changing filters first thing in the morning prior to building occupancy.
Portable room air filters should be seen as a last line of defense. I know very little about variations in quality and brand. The research shows that they can be effective, but not really my thing.
For buildings where owners want to make slightly more of an investment in ventilation, a central fan integrated supply (CFIS) is probably slightly better than exhaust fans. https://www.buildingscience.com/documents/information-sheets/information-sheet-ventilation-system. Unbeknownst to most technicians, a lot of premium thermostats (virtually all communicating tstats) have the controls for CFIS built in. So simply a matter of wiring a 6″ duct w auto damper and connecting to system. My guess is that 10% of houses are sitting on controls that would allow them to do this, but vast majority won’t ever realize it.
Given that intra-household transfer is one of the primary mechanisms by which covid is spread, it’s worth noting that everything above can be applied to households as well. If you suspect someone in your house may be sick, operating bathroom and kitchen exhaust fans continuously is likely somewhat protective. OTOH, if you have a natural draft water heater (which you shouldn’t!) there’s some chance that it will spill into the house under negative pressure. Keep a CO detector near the water heater and all other combustion appliances if you go this route.
D'angelo Barksdale - July 13, 2020
Jesse, this information is incredible! Thank you for breaking it down for a layperson and bringing up a variety of solutions. I was hoping to confer with my office building’s maintenance person sometime soon – your guidance here is invaluable!
Jesse Smith - July 14, 2020
Happy to help! Keep us updated on your progress!
Kris DzrContributor - July 14, 2020
I have a couple Honeywell HEPA air purifiers. No idea if they actually work against Covid, but they seem to work against allergies and we don’t get sick very often.
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