COVID-19 & HVAC Systems Summary Brief: Existing Systems June 19, 2020
It is not possible to cover all elements with this single sheet briefing, the intent is to deliver basic information with an invitation to further discuss based on site specific or portfolio needs. CAC-CE is not making any assertions or providing any cures. We are however sharing information that is the best available at this time which is likely to evolve as COVID-19 is better understood.
COVID-19 and possible transmission through HVAC systems is an area of significant attention and focus within the industry and design professionals alike. No simple answer exists as HVAC systems are complex and varied per application. Making a difficult situation even more vexing is that EXISTING systems present the greatest challenge as original design parameters never contemplated two of the three items being explored.
Generally speaking the COMBINED three approaches are being evaluated
Dilution (AKA Flushing): This is an approach where overwhelming amounts of outside air are brought into the facility to reduce/displace concentration of air within the facility. Typically the flush would occur after hours with recovery time built in so the interior space could recover from the added RH and temperature. For existing buildings the addition of motorized dampers and control sequencing for “after-hours” Flush would be needed in addition to monitoring both RH and temperature to ensure ASHRAE standards are maintained.
Filtration: MERV ratings are a standard that rate filter efficacy for particulates. In general the higher the MERV rating the smaller particle can be captured. This again becomes problematic with respect to retrofit. Unless a system is designed for the pressure changes of a MERV-13+ filter the system will not function properly. Compounding that is determining if the filter rack/retainage system is equally rated as it provides little benefit if the filter is capable of capturing small particulates but the housing it is contained in does not. ASHRAE Filtration & Disinfection
UV Light & Bi-polar Ionization: This holds promise but its efficacy in killing organisms has several variables. Simply placing a UV lamp in a machine without any other considerations may not be effective but unlike items 1 and 2 would not general adversely affect system performance ASHRAE Filtration & Disinfection
To support clients with this issue CAC-CE has created a dedicated page with active links to independent resources: https://www.cac-ce.com/covid-19 . Addressing your inquiry directly is the ASHRAE link https://www.ashrae.org/technical-resources/resources which contains data and support of various positions.