According to the World Health Organization (WHO), COVID-19 is primarily transmitted through respiratory droplet particles 5-10 μm. These droplets typically fall to the ground within ±6 feet. Droplets smaller than 5 μm are referred to as “droplet nuclei” and are often caused by partial evaporation of the larger droplets. These droplet nuclei can become suspended in air and form an aerosol traveling longer distances and surviving for 3-7 days. Per the CDC, typical virus particle size in an aerosol is 0.05 to 0.15 μm. Since airborne droplet nuclei may be a means of the virus spread, efforts are being made by building operations to reduce such risk thru improved ventilation and filtration. (The symbol “μm” is a micron which is equivalent to 1/1000 millimeter. For reference, a human hair is about 100 microns in diameter.)
Action by The College of Wooster
The College of Wooster continues to seek and follow guidance on building HVAC systems relative to Covid -19 as we have for the past year. The Facilities staff is pursuing guidance and recommendations from current /relevant published literature by such recognized entities as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Centers for Disease Control (CDC) as well as from Consulting Engineer H. Lewis Hinkel, Jr., PE of HLH Engineering Consulting, LLC, of Wooster, OH.
The College of Wooster Facilities department is continually inspecting and performing preventative maintenance (PM) on the HVAC systems to best assure proper operation with minimal downtime of these critical systems (i.e. fans, pumps, chillers, boilers, filters, automation system controls and their calibration) as well as regularly replacing air filters to maintain proper air flows and cleanliness.
The College of Wooster is using MERV-13 air filtration in the majority of the campus HVAC central Air Handling Unit systems in accordance with the recommendation from ASHRAE. There are some smaller units on campus which cannot incorporate such an air filter due to either physical size or air pressure drop limitations. (MERV is an air filter rating system and stands for Minimum Efficiency Reporting Value. The higher the MERV rating the better. Prior to Covid-19, many HVAC systems were operated with MERV-8 air filters.)
The College of Wooster is operating the HVAC central Air Handling Unit systems at a higher than normal level of outdoor air ventilation to better dilute the potential contaminants. This is a constant balancing act as too much outdoor air may exceed a systems capability to properly dehumidify and thus cause other Indoor Air Quality issues such as mold. Thus the outdoor air is increased within the reasonable limits of the existing HVAC systems.
The College of Wooster is operating the HVAC central Air Handling Unit systems for continuous air circulation and ventilation 24 hours a day / 7 days a week for improved filtration and dilution of potential contaminants.
The College of Wooster is performing many of the above tasks related to system monitoring and adjustments thru the campus networked Building Automation System (BAS) via a remote computer. The majority of the HVAC systems on campus are at least partially connected to the BAS. Thus the College can often start/stop fans and make changes to the heating / cooling and ventilation systems without a physical presence. Furthermore, many of these task are automated via scheduling thru the BAS.
The College of Wooster is taking the above action steps in an effort to improve the indoor environment to help prevent the spread of the virus within the space and in an effort to prevent the transmission of the virus via the HVAC system to other spaces. It is not possible to guarantee complete transmission prevention due to limitations of air filters, even the ASHRAE recommended MERV-13 air filter. The operating changes for both increased and continuous ventilation also increases energy consumption.
The College of Wooster is operating the HVAC systems in the above manners throughout the Covid-19 Pandemic regardless of the associated increased operating costs because of its commitment to safety.
Please submit any questions to Associate Vice President of Facilities, Design and Construction Mike Taylor at firstname.lastname@example.org or to our lead Consulting Engineer H. Lewis Hinkel at email@example.com.
Date updated: 09-14-2021