“Improving UUS:E Building Ventilation” — October, 2022

At UUS:E President Peggy Webbe’s request, Jim Adams prepared the following summary of the Meetinghouse ventilation status. He expressed his willingness to discuss this issue further with interested persons …

The UUS:E Building & Grounds committee (B&G) has implemented various measures to improve the indoor air quality within the Meetinghouse. These measures help to reduce the risk of COVID-19 transmission through a combination of fresh air (ventilation, best choice) and filtration (air purifiers, acceptable alternative). Note that these measures, while providing significant improvements do not eliminate the virus transmission risk inherent with indoor spaces. Also, any such measures can never make the air quality equivalent to being outside.

Transmission of viruses, like COVID-19, is inherently higher risk in an enclosed space or building where the exhaled breath of an infectious person can be transported in the air and remain aloft for hours. Bringing fresh outdoor air into a room (ventilation) can dilute and/or displace any present airborne virus, reducing the risk of infecting others. Where increased ventilation is not possible, the use of HEPA air purifiers is an alternative means of removing the virus from the air. None of these measures completely eliminate the viral risk.

Experts agree that improved air quality should be incorporated as part of a layered defense against COVID-19. It is recommended that this be done using outside air ventilation and/or air purification, targeting a combined 4 – 6 air changes per hour (ACH) though a combination of these approaches. ACH is a simplified way of quantifying the amount of ventilation or filtration flow relative to the size of the space involved. For example, if your ventilation systems flows 4000 cubic feet of fresh air per hour into a 1000 cubic foot room, that equates to 4 ACH (4000/1000). However, due to the mixing involved during that hour, this does not mean that all air in the room is replaced 4 times per hour. In fact, due to mixing, it would take approximately 45 minutes to replace 90% of the room air with a flow level of 4 ACH. As and mentioned previously, these levels of air flow can never make an indoor space equal to outdoors, where air replacement around a person(s) occurs within seconds with even the slightest breeze.

A major component of the air quality improvements is provided by existing features of the building heating and air conditioning (HVAC) system. The HVAC system includes 3 heat recovery ventilators (HRV) which introduce fresh air into the building when required. Up to now, these HRVs were controlled by wall mounted CO2 sensors, and only provided fresh air when enough people were present in a space to bring the CO2 levels up to uncomfortable levels (which was rarely the case). B&G recently made changes to the HVAC control system (aka “new thermostats”) to allow the HRVs to now be used on demand. A large HRV now provides 4 ACH of fresh air to the sanctuary, and the 2 smaller HRVs provide 1 ACH of fresh air to the remaining common spaces and offices upstairs, and all areas on the Garden Level except for the classrooms. To achieve the target 4 ACH in these common spaces and offices, air purifiers with the required flow have been put in place throughout the building. All bathrooms utilize motion detector actuated vent fans for these low occupancy spaces.

The RE classrooms all have their own wall mounted HVAC unit, which provide heating and cooling. However, they unfortunately do not have any fresh air capability. Therefore, each classroom space has been provided with special ventilation window fans which provide at least 4 ACH of fresh air for these spaces, year-round. Testing was conducted by B&G to confirm the fans provide the required 4 ACH, and that the HVAC units are able to maintain comfortable temperatures in the room during winter.

For all of the improvements to work, they must be turned on properly when spaces are occupied. Instructions have been placed above each thermostat describing how to turn on the HRV ventilators, and instructions are in each classroom describing how to utilize the window fans. Air purifiers should be turned on manually when people are present for significant time in the other spaces.