Library Board of Trustees Agenda and Packet 2020 09 10

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in part to the lack of universal compliance. This memo suggests mitigating SARS-CoV-2 transmission by restricting room occupancy based on the known room ventilation rate. (Other contributors have made prior recommendations: e.g., see [2] and citations therein.) This proposed focus on ventilation system performance and room occupation number provides a mitigation layer which is less dependent on the actions of individuals or the quality of masks they are able to obtain[7]. A useful metric for evaluating the effectiveness of ventilation systems is the concept of cubic feet of clean air per minute per person (cfm/person) [8] . For the purpose of virus mitigation, here we define "clean" air as either outside air, or if recirculated, then filtered by at least a grade MERV rating 13 filter, or higher. In [8] cfm/person refers to outside air only. If a building operator is given a design figure for cfm, then they should try to determine if it is for outdoor air, or a mix of outdoor and recirculated air, and if recirculated air, then how is it filtered before reuse. A problem facing operators of classrooms and lecture halls is how to safely increase occupancy given the limits of existing building HVAC infrastructure. A recent technical report for the University of Colorado campus suggests supplementing HVAC recirculated air with portable air cleaners to achieve a mixing ratio of 1:2 to 1:4 for outside to recirculated, cleaned air[9]. A higher mixing ratio of outside to recirculated air might be desirable for various reasons [8], but the maximum cfm of outside air might be limited by existing HVAC installations. Also, introduction of extra outside air can expend more energy for heating and cooling. 1 Some public spaces are designed for outside air ventilation rates as low as 5 cfm/person for auditoriums, 9 cfm/person for museums, 17 cfm/person for offices, and 26 cfm/person for health clubs[8]. However, at least since the 1853 Crimean War it has been "observed that diseases spread faster in 'My personal preference is to open windows and skylights for natural ventilation but modern era commercial and industrial buildings seldom have windows and skylights that open since it has long been known that natural ventilation decreases control on the air exchange rates[10], and natural ventilation decreases precise control of temperature and humidity. Future air processing system controllers could be designed to detect and ac- commodate natural ventilation from windows and skylights which might save energy and improve indoor air quality at the expense of precise temperature and humidity control which in many cases is unneeded and annoying if it causes a large temperature differential between outdoors and indoors. 2