One of the first things to consider before modifying ventilation in a particular building is how it is ventilated: Is there a mechanical system that brings outdoor air into the building and distributes it to the occupied spaces? What kind of system is it (e.g., central or local)? How much outdoor air does the system provide? How is the outdoor air intake rate controlled and can it be modulated? However, it is essential that such efforts recognize the large amount of variation between buildings and their ventilation systems, which directly relate to what can and should be done in a given building. Given the impact of ventilation rates on airborne infectious disease transmission, improving ventilation is clearly important (Morawska et al. It is therefore essential to identify the specific airflow of interest when discussing ventilation. Some people think of ventilation exclusively as outdoor air delivery, while others think of it as air supply to an occupied space without reference to the amount of outdoor air it might contain. Note that this definition does not mention outdoor air delivery. This usage is consistent with ASHRAE Standard 62.1, which defines ventilation as “the process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space” (ASHRAE 2019a). In this article we use the term “ventilation” broadly to include outdoor air and exhaust ventilation, heating and cooling, humidification and dehumidification, and contaminant removal using filtration and other technologies. However, in pursuing efforts to address ventilation it is important to understand that potential changes in ventilation depend on the specific building being considered, its existing ventilation and space conditioning systems, the local climate, and outdoor pollutant levels, among other factors. This increased attention to ventilation is a positive step given the well-established connection of ventilation to indoor air quality (IAQ) and to the health, comfort, and performance of building occupants (ASHRAE 2020). 1970 Wargocki 2021), with increased interest driven recently by the pandemic, climate change, and other issues. The importance of ventilation has been recognized for as long as people have occupied buildings (e.g., Beecher and Stowe 1869 Janssen 1999 Klauss et al. The cited organizations stress that ventilation is one element of a layered approach to managing the risk of airborne disease transmission other measures include handwashing, face masks, vaccination, and distancing. In response to the covid-19 pandemic and in recognition of the importance of airborne disease transmission, there have been multiple calls to ensure adequate building ventilation, in some cases recommending increased ventilation rates (ASHRAE 20 REHVA 20). Improvements to ventilation system performance vary by building, use, existing system capacity, local climate, and other factors.
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