Recent research explores the seasonality of COVID-19 (Hao, 2020; Araujo & Naimi, 2020) and the influence of relative humidity (Moriyama et al., 2020). However, it is the psychrometric overlap of climatic seasons and HVAC system operation that determines the indoor environment — where most viral propagation and human response occurs.
Research links air between 40%-60% relative humidity (RH) with less-effective aerosol travel, shorter airborne and surface survival times, lower transmission rates (Noti et al., 2013; Marr et al., 2019; Wang et al. 2020), and more effective patient lung repair functions (Kudo, 2019). Patient respiratory benefits include less-viscous mucous membranes, more effective cilia-related and other antiviral actions in the lungs, and a more productive cough.