Quantifying the impact of UVC in reducing airborne pathogen transmission and improving energy efficiency for healthy buildings: Kahn-Mariita equivalent ventilation model

There is growing evidence that viruses responsible for pandemics, such as MERS and SARS, are mainly spread through aerosols. Recommendations have been introduced to reduce the transmission risk of virulent airborne viral particles by increasing ventilation rates, expressed in air-changes-per-hour (ACH), effectively improving the dilution of airborne pathogens via mechanical ventilation. However, the infrastructural and operational costs associated with upgrades of Heating, Ventilation, and Air Conditioning (HVAC) systems make these solutions expensive. It is well documented that UVC disinfection can help lower exposure risks by inactivating viruses in shared enclosed spaces, and the performances of such solutions be translated into equivalent ventilation (equivalent ACH or eACH). Here, we present the first framework to extract the optimum UVC output requirements for a target eACH, and improve facilities ability to comply with ventilation guidelines at lower energy costs. The Kahn-Mariita (KM) model considers the air quality of a shared enclosed space over time by supplementing existing mechanical ventilation with localized UVC air treatment, whether in recirculating units or upper-air systems, and extracts the systems requirements based on end-user needs by incorporating variables such as room size, occupancy, existing ventilation, and target eACH. An example of a conference room shows that a UVC chamber with an air recirculation rate of 160m3/h increases the ventilation from ACH=3 to eACH=7.9 and reduce down-time from 46 minutes to <10 minutes with as little 1W of UVC output. A recirculation rate of 30m3/h however offers no noticeable benefits above 200mW, with a maximum reachable eACH=3.9 and down-time of approximately 31 minutes. The KM model is unique in that it allows for the first time to find the optimum UVC output needs to ensure air quality is maintained and transmission risk minimized, while increasing energy savings. Recent studies suggest mechanically increasing fresh air supply will more than double the energy costs of HVAC systems, while the use of UVC reduces energy demand as much as by 50%. The KM model approaches air quality and energy efficiency in a unified way by incorporating UVC as a supplement to existing ventilation to increase eACH, reduce down-time, and increase the closed space occupancy.