Optimizing upper-room UVGI systems for infection risk and energy

The effectiveness of UV-C irradiation at inactivating airborne pathogens is well proven, and the technology is already advocated for control of some respiratory diseases such as Tuberculosis. UV-C air disinfection is also commonly promoted as an energy efficient way of reducing infection risk in comparison to increasing ventilation. However determining how and where to apply UVGI devices for the greatest benefit is still poorly understood. This paper focuses on upper-room UVGI systems, where microorganism inactivation is accomplished by passing contaminated room air through an open UV field above the heads of occupants. Multi-zone models are developed to assess the potential impact of a UVGI installation across a series of inter-connected spaces such as a hospital ward; this may comprise rooms for one or more patients that are all connected to a common zone that may be a corridor or may act as a communal space, housing fore xample the nurses station. Simulation of dose couples the ventilation, air mixing and upper-zone average field to explore factors influencing device coverage. A first-order decay model of UV inactivation is coupled with the room air model to simulate patient room and whole-ward level disinfection under different mixing and UV field conditions. Steady-state computation of quanta concentrations are applied to the Wells-Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative benefits of different system options for susceptible patients co-located with an infectious source or in nearby rooms. In each case energy requirements are also calculated and compared to achieving the same level of risk through improved ventilation. A design of experiment technique is applied to sample the design space and explore the most effective system design for a given scenario. Devices are seen to be most effective where they are located close to the infectious source. However, results show that when the location of the infectious source is not known,locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones.