Effectiveness of upper-room UVGI systems in spaces conditioned by localized air conditioning systems : enhancing air quality and energy performance -

Abstract

Providing thermal comfort and good indoor air quality (IAQ) at minimal energy cost has been considered a priority in the field of heating, ventilation, and air conditioning (HVAC) for the past couple of decades. It is widely known that the use of return air in any air-conditioning system results in a decrease in its energy consumption, but also results in high pollutant and bacteria concentrations that may reach unacceptable levels in the occupied zone. One of the plausible methods used for air disinfection is the Upper-Room Ultraviolet Irradiation (UR-UVGI) systems that can effectively inactivate airborne bacteria, especially if there is air mixing between the upper irradiated zone and lower occupied zone. This work aims to investigate by modeling and experimentation the effectiveness of UR-UVGI in improving air quality in localized air conditioning systems: 1) vertical localizing mixed Displacement Ventilation (DV) combined with Chilled Ceiling (CC) system; 2) horizontal localizing (zoning) using ceiling diffuser that emits the air from the perimeter (sides) while the air return is through the center ensuring that the returned air from the conditioned zone is taken upward to be reused. A commercial computational fluid dynamics (CFD) software is used to simulate the flow, thermal, and species transport in the conditioned space. The airborne bacteria transport and its decay when UV field is present are simulated using Eulerian approach and neglecting gravitational effects; whereas the gravitational settling and deposition effects of large bacteria-carrying particles are simulated using Lagrangian method. The air flow and thermal boundary conditions of the diffuser are obtained from experiments and are used as inputs to the CFD models. The CFD models are validated using air velocity and temperature measurements made at several positions in two climatic chambers to test both horizontal and vertical localization-zoning systems. Since the vertical localization system (CC-DV) is based on vertical transport, a