This work develops a standalone autonomously controlled personalized ventilation (PV) unit in a naturally ventilated (NV) office space to maintain acceptable thermal comfort (TC) under steady and transient indoor conditions and activity levels. The NV-PV proportional integral derivative (PID) controller adjusts the PV supply temperature (T_SPV) at the occupant set flow rate (Q_SPV) based on predicted TC using a regression model. The target TC level that the controller attains at all times is between 0 (neutral) and 1 (slightly comfortable). Process transfer functions were developed and then used to find the adaptive PID tuning coefficients using the Internal Model Control (IMC) method. The controller was tested in a case study at indoor temperature range of 25 to 33 °C with relative humidity range of 55% and 80%. It was shown that the NV-PV controller adjusted T_SPV to maintain acceptable TC under transients of indoor conditions and metabolic rates.

Creating a micro-environment around infected occupants constitutes an effective strategy in reducing contaminants spread insuring a relatively clean macroclimate decreasing the risk of infection for occupants circulating in an office space. In this work, the ability of ceiling personalized ventilation (CPV) system assisted by desk fans (DF) or chair fans (CF) was studied with respect to confining contaminants spread in typical office space while considering possible occupant shift. A 3D computational fluid dynamics (CFD) model was developed to simulate particle spread. The developed model was validated experimentally with respect to concentration values using a thermal manikin in a climatic chamber with controlled particle generation. A parametric study was followed to determine the effect of the occupant shift from CPV design position, the CPV+DF or CF configuration, and the canopy angle on confinement performance for minimal particle spread in the space. The CPV jet and diffusers’ flow canopy favored particle deposition within the microclimate region leading to their removal from indoor air. For no occupant shift, assisting the CPV jet by DF or CF was very efficient in particle confinement. However, in the cases of critical backward occupant shift, flow asymmetry was formed around the occupant leading to particle spread and leading to asymmetry attenuation when operated with CF. The highest particle confinement was obtained for a canopy angle of 45° for the case of CPV assisted by CF due to forming a recirculation zone between the CPV and jet diffusers; hence trapping particles and reducing their spread to the macroclimate. It was found that a total supply flow rate of 60 L/s for MV is required compared to 43.5 L/s for the optimal CPV design, for equivalent average particle concentration within the macroclimate zone at the critical generation plane, leading to 62% reduction in power consumption of the supply fan.

Localized airflow can result in both temperature and pollutant concentration segregations with limited mixing between adjacent environmental zones. However, when the bacteria source is within the environmental zone, it becomes important to look for effective methods to disinfect the localized air and prevent cross-infection among occupants in the same zone. This work investigates the effectiveness of upper-room ultraviolet germicidal irradiation (UVGI) in reducing airborne bacteria transmission within a zone conditioned by localized ceiling-mounted air- conditioning system that recirculates return air. A computational fluid dynamics (CFD) model was developed to simulate the transport and inactivation by UV of Serratia marcescens, an extremely UV-susceptible microorganism. The CFD-UV model was validated using measurements of airflow, temperature, and UV irradiance. Numerous CFD simulations were performed for a case study to determine the maximal fraction of return air that can be recirculated for energy conservation without violating the indoor air quality standards for CO₂ and bacteria concentrations. Results revealed that a maximum of 23% return air can be tolerated when minimal UV output of 15 W is delivered to the space. The use of the optimal setting reduced the energy consumption of the system by 15% compared to 100% fresh air case without UVGI.