Desk fans for the control of the convection flow around occupants using ceiling mounted personalized ventilation

This study aims at studying by modeling and experimentation the performance enhancement of ceiling-mounted personalized ventilation (PV) nozzle when assisted by small desk-mounted fans to reduce the effect of thermal plume generated by the occupant. Detailed computational fluid dynamics CFD simulations were performed to study the flow, thermal, and CO2 concentration fields around an occupant using a single jet ceiling-mounted PV nozzle in the conditioned space while the fans are on. The CFD model was integrated with a bioheat model to determine the corresponding human body segmental heat fluxes and convective plumes for predicting the occupant segmental and overall comfort. The CFD model was validated with experiments using a cylindrical heat source and comparing measured velocity, temperature and CO2 concentrations in the vicinity of the nozzle and the cylinder. Good agreement is found between the measured and the numerically predicted values. The performance of the PV nozzle assisted with desk fans is assessed by evaluation of ventilation effectiveness in the occupant microclimate and comfort conditions and results are compared with single jet PV and co-axial jet PV, both without the use of desk fans. The desk-mounted fans were able to reduce the convection plumes around the occupant and improved the performance of the single jet PV nozzle by doubling the ventilation effectiveness and improving comfort. They permitted also to achieve a reduced energy saving by up to 13% when compared with conventional mixing ventilation systems.