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Abstract
This study investigates and optimizes the performance of ceiling-mounted personalized ventilation system when assisted with chair-mounted fans. Detailed computational fluid dynamics simulations were performed to study the velocity, temperature, and CO2 fields around the microclimate of the occupant. The computational fluid dynamics model was integrated with a bio-heat model to determine the corresponding segmental skin temperature and local and overall comfort and sensation. The computational fluid dynamics model was validated experimentally using a thermal manikin in a climatic chamber. The segmental skin temperature, velocity field, and CO2 field were validated experimentally. The predicted values and the measured values showed good agreement. The validated computational fluid dynamics model was used to optimize the height of the chair fan and the fan flow rate for the best combination of indoor air quality and thermal comfort. The chair fan's configuration to achieve the best thermal comfort and the best indoor air quality occurred at different fan heights. The optimal fan height and flow rate for best thermal comfort were 40 cm (15.75 in.) above floor level and 10 L/s (0.35 ft3/s), respectively. However, the optimal fan height and flow rate for best air quality were found to be 50 cm (19.69 in.) above the floor level and 10 L/s (0.35 ft3/s), respectively. At this configuration, the chair-mounted fans were able to reduce the thermal plumes and improve the performance of the personalized ventilation system by nearly doubling thermal comfort and ventilation effectiveness. The use of chair-mounted fans allowed for the achievement of energy savings up to 17% when compared with conventional mixing ventilation system.
Nomenclature: Symbols
| C | = | carbon dioxide concentration (ppm) |
| CF | = | chair fan |
| CFD | = | computational fluid dynamics |
| d | = | diameter of the honeycomb holes, m (ft) |
| D | = | diffusion of Carbon dioxide, m2/s (ft2/s) |
| DV | = | displacement ventilation |
| H | = | fan height above ground, cm (in.) |
| IAQ | = | indoor air quality |
| MV | = | mixing ventilation |
| PV | = | personalized ventilation |
| = | total flow rate, L/s (ft3/s) | |
| t | = | thickness of the honeycomb flow straighteners, m (ft) |
| T | = | temperature, °C (°F) |
| y+ | = | dimensionless wall thickness |
Greek symbols
| ϵ | = | effectiveness |
| μ | = | dynamic viscosity, kg/m·s (lbf·s/ft2) |
| ν | = | kinematic viscosity, m2/s (ft2/s) |
| ρ | = | density, kg/m3 (lbm/ft3) |
Subscripts
| B | = | breathing zone |
| F | = | fresh air |
| f | = | fan |
| R | = | return air |
| t | = | turbulent |
| v | = | ventilation |
Additional information
Notes on contributors
Bachir El-Fil
Bachir El-Fil is an MS student.
Nesreen Ghaddar
Nesreen Ghaddar, PhD, Member ASHRAE, is a Professor.
Kamel Ghali
Ghali Kamel, PhD, Associate Member ASHRAE, is a Professor.