Chair fan-enhanced displacement ventilation for high IAQ: Effects on particle inhalation and stratification height

Abstract

Displacement ventilation (DV) is widely employed in buildings to achieve a high indoor air quality at 100% fresh air at floor level. To reduce energy consumption, common practice dictates selection of the minimum supply flow rate to provide a stratification height just above the breathing zone. While this practice generally results in acceptably low gas contaminant mixing ratios in the breathing zone, it may not be sufficient to protect occupants from particulate phase contaminants, since the latter tend to accumulate at a lower height under the influence of gravity.The aim of this work was to investigate the possibility of reducing breathing zone particle concentrations in DV conditioned spaces by installing fans in the arm rests of office chairs. By blowing air upwards, these chair fans (CF) can shift the equilibrium particle accumulation height out of the breathing zone, and create an envelope of clean air around the occupant. The proposed combination of DV and CF system performance was investigated theoretically and empirically using computational fluid dynamics (CFD) and controlled chamber studies involving aerosolized particles, respectively, and potential energy savings were evaluated with respect to conventional DV.It was found that with the appropriate selection of the CF flow rate, it is possible to realize a 30% reduction in DV energy use for a given level of thermal comfort and IAQ covering the inhalable particle range. Interestingly, oversized CF can result in increased contaminant exposure relative to the DV-only system. We report CF selection methodology to avoid this outcome.