13. Air-Condition and Refrigeration

Downward laminar airflow (LAF) systems have been adopted in many modern hospital operating room (OR) ventilation systems. In downward LAF systems, well- filtered conditioned air is supplied directly over the operating table by means of ceiling-mounted diffusers. This form of localized supply of air has an inherent drawback. In the region outside the coverage of the diffusers, there is a tendency for room air to recirculate and re-entrain into the supply air jet. Air contaminations, such as airborne bacteria- carrying particles (BCPs), could be trapped in the recirculation. Room air entrainment poses a risk of BCP contamination of the sterile equipment and the exposed wound, also called the surgical site infection (SSI). In this study, the effect of ceiling returns on the recirculation is experimentally investigated through smoke flow visualization and particle image velocimetry (PIV). A novel laser sheet generator was developed for the experiments. The results show that the application of the ceiling returns can eliminate the room air recirculation. However, short-circuiting of the supply air to the ceiling return could be induced in high ceiling-return flow rates. The results gave significant insights on the flow characteristic inside the OR and could be beneficial for the medical society.