DISPERSION OF EXHALATION POLLUTANTS IN A TWO-BED HOSPITAL WARD WITH DOWNWARD VENTILATION SYSTEM

摘要

A downward ventilation system has been proposed as a standard ventilation design by Centers for Diseases Control and Prevention (CDC) for isolation rooms to reduce the risk of cross infection for airborne transmission diseases. The expected airflow pattern of a downward ventilation design is to supply cool and heavier clean air from a ceiling diffuser to push contaminant down and be removed from outlets at the floor level. It is hoped to produce a "laminar" (strictly speaking should read as unidirectional) flow to avoid mixing and reduce cross infection risk. Experiments were carried out in a full-scale experimental hospital ward with a downward ventilation system to investigate the possibility of applying downward ventilation in a general hospital ward. Two life-sized breathing thermal manikins were used to simulate a source patient and a receiving patient. From our study, this "laminar" air flow pattern was shown to be impossible to be obtained due to the turbulent flow mixing and the flow entrainment into the supply air stream. The thermal plumes above people induced flow mixing. We studied the effects of locations of the supply opening and the extraction opening on the flow pattern and pollutant exposure level in the occupied zone. A number of practical recommendations are made from this study.