TY - JOUR

T1 - Dispersion of Exhalation Pollutants in a Two-bed Hospital Ward with a Downward Ventilation System

A1 - Qian,Hua

A1 - Nielsen,Peter V.

A1 - Hyldgård,Carl-Erik

AU - Qian,Hua

AU - Nielsen,Peter V.

AU - Hyldgård,Carl-Erik

PB - Pergamon

PY - 2006/12/13

Y1 - 2006/12/13

N2 - The Centers for Disease Control and Prevention has recommended the use of downward ventilation systems in isolation rooms to reduce the risk of cross-infection from airborne transmissible diseases. The expected airflow pattern of a downward ventilation design would supply cooler and slightly heavier clean air from a ceiling diffuser to push down contaminants, which would then be removed via outlets at floor level. A "laminar" (strictly speaking, unidirectional) flow is expected to be produced to avoid flow mixing and thus 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. Computation fluid dynamics was also used to investigate the airflow pattern and pollutant dispersion in the test ward. Based on both experimental and numerical results, the laminar airflow pattern was shown to be impossible to achieve due to turbulent flow mixing and flow entrainment into the supply air stream. The thermal plumes produced above people were found to induce flow mixing. We also studied the effects of the locations of the supply and extraction openings on both the flow pattern and pollutant exposure level in the occupied zone. A number of practical recommendations are suggested.

AB - The Centers for Disease Control and Prevention has recommended the use of downward ventilation systems in isolation rooms to reduce the risk of cross-infection from airborne transmissible diseases. The expected airflow pattern of a downward ventilation design would supply cooler and slightly heavier clean air from a ceiling diffuser to push down contaminants, which would then be removed via outlets at floor level. A "laminar" (strictly speaking, unidirectional) flow is expected to be produced to avoid flow mixing and thus 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. Computation fluid dynamics was also used to investigate the airflow pattern and pollutant dispersion in the test ward. Based on both experimental and numerical results, the laminar airflow pattern was shown to be impossible to achieve due to turbulent flow mixing and flow entrainment into the supply air stream. The thermal plumes produced above people were found to induce flow mixing. We also studied the effects of the locations of the supply and extraction openings on both the flow pattern and pollutant exposure level in the occupied zone. A number of practical recommendations are suggested.

KW - Infection control

KW - Downward ventilation

KW - Hospital ventilation

KW - Airborne transmission

KW - Breathing exhalation jet

KW - Flow visualization

U2 - doi:10.1016/j.buildenv.2006.03.025

DO - doi:10.1016/j.buildenv.2006.03.025

JO - Building and Environment

JF - Building and Environment

SN - 0360-1323

IS - 3

VL - 43

SP - 344

EP - 354

ER -