Impact of Moving Objects on Contaminant Concentration Distributions in an Inpatient Ward with Displacement Ventilation

Moving objects can disturb stratified flow and contaminant concentration gradient in an inpatient ward with displacement ventilation. This investigation uses computational fluid dynamics (CFD) to study the effect of objects moving, such as a visitor or caretaker walking, the changing of sheets on a patient's bed, and the swinging of an entrance door for up to four seconds, on the contaminant concentration distributions in a single inpatient ward. The CFD was validated by using the measured distributions of air velocity, air temperature, and contaminant concentration from the mockup of an inpatient ward. The contaminant was assumed to be breathed out by the patient lying on the bed. The results show that moving objects can cause a 10 to 90 second swing in the contaminant concentration distribution. The averaged concentration change in the breathing levels in the ward was generally less than 25%, so the risk level should remain the same. The closer the location of the moving object to the contaminant source, the larger was the change in the contaminant concentration. The displacement ventilation with 4 ach in an inpatient ward with a moving object can still produce the same air quality level as overhead mixing ventilation with 6 ach.