Pulsating jet ventilation add-ons performance for reducing the contaminant spread in classrooms: Portable air cleaners vs. upper room UVGI

Abstract

This paper examines the extent to which “add-on” cleaning devices in a classroom ventilated with a pulsating jet ventilation (PJV) system are able to reduce the contaminant spread risks between students when one of them is infected. Two types of “add-on” devices are investigated: portable air cleaners (PACs) and upper room ultraviolet germicidal irradiation (UR-UVGI) lamps. The cleaning effectiveness of each system is evaluated by comparing the contaminant concentration reduction ratio (CR) within the breathing layer in each group of students and the intake fraction (iF) with their corresponding values of standalone PJV operation under the same conditions. Detailed 3D computational fluid dynamic (CFD) models were developed and validated against published experimental data. A parametric analysis was performed by varying the PJV supply flowrate and its period of intermittency to establish the PJV operating conditions that maximize the cleaning and protection effectiveness of each “add-on” device at acceptable thermal comfort and CO2 levels.It was found that for maximum cleaning effectiveness, the PJV system is recommended to operate with an UR-UVGI system at supply flowrate between 250 l/s and 350 l/s with a range of intermittency periods between 4 min and 5 min. However, for a maximum protection against cross-contamination, the PJV system should operate with PAC devices at 400 m3/h for PJV flowrate ranging between 250 l/s and 350 l/s irrespective of the intermittency period with iFmax values between 1.47×10−4 and 0.67×10−4. The addition of “add-ons” resulted in a maximum of 7% increase in the overall energy consumption.