Fundamental factors affecting upper-room ultraviolet germicidal irradiation - part II. Predicting effectiveness

Area of Science:

• Environmental Health Engineering
• Infectious Disease Control
• Applied Microbiology

Background:

• Upper-room ultraviolet germicidal irradiation (UVGI) offers a promising alternative to increasing outdoor air ventilation for reducing indoor airborne microorganisms.
• UVGI utilizes modest vertical air circulation for efficient air irradiation with low noise and power consumption.

Purpose of the Study:

• To test the hypothesis that upper-room UVGI efficacy against airborne infectious microorganisms can be determined by a dimensionless UVGI effectiveness index.
• To characterize the adequacy of vertical air circulation, UVGI amount, and their interaction.

Main Methods:

• Developed a UVGI effectiveness index, independent of microbiological testing.
• Calculated an irradiation number (based on UV fixture power output) and a mixing number.
• Compared the effectiveness index with experimental measurements in a room-size chamber.
• Utilized a two-box model to predict microorganism concentration reductions and compared with experimental data.

Main Results:

• The UVGI effectiveness index correlated well with experimental measurements.
• The study provides insight into whether UV quantity or air circulation intensity is the controlling factor for effective UVGI.
• An equation was developed to relate UV fixture power output to mean fluence rate.

Conclusions:

• The developed UVGI effectiveness index is a viable tool for assessing the efficacy of upper-room UVGI systems.
• This index facilitates the design and application of UVGI for reducing airborne disease transmission.
• Further research can refine the understanding of UVGI parameters for optimal performance.