Part 3: Purifii™ Upper Air UVGI: Real-World Applications


How effective is the Luminii upper air UVGI Luminii system in real-world settings? Luminii developed a calculator, with the help of industry experts, that uses well-established, published methods to calculate disinfection efficiency based on UVGI system inputs. It then estimates the infection risk for a variety of pathogens by applying the Wells-Riley infection risk model. 

Generally speaking, pathogens, in addition to odors, CO2, and other contaminants, are removed from a room through a ventilation system. In the U.S., ASHRAE Standard 62.1 determines the ventilation requirements for acceptable indoor air quality for commercial buildings. A standard metric for ventilation rate is air changes per hour (ACH) — the number of times the volume of air inside a room is replaced with fresh, outside air per hour.

For a room with an upper air UVGI system, effective air changes per hour (eACH) can be used as a metric to gauge the level of disinfection resulting from the UV system. Based on a space’s size, type, UVGI fixture quantity, UVGI fixture placement and a few other inputs, the tool calculates multiple parameters of germicidal effectiveness including the eACH that result from the system.

The 2020 pandemic has led to ASHRAE recommending increased mitigation of infectious aerosols through increased ventilation and UVGI to supplement outside airflow. 

Due to the large variation in emission rates and the assumption of a well-mixed space, numbers produced from any risk calculation should be used more for comparison, as we compare risk with and without UVGI, rather than for absolute infection risk percentages. Taking into account these considerations, Luminii’s UVGI system delivers efficient risk reduction equivalent to large changes in a space’s ventilation. 

Envisioning Success — Reducing Infection Risk

Coffee to stay.

If we consider a café with a front of house area of approximately 700 square feet, four fixtures are required to cover the space. The fixtures generate a total average fluence of 5.63 μW/cm^2 for the entire space. Based on ASHRAE guidelines, the café would have ventilation that generates 1.9 ACH (bringing in a volume of outside air equivalent to 1.9 times the volume of the space per hour). 

Patrons typically spend an hour with 20 total people in the space who are standing and talking. If one person infected with COVID-19 (SARS-CoV-2) were in the space, there would be a 1 percent chance of infection to all people in the space. By installing Luminii’s UVGI system, the risk of infection goes down to 0.1 percent. This 90 percent infection risk reduction is created by increasing the effective ventilation rate to 38.5 ACH, larger than any typical ventilation system alone would generate for this space. 

In the classroom.

For a typical 600 square foot K-12 classroom, ASHRAE guidelines dictate a 2.7 ACH ventilation rate. Students and teachers typically spend a total of six hours in class per day with 12 people per class (assuming reduced occupancy based on current social distancing guidelines), the calculator can evaluate the infection risk and risk reduction. 

If a teacher were infected with COVID-19, students in the class would have a 10-50 percent chance of infection that goes down to 1-9 percent with Luminii’s UVGI system. If a student were the infected person, the rest of the class would have a 2-9 percent chance of infection based on how much the student talks and engages during class that drops to 0.3-1 percent with the UVGI system. This 86 percent risk reduction results from increasing the total air changes per hour to 25.8 with four Luminii fixtures. 

Similarly, for Influenza A, a sick teacher poses a 40 percent risk of infection to the class compared to 10 percent with UVGI; and a student poses a 7 percent risk compared to 2 percent with UVGI. UVGI systems can help make teachers and students alike safer and reduce the spread of infections across schools.

Group exercise.

Group fitness is highly conducive to spreading airborne pathogens. The increased respiratory level means that any infected person in the room outputs more infectious particles. Take a 650-square-foot fitness studio with 16 participants in addition to an instructor. ASHRAE guidelines would estimate 3.7 ACH. If a participant in the class were infected with COVID-19, they would pose a 4 percent risk of infection to everyone in the class. With four fixtures laid out, the risk of infection would be reduced to 1 percent. If the instructor were infected, since they are talking loudly to the class, this would pose a 20 percent chance of infection to the class that would be reduced by 75 percent with Luminii’s UVGI system. 

The four fixtures create an additional 19 eACH that helps keep the classes safe while enjoying fitness together. Outside of the pandemic, the flu can also spread in group fitness classes. The class has a 50 percent chance of infection from an infected instructor, and a 10 percent chance of infection from an infected participant. These risks get reduced by 4 percent with the UVGI system in place.

Senior living.

Common areas at a senior living facility can create a dangerous situation for residents who are highly vulnerable to airborne infections. Installing six UVGI fixtures in a typical 1,000 square foot common area provides a simple way to increase the safety of social gatherings at senior living facilities. A 1,000 square foot space has an expected ACH of 1.2 based on ASHRAE standards. If we consider a group of 15 people in the common area talking with each other for an hour, one person infected with COVID-19 would pose a 1 percent chance of infection to the other occupants. That risk goes down to 0.1 percent with Luminii’s UVGI system. In the proposed layout, the system creates an additional 49.5 eACH, keeping those at the highest risk for serious complications much safer from coronavirus infection. Likewise, if there were someone infected with the flu, they would cause 4 percent risk of infection to anyone in the room, compared to a 0.7 percent risk of infection with the UVGI system in place.

Airborne Control Simplified

When you examine the numbers, it is evident that Luminii upper air UVGI contributes a useful addition to existing solutions for airborne infection control. The proof is in the case studies — and a return to normal for businesses utilizing Purifii.