UVGI air filtration units can improve the ventilation and clean air in restaurants and other common spaces, helping mitigate the risk of virus and airborne disease spread.
Many foodservice facilities have been struggling with COVID and providing the appropriate ventilation systems in their dining rooms while complying with mandates on occupancy and other mediation efforts. They may be unaware that there are systems that can help with virus mitigation in restaurants.
UVGI air filtration units typically come complete with high-capacity UVGI and MERV filters and can be used safely in any indoor space where there is a risk of virus spread. These units can reduce the risk of airborne infections while creating a clean and safe indoor environment for customers and staff.
Recommendations for virus mitigation strategies and building guides
ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) has published extensive recommendations on Coronavirus (COVID-19) with response resources from ASHRAE and others. ASHRAE’s guidance has been formulated to help designers retrofit and plan improvements to indoor air quality and slowing the transmission of viruses via HVAC systems. A couple of the designer’s underlying efforts should be increasing outside air to spaces and treating return air. The designer should also be concerned with mechanical filtration of the supply air and maintaining indoor comfort as defined by the design temperature and relative humidity. Read more on ASHRAE mitigation strategies and building guides.
UVGI air filtration units help reduces the probability of airborne infection
UVGI air filtration units should have highly efficient UV resistant air filters with a rating of MERV 13 or better. Behind these filters are safe UV-C bulbs that do not produce any respiratory irritant ozone. These particular UV-C bulbs operate at the 254-nanometer wavelength. This wavelength is critical for its germicidal inactivation properties.
Claims of 99% or greater efficiency on UV-C bulbs should be met with some skepticism in real-world applications. Although the UV-C bulbs are 99% efficient in neutralizing viruses, this doesn’t mean that by deploying one of these units, 99% of pathogens present will be destroyed. It is essential to understand whether the manufacturer can calculate the unit’s clean air delivery rate (CADR) and the probable reduction in airborne infections using a Wells-Riley mathematical model associated with the airborne transmission of respiratory diseases. The manufacture can go into greater detail on what the equation is all about. Still, in its most basic terms, it considers the number of people in the room, the intensity of the UV-C bulbs in the device, and the time the air is exposed to the bulbs.
What is Clean Air Delivery Rate?
Clean Air Delivery Rate (CADR) is a metric providing the volume of air that has been cleaned of harmful pathogens.
How do you calculate Clean Air Delivery Rate (CADR) for UVGI air filtration units?
How does one calculate CADR (Clean Air Delivery Rate) and reduction in infection probability? Fortunately, there is an industry formula that any competent supplier or manufacturer can access to provide this information. It is called the Wells Riley Equation.
- Q = Clean/Uninfected Airflow
- t = Time
- p = # of People
- I = respiratory rate
It is essential to understand what the resulting information indicates.
- Must be calculated to determine UVGI solution overall effectiveness
- Used to calculate infection probabilities in an occupied space
- Probability decreases as exposure time (t) decrease and/or clean airflow (Q) increases.
- Infection probabilities for different disinfection solutions can then be compared.
- Wells Riley only accounts for airborne infections – infections from close contact can be mitigated with masks, social distancing, and cleaning
That last bullet point is an important consideration. An Ultraviolet Germicidal Irradiation (UVGI) device is used in conjunction with established mitigation protocols such as social distancing, wearing face masks, and increased sanitizing (handwashing, disinfecting.)
When calculating a system’s effectiveness, the essential variables are clean air available, time, the number of people, and respiratory rate (seated, active?)
For example, a typical restaurant with 30 customers has a ventilation rate of 450 CFM ( 212 l/s), which is 15 CFM ( 7 l/s) of outside air per customer. Adding 1000 CFM (472 l/s) of clean disinfected air reduces the probability of airborne infection by 3.4 times in this example. Fewer people or more UVGI air filtration units in the restaurant would decrease airborne infection probability even more. Other infection probability rates can be calculated by application and occupancy.
When choosing your UVGI air filtration device, it is important to understand its actual clean air delivery rate. With that information, you can compare one system to another to determine how much of a reduction in infection probability you will get. Relying solely on an efficiency number (%) does not represent how effective a system would be in reducing infection or neutralizing the virus.
Our recommended next article would be: How effective is Ultraviolet Germicidal Irradiation (UVGI) lights in neutralizing a virus?
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