Overview: Ultraviolet germicidal irradiation (UVGI) has been used for decades to purify air in hospitals and labs that need to ensure microbes aren’t introduced or distributed by the ventilation system. UVGI is also used in a less intense installation to keep cooling coils clean and free of biofilms. UVGI can also be used in-room as part of an upper-room disinfection system, portable air cleaner, or surface disinfection. The history and means of using UVGI for pathogen control in building ventilation systems and rooms is well-documented. Along with fresh air ventilation and filtration, UVGI is one of the best proven technologies for removing pathogens from the air, including COVID-19.
Removes, Dilutes, or Inactivates Pollutants: UVGI inactivates pathogens in the air and on surfaces, with proper design. UVGI systems are usually designed for a specific worst-case pathogen, and others that are more easily inactivated are then also removed from the air stream. UVGI does not filter out particulates or VOCs.
Harmful Byproducts: UVGI is a well-developed industry, and lamps are designed to prevent the emission of light in wavelengths that can produce ozone. As long as the UVGI system installed is from a reputable dealer, the systems should be free of harmful byproducts.
Added Energy: Each type of UVGI system has different design requirements to provide effective microbial disinfection, resulting in differing levels of energy consumption. Disinfection is a function of irradiation intensity, time, and the desired reduction of the target pathogen(s). See below for more details.
In-Room Surface UVGI
- About 01 W/m2 (1.0X10-4 W/sf) UVGI intensity at surfaces.
- In 1,000 sf room with 10 ft ceiling, about five 55 W UV lamps. At 1,000 hr/yr, this is a utility cost of about $27.50/yr per room.
- Long duration inactivates pathogens instead of high intensity.
- Can be programmed with building automation to operate during scheduled unoccupied hours and limit energy use.
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- Intensity between 0.03 to 0.05 W/m2 (3.3 to 5.5x10-4 W/sf) with disinfection time based on ~1.2 ACH airflow in room.
- In 1,000 sf room requires around three 55W UVGI lamps. Operating at 1,000 hrs/yr, this is a utility cost of about $16.50/yr per room.
- Optimal designs have UV emitters around perimeter of room, poorest performance if emitters along one wall. Improved performance reduces required energy for disinfection.
- Do not provide surface disinfection, only air.
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In-Duct or Air Handler UVGI
- Highest energy use has intensity of 1 to 10W/m2 (0.3 to 1.1 W/sf) needed to disable pathogens in single pass of airflow.
- For above classroom served by 10sf duct, flow is 50 ft/min. Requires twenty 55W lamps. At 1,000 hr/yr, utility cost is $110/yr per 10,000 ft3
- Intensity reduced to 1 to 100 µW/cm2 if designed to clean cooling coil, but then airstream isn’t purified in single pass.
- For 10sf coil, would need 75W lamp power. At 1,000 hrs/yr, utility cost is about $7.50/yr.
- Can result in net energy savings from reduced pressure drop across cooling coil, but only partially cleans air, depending on flow rate.
Beyond the Pandemic
In-room surface UVGI
- Items shaded from UV light will not be disinfected, requiring careful design to sanitize high-touch surfaces.
- UV-C (200-280 nm) can’t be used in occupied spaces, but inactivation can be faster than UV-A designs.
- UV-A (315-400 nm) range is considered safe for use in occupied spaces, but inactivation is about 1,000x’s less effective. Usually this is countered by longer irradiation periods, including during occupied hours. However, research is ongoing regarding long-term exposure risks to UV-A.
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- UV lights must have louvers if ceiling height is less than 10ft to direct UV radiation away from occupants.
- UV resistant paints and materials may be needed to protect room surfaces.
- Hanging ceiling decorations will interfere with disinfection of room air.
- Can be used while space is occupied with proper design.
- Won’t disinfect surfaces, only the air in the space.
In-Duct or Air Handler UVGI
- Reduces concerns about material degradation and occupant exposure to UVGI.
- Relies on dilution of space air with cleaned air for IAQ improvement, has reduced impact on in-room transmission of pathogens.
- Cleaning of coils through UVGI can decrease pressure drop, mitigating some of the energy from adding UVGI.