Air desinfection by UV-C as an anti-Covid measure


Our clients have been recently seeking advice about various anti-Covid strategies including UV-C air desinfection. We prepared for you a brief summary of available UV-C technologies and its application based on the ASHRAE knowledge. Should you have any questions about anti-Covid strategies for HVAC systems do not hesitate to ask OPTIMAL for consultation.

Ultraviolet Energy (UV-C)

  • Ultraviolet energy inactivates viral, bacterial, and fungal organisms so they are unable to replicate and potentially cause disease.
  • The entire UV spectrum is capable of inactivating microorganisms, but UV-C energy (wavelengths of 100 – 280 nm) provides the most germicidal effect, with 265 nm being the optimum wavelength.
  • The majority of modern UVGI lamps create UV-C energy with an electrical discharge through a low-pressure gas (including mercury vapor) enclosed in a quartz tube, similar to fluorescent lamps.
  • Roughly 95% of the energy produced by these lamps is radiated at a near-optimal wavelength of 253.7 nm.
  • UV-C light-emitting diodes (LEDs) are emerging for use.
  • Types of disinfection systems using UV-C energy:
  • Requires special PPE to prevent damage to eyes and/or skin from overexposure.
  • The Illuminating Engineering Society (IES) Photobiology Committee published a FAQ on Germicidal Ultraviolet (GUV) specific to the COVID-19 pandemic.

For more information, see the ASHRAE Position Document on Filtration and Air Cleaning.



  • Have been common in the UV-A spectrum (315 – 400 nm)
  • LEDs are starting to be produced in the 265 nm range
  • Efficiency is dramatically less than current low-pressure mercury vapor lamps
  • Minimal UV output compared to a low-pressure mercury vapor lamp
  • For equal output, UV-C LEDs are more expensive than current low-pressure mercury vapor lamps
  • Limited availability; not yet practical for commercial HVAC applications

For more information, see the FAQ on Germicidal Ultraviolet (GUV) published by the Illuminating Engineering Society (IES) Photobiology Committee. 

UV-C In-Duct Air Disinfection



  • Banks of UV-Lamps installed inside HVAC systems or associated ductwork.
  • Requires high UV doses to inactivate microorganisms on-the-fly as they pass through the irradiated zone due to limited exposure time.
    • Minimum target UV dose of 1,500 µW•s/cm2 (1,500 µJ/cm2)
    • Systems typically designed for 500 fpm moving airstream.
    • Minimum irradiance zone of two feet
    • Minimum UV exposure time of 0.25 second.
  • Should always be coupled with mechanical filtration.
    • MERV 8 filter for dust control
    • Highest practical MERV filter recommended
    • Enhanced overall air cleaning with increased filter efficiency


UV-C Upper-Air Disinfection



  • UV fixtures mounted in occupied spaces at heights of 7 feet and above.
  • Consider when:
    • No mechanical ventilation
    • Limited mechanical ventilation
    • Congregate settings and other high-risk areas
    • Economics/other
  • Requires low UV-reflectivity of walls and ceilings
  • Ventilation should maximize air mixing
  • Use supplemental fans where ventilation is insufficient



UV-C In-Duct Surface Disinfection



  • Banks of UV-Lamps installed inside HVAC systems, generally focused on:
    • Cooling coils
    • Drain pans
    • Other wetted surfaces
  • UV irradiance can be lower than in-duct air disinfection systems due to long exposure times.
  • Goals are:
    • Even distribution of UV energy across the coil face
    • Generally, 12 to 36 inches from the coil face
    • Operated 24/7



UV-C Portable Room Decontamination

  • For surface decontamination
  • Portable, fully automated units; may use UV-C lamps or Pulsed Xenon technology
  • Settings for specific pathogens such as MRSA, C. difficile, both of which are harder to inactivate than coronaviruses.
    • >99.9% reduction of vegetative bacteria within 15 minutes
    • 99.8% for C.difficile spores within 50 minutes


                                                                                                                     (Rutala et al. 2010)



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