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
- 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
- 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
- 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
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
For more information, see the ASHRAE
Position Document on Filtration and Air Cleaning.
- Have been common in the UV-A spectrum (315 – 400
- LEDs are starting to be produced in the 265 nm
- Efficiency is dramatically less than current
low-pressure mercury vapor lamps
- Minimal UV output compared to a low-pressure mercury
- 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
- Requires high UV doses to inactivate microorganisms
on-the-fly as they pass through the irradiated zone due to limited
- Minimum target UV dose of 1,500 µW•s/cm2 (1,500
- Systems typically designed for 500 fpm moving
- Minimum irradiance zone of two feet
- Minimum UV exposure time of 0.25 second.
- Should always be coupled with mechanical
- MERV 8 filter for dust control
- Highest practical MERV filter recommended
- Enhanced overall air cleaning with increased filter
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
- Requires low UV-reflectivity of walls and
- Ventilation should maximize air mixing
- Use supplemental fans where ventilation is
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
- 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
- >99.9% reduction of vegetative bacteria within 15
- 99.8% for C.difficile spores within 50 minutes
(Rutala et al.