Owners and facility managers looking for a way to disinfect the indoor air in offices, medical centers, retail stores, schools and residential care facilities will find that their HVAC system may provide the safest and most cost-effective approach.
Buildings equipped with a ducted heating, ventilating and air-conditioning (HVAC) system are prime candidates for in-duct ultraviolet (UV-C) units that can provide whole-building air sanitizing.
UV-C germicidal lamps emit 253.7 nanometer wavelength irradiation that, in sufficient doses, disables virus, bacteria and mold.
While effective against pathogens, UV-C irradiation can also be harmful to human eyes and skin. Eyes are particularly at risk if a person looks directly at a UV-C lamp when it is turned ON. For this reason unshielded UV-C lamps in ceiling, wall or floor mounted fixtures should not be installed and operated in occupied spaces.
By placing ultraviolet lamps in HVAC ducts, they are remote and hidden from view. In addition, the lamps can disinfect air in multiple rooms throughout the building continuously.
The UV-C in-duct equipment usually consists of lamps (replaceable) and a metal electrical box containing the ballast and wiring. An opening is cut in the sheet metal duct, the lamp portion of the UV-C unit is inserted into the duct. The electrical box remains on the outside of the duct and is secured with sheet metal screws. Line voltage from the building is wired to the electrical box.
Some units have additional features such as LED lamp operation indicators located on the electrical box or remote lamp operation indicators, sight glass for observing the lamps in the duct and quartz sleeves to protect the lamps from deposits of dirt or dust and from the cooling effects of high air velocities in the duct, ensuring optimum performance.
When considering purchase of UV equipment for UVAC systems, the key to effective air disinfection is proper sizing of the units. The UV equipment can be installed either on the supply or return side of the HVAC system, normally near the air handler plenum.
The best approach is to let a specialist where you are purchasing the ultraviolet equipment perform a calculation that will determine the UV equipment requirement. The following information is required for the calculation:
- Duct dimensions: width, height (or diameter)
- Duct length: total length of straight duct where the equipment will be installed
- HVAC system blower CFM
- Average temperature of air in the ducts
With these values the specialist can recommend the optimal number of lamps needed to effectively disinfect the air in the building.
The primary advantages of in-duct UV-C systems are:
Continuous air disinfection throughout the building
- Low maintenance - annual lamp replacement
- Safe - occupants are not exposed to UV-C irradiation
These types of systems have been used by hospitals for many years and have proven highly effective. They can be equally effective for any building equipped with a ducted HVAC system.
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