Awareness of indoor air quality has increased substantially in recent years, and the systems that supply air to our living and working spaces are critical to the maintenance of a healthy indoor environment.
Although 10% of the sun’s radiation is composed of UV light, virtually all of the sun’s UVC rays are blocked by the Earth’s ozone layer, so most UVC exposure is created by artificial means.

There are three types of UV light: A, B, and C, each representing a different section of the UV light spectrum. Type C, known as UVC, is the form used for germicidal activity. When UVC light is used for this purposes, it is referred to as UVGI, ultraviolet germicidal irradiation.

HVAC UV Lights range

UVGI “deactivates” or kills microorganisms, including viruses, bacteria, molds, and other fungi by disrupting their DNA.

UVGI lamps are categorized by the internal pressure of the gas in the lamp. Low-pressure lamps are, by far, the most commonly used in HVAC systems.
They operate best at 72ÌŠ - 105ÌŠ F, less effectively below 72ÌŠ, and are not operable below 32ÌŠ F.
Medium-pressure lamps are typically used where critical levels of disinfection are required.

So, the question is, how effective is UVGI at killing (deactivating) bioaerosols in the airstreams of HVAC systems? The answer is, “The technology can be effective, but many variables can impact its effectiveness.”

The effectiveness of UVGI depends on a number of factors. For example, a single UVC lamp randomly placed in an HVAC system would not be nearly as effective as multiple lamps of the same intensity installed at strategic locations. To get maximum benefit from UVGI, the installer should be well-trained in proper placement of lamps and the proper intensity and number of lamps needed for optimal deactivation of bioaerosols.
It is not possible to “overdose” with UV. Your HVAC professional will be able to recommend the right amount of UV protection.

Any installation of a UVC lamp in an HVAC system should include a method of visually inspecting it periodically.

UV Light Installation

Note that, dirty lamps will result in reduced effectiveness, and the rate at which a lamp will become dirty depends on the cleanliness of the air that passes by the lamp. If the lamp has become dirty, it should be cleaned with a lint-free cloth and commercial glass cleaner or alcohol.

Remember,UVC lamps have a limited lifespan and their effectiveness reduces over time. In HVAC systems, they typically need replacement after one to three years, depending on the manufacturer’s specifications.

In last, UVC increase the value of all air conditioning and air-circulating systems by maximizing system efficiency, prolonging blower life and providing healthier air to breathe. UVC Germicidal Fixtures keep coils clean all of the time, enabling HVAC systems to perform as originally intended. They'll often pay for themselves in months and can help you save many thousands of dollars in on-going energy and maintenance costs.

--Resource: NADCA