Improving Indoor Air with Germicidal Ultraviolet Light

For years now ultraviolet technologies have had more than just water treatment applications and while consumer demands have continuosly grown for water purifying devices, a lot has happened in air purifying. Improving indoor air quality with germicidal ultraviolet (UV) light has been used since the 1950s in food preparation and in medical applications. Now other serious health problems have emerged, and air quality in homes and commercial and industrial buildings has become an issue because of less fresh air and ventilation. Heat, ventilation and air conditioning equipment along with enclosed spaces can harbor fungi (mold and spores) airborne viruses and bacteria. With the development of products described in this article, there are now various configurations of fixtures utilizing germicidal ultraviolet light that can be used to protect against infection due to airborne microbes.

Germicidal Lamps

The ultraviolet germicidal lamps used for disinfection are short wave low-pressure mercury vapor tubes that produce ultraviolet wavelengths that are lethal to microorganisms. Germicidal lamps should not be confused with sunlamps or backlight lamps, for while these also are ultraviolet lamps; the ultraviolet produced is of longer wavelength and is not useful for germicidal applications. Typically, 95 percent of the ultraviolet energy emitted from germicidal lamps is at the mercury resonance line of 254 nanometers. This wavelength is in the region of maximum germicidal effectiveness and is highly lethal to virus, bacteria and mold spores.


UV air duct disinfection. For use in residential, commercial and industrial applications, ultraviolet air duct disinfection fixture can be applied for two types of applications in HVAC equipment either treatment of the air stream or surfaces within the air handler. With the proper system design and installation the moving air can be disinfected with germicidal ultraviolet light. Typical residential systems are sized for a minimum nominal 80 percent bacteria deactivation rate, commercial applications for 90 percent, and up to a 98 percent deactivation rate is essential for hospitals and pharmaceutical laboratories.

Installation of air duct disinfection fixtures is recommended to be perpendicular to the airflow because the lamp rays will travel the full length of the duct, thereby increasing the exposure time and effectiveness of the fixture(s). Mounting of the fixture requires cutting a hole within the duct wall to insert the lamps across the duct and attaching the lamps to the wall of the duct with brackets. Once installed, it is normally recommended that the unit remains on continuously and not cycled off and on with the fan of the air handler, as cycling of these germicidal lamps may reduce their rated life.

Germicidal ultraviolet fixtures are sized based on time and intensity—that is, time that the air or the surfaces are in contact with the germicidal ultraviolet light and the intensity of the fixtures to be utilized. The following information is required to size an ultraviolet system for duct air treatment.

  • Duct or plenum size.
  • Length of compartment or duct where units are to be installed.
  • Air speed typically provided in cfm (cubic feet per minute).
  • Approximate air temperature.

This information would be presented to an ultraviolet application specialist at the manufacturer’s facility in order to calculate the approximate contact time and the lamp output required under these conditions so a recommendation of fixture size and quantity can be made.

Systems can be provided with lamp operation indicators to provide positive indication of germicidal ultraviolet lamp operation. Currently there are systems available with a
sight port window (a visible glow through clear sight glass), which mounts to the duct wall or an LED display either on the housing of the fixture or remotely installed.

UV room air sanitizers. For use in residential, commercial and industrial applications, another alternative to disinfecting air utilizing germicidal ultraviolet light is to use self-contained germicidal ultraviolet exposure chambers, also referred to as room air sanitizers. Fixtures are available in a number of different configurations
to adapt to virtually any setting. Ultraviolet room air sanitizers can be mounted on a ceiling or wall or are available for portable or mobile use. Air is drawn into the fixture through a washable electrostatic particulate filter. It then is forced into an ultraviolet exposure chamber where it is irradiated by germicidal ultraviolet light. Purified air leaves the exposure chamber through the louvered exhaust panel. Depending on the size of the room and air changes per hour required by the application, fixtures can be sized accordingly.

There are several advantages to utilizing systems with this type of design. For starters, the fixtures can be tailored to most effectively improve room air quality. In addition, there is little to no installation cost—just plug the fixture into an appropriate outlet—making this type of unit easy
to use. A properly designed fixture should pose no risk of accidental ultraviolet exposure of occupants in the treated area. Additionally, this style is relatively portable and, therefore, can be applied to different areas as needed.

UV upper air disinfection equipment. Another choice for disinfecting air utilizing germicidal ultraviolet light—
if duct installation or room air sanitizers are not the most ideal—
is to use fixtures designed for upper
air disinfection. Designed for
use in commercial and industrial applications, the process purifies the upper air of an occupied room in order to reduce the risk of occupant to infectious airborne microbes. These fixtures project the germicidal ultraviolet rays across the upper room air thereby destroying bacteria and viruses that are carried into the ultraviolet field by convection currents of air circulation. It is an important requirement when applying indirect germicidal ultraviolet to upper air
to keep the radiation in the occupied level (below 61?2 ft.) within acceptable limits (0.2 microwatts per square
centimeter for eight-hour exposure
is a standard set by the American Conference of Governmental Industrial Hygienists). Therefore, mounting in the appropriate position
is essential for safe use. Occasional ultraviolet measurements are required to ensure that ultraviolet intensities
are within the allowable exposure limits and minimum levels in the treated field.

This type of fixture is relatively efficient due to the long, unobstructed path of the ultraviolet rays, and occupied areas can be treated without the need for special precautions or protective clothing.

Ultraviolet Equipment Maintenance

Equipment maintenance consists of cleaning the lamps periodically to ensure maximum expected output. Lamp replacement typically is recommended on a yearly basis.

In addition, there are easy-to-use handheld meters available that can
be used to check the intensity of
aging ultraviolet lamps and survey installation areas to ensure that the ultraviolet radiant exposure of personnel within the treated area is within acceptable limits.

It is time to start improving indoor air quality using germicidal ultraviolet technology. This economical technology—low pressure, germicidal ultraviolet light requires very little power to operate—has been under utilized as an efficient means of controlling airborne contaminants for far too long. Now with the numerous fixture choices available to suit most applications, it should be quite easy to select an appropriate style that will be the solution for attaining most air quality goals.

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About the author

Greg Boehme is applications engineer for Atlantic Ultraviolet Corp. For more information go to