Air Handling, Ventilation, and Air Quality Atlantic Ultraviolet

Improving indoor air quality with germicidal ultraviolet light…
By Greg Boehme, Applications Engineer, Atlantic Ultraviolet Corporation

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 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 virus and bacteria. With the development of ultraviolet products described below, there are now various configurations of fixtures utilizing germicidal ultraviolet light that can be used to protect against infection due to airborne microbes.

Germicidal ultraviolet 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 blacklight lamps, for while these are also ultraviolet lamps; the ultraviolet produced is of longer wavelength and is not useful for ultraviolet germicidal applications. Typically 95% 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.

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

Installation of air duct ultraviolet fixtures is recommended to be perpendicular to the airflow. This method is most effective, as the lamp rays will travel the full length of the duct therefore increasing the exposure time and effectiveness of the fixture(s). Lamps mounted parallel to the airflow will only radiate out towards the wall of the duct; therefore, the air is only irradiated while passing by the lamps. Mounting of the fixture requires cutting a hole within the duct wall to insert the lamps across the duct, and supported to the wall of the duct with brackets. Once installed it is normally recommended that the unit remain 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. Note that multiple fixtures may be required in some cases to increase the intensity to meet the required disinfection rates. The following information is required to size an ultraviolet system for duct air treatment: 1) Duct or plenum size 2) Length of compartment or duct where units are to be installed 3) Air speed typically provided in CFM (cubic feet per minute) and 4) 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.

Ultraviolet room air sanitizers. For use in residential, commercial and industrial applications another alternative to disinfecting air utilizing germicidal ultraviolet light (especially if duct installation is not available or practical) 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 in a ceiling, on a wall or are available for portable or mobile use. Air is drawn into the fixture through a washable electrostatic particulate filter, forced into ultraviolet exposure chamber where it is irradiated by germicidal ultraviolet light and then purified air leaves 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 provide effective room air changes required (blowers within the exposure chamber control the air flow through the chamber). In addition, there is little to no installation cost - just plug the ultraviolet 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 treated area (all germicidal ultraviolet radiation should be contained within the exposure chamber). Additionally, this style is relatively portable and therefore can be applied to different areas as needed.

Various features and options are available on these type of ultraviolet fixtures to make ideal for specific applications.

Ultraviolet upper air disinfection equipment. For use in commercial and industrial ultraviolet applications yet another choice for disinfecting air utilizing germicidal ultraviolet light (if duct installation or room air sanitizers are not the most ideal) is to use ultraviolet fixtures designed for upper air disinfection. The principle application is to purify the upper air of an occupied room in order to reduce the risk of occupant to infectious airborne microbes. These fixtures are designed to 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 6-1/2 feet) 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 for ultraviolet). Therefore mounting in the appropriate position is essential for safe use. Occasional ultraviolet measurements are required to insure that ultraviolet intensities are within the allowable exposure limits and minimum levels in the treated field. Some ultraviolet fixtures utilize variable output ballasts that can be adjusted so that installation will comply with the standard.

This type of fixture is relatively efficient due to long unobstructed path of the ultraviolet rays.