AIR QUALITY (FILTRATION & PURIFICATION)
Austin Air Systems - Information will be available soon

Ultraviolet Air disinfection is the safe, easy and reliable way to
make it healthier indoors!

The solution for Microbial Contaminants in HVAC systems. Dirty Socks Syndrome. Sick Building Syndrome. These are some of the names given to mold and bacterial problems in HVAC systems. Ultraviolet light is a very cost effective method of destroying bacteria, viruses, yeasts, and molds. Ultraviolet light will kill or inactivate these micro-organisms. The benefits are many; increased HVAC coil efficiency, lower maintenance costs, improved indoor air health, and it's very affordable.

For over 70 years, ultraviolet light has been an effective tool in destroying harmful pathogens. Many of the molds, bacteria, and fungi, that cause odours and problems in your air handling system, can be eliminated with the installation of ultraviolet light. It is used widely in industry to keep food and liquids germ-free during processing and packaging. It's also used in aircraft ventilation systems to prevent the spread of pathogens and infectious disease.

Our UV air disinfection equipment 'floods' an area of a home or buildings HVAC system with UV light. As it circulates throughout the system, it is automatically disinfected. This simple process dramatically reduces airborne bacteria, viruses and allergens.

Shown here is the UVInnovation UVIDII. Placed inside air duct. Ideal for homes and businesses

Shown here is the UV Innovation UVIP. ideal for apartments, boats, cars, etc.

Features:

• Medical studies prove the effectiveness of ultraviolet light.
• Available for residential, commercial, industrial, and also portable applications.
• Eliminates or prevents mold growth on HVAC coils, allowing them to operate at peak efficiency.
• Actually destroys bacteria, viruses, fungi, yeast, and molds.
• Inexpensive to operate. Only pennies per day.
• High output, long life UV lamps.
• Great for homes, restaurants, offices, hospitals, schools, etc.
• Surface or airborne microbial control.
• Low maintenance and reduced costs.

The EPA says that indoor air is one of the top five environmental health risks of our time. And the Centre for Disease Control offers guidelines for using UV to disinfect the air.

UV Air disinfection systems work automatically -24/7

UVGI can control microbial growth on filters subject to moisture or high humidity. Photos A and B show an unirradiated and irradiated filter bank, respectively. The unirradiated filters show natural contamination from various fungal species, including Aspergillus and Penicillium, while the irradiated filters show no evidence of microbial growth. The system in Photo B used lamps that produce a rated intensity of 100 microW/cm2 at 1 m from their midpoints.

Microbial growth on unirradiated filters	Microbe-free irradiated filters
Photos courtesy of Airguard Industries, Louisville.

TYPES OF MICROORGANISMS
The variety of microbes encountered by a given UVGI system is essentially unpredictable. It depends to some degree on the type of facility and geographic location.

All viruses and almost all bacteria (excluding spores) are vulnerable to moderate levels of UVGI exposure. Because viruses are primarily contagious pathogens that come from human sources, they are found in occupied buildings. Bacteria can be contagious or opportunistic, with many found indoors; however, some are environmental. Certain facilities, such as agricultural buildings, may disseminate unique types of bacteria such as spore-forming actinomycetes.

Spores, which are larger and more resistant to UVGI than most bacteria, can be controlled effectively through the use of high efficiency filters. The coupling of filters with UVGI is the recommended practice in all health care settings8 and for UVGI applications in general.

DESIGN PARAMETERS
A number of parameters must be considered when considering UVGI products for HVAC designs. The most important factors are the airflow or HVAC equipment that will be disinfected, the lamp wattage and distance, and the ventilation system design itself.

Air-stream characteristics
The characteristics of an air-stream that can impact UVGI design are relative humidity (RH), temperature, and air velocity.
Increased RH is commonly believed to decrease decay rates under ultraviolet (UV) exposure. However, studies on this matter are contradictory and incomplete at present. Fortunately, because most UVGI studies were conducted under normal indoor conditions, typical room and in-duct applications are not likely to differ greatly. Air temperature has a negligible impact on microbial susceptibility to UVGI10. However, it can impact the power output of UVGI lamps if it exceeds design values.

Operating a UVGI system at air velocities above design will degrade the system's effectiveness because of the cooling effect of the air on the lamp surface, which, in turn, will cool the plasma inside of the lamp. UV output is a function of plasma temperature when power input is constant.

Not all UVGI lamps have the same response to cooling effects. Some lamps have different plasma mixtures; overdriven power supplies that respond to plasma temperature; or UV-transparent, infrared-blocking shielding that limits cooling effects. Data from the manufacturer should be consulted to determine the cooling effects or the limiting design air velocities and temperatures within which the lamps can be efficiently operated.

Figure 5: calculated additional light intensity from reflections and inter-reflections. Total intensity is the sum of direct, reflected and inter-reflected UV light.

VENTILATION SYSTEM DESIGN
A number of ventilation system parameters can impact UVGI design. Air velocity and air mixing. Doses are determined by the time of exposure and UVGI intensity, both of which are dependent on the velocity profile and amount of air mixing in the air stream. The velocity profile inside the duct or chamber depends on local conditions and may be impossible to know in advance with any certainty. In any event, the design velocity of a typical UVGI unit is similar to that for filter banks -- about 400 fpm. Sufficient mixing will occur at these velocities to temper the effects of a non-uniform velocity profile.
The amount of air mixing that occurs will affect system performance to a degree that depends on system configuration. This is illustrated in Figure 4
which compares the survival predictions for mixed- and unmixed-flow conditions in square ducts of increasing dimension. The error resulting from the assumption of complete mixing will decrease as system dimensions increase.
In systems where the lamps do not span the entire duct width or length, the assumption of complete mixing also will result in larger differences, compared to unmixed flow. The important point is that system operation will lie somewhere between these two assumptions, which provide limits describing system efficiency.

Figure 6. Ray-tracing computer model of a cooling coil bank irradiated with a UVGI lamp. Rays are color-coded from blue to red in order of decreasing intensity. Image was generated using Photopia software from Lighting Technologies, Inc., Boulder, CO.

Using reflectors. Reflectivity can be an economical way of intensifying the UVGI field in an enclosed duct or chamber. A surface with a reflectivity of 90 percent will reflect 9/10 of the light it receives.

The results of a computer-generated analysis of reflectivity are shown in Figure 5. The components of reflectivity -- both direct and inter-reflected -- will clearly sum to greater than the initial direct intensity. This can occur whenever the surface is mostly enclosed and highly reflective. Such designs can considerably improve economics.

Figure 6b. Ray-tracing computer model of a cooling coil bank irradiated with a UVGI lamp. Twenty reflections are shown with 90 percent reflective surfaces. Image was generated using Photopia software from Lighting Technologies, Inc., Boulder, CO.

Two types of reflective surfaces exist: specular and diffuse. Specular surfaces produce mirror-like reflections that are directionally dependent on the source, while diffuse surfaces produce non-directional reflections that spread equally in all directions. Non-glossy white paper is a good example of a diffuse surface. Most materials possess a combination of specular and diffuse properties and exhibit a degree of directional dependence. For UVGI design purposes the degree of directional dependence is usually not critical.
Some materials reflect visible light, but not UV light. Polished aluminum is highly reflective to UV wavelengths, while copper, which reflects most visible light, is transparent in the UV range.

Figure 6c. Ray-tracing computer model of a cooling coil bank irradiated with a UVGI lamp. The staggered 5/4 coil tubes are 0.5 in. dia. with six fins per inch. Image was generated using Photopia software from Lighting Technologies, Inc., Boulder, CO.

No simple method of calculating the three-dimensional UVGI-intensity field for specular reflectors exists. Ray-tracing routines using Monte Carlo techniques, are one approach, but the results do not easily lend themselves to analysis. However, they can be rather useful for examining complex geometries, such as when cooling coils are irradiated. Figure 6 shows ray-tracing diagrams of a UVGI lamp irradiating a bank of cooling coils from three perspectives. Note how few of the rays penetrate the coils, even after 20 reflections. Also note how the copper tubes absorb many of the rays -- although (pure) copper is transparent to UVGI the water inside is not.

Combining with filtration
UVGI systems generally are used in combination with HEPA filters, a practice usually recommended for isolation-room applications. For other applications, however, HEPA filters do not offer a significant enough improvement in microbial-removal rates over high efficiency filters to warrant their exclusive use with UVGI.

Recirculation systems
UVGI systems that recirculate room air or that are placed in a return-air duct or mixing-air plenum deliver multiple doses to airborne microorganisms. Although the effect is partially dependent on the air change rate, the result is an effective increase in removal rate in comparison wit a single-pass system.
Calculations of removal rates for UVGI and associated filters in recirculation systems can be performed by evaluating the system minute-by-minute, including filtration rates, outside-air rates, and any microbial contaminants.

Lamp considerations
The hardest part of sizing a UVGI system is determining the lamp wattage for the stated disinfection goal. The intensity field caused by the lamp and the reflectors must be modeled and averaged before equation 1 is used to predict the disinfection rate.

Calculating the Intensity Field of a UVGI Lamp The intensity field of a UVGI lamp can be computed using the following radiation view factor from a differential planar element to a cylinder, perpendicular to the cylinder axis (Modest, M.F. 1993. Radiative Heat Transfer. McGraw-Hill, New York): The parameters in the above equation are defined as follows: where l = length of the lamp segment, cm x = distance from the lamp, cm r = radius of the lamp, cm The intensity at any point will be the product of the view factor and the surface intensity of the lamp. The surface intensity is simply the UV power output in watts divided by the surface area in cm2. To compute the intensity at any distance from the midpoint of the lamp, multiply the above equation by 2. From any location other than the midpoint, divide the lamp into two unequal segments and add the two view factors. View-factor algebra (see reference) can be used for other locations. If we assume that complete mixing occurs, then the intensity field for any duct can be computed by averaging the field in all three dimensions.

Lamp-intensity field
An exact description of the lamp-intensity field is necessary to accurately determine the dose that is to be delivered to an airborne microorganism. Lamp ratings often are the sole parameter used for sizing a UVGI installation. Although this may be a conservative approach when distances to the lamp exceed 1 meter, oversizing and prohibitive economics can result.

If complete mixing is assumed, then any intensity field can be described by the single value of average intensity. This requires computing the intensity at every point in a three-dimensional matrix defining the duct. We need to know the field caused by the lamp and, if necessary, the field caused by the reflections. Although the inverse-square law has been used for this purpose, it has proven to be inaccurate close to the lamp. An improved approach is to use the radiation view factor from a differential planar element to a cylinder as detailed in the sidebar Calculating the Intensity Field of a UVGI Lamp. Ignoring reflectivity, the average intensity field can be conservatively computed by applying Equation 3 to a three-dimensional matrix.

There are view factors that can be used for computing the reflected intensity from flat parallel or perpendicular surfaces. Consult any thermal-radiation textbook for such view factors. First, use Equation 3 to determine the intensity at the flat surface. Then, use the appropriate view factor to determine the reflected intensity after multiplying by the reflectivity.


Table 1: presents a comparison of UVGI systems that were sized using the view-factor method and may be used to approximate the performance of similar systems.

CONCLUSIONS
Although simplistic, the methodology presented here is more accurate than any previously published method for sizing UVGI systems. The authors hope that these principles will lead to successful applications and avoidance of the design problems that have hampered the industry and perplexed engineers. Although the goal of eliminating airborne disease might remain unachievable, the information presented here may help lead the industry back to the path of continuous improvement.

The use of ultraviolet germicidal irradiation (UVGI) for the sterilization of microorganisms has been studied since the 1930s. Microbes are uniquely vulnerable to the effects of light at wavelengths at or near 2537 Angstroms due to the resonance of this wavelength with molecular structures. Looking at it another way, a quanta of energy of ultraviolet light possesses just the right amount of energy to break organic molecular bonds. This bond breakage translates into cellular or genetic damage for microorganisms. The same damage occurs to humans, but is limited to the skin and eyes.

The ultraviolet component of sunlight is the main reason microbes die in the outdoor air. The die-off rate in the outdoors varies from one pathogen to another, but can be anywhere from a few seconds to a few minutes for a 90-99% kill of viruses or contagious bacteria. Spores, and some environmental bacteria, tend to be resistant and can survive much longer exposures. UVGI systems typically use much more concentrated levels of ultraviolet energy than are found in sunlight.

Some properly designed, and well-maintained, UVGI installations have proven highly effective, as in certain hospitals, and some studies perfomed in schools. CDC guidelines recommend the use of UVGI only with the simultaneous use of HEPA filters and high rates of purge airflow. The germicidal effects can also be species-dependent.

Laboratory tests have achieved extremely high rates of mortality under idealized conditions. In actual applications, many factors can alter the effectiveness of UVGI, including the following :

• Exposure time (the air velocity must allow for a sufficient dose).
• Room air mixing (for non-powered applications like ceiling units).
• Power levels.
• The presence of moisture or particulates provide protection for microbes
• Dust settling on light bulbs can reduce exposures, maintenance is necessary.