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UV-C lamps for Indoor Air Quality improvemnet in HVAC system 3
- Thread starter Mechya
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3
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The following is a sanitized excerpt from a paper I wrote after reviewing one vendor's "technical" material:
The use of ultra violet-c light (UVC) as a germicide is an established and proven technology. UVC has been used in the health-care industry for many years to supplement other methods of sterilization. It is only recently, with the increased emphasis on indoor air quality and potential biological attacks that UVC has been heavily promoted for HVAC applications. UVC works as a germicide by penetrating the cell walls and damaging the genetic structure of the organism. In order to effectively kill and organism using UVC, it must be exposed to UVC to a minimum combination of intensity and duration. The exposure factor is measured on a surface, and it generally characterized as micro-Watt seconds per square centimeter. High exposure levels may be achieved by high intensity, long duration, or suitable combination. The required exposure levels for common micro organisms range from 6,500 to 60,000 ?W?S/cm2, and can be as high as 111,000 ?W?S/cm2 for some mold spores.
The specification for the vendor’s unit lists a light intensity of between 122 and 158 ?W /cm2 . Therefore to achieve a lethal dose of UVC from this system, any microorganism would require a significant exposure duration, 41 seconds to achieve the lowest 6,500 ?W?S/cm2 exposure. From this we can conclude that the system will be ineffective in killing microorganisms that remain suspended in the air stream. In fact the vendor’s literature focuses on keeping surfaces free of growth.
The information provided is largely lacking in quantifiable technical data. The majority of the information may be categorized as anecdotal or testimonial. The “Test” conducted at some user’s facility does not appear to have followed recognized scientific method, as no mention of a control sample is provided. Therefore the test results do not necessarily lead to the stated conclusions.
Furthermore, there are numerous negatives associated with UVC and the associated current technology. These include:
• UVC is damaging to human tissue, especially the eyes. This would require that any system installed must provide suitable interlocks to ensure that the light is turned off before opening any access cover. Also, the installation must ensure that no light leaks into occupied areas.
• UVC is damaging to plastics and other elastomers. Therefore, any materials exposed must be tested for UV stability.
• UVC light sources are short-lived and costly. Expected life in a stationary installation is one year, with a per-bulb cost of $100 to $150.
• UVC light sources contain toxic materials such as mercury, phosphor and thallium. Should a light source break, these toxins would be introduced directly into the HVAC air stream.
The use of ultra violet-c light (UVC) as a germicide is an established and proven technology. UVC has been used in the health-care industry for many years to supplement other methods of sterilization. It is only recently, with the increased emphasis on indoor air quality and potential biological attacks that UVC has been heavily promoted for HVAC applications. UVC works as a germicide by penetrating the cell walls and damaging the genetic structure of the organism. In order to effectively kill and organism using UVC, it must be exposed to UVC to a minimum combination of intensity and duration. The exposure factor is measured on a surface, and it generally characterized as micro-Watt seconds per square centimeter. High exposure levels may be achieved by high intensity, long duration, or suitable combination. The required exposure levels for common micro organisms range from 6,500 to 60,000 ?W?S/cm2, and can be as high as 111,000 ?W?S/cm2 for some mold spores.
The specification for the vendor’s unit lists a light intensity of between 122 and 158 ?W /cm2 . Therefore to achieve a lethal dose of UVC from this system, any microorganism would require a significant exposure duration, 41 seconds to achieve the lowest 6,500 ?W?S/cm2 exposure. From this we can conclude that the system will be ineffective in killing microorganisms that remain suspended in the air stream. In fact the vendor’s literature focuses on keeping surfaces free of growth.
The information provided is largely lacking in quantifiable technical data. The majority of the information may be categorized as anecdotal or testimonial. The “Test” conducted at some user’s facility does not appear to have followed recognized scientific method, as no mention of a control sample is provided. Therefore the test results do not necessarily lead to the stated conclusions.
Furthermore, there are numerous negatives associated with UVC and the associated current technology. These include:
• UVC is damaging to human tissue, especially the eyes. This would require that any system installed must provide suitable interlocks to ensure that the light is turned off before opening any access cover. Also, the installation must ensure that no light leaks into occupied areas.
• UVC is damaging to plastics and other elastomers. Therefore, any materials exposed must be tested for UV stability.
• UVC light sources are short-lived and costly. Expected life in a stationary installation is one year, with a per-bulb cost of $100 to $150.
• UVC light sources contain toxic materials such as mercury, phosphor and thallium. Should a light source break, these toxins would be introduced directly into the HVAC air stream.
I would second MintJulep's analysis. As a matter of fact, I actually suspect the market incursion into HVAC by UV mfrs is a result of losing market share - because of falling out of favor with the health industry.
Our experience has been that they are too dangerous, too maintenance intensive, and too unreliable for robust sterilization. Exposure time for kill of biologicals is not insignificant. A constantly moving airstream is problematic at best. They usually require that the contaminant has already impinged on a filter.
If you need that type of confidence, might as well use HEPA anyway - then you don't need the UV, and you don't irradiate your laboratorians or maintenance technicians.
Our experience has been that they are too dangerous, too maintenance intensive, and too unreliable for robust sterilization. Exposure time for kill of biologicals is not insignificant. A constantly moving airstream is problematic at best. They usually require that the contaminant has already impinged on a filter.
If you need that type of confidence, might as well use HEPA anyway - then you don't need the UV, and you don't irradiate your laboratorians or maintenance technicians.
Thank you MintJulep that was a good read. Have you done any similar research on other technologies?
One that has been brought to my attention is the Strion Air Filtration system. Do you (or anyone else out there) have any experience with this?
Thanks,
Walkes
One that has been brought to my attention is the Strion Air Filtration system. Do you (or anyone else out there) have any experience with this?
Thanks,
Walkes
ChrisConley
Mechanical
I just was given a catalogue on Strion Air as well walkes. Haven't had much time to review but it looks like it may have some areas of applications. The low pressure drop is definetly attractive, I'd like to see what the life of the unit is like.
On the area of UVC for air treatment I have read some very usefull documents from Sanuvox Technologies
Their latest HVAC offerings dealt with many of the issues MintJulep offers relating to exposure time and killing dose. They seem to be the only manufacture that I've found that used some science and engineering to determine how to use their product effectively.
On the area of UVC for air treatment I have read some very usefull documents from Sanuvox Technologies
Their latest HVAC offerings dealt with many of the issues MintJulep offers relating to exposure time and killing dose. They seem to be the only manufacture that I've found that used some science and engineering to determine how to use their product effectively.
Mechya, I am a HVAC person in a hospital an have had the following experience. Two new air handlers in a non clinical area. These units have a over 30 UV tubes and a ballast for each. Tubes need to be replaced annually at $87 ea. Twenty ballasts are toast after three years. The Sterile-Aire folks said the ballasts $160 each may last up to five years. Well, do he math. I have abandoned these lights and consider them trendy junk. Why they were even spec'ed for office space is beyond me. OH, the Sterile-Aire folks said the ballasts do not last due the humid environment near the cooling coil. So fella's put them in d dry place. I give up. Ken in Oregon
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