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  1. #14
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    Quote Originally Posted by charles2 View Post
    When you develop cataracts you'll know why.
    I already have them in both eyes, but I grew up in the desert.

  2. #15
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    Quote Originally Posted by sktn77a View Post
    Anybody have any reliable data on either of these hypotheses?

    Keith
    Here's a study that also links to the work of several others regarding UV lights: http://aem.asm.org/cgi/content/full/67/8/3712

    Seems like the real question is whether these lights produce an intense enough output to kill pathogens even though they are passing by only briefly. With a reasonable amount of air delivery there would be a 'repeat' effect - say every 15 minutes or so the system would have conditioned all the air in the space 1x. So a cumulative exposure would result in the course of a typical day.

    We did a very large frozen yogurt plant here in Sacramento, system was required to be 100% outside air for food manufacturing of that type. Filtration was sock filters, then 24" thick cartridge filters, followed by one huge bank of UV lights. That was in 1988, years before I heard of a residential application.

  3. #16
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    Feb 2007
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    999

    strictly anecdotal

    Quote Originally Posted by sktn77a View Post
    Warning! Scientific hypothesis only. This is purely speculation based upon my research experience in bacteriology and virology using UV sterilization hoods. I suspect the UV light in the coil case works in killing stationary mold ansd spores because the UV exposure is continuous. I cannot fathom how the lights in the return ducts have any effect on moving bacteria, etc, in the air as the exposure time has to be way too short (less than a second at typical duct air velocities).

    Anybody have any reliable data on either of these hypotheses?

    Keith
    Many years ago, I visited a (really) small, privately owned sterile pharmaceutical manufacturing plant, doing freeze drying of product (this is important).

    The "sterile" filling room had no HEPA filtration, no positive pressure, only several horizontal laminar flow work stations. There were numerous u/v lights with deflector hoods, mounted around the perimeter at very high level. The principals spent many hours in the filling area. The FD equipments used circulating trichloroethylene as the shelf refrigerant.

    The company had been acquired by another with which I was associated. The equipment was relocated and reinstalled, however, the filling areas were first class; under constant positive pressure with HEPA filtration, but no u/v lights, and generally met Class 100 conditions.

    The equipment must have been leaky (perhaps as a result of the move) as it required frequent top-offs of the TCE. There was no ventilation system to remove the fumes.

    Bottom line: shortly afterwards, the former owner developed cataracts. Several years later, he was forced out of the company and I became intimately involved in the operations of the company, including the FD equipment.

    A year or so after that, I joined a major pharmaceutical company (sterile product, but no FD) and within a year developed my first cataract. I was 40 years old at the time.

    I had no contact with u/v, but I wouldn't rule it out as a possible cause of cataracts. On the other hand, TCE has been pretty much banned (I tried to buy some, but couldn't find any). I believe it is deemed as being carcinogenic. One thing, you get one helluva buzz from it.

    I attribute my (early) cataract to frequent inhalation.

    Amp

  4. #17
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    Quote Originally Posted by charles2 View Post
    - Not necessarily, you have to consider media surface area.

    Given the same materials and construction, doesn't a 2" thick filter have exactly twice the area of a 1" filter?

    - google it

    I did - nothing came up.

    - That depends on who you ask

    I'm asking you and everyone else here who knows more than I do.

    - I think "acceptable pressure drop" greatly varies between systems

    Alright, let's say the system is a Ruud UBHC-17J11NFD air handler over a Ruud RCBA-3765G indoor coil.
    is the rcba an "M" style coil? if it is, i wouldn't go above merv8.
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

    "Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington

  5. #18
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    Jul 2008
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    551
    Quote Originally Posted by sktn77a View Post
    Warning! Scientific hypothesis only. This is purely speculation based upon my research experience in bacteriology and virology using UV sterilization hoods. I suspect the UV light in the coil case works in killing stationary mold ansd spores because the UV exposure is continuous. I cannot fathom how the lights in the return ducts have any effect on moving bacteria, etc, in the air as the exposure time has to be way too short (less than a second at typical duct air velocities).

    Anybody have any reliable data on either of these hypotheses?

    Keith
    The University of Missouri - Columbia Electrical Engineering department did some work in a similar area back in the early 2000s. They were developing a quick sterilization method using UV spot lights and some sort of powder activating agent that would kill just about everything with a single pass of the UV light. Typical exposure for an area was well under 1 sec.

    I'm not saying this help much, but it does point to the possibility of some microbials/bacteria being very susceptible to very short durations of UV exposure. I'd guess it kills some things well and does nothing for many others.

  6. #19
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    Feb 2001
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    447
    Quote Originally Posted by smittyii View Post
    is the rcba an "M" style coil? if it is, i wouldn't go above merv8.
    Yes, it is an M. I had pretty much settled on MERV 8, but I'd still like to know what brand/model pleated disposable filter is the best value, i.e. lowest pressure drop, longest lasting and least expensive. Also would like to know who makes filter grilles for 2" and thicker filters.

  7. #20
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    Quote Originally Posted by badtlc View Post
    The University of Missouri - Columbia Electrical Engineering department did some work in a similar area back in the early 2000s. They were developing a quick sterilization method using UV spot lights and some sort of powder activating agent that would kill just about everything with a single pass of the UV light. Typical exposure for an area was well under 1 sec.

    I'm not saying this help much, but it does point to the possibility of some microbials/bacteria being very susceptible to very short durations of UV exposure. I'd guess it kills some things well and does nothing for many others.
    Maybe the powder was arsenic... and the UV had little or nothing to do with the death of the little critters. Besides, airflow, mysterious powdered materials...sounds more like a ME or MS project. Those darn EE need to stick to E&C work.

  8. #21
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    Jul 2008
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    Quote Originally Posted by motoguy128 View Post
    Maybe the powder was arsenic... and the UV had little or nothing to do with the death of the little critters. Besides, airflow, mysterious powdered materials...sounds more like a ME or MS project. Those darn EE need to stick to E&C work.
    No, it was a proprietary powder the university now owns the patent on. It was developed for quick sterilization of both an area exposed to anthrax and planes making international flights. The powder essentially enhanced a special property of UV light. It fell into the EE department's realm because they were studying different frequencies of UV light and trying to optimize the light source for both effectiveness and efficiency.

    Now that I think about it, I think the project was done in conjunction with a faculty member from the chemical engineering/biological engineering department.

  9. #22
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    Quote Originally Posted by charles2 View Post
    Yes, it is an M. I had pretty much settled on MERV 8, but I'd still like to know what brand/model pleated disposable filter is the best value, i.e. lowest pressure drop, longest lasting and least expensive. Also would like to know who makes filter grilles for 2" and thicker filters.

    I would never use a filter grill unless you have absolutely no space at the return of the air handler/furnace or if hte AH is buried deep in the attic where it's hard ot reach. They even make right angle filter housings... so there's really no excuse. Media filters and EAC's only need about 7-1/2" of space next to the air handler. Some even less.

    I believe they do make 4" filter grills as well. The probablem is that most central return grills are usually undersized as it is, and adding a filter makes it worse. The bigger the better...in all dimensions. I believe if possible you want the velocity under 300fpm, 500fpm maximum.

  10. #23
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    Quote Originally Posted by badtlc View Post
    No, it was a proprietary powder the university now owns the patent on. It was developed for quick sterilization of both an area exposed to anthrax and planes making international flights. The powder essentially enhanced a special property of UV light. It fell into the EE department's realm because they were studying different frequencies of UV light and trying to optimize the light source for both effectiveness and efficiency.

    Now that I think about it, I think the project was done in conjunction with a faculty member from the chemical engineering/biological engineering department.

    Sounds like a interesting project. It might be that the powder was activated by the light and a chemical reaction occured forming a new compound that was deadly to the microbes, but safe to handle for humans.

    If the military or government was involved, sometimes functionality and effetiveness come before safety and long term health side effects. My wife was happy she never got the anthrax or some other vaccine just before she left the Navy in the mid 90's. I believe it's had some bad side effects especially for women hoping to have children some day.

  11. #24
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    Feb 2001
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    447
    Quote Originally Posted by motoguy128 View Post
    I would never use a filter grill unless you have absolutely no space at the return of the air handler/furnace or if hte AH is buried deep in the attic where it's hard ot reach.
    I'm interested to know why you hate filter grilles. Are thicker filters that much better than 1" pleated filters, or less expensive to use?

  12. #25
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    Quote Originally Posted by charles2 View Post
    I'm interested to know why you hate filter grilles. Are thicker filters that much better than 1" pleated filters, or less expensive to use?
    More surface area = less restriction. The thicker the pleat, the lower the pressure drop with the same media. 1" filters are fine if they are large enough for the airflow requirements (which they are often not), not over 7 or 8 MERV and they are changed regularly.

    Filter grills serve their purpose is many situations, but again, if you have hte space and the furnace/AH is accessible, why not do it right. Another disadvantage is that you now pulling a larger vacuum on the entire lenght of ductwork between the grill and the furnace. So if the ductwork isn't sealed tight, unfiltered air is pulled through the furnace. If you locate the filter adjacent to the furnace. You are only worried about the connection between the filter housing and furnace and the access door on the blwoer itself, not hte upstream ductwork. This can be a big difference if the return uses panned joists and/or wall cavities.

    I'm also not a fan of central returns. It's a compromise builders make to cut costs. They are done because it's cheaper that way... and for no other reason. Correct duct sizing is still far more improtant, but multiple returns can help. I think it can also reduce stratification to some degree, althouugh it's the job of supplies to mix the air.

  13. #26
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    M style coils require very good return air flow. unless the return is oversized i wouldn't use a 2" filter on a ruud or rheem M coil.
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

    "Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington

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