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  1. #1
    Join Date
    Sep 2005
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    Richardson, TX
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    Charged media electronic air cleaners

    Howdy all,

    I've read through a number of threads and believe I understand the reservations that some of you have about smallish EAC's on large-ish residential units. But do those concerns about keeping poor hold of dirt at higher flow rates apply to charged media units as well? It seems like using charged media would give plenty of opportunity to hold on to the dirt. Since they look closer to a cheap fiberglass element, am I correct to assume there aren't concerns about high pressure drop concerns as soon as the smallest amount of dirt is captured?

    More detail: 18 months ago I had a 4-ton unit installed and they put a 20"x25" MicroPower Guard in the existing 1" filter holder attached to the existing plenum. It's a charged-media electronic air cleaner which uses removable pads with carbon-graphite center charging screen. Before you think this is a wacko product, Goodman/Amana sell a version of it (although I guess that doesn't mean it couldn't still be wacko). You can read their specs on it here (which shows a .17" drop at 300 FPM).

    In short, I ran out of filter media and am trying to decide if I want to buy more replacements, or if they are a risk to my system (and if so, what I should switch to?). We are relatively free of allergies, although the wife complains on rare occasion - so I need to be able to present a coherent reason to her if I don't go with something more "special" than the cheapest thing on the Home Depot shelves.

    Thanks,

    Marc

  2. #2
    Join Date
    Jun 2005
    Location
    The Gray Northwest
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    I would not say your MicroPowerGaurd is a "risk" to your system. If your are happy with it's performance, than keep it. In my opinion, there is too much concern about trying to "micro-filter" the air in our homes. The best way to keep your indoor air "healthy", in my opinon and expierience, is to bring in "fresh air" from outside, which unfortunately, most home systems do not do.

  3. #3
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
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    .17" is a lot of resistance for any standard blower to handle. With a 4 ton unit you should have 400 CFM x 4 = 1600 CFM of air flow. with a 20 a 25 filter, that is 20 x 25 = 500 square inches of filter area. divide that by 144 sq inches per square foot, you get 3.47 square feet of filter area. divide 1600 CFM by 3.47 and you get a velocity of 460 feet per minute.

    According to the fan laws, the pressure drop goes up as the square ov the velovity increase. 460 divided by 300 is an increase of 1.536. 1.536 * 1.536 = 2.359. 2.359 * .17 = 0.4 inches pressure drop. This does not even allow for the net free area of your filter grille being only 70 to 80% of the listed size or the reduction in surface area caused by the 1" border going all the way around the filter. msot residential Air handler blowers can only produce rated air flow at .3 inches to 0.5 inches total external static pressure (ESP). Furnaces will produce .5 to .8 inches ESP This includes pressure drop across the filter, ducts, return grilles, supply grilles, cooling coils and other accessories.

    In short there is no way your system is going to work properly with your filter installation.

    Either add another filter grille and filter along side the one you have to double the filter surface area so you only have 1/2 the velocity(and reduce the pressure drop to 1/4 (.5 * .5 = .25). Or get rid of that restrictive filter.

    By the way, after three months of use, the pressure drop across that filter is about double the clean filter pressure drop!!!!
    Remember, Air Conditioning begins with AIR.

  4. #4
    Join Date
    Sep 2005
    Location
    Richardson, TX
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    Thread Starter
    Quote Originally Posted by Kevin O'Neill View Post
    .17" is a lot of resistance for any standard blower to handle. [...clip supporting data - thank you!]

    In short there is no way your system is going to work properly with your filter installation.

    Either add another filter grille and filter along side the one you have to double the filter surface area so you only have 1/2 the velocity(and reduce the pressure drop to 1/4 (.5 * .5 = .25). Or get rid of that restrictive filter.

    By the way, after three months of use, the pressure drop across that filter is about double the clean filter pressure drop!!!!
    My gut told me that was what the answer would likely be - but then I started to question it since Amana/Goodman sells them. Their website doesn't list restrictions on which units can have what size filters, but maybe (to give them the benefit of the doubt) they do have an internal spec that the unit can only be used on 4+ ton units if the filter is over a certain size. Or maybe we shouldn't give them the benefit of the doubt.

    Thank you again for the confirmation,

    Marc

  5. #5
    Join Date
    Mar 2008
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    So would these EAC's be ok to run on a 3 ton unit?

  6. #6
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
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    Quote Originally Posted by uprise View Post
    So would these EAC's be ok to run on a 3 ton unit?
    Not that size. It is too small for a 3 ton. If you used 2 of them side by side to double the surface area, then it should be OK.
    Remember, Air Conditioning begins with AIR.

  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    Find a new filter!

    That .17"wc pressure drop is at 300fpm. With 1600 CFM through a 20x25 filter, the velocity of the air is more than 50% hither than the velocity that .17" pressure drop is at.
    Pressure drop through a filter doesn't scale linearly with the velocity, so even though the velocity is just over 50% higher than the pressure drop of the filter was rated at, the actual pressure drop of the filter in your system can be much higher than 50% greater than the rating.

    The higher velocity through the filter also degrades the performance, so you won't get anything like the filtration they claim.

    That type of filter is not a new concept. I'll be nice and just say that they have never worked out as well as the marketing materials claim...

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