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  1. #1
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    Electronic Air Cleaners

    I have converted a portion of a warehouse into a home. The home is well sealed and insulated. It is about 2500 SQFT. The warehouse itself is 16,000 sqft.

    I have a bad dust problem. I have to change the filters in my 4 ton heat pump every month and they are pretty clogged even then. I am using better than average, but not the most expensive filters because the really good one won't last two weeks.

    I have looked at several electronic air cleaners including the Honeywell F300E. I can get one of these for about $385 in a 20x20 and $400 for one in 20x25.

    My filter/plenum opening is 20 x 21. Should I get a 20x20 or a 20x25?

    http://honeywell.electronicaircleaners.com/duct.html

    Will this air cleaner make a big difference in the dust? Should I be looking at something else?

  2. #2
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    First thing is you need to kake your living space positive pressure so as not to infiltrate pariculate from the warehouse in to the living space. Second for just particulat I would just up the filter quality to somewhere between a Merv 8 and a Merv 12 filter on the heat pump. And I would go at least 4 inchs thick on the filter so as not to effect the operation of your HVAC unit. And to decrease the frequency of filter changes. As you get the space cleaned up the time between filter changes will increase.

  3. #3
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    Thread Starter
    Quote Originally Posted by genesis View Post
    First thing is you need to kake your living space positive pressure
    How do I do this? The problem does seem to be infiltration. The living space is clean, the dust seems to come from the warehouse.

  4. #4
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    Quote Originally Posted by Bill_Marsh View Post
    How do I do this? The problem does seem to be infiltration. The living space is clean, the dust seems to come from the warehouse.
    It's hard to say without seeing it. But it could require some additional ductwork and/or equipment to be added to your system if your living area is actually under less pressure that the warehouse. This could be verified by an HVAC technician with the proper pressure testing equipment. The problem is sometimes addressed by increasing the air pressure in the living air to a point that's a little higher than problem area, which in your case is the warehouse. The location and configuration of the existing supplies and returns can also be a problem.

    It also sounds like part of the problem is that you don't have enough filter area for the 4 ton heat pump, which must move the air at a minimum volume of 1600 CFM to support that system. So your 20 x 20 filter setup is only allowing you to use a filter that is only about half the size you need. I would recommend having the ductwork expanded to allow a filter rack that would accommodate 2 disposable filters that would total at least 769 square inches of area. (A 20 x 20 = only 400 square inches.)

    I would definitely not recommend having an electronic air cleaner installed in that environment. Even the larger 20 x 25 unit (500 sq in) would be a disaster at 1600 CFM with that level of particulates.

  5. #5
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    Thread Starter
    Quote Originally Posted by midhvac View Post
    It's hard to say without seeing it. But it could require some additional ductwork and/or equipment to be added to your system if your living area is actually under less pressure that the warehouse. This could be verified by an HVAC technician with the proper pressure testing equipment. The problem is sometimes addressed by increasing the air pressure in the living air to a point that's a little higher than problem area, which in your case is the warehouse. The location and configuration of the existing supplies and returns can also be a problem.

    It also sounds like part of the problem is that you don't have enough filter area for the 4 ton heat pump, which must move the air at a minimum volume of 1600 CFM to support that system. So your 20 x 20 filter setup is only allowing you to use a filter that is only about half the size you need. I would recommend having the ductwork expanded to allow a filter rack that would accommodate 2 disposable filters that would total at least 769 square inches of area. (A 20 x 20 = only 400 square inches.)

    I would definitely not recommend having an electronic air cleaner installed in that environment. Even the larger 20 x 25 unit (500 sq in) would be a disaster at 1600 CFM with that level of particulates.

    I was about to buy an electronic air cleaner when your response came through.

    I also have a 2 ton heat pump that services the bedroom and another room, so the 4 ton really only services about 1800 SQFT.

    The 2 ton comes on at night and the 4 ton during the day.

    I could enlarge the plenum on the 4 ton, but I would still have an intake in the air handler of 20x20, however an enlarged plenum could easily increase the filter area.

    I have two 14" and one 12" return feeding into the return plenum. Would this be enough?

    I don't exactly understand how to increase pressure in the living area without somehow drawing in air from outside the dwelling area. Otherwise in a closed system it would seem there would only be circulation of the air in the home.

    I am not an HVAC tech, but I am a general contractor. My system was designed by an HVAC professional who is no longer available. Deceased.

    Am not sure why it would be a "disaster" to install an electronic air cleaner with 1600 CFM?

    Your advice would ba appreciated.

    Bill

  6. #6
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    Definitely need someone to check the place out that has the tools needed to test for pressure imbalances between your living space and the warehouse, imbalances from room to room within the space, and and a blower door infiltration test to check the infiltration rate of your living space.
    If you have any infiltration from the warehouse, you will need to correct it.

    In a situation like yours it is especially important to get the place sealed up as tight as possible and use mechanical ventilation of actual outdoor air for all of your fresh air intake, and keep the place under a very slight positive pressure. The warehouse is not outdoor air, so you don't want any infiltration from it.

    Assuming infiltration is the problem, once you get that fixed, your problem with filters getting dirty, and the dust problem in general, will probably go away.

  7. #7
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    Also, unless the place is VERY poorly insulated and built, 6 tons of AC is probably MASSIVLY oversized. Even if the living space is in a corner of the warehouse, you have no solar heat gain whatsoever on 2 full sides of the house, and possibly none at all through the "roof" if the living space does not extend to the roofline of the warehouse.

  8. #8
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    Mark brings up a good point about the sizing. There are some potential issues with that.

    You can have an imbalance in an room between the return and supply pressures that can create a negative pressure in one area and not in another area, if for example, you have a little more return CFM being drawn from a room than you have supply CFM being delivered to that room. And let's say that the door to that room is closed. This puts the room into a negative pressure. Any air leaks between that room and the warehouse, outside area, or above a suspended ceiling will draw *unfiltered* air into the room. This is an example of a condition that could possibly be addressed without bringing outside air in.

    There's no way of knowing where the problem areas are without conducting tests.

    A 20 x 25 EAC could prove to be disastrous in your case at 1600 CFM because the velocity of air going through that 20 x 25 EAC is going to be too high (461 FPM) for it to operate at anywhere near peak particle capturing and retaining efficiency. The other big issue is that EAC's lose those efficiencies at a much lower CFM when only a minute layer of dust builds up on the cells. The cells utilize high DC voltage to place an opposite charge on the particles. The charged particles are attracted to the cell plates that have an opposite charge to the particle's charge. This attraction must be powerful enough to be able to draw the particles to the cells and hold them there. As a tiny layer of dust begins to coat the cells, it weakens the attraction energy. When you factor in the increased attraction required to catch the faster moving particles (461 FPM) things become much worse. A 20 x 25 EAC is hard pressed to catch those "fastballs" at 461 FPM even when the cells are spotlessly clean and brand new. The ideal velocity is 300 FPM.

    Disposable filters don't have the problem of becoming less effective at capturing and retaining particles when they build up a little dust. They actually trap more particles when that occurs.

  9. #9
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    Maybe for the warehouse an industrial ionizer like the MI-1500 would help in the airspace since it will cause the majority of the particles as small as condensation nuclei (not all of them but the vast majority which sizes from .0001micron to .000001micron....anything that can accept a charge that will continue to clump until heavy enogh for gravity to pull it out of the air but then you vacuum it up or sweep it up and that logically seems that if it can't get into the filter it wont have to be changed as often...and the air would be cleaner anyhow.

  10. #10
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    Quote Originally Posted by mark beiser View Post
    Also, unless the place is VERY poorly insulated and built, 6 tons of AC is probably MASSIVLY oversized. Even if the living space is in a corner of the warehouse, you have no solar heat gain whatsoever on 2 full sides of the house, and possibly none at all through the "roof" if the living space does not extend to the roofline of the warehouse.
    Thnk you Mark,

    Actually I do not run the 2 ton. I do have a problem you might not realize and that is not the cold. During the winter It easliy stays warm. During the summer, the inside temperature near the top of the warehouse is really high due to poor ventilation there.

    I am installing some passive vents in the warehouse roof. That will help this summer. The AC has to work hard to fight against the natural heat buldup otheriwise. Think an ice cube in an oven!

    I am calling the tech support line of a local HVAC supply place today and also getting the advice of a local HVAC contractor who owes me some favors for recommending him on several jobs.

    Thanks for the advice, but I guess it is going to take some local talent to gice me the answers I need.

  11. #11
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    Be aware that less than 0.5% of HVAC contractors are capable of performing the type of testing you need done.

    Try the "Locate a CI contractor" link at www.comfortinstitute.org
    Some good information links there too.

  12. #12
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    how do you get the 461 fpm?

    hi guys,I 've been reading alot of threads on IAQ and airflows and was wondering how you can come up with the fpm velocity from the size of eac opening? I see this thread is old but if anybody gets e-mailed that was in the thread any replies would be appreciated, expecially mid hvac since you were the one to post the estimated velocity of 461 fpm, Thanks in advance.

  13. #13
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    Quote Originally Posted by brdman View Post
    hi guys,I 've been reading alot of threads on IAQ and airflows and was wondering how you can come up with the fpm velocity from the size of eac opening? I see this thread is old but if anybody gets e-mailed that was in the thread any replies would be appreciated, expecially mid hvac since you were the one to post the estimated velocity of 461 fpm, Thanks in advance.
    By plugging the 1600 cfm of airflow and the 20x25 air cleaner dimensions into an airflow calculator like this one. http://www.engineeringtoolbox.com/du...ons-d_883.html

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