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Static Pressure Thread: Air Handlers

Discussion in 'Residential' started by Doc, Aug 2, 2006.

  1. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    Measuring static pressure on air handlers has been
    a huge area of confusion in this biz.

    It often seems like each manufacturer rates the fans in it's equipment
    under a different set of variables each time. This is where the
    confusion begins.

    There are no set conditions & this is why it is so important to look
    at the footnotes provided in the fan performance data of each
    particular piece of equipment.

    Some will include a wet coil others a dry coil. Some include a filter
    in the pressure drop, others have a pressure drop table for different
    media types.

    Lets take a look at how & where to measure it on a residential air handler.

    The tools required to take these measurements can be found in this
    same forum under the static pressure: tools required thread.

    Here is the test subject:

    [​IMG]

    A upflow air handler in a basement with a clean coil.

    Here is the reading taken before the media filter:

    [​IMG]


    This is the reading taken after the media filter:

    [​IMG]


    This is the reading taken after the coil:

    [​IMG]

    Keep in mind all these readings are on the return or negative side of
    the fan, notice the magnehelic port used is the low side.

    Here is the supply side reading:

    [​IMG]

    This reading is on the positive side of the fan & requires you to hook
    to the high side port of the magnehelic.


    What are some of the things I need to take into account before I can
    determine if the static pressure readings we have are acceptable?

    What are my pressure drops & Total External Static Pressure readings?

     
  2. Swampfox

    Swampfox red tagged

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    You tell me
     
  3. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    Now where would the fun be in that? :roll:
     
  4. Swampfox

    Swampfox red tagged

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    well i can understand taking a supply and return reading, but the 3 readings on the negative side of the fan confuses me, teach me something
     
  5. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    Okay now we are getting somewhere. :wink:

    Most air handlers are rated for the factory installed filter & a clean coil that is wet or dry depending on how it was rated in the lab. The condition the coil was rated for should be listed in the footnotes of the equipments fan performance data.

    The reason I have 3 return readings is to show the pressure drop of the filter & the pressure drop of the coil.

    This can be very handy during troubleshooting to help identify areas of restriction. Such as Paul Harvey equipment killer filters & restricted coils.

    We always record the pressure drop on a new clean coil so we have that data for future use, sort of a way to track when a coil is at the point it should be pulled & cleaned. Also lets you know if the coil pressure drop changes signifigantly that the fan curve will be useless & other ways will need to be used to verify fan airflow.

    If you have a clean factory installed filter in the factory filter rack & a clean coil that is at the rating conditions the fan was rated at the readings in the supply & return are fine.

    Clear as mud or did I do okay?
     
  6. Swampfox

    Swampfox red tagged

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    The light bulb is flickering a little, Im guessing thats about an average pressure drop for a media filter? but the one for the coil seems to be a bit high, dirty coil?
     
  7. Abby Normal

    Abby Normal On Permanent Vacation

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    As we discussed before we are looking at a reading after the media air cleaner and after the coil. Any readings right at the base of the actual air handler?
     
  8. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    That reading after the media is being taken in the return plenum.

    The return opening of the air handler & the opening of the return plenum are the same size so I assumed no pressure drop at that point.

    Think I should have taken one in the filter rack of the air handler?
     
  9. Abby Normal

    Abby Normal On Permanent Vacation

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    Was just wondering if the plenum was more like a square elbow without vanes?
     
  10. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    Yes that's exactly what it is. :wink:
     
  11. Swampfox

    Swampfox red tagged

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    so, whats the TESP? ~.045?
     
  12. Doc

    Doc Insert clever and witty comment here

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    5,892
    Yes but that can't be used to determine fan CFM from the fan performance data in this application. :shock: :roll:

    Why can't the manufacturers make it a little more confusing?
     
  13. Special Ed

    Special Ed Groupie

    Messages:
    91
    Location:
    Jacksonville, FL.
    Okay, I'll admit it: I'm a little lost.... If you took a reading before the filter media & one after the AHU, would that give you TESP? If so, it looks to me like the reading is .5, right where most mfg.'s like it, right?

    I'm probably wrong but keep in mind this is something I never learned at votech - they never taught it. But I'm sure as heck willing to learn! :D
     
  14. Doc

    Doc Insert clever and witty comment here

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    5,892
    This is where a lot of the confusion is Ed.
    If the filter used was a factory filter installed in the equipments filter rack then testing like you mentioned is okay.

    That media filter installed was not a factory filter & had a greater drop than the factory filter. The additional pressure drop has to be accounted from that installed media.

    This is one reason that it is a necessity to have the fan performance data for the equipment being tested.

    We were called in to balance a state office building here a few years ago.
    The installed equipment was Amana modular 5 ton air handlers with external filter racks.

    The installing contractor told us the fans were moving plenty of air & that all was ready for us. After looking at the fan performance data we found that the pressure drops for the coil & filters were not included in the fan data, it was rated for the blower section only! :shock:

    Needless to say he measured a very low TESP because he didn't allow for the drop of the coil & filters & thought he had airflow when in reality the TESP was over 1" W.C.

    The fan that was supposed to be moving 2000 CFM was only moving around 1400 CFM.

    They never taught us any of this stuff in vo-tech either Ed, that is one reason I keep posting the airflow items so questions can be asked & hopefully answered.
    We were taught to use our hands as flowhoods in vo tech. :mrgreen:
     
  15. Abby Normal

    Abby Normal On Permanent Vacation

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    You would figure it would not be all that hard to have the actual fan curve in the OEM manual, or a couple factory taps just to measure the blower
     
  16. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    This is one thing I don't get either C.

    It would make life so much easier to rate the blower ONLY then there would be no guess work or confusion.

    That is one reason I liked the way Amana was doing their modular air handlers, much easier to determine fan airflow.
     
  17. Special Ed

    Special Ed Groupie

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    91
    Location:
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    So you're saying the reading doesn't include what the blower is rated at? That is confusing!
     
  18. Abby Normal

    Abby Normal On Permanent Vacation

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    The ESP readings always depend on the fine print.

    Some times the fine print says "includes filter that ships with unit" , or "excludes filters", or "based on a wet coil".

    If you knew excatly how the blower itself worked, you would be better off.

    The modular ones doc was talking about, the ratings were just for the fan cabinet itself, was actually a blessing rather than a curse, just that the contractor thought it included the coils, filters etc.
     
  19. Doc

    Doc Insert clever and witty comment here

    Messages:
    5,892
    C nailed it with the statement about the fine print, this will determine how it is rated.

    What gets everybody in a tizzy is how they include the coil, wet/dry, voltage, and filter in the TESP. It is for one set of variables nothing else.

    It gets really hairy when any of the variables the fan is rated at change. For instance the coil gets dirty, pressure tested with a pleated filter in place when rated with a fiberglass, etc.......

    This is where you have to use some formulas or alternate methods to determine airflow.

    Interested in how to do it??
     
  20. Special Ed

    Special Ed Groupie

    Messages:
    91
    Location:
    Jacksonville, FL.
    You've piqued my interest....

    How do you do it? :D