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  1. #1
    Join Date
    Sep 2004
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    Location of static pressure measurements on air handler?

    Just looking to check my static pressures as I suspect they are high on my 2nd floor air handler. I have a standard hydronic system with boiler and air handler 1 in the basement and airhandler 2 in the attic; each with its own condenser located outside. I'm located in New England.

    They are both setup the same except the attic air handler has a ductopus while the basement is all sheet metal.

    Return duct, return plenum, airfilter, air handler, cooling coil, blower, heating coil, feed plenum, feed duct work.

    Where should I take the static? There are conflicting answers out there and I only want to drill holes once. I'm thinking just before the blower for the negative static and just after for the positive static. But I'm torn because that will include the pressure drop from the heating coil and perhaps I should just take it in the feed duct a couple feet down and assume laminar flow.


    -Chris

  2. #2
    Join Date
    Jan 2004
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    On an air handler.
    The static(ESP) pressure is taken between the air filter and coil, and in the supply plenum BEFORE the hydronic coil, if its an add on coil.

    Unit footnotes must always be read to see if they have an allowance for the air filter or not.

    This is something best done by a contractor. But finding one that will do it is hard to do in many areas.
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  3. #3
    Join Date
    Sep 2004
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    I work in research and development and am used to instrumenting industrial equipment (EE Major). I may not always know where the sensor is supposed to go but I sure can install, wire, and log to a PLC. Rest assured I'm not going to screw anything up measuring static pressure just wanted to be sure where the measurements are supposed to go.

    Between airfilter and coil I have 0.2 and before the hydronic coil I have 0.12 for a total of 0.32 on my 1st floor. Which I think is good? If I take the filter out the it drops by 0.05 (Air bear MERV 8 24 x 25 x 5 I believe).

    Now it is time to sweat my but off and climb in the attic. I'm installing a permanent pressure gage up their to log pressure electronically so I don't have to waste money changing filters that don't need changing. I'l report my numbers in a little bit; I'm suspecting there is massive restriction up their as there is only ONE return (in the hallway of my cape) and 4 outlets in a ductopus flex configuration.

    -Chris

  4. #4
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    Sep 2004
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    The attic numbers are -

    Intake - 0.35 (One ONE return at the top of my stair well ) Filter is worth 0.05 .
    Exhaust - 0.20

    Can anyone quanitify just how much of a difference adding additional returns would increase performance?

  5. #5
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    That would depend on the size of the return, and the duct size.
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  6. #6
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    Sep 2004
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    We have a TSI capture hood at work; I think I may grab it and measure the registers with the system as is then disconnect the return from the plenum to get an idea of flow increase.

    Just a simple "feeling with my hand" with the filter door removed and filter removed made a large difference in velocity of air exiting the registers in my bedrooms. But I'm a numbers guy so it appears I need to do a little more work.

    Thanks for the info on the correct location for the pressure measurements.

  7. #7
    Join Date
    Aug 2002
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    Both statics are less then I would have expected.

    Low PD for te Air bear as well.

    Your hood will measure delivered air,not including duct leakage.

    Could have the correct air flow now,be careful before increasing it.Could lower the static,and the fan speed to be sure the air flw is correct.

    You are taking the return "In" the air handler,correct?
    Last edited by dash; 08-09-2008 at 06:25 PM.

  8. #8
    Join Date
    Jun 2005
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    SW Wisconsin
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    Quote Originally Posted by 2000silverz View Post
    We have a TSI capture hood at work; I think I may grab it and measure the registers with the system as is then disconnect the return from the plenum to get an idea of flow increase.

    Just a simple "feeling with my hand" with the filter door removed and filter removed made a large difference in velocity of air exiting the registers in my bedrooms. But I'm a numbers guy so it appears I need to do a little more work.

    Thanks for the info on the correct location for the pressure measurements.
    It appears your test got a good velocity increase.

    I have no clear idea what you are dealing with on that unit.

    HOWEVER, if you install another Return duct, be sure to install an oversized filter rack & properly size the Return run. Using two filter racks, all filters should be on the return racks, & none in the air handler.

    If done properly there should be a fair increase in velocity & CFM.
    Are the blower blades & E-Coil clean? What are the blower specs?


    If you do not have humidity problems & it is an older lower SEER unit, you could go as high as 450-CFM per ton of cooling on a wet E-Coil.

    Check for duct leaks on both Supply & Returns & seal any leaks with mastic.
    Then use that Capture Hood to measure the CFM to each room.


    Let us know your results. - udarrell

  9. #9
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    Sep 2004
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    41
    Here are some photos taken a couple years ago when we built the house.







  10. #10
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    What is the tonnage of the basement unit.

    The return fittings are restrictive,and the static is only .2 return?

  11. #11
    Join Date
    Sep 2004
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    41
    Attic unit 1.5 ton.
    Basement unit 2 ton.

    On the basement unit there is an additional tap on the return which isn't there in those pictures. The basement is now finished and they added two additional returns; one attached just to the left of filter (10"). The other was added into the trunk return line.

    Just because you mentioned it I closed off both returns in the basement and blocked the outlets and the static went up by 0.1 to 0.3 on the return. But like I mentioned the 1st floor / basement setup works great; low humidity and nothing unreasonable in the duty cycle department. There are NUMEROUS return leaks though because my floor joists are TGI's and when they capped two runs to use for returns they never sealed up the TGI beam joint so if you added them all up I would guess I have a good 4" x 4" leak.


  12. #12
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    Return changesand equip. sizes make sense now ,with the lower static.


    Duct leaks will raise it ssome,when fixed.

  13. #13
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    What size boiler is that Burnham.

    Looks a bit oversized. For the piping that hooked to it.
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