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  1. #14
    Join Date
    Jul 2007
    Location
    Delaware
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    3,824
    little bit of pressure.
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    Always here

  2. #15
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    gas heater check just prior to blower and prior to the coil. Reason for that is a heater is designed to push x amount of air. The designers don't know what coil your putting on it so they do it for the heater itself. for an airhandler (coil and blower in same cabinet. ) check incoming and outgoing. Reason for this, is that the designers know what coil is in the cabinet and designed appropriately.

  3. #16
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,248
    Wow.....allot of questions being tossed out here.

    To the OP, if your return sp is greater than supply the return is undersized or you have dirty filter. Systems that I do I always have the return sp is less. No rule of thumb, but I want to keep return sp low because it's easier to push the air than draw the air.

    There is talk of pd across the coil, bear in mind the coil will have a pd for wet and dry conditions....always design for wet conditions and a dirty filter. The only real way to know if the coil is dirty is take a reading across the coil, I.E., before and after. Hopefully you will have mfr literature to tell you what the pd should be at the cfm your system is providing, and coil status (wet or dry)

    The question was asked about literature to read...I will think about that and see if I an find something, but SMACNA manuals or ASHRAE fundamentals comes to mind. If you have a specific question, post and I will try and answer.

    I disagree that dirty filters etc. result in higher operating costs the system is working more. It is actually working less. Take a blower and run it wild with no restrictions....amps go up. Stick board in front of the outlet and restrict flow and amps go down...it's moving less air and doing less work. Your losing efficiency, which wastes energy and is a loss of efficiency causing the system to run longer.

    What is important is tesp. If the coil is cut in, add that to tesp when looking at blower curves. If the coil is integral to the air handler, disregard unless your trying to find out if its dirty.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  4. #17
    Join Date
    Jul 2007
    Location
    Tulsa, OK
    Posts
    975
    Name:  TOTAL EXTERNAL STATIC PRESSURE.jpg
Views: 27
Size:  5.0 KBBefore the coil period, and as close to a good center of R/Air at heater cabinet with filters installed. Your after the fan wheel input and output with a ****Wet Evap Coil****. This is full load evaluation at the home installed instead of just a factory chart. Remember Factory charts are bench test best guides to help the tech, it's up to you to make a real on site decision of many factors like supply vents closed and furniture to low to allow stratification of airflow, returnable airflow to the return grills and many many more more only real world experience techs finally learn home to home new or used!

  5. #18
    Join Date
    Jun 2011
    Posts
    229
    Hm, sounds like there are alot of factors for SP and many routes to take...

    Maybe just a general checklist of things to check for Low readings, and high readings.

    Low SP causes & High SP causes.

    I do understand now the purpose of checking SP without the coil in the way because the Manufacture designed the Furnace W/O the coil in place. What do people usually do in uplflow/downflow/horizontal applications for checking the supply side? Remove the high temp limit or drill another hole?

  6. #19
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    There is a member here by the name of rundawg who made a static pressure manual and posted it here some time ago.

    It was a great piece on the topic.

    Do a search on his name and I'm sure you'll find it.

    If anyone is interested send me an e-mail or pm me and I'll send you some of the static pressure training material we use in our classes too.
    Have you set up a Google alert for Carbon Monoxide yet?
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  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    "hvac r us 2" made a video that will help many.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #21
    Join Date
    Jun 2011
    Posts
    26

    Static

    I was told that esp should be taken distance of 2.5 times the diameter of the blower wheel from the center of the blower shaft.

  9. #22
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    As a general rule, you're right

    Quote Originally Posted by JBM1000 View Post
    Name:  TOTAL EXTERNAL STATIC PRESSURE.jpg
Views: 27
Size:  5.0 KBBefore the coil period, and as close to a good center of R/Air at heater cabinet with filters installed. Your after the fan wheel input and output with a ****Wet Evap Coil****. This is full load evaluation at the home installed instead of just a factory chart. Remember Factory charts are bench test best guides to help the tech, it's up to you to make a real on site decision of many factors like supply vents closed and furniture to low to allow stratification of airflow, returnable airflow to the return grills and many many more more only real world experience techs finally learn home to home new or used!
    But if you look closely at the manufactures info you'll find that YORK for instance , gives ESP values WITHOUT filters And very intelligently then gives some instruction as to why you may for instance need 2 return elbows and filters for say a 5T unit
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  10. #23
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    Gib's Son I agree with both ideas

    Your's
    I disagree that dirty filters etc. result in higher operating costs the system is working more. It is actually working less. Take a blower and run it wild with no restrictions....amps go up. Stick board in front of the outlet and restrict flow and amps go down...it's moving less air and doing less work. Your losing efficiency, which wastes energy and is a loss of efficiency causing the system to run longer.
    I think the underlined sentence agrees with " result in higher operating costs the system is working more." that you said you disagree with

    But I like your point about amp draw. Counter intuitive isn't it!
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  11. #24
    Join Date
    Feb 2011
    Location
    New Jersey
    Posts
    170
    When a furnace tune-up is being performed by reputable person/agency do they undertake such static pressure tests in supply and return and thus adjust (if possible) accordingly? Or, this is something completely out of the purview of maintenance?

  12. #25
    Join Date
    Jul 2005
    Posts
    5,365
    Quote Originally Posted by genduct View Post

    I think the underlined sentence agrees with " result in higher operating costs the system is working more." that you said you disagree with

    But I like your point about amp draw. Counter intuitive isn't it!
    With a constant cfm ECM blower the amps will go up as the filter becomes restrictive.

    I assume that Gib's Son was responding to Desuperheater's statement. But here's what he actually said "Less ESP at equal CFM means the blower is working less, might last longer and will use less energy." Which is correct. HTH.

  13. #26
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058

    It should be

    Quote Originally Posted by wisepole View Post
    When a furnace tune-up is being performed by reputable person/agency do they undertake such static pressure tests in supply and return and thus adjust (if possible) accordingly? Or, this is something completely out of the purview of maintenance?
    determined at installation and bench marked. It should be checked on each maintenance call to help determine if the system is functioning propperly.

    Most companies will not check it because they do not know what it should be, or where to take the measurements.

    Reputable person/agency is a relative term.

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