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Thread: Delta T help

  1. #1
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    Delta T help

    I have a Honeywell Prestige IAQ t-stat that is alerting me to a high delta-t. It is set at 35 deg after 10 mins, and the logs are showing 36 (69 at return, 105 at discharge). I set the values myself based on the Honeywell manual. The sensitivity is set at the default of 3.
    I have a hydro air system with a TAM-7 air handler, and the filter is clean. Does this sound like a reasonable number, or something I should be concerned about?
    Thanks!

  2. #2
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    What testing equipment was used to set this system up?

  3. #3
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    The system was in the house when I bought it, so I have no idea. I just set the alerts up based on the IAQ guide.

  4. #4
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    With a hydro-air system I see no reason for worrying about what the temperature rise (maximum) is over the air handler/coil. If this was a fuel burning furnace then yes.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  5. #5
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    Turn your boiler or water heater down slightly, or raise the air speed.
    Make sure your air filters are clean.
    "The only true wisdom is in knowing you know nothing" Socrates

  6. #6
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    If the boiler is using outdoor reset. Then the temp delta will increase as the outside temp drops.
    Contractor locator map

    How-to-apply-for-Professional

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

  7. #7
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    Quote Originally Posted by ejordan View Post

    I have a Honeywell Prestige IAQ t-stat that is alerting me to a high delta-t.
    It is set at 35 deg after 10 mins, and the logs are showing 36 (69 at return, 105 at discharge).

    I set the values myself based on the Honeywell manual.
    The sensitivity is set at the default of 3.

    I have a hydro air system with a TAM-7 air handler, and the filter is clean.

    Does this sound like a reasonable number, or something I should be concerned about?
    Thanks!
    35'F seems to be a low dT IMO.
    However, we don't know anything SPECIFIC about
    Your BUILDING THERMAL ENVELOPE nor YOUR EQUIPMENT.

    A reasonable number for dT should be determined based on
    the maximum heating required
    for the Month(s)/ Season
    and an anticipated air flow rate range
    given the TAM-7 characteristics and Your particular Blower Set-up.


    REF.:

    https://forwardthinking.honeywellhom...ew/69-2678.pdf
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
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    Quote Originally Posted by mgenius33 View Post
    Turn your boiler or water heater down slightly, or raise the air speed.
    Make sure your air filters are clean.
    Filters are clean. Thanks for the advice, I'm handy but not comfortable with adjusting the boiler or air speed

  9. #9
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    Quote Originally Posted by beenthere View Post
    If the boiler is using outdoor reset. Then the temp delta will increase as the outside temp drops.

    No outdoor reset afaik

  10. #10
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    Thanks Dan, that helps. The ref you linked is what I used to set the dT. No clue what the envelope is or how to determine max heating required.

  11. #11
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    Quote Originally Posted by mgenius33 View Post
    Turn your boiler or water heater down slightly, or raise the air speed.
    Make sure your air filters are clean.
    Adjust the Honeywell Prestige IAQ t-stat to a noticably Higher dT limit.
    Also, see Posts # 4 & # 7.

    T-stat is providing an Alert, Not actual control of dT.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
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    Quote Originally Posted by ejordan View Post
    Thanks Dan, that helps. The ref you linked is what I used to set the dT.

    No clue what the envelope is or how to determine max heating required.
    DT is dependent on the equipment performance, not the IAQ manual.

    Envelope = Interior-to-Exterior boundary

    Maximum Heating requirement is determined in an ACCA Manual J calculation.

    https://up.codes/s/building-thermal-envelope

    https://www.wbdg.org/guides-specific...e-introduction
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
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    Thanks Dan - I'll up the dT alert setting (understand it is an alert, not actually controlling anything). I think this is what I was really looking for, some confirmation that I don't have a problem with my equipment and need to adjust dT alert threshold. I'll try to read up on Envelopes and understand a little better, but I'm just a tinkerer with all this, and understand I need a pro to do it right. Thanks again to all for your replies!

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