Results 1 to 9 of 9
  1. #1
    Join Date
    Jun 2008
    Posts
    63

    Delta T too high?

    Can delta T be too high? If so, what does it indicate, and how high does it need to be before you call for help?
    I told a friend about checking delta T as suggested here and it should be 20F or so. His is 28.
    Thanks for the good info on this site. It helps the home owner and increases business for the hvac pros.

  2. #2
    Join Date
    Apr 2007
    Posts
    6,285
    low air flow....dirty filter....low latent load.


    20F is a myth.....it can be 10 or much higher.....all depends on the condition of the air entering the system and it's velocity.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,334
    Have him change his air filter and then check the delta T again.

    20^F is not carved in stone. Depending on how humid it is in the house, the delta T can vary between 16 - 22^F.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,033
    On the other hand. Since we don't know what system it is. It could be the right delta, it might be a HV system. And 28°F delta would be about text book perfect.
    Contractor locator map

    How-to-apply-for-Professional

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

  5. #5
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    I have seen 30 degree TD on mini-splits. I have seen 30 degree TD on VS indoor units with a TXV in the first minute of run time when set to enhanced dehumidification mode.
    Remember, Air Conditioning begins with AIR.

  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,985
    Quote Originally Posted by jax1 View Post
    Can delta T be too high? If so, what does it indicate, and how high does it need to be before you call for help?
    I told a friend about checking delta T as suggested here and it should be 20F or so. His is 28.
    Thanks for the good info on this site. It helps the home owner and increases business for the hvac pros.
    A 28 delta T is a bit out of bounds for these higher SEER systems.

    Back in the 6 EER & lower systems the larger compressor capacities to coil size resulted in low suction/temp conditions even with moderate load conditions.
    The actual RA & Return Entering air delta-T could go as high as 35-F on systems less than 7-EER, an 8 EER was around 32-F delta-T. Therefore, one can see why when sized right, they were terrific for latent load dehumidification.


    If there were almost no latent load & low airflow, it could be achievable with the unit you checked. With a 28-dT, I would up the wet coil CFM to 450-cfm per/ton of cooling.
    Last edited by udarrell; 06-23-2008 at 01:08 PM. Reason: Stating actual delta T data vs EER

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,033
    Quote Originally Posted by Kevin O'Neill View Post
    I have seen 30 degree TD on mini-splits. I have seen 30 degree TD on VS indoor units with a TXV in the first minute of run time when set to enhanced dehumidification mode.
    More fine examples of why a properly operating system could have a high delta.
    Contractor locator map

    How-to-apply-for-Professional

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

  8. #8
    Join Date
    Jun 2008
    Posts
    63

    calling for service

    I checked with the homeowner and the system is a variable speed. He doesn't know about hv, txv, or enhanced dehumidification, so he's calling the techs. Thanks for the input. At least now he knows what they should be looking for.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,033
    Never hurts to have it checked.
    Since it is a VS blower he may have checked it while it was in a lower speed for dehumidification.
    Contractor locator map

    How-to-apply-for-Professional

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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event