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  1. #27
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    Aug 2003
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    Fort Worth, TX
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    Any time we connect gauges and measure temperatures and pressures, it's at best a snapshot of how that system is operating in the short window it is observed.

    Data logging is another ballgame; doing such on my own home system opened doors of understanding for me which since I've parlayed into diagnostic tools.

    Note the attached graphs. This data was harvested over a four hour run time where the system was pulling the house temperature down from 78 to 75 while the outdoor air temperature continued to increase. During this measured interval, the data reflects that as the specific humidity in the home fell, the sensible heat ratio went up, while total capacity fell due to decreasing heat load, in spite of outdoor temp climbing.

    This data run shattered some system behavior assumptions for me. Any time assumptions are obliterated by real time data is a good time for me.
    Attached Images Attached Images    
    Building Physics Rule #1: Hot flows to cold.


    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure


    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

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  3. #28
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    Jun 2018
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    Thread Starter
    Quote Originally Posted by Shophound View Post
    IAt minimum, if an attic must be ventilated it should run no warmer than outdoor ambient temperatures.
    Is this achievable?

  4. #29
    Join Date
    Mar 2009
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    Mount Holly, NC
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    Quote Originally Posted by Kelevra View Post
    The downstairs unit (3.5 ton) has 13 registers with a filter size of 25x32x1. The upstairs unit (2.5 ton) has 6 registers with a filter size of 20x25x1.

    Here are a few pics of the repair work:





    And here are just some general pics of my ductwork in the attic:



    At best you have enough ducts for 2.5ton on the 3.5 Ton unit, and just over 1 ton of airflow on the 2.5 ton system...

    Unless the ducts are much larger than the norm.
    The TRUE highest cost system is the system not installed properly...

    Find a HVAC-Talk Contractor by clicking here

    Do you go to a boat repairman with a sinking boat, and tell him to put in a bigger motor when he tells you to fix the holes?

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  5. #30
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    Jun 2018
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    Thread Starter
    Quote Originally Posted by vstech View Post
    At best you have enough ducts for 2.5ton on the 3.5 Ton unit, and just over 1 ton of airflow on the 2.5 ton system...

    Unless the ducts are much larger than the norm.
    Are you basing this on the register count/air filter size or the pics of the ductwork? The pics are only a sample of the entirety of the ductwork.

  6. #31
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    Quote Originally Posted by joemach View Post
    Thanks udarrell,

    That even explains it better. I always take a condenser Delta T, but never really understood what it meant. Especially with the different SEER ratings and how that changes the condenser Delta T.

    So much valuable info on this site. And so many knowledgeable folks who are so willing to share.

    Just when I thought I was beginning to understand this trade, I find out there is so much more to learn.

    Thanks to all you with so much knowledge that make me feel so dumb.
    To quote someone that used to post stuff that made me think...

    You are not done learning until you are dead...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

  7. #32
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    Sep 2005
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    Atlanta GA area
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    Quote Originally Posted by Kelevra View Post
    Is this achievable?
    The only times I have seen this... is a foamed attic or a couple inches of hard foam boards on top of the deck (under toe roofing material).

    Personally... it just does not make sense to not do something about that oven just 1 ft of insulation above the area we are trying to keep comfortable.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

  8. #33
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    I used to live in Houston... left in 1987...

    I can say from experience: the latent load down there is HORRIBLE!!!
    Add to that... houses are not built well in terms of resisting air movement from outside to inside.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

  9. #34
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    Quote Originally Posted by Kelevra View Post
    Is this achievable?
    I achieved it with a reflective metal roof on my home. Data logged the attic for three summers. Only on the hottest afternoons did the attic air temperature go above outdoor ambient, and that by only a few degrees, instead of the forty plus it once would with the old asphalt roof.
    Building Physics Rule #1: Hot flows to cold.


    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure


    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

  10. Likes ga-hvac-tech liked this post
  11. #35
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Quote Originally Posted by Kelevra View Post
    Are you basing this on the register count/air filter size or the pics of the ductwork? The pics are only a sample of the entirety of the ductwork.
    *
    Attached Images Attached Images  

  12. #36
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    .Name:  tenor.jpg
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    Sent from my SM-N910W8 using Tapatalk

  13. #37
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    Quote Originally Posted by BALloyd View Post
    .Name:  tenor.jpg
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    https://encrypted-tbn0.gstatic.com/i...CbX3-DThCJagyg

  14. #38
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    .Name:  935e0630-1ed0-4f87-a098-c69bf34a60af_text.jpg
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