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Thread: Efficient Duct Design? I have concerns

  1. #61
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    Yep. Anyhow, Latent heat has to go first. Then sensible.

  2. #62
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    Your error is that your condenser wont run long enough to keep the evaporator cold. It will cycle on and off. Commercial buildings get past this issue with reheat. Reheat isnt something that you find in homes.
    Anyhow we are mainly talking about HUMID climates like South east Florida.

  3. #63
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    Quote Originally Posted by Jimmy111 View Post
    Yep. Anyhow, Latent heat has to go first. Then sensible.
    The air gets down to the dew point via sensible cooling solo with no latent. Then it’s a combo of latent and sensible walking hand in hand.

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  5. #64
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    Yes, However we are talking about Humid climates. The Dew-point is 75 - 80F.
    In in really humid places, you can hop in your car, start it up and turn on the ac and suddenly you cant see anymore with all the fog coming out of your vents and you feel like someone just hit you with a cool wet rag.

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    Quote Originally Posted by Jimmy111 View Post
    Yes, However we are talking about Humid climates. The Dew-point is 75 - 80F.
    In in really humid places, you can hop in your car, start it up and turn on the ac and suddenly you cant see anymore with all the fog coming out of your vents and you feel like someone just hit you with a cool wet rag.
    That’s really all supply air from any ac unit. Cool clammy close to 100% rh air.

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  9. #66
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    Quote Originally Posted by Jimmy111 View Post
    Yes, However we are talking about Humid climates. The Dew-point is 75 - 80F.
    In in really humid places, you can hop in your car, start it up and turn on the ac and suddenly you cant see anymore with all the fog coming out of your vents and you feel like someone just hit you with a cool wet rag.
    Thats why I always keep the blower on medium high to high and the AC on and adjust the temperature until the air blowing on me is comfortable. I usually like it around 72f to 80f and ultra low humidity coming out of the vents.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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  11. #67
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    Quote Originally Posted by Jimmy111 View Post
    Did some work and lived in Davie. Ductboard is used a lot. Sheetmetal can be hard to find and has a tendency of collecting then dripping condensation. A large percentage of houses are block and for the most part stay reasonable cool (or warm) . The big design issue is Humidity. You need a really big evaporator and a just enough condenser and much lower airflow than you would use in most hot climates. You over size the condenser and the unit will just cycle on and off and never remove the humidity. A 5 ton fan coil and 2 ton condenser is quite common. The Fancoil may be able to produce 2000 cfm but it is run on the lowest speed possible.
    Someone please tell me if I misunderstood something but a 5-ton fan coil, even on its lowest speed setting and at 0.5 static will still be at well over 1000 CFM. How can this work successfully with a 2-ton condenser and run cold enough to remove (enough) humidity?
    Also, are they running with the 5-ton txv or.... what exactly? I've never seen a grossly mis-matched system, let alone on purpose!
    Thanks!

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  13. #68
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    BTW I say over 1000 CFM conservatively. Most psc and constant torque will run closer to 1200 CFM on low speed.

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    Quote Originally Posted by Jimmy111 View Post
    Did some work and lived in Davie. Ductboard is used a lot. Sheetmetal can be hard to find and has a tendency of collecting then dripping condensation. A large percentage of houses are block and for the most part stay reasonable cool (or warm) . The big design issue is Humidity. You need a really big evaporator and a just enough condenser and much lower airflow than you would use in most hot climates. You over size the condenser and the unit will just cycle on and off and never remove the humidity.

    A _ 5 ton fan coil and 2 ton _ condenser is quite common.

    The Fancoil may be able to produce 2000 cfm
    but it is run on the lowest speed possible.
    _ VERY ODD equipment selections _
    are ONLY provided by the many SUPER HACKERS
    that keep the competent HVAC industry contractors Real Busy.
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

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  16. #70
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    Select systems that are designated
    with a currently active AHRI rating
    .



    === === ===

    https://www.trane.com/content/dam/Tr...en_12-2019.pdf

    === === ===

    Guidelines

    The selection of DX evaporator coils must be based on the compressor-bearing product requirements.

    Improper coil selection can cause the system to shut down due to a
    safety control, or worse, it can cause the compressor to fail.

    Therefore, the guidelines of the condensing unit manufacturer should always be followed in component selection.
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  17. #71
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    Quote Originally Posted by R600a View Post

    Thats why I always keep the blower on medium high to high and the AC on
    and adjust the temperature until the air blowing on me is comfortable.

    I usually like it around 72f to 80f and ultra low humidity coming out of the vents.
    There is NO Such _ Phenomena _ alluded to ...
    _ Low Humidity Supply Air while in any usual COOLING Mode.

    ... DESERT may provide some decrease in humidity. LOL
    " ... Yes, However we are talking about Humid climates. ... "
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  18. #72
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    Quote Originally Posted by dan sw fl View Post
    There is NO Such _ Phenomena _ alluded to ...
    _ Low Humidity Supply Air while in any usual COOLING Mode.

    ... DESERT may provide some decrease in humidity. LOL
    " ... Yes, However we are talking about Humid climates. ... "
    I was referring to in the car using the AC with the heater for reheat.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  19. #73
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    The air discharging from a normally operating AC system is not low RH - rather it is at or close to 100% humidity. At the evaporator the air was chilled to the dew point. After the evap. coil the air flow contains pretty much all the moisture that it possibly Can contain. <g>

    PHM
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    Quote Originally Posted by R600a View Post
    Thats why I always keep the blower on medium high to high and the AC on and adjust the temperature until the air blowing on me is comfortable. I usually like it around 72f to 80f and ultra low humidity coming out of the vents.
    PHM
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    The conventional view serves to protect us from the painful job of Thinking

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  21. #74
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    Oh; I see you beat me to it. <g>

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    Quote Originally Posted by dan sw fl View Post
    There is NO Such _ Phenomena _ alluded to ...
    _ Low Humidity Supply Air while in any usual COOLING Mode.

    ... DESERT may provide some decrease in humidity. LOL
    " ... Yes, However we are talking about Humid climates. ... "
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  22. #75
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    2000+ posts. Why not apply for Pro Membership and see how the other half lives? <g>

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    Quote Originally Posted by Scoobie View Post
    That’s really all supply air from any ac unit. Cool clammy close to 100% rh air.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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  24. #76
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    Three years in and well past the 15 post minimum. You seem qualified for Pro Membership. And applying now would make it the perfect time. <g>

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    Quote Originally Posted by Jimmy111 View Post
    Yes, However we are talking about Humid climates. The Dew-point is 75 - 80F.
    In in really humid places, you can hop in your car, start it up and turn on the ac and suddenly you cant see anymore with all the fog coming out of your vents and you feel like someone just hit you with a cool wet rag.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

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  26. #77
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    Quote Originally Posted by Poodle Head Mikey View Post
    The air discharging from a normally operating AC system is not low RH - rather it is at or close to 100% humidity. At the evaporator the air was chilled to the dew point. After the evap. coil the air flow contains pretty much all the moisture that it possibly Can contain. <g>

    PHM
    -------
    In my truck the evaporator runs just above freezing and I adjust the reheat until the supply air is 72f to 80f and much lower humidity. It dries me out after sweating in an attic much faster than ice cold high humidity air does. I didn't make it very clear what I was talking about.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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  28. #78
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    Quote Originally Posted by Poodle Head Mikey View Post
    Three years in and well past the 15 post minimum. You seem qualified for Pro Membership. And applying now would make it the perfect time. <g>

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    Why would it make it the perfect time??

  29. #79
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    Quote Originally Posted by dan sw fl View Post
    There is NO Such _ Phenomena _ alluded to ...
    _ Low Humidity Supply Air while in any usual COOLING Mode.

    ... DESERT may provide some decrease in humidity. LOL
    " ... Yes, However we are talking about Humid climates. ... "
    Of course the cold discharge air has High relative humidity. For about 2 seconds until it comes in contact with the warm room air. And the relative humidity drops like a rock. You confuse Relative humidity with absolute humidity.

  30. #80
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    Quote Originally Posted by Jimmy111 View Post
    Why would it make it the perfect time??
    There's no better time than the present.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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