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  1. #1
    Join Date
    Sep 2013
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    Charlotte, NC
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    Question Coil size Vs dehumidification Vs efficiency sweet spot?

    I live in Charlotte NC and humidity is a real issue in the summer. I am about to get my 21 year old HVAC replaced in my townhouse and I am trying to decide if I should go with a smaller coil option and sacrifice efficiency to get better dehumidification. I wanted some input on how much is it really going to matter especially with a variable speed heat pump, am I overthinking this? I am hoping to get away without a whole house dehumidifier.

    I have talked to a few installers and my local Bryant guy sells Heil / Comfort Maker (ICP) variable speed heat pumps for a good value over the Bryant 288BNV variable speed unit. He said he would go with the 30 or 36 size coil but I wanted some more opinions before I decided if I should maybe go with the 24 size coil.

    Here is the setup with coil options:
    Heat pump: HVH824GKA
    Furnace: G9MVE0401712A
    Coil Options:
    END4X24L17A - 15 SEER
    END4X30L17A - 15.5 SEER
    END4X36L17A - 15.5 SEER
    END4X42L17A - 15.5 SEER
    http://www.icpeqp.com/AHRIratings/ra...spx?Brand=Heil

    Thanks for any help!

  2. #2
    Join Date
    Jun 2005
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    SW Wisconsin
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    This is only my personal opinion:
    That small SEER difference doesn't mean squat, you won't be operating at their SEER lavatory test conditions...! With your specific type of conditions there may not be any difference in the 'actual' SEER levels achieved...

    Not only that but the smaller coil should get the humidity down faster & achieve comfort levels sooner.

    I'd go with the END4X24L17A 15-SEER coil because the smaller capacity compressor's used in the new higher SEER units can normally pull the pressure/temperature lower using a smaller coil to achieve a colder coil.

    These smaller capacity compressors have more trouble pulling down Indoor high humidity combined with high indoor temperatures conditions.

    You might even run the system at 700-CFM for a colder coil & longer run-times.
    The heat pump will have a suction-line accumulator & the TXV's target superheat will probably be around a lower 8F.

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  4. #3
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    The sensible verses latent cooling ratio is all about the amount of air flowing through the cooling coil. Slowing the air flow decreases the sensible cooling and increases the latent cooling. This is the most important part of setting up the a/c after getting the equipment in place. Larger coils will remove more sensible/latent btus per watt. The any negative is that more liquid moisture is left on the coil at the end of the cooling cycle. With +1 hour off cycle most of the moisture left on the coil re-evaporates back into the home. On a vertical coil, expect about .75 lb. per ton on 15 SEER coil.
    VS blowers are easier to most optimum air flow to max the dehumidification rate from any a/c.
    On a hot day with 45 min. cooling cycles with a +30^F split should yield 50%RH. 75^F, 50%RH, 55^F dew point return (space condition) need a 45^F coil temp.
    Evenings and rainy days with +70^F outdoor dew points have much shorter cooling cycles and will have +60%RH indoors because of the moisture levels in the infiltration/ventilation and moisture from the occupants. During the low/no sensible cooling loads and the outdoor dew points, the a/c does not run enough. Reheat or small whole house dehumidifier are the only ways to maintain <50%RH during these conditions.
    Start with the a/c of your choice setup the best you know how. Then get a good %RH meter and watch what happens. Getting an adequate amount of fresh air and normal occupancy during low sensible cooling for several days will raise your indoor %RH to levels where mold and dust mites during extended wet weather.
    Dry years like this winter in FL are not a serious problem, during the extremes expect the worst, mold and dust mites.
    A heathy home should have a filtered fresh air change in 4-5 hours. Even manual J makes the point that any designed fresh air system, +50 cfm, will need supplemental dehumidification.
    Hold off on the dehumidification until the your comfort level suffers and the %RH meter shows the need more moisture removal.
    Keep us posted on how this works out.
    Most a/c manufactures are now offering small whole house dehumidifiers.
    ULtra-Aire is sight sponsor and the pioneer of the concept.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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  6. #4
    Join Date
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    Thread Starter
    Thanks for the responses! I am trying to understand how big of a difference coil size makes or if it is going to not really matter in the end. Is there any training or simple examples showing how much difference in coil temperatures there is between different coil sizes?

    udarrell, I want to make sure I understand your comment about pulling down a smaller coil, do you mean pulling down the coil temperature? The TXV will maintain the superheat temperature differential with any of the coil options but the total coil temp will be warmer with a larger coil thus making it harder to stay below the dew point of the air, correct?

    The Heil (ICP) communication thermostat "Observer" has a dehumidification setting which I assume drops the furnace variable speed motor to a lower setting. Will dropping the fan speed be enough compensation for a larger coil?

  7. #5
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    udarrell, I want to make sure I understand your comment about pulling down a smaller coil, do you mean pulling down the coil temperature? The TXV will maintain the superheat temperature differential with any of the coil options but the total coil temp will be warmer with a larger coil thus making it harder to stay below the dew point of the air, correct? Correct; can make a big difference with heavy latent & sensible loads, because these smaller capacity compressor's can more easily pull the coil temp down lower.
    The Heil (ICP) communication thermostat "Observer" has a dehumidification setting which I assume drops the furnace variable speed motor to a lower setting. Will dropping the fan speed be enough compensation for a larger coil? NO, The smaller 2-Ton coil will still get the coil colder for better dehumid performance...
    I'd go with the END4X24L17A - 15 SEER & probably the Heil (ICP) communication thermostat "Observer"; under your high humidity loads the 2-Ton 15-SEER might very well outperform the larger coils SEERS ratings; because over-sized coils work better in dryer climates, because the larger coils may spend more time trying to bring the coil-temp & humidity down where you live...
    Last edited by udarrell; 04-16-2018 at 10:49 PM.

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