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  1. #1
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    Sep 2014
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    Is add on dehumidification necessary

    I am going to be building a new home in the Austin TX area and will probably go with a Trane or Lennox variable speed heat pump (XV 20 or 18 and Lennox comparable model) and was wondering if they can really provide dehumidification below 50%. I have heard adding an ERU will get the the humidity down however I have also heard that going with a stand alone dehumidifier that also ventilates is a better way. I should add that this will be a two story 2400sq ft with three zones. Conversation with contractors have been around one 4 ton unit.
    Your thoughts would helpful.

  2. #2
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    May 2000
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    Indianapolis, IN, USA
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    Whole house ventilating dehumidifier is the best solution, it will dehumidify when there is no need for cooling.

    There was a thread on here about poor dehumidification on low when you have a fraction of your refrigerant going through the big coil.

    How well you building the house? 4 tons for 2400 sq ft new construction says lots of windows or not built like a fortress. Spend a bit more on a tight house (foam insulation for example), smaller A/C and save for the life of the house.

  3. #3
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    Thread Starter
    We are finalizing the house plans now. It will be foam with good windows, not top of the line but definitely not the bottom. The first floor will have a covered porch on three sides. The house will be tight and will be well insulated with all of the hvac in a conditioned space. I have just been having some what if questions with the a couple of contractors. They have not seen the plans and have all said they can get very specific once they get a copy.

  4. #4
    Join Date
    May 2004
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    south louisiana
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    you could do it with 3 tons.
    the tradeoff for the higher cost of foam insulation
    is smaller hvac system.

    if you oversize you'll never get the dehumdification.
    in a tight house, you'll need to add fresh air.
    you should include fresh air in at the design stage.

    dehumidification has been sacrificed for higher SEER ratings.
    apparently it works in climates other than hot/humid.
    in hot/humid climates you are building in a problem.

    we all know if you are looking at 18-20 SEER that the
    hvac co will sell you two stage unit, so that it operates at
    low speed 98% of the time.
    that is the cya for the hvac co. most have not worked
    with foam encapsulated homes & have issue with sizing.

    I'm meeting with a client & his hvac co later this morning
    about a sizing issue in a foam sealed house. 2400 sq ft
    & hvac contractor is using 500 sq ft per ton as his sizing
    method, rather than doing an actual load calc.

    get a load calc, make sure they enter that the house is
    tight, not average or lose construction. it makes a huge
    difference.

    if you do stay with 4 tons, add a whole house dehumidifier.

    best of luck
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by Bskip View Post
    I am going to be building a new home in the Austin TX area and will probably go with a Trane or Lennox variable speed heat pump (XV 20 or 18 and Lennox comparable model) and was wondering if they can really provide dehumidification below 50%. I have heard adding an ERU will get the the humidity down however I have also heard that going with a stand alone dehumidifier that also ventilates is a better way. I should add that this will be a two story 2400sq ft with three zones. Conversation with contractors have been around one 4 ton unit.
    Your thoughts would helpful.
    if you do stay with 4 tons, add a whole house dehumidifier.

    best of luck
    energy_rater_La

    It is even more critical than this. If you going to have adequate fresh air ventilation in a climate that has outdoor dew points +60^ F and occupants that add moisture to your home, you need supplemental dehumidification to maintain <50%RH inside your home during low/no cooling loads.
    Most in green grass climates live on the edge of having mold problems, dust mites, and other biological growing in their home. Our posts are filled with suggestion about avoiding fresh air ventilation/infiltration suggestion about over cooling trying to control humidity.
    We also have many post about complicated a/c system that are difficult to setup and maintain and are unable to maintain humidity control during low/no cooling loads and high outdoor dew points.
    Many suggest a good air tight home (you got that) and simple single speed a/c and a whole house dehumidifier with the ventilation option. This gets you good air circulation throughout your home, the cooling set point to meet your need, the %RH setting you want, and fresh air when the home is occupied. In addition, you can turn off the a/c when the home is unoccupied and the %RH you want with minimal energy cost. A small whole house maintain 50% RH for pennies a day during unoccupied time.
    Looking forward to the discussion.
    Keep us posted.
    Regards TB
    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"

  6. #6
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    Sep 2014
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    Thread Starter
    Thanks for all of the comments, and teddie bear, one of the contractors did say going with the top of the line variable speed compressor may not be the most effective approach. This particular dealer uses Aprilaire add on stuff with Trane hvac equipment. I do not know much about Aprilaire equipment yet, as I have focused much of my dehumidification research on the Ultra-aire line.

  7. #7
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by Bskip View Post
    Thanks for all of the comments, and teddie bear, one of the contractors did say going with the top of the line variable speed compressor may not be the most effective approach. This particular dealer uses Aprilaire add on stuff with Trane hvac equipment. I do not know much about Aprilaire equipment yet, as I have focused much of my dehumidification research on the Ultra-aire line.
    Help out your a/c contractor with the info you come up with. Traditionally, Aprilaire is great company and been around for years with air filters and humidifiers.
    They recently started with dehumidifiers. Ultra-Aire pioneered whole house dehumidifiers with the fresh air ventilation option for +20 years. The Ultra-Aire are the most efficient units by upto 50% according to Energy Star. Controlling the fresh air is also unique with ventilation on a a occupancy schedule.
    Get the best dehumidifier you can afford.
    UA is available to any contractor from many wholesalers and from the factory direct.
    Hang in their and keep us posted.
    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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