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  1. #1
    Join Date
    Sep 2009
    Location
    South Florida
    Posts
    53

    For South Florida House, What should I set the Humidity Control at?

    My new system has a communicating tstat with humidity control. I have it at the lowerst setting which I believe is 42 or 43%. Would it be better to set it higher? For those that live in hot humid climates, what level of humidity do you find most comfortable? Based on your recommendations, I will try that setting and adjust the temp to my comfort level. Thanks.

  2. #2
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    here in Miami,

    for a couple of reasons i like setting the humidity level at 55% on the communicating stats

    in general i notice that this lets the ecm's "on" delay profile remove enough humidity to keep things well below 55% without having to lower the blower speed by 20%

    which in turn "keeps" total system capacity, as opposed to lowering system capacity as does the 20% blower speed reduction

    so, as long as the blower "on" delays are correct, 55% is what i leave the humidity setpoint at



    .

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,435
    When using whole house dehumidifiers, we suggest 50%RH as the typical setting with a 75^F T-stat. Some prefer raising the t-stat to 78^F and lowering the dehumidistat to 45%RH. When using ceiling fans, 78^F, 50%RH is very comfortable.
    Like too here about maintaining 50%RH during wet, cool weather much less 45%RH. My experience shows you need a whole house dehumidifier to provide real humidity control during wet cool weather. Although FL as not all that much wet weather in the last year.
    Keep us posted on your results. Are you providing fresh air ventilation?
    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"

  4. #4
    Join Date
    Sep 2009
    Location
    South Florida
    Posts
    53
    We rarely use fresh air ventilation in order to keep humidity and allergen load down.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,435
    Quote Originally Posted by chillimd View Post
    We rarely use fresh air ventilation in order to keep humidity and allergen load down.
    No fresh air = full load of accumulating indoor pollutants. Fresh air pruges indoor pollutants and renews oxygen. You have a alot of potiential for indoor quality improvement with an air change of fresh air every 5-6 hours.
    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
    Join Date
    Sep 2009
    Location
    South Florida
    Posts
    53
    Quote Originally Posted by teddy bear View Post
    No fresh air = full load of accumulating indoor pollutants. Fresh air pruges indoor pollutants and renews oxygen. You have a alot of potiential for indoor quality improvement with an air change of fresh air every 5-6 hours.
    Regards TB
    How do you I suggest I accomplish this with the high heat and humidity outside, and with the inability to do it at night because I don't care to leave windows on the ground floor (one story home) open while we sleep.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by chillimd View Post
    How do you I suggest I accomplish this with the high heat and humidity outside, and with the inability to do it at night because I don't care to leave windows on the ground floor (one story home) open while we sleep.
    Buy a dedicated`dehumidifier that brings in fresh air.

    Not saying you need one but that's the answer.


    Maybe a Thermastore or Aprilaire.

  8. #8
    Join Date
    May 2009
    Location
    New Caney, Texas
    Posts
    360
    chillimd
    How do you I suggest I accomplish this with the high heat and humidity outside, and with the inability to do it at night because I don't care to leave windows on the ground floor (one story home) open while we sleep.
    A ventilating dehumidifier, Honeywell and Aprilaire as well as a few others. Keeps your humidity level at a comfortable level. Usually recommended at between 40 to 60%. Set up to bring fresh air into the home, Ventilating, it will cool and clean, and dehumidify air before putting it in your home.
    Good Things Come To Those Who Wait, But Only the Things Left Over By Those Who Hustle.

    Abraham Lincoln

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,435
    quickcat46 & Dash got it pretty close. A small difference of opinion on the brands of ventilating dehumidifiers though. Therma-Stor started this idea of providing filtered fresh air 15 years ago. Their brands are Ultra-Aire/Santa Fe. The design is much more mature, more refined and effecient than most others. UA is easily set up to bring in a correct amount of fresh, filtered air and blend the air with air in the home when occupants are in the home. The system also maintains the desire %RH the occupants want. Check it out.
    Regards TB

    http://www.ultra-aire.com/images/pdfs/UA-65_sheet.pdf
    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"

  10. #10
    Join Date
    May 2009
    Location
    New Caney, Texas
    Posts
    360
    teddy bear
    quickcat46 & Dash got it pretty close. A small difference of opinion on the brands of ventilating dehumidifiers though. Therma-Stor started this idea of providing filtered fresh air 15 years ago. Their brands are Ultra-Aire/Santa Fe. The design is much more mature, more refined and effecient than most others. UA is easily set up to bring in a correct amount of fresh, filtered air and blend the air with air in the home when occupants are in the home. The system also maintains the desire %RH the occupants want.
    Sorry my bad T.B., I got April Aire and Ultra-Aire mixed up. Ultra-Aire and Honeywell and some others I am sure make the Ventilating Dehumidifier. I will say that I really liked the Ultra-Aire design and all just had a hard time finding a distributor in my area.
    Good Things Come To Those Who Wait, But Only the Things Left Over By Those Who Hustle.

    Abraham Lincoln

  11. #11
    Join Date
    Sep 2009
    Location
    South Florida
    Posts
    53
    It appears these systems pull outside air and dehumidify it before adding it into my system and then into the home. It then pushes allergens into the home which my return grille filter must then remove since a whole house purifier won't fit into my short return duct. Any way to filter the allergens before entering the house?

  12. #12
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    The wisdom I read is you ideally want outside air to be filtered and conditioned before it gets to anyone's lungs. Filtering should be obvious, and a normal installation will have it.

    Conditioning... Like you I am a homeowner in a hot-humid climate. This is not one of those Wisconsin "green grass" climates but cooling dominated and near tropical. There are other ways to get fresh air besides an open window or a ventilating dehumidifier... It seems to me a simple fresh air duct to the return plenum should be something worth a discussion. Its airflow will be proportional to AC runtime unless there is a common timer mechanism to close off intake once a certain minutes/hour quota is met. Most AC pros know how to easily do this with an Aprilaire 8125 kit or equivalent.

    The thing that most troubles me about a ventilating dehumidifier as I understand it, is I see no effort to condition the outside air before it goes into the house. Correct me if I am wrong, but is not the fresh air input simply on a timer, and then the dehu runs once enough humidity has been brought in to trigger the dehumidistat? As opposed to say, having the automatic controls run the dehu simultaneous with air intake, whenever practical. It would appear to be more efficient to remove humidity from truly humid (outside / dewpoint 75-80F) air, than to remove it from house air once the indoor humidity reached 51% RH (dewpoint 55-59F) or whatever you have set.

    It might be a mistake to assume the ventilating dehumidifier will dehumidify simultaneous with bringing in that outside air. With a fresh air duct to the central HVAC however, and assuming fan set to "auto", the conditioning will occur at the point of entry. Am I right on this matter, or do you think I am all wet?

    Before you think I am anti-dehumidifier, I have several and use them heavily. They are great for removing humidity once in the house. It is the controls situation that I wish to question and especially the controls for ventilating. There are some notable professionals who report that with a tight house, they can achieve really low indoor humidity without using a dehumidifier. Ask someone like Carnak, who lives in a climate even more hot and humid than yours.

    Best of luck -- Pstu

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Pstu,

    After reading this:

    http://www.ultra-aire.com/images/pdfs/UA65-manual.pdf

    I can see what you're talking about re: the unit's controls.

    Why not control it thusly: an outdoor humidistat measuring dew point. If dew point < 55F, ventilation without dehumidification is possible. Above 55, the dehumidifier will run when ventilating air is called for, regardless of indoor humidity. When the damper is closed, the indoor humidistat takes over, along with a CO2 sensor to determine when fresh air ventilation might be needed again.

    The unit's "brain" (electronic control board) can be programmed to run the blower every "x" amount of time increment if the unit is off and not dehumidifying. During this short run time, the CO2 sensor measures the return air from the house and determines if the levels are at trigger points or not. If yes, fresh air damper opens, and if outdoor dew points are high, the compressor turns on. If outdoor dew points are low enough, the compressor does not operate but the blower does.

    Once the CO2 sensor is satisfied, the unit will either shut off if both CO2 and indoor humidistat are happy, or continue running if indoor humidity levels are still too high.

    Any ventilating dehumidifer manufacturer could market this as "green" or "smart" technology, with a parallel emphasis on unsurpassed indoor comfort and air quality.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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