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  1. #1

    Setting for Humidity & De-Humidity

    We have two Carrier systems with programmable thermostat with humidity control, but I do not know what to set the Humidity & De-Humidity to. We live in Orlando Florida and keep the inside temperature to 76F.

  2. #2
    Join Date
    Jan 2009
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    Keokuk, IA
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    Humidity only work with a humidifier. I'm not sure if you have one installed, or if you need on in your location (FL).

    Recommended humidity levels by most health organizations are 40-60%. Some pros on here recommend 50% or less. But it will depend on how well sealed your home is and if you unit is installed and set-up correctly.

    Lower humidity will allow you to feel more comfortable with warmer indoor tempratures. Maybe try 50% or 45% and see how it feels and if the system maintains that humidity level.

  3. #3
    Join Date
    Aug 2003
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    Fort Worth, TX
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    I would love it if the American public had a better understanding of dew point temperature and how it relates to human comfort. We've heard relative humidity used on weather reports since forever, with perhaps a passing mention of dew point, mainly for any viewer/reader with perhaps a little more than a passing interest in meteorology.

    For average desirable (target) indoor air temperature ranges (72-78 degrees F), an indoor dew point temperature of 55 degrees or less is optimal for human comfort, and for keeping the building interior and contents sufficiently dry.

    As an aside for Motoguy, I just got done checking the outdoor dew point temperature trend log at my employer's location. For the past two days the outdoor dew point temperature actually declined as the outdoor temperature rose, and it increased during the night. This is a common summertime pattern for our area, but may not be everywhere else, in particular for our condo dwelling friend Smoss in Vermont. Should I find myself so inclined I might check his local weather dew point data just out of curiousity (and definitely WOULD do so prior to making a post about his local weather conditions again ).
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    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


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  4. #4
    Join Date
    Jan 2009
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    Quote Originally Posted by shophound View Post

    As an aside for Motoguy, I just got done checking the outdoor dew point temperature trend log at my employer's location. For the past two days the outdoor dew point temperature actually declined as the outdoor temperature rose, and it increased during the night. This is a common summertime pattern for our area, but may not be everywhere else, in particular for our condo dwelling friend Smoss in Vermont. Should I find myself so inclined I might check his local weather dew point data just out of curiousity (and definitely WOULD do so prior to making a post about his local weather conditions again ).
    That is interesting. I wonder if it follows the same pattern in the winter as well. It's pretty consistent in the midwest. Dewpoint is often regulated by overnight temperatures... or more specifically lack of solar radiant heat as well as ground temperatures. So the spring is often dryer than the opposite time of the year in the Fall since there's a lead/lag scenrios with ground temps and that amount of sunshine.... at least in more northern states with 4 real seasons.

    My only guess in your case is that in the afternoon you have a high pressure weather system blowing hot dry air off the northwest (desert). In the evening, the weather calms, and natural processes radd moisture to the air. I think in hotter climates, many plants stop respirating in the heat to conserve water, then evaporate more moisture in the evening.

    Local climate will definitely have an impact. I'm pretty sure Houston weather on the coast is far diffrent form Dallas/Fort Worth area.... and even that will vary as you moe towards Arizona and New Mexico.

  5. #5
    Join Date
    Aug 2006
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    Dallas (Plano), TX
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    Here's an example of what Shophound is talking about, specific for his DFW location/climate.

    The red line is outside temperature - it got past 102 (F) on July 2nd (red line). Yet outside RH dropped almost as fast down to almost 25% (blue line). The combination of the two kept Dew Point (green line) relatively flat from about 10 AM - 7 PM in spite of the rapid rise of intense heat.



    A broader picture of DFW Dew Point, versus outside temperature and humidity is shown below.



    Best regards,

    Bill

  6. #6
    Join Date
    Jan 2009
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    Bill, it sounds like you're trying to correlate dewpoint to a change in RH. RH is a derived unit that is dependant on the temperature. Dewpoint correlates to the actual amount of moisture in the air (except air pressure... which we assume is constant).


    That chart supports what I was saying. There's a upward trend of dewpoint in the daytime and drop overnight. But compared to the midwest, it has fairly low RH, in part because the sun is so direct, that the air temps stay warm enough overnight that this time of year you never have condensation.

    The drop in RH is expected, since the outside temprature is rising.

    Since the water is not condensing overngiht, I can only guess that moisture is driven out of the ground and plants by the high ambient temps in hte afternoon, and reabsorbed over night.

    So maybe I mistyped or Shophound misread my post. But it appears the charts support what I was trying to say, in that overnight temperature and conditions often have a limiting effect on dewpoint.

  7. #7
    Join Date
    Aug 2006
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    Dallas (Plano), TX
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    Quote Originally Posted by shophound View Post
    ... I just got done checking the outdoor dew point temperature trend log at my employer's location. For the past two days the outdoor dew point temperature actually declined as the outdoor temperature rose, and it increased during the night. This is a common summertime pattern for our area, but may not be everywhere else ...
    I was just trying to provide some factual support for what Shophound said, noting that my location is (relatively) the same as his (DFW), and that I have an HVAC monitoring system ( http://welserver.com/WEL0043/ ) that easily provides facts to interesting subjects.

    Best regards,

    Bill

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