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  1. #14
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Shophound View Post
    Untrue. I do it every day in summer with single stage cooling. Lately indoor humidity levels have been in the low 40% range.

    I also live in what's known as a "mixed-humid" climate. It's been very dry this year, which may partly explain my performance, but we had rain Saturday, higher humidity yesterday, and I still stayed in the low forties, no sweat (literally!). In fact I even turned the ceiling fan off at one point in the afternoon and raised the stat one degree.

    I'm not sayign its' not possible. My downstairs is 38-48% withotu even slowignhte blower when it's above 80F outside. I'm jsut saying that in some homes it's not possible. In my last home ,the unit was oversized and even running the 2 stage scroll in high stage with low airflwo, and using 350CFM/ton on top of that helped a LOT but still didn't keep it all that dry. Infiltration was also a major factor in such a small home.


    The smaller the home, the greater the surface area to volume ratio is. So infiltration is comparatively greater. Same with a single story home, vs. 2 story.

  2. #15
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    Quote Originally Posted by motoguy128 View Post
    I'm not sayign its' not possible. My downstairs is 38-48% withotu even slowignhte blower when it's above 80F outside.-
    If I'm not mistaken, didn't you state in another thread you started that your indoor humidity levels on the first floor are running in the low to mid fifties? And that you had encapsulated your attic, but not completely (complete with not removing the cellulose insulation on the attic floor) or have I mistaked you for someone else (lots of threads here...easy to get confused)?

    I'm jsut saying that in some homes it's not possible.
    You said many homes. Let me quote it:

    Quote Originally Posted by motoguy128
    Keep in mind that achieving a 45% RH in many homes in most climates is not realistic.
    The "many homes" might be closer to correct, but "most climates" would not be. Keep in mind that a large chunk of our great nation is arid to semi-arid. Even average a/c systems can maintain 45% or lower at normal room temps in these climates. I've lived in and repaired many a/c systems in arid climates.

    Quote Originally Posted by motoguy128
    The smaller the home, the greater the surface area to volume ratio is. So infiltration is comparatively greater. Same with a single story home, vs. 2 story.
    The infiltration aspect being larger with smaller homes is not always true, nor is it always true regarding single story structures. There are many drivers behind infiltration. Some mechanical, some natural, and the particular building's design must also be factored. Until you consider all of them for the particular structure that has your attention, general "rule of thumb" observations I tend to regard with reservation.

    I am certain there are single story structures with larger surface area to volume ratios than two story structures that outperform the two story counterpart in terms of pressure and thermal boundaries. As a basic component, stack effect is generally not as enhanced in a single story stucture, particularly one slab-on-grade, vs. a two story structure also slab-on-grade. Again, it depends on the structure's design and quality of construction.

    Whether a house is 1,500 square feet or 3,500 square feet, there are desirable and undesirable levels of air changes per hour that are pretty consistent. The larger home may require more ACH in general because it can hold more people.
    • 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.

  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Cool to dehumidify won't happen until the humidity is more then 5% above set point.
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