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  1. #1
    Join Date
    Mar 2006
    Posts
    254

    US recommended AC temp to save energy

    I heard that it was 76 F, my bro said to set thermostat at 78F.

    It's not extremely hot where I live, but my condo is above two garages.
    Heat rises from there and my living quarters actually rise during 8 PM and
    10 PM. It must be from the days accumulation of heat from those garages.

    Anyways...what I noticed is...when I set my AC at 76F, it got to 78F
    fairly quickly and the unit (good unit, all OK).
    It cycled on fairly regularly, as it should. Short cycles.

    So...I set my thermostat at 75F. The initial cooling took awhile longer to get it to 75F, but it keeps the AC from rising to 77F longer (?) to start up the AC again. Apparently.

    I wonder if it's a case of "either or" to do my part on saving energy.
    Quick cycles or just slightly longer cycles setting the thermostat at 75F.

    It's almost like it's a toss up. I think by going "not green" and setting my
    stat to 75F is the same or even better than the reccomended
    setting of 76F or 78F. It seems that way, anyways, despite the US dept. of energy.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    Thats because its over sized, and cools to quick at the higher temp setting.

    Try lowering your CPH.
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  3. #3
    Join Date
    Mar 2006
    Posts
    254
    BeenThere

    CPH?

    Then we go into the same issue thing about putting bigger sized registers on the wall.

    I go to sell my unit. The first thing the potential buyer sees on the LR wall is this really big sized register on the wall near the ceiling.

    8"x16" grill register is on there now. How will it look going bigger when I go to sell my condo and that's the first thing they notice when they walk in? Odd is what it will look like.

    beenthere has been advising me for 3 months since my new install on a small condo with a 2 ton unit. He suspects my ducts are undersized. I agree. But damn...bigger registers.

    I suppose if I go bigger and paint them the same color as the wall...they won't look so freakishly large.

    beenthere...also...I'm getting 52F reading from registers when the ambient room temp is 76F as the AC starts to cool the rooms down to the desired setting.

    Before anyone says that is great...it's too good...it indicates undersized ducts?

    I don't regret my 2 ton instead of a 1.5 ton. I'm gonna have to rethink what beenthere has been saying about this install and my 8" duct work and 6" ducts to smaller rooms.

    Damn tho...the esthetics! Larger than 8x16 registers on a prominant living room wall as potential buyer walks in the door and catches their eye.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,879
    A 24° temp difference is a indication of low air flow.

    CPH = Cycles Per Hour.
    If you have a digital thermostat. If your CPH is set to 3, going to 2, can give you a longer on time, and longer off time. Can save money by not short cycling.
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  5. #5
    Join Date
    Mar 2006
    Posts
    254
    beenthere...Can you have total airflow high and abnormally cool out each duct and therefore not make the most of the system?

    I suppose so. So I guess it's get bigger ducts and larger vents or add another vent somewhere in the LV-Dining room/kitchen area.

    Right now there are only two vents that area.

    I am guessing the only alternative is to increase those 2 vents size that serve your living area,
    or add another vent somewhere there to make the most of your cooling tonnage.

    The bedroom has the large vent and bathroom and small second bedroom...all are well cooled.

    My living room/dining room/galley kitchen and hallway are all served by just my large vent and a smaller vent just above the galley kitchen counter top.

    That's why I have all the other rooms open and a back bedroom fan blowing forward.

    Here is a pic showing 2 vents that serve LR/DR/Galley Kitchen/Hallway.

    My condo vents were meant to heat..not cool. Thus the limitations of vents.

    I have a sloped ceiling living room, so..the only place to possibly add another duct is to the kick wall just opposite that smaller kitchen vent. Or larger uglier vents that now exist at these two locations.


  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    Its the velocity that is high coming out the registers, not the volume. Thats why the air is so cool.

    Increasing any of those 2, or both, will help to cut down on the air noise coming from them.


    Since you have a 24° delta, I would guess that your air flow is less then 700 CFM.
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  7. #7
    Join Date
    Mar 2006
    Posts
    254
    I can take a piece of tissue paper, and it will suck up to the large adequate intake grill, but I also get a feeling of air being forced out too. Does that make sense?

    Its almost as if this new AC and Carrier Performance furnace blower is sucking up more than the ducts can handle...thus the outflow at the return vent (at the same closet area).

    A local return duct grill should not get a feeling of pushing out air, even tho it sucks up a piece of tissue paper.

    Am I close?

  8. #8
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    Quote Originally Posted by caslon View Post


    a larger vent installed straight and painted to match the wall would look much better than what you have now.

  9. #9
    Join Date
    Sep 2008
    Location
    Atlanta area
    Posts
    47
    Quote Originally Posted by caslon View Post
    I don't regret my 2 ton instead of a 1.5 ton..
    Really? If it short-cycles it's too big, and NOT saving you on your electricity bill. You don't think that your problems with the airflow volume and perceived vent temps (to say nothing of having to have really large vents/ducts as a band-aid) would go away with a smaller unit?

  10. #10
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    Quote Originally Posted by deckeda View Post
    Really? If it short-cycles it's too big, and NOT saving you on your electricity bill. You don't think that your problems with the airflow volume and perceived vent temps (to say nothing of having to have really large vents/ducts as a band-aid) would go away with a smaller unit?
    A 25% reduction in CFM would make lots of duct systems work better!

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