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  1. #40
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,763
    Is this a comfort issue, or a "why is my ac running all the time" issue?

    One may be a performance problems, the other a problem of improper/no homeowner education by the HVAC company (when temperatures go beyond design, do not expect equipment to move temperatures quickly. Sizing is a balancing act that dictates really good design means equipment needs long run cycles. To accomplish this, rapid recovery at beyond design temperature can not be achieved or you get short cycles and clammy, moldy house at milder temperatures.)

    Are you willing to try an experiment? Drop your program set point by 1f at each time period and see if your comfort improves.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  2. #41
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Quote Originally Posted by jlbartley View Post
    There is a cold air return on the wall that the thermostat is mounted on. It is right next to it. Is this good or bad.
    Have your HVAC guy check to see if where the thermostat wiring cable pokes through the wall behind the thermostat, if that hole is sealed or not. If it isn't, let him seal it.
    • 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. #42
    Join Date
    Mar 2008
    Location
    Baltimore MD and Ridgebury PA
    Posts
    542
    Quote Originally Posted by tedkidd View Post
    Is this a comfort issue, or a "why is my ac running all the time" issue?

    One may be a performance problems, the other a problem of improper/no homeowner education by the HVAC company (when temperatures go beyond design, do not expect equipment to move temperatures quickly. Sizing is a balancing act that dictates really good design means equipment needs long run cycles. To accomplish this, rapid recovery at beyond design temperature can not be achieved or you get short cycles and clammy, moldy house at milder temperatures.)

    Are you willing to try an experiment? Drop your program set point by 1f at each time period and see if your comfort improves.
    Quote Originally Posted by jlbartley View Post
    We have a newly built house that the AC is taking longer than I would expect to drop the temp 2 degrees. I'm wondering how long we should expect it to run under the conditions I've specified below. Any help would be really appreciated.

    Scenario:
    The house temp was maintained at 78 deg from 4:00pm to 9:00pm. At approx 9:00 pm the thermostat kicked down to 76 deg. The outside temp was 75 deg with the sun fully set but it was more humid than inside (not horribly) but enough that to sleep comfortably we wanted to keep the air on.
    The AC ran for 120 min straight never shutting off, to drop the temp to 76 deg.

    We also run a dehumidifier in the basement that keeps the humidity down there at approx 55%.
    Tedkidd, I understand your concern with temperatures beyond design conditions etc but if I am reading the OP correctly then the OD temp was only 75, the sun had set, and the ID temp was already 78 yet it took 2 hours to bring the temp down to 76. I doubt such conditions could be considered to be outside the design conditions. That being said, I agree that generally speaking homeowners are not well educated about the abilities of their systems and therefore often expect the impossible. It's possible the system is running at peak performance... I just don't find it likely. If it takes 2 hours to cool 2 degrees when its 75 outside then how can it expect to maintain ID temps when its 80 or 90 outside?

    Homeowner, am I correct with my above statement as to the conditions at the time the unit began running? Barring any unusual features within the home that could be causing a heat gain (latent or sensible) it does seem odd. However, I am not looking at your house and can only suggest that if you are not satisfied with the answer from your HVAC contractor that you have another contractor come and check the system out as well.

  4. #43
    Platchford - You are correct with what you've stated. The house was maintained at 78 deg, the outside temp was 75 deg and it took 2 hours to drop the temp to 76 indoors.

    I have 2 main concerns with why I want to address this:
    1 - We have a 1 year warranty on the house. If something is wrong with the AC, we have a limited amount of time to get it fixed without having to pay for it. If we don't deal with it now and something's wrong we're going to be out of money at a later date.

    2 - What is this costing us? I'm dreading getting our next elec bill. Seems like it's going to be outrageous although I'll let you know when I get it.

  5. #44
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,763
    How much insulation in attic? The attic temperatures are likely to be hottest at the times he's mentioned, if there isn't much insulation then that might be where the load is.

    Has a blower door test been performed? Might be time for an energy audit.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #45
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    7,183
    Quote Originally Posted by jlbartley View Post
    We have a newly built house that the AC is taking longer than I would expect to drop the temp 2 degrees. I'm wondering how long we should expect it to run under the conditions I've specified below. Any help would be really appreciated.

    House specs:
    1950 sq ft new construction house, single story + basement
    >>>>>>>>>R60 Ceiling insulation<<<<<<<<<<<
    >>>>>>>>>>>R19 - 2x6 walls<<<<<<<<<
    house faces north with AC unit at the front of the house
    there are large windows to the south of the house but no windows on the east and very few on the west
    the AC unit is a 3 ton 13 seer Carrier 24ABB
    From the OP
    “If You Can Dodge A Wrench You Can Dodge A Ball”

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