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Well, it's about 90 degrees today and here again so DH and I will argue over leaving the AC on all day. To save energy, is it advisable to leave the AC on all day with nobody at home at some temperature, and then adjust it in the evening for bedtime or leave it off and then just turn it on late afternoon? What is the optimal setting for the thermostat for energy savings? We have 2 zones (1 upstairs 1 downstairs) and ceiling fans. We have 10' ceilings downstairs and 9' upstairs and ceiling fans in all but 2 bedrooms, and normally set it for 72 degrees when sleeping.
I have always felt it better in humid climes to leave it on all day, at a higher than comfortable level while out, and reset it to a more comfortable setting when home.
This reduces the amount of work the unit has to do to remove humidity, while still reducing the energy required to maintain the climate controls.
when it is hot and humid, I leave it on all day. If we are gone, I adjust the temp up to 78 or so. lower it for sleeping to around 70 to 72. our problem is we have only one unit and a two story house. the upstairs gets pretty warm, and I am not going to lay in bed and sweat all night! I think that if you leave it on, it will not run as much because things stay more stable. if you turn it off and have windows open, then close up and turn it on, it seems to have to work harder.
If you have dual zones, is it advisable to use both of them, for instance if we do not go upstairs? We currently have our downstairs zone on 78, and the upstairs is off.
Turning the whole thing OFF OFF is a bad idea. The idea is with by allowing the "setback" the a/c runs less when there is no one home and THAT has to save something. Three percent savings? - HVAC-Talk: Heating, Air & Refrigeration Discussion
The savings are based on how expensive it is run your particular unit in your house, generic models that predict this cannot take into account what effect various setback times and percentages will have on your home remaining too warm by the time you want to relax after work. Can't find link to the home, jsut office: http://www.nrel.gov/docs/fy05osti/34931.pdf
Some of the national labs have done studies of how to make home thermostats that can "learn" the characteristics of what various outside temperatures do to the length of time it takes your house to cool off,
when it is hot and humid, I leave it on all day. If we are gone, I adjust the temp up to 78 or so. lower it for sleeping to around 70 to 72. our problem is we have only one unit and a two story house. the upstairs gets pretty warm, and I am not going to lay in bed and sweat all night! I think that if you leave it on, it will not run as much because things stay more stable. if you turn it off and have windows open, then close up and turn it on, it seems to have to work harder.
I have a two story home. I installed dampers in the duct work. I send most of the A/C upstairs and let it fall down.In winter I send most of the heat downstairs and let it rise.
Hey, Bibit! Since we are neighbors, I am going to weigh in. We have 2 units, as w/ your set up. We had problems regulating the temp, until one of the techs explained to us to forget the time set backs on the thermostat - to keep it at the same temp all the time. He said - keep the upstairs unit 2 degrees cooler than the downstairs unit. Once we set the downstairs unit at 73 d. and the upstairs at 71 d (wh/ is where we keep it year round) we have had lower bills and very even temps, even on the hottest days.
Good luck - it has been a bit toasty the last two days . . .
Thanks all! It's a blessing that DH has so much faith on City Data and believes much of what is being posted here so we will leave it on with a temperature differential of 2 degrees b/w upstairs and downstairs. We do have dampers on and they were open since the winter. They actually had to be adjusted since they were closed, so in the winter, our bonus room was like Antartica, and our bathrooms like Florida! We had that down pat including moving the thermostat to the master bedroom as the temperature differential was tricking the upstairs thermostat because of downstairs. Just goes to show that builders just slap on stuff in there without checking. Supposedly, they just follow the architectural plans.
However, despite that, one of the south west facing rooms does not appear to be cooling as well. Very little air is coming out of the vent despite it being open full. DH said there were only 2 dampers and that controlled all the duct work so I still can't figure out why that room is warmer than the rest. We keep all the windows closed and blinds down and shut, plus tinted all the windows on that side of the house, including the leaded glass front door. Hopefully, leaving it on all day solves the problem. Should we also leave it on, perhaps at a higher setting, even if we are gone for an extended period of time, like a week? Does running the ceiling fans help cool the house while the AC is running?
The best thing to do when you leave for the day is simply turn is up 2 deg. from your normal setting and no more. This will allow the system to catch up when you come home again. Otherwise it will labor for hours which will defeat the energy savings you intended. As for the air flow and damper situation, you need to call some one to look at it. There might be a duct issue, are something that was incorrect from the start.
Oh and the ceiling fans only help with comfort to you not in any additional cooling for the home. Really dosen't make much difference.
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