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Thread: Which A/C setting is more efficient?

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    DIY Member Squ1rrel's Avatar
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    Default Which A/C setting is more efficient?

    Hey All,
    With those nice 100+ degree summers rolling in, I had one rather asinine question for all the HVAC gurus here. Which is more efficient when I am gone all day? Completely shutting my A/C off, or setting it to a higher setting than when I am home, such as 80-85 degrees. My apartment is decently insulated (it's also quiet! Amazing!), but I still come home to an uncomfortably warm place if I do not run the A/C at all, and it seems to take a while to get the place cool again. Thanks in advance!

  2. #2

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    Going to depend on the performance of your home. Usually, it will cost more to bring the temp down than "holding" at a reasonable temp while you are not there.

    Remember, AC is not all about temperature, more importantly is relative humidity. When you raise the temp / RH it effects everything in your home, so you are not just reconditioning the air.

    The holding temp will depend on your home. Some homes would never reach 80-85 in a day, others could reach it in a matter of hours. I would strive for a temp which allows the AC to run once or twice an hour to try and keep the humidity in check. Again, there is not a one solution fits all.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    After extended off time, the entire structure, including furniture, walls, floors, etc. can get hot. These will reradiate heat back at you until you reach an equilibrium and can take a day or so to reach the new ambient temperature. So, as was said, it depends on how long it is off, and how fast the house warms up. Continuous swings of humidity levels doesn't help the furniture (assuming it is wood), either. But, a few degrees still helps, and may not be noticable. It's a balance between efficiency and comfort. If the outlet of the a/c is blowing on you, you may not notice that the walls and couch are hot.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member Squ1rrel's Avatar
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    Thanks to both replies! We don't get alot of direct sun, being on the North Eastern wall,and humidity is a relative constant (usually staying between 40-60% even in the summer). That being said, the registers are placed in odd locations, and don't blow directly on ANYTHING (one points into a dining area, and the other is on the top part of the bdrm wall and kinda blows down and to the sides), so if the whole apartment isn't cool, ya notice. After 8 hours, it just tends to take about two hours to get to the 70 I find comfortable if I have the a/c off entirely. If it is set to a higer temp, it only takes about 20-30 minutes. I'm just willing to put up with the heat if it means a decent savings in the pocketbook

  5. #5
    Plumber jimbo's Avatar
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    A programmable set back thermostat will help. If you contact your local electric company, they can probably recommend settings to optimize energy use.. The energy star people definitely recommend setting the temp back when away.

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    Computer Programmer Bill Arden's Avatar
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    Your local electric company may have a "cycled air" program where they discount the power price in exchange for letting them turn off the system for 15 minutes at a time.

    Personally I am now using ground source water for cooling and a window unit for humidity control and I find the unit works better at night and in the morning when it's cooler outside.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

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