Best air conditioning temperature
What is the best setting for a programmable thermostat?
What is the best air conditioning temperature for energy savings? Our condo recently had all its units upgraded to ENERGY STAR air conditioning units. Ours came with a Honeywell digital programmable thermostat. I'm trying to decide how to set it for its four daily settings. I'd like to keep my electricity costs down while still being comfortable when I'm at home.
Answer from Green Energy Efficient Homes
The best air conditioning temperature to set your programmable thermostat to is the highest possible for each phase in the thermostat cycle. The warmer you let your condo get, the more you'll save. There are three situations to consider: when you're away from your home, when you're at home and up and about, and when you're asleep.
Most people set their programmable thermostat to around 78F when they're up and about, and let the temperature climb to 82F when they're away or asleep. This is a pretty narrow temperature range and won't do much to cut your energy costs. I suggest letting the temperature rise a lot more than 82F when you're away. The key is to make sure the house is comfortably cool by the time you get home, so you could set your 'away' temperature as high as 90F and just set the thermostat to start cooling 15 to 30 minutes before your expected return. (Note that the higher you let the indoor temperature climb while you're away, the longer it will take for the condo to reach its comfort temperature again.) This works well if you work a regular day job, but of course there may be times when you get home to an uncomfortably warm house. Another option is to get an intelligent home control system that lets you change the temperature remotely with your cell phone.
I've heard various 'experts' claim that you'll use more energy cooling down a warmed-up home or condo than you save by letting it warm up. That's just plain wrong; it violates the second law of thermodyamics. Whether you have a high efficiency air conditioner or an old clunker, and whether you have good insulation in your walls and attic or none at all, In hot weather your home is constantly absorbing heat from outside. The bigger the temperature difference between the hot outdoors and the cool indoors, the more heat the indoors will absorb, and the more energy it takes to keep the room at a given temperature. If you shut the air conditioner off, or let the temperature rise while you're out, you'll be saving energy during the time you're away. Yes, it will use more energy once you come back to cool the place down to a comfort level, than if the rooms were already cool. But don't forget you saved energy by not keeping the place cool while you were out.
I suggest setting the comfort temperature on your programmable thermostat to 82F to start, and after a few weeks seeing if you can bump it up to 84F. You can get used to a warmer temperature and still be comfortable. My family and I lived in Costa Rica for a year, where it was 90 to 95F year round, and we got quite comfortable with just ceiling fans most of the time. You'll save a lot of electricity just by going from 78F to 82F, and even ore if you let it slide up towards 84F. Remember that an air conditioner removes moisture as well as cools; much of the cooling sensation comes from the dryer indoor air, which is less effective at cooling heat. So 84F indoors will feel cooler than 84F outdoors on a humid day.
At night the best air conditioning temperature is one that lets you sleep comfortably with just a sheet over you. Remember that when you go to bed you will feel warm from having been active, but within 20-30 minutes of inactivity you will start to cool down. A nighttime setting of 84F or 86F should be perfectly comfortable while you're asleep. That makes a lot more sense than setting the air conditioning temperature low and piling on the duvet and blankets. If you have a ceiling fan in your bedroom you can let the temperature climb even higher, since the gently blowing air will help you stay cool.
So the best air conditioning temperature is whatever you can tolerate while still feeling comfortable. Letting the temperature climb towards 85F or even 90F while you sleep or while you're out will save you more than sticking with the standard 82F. The higher you can go for both comfort and sleep or away settings, the more you will save. A programmable thermostat is the best way to achieve these savings. Just remember to keep pushing the limits - upwards of course. Your body will acclimatize to warmer temperatures, and the best air conditioning temperature in May when the cooling season kicks in, is probably a notch or two higher than what you find comfortable in August.
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