"When everyone leaves, all the air conditioners switch off."
That's often substantially more inefficient than keeping it at the temperature desired, or adjusting the desired temperature to mitigate it somewhat.
That's often substantially more inefficient than keeping it at the temperature desired, or adjusting the desired temperature to mitigate it somewhat.
Even among people who service AC units I've encountered the misconception that it is more energy efficient to keep a space at the desired temperature than it is to let it heat up and then cool it back down again, but thermodynamics say it is not so. It could conceivably be more cost efficient if your energy costs are variable.
Air temperature is only one contributing factor for comfort in a home. Surface temperatures take longer to achieve and the larger the gradient the longer it can take.
There are multiple factors to take into account, including the highest temperature the home gets to, that is dependant on location and weather patterns.
If you keep the temperature in the home to 28-30 degrees then later cooling to lower temperatures before bed time you can reduce costs and energy expenditures than if you let it rise to 34 degrees or more and only lowering it when you get home. Or, what you save in costs you expend in otherwise like poor sleep.
Lowering it advance, on a schedule makes more sense if you want surface temperatures to also be reduced.
The blanket disabling of air conditioning when not home is not the only solution, and often is sub-optimal.
Most people actually measuring it come up with more savings when cutting the AC during the longer spans when nobody's there (usually during the hottest part of the day).
Regular heating can waste a lot of energy to heat the entire structure of the house, especially if you have thick walls, so it does more make sense to try and keep the temperature stable.
In general using a large setback will save more energy by not constantly cooling the home than it costs to return the house to a desired setpoint later.
Admittedly, this will probably not work that well in a Minnesota winter, or an Arizona summer, but I think a surprising number of people could benefit.