> If you haven't run the numbers you could in fact be wasting more electricity by fully turning off your system when you aren't home
I've seen similar statements a few times, even in this HN thread. Most articles just repeat the statement without showing any numbers. This article does show numbers and the graphs. From the article:
> What we found was that even when the A/C temporarily spikes to recover from the higher indoor temperatures, the overall energy consumption in the setback cases is still less than when maintaining a constant temperature throughout the day.
They are multiple reason why it is better to leave AC on. But it really depends on the house.
One main reason is that when AC is off is that humidity increases which causes cooling harder. This is because the cooling process of an AC unit involves removing humidity from the air as well as heat. When the air is humid, the AC unit has to work harder to remove the excess moisture from the air, which can decrease its overall cooling efficiency.
The other reason is that house and furniture will store heat and then cooling will get harder.
Digging into the article, it's a hypothetical home and they are only testing fully off versus ideal temperature blasting.
I don't think it's always true, which is why I listed the factors that can influence it.
But I am also getting into home automation and just watched a video where some one ran through the numbers on their specific house after getting electricity monitoring connected to their heating and Home Assistant. It's not that clear cut and really depends on your specific home.
I don't see how this could be possible, because it should always cost more energy to maintain a higher temperature gradient, assuming a non-zero R-value. If there are other factors you're optimizing for, such as energy cost rather than overall usage, then I could see how avoiding peak pricing could net savings in cost, but the laws of thermodynamics are pretty absolute if you're optimizing for energy consumption.
You're assuming that the system is the same in both cases. It's not.
1. You run the A/C all day: the gas stays both cold, and dry. Cold, dry air is, it turns out, ok as an insulator. Not very good thermal conductivity at all.
2. You turn the A/C on at the end of the day in a warm, humid environment. The air is moist, which causes two compounding problems: first, the volume of air you need to cool just holds more energy than it would if it was dry. But second, because moist air is more thermally conductive, it's better at coupling heat in from the outside, so more energy is coming into the system as you're trying to cool it.
At least, that's the argument. I haven't run the numbers to check orders of magnitude or anything. I wasn't expecting the difference in thermal properties of dry and moist air to be that significant, but there are some very interesting numbers at https://www.engineeringtoolbox.com/moist-air-properties-d_12....
I've seen similar statements a few times, even in this HN thread. Most articles just repeat the statement without showing any numbers. This article does show numbers and the graphs. From the article:
> What we found was that even when the A/C temporarily spikes to recover from the higher indoor temperatures, the overall energy consumption in the setback cases is still less than when maintaining a constant temperature throughout the day.
Full data on https://theconversation.com/does-turning-the-air-conditionin...