Let me paint you a scenario where this is possible: you leave home at 9 AM, and the A/C stops. The house slowly gets hot, maybe 95°F. You plan to arrive at 9 PM, so you program the A/C to get the house to 76°F, which the thing thinks it can do in 1 hour at full blast. But the energy price between 8 PM and 9 PM is the highest of all day: you just programmed the A/C to the worst.
Instead, now you leave it keeping 76°F, and the thing can do it working at 10%. You consume more energy at the end of the day, but the consumption is spreaded through the cheapest hours in the middle of the day, and only a small fraction of it is consumed in the expensive hours from 6 to 10 PM. This is how freezers work, cooling intermitently as the thermostate goes off limits.
I would test if it is worthy money wise, not energy wise, to put the A/C at full blast in the cheapest hours. Say from 4 to 6 PM (the cheapest here in Spain), to get the house as cold as possible, and then try to play with A/C at maybe 5% letting it rise until reaching 76°F at 9 PM.
> I would test if it is worthy money wise, not energy wise, to put the A/C at full blast in the cheapest hours. Say from 4 to 6 PM (the cheapest here in Spain), to get the house as cold as possible, and then try to play with A/C at maybe 5% letting it rise until reaching 76°F at 9 PM.
Depending on how big the house is and how well insulated it is, it very well may make for a big thermal battery and this would work well.
If small and/or poorly insulated or drafty then this will not work well.
It might be, you should research how your region produces energy.
For example, where I live the energy produced from 10:00 to 18:00 is almost 100% solar, eolic and nuclear (https://www.esios.ree.es/es/balance?date=04-07-2024&program=... , orange and red bars are solar, light green are wind, dark blue are nuclear). Energy after 19:00 starts to draw gas (yellow bars) to cover the fall in solar production, peaking at 21:00. Incidentally, this also matches prices going from ~5 cents/kWh to ~20 cents/kWh (https://t.me/tarifaluz/3665). So for me it's both ecofriendy and moneyfriendly to shift as much consumption as possible to the 13:00-18:00 hours.
Eco-friendly, possibly, buy cheaper? Maybe not. It depends on when you arrive home. If you arrive home during peak hours when your utility prices are higher, it can be cheaper to run the a/c earlier, while you're not home, to at least get the temperature down into the rough ballpark of where you want it, and then maintain that temperature into the peak hours.
Even the eco-friendly bit isn't always clear, depending on your equipment. It might use less energy overall to maintain your desired temperature 24/7, even when you aren't there. Your particular equipment may run less efficiently if it has to go on full blast for an extended period of time to do a large temperature change when you first get home.
Not always because it depends on many factors such as demand energy pricing. The house also has heat inertia, meaning it could take hours to reach a ceratin temperature, so you'd have to turn on the AC hours in advance before you arrive home.
Cool thing is I don’t care about the temperature of the solid mass inside of where I am, just the air really.
I know when I turn on the A/C in my office, it’s not going to cool the concrete wall/floors/ceiling much in the 8h I’m there before I shut it off for the day. And that’s fine.
The solid mass inside the building, the walls and floors heat the air and the AC is working harder to keep up. Also exposed glass to direct sunshine that creates a greenhouse effect.
It uses the least energy, but here we are talking about demand shifting to make use of variable electricity sources. It can be worth using more cheap solar energy in the middle of the day instead of less natural gas later on.
The key point is that an insulated house acts as a heat/cold storage device, so it's like buying booze and pouring it into a (slightly leaky) bucket during happy hour, to drink later. Even if you loose a bit to the leaks, you're still saving money overall by buying the booze when it's cheap.
Instead, now you leave it keeping 76°F, and the thing can do it working at 10%. You consume more energy at the end of the day, but the consumption is spreaded through the cheapest hours in the middle of the day, and only a small fraction of it is consumed in the expensive hours from 6 to 10 PM. This is how freezers work, cooling intermitently as the thermostate goes off limits.
I would test if it is worthy money wise, not energy wise, to put the A/C at full blast in the cheapest hours. Say from 4 to 6 PM (the cheapest here in Spain), to get the house as cold as possible, and then try to play with A/C at maybe 5% letting it rise until reaching 76°F at 9 PM.