You can set your own schedule with Nest, you don't have to let the AI take over. Mine is fully on my own manual schedule.
Personally I think it's significantly better than what was common ( in the UK ) before, but the tech is dime a dozen, and new houses should probably come with underfloor, and control per room, though most still don't.
If it only takes one of heating or cooling to do this, not both, a standard "dumb" thermostat can of course do this just fine. Just set it to "cool" or "heat" mode and set a temperature. But of course you will need to change modes as the season changes (unless you live somewhere where only one mode is ever needed).
If you want to not have to change modes when the season changes, it gets more complicated, because the simple control system in the standard thermostat is too dumb for that. For example, suppose you set your temperature to 75. The actual temperature rises to 76, above the setpoint, so your A/C comes on. It cools the house to 74 and then the thermostat shuts it off (you have to have some buffer so the A/C doesn't come on again almost immediately). Now the temperature is below the setpoint, so your heat comes on. It heats the house to 76 and then shuts off. Now the temperature is above the setpoint... You can see what's going on.
From a pure design perspective, the right way to solve this problem is an outside temperature sensor (and probably a sun sensor as well since sunlight is a significant heat input to your house), so the system can predict what will happen when both cooling and heating are off. Given reliable sensors, the control algorithm is fairly simple (automatic climate control systems in cars already do it). I have never seen this in a house, though. I'm not sure why.
And if you loosen that spec, then, as others have already pointed out, just having two setpoints, a lower one for heating and a higher one for cooling, will be sufficient as long as the difference between them is large enough (probably 2 degrees or more would be enough for many use cases). That would be simpler than adding a PID controller.
The linked esphome docs are actually great whether you care about esphome or not - they explain all of this very well and you can tell from the configuration values and samples what kind of logic goes into all of this.
I am perfectly comfortable (and therefore want my system to turn off) after my AC has been running long enough to drop the humidity a bit, even if the temp has only dropped a fraction of a degree. As humid air leaks in, I want the AC back on even if the temp has barely increased a degree. Basically the heat index in my house swings enough to change my comfort and therefore could be a useful trigger, even if the temperature doesn't swing nearly enough to be a useful trigger.
The Nest even has a humidity sensor, but it only gets used in very specific (hardly useful) situations.
I considered writing a Works With Nest app for this. Then that platform disappeared in favor of Works With Google, but I never found the time for either...
You could try wrapping your thermostat in a wet sock.
Actual web-bulb thermometers would either require manually adding water when you want to make a measurement, or have a large tank of water that gets continuously wicked onto a cloth which is wrapped around the thermometer. The general idea is that, if the surrounding air is dry, the water in the cloth will evaporate and cool the thermometer below the temperature of the air itself (the "dry-bulb temperate"). This is just the same evaporative cooling effect that makes sweating and swamp coolers work. If the surrounding air is very wet (humid), very little evaporate cooling will occur, and the wet-bulb temperature will be very close to the dry-bulb temperature.
I'm not sure how well a thermostat that only used the wet-bulb temperature would work. To actually calculate relative humidity, you would need at least a wet-bulb and dry-bulb measurement. But given that relative humidity in most places probably doesn't swing that wildly, I imagine that just finding a comfortable wet-bulb temperate for your thermostat might work okay in practice.
Rigging a wet sock (with constant wicking from a water source) onto my actual wall-mounted Nest Thermostat would never fly, as I said, but I have no qualms about doing this experiment with my Nest Temperature Sensor, being a small and relatively cheap thing that I can easily steal for a while...
According to a psychrometric chart [0] it looks like if the dry-bulb temperature stays locked at 70F, while the RH drops from 60% to 40%, the wet-bulb temperature will drop from 62F to 56F. Or if the dry-bulb temperature stays locked at 80F while the RH drops as before, the wet-bulb temperature will drop from 70F to 64F. That's linear enough for my purposes.
Therefore if my conventional (dry-bulb) set point is 75F in the summer, and I'm most comfortable around 50% RH combined with that 75F, then I'll try a set point of 63F with my Nest using the remote Sensor wrapped in wet cloth!
Apparently I also need continuous airflow over this wet-bulb thermometer. I wonder how much.
[0] https://hvacologist.com/2022/02/21/wet-bulb-temperature-vs-d...
When I get back from a run in August at near heatstroke levels I will almost never cool down if it's not set on the "chilly" side. Conversely, in winter when heatstroke is replaced with near frostbite I am chilled to the core and need much higher heat to ever warm up.
E.g., if the thermostat expected a temperature of 75 F at 12 PM but it was actually 78 F, then you know the house received a lot of sunlight and can correct accordingly.
As others have indirectly pointed out, for the range of circumstances a given house is going to encounter, the linearizing assumptions in a standard PID controller are probably sufficient. If tuned properly, the "differential" portion of the PID controller will shut down the heater earlier when it's warmer out and/or there's more solar energy coming through your windows.
Why ? What would be so hard in detecting "every time I don't do anything temperature goes up therefore summer and I need to use AC" ?
> If you want to not have to change modes when the season changes, it gets more complicated, because the simple control system in the standard thermostat is too dumb for that. For example, suppose you set your temperature to 75. The actual temperature rises to 76, above the setpoint, so your A/C comes on. It cools the house to 74 and then the thermostat shuts it off (you have to have some buffer so the A/C doesn't come on again almost immediately). Now the temperature is below the setpoint, so your heat comes on. It heats the house to 76 and then shuts off. Now the temperature is above the setpoint... You can see what's going on.
All would it take is to put a gate "if I used cooling to correct temperature last time, don't use heating for few hours or until it drops to higher difference and vice versa". You're trying to portray it in way more complicated way that it is.
> From a pure design perspective, the right way to solve this problem is an outside temperature sensor (and probably a sun sensor as well since sunlight is a significant heat input to your house), so the system can predict what will happen when both cooling and heating are off. Given reliable sensors, the control algorithm is fairly simple (automatic climate control systems in cars already do it). I have never seen this in a house, though. I'm not sure why.
Too simplistic. Which side of house you monitor, is it in shade or does it show temperature when sun heats up the wall ? Which room is closest to "hot" wall/window?. It would be a lot of work for very little improvement
There's an additional complication for multi-story houses that I didn't mention before. In multi-story houses, when you're cooling, you want most of the ducted airflow to be directed to the upstairs outlets, to take advantage of natural convection (cooler air sinks); similarly, when you're heating, you want most of the ducted airflow to be directed to the downstairs outlets (warmer air rises). That requires adjusting dampers in the ducts, usually just downstream of the output of your HVAC unit. Unless that adjustment can be automated (which would require automatically controlled motors on the dampers, something I haven't seen marketed, though again I'm not sure why), your airflow will be suboptimal for either heating or cooling if the system automatically switches between modes.
A typical suggested application is controlling the airflow to a room using a thermostat to open or close the damper, but they can be hooked up to anything with a switched output.
As an example, this damper has an adjustable bleed rate, with a 2 wire input for switching the state:
https://www.resideo.com/us/en/pro/products/air/forced-air-zo...
(Click the "Install" tab to access installation guides)
In effect, two strips of metal were bonded together forming a coiled "spring." Because each metal had different coefficient of thermal expansion, the spring would expand or contract to different lengths depending on the temperature. Place the electrical contact at the temp where the heater or HVAC should turn on & bam.
No electronics at all, just a temperature-dependent mechanical switch.
I had a problem with the temperature in my house often being wrong, so I bought a smart thermostat. Now I have ten problems.
Seems to be a Google habit. I regularly get "commute traffic reports" several hours before or after I leave home or the office. Of course there's absolutely no way to set the alert schedule yourself.