this post was submitted on 26 Dec 2024
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my high efficiency HVAC unit would like a word with you.
what you're saying is basically you can replace anything with a RPI. yes, in theory, you are correct. but, unfortunately for you, there are nuances that you didn't take into account. such as, startup/shutdown procedures, cool down cycles, heat pumps, dual compression ac units, etc.
This made me think:
What about thermal runaway protection? I'm betting that might be easily overlooked in a custom "smart device" if, for whatever reason, the temperature sensor were to fail and keep reporting "Hey it's still only (below_target_F_degrees) in here! Keep that heat on full blast!"
This was an issue that made jank 3D printers catch fire and burn houses down until it was mitigated with open source firmware.
Point being, unless there's a "custom smart thermostat project" that's vetted and trusted, stuff like this might be overlooked in someone's Python project, wherein it's bog standard, low level, possibly redundant, in consumer devices. (Especially thanks to safety standards.)
Should there be an open-source smart thermostat project that's looked over by thousands of HVAC turbo-nerds and engineers? Yes. Yes there should! Might already be?
All of that is handled by the HVAC (if there's anything to handle) and not the thermostat
Thermostats can be (and most often are) a bimetallic strip that bends one way as it cools and bends the other way as it warms, and that flips some switches that you set for temperature ranges which then demands cool or hot from your hvac
That is the simplest possible thermostat and works great for setting a temperature, but that's not the ideal thermostat. The temperature your house "feels like" also depends on humidity. You may also care about the temperature more in a spot further from the thermostat and getting accurate measurements in that location can save you money and waste less gas. There is also the decision of how long you should run a furnace and, in the case of multiple stages, which stage you should run, although some furnaces control the stages themselves. Then there is air flow. Controlling the fan separately is useful if the house doesn't evenly heat. Sometimes you can just have the fan turn on more often and use the actual furnace less, saving gas again.
Also sometimes it makes sense to heat your house slightly more during high demand hours to save money. I dunno there is just a lot that could be done with an intelligent thermostat, it's one of the few things that makes sense to make smart to me.
Those are all very nice things to have in an improved thermostat, I agree completely
The point I was replying to was making the erroneous claim that basic operation of an HVAC isn't possible with an RPI thermostat because of things the thermostat doesn't handle
Ah sorry yea agreed, at least for the units I know about
I think what you're failing to understand is that newer HVAC units are designed to be run in a specific way. if you disregard that, and run it like a unit from the 1980s you will halve the life of the unit.
yes, most of the "brains" are on the unit itself but without proper "eyes" the brains are useless.
I'm not even an HVAC tech but I've worked on them enough to know it's a dumb idea to just replace your thermostat with "a raspberry pi and a bunch of 24v relays". there's just too much risk of things to go terribly wrong and multiple people literally die.
Not missing that, as I and yourself said it's done via the actual HVAC unit and not the thermostat
No, the nicer features just don't get used, it doesn't make the entire unit not work
Lol, people aren't going to die if you replace your thermostat with an RPI unless you wired the thermostat so poorly that you somehow manage to schock someone touching the thermostat
Again: thermostats just tell the HVAC to run and which part to run, any other advanced features are not required to be catered to in order to work. My brand new fancy schmancy heat pump with all those cool features listed runs off the same $2 Honeywell thermostat my old heater did, if I want the advanced features like zone sensing I can upgrade my thermostat, but my heat pump works without them just fine