How would I make a HVAC simulator to see what a thermostat would do if the indoor temp was 400°F

Submitted ⁨⁨2⁩ ⁨weeks⁩ ago⁩ by ⁨batvin123@reddthat.com⁩ to ⁨askelectronics@discuss.tchncs.de⁩

I bought a nest gen 2 thermostat to play with a open source project that revives old nest thermostats (nolongerevil.com). Since I don’t want to install it into the home, because it will be a toy. I was thinking of building a test rig using a arduino or esp32 to simulate a HVAC and indoor temperature. I’m IT guy, not a HVAC guy, I think this would be a good learning project. Any suggestions?

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Kolanaki@pawb.social ⁨2⁩ ⁨weeks⁩ ago
At those temps I can take a pretty good guess as to what it would do:

Melt.

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- cmnybo@discuss.tchncs.de ⁨2⁩ ⁨weeks⁩ ago
  That’s right around the melting point of some types of lead free solder.
  
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- batvin123@reddthat.com ⁨2⁩ ⁨weeks⁩ ago
  Yeah I want to simulate the temperature readings. No blow torches or extreme heat preferred.
  
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  - Kolanaki@pawb.social ⁨2⁩ ⁨weeks⁩ ago
    Any particular reason? Just for funsies?
    
    Cuz I mean, if you really want to measure oven temps you can get thermometer probes that can withstand that kind of heat to make sure your food is at temp. No simulation required.
    
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  - batvin123@reddthat.com ⁨2⁩ ⁨weeks⁩ ago
    It would be fun to torch a google device while laughing psychotically.
    
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Chozo@fedia.io ⁨2⁩ ⁨weeks⁩ ago
I used to work as a PQI contractor at Nest, and we actually had test setups like this in the office that were just a circuit breadboard mounted on a plate behind the thermostat. The thermostat doesn't really "communicate" with the HVAC control system at all (all it does is just send ~3V along the circuits based on its current mode), so as long as you have the circuits routed properly on your board, the thermostat will think it's connected to a real system.

The stock firmware doesn't let you go above a certain temp (like 80F or something, I forget the exact limit). But if your custom firmware allows it, the only thing that would realistically happen is that it just runs a 3V circuit to what it thinks is the heater, infinitely, since nothing is actually causing the ambient temperature to raise at all. The ambient temp reading comes from a sensor on the thermostat, itself.

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Canonical_Warlock@lemmy.dbzer0.com ⁨2⁩ ⁨weeks⁩ ago
HVAC-R tech here.

Not sure what you mean about simulating high temps on the thermostat. If you want to trick the thermostat into seeing a higher temp than it is actually at then you would need to find the temp sensor on the thermostat (usually a thermistor) and replace it with something where you can manually control the input like a potentiometer if there was a thermistor there.

If you’re talking about simulating calls from your thermostat to your hvac system, then you can usually do that with just some jumper wires if your hvac system has a built in transformer (almost all new systems do). You just remove the thermostat and jumper the hot wire (R or Rc) to whatever call you want to make.

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Sibbo@sopuli.xyz ⁨2⁩ ⁨weeks⁩ ago
It contains lots of plastic, that will melt. Also, electronics are designed to work up to 80°C or so, then there is some safety margin, and then they will also just cease to function correctly.

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czardestructo@lemmy.world ⁨2⁩ ⁨weeks⁩ ago
Everyone is over thinking the hell out of this. Almost all thermostats use a cheap NTC resistor, just change the resistance so the hardware thinks its at the whacky temperature. Or you could figure out the bias voltage the system uses through the NTC then apply your own external voltage to trick the system.

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rain_enjoyer@sopuli.xyz ⁨2⁩ ⁨weeks⁩ ago
I don’t think anyone designed it to do that, becsuse 220C is like 100C above critical point of some common refrigerants (evaporation/condensation stops being a thing at this point and heat can be transferred only from hot to colder and not very efficiently)

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