2 stage cold (air conditioning)

Hi. I’m brand new here and I absolutely want to have open source smart products. I see that hardware sales are halted and that’s a shame, I’d buy one in a heartbeat, since I’m not the best at the hardware side of RPi setups.

If I DIY a RPi thermostat, does the software itself support 2 stage cold (air conditioning). I live in Tucson, AZ and trust me, two stage is a great idea here. I can only seem to find mention of that related to heating.

Hello @Robert. :wave:

For a while there was no way to buy the hardware, but I’ve stepped up and started building the hardware and making it available for sale at https://www.tindie.com/stores/eternalsunshine/ That is my personal store, so any praise, suggestions or complaints about the store should be directed at me.

The software does not currently support 2 stage cooling.

Is 2-stage cooling something your current HVAC system supports? If so, could you share some info about it? Even just a photo of the wiring inside your thermostat might be illuminating.

If it’s just a matter of flipping an extra relay to turn on additional cooling power, it should be possible to write additional code to repurpose the 2nd stage heat relay to be a 2nd stage cooling one.

If you or someone you know has the time and skills (mostly Javascript programming), I can help support you in implrmenting it. Explaining how the code works, helping test it, doing code reviews, and that sort of thing. I just don’t have the time to take on writing this feature by myself right now.

Another person has asked about repurposing the relay for 2nd stage heat to do dehumidification, so there is interest in these sorts of modifications. Perhaps we could find a way to select what function of that relay and build all of these into the same image for people in the future.

This is exciting and thank you for doing it along with considering my request! Here’s a look behind my spying, closed source, Google owned Nest.

I think Nest tends to label a stage as airwave, once the home HVAC system becomes cold or maybe close to the thermostat temperature, I think, I’m not sure but I think it blows the remaining cold air using the fan without having the air compressor on.

Here is the model of heating/cooling system I own. I think many systems in my part of the country have this feature, regardless of brand and make. Lennox LRP16-3 TTC heating/cooling system

Thank you for giving this a look!

Excellent. By the looks of the wiring, it’s all relay based (which is good) and you have a total of 5 functions: the fan, 1st/2nd stage cooling and 1st/2nd stage heat.

The HestiaPi ONE can only accept a maximum of 4 relays. Accepting more would be a substancial hardware change and would deserve to be an entirely different model.

This means that, barring any hardware changes, you would have to give up that second stage heat to get the second stage cooling. Seeing as how you said you’re in Tucson, I have a feeling you might be okay with this!

There’s still the matter of the software not supporting 2nd stage cooling, but it is a whole lot easier to update the software than it is to update hardware!

I didn’t find the LRP13-3 manual, but if it’s a heat pump, typically the way they work is to run the compressor as partial power (e.g. half power) for stage 1 and full power at stage 2.

Side nite: I have seen some multi-zone units that will have what I would call a faux stage 1. They just run the fan to mix air between the zones and only turn on cooling if two zones get out of range. It can be helpful if you have similar set points, but it can be counterproductive if one room wants to be cooler and all the HVAC ever does is mix the air with another room which is set to be warmer. The result is that the zone with the cooler set point will never get into range. Adjusting the set points of zones to be the same kinda defeats the purpose of having zones, so if they’re going to have fancy control logic in there to do stuff like this, they need to make it quite a bit better!

Forgot to say, my coder friends are way too busy unfortunately. I could chip in some dollars for Fiverr if you think it could go a long way outsourced.

You can try Fiverr, but there’s quite a bit of a learning curve to writing JS code for OpenHAB. This isn’t like a 20 minute task. Plus testing would also be difficult.

I’d like to get that feature in there (along with whole house dehumidification), but I just have too much going on in my life right now. This will have to go in the “someday, maybe” bucket for me.