Help me understand TRVs alongside smart thermostats (NEST) -- does it make sense?

I have a NEST learning thermostat, but I also wanted individual control of each room. The 2 concepts to me, seem opposed. I think I misunderstand how it all is supposed to work together so I have some questions.

I have bought TRVs for all my radiators and installed them. They are the Aqara E1’s. The nest thermostat is placed in the living room. It’s connected to a combi boiler.

Each room does have temp sensors as well.

  1. If the temperature on the nest is below that of any single one of the TRV’s, surely that TRV is never going to reach its target temperature. Temperature control then appears to me to make little sense on the TRVs.
  2. If the TRVs limit the temprature in the room which has the nest, and the nest is set higher than those TRV’s, the nest thermostat is probably never going to reach its target temperature and so therefore it will never stop the boiler, wasting energy.

I want room control but the very concept seems to be at odds with the idea of a whole-home thermostat. Am I wrong?

I have an idea that if the temperature control of a TRV in any room goes higher than the NEST, the nest could be automated to match that highest temperature. That would surely solve (1). has anyone done this? Is it even a good idea?

(2) seems unsolvable as nest does not support external sensors. If I’m in bed and I want downstairs TRVs to be set very low, the Nest is going to think its super cold and never stop the boiler even though upstairs is set to my liking. Unless this isn’t a problem from an energy efficiency point of view…not sure.

Either way, all of my thought process seems to go down a road that makes NEST redundant. Is that right?

Possibly I could use only the off/on control of he TRV’s and ignore the temp control (when set to on, just set to a high or comfortable temp). Then when in bed, just turn the ones im not sleeping around off. But, theres still that complication about the fact that one of those rooms, is also the one the nest is in.

Without remote sensor support, the Nest is not your best bet for this combination, I’d expect.
Even the ones that do support remote sensors, as far as I know, do not support arbitrary remote data, only their own remote sensors, which is too bad, since your TRVs could feed at least temperature, if not occupancy, data. (If anyone knows of a good local-API thermostat that accepts arbitrary remote room data, please let me know!)
I do think a wall thermostat is a useful piece of your real-world interface, so I wouldn’t bin it entirely, even if you ditch the nest!

Perhaps you can fake whole home control with some clever automation!

  • You’d want to use the thermostat’s target as a ceiling for the TRVs.
    • Probably manual thermostat adjustments should be applied to any TRV se to the temp ceiling.
    • automate, via schedule or sensors, which subset of TRVs are tied to the temp ceiling, and which have some ‘lower’ temperature.
  • The active remote sensor group should be all rooms where the TRV target is equal to the ceiling PLUS any rooms where the current temperature is below the room’s TRV target temp.
    • This should keep the boiler on if any room needs heat, even if the TRV is set low.

I think this would handle the case of the set of heated rooms changing that the nest isn’t gonna handle great.

EDIT: However, having a Ecobee AND a Honeywell via the Lyric integration it doesn’t appear either offers a service for including / excluding sensors from the active set. I don’t know if that’s a limitation of the integrations or a limitation of the manufacturer’s APIs. Perhaps there’s a feature request there?

In that case, you could use the nest as a real-world interface to set the maximum temperature, and have visibility on your temp ceiling (as well as the local room temp) by mirroring any changes to the nest, and applying any nest-side manual adjustments to the ceiling set, and just have a smart relay turn the boiler on or off based on whether or not any TRVs are below their temp target. You’d need some logic to ensure you’re not cycling the boiler too often, I expect, for safety.

Thanks a lot for this detailed response, it all makes sense. I’m sort of surprised there appears to be no prior art for this considering it is a setup you’d think a lot of folks might end up having.

I think one possible shortfall is the nest “learns” and this often means just lowering the temperature at certain points. Though maybe this can be overridden or configured using schedules.

(If anyone knows of a good local-API thermostat that accepts arbitrary remote room data, please let me know!)

This would be great, I can’t believe it doesn’t exist!

Hi, I’m having a similar kind of problem, with both a nest and Aqara E1 thermostats. I was wondering how you ended up working things out?

I’ve got the same gear and have been thinking about this from the other angle…

Let Nest basically be a dumb on off switch for the boiler.
Let the temperatures set on the TRVs be the main driver.
If any TRV is set to a higher target than the current temperature in any room, have HA tell Nest to turn on the boiler.
If all TRVs (which are on) are at or above their target temperatures, have HA tell Nest to turn off the boiler.

That pretty much covers room by room temperatures, and won’t leave the boiler running unnecessarily (unless you screw up one of the target temps!)

Then work in the other things, like turning off the TRV when an open window is detected, etc.

Hey! I’ve the same setup, and I was wondering if your Nest is configured as an OpenTherm connection ?

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