I’ve had a Google Nest thermostat for a couple of years. It’s OK for what it does but it’s not very flexible, especially in its lack of thermostatic radiator valve (TRV) integration, and I’m now considering upgrading to something better.
I think my ideal system would focus on TRVs, with each one able to demand heat (via HomeAssistant) when it falls below temperature. I feel tempted to try a DIY approach along those lines but there’s probably a lot to be said for pre-built integrated systems (Tado, Neatamo?). From what I’ve read though, they seem to revolve around a controlling thermostat. That seems to me reminiscent of old style wall thermostat (typically in the coldest part of the house such as the hall) acting as a master controller. It’s not clear to me what benefit that would bring to a TRV-centric system, or if it could even be a hindrance.
Can anyone outline how the TRVs and central thermostat work together in thse types of system? Would anyone recommend a DIY approach, or are they best avoided in favour of a popular system?
The master thermostat in system with such one is used to control the boiler/furnace, so if that thermostat does not request heating, then none of the thermostats gets heating.
If you do not have your own boiler/furnace, then this master thermostat makes no sense.
I have a district heating and I use a Homematic IP setup.
None of the TRV is a master. TRVs are grouped in rooms and those rooms can be grouped with wall thermometers too, so you can get a common temperature for the room and not just a temperature from the TRV, which is usually placed right next to the radiator and therefore prone to being affected in extreme degrees from the heating. Window/Door sensors are available too for the rooms.
The system operate with either cloud or a central control unit (CCU), which is local. The CCU can be emulated in HA with a pretty cheap USB RF device for the system, but the system is somewhat resilient against connection problems and hangs/restarts of the CCU/cloud, because the TRVs, wall thermometers and window/door sensors talk with each other directly.
I can recommend the Homematic IP devices.
DIY is an option, but can be a big challenge.
You need to have TRVs without internal logic or atleast an internal logic that can be deactivated, or you will be fighting that when setting up your own control systems. The issue here is that the TRVs often have logic that try to predict the heating requirement and set the valve accordingly, which makes it hard to control the valve externally from the TRV. You can use the target temperature, but it means you will go way over your wanted target temperature to make it heat as wanted and way under to make it stop heating, which means a lot of work on the valve and especially battery operated TRVs will die fast on the battery then.
If you go with exosystem of TRVs, then make sure that wall thermometers are a part of it and they can communicate with the system to get a common temperature for a room. System without wall thermometers are really not that good, like the Danfoss TRVs that have internal logic to handle the heating but no wall thermometers in their ecosystem, so they are relying solely on the TRVs temperature, which makes it jump around a lot.
Understood. I have my own oil-fired boiler (I don’t think we have much district heating here in hte UK, certainly not in rural properties like mine). Most systems I’ve encountered have had a master thermostat, often sited in a hallway as that’s typically the coolest part of the home. The boiler supplies heat until the hallway is up to target, and any TRVs simply restrict their rooms to a lower temperature - they’re not able to demand heat. My current system is like that, based on the Nest thermostat. If I want more warmth in my living room, I have to turn up the hallway heat. That has always struck me as a consequence technology limitations and not particularly satisfactory.
I understand some systems have TRVs that are able to demand heat, which would be a big improvement. I rather expected that in such systems the boiler would start when any TRVs calls for heat and shut down when all are satisfied, with the concept of a master thermostat being ditched as redundant. I hadn’t considered the problem of fluctuations caused by TRVs over/under-shooting, that’s an interesting point.
I picked up an Aqara radiator thermostat a few days ago with have a few more on the way, and I finally got around to integrating the Nest thermostat into HomeAssistant yesterday. I also have some Aqara temperature sensors on order, and they can act as external sensors for the radiator thermostats. Perhaps I’ll spend some time experimenting to see what I can do with those components as a first step. If nothing else it might help me to understand some of the issues involved and get a better idea of what to look for in a complete system.
Thanks for a very helpful and well considered reply.
Play with it and learn, then you will be able to do it.
I have the Homematic IP system, but I have just recently switched over to control it myself and I have fought the logic in the TRVs, since mine can’t be deactivated.
I have found that my wall thermometers is the best source for temperature control, so I take the measured target temperature and subtract the measured temperature.
This difference is then used to add to the measured temperature on the TRV and set that as the target temperature.
I have a few corrections though.
If I need heating then the target temperature on TRV will be set higher, but I have limited it to a max of .5 higher, because this will prevent it from just going nut and start a crazy heating cycle. With district heating I pay for the heat coming in, but if the water is still hot going out, then I just paid for something I did not get the benefit from, so the heating needs to be kept down, so the water going out is somewhat close to cold. If you have your own boiler/furnace, then this might not be that important.
If the temperature is needing to be lowered, then the difference from the wall thermometer is negative and I then multiple it with 3 to get an even lower value. This is to force the TRV logic to actually turn down the valve, ie. the fight against the logic.
As I mentioned this fight against the logic can drain the batteries on the TRVs, so I have made then mains powered instead.
The batteries have been removed and replaced with a piece of round wood around the same diameter as the battery, but a bit shorter.
In one end I have then placed a screw to act as the anode or katode of the battery. My TRVs need 2x batteries of 1.5V, so 3V in total and since they are serial connected, then I only need the connectors between the batteries and the TRV and not the one between the batteries themself.
I have then adjusted the screw to have the correct length compared to the original batteries, so that it sits perfectly in the battery compartment.
Each piece of wood have then been made with a little groove for running a wire along side it.
I have then soldered a piece of wire to each screw and the other end I have soldered on to the GND and 3V3 on one of these.
Now it is just a question handling the wire inside the TRV and exit it from it and then lead the wire down to a socket, where the voltage regulator can be put into a USB charger and you will then have mains powered your TRVs.
I think a .5A USB charger could do it, but I always use a 1A or 2.1A instead, just to be sure.
Sounds like an absorbing project. You presumably find that you want more control than the Homekit package provides by default, which is an interesting point. I hadn’t realised the adjusting of TRVs would be so complex, I’ll bookmark this post for reference if and when I get around to trying to automate mine. Thanks again.
I’m using some Aqara E1 radiator thermostats, which are paired with an Aqara E1 Zigbee hub. I have some HomeAssistant automations that are triggered when any of the TRVs register a change in their target or current temperatures. If any of the TRVs is below its target it’s treated as a heat demand, which sets the Nest thermostat to a high temperature, which fires up the boiler. If none of the TRVs are below their targets then the Nest is set to a low temperature so the boiler turns off. It’s not sophisticated but it works acceptly well for me.
However…
One of my Aqara thermostats developed a fault earlier this year. It was replaced promptly under warranty without fuss, but I noticed just today that another has exhibited signs of what could be the same fault. It’s not easy to describe. The cap of the termostat rotates to set the target temperature manually, and it can also be pressed (like clicking a button) to display the current setting. The fault that the earlier unit developed was that it was no longer possible to ‘click’ the cap downward, as if it had seized. This was only the case when the valve was closed, i.e. when the piston in the thermostat was pressing down on the valve to hold it shut. It felt very much as if the piston was pushing down too far, resulting in back pressure pushing against the cap and preventing it from clicking down. I had a spare thermostat so I was able to fit that in place of the faulty one and it behaved as expected, confirming that it wasn’t a problem with the radiator valve. The one that I noticed playing up today had its batteries replaced a couple of days ago, which involves a re-calibration. I think that sets how far the piston should push down, so I’m wondering if that has made it try to push too far. Performing the recalibration again didn’t help when I tried earlier today, but that unit does now now seem to be working again, although it takes quite a bit more pressure to click it when it’s closed than when it’s open. I don’t yet know what to make of it to be honest.