Winter is coming

The air-con is great for cooling in the winter, though that obviously has a cost, it is not as bad as I expected, and I have systems set up to control when it is on, and in which rooms, etc.

The air-con could be used for heating in winter, as it works out more than 100% efficient. The issue is that even with the new silly prices I think gas is still a lot cheaper. I do need to do the sums, which will depend on the tariffs I can get for my electricity and using a second battery. But even that is not simple, even with a second battery, and charging when very cheap at night, because that only works up to the capacity of the battery. If the air-con used for heating exceeds that capacity then we are back to expensive electricity compared to gas.

So my next project is improving the gas central heating. First step is a smart meter with half hour stats via MQTT using an in home display that connects to my MQTT server. It is on order now. This will help track the cost and usage more accurately.

But I also need finer control of individual room heating. At present we have two heating loops (up/down) and some thermostatic radiator valves. This provides limited options.

Per room control

A key factor is per room control. I already have my own temperature monitoring which I use to control the air-con for cooling. But for heating my only real control is heating on or off for whole floor.

My plan it to fit each radiator with an "actuator". I was originally thinking a shelly thermostatic radiator valve with wifi, but to be honest that is not what I really want, and an actuator and simple shelly 1 to control it is easier. I can then turn the radiator in any room on or off based on my temperature sensor which is located near the bed (for bedrooms) rather than next to the hot radiator itself.

I can then set controls for target temperatures during day and night so that the room is heated only when needed, and only to the needed temperature per room.

I already have logic to link the room control status to an aggregate for the heating itself, ie. any room heating on a floor means the floor level gas boiler heating is turned on.

Room occupancy

One of the key reasons for this is not just that different rooms need different targets (my wife and I prefer quite different temperatures), but also that not all rooms are always in use. We have a couple of guest rooms, for example.

At present I include a room manually in the controls and adjust the radiator valves manually, but once I have an actuator I can be smarter.

Just to be clear, this is not quite the same as "occupancy" for, say, lights coming on and off - for which there are various sensors. This is occupancy along the lines of "the guest room is in use today". So I can ensure it is heated (or cooled) sensibly for the day/night, and ready for when someone goes to bed - that means knowing hours before and keeping things going all night, etc.

My current thinking is any use of the light switch in a room marks the room for occupancy for next 24 hours or some such, maybe 18 hours...

That way a room that is not in use is not heated (or cooled when we get back in to summer), but a room that is in use gets heated (at night for bedrooms, based on a temperature profile).

It also means that when my wife goes in the room during the day to make the bed because we are expecting a guest, the room will be ready when they arrive, etc.

Anyway, once I have this working, I'll post some more details and pictures.

Note: these actuators come in a variety of fittings, modes, and voltages. Take care to order the right one. Pictured is Danfoss Actuator TWA-A 230V NC (RA) Danfoss manifold 088H3112. This is 230V activated so ideal for using with a Shelly, NC (normally closed radiator), and a fitting that works to replace a normal Danfoss thermostatic radiator valve fitting. Note, this seems to use about 2W to hold "open".


  1. Have a look at the Aqara FP1 detectors for room occupancy. I have one which is great for this. Integrated with something like Zigbee2MQTT you can feed in to your MQTT server.

  2. I've come at this project from the opposite direction from you, starting with TRVs, then adding Daikin control on top this summer.

    Thermoelectric mains actuators under MQTT control are great. They're basically silent, which makes them much better than most smart TRVs, especially for bedrooms. I wish my wife had let me run wires under the floor though, rather than had to plug and switch them all locally. I had to use Shelly Dimmers for the bedrooms, otherwise I got woken up by the relays clicking on in the morning.

    I look forward to seeing how you deal with this. Your code for predicting room temperatures was very helpful for stopping my own aircon from overshooting.

    1. Relays are an interesting point - it may be I end up making something with a solid state zero crossing relay perhaps, but using a dimmer is an interesting idea. I also thought I saw at least one actuator described as PWM controlled - though on/off usually works fine. I'll end up running fused spur with a shelly in it to each radiator point anyway I am sure.

  3. Have a look at Drayton Wiser smart TRVs. They're fairly cheap - less than £40 each when I last looked. They talk ZigBee back to a central controller, which can be wired to your boiler. It talks to the cloud, but has a local API, so you can poke it from HA or your own code. It'll do what you want out of the box - fine grained per room scheduling - or you could just set it to a flat profile and control it from elsewhere.

    1. My house is old. With strange layout and thick walls. Running new power or network cabling is not likely any time soon. But I put a lot of effort into providing working WiFi coverage for the whole house. So... does anyone know of any smart TRVs which run on batteries and are controllable over WiFi (not using something else which will cause additional interference), as well as having an open-enough API that I can put them on the no-internet-access-allowed subnet?

    2. Shelly TRV’s are great and work locally etc

  4. The logic of not heating a room which isn't in use remains dubious. It forces the adjacent rooms to have more heat put into them to maintain temperature, and if the exterior walls get cold enough that condensation forms within them then you lose a lot of heat next time you want the room warmer. Personally I follow the mantra of heating the entire house.

    1. Several of our internal walls are thick welsh stone as well, so not a simple here...

    2. We've used it to set temperatures a few degrees apart in different rooms, and that seems to be productive - bedrooms can be a little cooler than the living room. Also we had slightly different schedules in different rooms - stop the heating in my office at 5pm, but later in the living room. You're quite right that anything more extreme than that can be problematic.

  5. I'd talk to your boiler manufacturer before you do anything else.

    There's usually a "minimum load" for a domestic condensing boiler on the CH loop which is more than one radiator.

    I was thinking of doing a similar thing to you (we have downstairs and upstairs CH circuits) but the boiler manufacturer advised that running a single radiator would invalidate the warranty due to the danger of overheating the boiler.

    YMMV of course.

    Also zigbee is a pile of shit which fucks up 2.4GHz wifi even more than it already is, so avoid like the plague is my advice.

    https://www.metageek.com/training/resources/zigbee-wifi-coexistence/ is useful

  6. Have you considered an under floor installation? Appreciate not everyone wants to rip a house appart to do this. I actually did do this. Based on a wet system and 3 kilometres of piping later, I can safelty say I would never go back to a rad system, which were next to useless in a 120 year old house with high ceilings!
    - Runs at 40 degree C temps so can easily be converted from regular boiler to new heat pump variety
    - No Rads in all the annoying places houses tend to have them
    - Heat is uniform throughout each room/zone (no hot/cold spots)
    - Each room individually temperature controled (manifolds break heating per room/zone)
    - Warm floors are nice to walk on in the winter
    - Infra red cameras take great images when the heating is on :)

    - Rooms do heat more slowly (you have to pre plan each rooms temperature setpoint)
    - VERY disruptive to install in every room

    I do also have AC in each room, so these can always provide a fast boost if some family member is particularly cold and a standard setpoint is too low.

    I use heatmeiser control unit and each room is its own discrete temperature zone

  7. Careful with actuator valves, while I'm sure you're looking for somehing smaller than a Honeywell style 2 port valve (unless hidden under a floor). The valve actuator in the Honeywell is a synchronous AC motor, the reliability is poor.
    Also, consider a 'set back' temperature for unused rooms. I installed underfloor heating in a large volume extension in a previous home. The instruction was to maintain a 'set back' temp of about 15ºC. Obvs with underfloor the issue, typically, is time & energy to get heat into the large mass that is the floor slab (unless, like me one uses underfloor panels).

  8. The SCOP of my A/C units for heating is 4.1
    I might be mistaken but I take it to mean their 410% efficent, electricty in 1kw - heat out 4.1kw
    electricity currently being 3x the price of gas and a boiler being 90% effficent that makes A/C a cheaper way to heat your house, plus is faster/more responsive.

    One thing to be aware of is when the dew point outside drops below the coil temperature of the outdoor unit (depeding on load, usually 5deg below ambient) it freezes up restriciting airflow and dramatically reducing the SCOP and thats the point your better off using gas.

    1. Yeh, I need to get metering on the gas to work out for sure. What I do know is I can raise temp in a bedroom with on radiator very quickly, often needing only a minute or two of being "on", but the aircon can be pulling 2½kW for much longer to heat the room. It could be that I actually "use" gas at a much higher rate, obviously, and that is what I need to check. Thankfully I have choices now.

  9. Sorry, I wan't quite accurate here, when the dew point outside drops below the coil temperature of the outdoor unit AND BELOW FREEZING POINT.
    You can go below the dew point without problems
    You can go below the freezing point without problems
    Its when you have both together ( quite common in UK winters ) you get problems, I simple script can be used to spot this condition.

    You've got some BIG a/c units there, Mine only pull 1kw at full power.


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