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.
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".