Advanced control of Evohome system

[stuiow]

Hi all,

I have a request to submit to add something that maybe bespoke to myself, probably other's too though.

I have an oil boiler on my heating system, but also a wood burning boiler too.

The Evohome system has boiler control wirelessly (for the oil boiler) and wireless rad valves on all radiators, as well as 2 wireless BDR91's to control the hot water/central heating 2 port valves.

Is there a way that Tomoticz can control each of these components? So that's the 2 x BDR91's and the wireless rad valves.

When running my oil boiler, all is well, however, when I want to run my log burner, I need all rad valves to be open, and both the 2 port valves to be closed (otherwise the pump from my wood boiler goes down that route and heat my oil boiler, I would rather heat my radiators! haha).

I can open all radiator valves fine with Evohome, I set the system to 25c in all rooms but I also physically turn my oil boiler stat all the way down so it's effectively off so when heat is called from the oil boiler, the oil boiler does nothing, but I need those 2 port valves closing!!

Many thanks

Stuart

[dwmw2]

I have a vaguely similar system. The heat comes from either an oil boiler or coal fire, and is pumped round the radiators.

In my case though, the oil and coal burners are in parallel — the cooler water comes back from the radiators, and the pipe splits and takes it to both heaters. Then the heated water then comes back together just before the pump, and is pumped round the system.

When the coal fire isn't in use, it would be nice to physically shut off that pipe so that all the water is going through the oil side and getting heated. I haven't implemented that yet, but I should. But since lighting the fire is a manual process, I'm happy with that not being automated. (Besides, the coal fire acts as a kind of radiator, albeit slightly cooler because it's getting second-hand water from the other radiators.)

On the other hand, when the coal fire is burning, it's actually quite useful to have it going through the oil boiler too. When the coal fire is burning well, the oil boiler's own thermostat means that it doesn't actually do anything. And when the coal fire gets low and isn't producing enough heat, the oil boiler does kick in. We'd have some very cold mornings without that!

I suppose you could have an automatic system which opens the valve to let the water flow to the boiler only when it's cool enough — very similar to the thermostat which is already on the boiler itself. But I'm not sure if it's really worth it. Even if you do automate it, I think you'd want it to be autonomous so that it works even when Domoticz is AWOL. You *always* need to design for failure modes.

My main desire, FWIW, is for Domoticz to automatically tell the evohome system to open up the radiator valves, when the coal fire is burning too fast and we need to dump heat from the water in the pipes. It's scary when it boils...

[StanHD]

Hi Stuart,

Perhaps you could use the "reverse" logic of one of my methods.

I currently check the status of my Velux Windows and Outside Doors. If any of them are open then Domoticz sends JSON commands to the appropriate Evohome radiator valves setting them to 16° to avoid heating the outside world.

Perhaps you could sense the temperature in the Coal Boiler (I use 1-Wire for all my flow & return temps), and if this goes > 85° then send JSON commands to a few radiators to set them high and open them up?

Make a virtual switch, maybe call it something like "Boiler High Temp"

In the "On Action":-

http://<User>:<Password>@<IP>:<Port>/json.htm?type=setused&idx=1049&setpoint=35&mode=PermanentOverride&used=true

Idx = Domoticz idx for your Evohome Valve.
setpoint = whatever you can set as a max for the Evohome valve.

In the "Off Action"

http://<User>:<Password>@<IP>:<Port>/json.htm?type=setused&idx=1049&setpoint=21&mode=Auto&used=true

(Note the setpoint is irrelevant when setting back to mode=Auto)

Set all this up using Blockly or Lua and you could include some alert messages?

If [Boiler Water Temp] > 85°
Do Set [Boiler High Temp] On, Send Message etc.

I would then make it a manual operation to turn off [Boiler High Temp] when all is back under control?

What do you think?

[ShirlOlive]

That is amazing to hear about the advance control evohome system. Managing windows and doors becomes tough. Renovation is must and to ensure it useful content helps a lot.