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Very interesting topic!

At the moment I am building 'zone' temperature control with an custom build system. I have a house with floorheating divided in 29 sections. Every section has a servo valve. The servo valves are very simple units if you supply 220V to them they open, if you switch them off they close. Since I have homeseer with click-on-click-off (for switching 220V) and oregon scientific temperature meters (in every room) I can switch valves based on a scripts in homeseer.

The current status is that everything is connected and I am thinking of how to program everything. One of the problems is the fact that i cannot control my bosch heating system. This done with an bosch opentherm termostat in the living room and an outside temperature meter. I have multiple temperature sensors connected the heating system, so i can check water temperatures going in or out of the system.

I am thinking of programming a 'duty cycle' of 1 hour. If I devide that 1 hour in 4 times 15 minutes i can switch 4 options:
- 15 min open
- 30 min open
- 45 min open
- 60 min open
(0 min is an option off-course)
The living room zone where the termostat is will have a 100% duty cycle unless the other zones cannot reach the required temperature. After every hour I check the temperatue in the room against the desired temperature and ajust the duty cycle for the next hour. I have no idea if this will work or not. Any comment is welcom!

Regards,
Bart

HI Bart
I don't think thats gonna work optimal.
What if the temp at the thermostat is reached, then it will switch off.
and what if you put it very high, it will go on running even when all the valve are closed.

I have the same problem, like mots of us we are still not bale to control the Hvac system by opentherm with our Domoticasystem.
But my Nefit has a potential free contact, I can switch my system on with that and the opentherm thermostat will show that.
But i Can't put it off with the thermostat

So I replaced my opentherm thermostat with a Proliphix Ethernet thermostat, which can be fully controlled by Domotica.
That would solve your problem for sure.
You will have to give up the opentherm and modulating of the HVAC, i don't like that anyway, my heating system runs much smoother now also.
http://www.domoticaforum.eu/viewtopic.php?f=23&t=3961

Hi Pieter,
Thanks for you input. I have been looking at a Proliphix Ethernet thermostat but I could not figure out what it would bring me. The advantage above a normal thermostat is that you can set the temperature (with HomeSeer) and switch on the heating while the temperature at the thermostat is already reached (propably by setting the set temperature higher).

The Bosch thermostat seems to be however not that useless. It has two features which seems to make it usefull.
One: It is equiped with an outside temperature probe. Based on the outside temperature the heating curve (stooklijn) and maximum water temperature is defined.
Two: You can base the heating on/off not only on actual temperature at the thermostat, but also on the return temperature of the water. You can mix the two parameters how you want. From only the room temperature to only the return water temperature.
The combination of the two results in very controlled (gentle) heating that prevent temperature overshoots. And prevent the switching off of heating when the temperature at the thermostat is reached.

Based on this I am now switching the different zones/rooms in the house with a simple on/off script. I read a temperature in a zone/room (with Oregon Scientific), compare it with the desired temperature (Set in a virtual device in HomeSeer) and then switch the servo motor of that zone/room (with ClickOnClickOff). This seems to be working, but it is not cold enough jet to test it to perfection.

I will keep you updated!
Bart