Re: Re: Domotiga

[Simon Haslam <simon_haslam@xxxxxxxxxxx>]

--- On Tue, 21/12/10 keynet-technology.com wrote:
>> BTW at the moment I'm altering the boiler flow temp by switching
in a resistor in the weather compensation circuit (using a 1-wire
controlled relay) but have lofty aims of building an Open Therm interface
to set the flow temp... one day...

>Well now that I'm interested in. I have a Vaillant Ecomax boiler c.
2004, but haven't found any documentation on how to control its flow temp
except by a Russian interface ...snip...

No that's not me - I've got a Viessmann Vitodens 100 WB1B. I liked the spec
of the Vaillant boilers but they're not a part of Open Therm so only have a
proprietary interface - looking at that reference though it looks like
someone has made good progress.

I think your easiest route if you have the weather compensation controls (I
seem to remember they were in an add-in box) is to do like I have and
change the resistance of the outside temp circuit. I assume most
manufacturers use a thermistor (mine is NTC) and so you should be able to
find the resistance to simulate a certain outside temp that you need to get
a certain flow temp. Mine has a switched-in resistor wired in parallel with
the existing thermistor - I did this so that the sensor circuit is never
open (there's a boiler failure code for this condition - I don't know how
sensitive it it but I didn't want the boiler locking out). The downside is
that that outside temp still influences the flow temp. If there is
something that you could connect that has variable resistance that would be
better still - you could do away with the outside sensor altogether and use
your own sensor and control logic.

For anyone interested in Open Therm there has been some progress over the
years and an older version of the the spec is available online (http://www.domoticaforum.eu/viewtopic.php?f=7&t=2046&hilit=opentherm)
- it doesn't look that difficult apart from building the interface. A
couple of inspiring links:
http://palebluedot.nl/jml/arduino/24-openthermmon.html
http://www.tclcode.com/opentherm/
So far these projects have essentially sniffed traffic between the master
(room controller) and slave(boiler). In my case it would be a bit more
challenging as I won't have an Open Therm room controller - the HA system
will act as the master. Not sure whether that may be too ambitious
though...





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