Small update!

It has been a while since I posted something here...the truth is, not much has happened in the electronics front.

The JeeTherm has been working flawlessly since I installed it, on the 15th of January, so that it over 2 months ago. During those 2 months, we had some serious cold coming this way, I measured -15C on my weather station! That is the lowest ever recorded here.

One interesting thing about this whole story of the efficiency of an HR boiler, is that, due to some graphics I found I limited the temperature setpoint of the boiler to 55 degrees, as this is the limit above which the efficiency decreases rapidly, thinking that, if it gets really cold, I could raise this limit, as it is all software anyway, and there was no need to recompile anything (on the JeeTherm the limit is 80C, on my PID controller implemented in PHP, the limit is 55C).

As the cold came and settled in, I noticed that the boiler, and the whole heating system was still able to warm up the house, and keep it warm, even in the coldest days! so I ended up never having to raise it! I was glad, I had days where the boiler worked nonstop, but down to a simmer. My energy saving correlation calculation also indicated that the gas spent was way below expectations, although the curve fitting was not done with any data in that kind of cold range.

What bothers me the most, is that I could never really find any good info about this efficiency story. In many forums you can find people saying that an HR boiler needs a 20C difference between feed and return to operate at optimal performance, but all the graphics I find of performance, none indicates such a difference, the efficiency being a simple function of the return temperature. Furthermore, if that is the case, then the boiler should be set to start modulating to try and achieve such a difference, but the behaviour I see with my boiler is that it modulates to have a 7C or 8C difference between feed and return. sometimes even 5C. I start to think that all that matters is the return temperature...and that one, I have it limited to 55C now!

Project finished!

This is it! The OpenTherm JeeNode/Arduino interface is finished! and all ready to roll!

The prototype had been working for almost two months now, and finally the boards arrived from fabrication, I think the result was worth waiting for, and worth doing it! I got three identical boards, so if I mess up one I can go on with the next:

Bare boards

Very simple, but very effective :)
I thien collected the components, whe to buy the optocouplers, and incorrectly bought the 4N35 instead of the 4N27 that the prototype used, but only realised after they were already soldered, so I tested it, and they work fine! crisis averted:

All ready for assembly

Mounted everything, both the JeeTherm, and a JeeNode v4 I had around still to be assembled, and put it all in the enclosure:

Assembled, and in the enclosure, attached to the JeeNode

Another view

Had to fiddle a bit more to get the screen fitting in the cover, and connected to the JeeNode:

All ready for action

Checked that it all worked, and got it connected, instead of the prototype. It is now running happily:

Talking to the boiler

I am quite proud of the final result, it looks good and well packed, and I tried not to cut any corners this time, took my time, and tried to do it patiently...very often I end up messing up things in the rush to get them finished.

It is now in beta test phase, if it works well for the coming days, then I will attach it permanently, now it is still floating :)

Already thinking of the next project!