Wednesday, March 28, 2012

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!

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