flubbed the version control again

  We got the data we needed for St Columba’s – more on that gradually – but one part of what we did was still a failure – we didn’t capture any readings above 50C on the radiators, even though we know very well, from the thermal imager if nothing else, that they were hotter than that.  Since we’ve seen that one before, as Iain said to me, this smells very much like a version control problem.   Still, since for us one of the most important skills to share is how to debug these things, I’m checking everything in order, “by the book”.
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how should we tape the sensors?

I’ve been testing whether it matters how our DS18B20 temperature sensors are affixed to the radiators – it’s a classic round peg in a square hole problem.  We want to know what temperature the water is inside the radiators, and all we can do is tape a sensor to the surface metal.  The question is really, how fiddly should we be about that process, and what do the readings actually mean?  I had the thought that shielding the side of the sensor that’s away from the radiator might make the reading approach the truth better, and so I set up that test. A saucepan stands in the for radiator; a sensor in the water gives the actual temperature, and two sensors strapped to the side give the insulated and uninsulated results. The insulation is just 6 layers blackout curtain lining I had lying around; it’s suppose to have reasonably good thermal properties.

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drains??? why care about them?

ccm-drains-1925-circled… because if they back up,  you end  up clearing very mucky stuff away from very expensive boilers, of course.

That was the problem back in 2012 when I looked up these Christ Church Morningside drainage records, anyway.  One of the access points is right next to their two boilers.  The ignition on one is still a bit touchy –  I guess they didn’t like what came up any better than I did!  At the time we wanted to know whether there was any connection to the drains out the back.  The answer appears to be “no”.

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testing heat output at St Columba’s

stcs-radSt. Columba’s by the Castle – where we ran an Innovative Learning Week event last year –  has an interesting follow-up question for us.  How much will  it help the space warm up  when they remove that wood paneling around the radiators?

Whenever I look at them, I think “this is a place that takes the name ‘radiator’ seriously” – after all, there will be radiation off that nice exposed surface.  Unfortunately, radiators are misnamed. They really heat spaces almost entirely by convection.  These are designed to take cold air in at the bottom, heating it so it rises and comes out the top.  You can’t see from the picture, but there is actually a grill in the shelf above the radiator.  Not so underneath.  The air intake is seriously obstructed, whereas the air outflow is just slowed down by extra turbulence, dumping heat right there instead of further into the space.

Answering their question starting from first principles is tricky.  There are data sheets that will tell us how much heat output this radiator would give if unobstructed, but of course, not what happens with all of the interesting things that happen to them in practice.  And I know from talking to Dimitri about building a test rig for the hot wire anemometry that turbulence is tricky stuff!  They’re really looking for “how much more heat output will we get, and will it be enough or do we need to make more infrastructure changes”.  It’s a bit hard to mount equipment on the radiator for the “before” picture.  These are my thoughts about how we might answer the question.

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