Radian

It's a good point you make there about all our other impressive technical achievements but we still can't find a bit of wood behind drywall. Actually we probably can with Terahertz waves but we have to have contacts in the defence industry to swing that.

Does it have a manual calibration that you have to perform before measurement?

That was my comment. Given that UFH pipes have a flow temperature greatly in excess of what we tend to think about with insulation in other places, building regs don't discriminate (AFAIK) between losses at ambient and the directly heated screed. Therefore going beyond regulation minimum would seem to be sensible.

Oh yes, I could suggest any number of simple electronic circuits to provide a power switch but I wondered if there was a more direct way that anyone could simply and safely connect up a CT and contactor.

Close but no cigar: https://docs.rs-online.com/8122/0900766b80080c05.pdf The coil for this contactor requires 4.2VA at 110V so 0.038A or switching at around 10kW of generation. The question is, how happy would the windings of a CT be at 110V?

Looks perfect!

Being badgered about x-mas prezzie and all I can think of that might be handy is a stud finder Amazon because it's just about too late everywhere else. I looked but there were just so many and I don't trust any of the reviews. Figured someone here might have got one that actually finds studs, screws, cables etc.

Yes of course. I keep thinking in terms of export in relatively low power situations. If a relay pulled-in above, say, 20A flowing out of the generator then that'd be fine. Just needs a 1000:1 CT and AC coil relay that would operate at 20mA e.g. 1200 Ohms 24VAC coil.

Oh, what am I saying. AC would need rectifying then you've no idea re. import export. Scratch that.

That's interesting. Maybe a 1000:1 CT could drive a small relay (i.e. 13mA for 3kW generation) with a parallel diode to discriminate between import and export.

Haha, that's shut me up! 🤣 Well, not exactly. The ability to put variable power into an immersion comes from solid-state switching the power far more rapidly than a mechanical relay could. But in your case, as you've already figured out, that's unnecessary. Is there a software API for the generator output that's giving you that display?

"[Eddi] it's quite a complex and expensive bit of kit for what is a very simple situation" "the device I'm looking for would have an internet-linked sensor that detects exported energy and would then command the immersion element to turn on" Agreed the Eddi is overpriced by a significant margin but it's providing no more functionality than what you're asking for. You're underestimating what you would actually need to make the savings you're after.

Does this mean you're going down the EWI route? That would involve a considerable amount of additional expense - making the cost to address the problems with injected CWI look tiny. Insulation installers have lots of tricks to manage the problems you've highlighted except for your cable which really needs to be re-run, even though I'm guessing it's already effectively de-rated (you're not really using 19kW are you?) You probably read my views on EPS and cables, which chime with your findings from the supplier. But while I'd personally be OK with an 80A cable on a 32A MCB in insulation, it seems like it might be relatively easy to deal with this one item. Even if it just meant replacing it with a 16mm2 SWA cable in the cavity.

Given that you also say you have no carpet, I doubt if you have curtains either. Unless triple glazed with low-E glass, large windows will have a noticeable cooling effect on your skin as your body heat radiates away. To an extent this is also cooling the fabric of the room as well so the easy win here is curtains.

OK, that's a reasonable amount of insulation. I would expect it to take 4 or 5 hours to bring the room up a couple of degrees depending on floor finish. You really need a cheap temperature logger to see what's actually happening.

How is the ground floor constructed? For all we know the UFH could be shorting to ground. Of course it won't be but the first thing I noticed was setting the timer for 20oC at 6:30 - which smacks of you expecting things to warm up by 7, when you fire up the woodburner. The response time of UFH is going to be such that you'd come in and out of setback at a much earlier time. Do you have a log of indoor temperature throughout the day? I'm not so familiar with ASHP when used with UFH but it might be that people would even suggest having no setback at all.

You can eliminate the temperature sensor if you power the resistor with a constant current source. The voltage measured across the resistor is then proportional to the cooling effect of the airflow. You need to have quite a high resistor temperature in order to minimise the effects of ambient temperature (which of course is another parameter you'll be measuring anyway so can be compensated for). But for this reason I've smashed 6V bulbs to expose their filaments which can be held just on the verge of incandescence to maximise the accuracy. I did once try getting wind direction by having three such sensors in a triangle and attempting to correlate changes in velocity between them but I did it so long ago that I was using a BBC Micro to do the processing and never got sensible results. Quite fancy revisiting that idea with some ARM power.

I'm beginning to wonder how all this is going to impact on our energy security. The flipside of £40/day bills is the strain which that kind of energy demand puts on our generators and networks.

Just about everyone lives in a house for the most part of their lives. Building science should be in the curriculum IMO. It's a great practical application for some maths and physics that would therefore actually be of benefit to everyone.

Except for when they send you a photo of water literally running down the walls asking if you'll come and fix the leak 🙄 Seriously.

That looks like a steep roof pitch, 50o?

That's the first time I've heard that being said. I'm shocked.

But how airtight are the carcasses for your units? They're usually made from flimsy stuff at the back dry slotted into rebates. Liberal application of Ilbruck FM330 (doesn't have to be pretty) along the wall/floor interface would be my plan.

Thinking about how to revisit this job and I think I'll try a length of PVC tube on the end of the nozzle. Two man job - one to operate the gun the right way up and another reaching under the cupboards. When I say man...

Flir One for Android smartphones for £221 is the lowest cost thermal imager I know of. If you get one you'll find it incredibly handy for all sorts of things. I've been mapping out the location of my CH pipes as well as finding air leaks: