Underfloor wet heating - alternative to mixer?

[pjdesign]

Boiler Temp 80 ish. Baz

[Tim]

Doh! Yes - that would be an irrelevant consideration in my setup,so I didn't think of it - but I could see that it would matter in certain types of installation.

Ta.

Timbo

[Tim]

OK - can help from a physics POV here... The inflow pipe will try to get to 80C...

But with a low flow rate, it will be unable to maintain the surface of the floor at a high temperature. Sufficiently low flow rate, and it won't even manage to maintain a decent thermal gradient from the pipe to the surface.

So the low flow rate 80C water entering the pipe will be instantly cooled and will lose a little bit of heat (as in joules) into the floor and thus drop temperature quickly.

Yes - that works in theory...

Rather like spilling exactly one drop of boiling water on your hand. Doesn't really do much.

Tim

[Pete C]

Hi,

What sort of floor are you planning to have? If stone then a counterflow system should be fine. It may be warmer near the flow/return end, so that part could be located where the most warmth is needed.

Also what is underneath will make a difference, if a thick slab then it will average out the heat better than a thin screed and insulation.

If you have a radiator valve over the warm end, that could accelerate it's switching off as the floor warms up so to help minimise overshoot.

If you want to limit the temperature of the room overall, then another radiator valve in series elsewhere will control the room temperature.

Eg for a conservatory, if more heat is desired by the windows, start there and zig zag flow and return back towards the wall of the house.

Also spacing the flow/return pairs of tubes slightly wider at the flow/return end and slightly closer at the other end will help to balance the output if needed.

If really concerned about it try temporarily laying the pipes into sand with the tiles on top, that would give some idea of what to expect.

cheers, Pete.

[The Natural Philosopher]

I think yiou have it right,.

Bite the bullet and use the proper system.

[The Natural Philosopher]

Thats what I bought - polyplumb 8 way manifold,aux pump, two way valve amd loads of isoaltaion and drain taps and balancing flow meters for each circuit and a temp reduction valve. All for about £250 IIRC, and it was a piece of piss to install. The manifold handles all the polypipe underfloor circuits, and the two main connections simly go to flow and return on the boiler.

The only tricky bit was to put in a relay so that the boiler pump could be called up for ordinary CH without forcing the UFH pump on as well.

[The Natural Philosopher]

My manifold/pump assy. takes up less space than the radiator I have in the airing cupboard.

Anything that isn't designed properly or controlled properly is going to perform badly. You are a classic case in point.

>

[The Natural Philosopher]

Dream on Tim.

When I levelled my U/F heated floor prior to laying laminate, you could see the wet bits betweenteh double spiral, and the dry bits above it.

The doble sopral simply spreads teh overall heating effect more or less eenly across teh total floor area.

It does not stop localised hot spots on the floor surface, still less inside it.

I think you are asking for a cracked screed.

[Tim S]

I'm designed badly? As for control, you'll hav eto ask my wife :-/

Timbo

[Tim S]

Yeah, I think that considering I'm going to blow a wad on the conservatory (have 2 bods in today to quote) I'll put the better system in just to be safe.

Tim

[Tim S]

That's certainly very interesting...

I guess it's one of those things - it either works OK forever or it buggers your floor. I suspect that in many cases the Danfoss would work, but I'm one of those unlucky sods that if it's going to pear up, it will do it to me!

[G&M]

And so parts of the floor would overheat. This would be especially damaging for a wooden floor.

[The Natural Philosopher]

[The Natural Philosopher]

Yes. I have a bit of a 'cold bridge' near one door threshold - no way to avoid it really, and you can walk across teh floor in bare tootsies, and know exactly where it is.

Screed is not a massicvely good heat conductor at all.

Iadeally you want zillions of tiny pipes all at 40C or so in it. Practically a double helix or two with regulated flow temps is the best solution.

Apart from the now sticking motorised valve, my system was dead easy to install, and has after all the calcs and pressure tests etc, performed exactly as it was supposed to.