UFH calculations

[wookey]

I've done all my heat-load calcs for new workshop/extension (and revised rest of house accordingly), but I need some help doing the UFH calcs/layout.

Given a known worst-case heat load, how do I calculate how much pipe and at what spacing, and at what flow temp? I seem to have slightly too many variables.

Clearly floor-constuction matters. One room (2kW load at -1C, 27m2) is 150mm concrete+ 60mm screed containing pipe (i.e super-slow, high thermal mass).

The workshop (900W load at -1C, 14.5m2) is 50mmXPS (k=0.036W/m2K) under 12mm multipro (0.26W/m2K). How do I decide if I need ali spreader plates? The workshop is going to be mostly full of Oh, how I wish it was better so I'm planning to put all the pipe in the open bit down the middle as closely spaced as possible. Spreader plates (that I've found) go no narrower than 120mm spacing. That allows approx 40m of pipe. What temp would that need to get 900W out of given that construction?

There must be some standard sums for this but I've failed to find them online. Everyone just offers a 'design service', but don't state their assumptions (or allow for geeks who want to control everything with 1-wire).

Clues welcome.

Also any advice on suppliers and compatibility would be useful. Right now I just want to buy some pipe so I can put the floor down and get my shed back (a shed's-worth of Oh, how I wish it was better has been scattered round house and garged since March now). But that means choosing pipe, which means picking a size. I'm not sure to what degree picking a pipe effectively chooses a manifold? And choosing a manifold chooses actuators (how many threads are in use?). How compatible is stuff from different suppliers?

Should I pick PEX pipe or Pex-Alu-Pex? The latter stays when you bend it which is good, and is presumably tougher but costs a bit extra. Anything else I should know?

Given funny-sized pipe (e.g 16mm), how can I pressurise it if I haven't bought the rest of the stuff yet (e.g. manifolds). A suitable t-piece + pressure gauge + navitron solar system pressuriser seems like it should do the trick. Are there handy adaptors from UFH size to 'normal plumbing'?

That's enough questions for now... :-)

[pb]

There must be some standard sums for this but I've failed to find them online. Everyone just offers a 'design service', but don't state their assumptions (or allow for geeks who want to control everything with 1-wire).

I had Uponor and Maincor do the sums for me when we were fitting UFH.  Both of them were fairly happy to discuss their assumptions in as much detail as I wanted and I think both of them ended up sending me a spreadsheet with the calcs in.  I'll see if I can find a copy.

Also any advice on suppliers and compatibility would be useful. Right now I just want to buy some pipe so I can put the floor down and get my shed back (a shed's-worth of Oh, how I wish it was better has been scattered round house and garged since March now). But that means choosing pipe, which means picking a size. I'm not sure to what degree picking a pipe effectively chooses a manifold? And choosing a manifold chooses actuators (how many threads are in use?). How compatible is stuff from different suppliers?

It doesn't seem to matter very much.  The standard manifold fitting seems to be a 3/4" male thread and all the pipe suppliers then sell you the appropriate compression adapter to suit their particular pipe.  Folks like Antares can supply the adapters for all the common pipes and I think even Toolstation carry the appropriate bits for 15mm PEX and 16mm MLC.

Should I pick PEX pipe or Pex-Alu-Pex? The latter stays when you bend it which is good, and is presumably tougher but costs a bit extra. Anything else I should know?

I used a mixture of MLC and PB and there didn't actually seem to be much to choose between them overall.  For our first floor I had to thread the pipe through the joists and obviously that would have been a nightmare with MLC.  But for the ground floor, which was basically just a question of uncoiling the pipe and laying it in a double zigzag, I got on fine with both.  I'm not sure I'd want to use plain PEX which is sort of the worst of all worlds: it's almost as hard to bend as MLC but it doesn't hold its shape afterwards.

Given funny-sized pipe (e.g 16mm), how can I pressurise it if I haven't bought the rest of the stuff yet (e.g. manifolds).

For 15mm PEX/PB it's obviously easy.  For 16mm MLC I would buy a couple of the 2-port plastic manifolds from Toolstation or Screwfix (about £7 each if I remember right).  Or you can get couplers to go straight from 16mm MLC to 15mm universal compression: all the pipe suppliers do them, or Antares again.

[Richard Owen]

The workshop (900W load at -1C, 14.5m2)

With such a low heat load, are you sure you want to go to all the trouble of laying UFH?

Is there a little bit of wall you could just stick a rad on?

[titan]

It is a while since I did mine, Hepworth used to have some useful guidance figure on their site but I can't find it now. ISTR  that generally at the standard 200mm spacing and 15mm pipe a figure of 100W/m2 for solid floors and 75W/M2 for other constructions are used.( needs checking) Closer spacing and larger pipe only affects the speed of heating, but allows lower flow temperatures. I wanted separate manifolds without a blender and pump and the only supplier I could find then was Pulsar Direct which use 16mm Euroconas connectors. You can build your own manifolds from them from components, flow meters really help with balancing the loops,  and the prices were good at that time. They also did their own calcs for my installation supplied with the pipe and fittings. Personally I would get all the pipe and manifold bits together it will be much easier to fill , flush, vent and pressure the system  with it all connected. The flow and return manifold connections are BSP.  I don't think the Alu-pex is a big advantage as you need to fix the pipe anyway.

[wookey]

Richard, you have seen the average fettler's shed, right? Room for a radiator! Ho ho ho.

I don't see laying UFH as much of a faff relative to completely emptying the place for re-roofing and floor+ wall insulation.

Useful info there chaps, thanks.

When I asked about threads I meant for the actuators rather than the flow+return connections, but I guess that's useful to know too. Maybe it's 3/4" both sides?

[pb]

When I asked about threads I meant for the actuators rather than the flow+return connections, but I guess that's useful to know too. Maybe it's 3/4" both sides?

Usually the valves themselves are built into the manifold and the actuator itself just pushes a pin in and out, same as a TRV head.  So I'm not sure it makes any sense to talk about "both sides" of an actuator.  Am I misunderstanding the question?

[Richard Owen]

In which case, with such a small heat load, I wouldn't worry too much about it.

Your only risk is underheating it, so just cram in as much pipe as you can (which isn't going to be that much) and enjoy.

[wookey]

The only catch there is that at some point putting pipe closer together doesn't really help. (100mm? 50mm?) and there is a pumping cost (and length of pipe cost) to going too crazy. I can put in 39m at 150mm spacing.

Robbens site says that with floating floors you can get 70W/m2 with 55-60C water and 200mm spacing, which seems a tad disappointing. I was hoping for a lower water temp. 70W/m2 is just about sufficient so if I put it in at 100mm I might get to turn the temp down.

pb, by 'both sides' I mean one 'side' where the actuator head goes and the other 'side' where the UFH pipe fits in.

[offthegridandy]

I wouldn't put UFH into any floor other than solid conc or screed my self.  Done it under wood floors using pug and spreader plates.  The efficency was lousy against the rest of the property.  Ripped the floor out after 2 expensive years and put in a beam and block and screed floor and bills went down  by huge margin.  And it was great fun fitting a beam and block floor underneath the in situ pex pipes.

In a small area like yours I'd space pipes at 200centres and adjust flow rate on manifold.

Andy

[knighty]

are you going to be heating the shed all of the time, or just occasionally when you need it ?

if you're going to heat it all/most of the time... it doesn't really matter of there's piles of stuff on top of the floor... the floor will heat the stuff ontop of it and then that will heat your room....

(even without the pipe under it, if the stuff in the shed is cold it will suck a lot of the heat in)

[wookey]

Just occaisionally. Which may in practice only keep my feet warm, but I'm hoping that a large radiative surface will help if 'feel' adequately warm - we'll see.

[winny]

I recently installed ufh (concrete) and decided on a diy system, made own manifolds etc and instead of using actuators, I installed radiator style thermostatic valves in each room.  ufh loop from flow manifold runs to the thermostatic valve at a convenient point and then continues undrfloor through the rest of the loop and then back to the return manifold.  Works very well!

I'd agree with the comment about putting more pipe in and regulating the flow, I ran short of pipe in the en-suite and it doesn't get quite as warm as I'd like.

Make an educated guess and go for it!

[acresswell]

Wookey,

realise your last post for this topic was in January, so it might be too late - but I've just had a thought (whilst thinking about my own pipe layout for UFH)

Could you organise the pipework layout so the the flow starts with the pipes in the centre (relatively uncovered) part of the room and then gradually works outwards towards the edges of the room (getting further apart)?  It would mean that you'd get most benefit from the hottest flow water in the middle of the room, but also have a bit of heat under the clutter to avoid any issues where warm air meets cool walls and ventilation is restricted by clutter.  

Alternatively, could you run two separate pipe loops under the floor?  One would be central, and one around the outside (under clutter).  You could then start by just connecting one to the manifold.  If it turns out to be insufficient then you connect the second loop - either to the manifold (in parallel), or in series with the first loop.  If it turns out that you didn't need the second loop then it's only cost you a bit of pipe and time...

Adrian

[wookey]

I've been real busy, so not it's not too late, but I have just been told I need to get this sorted this w/e and stuff bought next week :-)

And that variable-spacing layout is indeed a good idea.

I've downloaded the British standards for UFH design in the meantime, which I hope will help with some first-principles design.

[wookey]

Whinny - how did you make your own manifolds? I'm very interested in using radiator-style TRV's because I want to put HR20s on and thus have proportional flow control on each loop. Normal manifolds don't provide enough spacing for this. It's not obvious to me how to string a load of radiator valves together to make a manifold