UFH Design Review, Passive Slab

[Nickfromwales]

7 hours ago, Duncan62 said:

I have avoided under shower and kitchen cupboards (some of them) simply because I have 3 x 100m loops, which works nicely for buying and fitting.

I shall not do serpentine as it looks (much) more difficult for this mortal to install

OK.

I think you should have more loops / zones. If I was designing this as' your M&E guy', I'd have a loop per space. The bathroom should be at 100mm o/c and be as fully populated as is practicable. Space A-01 should be fed by taking the loops under the wall. Space A-02 is fine. A-07 should also be at 100mm o/c as it is a rising space to FF.

 

Consider the effects of the days solar gain, and how it will affect each space. IMHO, the current design does not. You have some small, confined spaces, which will 'out-perform' the other, larger open areas.

[John Carroll]

1 hour ago, Duncan62 said:

 

Thank you Terry: I plan to use the bottom side wall in the plant room which is 900mm wide. Enough for a 3x Out and 3x Return manifold + pump?

 

Yours doesn't look too big?

 

 

The Willis should be installed  with the heating element underneath otherwise air can build up causing problems.

[Mike]

2 hours ago, Duncan62 said:

I plan to use the bottom side wall in the plant room which is 900mm wide. Enough for a 3x Out and 3x Return manifold + pump?

Mine just fits in 900mm, excluding the filling loop (though that could be repositioned), but doesn't have a plate heat exchanger like @TerryE

[Duncan62]

What UFH pipe do people recommend for installation direct to mesh, 75mm below the surface with 200mm total depth of slab?

PEX AL PEX or PERT AL PERT?

16mm as standard?

and why?

Edited April 24 by Duncan62

[JohnMo]

8 minutes ago, Duncan62 said:

What UFH pipe do people recommend for installation direct to mesh, 75mm below the surface with 200mm total depth of slab?

PEX AL PEX or PERT AL PERT?

16mm as standard?

and why?

 

I like Pert-al-Pert as it has no memory so is easy to work with. Modern UFH I would only use 16mm - easily available, carries plenty of energy, low pressure drop. Anything else size wise is just a bad choice.

[Duncan62]

1 hour ago, JohnMo said:

 

I like Pert-al-Pert as it has no memory so is easy to work with. Modern UFH I would only use 16mm - easily available, carries plenty of energy, low pressure drop. Anything else size wise is just a bad choice.

 

great, thanks, like this?: https://underfloortradesupplies.co.uk/product/komfort-16mm-x-100m-pert-al-pipe-5-layer-barrier-white-multi-layer-ufh-pipe/

[JohnMo]

10 minutes ago, Duncan62 said:

 

great, thanks, like this?: https://underfloortradesupplies.co.uk/product/komfort-16mm-x-100m-pert-al-pipe-5-layer-barrier-white-multi-layer-ufh-pipe/

Something like that

[TerryE]

On 05/04/2024 at 00:10, John Carroll said:

The Willis should be installed  with the heating element underneath otherwise air can build up causing problems.

 

I have often pondered about this one.  It was first pointed out by JSH referencing the manufacturer installation instructions, and IIRC he got a bit heated about this point.  Why?  The primary use of the Willis is to act as an external heater on a copper vented (unpressurised) H/W cylinder.  Here we have open-loop heating constantly replenished mains-fed water.  This carries an element of dissolved air which will tend to come out of solution during heating and build up in inverts -- hence the recommendation to fit the Willis inverted.

 

TBH, even if I was redoing my CH system, I would still use a Willis and I would still fit it heating element up, because this issue doesn't apply for this use: the water is a small closed volume running in a pumped circuit.  In our case I filled our UFH loops 7 years ago, topped up with inhibitor / unfreeze, and then pressured the closed system to 1 bar.  Occasionally over the next month or so, I bled the system at the manifold to let out any air coming out of solution.  In the process the tiny amount of water lost when bleeding was taken up by the expansion tank dropping the pressure to 0.8 bar or so.  I then topped up the system back to 1 bar, and that's it: 7 years later, the system is still at 1 bar.  There is no more air to come out of solution.

 

So air build up is just not an issue here, and the Willis works happily in any orientation, and I am happier with the wiring and thermostat setting on top  where I can see them and have easy access.  So yes, for me heating element up works best.

 

Edited April 26 by TerryE

[Nick Laslett]

On 24/04/2024 at 13:12, Duncan62 said:

What UFH pipe do people recommend for installation direct to mesh, 75mm below the surface with 200mm total depth of slab?

PEX AL PEX or PERT AL PERT?

16mm as standard?

and why?

Some earlier discussion here. 
 

 

According to Wundatrade they recommend their Pert-Al-Pert for over floor systems. They recommended their PexB-Al-HDPE for screed. When I was researching this topic, I found very little to confirm a specific pipe for going into a concrete insulated slab foundation. 
 

https://www.wundatrade.co.uk/shop/home/water-underfloor-heating-solutions/joist-floor-heating-pipe/16mm-hdpe-al-pex-pipe/

 

[John Carroll]

On 26/04/2024 at 11:23, TerryE said:

 

I have often pondered about this one.  It was first pointed out by JSH referencing the manufacturer installation instructions, and IIRC he got a bit heated about this point.  Why?  The primary use of the Willis is to act as an external heater on a copper vented (unpressurised) H/W cylinder.  Here we have open-loop heating constantly replenished mains-fed water.  This carries an element of dissolved air which will tend to come out of solution during heating and build up in inverts -- hence the recommendation to fit the Willis inverted.

 

TBH, even if I was redoing my CH system, I would still use a Willis and I would still fit it heating element up, because this issue doesn't apply for this use: the water is a small closed volume running in a pumped circuit.  In our case I filled our UFH loops 7 years ago, topped up with inhibitor / unfreeze, and then pressured the closed system to 1 bar.  Occasionally over the next month or so, I bled the system at the manifold to let out any air coming out of solution.  In the process the tiny amount of water lost when bleeding was taken up by the expansion tank dropping the pressure to 0.8 bar or so.  I then topped up the system back to 1 bar, and that's it: 7 years later, the system is still at 1 bar.  There is no more air to come out of solution.

 

So air build up is just not an issue here, and the Willis works happily in any orientation, and I am happier with the wiring and thermostat setting on top  where I can see them and have easy access.  So yes, for me heating element up works best.

 

Not a problem, as you say, with a pumped Willis, but certainly (IMO) will tend to cause problems with the normal installation as the outlet temperature will run much higher due to the very slow circulation rate and release more air?,  I have read of the heating elements failing due to air build up if installed with the immersion on the top,