Wet UFH in new floor slab.

[Scarlet Pimpernel]

I know this isn't the plumbing forum, and I know it doesn't belong in Building, and I know I already asked the question once, and I know it's already been deleted, and I know I already received one response to the now deleted question. But I'd appreciate a more nuanced discussion. Sorry about the length of the post (I do have a reputation to keep up, but sometimes verbalising the problem helps to resolve it).
I'm going to be replacing the floor slab soon in the converted barn and ufh is an obvious future proof option. I have all options open for placing of insulation and ufh pipes. Ground source or air source HP would be the ideal heat source, but roof mounted solar panels is another possible option. There's plenty of roof and plenty of garden. I don't envisage installing the heat source pump for a while yet. I do have a Heat Recovery extract/intake system installed. I want to install the ufh pipes in the slab, and connect them to a manifold.
There's two rooms, one is about 60M², and t'other is about 25M². I'm happy to consider this one room as 20M² (it's the entrance hallway), and the big room as 3 X 20M². I understand that 20M² is the kind of ball park figure for an ufh zone. I'd envisage locating the manifold on the dividing wall in the smaller room (under the stairs), with pipes from the larger room exiting the floor and going through the wall to join the manifold. This would avoid six pipes going through the doorway.

The big question is, locate the pipes in the floor slab proper, or in the screed? Our heating pattern here is something like: April to October - no heating required (except for the very occasional cold evenings.
November to March constant background heating required, with January requiring a little boost from time to time.
Thus a constant 24 hour system during those winter months, with a long heat up time would make more sense. With the system off during the summer months. Indeed the mass of the walls, etc is a beneficial way of keeping the house cool in summer, and we occasionally close the shutters to avoid too much solar gain.

So despite advice already received, and with that additional information, do people think that locating the pipes, in the screed, but on top of an insulated floor slab is preferable to placing the pipes on top of insulation on top of the floor slab.

Edit, BTW, there is a fireplace in the big room.

 

[securespark]

do people think that locating the pipes, in the screed, but on top of an insulated floor slab is preferable to placing the pipes on top of insulation on top of the floor slab.

Bit confused here, they sound the same. Could you sketch a diagram?

 

[Scarlet Pimpernel]

Bit confused here, they sound the same. Could you sketch a diagram?

Not really needed, one system has the insulation below the concrete with the pipes laid on top of the concrete (with some protection or pipe clipping mats), the other has the insulation laid on top of the concrete, and the pipes are laid on that.
So one system does not insulate the concrete slab from the ufh, the other does.
I believe something like a 4 hour cycle is needed for the heating of the system where the insulation is below the concrete, whereas something like a 2 hour cycle is expected for the system where the pipes are insulated form the concrete slab.

So in one system the concrete slab is included in the insulation envelope, in the other it isn't.

 

[securespark]

Just a lowly spark, but having seen a fair few of these being constructed over the decades, I would say the latter system with the shorter cycle.

 

[IT Minion]

Thermal mass!

If you have the slab above the insulation then your floor will absorb and release heat slowly all the time. That means it'll soak up some heat during the hot summer days and release heat (keeping a steadier temperature) overnight when the heating is off.

The catch is that it will take longer to warm up when everything is cold.

 

[sxturbo]

You poor the slab, lay insulation, then ufh pipes, then screed

 

[gasbanni]

You poor the slab, lay insulation, then ufh pipes, then screed

Seconded.......If you have any doubts contact one of the manufacturers they will even draw up a layout and spec for you.

 

[Scarlet Pimpernel]

Thank you for the advice guys, but I was really looking for a discussion to compare the two different methods. Currently I'm erring towards including the concrete slab within the insulation envelope because in the conditions outlined, I suspect it would be beneficial, i.e. including the concrete slab within the 'heat store'.
In addition, as IT Minion suggested the concrete slab would serve it's purpose better during the summer months if included within the insulation envelope.

The other point that I would appreciate guidance on, is the ufh pipework exiting the floor and going through the wall to join the manifold, in order to avoid 6 pipes going through the doorway (for the 3 zones in the large room). Is this normal practice and what do I need to be aware of?

 

[jeds]

It's a question of thermal response. The heavy slab provides a battery of heat but also slower heat absorption and emission. i.e. a low thermal response. Insulated screed option provides higher thermal response. Warms up quicker and cools quicker. Which is best depends on how you use the spaces? If use is a higher percentage of the day then low thermal response might be an advantage. If, like me, you are out a lot then it would waste energy.

As a practical example; In my house I don’t programme the heating to come on at any set time. I’m home at different times, and sometimes not at all, so I don’t want the boiler blowing away when I’m not there. I come home and turn on when I need it. The house has high thermal response so it warms quickly – 10-15 minutes. It cools fairly quickly but I don’t want heating on at night anyway. It suits me and it’s cheaper to run. The alternative would waste too much energy for me. The house would be warm when I don’t need it.

 

[Scarlet Pimpernel]

I appreciate your comments, jeds, but I'm also aware of the cooling quality of the mass of the slab during the summer. Even the opportunity to have a reversible system, if needed, i.e. under floor cooling, if such a thing exists. As said previously, occasionally it is necessary, during the summer, to close the shutters to reduce solar gain.
We have mesh on the windows, so leave the windows wide open, even overnight.

The heating source would be ground or air source heat pump, or solar panels, so running costs would be reduced.
I would envisage a log burner going in to provide the occasional boost.