Fast getting to the stage on our barn conversion where various pipes, ducts, drains, etc will need to go in below the floor slab (its nearly all dug out) to take the various services - water, electric, etc.

We know where most of these need to go, however

I'm thinking now would be a good time to put a duct or ducts in to take the pipes from/to the yet-to-be-decided heat source, between the utility room and the outside of the barn.
This could be a GSHP or other such heat source, so I guess the ducts would need to take some sort of insulated pipes? (flow and return)

Has anyone got any ideas for sizes?

Or should I really decide what is happening before I do this bit!

Yes, I was thinking waste pipe would be good, or maybe something the same size but flexible so that I can curve it up gradually to come up through the floor of the Utility room.

Be very careful. I initially planned to use a twinwall duct for ASHP flow and return - which would require something like the JG Speedfit Barrier Layflat Plastic Pipe Coil - 28mm.

My builders merchant laughed as the term layflat gives the completely wrong idea. I am so glad I took the hint.

That pipe is as stiff as old boots. It would be a real issue to pull it in a duct with bends of any sort even 4 inch long radius bends.

In the end I covered the pipe in a hair lagging and directly laid it into an eps channel cut with a hot knife channel tool. The hair lagging is to keep the pipe away from the EPS (just in case of plasticiser issues although JG said it wouldn't be an issue). I broke through the wall just below DPC level at the ASHP end and created a box in the EPS at the other so I could access the right angle joint at the other end.

I'm not saying it can't be pulled through but my thinking was that the pipe should last as long as the UFH pipe. and at that stage the owners will be thinking of replacing the UFH and the ASHP pipe together.

I have 3No. 75mm eps layers under the UFH rc slab. The first eps layer was laid, then I cut the ground floor H&C water supplies in to the bottom layer (ducted as per wras rules), then laid the 2nd layer of EPS, cut for the feed and return ASAP, then laid the top layer of EPS. the H&C supply will run without joints from the manifolds to the taps.

Being dumb here, is it for the water ground loop of the gshp? Why does it need to be insulated, if it is under the slab insulation and in thermal contact with the ground?

(Edit: I could see the 'cold' and 'less cold' ends of the ground loop will need to be separated to stop heat from short-circuiting from one to the other)

Understand it needs insulating where it is inside the thermal envelope of the house, to avoid condensation.

That skinny insulation looks too thin for heat conservation. If the pipes are for an ashp or external boiler then they'll need more insulation.

The pipes are to get from the utility room inside the building, to the outside. To connect to a future yet-to-be-decided heat source. I'm thinking the manifold for the underfloor heating will go against the exterior wall in the Utility room.

I'm not making it very easy for myself - I think I should put more effort into choosing the heat source.
I have made a few enquiries about GSHP and maybe even water source but I don't think the pond is big enough at 500 square metres.

Posted By: jfbi used twin wall duct built into a stone wall for future use

I think we will have to do something like this to bring the pipes through the 450mm thick wall of the barn. Due to the sloping site the ground level is lower at the back so these pipes can come straight through the wall and exit at ground level.

GSHP ground loop pipe is not very flexible IME... even if you use PEX-A (which is more flexible than the usual HDPE-100). Unless your duct is pretty-much straight line you should give a bit of thought to pipe bend radius and access. Be wary of minimum permitted bend radius too... that is not the same as practical-to-pull-though bend radius, especially in cold conditions. It's a lot easier to lay it in a trench and cover it.

Do you know how many pipes you will have? Is the manifold going inside or out?
The last barn we did had eight 40mm PEX-A pipes coming in (through a trench insulated with Foamglas and then straight up through floor)... but then our manifold is indoors in the plant room.

Don't know if the attachment will work. These are the floorplans that we are currently working to, but at this stage we still have flexibility to make amendments (floor is almost dug out)
I'm thinking the pipes would exit/enter in the top left hand corner which will bring them out at ground level.

This could be a GSHP or other such heat source, so I guess the ducts would need to take some sort of insulated pipes?

and not forgetting duct for both electric power and control.