water underfloor heating installation

[Tim S]

TheOldFellow coughed up some electrons that declared:

[Tim S]

Grimly Curmudgeon coughed up some electrons that declared:

It's really about time someone did that sort of system based with PIR foam (aka Celotex). The extra efficiency would be a winner.

Cheers

Tim

[YAPH]

The OP said he's got screed floors :-)

[Doctor Drivel]

The system pump can pump past the TMV and into the loop, although at reduced pressure/flow. Ideally a positive stop is needed such as a zone valve. Then no circulation. When using a spring loaded NRV best after the pump. However if the system pump has a high pressure, some zones may have closed down, it may be best to have one on the UFH return as well and the UFH pump turned up to open both NRVs. You don't need to be a God to see that.

[YAPH]

So basically using NRVs to add resistance to the UFH loop to help prevent flow driven by the system pump? I think you could acheive the same effect by using your ordinary balancing valves to increase the UFH loop resistance.

But basically a non-zoned UFH loop is a bit of a kludge (as is much of conventional CH practice, to put it in context). Zoned with a motorised valve is preferable.

[Doctor Drivel]

You will still need a NRV after the pump and balance it down at the return end. Without the NRV heat will work its way into the UFH loop by force (pump) or convection.

Yep, a spur of the rad circuit is a kludge, as they operate at different temperatures, and operate very differently to each other. In a well insulated house, as say in a bedroom, it can work very well. It needs a quicker heat up than in a screed. Having it in soft copper at rad temperature and not touching the wooden floor above with masses of rockwool beneath (acts as sound insulation as well) with cheap cooking foil over the rockwool to reflect upwards (available cheap in commercial rolls) with thermostat control can do it. Of course no carpet on the floor as in all UFH.

You get sound insulation and no rads - so probably well worth it.

Yep most CH system are a kludge as they are just cheap, designed by rule of thumb, retrofit systems.

[YAPH]

Well that's even more of a kludge. I did it once with a very small area of UFH in the return of the radiator in a shower room. The area was so small it wasn't worth even bothering with a pump and TMV (it was as much to warm the tiled floor as to actually heat the room).

But I meant that a pump+TMV off the main heating loop, but not zoned, is a bit of a kludge.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember YAPH saying something like:

From the OP: "I am thinking to refurbish a first floor flat with screed floors and install water underfloor heating."

Now, I took that to mean he's putting in screed floors in order to install UFH. Disambiguation needed, to quote a horrible phrase beloved of wikipedia.

[YAPH]

Fairy Nuff, though if the OP's thinking of installing screed floors in a first floor flat that doesn't already have them he needs more than disambiguation ;-)

[Doctor Drivel]

If the floor is wood and suspended and the UFH circuit is spur off the rad circuit, I would use 12mm soft copper clipped to the side of the joists and running through the joists in 22mm holes, so the copper does not touch any wood. The UFH circuit then runs at rad system temperatures and heats the space between the floor boards and the insulation beneath. A room stat and

2-port zone valve gives on-off positive control and the same system pump is use - better if a Smart pump. In effect the UFH circuit is treated as a rad, and of course rockwool and foil under as I described. Very cheap to do. The room temp in the UFH system can run lower than with rads, as with all UFH. Danfoss make some mechanical wall stats that have the pipe to them. BES sell them. These gradually close the flow or return reducing flow in to the UFH loop. A dedicated UFH Smart pump can then be used. The circuit maybe on 80C initially until warm up and then the stat reduces the flow into the loop and the pump mixes with the return water with the flow reducing the UFH loop temperature.

[YAPH]

I did something like that in my kitchen, years ago. Rockwool suspended on netting slung between the joists, 15mm polybutylene run up and down the gaps between the joists, suspended close to the floor surface, plywood and ceramic tiles on top. All connected into the regular CH via a TRV under the floor set to open when ambient temp under the floor falls below about 18C, IIRC. It generally keeps the room nicely warm and pleasant to walk on, though a bit patchy - some hot and some cool patches.

[Doctor Drivel]

I assume the TRV had a remote temperature sensor. It should work well enough, as the water/heat will be restitcted through the UFH loop when approach setpoint. As I mentioned, Danfoss have dedicated mechanical UFH valves for the task.