Underfloor wet heating - alternative to mixer?

[Tim]

After lots of helpful comments on my plight to redesign my Dad's CH using a thermal store system, I was wondering if anyone could comment on this underfloor heating component:

the "Return Temperature Controller"

It claims to be a way of avoiding a 4 port mixer + local pump assembly by regulating the water return temperature.

The only thing I can see wrong is that it of course still presents

70+C water at the inflow end of the underfloor pipework.

So parts of the floor are presumably going to get rather hot???

Would you say my instincts are correct or would this type of regulation actually work?

Ta muchly,

Timbo

[Tim]

OK - one adittional thing... I just found the installation manual on their website and it does mention that the heating pipe must be run in a double-spiral config, so a flow and return pipe are alway adjacent.

Wonder if that's how they make such a simple system work? ie they are relying on the thermal conductivity of the screed to reduce the inflow/outflow differential and also using the return flow to indrectly cool the inflow... Sounds didgey - but it *could* just work?

Timbo

[pjdesign]

Hi Tim The valve is a Danfoss

used them in my conservatory. No mixers, works a treat. We use the room all the year round. It is super I wish I could do the whole house like it. Baz

[Christian McArdle]

It didn't give me a warm fuzzy feeling reading the specs. The "solid floor only" restriction is probably about the inability to limit temperatures to sensible values. There's probably an item in the instruction manual saying to run the boiler at 50C or something.

You really need to go the pump/TMV route.

Christian.

[Christian McArdle]

Ah. That makes more sense. It controls the power by varying flow speed. As this will produce a large temperature difference, you need to have the hot entrance pipes next to the cold exit pipe to ensure average heat transfer over the whole area.

However, the system would lead to localised hot spots, unless the floor is sufficiently conductive to ensure that the hot and cold parts produce an average.

At one end of the spiral, you get a 70C and a 20C pipe. In the middle of the room, you both pipes finally meet at around 45C. The approach gives an average 45C anywhere in the room, with some variation, however, depending on the exact flow rate chosen.

I'd probably still want a proper TMV and pump, though, even for a solid floor. I like the idea of a simple thermostat setting to set the floor temperature.

Christian.

[Tim]

The only fuzzy feeling I got was "ooh, that's simple to install and small and neat".

They do claim the boiler can run at a standard 81/70C.

I'm completely sure your instinct is well founded - I'm just being cheap and was wondering whether it is too good to be true or not. I notice that Baz found his Danfoss works in practise, so I'm still weighing it up...

'twoud be neat and simple though for one single little circuit - it seemed a lot of effort to install a 4port mixer and an extra pump for one room.

Thanks as ever for your expert opinion.

Cheers

Timbo

[Tim]

Hi Baz. Thanks for the feedback. I'm still weighing it up :?

Timbo

[IMM]

Make sure the flow temp is no more than 50-55C. A mixer should be used to ensure this, or a condensing boiler set to 50Cish and a priority system for DHW where the boiler temp is ramped right up. ECO-Hometec do boiler just for this.

[Christian McArdle]

Is a pump and TMV that much work to install? I suppose as time goes on, I forget that these things could be a little intimidating if you haven't done much plumbing before. I presume someone has packaged the lot into one box, so you just connect the room up to 2 holes and the CH circuit up to the others and apply electricity.

Christian.

[IMM]

Having 80C water through UFH pipes is ridiculous. It makes the floor far too, hot. Then there is expansion contraction, etc. The Danfoss system is assuming that the supply water is less than 55C.

No need for a 4 port mixer. A normal cheap 3-port will do.

[Tim]

I suppose not. It was mostly the extra pump that put me off, what with standard CH pumps being bulky. Unless they do little pumps for this sort of thing?

Tim

[pjdesign]

IMM. Read the link

"Maximum flow temperature 90°C "

" Used in systems which are predominately heated by radiators (normal system design temperatures 82/71°C) and where Underfloor Heating represents only a minor part of the system, for example a single room or small extension "

The water will not flow through the pipes at 82/71 because the water is only let out of the system after it has given up some of it's heat, so it is only topping up.

Baz

[Tim]

What's the practical difference between 3 and 4 port? I know roughly what they look like, so I presume the 3 port just short circuits the pipework under the floor when less heat is needed?

Would you use a 4 port if you needed more than one circuit off it?

Thanks :)

Tim

[IMM]

UFH is going to take up space with manifolds etc. If it is not designed and controlled properly they are perform terribly badly.

[IMM]

That is nonsense. A 90C floor is very uncomfortable to walk on.

[IMM]

A 4-port proportioanlly reduces one loop in favour of another. If mid way

50-50 to each. If open 25% then 25% to one and 75% to the other.

The simplest systems are from the likes of Polyplumb. Go to their web site. their equipment is expensive, but you can buy the component parts and do it yourself.

[pjdesign]

The floor does not get any were near 90. Surface temp is 20 to 25. I am using this system in my conservatory. Baz

[Tim]

Yes - I understand that bit - just wondered in what situations a 4 port would be called for, rather than a 3 port?

Wow - you're not joking:

[Quote from UNDERFLOOR HEATING PACK FOR 20 M SQ - SOLID FLOOR

Price you pay including VAT: £715.00

System includes Polyplumb pipe laid at 100mm centres to cover 20 m sq, Polyplumb easy lay floor panels, Polyplumb edge insulation, Polyplumb zonal regulation unit (consisting of pump, mixing valve and pipe stat), Honeywell room thermostat, Polyplumb pipe cutter as well as sufficient Polyplumb Pipe Stiffeners, Spigot Elbows and Tees.

System is designed to connect to existing central heating. Pack excludes necessary insulation required for floor slab [End quote]

Timbo

[IMM]

What is the flow temp in?

[IMM]

Look at:

the 4-port is half open 50% of the boilers flow through the UFH circuit and 50% back to the boiler. If it 100% one way it goes all into the UFH.

100% the other way 100% back top the boiler by-passing the UFH. The boiler return always has the same volume of flow back to it.