What to order for ground floor UFH.

[Nick1c]

Just as the weather turns we are ready to put in the UFH piping & think about pouring the slab.....

I sent the details to Wunda, asking for three zones, a Wilo pump and probes to put in the slab (thinking that it would be useful to know the slab temperature if using active cooling to ensure it stays above the dew point). 

This is what they have suggested:

 
   Specialist Tools
 
Components Qty
 
Wilo 22kW Yonos PARA (A) Rated 1 WUNDA PUMP STATION - Wilo

1 Isolation Valve (Red) 1

Isolation Valve (Blue) 1

6 Port Manifold 1

12 Zone Wiring Box 1

Actuator Valve 6

Touchscreen Digital Thermostat 3

Floor Probe 3

Perimeter Strip Insulation - Screed (50m Roll) 1

Perimeter Strip Insulation - Screed (25m Roll) 1

Cable Ties 10

16mm Wundapipe (80 metre coil) 5

16mm Wundapipe (100 metre coil) 

 

Having spent some time reading the UFH section on here & also looking at @JSHarris ‘over thinking things’ part of his blog I have some questions. 

- is it worth zoning the gf at all? It will be a 3 bed, 2 bath, reverse level house with near Passivhaus levels of insulation and good air tightness, there will be 2 people in it for most of the time. 

- as the slab is in an eps raft do we need expansion tape? Doesn’t the eps have enough give?

- is the in slab probe a good idea (it’s all of £5 IIRC)?

 

Anything else to think about?

 

TIA

[Jeremy Harris]

I don't think zoning really works very well with UFH in a house that's near passive house performance, TBH.  It changes temperature so slowly that I doubt that any UFH could effectively maintain one heated room at a different temperature to another.

 

Not sure what you mean by expansion tape.  Where would it go?

 

I fitted a temperature probe in a part of our slab that's fairly well clear of UFH pipes.  It slightly under-reads the floor temperature, perhaps by about 0.2°C or so.  Not sure why.  It was useful to satisfy my curiosity as to how things behaved, but I don't think I've looked at the slab temperature more than once or twice in the past couple of years, as it tends to be pretty stable.

[Nick1c]

My mistake, it is the 75m of perimeter strip insulation I was talking about. 

If not via a probe is the slab temperature controlled using flow/return temperatures when cooling?

I also forgot to ask if people feel that an all-singing all-dancing thermostat is worth it. 

Edited September 23, 2019 by Nick1c

[Jeremy Harris]

Just now, Nick1c said:

My mistake, it is the 75m of perimeter strip insulation I was talking about. 

If not via a probe is the slab temperature controlled using flow/return temperatures when cooling?

 

I gave up on trying to control slab temperature, and just switched to a couple of ordinary room thermostats.  They work very well, although I needed to set them to use their smallest hysteresis, easy enough as they have a switch on the back to do this.

[ProDave]

Are you looking for a packaged system or do you want to put it together yourself for the minimum cost?

 

I bought most of my stuff from ebay.  A 5 port manifold that came with a noisy pump that I later changed for a Wilo.  five £10 actuator heads, a £50 "no name" 3 channel manifold controller, and a 250 metre coil of pex al pex UFH pipe (I had two 50 metre lengths left from a previous job as well)

 

I do have the 3 downstairs rooms on their own thermostats but you won't get much temperature differential from one room to the next.

[Nick1c]

Due to lack of knowledge and time I plan to get it all from Wunda, it sounds like they are competitive on price and have good product. I do plan to lay it myself. 

It sounds like I may as well go for a single zone, as I won’t loose anything & it will save on controls. 

[Oz07]

I tried to get quotes without zoning. These people are off their heads if they think you could have any noticeable temperature difference in a well insulated house. For some reason they don't seem to agree with this school of thought. I think the expanding tape will be good for around pipes, but you could pick up a small roll from a merchant yourself.

[Andrew]

I’m in a similar situation. Our UFH requires twelve loops in the main house. I’d like this to be a single zone but the Wunda documentation says that their thermostats can only control a maximum of 4 actuators. Which is why I guess they have split it into 3 zones on our quote.

 

I have no idea if that’s a real limitation or if any other thermostats can control more than four actuators.

[ProDave]

If you look at the Wunda controller, it is simply a matter of how many terminals and how many wires you can get into them, and you really can't get more than 4 actuators connected to each zone.

 

But step back a bit.  The purpose of a "manifold controller" is to individually open / close each zones actuators, while at the same time turning on the pump and giving a call for heat output if any one zone is calling for heat.

 

Now if you are not zoning, and instead having all the zones operating as one, then a re think is needed.  You don't need individual actuators. You don't need the logic to turn the pump on, so the logical extension of that, is you don't need a manifold controller.

 

So a simple manifold without individual actuators. You simply turn the pump on and call for heat directly at the command of the programmer and perhaps a single room thermostat.

 

I would expect most of the UFH companies to regard that as completely alien thinking and just quote for the standard kit.

[Nickfromwales]

Wunda don’t do an Uber low temp manifold blending set, so you’ll be getting quoted for the thermo-mechanical type which is nigh on useless in a PH.  

Why they stopped selling the type that is necessary is beyond me, and I’ve petitioned their sales director to sort it......without reply.

The ratio of cool / cold vs heated flow are just not available so the valve just strangles itself to death. The one with a thermo-head & probe is what’s required. 

 Link

 

There are a lot of ‘gotchas’ in designing a system for a PH, so read up on Buildhub and save yourself some grief.   

[ProDave]

My flow temperature is lower than the blending valve will go, so I just rely on the ASHP regulating the flow temperature when in heating mode.  I just set the desired temperature on the ASHP control panel.

[Ed Davies]

13 hours ago, Nick1c said:

It will be a 3 bed, 2 bath, reverse level house

 

As in bedrooms and bathrooms on the ground floor, living rooms on the first floor?

[joe90]

I got all my UFH stuff from Wunda and found them helpful and reasonably priced, when a wrong part was supplied they were very quick to send the correct one. I agree with @JSHarris about one zone and a room stat, I just adjust the flow rate slightly to vary the temp into certain loops (lounge slightly warmer). I was lucky and had the old mixing head but also limit the ASHP temp like @ProDave says to limit the input temp. Also @JSHarris has recommended a return head (can’t remember the name of hand) that limits the flow and return temp difference. It’s on my very long to do list to get a new room stat with a small hysteresis.

[PeterW]

@Andrew @Nick1c you need to look at the design carefully on this, as the individual room heat needs affect the loop layout and the flow rates per loop. It’s not just as simple as chuck it in the floor, for example if you have a layout of 150mm centres, each loop requires a different flow rate to ensure heat transfer is correct. 

 

You can get Wunda to do this for you, or use a program such as LoopCAD that will do it for you once you’ve drawn your floor plan and added in the the thermal elements. It also ensures you don’t get overheating in common areas. 

 

 

[Nick1c]

@Ed Davies yes, 3 beds downstairs, 2 downstairs bathrooms. There will also be a bathroom upstairs next to the snug if we want to embrace horizontal living in our dotage. 

It sounds like I should skip ordering the pump as the ivar blending pump set might be needed. I think I will also reduce the zones to two. 

Edited September 24, 2019 by Nick1c
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[Nickfromwales]

19 hours ago, Nick1c said:

@Ed Davies yes, 3 beds downstairs, 2 downstairs bathrooms. There will also be a bathroom upstairs next to the snug if we want to embrace horizontal living in our dotage. 

It sounds like I should skip ordering the pump as the ivar blending pump set might be needed. I think I will also reduce the zones to two. 

The Ivar set comes with 2 control head options, one does 30-50^oC and the other does 20-60^oC, you'll need the latter. If you wish to marry the Ivar to a Wunda manifold, there is a conflict of Male > Male or Female > Female and you can't fit the inline ( Wunda supplied ) isolation valves directly. Your plumber will work it out, but for simplicity I just bolt together minus the iso's and put gate valves before the whole manifold arrangement.

You can buy the manifold from the same supplier that supply the Ivar set and then it'll all be compatible and will give you the manifold isolation as god intended. Just ensure that it's for 16mm pipe.

[Nick1c]

If I go for the Ivar blender do I not buy the first 3 items on the list from wunda & replace them with the Ivar & 2 gate valves, or am I better off replacing the first 4 items with an complete Ivar set?

As the pipes come together near the manifold what do I use to avoid hot spots - some form of conduit, or do I not worry about it?