UFH Design Layout & Low temperature Underfloor heating

[revelation]

Hi all,

 

We are getting closer to having our UFH pipes laid on the ground floor (in 50 mm liquid screed).  My design is as shown in the attached image (150mm centres) , however  have been told that its not the best way of having it and a spiral design would be better and give more even heating and less chance of any cracks.   Is that right or is my design perfectly adequate? 

 

All the runs are less than 80m long, I didn't want to go more than 150mm on the centres as I wanted to improve heat up times on the system and the plan was to run the UFH at as low temperature as possible so that the boiler is condensation mode all the time while the heating is on (If anyone has any further information on system design in that respect it would be much appreciated).

 

Thanks

[ProDave]

The UFH design should be the same regardless of the heat source.  That should be based on how much heat the building needs.

 

UFH should be fed with a manifold that incorporates a temperature blending valve so you can set the UFH temperature independent of the temperature of the water delivered from the boiler.  That will let you separately set the boiler temperature for maximum efficiency.

 

You might want a buffer tank between the boiler and the UFH.

[revelation]

Thanks for your reply. I guess I wanted to keep the temp from the boiler as low as is reasonably possibly. That way it would be running more efficiently than if it was coming out at say 60 degrees and being mixed at the manifold down to say 30-40. Does that make sense? 
 

I guess in that case my design looks ok?
 

 

[Adsibob]

On 24/01/2021 at 13:24, ProDave said:

might want a buffer tank between the boiler and the UFH

What dictates whether or not one should include a buffer tank?

[Temp]

Will it be oil or gas boiler?

[PeterW]

1 hour ago, Adsibob said:

What dictates whether or not one should include a buffer tank?

Any system needs a buffer tbh as it stops short cycling of the heat source when only one loop is calling for heat. 
 

On 24/01/2021 at 12:50, revelation said:

My design is as shown in the attached image (150mm centres) , however  have been told that its not the best way of having it and a spiral design would be better and give more even heating and less chance of any cracks.   Is that right or is my design perfectly adequate? 

With thin screed I would go with spiral as you will get uneven heating otherwise. 
 

You also won’t get a boiler to condense at those temperatures and I would put the buffer in as above. Just let the buffer call the boiler, a pair of stats can be used in tandem to stop it calling until the buffer is quite cool and it will manage the system better. No boiler will cope with only one of those loops being open and calling for heat. 

[Nickfromwales]

On 25/01/2021 at 05:11, revelation said:

I guess in that case my design looks ok?

No, as room 2 looks like it will overheat if serviced by the loops feeding from / responding to the kitchen thermostat. Room 3 the same? What are rooms 4, 5, & 6?

You should have that space serviced separately, and all the flow and returns to the kitchen should be lagged ( insulated ) to prevent unwanted heat loss into room 2, same elsewhere eg where the pipe runs are condensed and especially where they serve a different room. With 50mm screed i would want room stats and deicated zones throughout and to use a stat with a very good hysteresis, say 0.5oC or less.

Is this a 'passive' build? eg tested as air-tight and super insulated?

I would go for 120mm centres with 50mm of liquid as that's the worst type of UFH emitter you can get imho. Increased CSA and increased water volume / wider spread of pipes will lend itself to the lowest flow temp possible, but that will be dictated by the W/m2 that the dwelling requires to maintain a comfortable ambient internal temp vs outside temp. Serpentine layout as per your drawing is carp, go reverse / inverted and then you only have U-turns at the centre of each loop  

[revelation]

9 hours ago, Nickfromwales said:

No, as room 2 looks like it will overheat if serviced by the loops feeding from / responding to the kitchen thermostat. Room 3 the same? What are rooms 4 5, & 6?

You should have that space serviced separately, and all the flow and returns to the kitchen should be lagged ( insulated ) to prevent unwanted heat loss into room 2, same elsewhere eg where the pipe runs are condensed and especially where they serve a different room. With 50mm screed i would want room stats and deicated zones throughout and to use a stat with a very good hysteresis, say 0.5oC or less.

Is this a 'passive' build? eg tested as air-tight and super insulated?

I would go for 120mm centres with 50mm of liquid as that's the worst type of UFH emitter you can get imho. Increased CSA and increased water volume / wider spread of pipes will lend itself to the lowest flow temp possible, but that will be dictated by the W/m2 that the dwelling requires to maintain a comfortable ambient internal temp vs outside temp. Serpentine layout as per your drawing is carp, go reverse / inverted and then you only have U-turns at the centre of each loop  

 

All rooms will have stats (heatmiser) 

Sorry should have had them labelled properly

Room 2 is a utility room, Room 4 is toilet and wash basin Room 5 is a hallway area, and I am not sure whats going on with 6 as thats where the open staircase is.

The front and middle room are sitting areas/play room. 

 

The house is a mixture of new and 1930's, we will be externally insulating the old part of the house with 50mm of kingspan K5.  

 

The chances are especially with the ground floor we will be running the heating on low all of the time during winter so do you still think its best to lag them? And what would be used to lag as we will only have 50mm of screed?

 

The centres are currently around 150mm, I think if i reduce the centres I will have to introduce more runs and we may run out of space on the manifold.  

 

Is serpentine that bad?  Looks like its the easiest to do, would it cause any problems? 

 

[Nickfromwales]

If an open area has a stat in it, and the heating pipes to that zone traverse smaller enclosed rooms, then the likelihood is that the stat will call for heat way beyond the smaller rooms requisite for more het input, ergo that small room would overheat.

4 hours ago, revelation said:

The chances are especially with the ground floor we will be running the heating on low all of the time during winter

That may help out a lot, vs timed heating. Don't think for one minute that slowing down a loop at the manifold ( balancing ) will give temperature control, it won't.

 

4 hours ago, revelation said:

so do you still think its best to lag them? And what would be used to lag as we will only have 50mm of screed?

You'd probably be down to 25mm flexible conduit as 9mm wall on 16mm pipes would give you 34mm total. You'd only really have to insulate the flows, and group them at the absolute perimeter of any room they traverse. You only need 30-40mm between pipes where they congregate.

 

4 hours ago, revelation said:

The centres are currently around 150mm, I think if i reduce the centres I will have to introduce more runs and we may run out of space on the manifold.  

If the manifold is bought then yes. Just remember now is the time to get it right, not after it's too late. If it's new, they should accept returns.

4 hours ago, revelation said:

Is serpentine that bad?  Looks like its the easiest to do, would it cause any problems? 

IMO, yes. An old plumbing saying is, "enough 180o bends is a dead end", and inverted layout offers only 90o bends. Serpentine also puts all the heat at one end of the room and all the cool return flow at the other, so flow and return need strategic planning by design. Not important in a thicker, heavily insulated slab, but it will be notable with thinner insulation and a wafer thin emitter. I install UFH for others, so I have to be sure it all works A1 every time, and I would never do serpentine. As far as serpentine being easier? Not imo, but I am a 'seasoned' installer....  

[revelation]

4 hours ago, Nickfromwales said:

You'd probably be down to 25mm flexible conduit as 9mm wall on 16mm pipes would give you 34mm total. You'd only really have to insulate the flows, and group them at the absolute perimeter of any room they traverse. You only need 30-40mm between pipes where they congregate.

Sorry when you said lagging I thought insulation, so just some flexible conduit should be ok.

 

4 hours ago, Nickfromwales said:

If the manifold is bought then yes. Just remember now is the time to get it right, not after it's too late. If it's new, they should accept returns.

Its new but I bought it about 8 months ago and its been mounted on the wall, but haven't connected anything up to it yet.  The UFH companies seem to say 200mm spacing is fine, I thought 150mm spacing would have been decent, but I am learning quickly its not the best. We do have 100mm kingspan below the pipe too.

 

 

4 hours ago, Nickfromwales said:

IMO, yes. An old plumbing saying is, "enough 180o bends is a dead end", and inverted layout offers only 90o bends. Serpentine also puts all the heat at one end of the room and all the cool return flow at the other, so flow and return need strategic planning by design.

180 restrict the flow more than a 90 so I guess that makes sense, I'll try and make some changes.

 

I want to get the system set up as efficiently as possible, before beginning I didn't realise, the UFH companies haven't been giving very good advice either.

[Nickfromwales]

3 hours ago, revelation said:

I want to get the system set up as efficiently as possible, before beginning I didn't realise, the UFH companies haven't been giving very good advice either.

Some do give good service, and some just want the sale.....

[revelation]

which ones have you come across that give good advice?

 

Regards

[Adsibob]

On 01/02/2021 at 08:14, Nickfromwales said:

On 01/02/2021 at 04:00, revelation said:

Is serpentine that bad?  Looks like its the easiest to do, would it cause any problems? 

IMO, yes. An old plumbing saying is, "enough 180o bends is a dead end", and inverted layout offers only 90o bends. Serpentine also puts all the heat at one end of the room and all the cool return flow at the other, so flow and return need strategic planning by design. Not important in a thicker, heavily insulated slab, but it will be notable with thinner insulation and a wafer thin emitter. I install UFH for others, so I have to be sure it all works A1 every time, and I would never do serpentine. As far as serpentine being easier? Not imo, but I am a 'seasoned' installer....  

Can one mitigate the issues caused by serpentine by increasing the flow rate?