Strange Cemex claim about their flow screed.

[epsilonGreedy]

What "thermal efficiency" does 50mm of Supraflo offer over say 70mm of traditional screed. This is what they claim:

 

  Quote

 

Thermally Efficient

Improved thermal efficiency when used with underfloor heating compared to traditional screed. This is because of the flowing nature of Supaflo which fully encapsulates the heating pipes.

 

Expand  

https://www.cemex.co.uk/supaflo-self-levelling-screed

 

I think they mean improved heat transfer from UFH pipes to floor slab but is this a limiting characteristic of traditional screed with UFH?

[Conor]

They should strictly be saying "thermal conductivity"

 

The term efficiency is thrown about in such circles incorrectly all the time, e.g. Dyson and their "super efficient" heaters and cooling fans. 

 

You could argue that with a more thermally conductive slab, you achieve room temp faster than traditional screed, and therefore the heating switches off sooner, so energy losses by the system running would be reduced.

[jack]

  On 08/07/2019 at 08:01, Conor said:

You could argue that with a more thermally conductive slab, you achieve room temp faster than traditional screed, and therefore the heating switches off sooner, so energy losses by the system running would be reduced.

Expand  

 

Or it heats up faster, so you lose more heat through the floor faster? 

[Declan52]

Has that not always been one of the salesman pitches in that It will heat up quicker. But does it heat up quicker because it's not made from sand and cement or because it will only be 50mm thick. 

And because it heats up quicker you turn your heating of quicker but it will also cool down quicker so you will turn your heating back on quicker.

Any good screeder will pack the dry sand cement mix in against any ufh pipework when he is spreading it out so won't leave gaps around the pipes.

[Jeremy Harris]

I doubt there's much to choose between any screed in terms of thermal conductivity, TBH.  Cement-based screed mixes will all be around 1.0 to 1.8 W/m.K, so reasonably thermally conductive (roughly two or three times more thermally conductive than the water in the UFH pipes). 

[epsilonGreedy]

  On 08/07/2019 at 16:35, jack said:

Or it heats up faster, so you lose more heat through the floor faster? 

 

Expand  

 

  On 08/07/2019 at 16:59, Declan52 said:

And because it heats up quicker you turn your heating off quicker but it will also cool down quicker so you will turn your heating back on quicker.

 

Expand  

 

This reminds me of something, hang on... oh yes a distributed system of thermal stores encased in a thermally efficient metal case and individually tune-able per room.

[epsilonGreedy]

  On 08/07/2019 at 16:59, Declan52 said:

Has that not always been one of the salesman pitches in that It will heat up quicker. But does it heat up quicker because it's not made from sand and cement or because it will only be 50mm thick. 

 

Expand  

 

I am still struggling with the concept of a 50mm crust of set cement resting on 150mm of relatively squashy insulation sheet but that is another thread. 

[Declan52]

  On 08/07/2019 at 22:01, epsilonGreedy said:

 

I am still struggling with the concept of a 50mm crust of set cement resting on 150mm of relatively squashy insulation sheet but that is another thread. 

Expand  

But it's not squashy as you are spreading the weight of the concrete over a lot of sqm so the point load on any one area is small. 

[PeterW]

  On 08/07/2019 at 22:01, epsilonGreedy said:

 

I am still struggling with the concept of a 50mm crust of set cement resting on 150mm of relatively squashy insulation sheet but that is another thread. 

Expand  

 

50mm of concrete (which is essentially what you are talking about) has a span to depth ratio of 35:1 when reinforced, and reduces to 20:1 when non reinforced. So your 50mm of concrete could span 1000mm in either direction unsupported. The compressive strength of PIR is around 150kPa, or 15 tonnes per square metre... 

[epsilonGreedy]

  On 08/07/2019 at 22:28, PeterW said:

The compressive strength of PIR is around 150kPa, or 15 tonnes per square metre... 

 

Expand  

 

This feels reassuring but is PIR the default choice for underfloor insulation? I thought EPS or XPS was the typical choices, both of which are more spongy I assume.

 

  On 08/07/2019 at 22:28, PeterW said:

So your 50mm of concrete could span 1000mm in either direction unsupported. The compressive strength of PIR is around 150kPa, or 15 tonnes per square metre... 

 

Expand  

 

A possible fissure point in a screed flow with UFH pipes embedded would be where the concrete is thinner due to the pipe, in which case we are talking about the strength of 30mm

 

  On 08/07/2019 at 22:20, Declan52 said:

But it's not squashy as you are spreading the weight of the concrete over a lot of sqm so the point load on any one area is small.

 

Expand  

 

I was thinking of dynamic point loads once the house is occupied. When Swmbo and granddaughter start dancing to a Mama Mia dvd in the static caravan I can feel the loads on the floor.

[Jeremy Harris]

  On 09/07/2019 at 08:46, epsilonGreedy said:

 

This feels reassuring but is PIR the default choice for underfloor insulation? I thought EPS or XPS was the typical choices, both of which are more spongy I assume.

 

Expand  

 

 

EPS/XPS are similar to PIR in terms of compressive strength.  EPS is typically between 100 kPa to 300 kPa (i.e. EPS 100 = 100 kPa, EPS200 = 200 kPa etc).

[Ed Davies]

  On 09/07/2019 at 09:01, JSHarris said:

(i.e. EPS 100 = 100 kPa, EPS200 = 200 kPa etc).

Expand  

 

That is for 10% compression, though. Typical values for a more-realistic 1% strain are a little less than half that: (i.e, EPS 100 = 45 kPa, EPS 200 = 90 kPa). But, yes, it doesn't take a lot of spreading for these to take a lot of load.

 

https://www.insulationshop.co/image/catalog/pdf/Jablite/Jablite-EPS.pdf