Floor insulation comparison tool?

[jack]

I've been talking with some friends of mine who are in the middle of gutting and extending their house.

 

We were discussing insulation, and particularly underfloor insulation given that they're replacing all their downstairs flooring and installing UFH. At present, their builder is doing standard building regs structure of concrete, insulation (is 100mm rigid standard to meet current regs?) and screed with UFH on top.

 

I was thinking about how to compare the impact that better insulation would have on costs. Jeremy's excellent heat loss calculator potentially gives some clues, but I suspect that it works better for highly insulated houses where the air temperature (one of the required user inputs isn't much above the floor temperature. For a standard building regs house, for example, I assume the floor needs to be quite a bit warmer than the intended room temperature, so there'll be more losses through the underfloor insulation. 

 

This general question comes up quite a bit, and I think it would be nice if we could come up with a spreadsheet that lets us convincingly show the energy and financial impact of different floor buildups in different houses.

 

I'm happy to have a go at this (@JSHarris, if okay with you I may use your heat loss spreadsheet as a starting point). However, I'm unsure about how you'd go about calculating the necessary floor temperature to achieve a required heating output. I suspect that to do a proper job, you'd need a combination of Jeremy's spreadsheet to get heat load, and then work backwards to determine floor temperature. It may, however, be possible to simplify this by making some assumptions and reasonable estimates.

Any thoughts on this before I have a go?

 

[Jeremy Harris]

I've got a spreadsheet that works out the heat input to a house from a given floor area that's fitted with UFH on another machine. 

 

I could have a go later at combining this with the heat loss sums and tidying it up a bit to make it easier to use.  I've also got a simple U value calculator sheet, which will work out the composite U value for a floor easily enough, so may try and incorporate that, so someone could just select the insulation type, thickness, floor slab thickness, and UFH heat output needed and it could then give the floor heat loss to the ground.

[jack]

3 minutes ago, JSHarris said:

I could have a go later at combining this with the heat loss sums and tidying it up a bit to make it easier to use.  I've also got a simple U value calculator sheet, which will work out the composite U value for a floor easily enough, so may try and incorporate that, so someone could just select the insulation type, thickness, floor slab thickness, and UFH heat output needed and it could then give the floor heat loss to the ground.

 

Thanks very much Jeremy.

 

If that isn't too much trouble, I think it could be a very handy tool. The "how much insulation under my UFH" question comes up time and again, and it would be nice if we could show the energy and financial impact of doubling (for example) the minimum building regs spec.

 

Happy to help - please let me know if there's anything I can do.

 

Thanks

[vfrdave]

I am currently working through this for my own build currently and dont really know where to go.  The three options I have appear to be as follows:-

 

200mm Kore Grey insulation u-value 0.123

 

100mm PIR & 100mm Kore Grey  u-value 0.106

 

200mm PIR u-value 0.093

 

From worst to best I dont think there is a massive saving in energy costs compared to the extra cost of the insulation product, though will welcome all advice.

[Temp]

On ‎08‎/‎10‎/‎2018 at 14:21, jack said:

At present, their builder is doing standard building regs structure of concrete, insulation (is 100mm rigid standard to meet current regs?) and screed with UFH on top.

 

On top or in the screed? Is this wet UFH or electric mats?

[jack]

51 minutes ago, Temp said:

On top or in the screed? Is this wet UFH or electric mats?

 

Standard wet UFH (ie, screed on insulation, UFH loops in screed).

 

I believe they're going for engineered wood on top, but not sure whether that's a definite.

[Jeremy Harris]

I've knocked up a spreadsheet to calculate ground floor U value, heat loss to the ground, % efficiency and required floor surface temperature for a given UFH heat output:

 

 

Floor heat loss and UFH calculator.txt

 

As before, the file needs to be saved and then the extension changed from .txt to .xls, as the forum software doesn't allow any spreadsheet file types to be uploaded.

 

All and any feedback welcome, together with any bugs that are found!

[zoe61]

2 hours ago, JSHarris said:

Floor heat loss and UFH calculator.txt

Had a quick play with this now and seems good. Thank you very much!

 

Interestingly to achieve a 10% heat loss or less I need 200mm insulation. Much more than the average values that are recommended by UFH companies. 

 

Also watching a episode of  'Building Alaska' last night, obviously they have log burners but even so the insulation in those buildings was scarily thin!

[Jeremy Harris]

The 10% figure comes indirectly from building regs, in that the area-weighted average floor U value should be less than 0.25 W/m².K, which if translated into ground heat loss works out at about 2 W/m² maximum heat loss at design conditions.  Using 10% as a maximum allowable may result in a heat loss of greater than this, but should be under the design target of less than 5 W/m² loss.

 

Building control bodies don't seem to pick up on the fine detail of floor heat loss with UFH, because SAP doesn't account for it either.  Strictly speaking they should look at the underlying principle behind the area-weighted average floor U value criterion, and take account of the increase in heat loss that always results from fitting UFH.  At the moment, the assumption is that the design conditions are focussed on heat loss arising from room temperature alone, which it clearly doesn't for a house with UFH.

 

Worth bearing in mind that the heat loss from radiators or other similar forms of heating will often be lower than from UFH.

[jack]

47 minutes ago, JSHarris said:

At the moment, the assumption is that the design conditions are focussed on heat loss arising from room temperature alone, which it clearly doesn't for a house with UFH.

 

Indeed, and it was exactly this issue that led to me bringing up this issue.

Thanks very much for your work on this Jeremy. I'll have a play with it.

[Ed Davies]

3 hours ago, JSHarris said:

Worth bearing in mind that the heat loss from radiators or other similar forms of heating will often be lower than from UFH.

 

Yep, though there's another effect going in the opposite direction: normally with UFH the radiant temperature in the room will be more than with other forms of heating (UFH puts out a larger proportion of its heat as thermal IR than “radiators” or most other heating devices) so the air temperature can be a bit lower for the same apparent temperature for occupants and so the ventilation heat losses (particularly without MVHR) will be lower. I haven't done any arithmetic but I suspect the increased heat loss through the floor with UFH would be a larger effect but radiant temperature vs air temperature needs to be taken into account.

[Jeremy Harris]

14 minutes ago, Ed Davies said:

 

Yep, though there's another effect going in the opposite direction: normally with UFH the radiant temperature in the room will be more than with other forms of heating (UFH puts out a larger proportion of its heat as thermal IR than “radiators” or most other heating devices) so the air temperature can be a bit lower for the same apparent temperature for occupants and so the ventilation heat losses (particularly without MVHR) will be lower. I haven't done any arithmetic but I suspect the increased heat loss through the floor with UFH would be a larger effect but radiant temperature vs air temperature needs to be taken into account.

 

True, and anecdotal evidence suggests that the air temperature in the room can be around 1 deg C  cooler for a given comfort level because of this effect.