Celotex et al - loses performance?

[endecotp]

my assertion is that there's nothing PIR is filled with that, when it's all leaked out and replaced with air, leaves a sheet 2/3rds as insulative as when it rolled out the factory..

Have a look at figure 7 of
http://www.huntsman.com/polyurethan...ne Blown Polyisocyanurate Laminate Boards.pdf

It seems to be saying that air leaks in but pentane doesn't leak out - which I don't really understand. Are they saying that the cells are in partial-vacuum when new?

 

[^woody^]

The OP will lose much more more heat by going shopping on a single Saturday in February (opening front door to go out and come back) than he ever will by any supposed degration of PIR insualtion over his lifetime of living in the house.

 

[cjard]

they could be partial vacuum.. the mix gets incredibly hot in my experience (having played with 2 part foam) as it expands. It seems reasonable that a hot rigid closed cell could solidify before it's cooled completely, meaning it's at a lower pressure than the surrounding air when it's at the same temperature..

Ends up, the OP has to decide whether to believe it or not and what to buy. If he's justified his purchase decision to himself, then there is no cause for future complaint

 

[cjard]

That prompted me to do some googling: http://www.engineersedge.com/heat_transfer/thermal-conductivity-gases.htm

As expected the best include Krypton and Xenon (as used in windows) and Pentane (as used in PUR boards).

And now I have. Clearly thus it works out.. take out all the pentane and replace it with air, and your board mathematically went from a 0.02 lambda to a 0.03, so.. no better than polystyrene* indeed!

*which also uses pentane as a blowing agent, so might be in the same boat?

Glad I paid half price for my kingspan and fitted just shy of 300mm of it to my walls and roof now


I am still curious though, how a 4-16-4 double glazed panel can be u value 2.8 if air filled and 2.7 if argon filled (source: https://www.pilkington.com/~/media/Pilkington/Site Content/UK/Reference/TableofDefaultUValues.ashx)

 

[endecotp]

I am still curious though, how a 4-16-4 double glazed panel can be u value 2.8 if air filled and 2.7 if argon filled

The 16mm gap is large enough that convection matters. In foam cells it's practically all conduction.

 

[endecotp]

Something I don't understand yet is to what extent the advertised values are for aged products.
Some of the things I've read suggest that they are, but that may be according to US/Canadian standards. Celotex etc. quote their values are per BS EN something, and I don't know if that requires testing/similation of aged samples.

 

[cjard]

The 16mm gap is large enough that convection matters. In foam cells it's practically all conduction.

Mm... I'm not really seeing it, given the practically identical values for all the gap sizes in that doc.. there are indeed reasonable limits to the gap size before convection really does erode the savings, but if convection was a major factor I'd have expected a much bigger difference between 6 and 16..

So your assertion is that pentane in a foam board is great, air mediocre, but pentane vs air in a dg unit is a poor difference due to convection even if the gap is small enough that large scale convection is unlikely?

 

[endecotp]

I think convection will always be greater than gas conduction in a DG unit - but I'm not certain.
Convection is determined by entirely different physical properties of the gas - viscosity and heat capacity.
In particular, pentane would be a poor choice where convection matters because it has many molecular bonds hence many vibration modes and hence a high heat capacity. Noble gasses are monatomic which means they have very low heat capacity and so transport very little heat even if there is a lot of convective gas flow.