Can someone explain these EPS specifications?

[Radian]

Whenever I look at EPS insulating panels I often see a list of parameters such as these:

150mm White Polystyrene Board (EPS) for External Wall Insulation (pack of 4)

Thickness: 150mm

Width: 500mm

Length: 1000mm

Pack coverage: 2m²

Density: 10kg/m³

Weight/m²: 1.5kg

Weight: 3kg

Thermal Conductivity: 0.042W/mK

R-Value: 3.55m2K/W

Compressive Strength: 75kPa

Fire Rating (Reaction to Fire): E

 

Here R-Value is given in m2K/W so if I want to convert to U-Value I would naturally take the reciprocal 1/3.55 =  0.28

Now that would be 0.28 W/(m2⋅K) right? But from their numbers "Thermal Conductivity: 0.042W/mK" what the heck is that? Is that meter.Kelvin or milliKelvin or what?

[A_L]

38 minutes ago, Radian said:

so if I want to convert to U-Value I would naturally take the reciprocal 1/3.55 =  0.28

 

except that your wall has other elements as well as insulation, you have to add the R-values of these to the insulation R-value and take the reciprocal of the total R-value

 

41 minutes ago, Radian said:

"Thermal Conductivity: 0.042W/mK" what the heck is that? Is that meter.Kelvin or milliKelvin or what?

 

Yes it is meter.Kelvin, actually that is quite a high value, but O.K. if allowed for.

 

The compressive strength is usually the force required to compress the material by 10%, again this is an unusual value see attached pdf

 

KayMetzler EPS.pdf

[Radian]

Sorry @A_L I'm having a senior moment here. When I take 1/R for the product listed I get 0.28W/(m2⋅K) which seems about right for a U-Value when I compare it with my double glazed windows that were rated at 1.6W/(m2⋅K) but the same list gives Thermal Conductivity as being 0.042W/mK which you appear to confirm as also being measured in m2 per Kelvin.

 

What's confusing me is there's a big difference between 0.28 and 0.042 if they share the same units.

[Radian]

Oh Just realised. 0.042W per meter thickness per K! So yes, 1/0.15m x 0.042 thick = 0.28

Forget this ever happened.?

[SteamyTea]

Thermal Conductivity k or λ = W.m^-1.K^-1

 

To convert to R-Value, divide thickness [L] by λ

 

R-Value = m².K.W^-1

 

Take the reciprocal to get the U-Value

 

U-Value = W.m^-2.K^-1

 

So

k = 0.042

L = 0.15 [m]

 

R = 0.15 / 0.042

R = 3.57 m².K.W^-1

 

U = 1 / 3.57

U = 0.28 W.m^-2.K^-1

 

Edited December 31, 2021 by SteamyTea

[Radian]

Thanks @SteamyTea I think you see what I did there - not reading the units carefully enough. My science teacher is very likely rolling in his grave.

If not he has surely got himself into the Guinness Book of Records.

[SteamyTea]

2 minutes ago, Radian said:

My science teacher is very likely rolling in his grave.

If not he has surely got himself into the Guinness Book of Records.

My school Physics teacher was a PhD student.  Was the best teacher in the place.  Was studying the effects of strong magnetic fields on photon streams.

The Chemistry teacher was a Born Again Christian who thought the world was no older than 6000 years (or it may have been 4000, I switched off).

I cannot even remember who the Mathematics teacher was.

[Radian]

1 hour ago, SteamyTea said:

My school Physics teacher was a PhD student.  Was the best teacher in the place.  Was studying the effects of strong magnetic fields on photon streams.

 

Wow, that takes some doing - what with photons not being the teensiest bit charged! Must have been detecting the scattering of electron positron pairs in a magnetic field then?

Pretty obviously my dream Physics teacher would have been Richard Feynman who, incredibly, would be 104 now if he had not been stolen from us in 1988. I still feel very sad about that.

 

[SteamyTea]

9 hours ago, Radian said:

Richard Feynman

I watched his Fun to Imagine interview the other day.

[Radian]

Shame there are only a handful of Feynman videos.

 

Another good science communicator (who reminds me a lot of Feynman) is Canadian Building Science guy Joseph Lstiburek.

I don't see much mention of him in these forums which is a bit of a surprise given how relevant his talks are to what we're all into here.

To my mind, Joe sums it up when he relates how when its cold we don't swallow our sweaters but wear them on the outside (a few seconds in from this video)...

https://www.youtube.com/embed/rkfAcWpOYAA?start=622

 

 

[SteamyTea]

1 minute ago, Radian said:

relevant his talks are to what we're all into here

One problem with Canadian/Northern USA techniques is that there climate is very different from the UK (most of the populated area is 10° South of us.

Condensation risk is treated differently, as is ventilation/heating.

 

Walter Lewin is worth watching.

His last MIT lecture.

[Radian]

13 minutes ago, SteamyTea said:

One problem with Canadian/Northern USA techniques is that there climate is very different from the UK (most of the populated area is 10° South of us.

Condensation risk is treated differently, as is ventilation/heating.

 

True, but all the basic science is applicable to whatever construction work we're doing. I despair at the lack of basic understanding displayed by our typical building trades. To them the job is a 'goodun' if a big delivery of celotex turns up to site and finally disappears inside the building. Somewhere.

 

And because nobody ever rings them up at 2AM complaining that air is pouring into their new building, they don't have the same appreciation for air-tightness that they have for water.

[SteamyTea]

7 minutes ago, Radian said:

all the basic science is applicable to whatever construction work we're doing

Yes.

Why I think that people should engineers of the correct discipline, rather than architects and 'builders experience'.