Curtain Wall R-value/U-value

[Kakanthony]

Hi I am trying to model a curtain wall with U-value of 1 or R-value of 1.

Wondering is anyone know how can i get the Net U-value and R-value matched?

I got an U-value of 1 in the project construction but it gives me an R-value of 0.4 or similar?

Wondering is Apache simulate according to its U-value or R-value?

[PCully]

Apache treats the Constructions based ont he materials and properties you have specified to model them, the u-value, r-value etc are derived parameters to allow you to check how the Construction you have modelled matches to manufacturer data.

Remember there are 3 u-value calculation methods available in CDB (details nit he user guide) so you can choose the methodology most relevant to you and then confirm manually how the defined construction matches up if needs be.

I don't have a great deal of experience in matching up to theoretical targets like you have, perhaps some others can assist or comment?

Phil

[RossThompson87]

Hi,

I have been confused in the past by the R value reported in IES. To my mind the overall U-Value should be the exact reciprocal of the total R value. I contacted technical support and got the response below.

I believe the omission of surface resistances explains the unexpected value. Hopefully this can be sorted in an update because it cost me a bit of time figuring it out.

Ross

Thank you for your email enquiry.

I believe the problem here is you are not quite comparing like for like
since the U-value will also take into account the Surface Resistances
but the R-value does not. The U-value calculation methods for each
standard should be referenced in the Constructions database User Guide
should you need to investigate this further.

[RossThompson87]

Hi,

Actually I think it ultimately tuned out to be a bug. I just found another email:

I apologise for the delay in responding to you and my initial
misunderstanding of this. It seems you are quite right in your
observation but I cannot explain this discrepancy and will raise with
our development team to review this and if necessary correct the display
for a future update of VE. Thank you for pointing this out.

I hope this has been of some help.