Adjust U-Value of 4 layer ETFE Cushion

asked 2020-01-24 11:18:49 -0600

rafael.alonso
933 ●1 ●6 ●12 http://atmoslab.io

updated 2020-01-25 13:36:08 -0600

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi all,

I´m working on a project with an ETFE envelope, both for the facades and roof. These are made of 4-layered cushions with air gaps between them. To model the cushions in E+ I´ve used the detailed specs from the manufacturer as WindowMaterial:Glazing WindowMaterial:Gas objects.

E+ outputs show a resulting U-Value of 1.28 W/m2K which according to the local technical standards needs to be increased by 0.5 W/m2K to account for the curved nature of the cushion (and varying air gap thickness). Essentially a "safety factor".

Is there a way of doing so?

I´m aware of the WindowMaterial:SimpleGlazingSystem object, but that would change the thermal interaction between the ETFE layers, and affect the resulting internal cushion temperature - which is key for the comfort on the last floor, right below the roof.

It seems quite tricky to account for this safety factor while maintaining the precision that WindowMaterial:Glazing brings in this particular case. Has someone faced something similar?

Thanks in advance, Rafael

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Comments

May I ask what is the U value now? And what climate conditions dictated 4 layers?

Maxim ( 2021-03-01 03:11:46 -0600 )edit

What's the gap now? What's the U-value? We are developing a similar etfe structure and really need to understand the flexibility we have with the U. Thanks

Maxim ( 2021-03-01 03:15:47 -0600 )edit

This is for a project in South west France, close to the Atlantic coast. The U value according to the manufacturer was 1.8, which included a safety factor of 0.5 W/m2K according to NF EN ISO 673. From a simulation perspective, we got all the technical details from the ETFE film manufacturer, but I cant share those unfortunately. Hope this helps.