Polycarbonate Wall Performing Worse Than Single Layer?

[rest]

Good afternoon all,

I'm trying to analyze a polycarbonate wall system that is composed of two layers of hollow polycarbonate with an air gap in between but the results I am getting do not make sense to me. The U-Value of the polycarbonate is 0.023 Btu/hr-ft-F, but the result I am getting from Window7 for the wall is 0.075 Btu-in/hr-ft2-F. I haven't analyzed this material before but I was expecting to get a lower value for the system than for a single layer of the material. I've attached my analysis, any thoughts?

[Robin Mitchell]

Can you show the properties (a screenshot) that you entered for the polycarbonate? 

On Wed, Apr 10, 2024 at 1:46 PM rest <rest...@gmail.com> wrote:

Good afternoon all,

I'm trying to analyze a polycarbonate wall system that is composed of two layers of hollow polycarbonate with an air gap in between but the results I am getting do not make sense to me. The U-Value of the polycarbonate is 0.023 Btu/hr-ft-F, but the result I am getting from Window7 for the wall is 0.075 Btu-in/hr-ft2-F. I haven't analyzed this material before but I was expecting to get a lower value for the system than for a single layer of the material. I've attached my analysis, any thoughts?

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Robin Mitchell

Building Technology and Urban Systems Division
Energy Technologies Area
Lawrence Berkeley National Laboratory

[Robin Mitchell]

Also what version of WINDOW are you running? 

[rest]

I am running v7.7.16.0. See attached for the properties of the polycarbonate.