Air Wall Material Density


I’m trying to create a custom EP Construction that has air gap inbetween exterior and interior surfaces.
I wanted to be able to change the thickness of the air space, so I made a custom EP Material for air gap using Honeybee_EnergyPlus Opaque Material component. I largely copied specifications/values from Air Wall Material from EP Construction Library to make the air gap material.

While I was looking at the values of Air Wall Material from the EP Construction Library, I noticed that the density is 800 kg/m3. This looks really heavy and wanted to check if that’s how it is.

Thanks for your help in advance!

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@yoshikawa ,

Changing the thickness of air cavities does not have a significant impact on their insulation value unless you are decreasing them below ~5cm thick . This is because, beyond 5cm, the air in the cavity will exhibit similar convection patterns and give you similar rates of heat transfer. So there is no need to create new materials unless you want to test some really thin cavities.

Also, if you are looking to approximate a wall air cavity, you should use the F04 Wall Air Space Resistance material instead of the Air Wall Material:

The Air Wall Material is only intended to act as a virtual partition and isn’t meant for uses like yours here.



It makes sense. I figured that there was a reason for it, but just wanted to check. The air cavity that I’m running analysis with is 7cm, so I’ll just use the F04- material.