Need to model an atrium where the floor spandrels are perforated stainless steel reflector screens. Need to get the screen reflectance right.

First thought was to simply calc the average reflectance over a 2' sq sample using area weighted reflectances for the hole (R=0) and opaque parts (R=.5).  Crude but probably reasonable. Non?

Then I though of the Window7 tool that allows the calculation of a perforated screen transmission. The tool describes the perf optics to satisfy window7 but also serves up a mysterious "permeability factor" (PF) that varies with the hole diameter and spacing. Is PF simply the percent of the surface that is open, the balance being the opaque? This would be consistent, convenient and serve up an LBNL sanctioned number..

Unable to track down exactly definition of the PF though am told that must be calculated using the AERC 1 procedure.

So is my W7 tool strategy correct or to be corrected or not applicable?

David

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