[EnergyPlus_Support] EnergyPlus validation not working. Help

["taharvey2001" <taharvey@xxxxxxxxxxxxxxxx>]

We've been getting results for E+ that we found suspicious,
particularly with surface reflectivity, so we attempted to do a simple
real world validation for Energyplus using an simple solar box (a
thermal equivalent of the 3D rendering Cornell box). 

For the solar box, we used a solar box cooker with reflective panels.
In EnergyPlus we made the same R10 2' square insulated box with a
single clear glass window and used 100% reflective glazing for
reflectors (since E+ doesn't let you specify specularity on normal
materials - please change!).

We ran it on a clear sky solar date at the same tilt. Peak temp results:
Real Solar Box: 350 F
Hand calculated result: 360 F
EnergyPlus: 210 F
EnergyPlus (Finite Differencing): 117F

If i delete the reflectors, the solar gain changes only a tiny amount
and the box temperatures don't change - obviously the reflection is
not working properly - any ideas? (yes full interior/exterior with
reflections is turned on)

The second question is what is up with Finite Differencing? 




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