[TRNSYS-users] Internal glazing specification

[Antoine Gautier]

Dear users

 

I am really puzzled by Werner's post hereunder.

 <http://sel.me.wisc.edu/trnsys/mailinglist/archive2003/msg00297.html>
http://sel.me.wisc.edu/trnsys/mailinglist/archive2003/msg00297.html

 

If I understand it well, characteristics for internal glazing systems should
be specified regarding external glazing systems characteristics. For
instance internal transmittance should be different than normalized value if
spectrally selective transmission is performed by external glazing systems.
The reason invoked being that the same wavelength cannot be absorbed twice. 

However when I think about it,  I rather understand transmission coefficient
(thermal or visible) as a probability of transmission averaged on a
wavelength interval. Therefore I would intuitively conclude that each
glazing system transmits radiation as expected regarding its normalized
characteristics.

When I simulate a fictive 2 * double glazing system in WINDOW with a very
wide middle air gap I get the following results.

                                                           SHGC    Tvis

Initial double glazing                             0.54      0.78

2*double glazing simulated                    0.41      0.62

Characteristics of initial glazing**2         0.29      0.61

 

So Tvis resulting from WINDOW calculation is close to the square of initial
Tvis value but SHGC is in-between. 

I would need help to conclude. How should internal glazing systems be
specified in Trnbuild?

 

Also if Radiance users are amongst you I would be very interested to know
how they handle this issue when specifying transmissivity values for
internal glass materials.

Best regards

--

Antoine Gautier
Solamen SAS
+33 6 58 24 02 60

 <mailto:antoine.gautier at solamen.fr> antoine.gautier at solamen.fr

 

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