AW: [TRNSYS-users] solar radiation in second skin facade model

[Torsten Welfonder]

Dear Philip,
there are several things you have to know about modeling double facades with TRNSYS:

The geosurf factor only catches the direct solar radiation. The diffuse radiation is still treated 
area*(1-reflextion) weighted. So that it can happen for a double facade with an orientation with a lot of diffuse radiation that e.g. half of the radiation  is distributed to the single pane window where radiation was coming in and from there 
directly out again. You can see how much radiation is leaving through an external window on NTYPE 68 
for one window or NTYPE 73 for all windows of a zone. You might then add wall gains as a ratio of QSOUT if needed.


In TRNSYS 15 the NTYPE75 did output all absorbed radiation for an adjacened window for the surface side with front. 
So if the front side of the ADJACENT window is in the double-facade NTYPE75 showed a too low value for the office zone. TRNSYS16 tells you now only the part of the absorbt radiation which is going to the front or the backside of an ADJACENT window. Also you can check with the  solar balance for zones were solar radiation is absorbed.

About the treating of radiation in TRNSYS:
-all diffuse radiation in a zone is distributed area- absorption weighted on walls and for windows area*(1-reflextion) weighted -all reflected radiation in a zone is diffuse -direct radiation is distributed to inside surfaces with geosurf factors. -direct radiation is still direct radiation after falling through the first ADJACENT window. 
-All direct radiation entering a zone trough two ADJACENT windows in a row is treated to be diffuse in the last zone.  with kind regards,

your TRNSYS Hotline Team

T.Welfonder, M.Rudolph

-----Ursprüngliche Nachricht-----
Von: trnsys-users-bounces at engr.wisc.edu [mailto:trnsys-users-bounces at engr.wisc.edu] Im Auftrag von Philip van den Enden
Gesendet: 13 January 2005 15:58
An: 'trnsys-users at engr.wisc.edu'
Betreff: [TRNSYS-users] solar radiation in second skin facade model



Dear all,

I have a question concerning the model of a second skin facade: My model consists of two rooms: one represents the second skin facade 
(single glass (g-value 0,9) on exterior side, double glass (g-value 0,6) on 
the office side. So:

exterior | 2nd skin || internal office room

The problem is about the solar radiation entering the office room. Even 
without any sunshading device within the second skin, the total solar 
radiation absorbed in the office room (zone output 75) appears to be much 
lower than one would expect based on the total solarradiation entering the 
second skin and the g-value of the double-glass window (Qin*g-value).

I am not clear about what TRNSYS does with the solarradiation after passing 
the first single glass layer. Does it all become diffuse radiation or 
something else and therefore is treated differently by the second double 
glass-layer? I already put the geosurf factor of the double glass window on 
1, but that doesn't help much. Can anyone shed some light on this, or did 
anyone ever experience similar "glass-after glass"-problems? Thanks in 
advance,


Philip van den Enden



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