Pauline,
the view factor entered in TRNbuild is used for longwave radiation exchange of external surfaces.
As stated the value is used as a weighting factor between ground (Input 4) and sky temperature (Input3).
(See also Page 155 of 05-MultizoneBuilding.pdf)
If you have set both inputs to the same value a changing value of Fsky doesn’t have an impact.
For diffuse radiation calculation the slope of the surface is used. In addition, the shading mask includes
a sunlit fraction for isotropic diffuse radiation.
Dipl.-Ing.
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Von:
Gesendet: Donnerstag, 19. September 2013 09:33
An: David BRADLEY
Cc:
Betreff: Re: [TRNSYS-users] problem of sky temperatures
Thank you for your answer. Indeed, I read these differences in the manual but I don’t know for which case we need
to use one or other of these sky temperatures definition.
In fact, I have another question about the effects of the value view factor given for walls and windows.
According to TRNBUILD manual (page 72), the view factor must impact diffuse and long wave radiation as well as
convective heat transfer coefficients, so it is especially important for windows.
When I wanted to check these impacts using the IDSHAD outputs (total diffuse radiation on outside of external surface)
with differents values of view factors (equal to 0 or 0.5 or 1) for walls and windows, I saw no difference in the results.
Could you explain to me these results ?Should I use another outputs to check these impacts? Am I wrong or right
?Is my understanding of the view factor false?
Thanks a lot in advance for your answers.
Best Regards,
Pauline GELIN
Ingénieur Conception environnementale
10 avenue des canuts
69120 VAULX EN VELIN
T : 04.37.45.33.33
Ligne directe : 04.37.45.33.47
De :
David BRADLEY [mailto:d.bradley@tess-inc.com]
Envoyé : mercredi 18 septembre 2013 19:06
À : Pauline GELIN
Cc :
Objet : Re: problem of sky temperatures
Pauline,
Type69 and Type15 use different algorithms for computing sky temperature. The algorithms are discussed in the 04 Mathematical Reference manual.
Kind regards,
David
On 9/18/2013 08:40, Pauline GELIN wrote:
Hello,
sorry to ask again the same question but I can’t understand why the values of sky temperature from weather component type 15 and from component 69 (with inputs from the same type 15) are different.
Anyone could help me to understand?
Hanks a lot for your answers.
Best Regards,
Pauline GELIN
Ingénieur Conception environnementale
10 avenue des canuts
69120 VAULX EN VELIN
T : 04.37.45.33.33
Ligne directe : 04.37.45.33.47