[TRNSYS-users] Cooling and solar heat gains

[marcello.caciolo at cofelyaxima-gdfsuez.com]

Dear TRNSYS users,

We have a little problem with type 56. I send you enclosed a sample project illustrating our problem.

In type 56, we have one zone with 4 external glazed surfaces, with 4 orientations (namely ENE, 124 m2, SSE, 48m2, OSO, 124 m2 and Horizontal, 198 m2), and a boundary surface, with identical temperature.

There are no internal loads. External radiation is fixed to 1000 kJ/hm2 on ENE, 2000 kJ/hm2 on SSE, 600 kJ/hm2 on OSO and 800 kJ/hm2 on horizontal, and assumed totally direct (ITotal = IBeam), with a zero incident angle for each orientation (this is no realistic, but we wanted to avoid problems with angle-dependant transmission coefficient).

A cooling type is added to the building, in order to maintain ambient temperature to 26°C.

All the windows have a SHGC of 0.387, for 0° incident radiation, calculated by LBNL Window, and a ratio of frame of 10 %.

We expected cooling load, for static conditions, to be in the order of the result of following equation :

(IT_ENE*124+IT_SSE*48+IT_OSO*124+RadTotHor*198)*0.387*0.9
! 124 = WinSurf ENE, 48 = WinSurf SSE, 124 = WinSurf OSO, 198 = WinSurf Hor
! 0.387 = Win SHGC
! 0.9 = 1-ratioFrame

(TotalRad equation)

However, TRNSYS give us almost half of this load (P froid in this picture, VS AppSolaires calculated by TotalRad equation).

[cid:image002.jpg at 01CF97AA.BF095C90]

Do you have any idea of the reason our hand calculation is so far from TRNSYS calculation?

Thank you for your help !

Best regards,
Marcello Caciolo
Responsable Outils et Méthodes d'Analyse Energétique
[cid:image001.jpg at 01CF97A8.2250E320]

Cellule Efficacité Energétique et Environnementale - Pôle Projets et Réalisations
46 Boulevard de la Prairie au Duc
BP 40119 - 44201 Nantes Cedex 02
Tél.: +33 02 40 41 06 57
marcello.caciolo at cofelyaxima-gdfsuez.com<mailto:prenom.nom at aximaseitha-gdfsuez.com>
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