[TRNSYS-users] u-value of wall

[David Bradley]

Jan-Willem,



> /When defining a new wall, TRNBUILD calculates a standard U-value 
> determined /
>
> /with combined heat transfer coefficients of 7.7 W/m²K inside and 25 
> W/m²K /
>
> /outside (see volume 6 page 23). These U-values are correct for a 
> vertical /
>
> /wall separating an inside environnement from an outside 
> environnement, but /
>
> /not for horizontal walls and inside vertical walls. Does TRNBUILD take /
>
> /these distinctions into account or does it use these two standard /
>
> /coefficients (7 and 25) for every wall types ?/
>
The values displayed by TRNBuild always assume the 7.7 inside and 25 
outside regardless of wall orientation. Those values are NOT the ones 
used during the simulation. During the simulation, the inside and 
outside convection coefficients are determined by whatever method you 
have used in TRNBuild to specify them (input, constant value, schedule, 
or internal calculation). If you want to know the exact u-value of the 
wall, you choose the appropriate surface NTYPE among the Type56 outputs. 
The user does not have the ability to change the radiation coefficient 
in TRNSYS 16, only the convective portion. The algorithms used if you 
choose the "internal calculation" are described both in the Type56 
mathematical description (volume 6) and in the Type80 mathematical 
description.
Kind regards,
 David


> //
>

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Thermal Energy System Specialists (TESS), LLC 
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