Re: [TRNSYS-users] u-value of wall

[David Bradley <bradley@tess-inc.com>]

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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