U-value in Prebid

["Marco Sangiorgi" <sangiorgim@xxxxxxx>]

Dear TRNSYS users,

I'm a little perplexed about the calculation of the final u-value of walls
in Prebid. The resulting u-value is not just the "sum" of the thermal
conductivity of the layers that composes the wall, but it additionally
combines heat transfer coefficients of 7.7 W/(mē K) inside and 25 W/(mē K)
outside. ??

What is it for? Is it possible to change these coefficients?

Moreover, the Prebid asks for the convective heat transfer coefficients of
the walls. So those additional coefficients in the calculation of the
u-value don't represent the heat transfer due to convection. So, what do
they represent physically? And how have they been calculated?

Thank you,

Marco