Equivalent thermal resistance for tunnel

A delta-star transformation is used to derive the following parameters used to calculate the equivalent thermal resistance of the surrounding soil of a tunnel:

Symbol
$T_{4t}$
Unit
K.m/W
Formulae
$N_{c} N_{sys} \left(T_{s} + \left(T_{e} + T_{t}\right) \left(- \frac{\left(T_{e} + T_{t}\right) e^{- \frac{L_{T}}{L_{0}}}}{T_{a} + T_{e} + T_{t}} + 1\right)\right)$
Used in
$\Delta \theta_{c}$
Image
IEC standard 60287-2-3 Ed. 1.0 (2017) Figure B.1