Transient thermal resistance for yearly load

Effective transient thermal resistance in the earth for yearly load (transient period $\tau$ of 1 year):

For deeply buried cables and for tunnels, the yearly load variations play a significant role because of the very long constants at great depths.

Symbol
$T_{4y}$
Unit
K.m/W
Formulae
$\frac{\rho_{4} \ln{\left(\frac{D_{x_{y}}}{Do_{d}} \right)}}{2 \pi}$
$\rho_{4}$
Used in
$T_{4\mu}$