The temperature of the outer jacket is identical to the external temperature $theta_e$.
*** These formulae are valid when the outer temperature defines the load.
| $\theta_a+v_4 \Delta \theta_p-\left(v_4-1\right) \Delta \theta_x+\left(T_{4iii}+T_{4db}\right) v_4 W_{hs}$ | Heat sources buried |
| $\frac{W_{hs} T_{st} T_{sa}+\theta_t T_{sa}+\theta_{at} T_{st}}{T_{sa}+T_{st}}$ | Heat sources in ventilated tunnel |
| $\theta_t+T_{4iii} W_{hs}$ | Heat sources in channel (Heinhold) |
| $\theta_{at}+T_{4iii} W_{hs}$ | Heat sources in trough |
| $\theta_a+v_4 \Delta \theta_p-\left(v_4-1\right) \Delta \theta_x+\left(T_{4iii}+T_{tr}\right) v_4 W_{hs}$ | Heat sources in filled troughs |
