A heat source is defined as having a positive heat dissipation, whereas a heat sink is defined by a negative value.
*** These formulae are valid when the outer temperature defines the load.
| $\frac{\theta_e-\theta_a-v_4 \Delta \theta_p+\left(v_4-1\right) \Delta \theta_x}{\left(T_{4iii}+T_{4db}\right) v_4}$ | Heat sources buried |
| $\frac{\theta_e \left(T_{sa}+T_{st}\right)-\theta_t T_{sa}-\theta_{at} T_{st}}{T_{st} T_{sa}}$ | Heat sources in ventilated tunnel |
| $\frac{\theta_e-\theta_t}{T_{4iii}}$ | Heat sources in channel (Heinhold) |
| $\frac{\theta_e-\theta_{at}}{T_{4iii}}$ | Heat sources in trough |
| $\frac{\theta_e-\theta_a-v_4 \Delta \theta_p+\left(v_4-1\right) \Delta \theta_x}{\left(T_{4iii}+T_{tr}\right) v_4}$ | Heat sources in filled troughs |
