For each two-port component, the temperature difference across the component, ΔT, is expressed as:

Note that the temperature difference is attached to a component, and has therefore the same value at its two ports p1 and p2. It is available for postprocessing, for example with the lts.R1_DT variable, when considering a Conductive Thermal Resistor component with name R1.

The heat rate through a two-port component, P, is expressed in different ways depending on the represented device. Then, the heat rates at ports p1 and p2, Pp1 and Pp2, are defined from P. The different cases are summarized in Table 4-4.

Note that for thermal resistors components, the heat rate at port p1 has the same sign as the temperature difference ΔT across the component. In practice, when the temperature at port p2 is higher than the temperature at port p1 (ΔT>0), applying conductive heat transfer between these two ports is equivalent to apply a heat source (positive heat rate Pp1) at port p1.

For the heat pipe component, the port p1 should correspond to the evaporator side (hot side), and the port p2 should correspond to the condenser side (cold side). Therefore, the temperature difference ΔT across the component should be negative in normal operating conditions. With this setting, Pp1 is always negative as well, meaning that cooling is applied on the hot side.

For the heat rate source component, the heat rate is fully applied on port p2.

For the thermoelectric module component, the heat rates P1,src and P2,src can be expressed in different ways. See Theory for the Thermoelectric Module Component for more details.