This connector is used for 1-dimensional heat flow between components. The variables in the connector are:
T Temperature in [Kelvin]. Q_flow Heat flow rate in [Watt].
According to the Modelica sign convention, a positive heat flow rate Q_flow is considered to flow into a component. This convention has to be used whenever this connector is used in a model class.
Note, that the two connector classes HeatPort_a and HeatPort_b are identical with the only exception of the different icon layout.