Mixing volume with a heat port.
This model is identical to BuildingSystems.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume, except that it has a heat port.
Note that this model is typically only used to implement new
component models that have staggered volumes. In contrast to
BuildingSystems.Fluid.MixingVolumes.MixingVolume,
it does not set initialize_p to final in
order for this model to be usable in staggered volumes which
require one pressure to be set to initialize_p = not
Medium.singleState and all others to false.