Helper control model for the example Buildings.Fluid.HeatPumps.ModularReversible.Examples.BaseClasses.PartialOneRoomRadiator The control enables a PI control of the heat pumps compressor speed for both heating and cooling. Depending on a hysteresis, the heating or cooling mode is selected. If the radiator supply temperature drops below a critical value, the heat pump will turn to heating mode. This prohibits possible freezing or water condensation.