Controller for domestic water heater using heat pump - has timer to ensure off-peak operation and has simulator circuit to delay use of auxiliary element until last possible moment

摘要

The arrangement uses a heat pump as the principal heat source and an electric resistance heater as an auxiliary heat source. A timer relay ensures that the heater is operative only during the times when off-peak electricity tariffs apply. The heat pump is controlled by a conventional thermostatic switch, and the auxiliary element is controlled by a delay circuit which delays the switching on to stagger the onset of the off-peak load on the supply system. The control circuit monitors the water temp. and generates a ramp function, simulating the heating time. This function is used to determine the moment of switch-on so that the water has just reached full temp. when the off-peak period finishes.