Control for heat pump with auxiliary heat source

摘要

A method of controlling a heating system including at least a first stage heat pump and a second stage auxiliary heater, and a control that implements the method. The control shuts off the first stage heat pump during cold outside temperatures without the need to directly sense the outside temperature. The method includes selectively turning on the first stage heat pump or the second stage auxiliary heater based upon a measure of the amount of time at least one of the stages was on verses the time neither of the stages was on. This can be implemented with a counter that increases when neither the heat pump nor the auxiliary heater is on, and that decreases when either the heat pump or the auxiliary heater is on.