Estimating the heating seasonal operating cost of residential hybrid heat pump systems, including units retrofitted to oil, gas and electric furnaces

A method is presented for estimating the heating seasonal operating cost of a residential, hybrid heating system consisting of an electric heat pump and a warm-air furnace.The approach described is applicable to heat pump/control system/gas or oil-fired furnace which is sold as a package or to a heat pump/control system which is Intended to be added to an existing gas, oil or electric furnace.Recommendations are made regarding how such systems can be rated and the type of information that would assist consumers in comparing the operating cost of a hybrid heat pump system with that of a conventional heat pump or furnace.Different control strategies are accounted for and examples are presented (in the appendix) for estimating the heating seasonal operating cost of hybrid systems employing both single and two-speed com- pressors .