A comparative study of the thermal and economic performance of the parallel and series solar-heat pump systems, stand-alone solar, and stand-alone heat pump systems for residential space and domestic hot water heating has been undertaken for the United States using FCHART 4.0 [1]. The results are useful for a regional assessment of the viability of the different systems, and for assessing policies that will encourage the implementation of the most energy efficient system. The magnitude of the potential energy savings was determined for each system on the basis of an equal total system cost in the case of the series, parallel, and solar systems. The cost was governed by current federal tax credits, and found to be 10,000 dollars. The size and cost of the heat pump are the same in the series, parallel, and stand-alone heat pump systems. A line can be drawn across the United States north of which the parallel heat pump system saves the most energy, and south of which the solar system saves the most. The better of either the solar or the parallel systems consistently used less energy than either stand-alone heat pump or series systems for all locations. The conventional oil or gas furnace seasonal efficiency which would be required to save as much primary energy as the better alternative system was identified regionally. In all but the northern portions of the United States, conventional furnaces would use more primary energy than the better alternative system. The price that the solar collector in the series heat pump system would have to be so that a larger collection system could be installed and the series system would match the energy savings of the preferred system, whether solar or parallel heat pump, was calculated. This price was one-half to two-thirds of current collector prices. The break-even electricity price was determined which is the price below which the life cycle savings of the alternative system are positive. The better alternative was found to be economic against oil furnaces in all regions of the U.S., but economic against gas furnaces only in the Southwest.

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