Economic comparison of solar-assisted heat pumps

A study of the economic performance of a solar system, air-to-air heat pumps, and several solar-assisted heat pump systems (SAHP) for residential heating is presented. The study is based on a computer simulation which is supported by monitoring data from an existing installation, the Terrosi-Grumman house in Quechee, Vermont. Three different SAHP configurations as well as conventional solar and air-to-air heat pump systems are evaluated for a northern New England climate. All systems are evaluated both with and without a peak/off-peak electricity price differential.

The SAHP systems are: (1) the series system in which the solar storage serves as the energy source for the heat pump, (2) the series off-peak system in which the heat pump in the series system operates only during certain periods of the day under a special electric rate structure, (3) a parallel system in which the environment is the source for both the collector and the heat pump, and (4) a peak/off-peak parallel system in which oil is operated during the period of peak electricity price. Hybrid air-to-air heat pump/oil systems are also evaluated.

For all alternatives, two different economic analyses are used: (1) the rate of return which emphasizes the return earned on the capital investment, and (2) the life cycle critical price which compares the current capital cost to the present worth of the stream of all future energy savings.

Both economic measures select the air-to-air heat pump/on-peak oil system when there is a peak/off-peak electricity price differential. (In this case the ratio of off-peak to average price is 40 per cent.) When there is no price differential, the air-to-air heat pump/oil system is still preferred, but the oil system is now operated when the ambient temperature falls below ?6.7°C (20°F). When the electricity price is doubled (from 19.5 to 40$/GJ), solar/oil is the preferred system.