Residences require electricity for lights, appliances, and space cooling and thermal energy for space and domestic water heating. Total energy systems (TES) which provide both electricity and thermal energy can meet these needs more effectively than conventional systems because thermal energy rejected during the on-site production of electricity can be recovered to meet the heating loads. TESs based on fuel cell systems are particularly attractive because of their high efficiencies, quiet operation, and small size. This research evaluates a TES consisting of a fuel cell sub-system (FCS), an electric heat pump (HP), and a thermal storage tank (TS).

A model of a grid-independent, electric load following TES is developed to determine the energy required to meet the hourly average electric and thermal loads of the residence. The TES uses a heat pump to provide space cooling. Electricity for air conditioning, lights, and appliances is provided by the FCS. Space heating and water heating of the residence are provided by the thermal energy available from the FCS. The TES is designed so that, heating requirements that exceed the heat available from the FCS can be satisfied by the HP and an electric water heater. A thermal storage tank is used to store and transfer thermal energy from the FCS to the residence.

The results of the research include a comparison of the energy use by the TES to the energy use by conventional residential energy systems; an evaluation of the effects of climatic conditions on system performance and energy use; and a comparison of the life-cycle cost of the TES and conventional residential energy systems. The results indicate that total energy systems can reduce primary energy use by as much as 40 percent, but that to be economically attractive, the FCS cost must be reduced to approximately $500/kWe.