Exergy analysis of electrically- and thermally-driven engines to drive heat pumps: An exhaustive comparative study

The choice of driving a heat pump with an electrically- or a thermally-driven engine is a vexing question complicated by the carbon footprint and environmental impact of using electricity versus natural gas (or waste heat) as the main driver for the respective engines. Useful work generated by these two distinct engines is the focal point of this paper, addressing a key question: which engine presents a better choice for a given heat pumping application within the constraints of energy and environmental stewardship? We examine this question comprehensively through the methodology of energy, exergy, and availability analysis, explaining clearly, why the output of work from these two distinct engines is inherently vastly different. Thermodynamic consistency is guaranteed by satisfaction of the First and Second Laws applied to closed systems and their subsystems. The general conclusion is that thermally-driven engines are not industrious converters of heat to mechanical work, for heat pumps.