Energy Efficiency

Definition

Energy efficiency is the ratio between the useful energy output and the energy input of a thermodynamic system.

Theory and Application

Introduction

The energy efficiency metric originates from the early development of thermodynamic cycles, such as the steam engine and internal combustion engine. However, the metric can be applied to any thermodynamic system. It serves as a performance criterion of the corresponding system. Figure 1 illustrates a generic energy flow diagram of a thermodynamic system, with the system boundary shown by the dashed line.

Fig. 1

General energy flow in a thermodynamic system