ABSTRACT
This chapter explores the most common definitions of energy efficiency used in the market. Gross efficiency and net efficiency are primarily associated with energy systems involving the burning of fuels. Primary energy is the fossil-based fuels used directly in a unit operation. All physical material and energy in this world is governed by and conforms to two natural laws of physics. The concept of efficiency is derived from these fundamental laws by comparing any utility consumption in excess of the theoretical minimum. The concept of yield and efficiency is a useful measure of performance as it measures changes in performance of a manufacturing plant, product performance and services rendered. Although the concept of energy efficiency is a simple concept, there are many different definitions of efficiency used in the industry and tailored to specific systems or equipment items. Manufacturers, and even governments, come up with many different terminologies and different ways to calculate energy efficiency.
