By measuring energy-efficiency changes, we have a way of knowing if we have achieved our goals.
Energy efficiency is an interesting and useful concept for analyzing energy use.
Energy-efficiency loss occurs when more energy inputs are required to produce the same or reduced products or services. In reality, however, energy efficiency is difficult to measure. Because energy needs to be assessed relative to the amount of product or service provided, energy-use rates, commonly called energy intensities, are the measures ordinarily used to assess efficiency trends. Energy intensities reflect not only energy efficiency but also changes in other effects such as weather and extent of occupancy. However, the advantage of considering individual energy intensities is that you may easily measure and track them over time.