Energy
Efficiency: Definition 
"Take
the Stairs--Be More Energy Efficient"
Person A interprets the
sign as the "true" definition of energy efficiency. To Person A,
the elevator is not being used. He is still getting to where he
wants to go and using less energy in doing so.
Person B considers the fact
that she is not getting to where she is going with the same ease.
She does not believe that she is being energy efficient, but instead
she believes that she is "conserving energy" at a reduced level
of service—she has to walk instead of ride.
When it comes to trying to define
"to be energy efficient" or "energy efficiency", there does
not seem to be a single commonly-accepted definition of energy efficiency.
Along the lines of Person B’s thinking, it is generally thought
that an increase in energy efficiency is when either energy inputs
are reduced for a given level of service, or there are increased
or enhanced services for a given amount of energy inputs.
When EIA asked participants
in energy-efficiency
workshops to define "energy efficiency," participant definitions
reflected two different perspectives: either (1) a service perspective
or (2) a mechanistic, strict intensity, perspective.
Some participants believed that
energy-efficiency indicators could measure some kind of economic
well-being, and suggested that a wide range of indicators would
offer insight into the "ordinary business of life" and the relationships,
causes, and opportunities in observed trends. Another suggested
concept of efficiency is a strict technological (equipment-based)
concept. This concept cannot be strictly measured by broad intensities,
because intensities tend to carry structural and behavioral components.
Alternatively, some participants believe that differentiating between
intensity and efficiency is not possible. While others use complex
methodology to separate out the activity and structural effects
with the remaining unexplained portion considered to be an approximate
to the energy efficiency effects.
Most of what is defined as energy
efficiency is actually energy intensity. Energy intensity is the
ratio of energy consumption to some measure of demand for energy
services—what we call a demand indicator. However, at best, energy-intensity
measures are a rough surrogate for energy efficiency. This is because
energy intensity may mask structural and behavioral changes that
do not represent "true" efficiency improvements such a shift away
from energy-intensive industries. [See "Energy-Efficiency
Measurement: Discussion"].
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