Page 297 - Mechanical Engineers' Handbook (Volume 4)

286 Energy Auditing

While lighting and HVAC systems will usually occupy most of the auditor’s time in a
commercial building, other systems such as domestic hot water may warrant attention. The
approach of first investigating operation and maintenance practices and then measuring sys-
tem performance is usually appropriate for these systems.

3 PERFORMING AN ENERGY AUDIT—IDENTIFYING OPPORTUNITIES FOR
SAVING ENERGY
In almost every facility one can discover a surprisingly large number of opportunities to save
energy. These opportunities range from the obvious such as use of light switches to exotic
approaches involving advanced energy conversion technologies. Identification of ways to
save energy requires imagination and resourcefulness as well as a sound knowledge of en-
gineering principles.
The auditor’s job is to find ways to eliminate unnecessary energy-using tasks and ways
to minimize the work required to perform necessary tasks. Some strategies that can be used
to eliminate unnecessary tasks are improved controls, ‘‘leak plugging,’’ and various system
modifications. Taking space conditioning as an example, it is necessary to provide a com-
fortable interior climate for building occupants, but it is usually not necessary to condition
a building when it is unoccupied, it is not necessary to heat and cool the outdoors, and it is
not necessary to cool air from inside the building if air outside the building is colder. Controls
such as time clocks can turn space-conditioning equipment off when a building is unoccu-
pied, heat leaks into or out of a building can be plugged using insulation, and modification
of the HVAC system to add an air-conditioner economizer can eliminate the need to cool
inside air when outside air is colder.
Chapter 4 discusses methods of analyzing the minimum amount of work required to
perform tasks. While the theoretical minimum cannot be achieved in practice, analysis from
this perspective can reveal inefficient operations and indicate where there may be opportu-
nities for large improvements. Strategies for minimizing the work required to perform nec-
essary tasks include heat recovery, improved efficiency of energy conversion, and various
system modifications. Heat recovery strategies range from complex systems to cogenerate
electrical and thermal energy to simple heat exchangers that can be used to heat water with
waste heat from equipment. Examples of improved conversion efficiency are more efficient
motors for converting electrical energy to mechanical work and more efficient light sources
for converting electrical energy to light. Some system modifications that can reduce the work
required to perform tasks are the replacement of resistance heaters with heat pumps and the
replacement of dual duct HVAC systems with variable air volume systems.
There is no certain method for discovering all of the energy-saving opportunities in a
facility. The most common approach is to review lists of energy conservation measures that
have been applied elsewhere to see if they are applicable at the facility being audited. A
number of such lists have been compiled (see, for example, Ref. 3). However, while lists of
measures are useful, they cannot substitute for intelligent and creative engineering. The
energy auditor’s recommendations need to be tailored to the facility, and the best energy
conservation measures often involve novel elements.
In the process of identifying energy saving opportunities, the auditor should concentrate
first on low-cost conservation measures. The savings potential of these measures should be
estimated before more expensive measures are evaluated. Estimates of the savings potential
of the more expensive measures can then be made from the reduced level of energy con-
sumption that would result from implementing the low-cost measures. While this seems