Page 290 - Mechanical Engineers' Handbook (Volume 4)

2 Performing an Energy Audit—Analyzing Energy Use 279

Table 1 The Percentage of Energy Saved as a Result of Implementing Energy Audit
Recommendations in 172 Nonresidential Buildings a,4
Site Source
Savings Sample Savings Sample
Building Category (%) Size (%) Size
Elementary school 24 72 21 72
Secondary school 30 38 28 37
Large office 23 37 21 24
Hospital 21 13 17 10
Community center 56 3 23 18
Hotel 25 4 24 4
Corrections 7 4 5 4
Small office 33 1 30 1
Shopping center 11 1 11 1
Multifamily apartment 44 1 43 1
a
Electricity is counted at 3413 Btu/kWhr for site energy and 11,500 Btu/kWhr for source energy (i.e., including
generation and transmission losses).

time that is long enough for some of the early audit recommendations to be implemented.
The resultant savings can greatly increase the auditor’s credibility with the facility’s operators
and management, so that he or she will receive more assistance in completing his or her
work and his or her later recommendations will be attended to more carefully.
The amount of time devoted to analyzing energy use will vary, but, even in a walk-
through audit, the auditor will want to examine records of past energy consumption. These
records can be used to compare the performance of a facility with the performance of similar
facilities. Examination of the seasonal variation in energy consumption can give an indication
of the fractions of a facility’s use that are due to space heating and cooling. Records of
energy consumption are also useful in determining the efficacy of past efforts to conserve
energy.
In a surprising number of facilities the records of energy consumption are incomplete.
Often records will be maintained on the costs of energy consumed but not on the quantities.
In periods of rapidly escalating prices, it is difficult to evaluate energy performance with
such records. Before visiting a facility to make an audit, the auditor should ask that complete
records be assembled and, if the records are not on hand, suggest that they be obtained from
the facility’s suppliers. Good record keeping is an essential part of an energy management
program. The records are especially important if changes in operation and maintenance are
to be made, since these changes are easily reversed and often require careful monitoring to
prevent backsliding.
In analyzing the energy use of a facility, the auditor will want to focus his or her
attention on the systems that use the most energy. In industrial facilities these will typically
involve production processes such as drying, distillation, or forging. Performing a good audit
in an industrial facility requires considerable knowledge about the processes being used.
Although some general principles apply across plant types, industrial energy auditing is
generally quite specialized. Residential energy auditing is at the other extreme of speciali-
zation. Because a single residence uses relatively little energy, highly standardized auditing