Page 291 - Mechanical Engineers' Handbook (Volume 4)

280 Energy Auditing

procedures must be used to keep the cost of performing an audit below the value of potential
energy savings. Standardized procedures make it possible for audits to be performed quickly
by technicians with relatively limited training.
Commercial buildings lie between these extremes of specialization. The term ‘‘com-
mercial building’’ as used here refers to those nonresidential buildings that are not used for
the production of goods and includes office buildings, schools, hospitals, and retail stores.
The largest energy-using systems in commercial buildings are usually lighting and HVAC
(heating, ventilating, and air conditioning). Refrigeration consumes a large share of the en-
ergy used in some facilities (e.g., food stores) and other loads may be important in particular
cases (e.g., research equipment in laboratory buildings). Table 2 shows the results of a
calculation of the amount of energy consumed in a relatively energy-efficient office building
for lighting and HVAC in different climates. Office buildings (and other commercial build-
ings) are quite variable in their design and use. So, while the proportions of energy devoted
to various uses shown in Table 2 are not unusual, it would be unwise to treat them (or any
other proportions) as ‘‘typical.’’ Because of the variety and complexity of energy-using sys-
tems in commercial buildings and because commercial buildings frequently use quite sub-
stantial amounts of energy in their operation, an energy audit in a commercial building often
warrants the effort of a highly trained professional. In the remainder of this section com-
mercial buildings will be used to illustrate energy auditing practice.
Lighting systems are often a good starting point for an analysis of energy in commercial
buildings. They are the most obvious energy consumers, are usually easily accessible, and
can provide good opportunities for energy saving. As a first step the auditor should determine
the hours of operation of the lighting systems and the watts per square foot of floorspace
that they use. These data, together with the building area, are sufficient to compute the energy
consumption for lighting and can be used to compare the building’s systems with efficient
lighting practice. Next, lighting system maintenance practices should be examined. As shown
in Fig. 1, the accumulation of dirt on lighting fixtures can significantly reduce light output.
Fixtures should be examined for cleanliness and the auditor should determine whether or
not a regular cleaning schedule is maintained. As lamps near the end of their rated life, they
lose efficiency. Efficiency can be maintained by replacing lamps in groups before they reach
the end of their rated life. This practice also reduces the higher maintenance costs associated
with spot relamping. Fixtures should be checked for lamps that are burned out or show signs
of excessive wear, and the auditor should determine whether or not a group-relamping pro-
gram is in effect.
After investigating lighting operation and maintenance practices, the auditor should mea-
sure the levels of illumination being provided by the lighting systems. These measurements
can be made with a relatively inexpensive photometer. Table 3 gives recommended levels of

Table 2 Results of a Calculation of the Amount of Energy Consumed in a Relatively
Energy-Efficient Office Building for Lighting and HVAC 5
Energy Use (kBtu/ft /yr)
2
Miami Los Angeles Washington Chicago
Lights 34.0 34.0 34.0 34.0
HVAC auxiliaries 8.5 7.7 8.8 8.8
Cooling 24.4 9.3 10.2 7.6
Heating 0.2 2.9 17.7 28.4
Total 67.1 53.9 70.7 78.8