Page 298 - Mechanical Engineers' Handbook (Volume 4)

3 Performing an Energy Audit—Identifying Opportunities for Saving Energy 287

obvious, there have been numerous occasions on which costly measures have been used but
simpler, less expensive alternatives have been ignored.

3.1 Low-Cost Conservation
Low-cost conservation measures include turning off energy-using equipment when it is
not needed, reducing lighting and HVAC services to recommended levels, rescheduling of
electricity-intensive operations to off-peak hours, proper adjustment of equipment controls,
and regular equipment maintenance. These measures can be initiated quickly, but their ben-
efits usually depend on a sustained effort. An energy management program that assigns
responsibility for maintaining these low-cost measures and monitors their performance is
necessary to ensure good results.
In commercial buildings it is often possible to achieve very large energy savings simply
by shutting down lighting and HVAC systems during nonworking hours. This can be done
manually or, for HVAC systems, by inexpensive time clocks. If time clocks are already
installed, they should be maintained in good working order and set properly. During working
hours lights should be turned off in unoccupied areas. Frequent switching of lamps does
cause some decrease in lamp life, but this decrease is generally not significant in comparison
to energy savings. As a rule of thumb, lights should be turned out in a space that will be
unoccupied for more than 5 min.
Measurements of light levels, temperatures, and air flow rates taken during the auditor’s
survey will indicate if lighting or HVAC services exceed recommended levels. Light levels
can be decreased by relamping with lower-wattage lamps or by removing lamps from fix-
tures. In fluorescent fixtures, except for instant-start lamps, ballasts should also be discon-
nected because they use some energy when the power is on even when the lamps are
removed.
If the supply of outside air is found to be excessive, reducing the supply can save heating
and cooling energy (but see below on air-conditioner economizers). If possible, the reduction
in air supply should be accomplished by reducing fan speed rather than by restricting air
flow by the use of dampers, since the former procedure is more energy efficient. Also, too
much air flow restriction can cause unstable operation in some fans.
Because most utilities charge more for electricity during their peak demand periods,
rescheduling the operation of some equipment can save considerable amounts of money. It
is not always easy to reschedule activities to suit the utility’s peak demand schedule, since
the peak demand occurs when most facilities are engaging in activities requiring electricity.
However, a careful examination of major electrical equipment will frequently reveal some
opportunities for rescheduling. Examples of activities that have been rescheduled to save
electricity costs are firing of electric ceramic kilns, operation of swimming pool pumps,
finish grinding at cement plants, and pumping of water from wells to storage tanks.
Proper adjustment of temperature and pressure controls in HVAC distribution systems
can cut losses in these systems significantly. Correct temperature settings in air supply ducts
can greatly reduce the energy required for reheat. Temperature settings in hot water distri-
bution systems can usually be adjusted to reduce heat loss from the pipes. Temperatures are
often set higher than necessary to provide enough heating during the coldest periods; during
milder weather, the distribution temperature can be reduced to a lower setting. This can be
done manually or automatically using a reset control. Reset controls are generally to be
preferred, since they can adjust the temperature continuously. In steam distribution systems,
lowering the distribution pressure will reduce heat loss from the flashing of condensate
(unless the condensate return system is unvented) and also reduce losses from the surface