Energy Management for Water Treatment Facilities - Public Water Systems - page 1011

CHAPTER 30
Energy Management for Water
Treatment Facilities
INTRODUCTION
In recent years, dramatic increases in energy prices have made the public acutely aware
of the significance of energy costs. Energy, once a term used by relatively few scientists
and engineers, is not only well known to waterworks managers but also a household
topic of discussion. In the past, energy was rarely considered in the design and op-
eration of waterworks facilities. Now energy plays an important role in decisions that
pertain to the design and operation of water treatment plants, pumping stations, and
distribution systems. This chapter examines energy fundamentals, energy optimization,
and how these factors relate to capital and operating costs for waterworks facilities. A
generalized approach to an energy optimization evaluation is then presented, followed
by a discussion of energy conservation equipment and techniques.
ELECTRICAL ENERGY FUNDAMENTALS
Electrical systems are of either the direct current (DC) or alternating current (AC)
type. In direct current systems, the voltage remains constant, and current always flows
in the same direction. In alternating current systems, voltage and current follow sine
wave patterns, reversing direction regularly as shown in Figure 30-1, which represents
instantaneous power with coinciding voltage and current waveforms.
Apparent power delivered to an alternating current circuit is calculated by the vector
dot product of resistive power and reactive power. This relationship is illustrated in
the power triangle shown in Figure 30-2. Apparent power is expressed in units of
kilovolt-amperes (kVA); this is the demand placed on the electrical utility's system by
a customer. The resistive load actually performs work and is known as active power,
which is the power actually delivered to the customer; it is the value measured by a
customer's power meter as kilowatts (kW). Reactive load does not perform work but
is necessary to provide energy for changes in magnetic flux. The reactive demand on
a circuit is the algebraic sum of capacitive and inductive demands. When these de-
mands are equal, the sum is zero, and the reactive demand is zero. Under this condition,
the current and voltage function coincide, and a wave pattern (shown in Fig. 30-1)
results, with all power delivered to a circuit available as active power. When circuit
inductance is greater than capacitance, current will lag voltage, as shown in Figure
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