Page 202 - Alternative Energy Systems in Building Design

178 ENERGY CONSERVATION

In large commercial or industrial complexes where large amounts of electric power
are used for fluorescent lighting or heavy machinery, the efficiency of incoming
power, which depends on maintenance of the smallest possible phase angle between
the current and the voltage, is usually lowered, thus resulting in a significant waste of
energy. The cosine of the phase angle between the current and the voltage, referred to
as the power factor, is the multiplier that determines whether the electric energy is
used at its maximum to deliver lighting or mechanical energy or is wasted as heat.
Power P in electrical engineering is defined as the product of the voltage V and current
I times the cosine of the phase angle, or P = V × I × cosine phase angle. When the
phase angle between the current and the voltage is 0, the cosine equals 1, and there-
fore, P = V × I, which represents the maximum power conversion or delivery.
The principal components of motors, transformers, and lighting ballasts are wound-
copper coils referred to as inductance elements. A significant characteristic of induc-
tors is that they have a tendency to shift the current and voltage phase angles, which
results in power factors that are less than 1 and hence reduced power efficiency. The
power usage performance, which is defined as the ratio of the output power to the
maximum power, is therefore used as the figure of merit. The reduction in electric
power efficiency resulting from reactive power is wasted energy that is lost as heat. In
a reactive circuit, the phase angle between the current and the voltage shifts, thus giving
rise to reactive power that is manifested as unused power, which dissipates as heat.
Mitigation measures that can be used to minimize inductive power loss include the
installation of phase-shifting capacitor devices that negate the phase angle created by
induction coils. As a rule, the maximum power affordable for efficient use of electric
power should be above 93 percent. In situations where power-factor measurements
indicate a value of less than 87 percent, power losses can be minimized by using
capacitor reactance.

Electric Power Generation

and Distribution

It is interesting to observe that most of us, when using electric energy, are oblivious to
the fact that the electric energy provided to our household, office, or workplace is
mostly generated by extremely low-efficiency conversion of fossil fuels such as coal,
natural gas, and crude oils. In addition to producing substantial amounts of pollutants,
electric plants operate with meager efficiency and deliver electricity to the end user
with great loss. To illustrate this point, let us review the energy production and delivery
of a typical electricity-generating station that uses fossil fuel.
By setting an arbitrary unit of 100 percent for the fossil-fuel energy input into the boil-
ers, we see that owing to losses resulting from power-plant machinery such as turbines,
generators, high-voltage transformers, transmission lines, and substations, the efficiency
of delivered electric energy at the destination is no more than 20–25 percent. The
efficiency of energy use is reduced further when the electric energy is used by motors,