Civil Engineering Reference
In-Depth Information
Chapter 2
Units of Measure
Abstract
Units of measure
is the language of home energy information. We talk
about our energy consumption in terms of specific units used to measure the con-
sumption. Measuring is a vital part of the home energy information cycle. It is what
guides us toward the actions we need to take in order to conserve energy and protect
the environment. The ability to express those measurements in standard units has
long been a benefit in understanding energy consumption. Each type of fuel such
as electricity, natural gas, propane, fuel oil and others all have their own specific
units associated with respect to measuring their consumption. Other environmental
factors such as outside temperature affect our energy consumption. We measure
these as part of the home energy information cycle and they also have specific units
associated with them. We
derive
other values from the measurements to express
consumption in ways that are convenient to make comparisons over time and from
one location to another.
2.1
Electricity Units
Kilowatt-hours
(kWh) is the standard unit of measure for electricity. It is not the
easiest to understand primarily because it describes electric consumption over time.
In other words, it is a
rate
of electric consumption. This is how the electric compa-
nies charge us for the electricity we use. They track the number of kilowatt-hours of
electricity we use over the whole month and then charge us a standard rate (usually
10-20 cents) per kWh. We derive the unit kilowatt-hour from the unit of measure
called a
watt
. Electric power expressed in watts is the rate electric energy moves
through a circuit. One watt is equal to one joule per second. And 1000 W is equal
to 1 kW.
The watt was named after James Watt, a British engineer and inventor. He lived
from 1736 to 1819. The work of James Watt with respect to power resulted in the
steam engine that powered the industrial revolution [6]. However, most of what we
know today about electricity comes from Benjamin Franklin, a noted statesman and
inventor who lived from 1706 to 1790. Franklin's experiments in positive and nega-
tive electrical charges resulted in the electrical lighting we enjoy today [7].
