Environmental Engineering Reference
In-Depth Information
to the transportation and buildings sectors respectively.
Reducing the energy and emissions numbers is what
the rest of this chapter is about, and large reductions are
possible at little if any cost to the economy.
In what follows I discuss end-use energy ef
ciency
and include all the energy that goes into some application
(the primary energy), as well as looking at howmuch energy
is used compared to the minimum to do the same job.
Primary and End-Use Energy Ef
ciency
Primary energy is what goes into a process or a product and
includes what is used to make secondary forms of energy.
For example, electricity is not a primary form of energy. It
has to be generated in some fashion using some kind of fuel.
Electricity at the wall plug in the United States on the
average contains only
% of the primary energy used to
generate it. Totaling up all of the energy used in a building
has to include the energy used to generate the electricity
used, if we are to get at the primary energy use.
Suppose I have two houses heated by gas heaters of
%
ef
ciency, but one house is well insulated while the other
needs twice as much gas to keep it warm. The heaters have
the same ef
ciency, but the well-insulated house uses half
the energy and so in end-use terms it is twice as ef
cient.
Plug-in hybrid cars are on the road, getting part of their
fuel by charging their batteries from the electric power grid,
and part from running on gasoline. The miles per gallon on
gasoline will go way up, but the electrical energy needs to be
included too. The primary energy used to generate electri-
city plus the energy in the gasoline need to be counted in
getting at the total. If we ever get hydrogen-powered
vehicles, the energy required to make the hydrogen has to
be counted to get the primary energy requirement and the
overall ef
ciency.
