Environmental Engineering Reference
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of residential, commercial and office buildings. A seasonal energy storage
system is designed to store heat or cold energy during one season, when it
is not needed, for use during another season.
To be cost-effective, these types of technologies are usually applied
to groups of buildings, but cogeneration and seasonal energy storage sys-
tems may be sized for small-scale applications. District heating may in-
clude cogeneration or summer storage of solar energy for winter space
District heating usually involves supplying hot water for space heat-
ing and hot water use from a central production facility to a group of res-
idential or commercial buildings. District heating networks in Europe
serve large portions of the populations of some countries. In Sweden, 25%
of the population is served by district heating, in Denmark the number is
over 30%, in Russia and Iceland it is over 50%. In the United States, dis-
trict heating serves only about 1% of the population through older steam
supply systems. In Europe, many of the district heating systems were in-
stalled during the rebuilding that followed World War II.
District heat replaces relatively inefficient home heating systems with
a more efficient, centralized boiler or cogeneration system. This offers the
potential of major energy savings, although some heat is lost during the
distribution of hot water. A centralized boiler or cogeneration system can
be used to produce heat. Large, centralized oil-fired boilers can remove as
much as 90% of the energy contained in the fuel. Cogeneration systems can
also have a total heat and electricity efficiency approaching this.
District heating systems can use the waste heat from electric genera-
tion and industrial plants that would be released to the air or to nearby
water supplies. Some estimates suggest that district heating could save as
much as one billion barrels of oil per year in the United States.
In some European cities, waste heat from fossil fuel electric power
plants is used for district heating with an overall energy efficiency of 85%.
These plants were not originally constructed as cogenerating units. Waste
heat from industrial process plants can also be used. Geothermal sources
are used to provide heat for district heating systems in Iceland and Boise,
Hot water can be transported over longer distances with little heat
loss while steam heat distribution systems can only serve high-density re-
gions. The largest steam system in the United States is a part of New York's
Consolidated Edison Company and serves a small part of Manhattan Is-
land. The larger pipes or mains carry 200 to 250°F water under pressure. Re-
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