system is representative, this is a conservative as-
ally result in significant mass losses. For ex-
sumption, since the Ft. Jackson system is relatively
ample, the CRREL analysis of the Hawthorne
new and is undoubtly more thermally efficient than
AAP steam system described above has
the Army's average system.
shown that about 50% of the mass is lost in
While these savings are significant, the cost of
distribution.
replacing the piping systems would be enormous.
4.
Maintenance is lower and the systems are
Current replacement cost for high temperature wa-
safer as a result of lower temperatures and
ter and steam systems is approximately 00 per
pressures. Frequently buildings can be con-
lineal meter (0 per lineal ft). If we assume that
nected directly to the central system with-
the cost of the LTHW systems is 50% of the cost of
out heat exchangers because of the lower
the high temperature water and steam systems
temperatures and pressures.
they would replace, it would cost about .8 billion
5.
Cogeneration of electricity is more favor-
to replace all the Army's 5600 km (3500 mi) of sys-
able because the lower condensing tempera-
tems. Thus, the simple payback would be unac-
ture results in higher efficiency of the power
ceptable, at about 23 years. But since these systems
generating cycle.
are continuously being replaced, many opportuni-
6.
Lower density loads can be served economi-
ties exist to convert to LTHW in those instances.
cally. Because of the lower piping cost and
Even when building conversion costs are consid-
simpler systems, it becomes economical to
ered, conversion to LTHW may be less costly than
extend the distribution system into areas
replacing in-kind from a capital cost standpoint
where the loads are smaller and farther apart.
alone. When the reduced operating costs of LTHW
For this reason, even residential areas are
are considered, LTHW will have the lowest life cycle
served by low temperature systems in Eu-
cost in many cases.
rope.
7.
Low temperature systems are more easily
adaptable to many alternate sources of en-
ergy, such as solar, geothermal, and waste
CONCLUSIONS
heat.
The objective of this report was to present in-
formation on the efficiency of heat distribution
We hope that this report has helped provide
systems. Data were presented from several field
evidence of the major advantages of low tem-
studies conducted by CRREL on operating sys-
perature hot water systems. Perhaps the stron-
tems of Army bases. After studying this report
gest support for the concept comes from Europe
the reader will conclude that low temperature hot
where the vast majority of the systems are LTHW.
water is a superior means of heat distribution.
There the much higher penetration of district heat
The primary advantages of low temperature wa-
as a space heating means is primarily due to the
ter systems are listed below:
efficiency of the LTHW systems. If the DoD is to
remain committed to district heating technology
1. Capital costs are only about 50% of those for
on its bases we must begin to convert existing
high temperature water and steam systems.
high temperature water and steam systems to
This is a result of the much simpler system
LTHW. If this is not done, it will become increas-
with fewer provisions for expansion and
ing difficult to justify the use of district heating.
high pressures. In addition, the insulation
This is true, even when all the inherent advantages
and jacketing materials that can be used with
of district heating from energy efficiency and en-
LTHW not only perform better but they are
vironmental impact standpoints are considered,
less costly.
due to increased competition from alternate fu-
2. Heat losses are drastically reduced. As illus-
els, especially natural gas.
trated by the data given above, CRREL's
measurements have shown the heat losses
to be about 35% of those for a high tempera-
SELECTED BIBLIOGRAPHY
ture water system.
3. Leakage is usually much lower due to lower
ASHRAE (1985) ASHRAE Handbook., 1985 Funda-
temperature and pressure. This is particu-
mentals Volume, Chapter 15. Atlanta, Georgia: Ameri-
larly true when compared to steam systems
can Society of Heating, Refrigerating, and Air-Con-
where problems with condensate return usu-
ditioning Engineers.
23
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