experiences of the European systems (Werner 1984)
boiler plant operation was continuous. Savings in
it would seem reasonable to assume that the distri-
an entire year would be somewhat greater. Addi-
bution efficiency of a low temperature water system
tional savings might also be possible by switching
might be of the order of 90% or more. This com-
the buildings from heating domestic hot water with
pares very favorably with our estimate of 43% for
electricity to using the low temperature system for
Hawthorne AAP.
that purpose. This would require that the system be
Our estimates of mass losses from the Hawthorne
left in operation over the entire year, rather than
AAP steam system are also cause for concern. On
being shut down for the summer as is done now.
the average only 46% of the steam that leaves the
With the greatly reduced rate of heat loss from the
plant is returned as condensate. Relatively high mass
low temperature hot water system, the cost of heat
losses are commonplace in steam systems, prima-
losses from the system during the summer months
rily due to the problems associated with condensate
might not make this economically prohibitive, as it
collection and return. Makeup rates of 10 to 20% are
would be with the existing steam system.
normally considered good for steam systems. The
To determine if it would be economically fea-
Hawthorne system, however, has a makeup rate of
sible to convert the steam system at Hawthorne
54%. Some steam systems are even worse than the
AAP to a low temperature hot water system, CRREL
Hawthorne AAP system. For example, the author
contracted with the Sacramento District of the US
was recently told of a 10-year-old steam system
Army Corps of Engineers to prepare a detailed cost
designed to return all of the condensate that was in
estimate and preliminary design for the conversion.
fact returning only 10% of the condensate, i.e., a
The design work consisted of a concept design for
makeup rate of 90%. For a low temperature hot
the entire system and a detailed design for con-
water system, the makeup rate would most likely
version of three of the buildings. The estimated cost
be 5% or less. Here again a significant improvement
of the conversion contract was approximately .8
can be made by switching to low temperature hot
million and with contingencies, supervision and in-
water.
spection, etc., approximately .8 million was esti-
Economics is usually the driving force behind a
mated for the entire project. Of this cost, the build-
decision to retrofit existing steam and high temper-
ing conversion costs were about .1 million, with
ature hot water systems to low temperature hot
almost half of that cost being associated with asbes-
water operation. If we make the conservative as-
tos abatement due to pipe insulation containing as-
sumption that there are no leaks in the Hawthorne
bestos. The distribution system cost was ap-
steam supply line, we can make some estimates of
proximately .6 million. A temporary boiler re-
the cost savings that could be obtained from con-
quired during the plant conversion was estimated
verting to low temperature hot water operation.
to cost about
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.6 million.The fuel use for a low temperature system would
From the projected project costs and savings giv-
drop to about 48% (43%/90%) of the existing value
en above it was clear that this project was not eco-
just due to excess steam now used due to heat losses
nomically viable on the basis of energy savings
for the distribution system, condensate leaks, and
alone. This result could be entirely different if, due
overheating of the building due to inadequate con-
to other reasons such as health considerations or
trol. If we assume a value of /GJ for energy
required replacement of equipment, some portion
costs, the total fuel consumption for the 181-day
of the work was justifiable by other means. For
study period of 1,445.250 L (381,836 gal) would be
example, assume that the distribution system has
reduced to 693.720 L (183,281 gal), representing a
deteriorated to the point where it needs to be re-
savings of about 2,000.
placed regardless of whether the conversion to
In addition, the need to heat makeup water would
LTHW is considered. Thus the .6 million cost for
be reduced by a significant amount, resulting in
the distribution system would be subtracted from
additional savings. If we include the energy loss
the .8 million project total and the cost of the
due to mass leakage based on our previous calcula-
conversion would be lowered to about .2 million
tions, we can estimate these additional savings. In
plus contingencies, supervision and inspection, etc.
this case if we assume that 10% of the mass lost is in
Under this condition the project would most likely
the form of steam and the remainder is condensate
just meet the current Energy Conservation Invest-
then the total savings would be increased to 2,880
ment Program (ECIP) criteria of 10-year payback.
for the study period.
Another possibility might be if renovations of the
The study period did not represent an entire
buildings were being accomplished independently
heating season, only that portion of the season when
of a decision to convert to LTHW. In this case the
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