of increased maintenance on the boiler plant equip-
0.34 bars gage (5 psig) before distribution to the
ment or distribution system was apparent to the
individual family housing units.
operators at the time of the study, the long-term
Most of the main steam lines for the distribution
effect due to thermal cycling of the system is likely
system are contained in shallow concrete trenches
to be detrimental.
whose covers are at grade level and used as side-
All of the boilers are fired with no. 2 fuel oil,
walks. A small portion of the steam distribution
which is delivered by truck and stored in several
piping is directly buried in either steel conduit sys-
large holding tanks. Measurements on the boilers
tems or loose fill insulation materials. For a more
using combustion analysis have shown the efficiency
detailed description of the construction details for
to be around 85%. No steam flow data from the
these types of systems, see Phetteplace and Meyer
central plant are available due to lack of a functional
(1990). In most all cases the condensate return pip-
flow meter. The individual buildings are not
ing is routed entirely independently of the steam
equipped with flow meters, consistent with stan-
piping. Most of the return piping is buried directly
dard practice on most DoD installations. Daily boil-
in the soil and is uninsulated brass or steel piping.
er logs are maintained for the heating plant. These
The condensate return is by gravity in most places.
boiler logs contain various temperature and pres-
An unusual arrangement called a "sand pit" is used
sure readings taken on a hourly basis. Records of
in the condensate return system. The sand pits resem-
daily fuel used, in storage, and delivered are main-
ble sewer manholes in that the incoming conden-
tained on the boiler logs as well. By using limited
sate flows into a concrete basin and then out into the
data available from the boiler logs with heat and
outflow piping at the level of the condensate in the
mass balances for the system and some statistical
sand pit. Unlike a sewer manhole, the bottom of the
analysis, we can find some estimates of the losses in
sand pit is not concrete but is formed by the native
which we are reasonably confident. The details on
sandy soil. To the extent that this soil is not clogged
the development of the model used for this purpose
with particulates, the condensate is allowed to per-
are given in Phetteplace (1991a).
colate into it. This arrangement may account for a
significant portion of the mass loss from the distri-
bution system, as will be discussed later.
Heating loads on the
Very few of the buildings at Hawthorne AAP are
Hawthorne AAP system
Without meters on the buildings or at the plant it
equipped to use steam from the central system to
becomes necessary to estimate the heating load on
heat hot water for domestic uses. Electric hot water
the system from weather data. The concept of the
heaters are used in most cases. The notable excep-
heating degree day has been used extensively for
tions to this are two apartment buildings that have
this purpose. Details on its use can be found in
large hot water storage tanks in their basements.
ASHRAE (1985). For the purposes of this analysis
These are equipped with steam heat exchangers as
we need only to assume that the heating energy
well as electric heating elements. Although steam
required over a specified period of time is propor-
has heated these tanks in the past, the electric heat-
tional to the degree days accumulated over that
ers were in use at the time of our study. Personnel
same period of time. Werner (1984) proposes a much
from the operating contractor indicated that the elec-
more detailed model of the heat load in district
tric heaters have been used exclusively in recent
heating systems. From his study of the degree-day
years. Earlier they had been operated only when the
concept he concludes that it "... does not accurately
heat distribution system was not in operation.
explain the composition of the space heating de-
At the time of our analysis the operating policy
mand." Although it is agreed that the degree-day
was to turn off the central steam distribution system
concept does not accurately account for such factors
and the heating plant during times of low load. A
as solar gain and infiltration, we feel that for the
portion of the system that serves a residential sec-
purposes of an efficiency analysis such as this, its
tion of the base was sometimes shut down prior to
use is acceptable as an alternative to more compli-
the remainder of the system. The entire system was
cated models such as those proposed by Werner
shut down for the summer months and was occa-
(1984). Data from a fairly large (approximately 75-
sionally shut down and restarted during the "swing"
MW or, 255 MBtu/hr) steam district heating system
periods of the fall and the spring seasons as well.
on Ft. Wainwright, Alaska, (Phetteplace et al. 1981)
This practice was instituted several years earlier by
indicate that it does track the heat load reasonably
the operating contractor as an energy conservation
well if the effects of the distribution system losses
measure. Because the system is not used to generate
and domestic tap water heating are considered.
domestic hot water, this presents no problem from
For residential and office buildings normally
a heat supply standpoint. Although no evidence
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