1.12 m
(44 in.)
1.78 m
(70 in.)
Thermocouple
Heat Flux Sensor
100 mm (4 in.) Supply
Thermocouple
and Return Pipe
Heat Flux Sensor
64 mm (2.5 in.)
Insulation
~36 mm
(~1.4 in.)
38 mm (1.5 in.)
Thick Insulation
400 mm
260 mm
125 mm (5 in.) Supply
(16 in.)
(10.25 in.)
and Return Pipe
Conduit
Figure 5. Construction details for the MTHW common
Figure 6. Construction details for the MTHW individual
conduit site.
conduit site.
economics are not quite as favorable, but a detailed
[NPS]). These pipes are insulated with a mineral
cost analysis and refinement of the LTHW design
wool insulation of 38 mm (1.5-in.) thickness. The
might still identify an economically viable project
insulated supply and return pipes are encased in a
under ECIP criteria.
spiral wound steel conduit, which is approximately
3.2 mm (1/8 in.) thick. The supply and return pipes
are positioned within the conduit with the supply
pipe on top of the return pipe. The conduit has an
HEAT LOSS MEASUREMENTS
outer diameter of approximately 500 mm (20 in.),
Over the past few years we have instrumented
thus allowing for an air space between the pipe
operating systems on Army facilities in order to
insulation and the inside of the conduit.
make measurements of heat losses under realistic
field conditions. Ft. Jackson, South Carolina, was
MTHW individual conduit system
selected as one site because a large replacement
The individual conduit system (Fig. 6) employs
project was underway there on what would be clas-
the same construction features as the common con-
sified as a medium-temperature hot water (MTHW)
duit system described above. In this case the supply
system consistent with the definitions given in
and return pipes are approximately 100-mm (4-in.
ASHRAE (1992). Three types of heat distribution
NPS) Schedule 40 steel and each is encased in its
piping systems were instrumented.
own individual conduit of approximately 400-mm
In addition to the three sites at Ft. Jackson, two
(16-in.) outer diameter. The insulation on the pipes
sites were instrumented on a low-temperature hot
is mineral wool and is 64 mm (2.5 in.) thick in each
water (LTHW) system at Ft. Irwin, California. The
case.
LTHW system was a new system built to serve a
new barracks complex. The specifics of the construc-
MTHW shallow concrete trench system
tion of all of these systems are discussed below.
The shallow concrete trench system (Fig. 7) con-
sists of a cast-in-place concrete trench with cast-in-
place concrete covers. The interior dimensions of
MTHW common conduit system
The common conduit system has both the sup-
the shallow concrete trench at the Ft. Jackson test
ply and return piping in the same steel conduit (Fig.
site are 1 m (40 in.) in width and 550 mm (21.5 in.) in
5). This is a prefabricated system that conforms to
height. The trench walls are 140 mm (5.5 in.) thick
the Federal Agency Criteria for a class A system. This
and the trench covers are 150 mm (6 in.) thick, hav-
type of system is designed and installed in accord-
ing a lip of about 25 mm (1 in.) at the outside edge so
ance with Corps of Engineers Guide Specification
that the portion resting on the trench wall is about
(CEGS) 02695 (U.S. Army Corps of Engineers 1989).
125 mm (5 in.) thick. The supply and return piping
The class A conduit system used at Ft. Jackson
is approximately 125-mm (5-in. NPS) Schedule 40
consists of schedule 40 steel supply and return pipes
steel. Each pipe is insulated with 64 mm (2.5 in.) of
of approximately 125 mm (5-in. nominal pipe size
mineral wool pipe insulation.
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