TM 5-852-5/AFR 88-19, Volume 5
CHAPTER 8
UTILIDORS
8-1. General.
temperatures can result due to exposure to the
excess heat (<80EF). The heating of a large air
A utilidor is a conduit that contains multiple utility
space in the utilidor is less efficient than direct
systems such as water, sewerage, fuel oil, gas, elec-
heating and circulation of the water supply in the
trical power, telephone, and central heating in var-
winter. Thermal stratification can cause freezing of
ious combinations or in some cases all together.
the lower pipes in large utilidors even when the
They have been used at a number of military instal-
average air temperature is adequate. Figure 8-3
lations and civilian communities in the North
illustrates the temperature variation within a small
American Arctic. Utilidors are very expensive and
utilidor. The cold water line was placed on one side
can only be justified for special situations. In most
to maintain desirable temperatures for the consu-
cases individually insulated pipes in a common
mers and the hot water lines on the other side.
trench or on a common pile will be more
Under extreme conditions this cold water line froze
economical. Utilidors have been constructed above
and burst due to the thermal shielding, in spite of the
and below ground, and range in size from a simple
continuous circulation of hot water. When transport
insulated conduit to a walk-through passageway.
methods permit prefabrication of the major utilidor
Figures 8-1 and 8-2 illustrate typical utilidor
components is recommended to reduce construction
configurations that have been constructed recently
costs in the field. The heat sources for freeze
in the cold regions. These new designs typically
protection should be located near the bottom of
incorporate lighter construction materials than the
large utilidors if possible to ensure distribution of
reinforced concrete used previously at many military
heat. Sensitive piping (e.g. water) should not then
installations.
be shielded from these heat sources. If the heat
sources (i.e. steam and condensate lines) are
8-2. Design considerations.
operational all year, separate insulation of domestic
The thermal design of the utilidor is made in accor-
water lines is recommended to maintain acceptable
dance with the procedures in chapter 12. The foun-
cold water temperatures for domestic use. The
dation design must be in accordance with TM 5-
utilidors shown in Figure 8-1 all have prefabricated
852-4/AFM 88-19, Chap. 4. Both designs are
components. All of these units can be entirely
influenced by the types of utilities that are included.
prefabricated in a convenient unit length. A hydrant
The inclusion of power, telephone, and gas lines
unit on an above-ground utilidor of the type in
along with water and sewerage in a utilidor will not
figure 8-2b is shown in figure 8-4. When both water
cause design or operational problems. However, the
and sewage lines are exposed in the same utilidor,
inclusion of central heating lines is more complex.
the sewer access cleanouts must be sealed to
Their heat losses are usually great enough to protect
prevent cross connections. Flanged elbows or pipes
the water and sewage pipes from freezing but the
larger than 8 inches in diameter are large enough to
utilidor usually has to be much bigger to provide
insert cleaning or thawing equipment. Standard
continuous easy access to steam and condensate
fittings or smaller pipes do not provide adequate
lines, and therefore construction costs will increase.
access in both directions. Figures 8-5 illustrates
Problems also occur because this heat source is con-
details of sewer cleanouts that have been used for
stant and must operate all or most of the year. In the
this purpose.
summer, undesirably high domestic water supply
8-1
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