Quantcast Section 2. High Temperature Water Distribution Methods

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HIGH TEMPERATURE WATER DISTRIBUTION METHODS
Section 2.
1 TYPES OF DISTRIBUTION METHODS.  HTW distribution methods are similar to
those described for steam distribution systems. No provisions are needed:
however. for the disposal of drip line condensate as in a steam distribution
system.
1 . 1 Distribution Route.  I n HTW distribution circuits, the circulating pumps
m a i n t a i n positive circulation in the closed piping system at all elevations.
This permits laying the supply and return lines following the general contour
o f the land.  However, prior to selecting a route for the HTW distribution
system, a thorough evaluation of the location and economic factors should be
made.  A discussion of these factors is found in Section 2 of NAVFAC DM-3.8,
Design Manual, Exterior Distribution of Utility Steam, High Temperature Water
(HTW), Chilled Water (CHW), Fuel Gas, and Compressed Air.
1 . 2 Freezing.  To prevent freezing should the system be out of operation, the
d i s t r i b u t i o n pipelines are normally buried below the frost line.
2 ADVANTAGES OF HTW DISTRIBUTION SYSTEMS.  The major advantages associated
with the use of HTW distribution systems are listed below.
(a) Low Water Makeup Requirements.  HTW systems are completely closed
c i r c u i t s and very little water is consumed.  The most significant water losses
in normal operation are system leakage through pump glands and valve
packings.  Water can be lost also through vents or blowoffs because of changes
of volume when starting a cold system.  Minimum makeup water requirements
result in reduced feedwater treatment, and boiler blowdown is seldom necessary.
( b ) Lack of Corrosion.  S i n c e t h e w a t e r i s r e c i r c u l a t e d i n a c l o s e d
system, neither corrosion nor scaling occurs.  The system is always filled
with noncorrosive treated water.
( c ) Small Distribution Lines.  H i g h temperature differentials permit the
u s e of relatively small distribution lines throughout the system.
(d) No Traps or Pressure Reducing Value Stations Required. HTW systems
do not have traps, drips, or pressure reducing stations. HTW systems can meet
the need for several temperature levels without reducing the pressure of the
heating medium, a s required in steam distribution.
(e) Low Transmission Heat Losses.  S m a l l e r distribution lines have
smaller diameters, which result in lower heat losses than those that occur in
comparable steam systems.
( f ) High Thermal Efficiency.  The closed recirculation system operates
at a high thermal efficiency because:  f i r s t , all the heat not used by
c o n s u m e r s or not lost through pipe radiation is returned to the boiler plant;
a n d second, the heat loss in boiler blowdown is practically eliminated.  High
boiler efficiencies are obtained by the elimination of sudden changes in
firing rates which tend to produce poor combustion and high stack gas
temperatures.  This is possible because of the thermal flywheel effect
resulting from the large heat storage capacity of HTW. The system acts as an
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