Section 3. WATER TEMPERATURE CONTROL
1.
WATER TEMPERATURE CONTROL. The temperature of the large volume of water
in the wet pot must be maintained within the temperature range for the
mission, normally 70 to 85 deg. F, regardless of the ambient temperature in
the building. The designer should remember that the minimum allowable
temperature must be dictated by the thermal constraints of the stress
analysis and the dictates of the steel used in the fabrication of the wet
pot. Under all conditions, the temperature of the water in the wet pot shall
not be allowed to go below 34 deg. F. Water at temperatures near freezing
are unstable and unpredictable and may freeze suddenly.
The design must provide for the wet pot water to receive or give up heat as
required to control the temperature which may be affected by the occupants
during the mission. For example, divers using hot water suits which
discharge hot water into the surrounding water provide a sizeable heat input
to the wet pot water. Heating will normally be required only to bring the
wet pot temperature up to and maintained in the 70 to 85 deg. F range.
Wet pot water heating and cooling shall be accomplished by heating and
cooling the circulating water in a heat exchanger as shown in Figure 7-1.
The water-to-water heat exchanger should be provided with generous pressure
relief valves so that an internal failure in the exchanger will not result in
a dangerous pressure overload on the heating and cooling systems.
If the system is filled with fresh water it will have to be used at
temperatures above freezing. Under this limitation, it will probably be
possible to use water as the heat transfer medium from the cooler and then it
will be possible to use the same heat exchanger for heating and cooling.
This will limit the heat transfer rate of the cooling system as the
temperature goes below about 40 deg. F, but if a higher cooling rate is
required, it will be necessary to use a different cooling medium and a second
heat exchanger. NAVFAC Design Manual DM-3, Mechanical Engineering (Reference
(2)), provides information for use in selecting and installing water heating
and cooling systems. NAVFAC Design Manual DM-9, Cold Regions Engineering
(Reference (3)) provides additional information on water heating systems.
2.
INSULATION. The wet pot must be insulated to minimize heat loss and
condensation. Viewports on the upper side of the wet pot under conditions of
cooling will collect condensation. A plexiglass insulating cover installed
on the viewport as shown in Figure 7-2 will reduce condensate collection.
3.
LUBRICATION. Lubrication and protection greases for a wet environment
has been a hard task because of the overall requirements of withstanding cold
and hot water and still protect the steel. If the lubricant is to be used
totally submerged, the grease lubriplate is the best overall, but must not be
used in the dry environment because it is absolutely not compatible with
oxygen.
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