OF A SUBMARINE
A. HEAT AND HUMIDITY|
19A1. Heat gains inside a submarine. With
all the discussed facts in mind, the general
picture of air-conditioning in a submarine may
now be considered. Let it be assumed that
the air in question contains enough oxygen for
the needs of all the occupants within the given
space. A supply of oxygen compressed in
cylinders is carried on board submarines to be
released into the air if this need arises.
There is continuous production of heat,
given off to the air by hot engines, storage
batteries, galley stove, electric lights, electric
heaters, other devices, and human occupants.
19A2. Moisture gains inside a submarine.
There is also continuous production of moisture, given off to the air by evaporation from
four main sources: 1) storage batteries, 2)
cooking; 3) human occupants, and 4) the
bilges. This production of moisture averages
about 1000 pounds of water per day under
19A3. Elimination of heat and moisture. If
the submarine is running on the surface, it is
an easy matter to discharge this excess heat
and moisture outboard. But if the submarine
is submerged, it cannot be discharged outboard, and must be eliminated during recirculation of the air.
19A4. Transfer of heat between submarine
and ocean. A submarine is practically all
metal, and metal is an excellent conductor of
heat. In addition, the surface area of a submarine is fairly large. Moreover, the ocean is
filled with convection currents, either natural
currents or currents caused by the vessel's
motion. These facts combine to make the heat
transfer between submarine and ocean an
active process. Even when the temperature
difference between the vessel and the ocean is
small, the total heat transfer is considerable
because of the large contact area.
19A5. Loss of heat from ship to ocean. If
the submarine is warmer than the ocean water,
the interior heat of the vessel gradually passes
through the shell into the water. The temperature of the air inside drops and, when it
reaches the dewpoint, the water vapor in the
air begins to condense on every available
surface. For this reason, the interior surfaces
of a submarine are coated, wherever practicable, with cork paint, to prevent or reduce
this condensation to a minimum. The beginning of the condensation, however, depends
upon the dewpoint, and this can be controlled
by air-conditioning. Therefore, air-conditioning is just as essential for this purpose as for
the comfort of the crew. It is always advisable
to lower the dewpoint before a dive, if possible.
19A6. Gain of heat from ocean to ship. On
the other hand, if the ocean is warmer than
the submarine, there is a passage of heat from
the water into the ship., However small this
may be, it adds to the interior heat. The same
result occurs if the loss of heat from this
vessel to the ocean is less than the interior
heat production. In hot summer weather,
especially in tropical and subtropical regions,
the air temperature in a submarine may rise
to fairly high levels.
19A7. Refrigeration capacity of a submarine. In a submarine, only a few cubic feet of
space are available for air-conditioning machinery, and the cooling capacity is of necessity limited. It should be clearly understood
that the purpose of the air-conditioning system
is not to cool the submarine as a whole.
19A8. Humidity in a submarine. However,
there is room enough for sufficient air-conditioning machinery to control the dewpoint,
that is, to set it at any desired temperature.
Control of the dewpoint means control of the
relative humidity, and it is the relative humidity, more than the mere temperature of
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the air, that causes discomfort. With a build
up of a thousand pounds of moisture per day
in the air of a submarine, relative humidity
becomes a factor of major importance.
B. THE DEWPOINT|
19B1. Lowering the dewpoint. The dewpoint
of a sample of air is the temperature at which
that air is saturated with moisture. If the
temperature of the air is then further lowered,
some of the moisture must condense out.
Suppose that the air in a room is so high
in relative humidity as to be uncomfortable.
The method of reducing this relative humidity
is as follows:
The air in the room is drawn by fans into
and through the ducts to the air-conditioning
evaporator. There, in passing over the cooling
coils, its temperature drops below its dewpoint
and part of its water vapor condenses out,
inside the evaporation cabinet. The condensed
water is not permitted to get back into the
air, but is drained off into a tank. The air, now
lower in moisture content and slightly lower
in temperature also, continues its flow through
the ducts and is finally blown out into the
room again. This conditioned air mixes with
the moisture and warmer air still in the room,
resulting in an over-all condition that is drier
than the original unconditioned air.
19B2. Heat action in the evaporator. When
some of the moisture in the air is condensed
out of it in the evaporator, the condensation
is caused by the passage of latent heat from
the water vapor in the air to the refrigerant
inside the cooling coils. This removal of latent
heat reduces the total heat of the humidity of
the air. Refer again to the psychrometric
chart. While the lowering of the dry-bulb
temperature by itself means an increase in
relative humidity, this increase resulting from
the lowering of -total heat, or wet-bulb temperature, is always less in the range of high
air temperatures within which high relative
humidity is uncomfortable. The resultant
relative humidity is therefore always decreased.
19B3. Importance of dewpoint. It becomes
evident that in air-conditioning the significant
viewpoint is not the dry-bulb or ordinary air
temperature, but the wet-bulb temperature, or,
preferably, the dewpoint. The latter is preferable, because the dewpoint is the temperature
at which a given sample of air holds all
the water vapor it can. If the temperature is
lowered when the air is at its dewpoint, water
must condense out of that air.
When air is at its dewpoint, the dry-bulb
and wet-bulb temperatures are both the same
as the dewpoint temperature, the air is saturated, and its relative humidity is 100 percent.
The dewpoint is a factor through which all
relationships are correctly seen, and by the
use of which the operation of air-conditioning
19B4. Two actions on the air. The whole
subject is perhaps none too easy to grasp at
first glance, so it may be well to draw special
attention to a point that is usually overlooked,
but which is really the vital matter in the
operation of air-conditioning. It should be
clearly realized that the air is being separately
acted on in two different places where the
conditions are quite different. One place is in
the room itself; the other is in the evaporator
The room is the place a person occupies and
sees, and it is where he feels the satisfactory
or unsatisfactory quality of the air. But the
conditioning of the pair does not take place in
the room. The actual conditioning of the air
takes place inside the evaporator casing. The
environment in the two places is very different.
While in the room, the water vapor of the air
is usually warm and, to a certain extent, free
and expansive; but when it passes along with
the air through the ducts to the evaporator,
it suddenly is confined in a small cabinet
where it is cold. So it compresses together
and forms liquid drops (see Sections 16A7
19B5. Summary of air-conditioning principles. In a room, the air continuously gains
heat and moisture. In an evaporator, the air
is quickly and considerably cooled and loses
To be sure, when the air returns from the
evaporator to the room, it may lower the
temperature therein by a few degrees, but
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the essential requirement is either 1) the
reduction of relative humidity, or 2) the prevention of condensation in the room.
In the first case, the relative humidity in
the room is reduced by causing condensation
in the evaporator, that is, by cooling the air
to below its dewpoint in the evaporator.
In the second case, condensation in the room
is prevented by lowering the dewpoint of the
air in the room, and this again is done by
cooling the air, and hence removing some of
the moisture by condensation, in the evaporator.
When a submarine loses heat to the ocean,
the temperature of the air inside begins to
drop. If the dewpoint of the air is high, it is
not long before the temperature of the air
drops to the dewpoint, and condensation in
the compartment begins. This condensation
appears as a film of liquid water or droplets
on all available cool surfaces. The interior
surfaces begin to sweat; and that means,
always, a potential danger from short circuits
or grounds in electric systems. Remember
that the dewpoint is the temperature at which
the water vapor in the air begins to condense.
C. AIR-CONDITIONING IN DIFFERENT CLIMATES|
19C1. Various climatic conditions encountered. A submarine may be on patrol in tropical, arctic, or temperate waters. The atmospheric conditions and water temperatures vary
greatly in these different regions, and require
different operation of the air-conditioning
19C2. General rule for air-conditioning.
However, it is possible to set up a general
rule, as follows: Operate the fans or blowers
at such speed that the air leaving the outlet
sides of the evaporators is always below the
dewpoint; and adjust the louvers to give the
best distribution of air throughout the vessel.
The adjustment of the louvers for best air
distribution naturally varies in different classes of submarines, and even in different vessels
of the same class. Practical experience in each
submarine must dictate the fine points of
louver adjustment. If they are opened and
closed frequently in accordance with individual
caprice, proper air-conditioning of the vessel
19C3. Air-conditioning in temperate climate.
The handling of air-conditioning in temperate
climates is comparatively easy. It usually
requires attention only to the general rule
stated in Section 19C2. The blowers need not
be operated at full speed, and may often be
operated at minimum speed. The louvers may
be partly closed.
It is important that the operator should
frequently note the suction pressure and suction temperature at the compressors, in order
to keep the system operating at its most
efficient rate. When the air-conditioning compressors operate at 33 psi suction pressure
and 117 psi discharge pressure, the compressors are at their best. These pressures can be
obtained by adjusting the speed of the fan,
the compressor, or both. For example, if the
fan is running at 3/4 speed and the compressor
at slow speed, with a suction pressure rising
to 45 psi, the compressor should be speeded
up until the pressure drops to around 33 psi.
The fan should not be slowed down until the
compressor is running at full speed, and the
suction pressure is still up around 45 to 50 psi.
Then the fan can be reduced in speed. It
should not, however, be reduced below 1/4
speed on the rheostat; otherwise proper ventilation will be lost.
19C4. Air-conditioning in arctic climate. In
arctic regions and in cold winter weather in
temperate regions, the main problem is the
prevention of condensation within the submarine. Reference to the psychrometric chart
(Figure 16-1) shows that at lower temperatures, the dry-bulb, wet-bulb, and dewpoint
temperatures are closer together than they are
at higher temperatures. This means that a
drop of fewer degrees causes condensation.
Much closer attention to the temperatures,
therefore, is required in cold weather.
A usual condition is a low dry-bulb temperature in the vessel with a wet-bulb temperature close to it. The shell of the vessel and
other metal parts are usually colder than the
dewpoint by only a degree or two. Moisture
condenses on such surfaces, or, in other words,
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the vessel sweats, necessitating the use of the
air-conditioning system to dry it out.
Under these conditions, if an attempt is
made to dry the vessel by operating the compressors at low speed and the blowers at 1/2
speed, the suction pressure will be about 18 to
20 psi. If this pressure is continued for a
considerable time, the coils accumulate a coating of frost inside, and eventually become so
plugged up as to prevent air from passing
through. To prevent this, operate the compressors at slow speed, and the fans at full
speed. The suction pressure then rises to 25
psi or more, and the frosting stops, while the
drying of the vessel continues.
The proper method of starting the air
conditioning system, when the injection water
is at low temperature, is to operate with
manual control instead of automatic. If the
system is run on automatic control, it short
cycles, because of low head pressure; that is,
the suction pressure drops to 20 psi and the
compressor stops on the low-pressure cutout.
In a short time, the suction pressure builds
up to 40 psi, the compressor starts, and runs
a few minutes; then the suction pressure drops
back to 20 psi, and the low-pressure cutout
stops the compressor, alternating or short
cycling this way every few minutes. This
causes overheating of the starter and in due
time burns out the motor. In operating manually, run the air-conditioning compressors for
ten minutes, with the condenser water discharge valve closed, or until a head pressure
of about 100 psi has been obtained. The reason
for this is that there must be a difference of
60 psi between the high- and low-pressure
sides to operate an expansion valve. The compressors can then be switched to automatic
19C5. Air-conditioning in the tropics. In hot
climates, the air-conditioning system usually
must be operated at maximum capacity. In
general, the best procedure is to operate the
compressors at full speed and the blowers at
such speed that the temperature of the air
from the discharge side of the evaporators is
below the dewpoint. The conditions of high
air temperature in the tropics are naturally
adverse to effective air-conditioning, especially
when the large area of open water surfaces in
the bilges is considered. The plant must be
run so as to obtain maximum comfort and
protection of equipment against moisture, both
of which are obtained by abstracting the
largest possible quantity of water vapor from
the air. This condensing or wringing process
is accomplished by always maintaining the
temperature of the discharge air from the
evaporators below the dewpoint.
Recent experiments on the ventilation of
submarines in the tropics have shown that
improved results are obtained, at least on
some types of vessels, by ventilation in any
of the following ways:
1. Run the supply blowers at highest speed
allowable without overloading the motors.
2. Run the air-conditioning compressors at
highest speed allowable without overloading
3. Shut off the supply outlets to the control
room and conning tower when the upper
conning tower hatch is open; close the door
between the control room and the forward
4. Close all exhaust terminals from the
forward torpedo room to the forward engine
room while charging batteries, except the
galley range terminal when the range is being
5. Remove the air spreader plates over the
wardroom supply outlet on all Portsmouth
submarines of the SS228 class and up. These
spreader plates force air out into the passage
way and allow no circulation of air in the
6. Bypass all back-pressure regulators on
both air-conditioning coils.
7. Cause the thermostat cutout to be wide
open at all times in hot climates.
8. Use the normal fuel oil tank outboard
of the forward battery compartment early in
patrol in order to have sea water, which has
a higher heat conductivity constant than oil,
next to the pressure hull.
9. Shut off as many lights forward as possible. Use a fluorescent tube if available. A
20-watt tube furnishes twice the light with
only about one-tenth the amount of heat as a
50-watt electric light bulb. The forward battery compartment has three times as many
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lights on at all times as the after battery
10. Leave the air-conditioning condenser
circulating water suction and discharge valves
11. Close the supply outlets to the engine
rooms. Make no attempt to cool the engine
room with the ventilation system.
12. Do not use the present system for exhausting air from the after part of the submarine when submerged. Close all engine
room doors and the after engine room exhaust
bulkhead flapper; with the supply blower, take
a suction from the maneuvering room and
engine rooms through the engine air induction
lines in the superstructure, by way of the
main induction valve aft of the conning tower.
One ship reports air as being cooler
throughout since using this system.
13. Run only one conning tower air-conditioning coil at a time.
14. Secure the conning tower air-conditioning coil when the upper conning tower hatch
15. Rig all reserve fuel oil tanks to the main
ballast tanks as soon as fuel is used. On diving,
a considerable amount of heat is taken from
the pressure hull by water filling the tanks.
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Copyright (C) 2004 Maritime Park Association
All Rights Reserved
Version 1.10, 22 Oct 04