| REFRIGERATING AND|
A. PRINCIPLES OF MECHANICAL REFRIGERATION
8A1. Brief statement of principles. The mechanical refrigeration method used on
board a submarine is the vapor refrigerating process. In this process, the refrigeration passes
alternately through its liquid and vapor states. Such a refrigerant, therefore, must have special
qualities. It must boil at a very low temperature and it must be able to change its state from liquid
to vapor and vice versa readily. Above all it must be a safe refrigerant. This is more
important in submarines than in other types of vessels.
In the liquid state, the refrigerant picks up heat from substances or the air in spaces and in so
doing, vaporizes. The vapor, carrying the excess head, is then moved away to another location
where it gives up or discharges that heat, and is converted back to the liquid state.
The mechanical system in which the refrigerant is contained is a single airtight circuit of pipes
and mechanisms through which the refrigerant is pumped continuously, so that a given quantity is
used over and over. This requires an input of energy which is supplied by an electric motor.
FigureA-11 shows the cyclical arrangement of the essential elements of the refrigeration system;
namely, the evaporator, compressor, condenser, receiver, and thermostatic expansion valve. The
liquid refrigerant picks up heat and vaporizes in the evaporator. The vapor then goes to the
compressor where it is compressed to a pressure at which its temperature is above that of the
water flowing through the condenser. The compressed vapor then passes to the condenser where
sufficient heat is transferred to the water to cause the refrigerant vapor to condense. The
condensed refrigerant, now a liquid, flows next to the receiver, and then through the thermostatic
expansion valve to the evaporator.
8A2. The Freon 12 cycle. Let us follow through the cycle of operations, starting
from the point at which the heat to be removed enters the refrigerating system. This point is
where the evaporator is located. FigureA-11 shows a simplified diagram of the main mechanical
elements in the cycle.
8A3. Through the evaporator. The evaporator is simply a bank, or coil, of copper
tubing. It is filled with Freon 12 at low pressure and temperature. Heat flowing from the air
spaces or articles to be cooled into the coil will cause the liquid Freon to boil. Boiling can take
place only by the entrance into the liquid of its latent heat of vaporization, and then this latent heat can come only from the surrounding substances. Hence, their
temperatures are lowered. The latter portion of the evaporator coil is therefore filled with Freon
vapor at low pressure, carrying with it the unwanted heat.
8A4. Through the compressor. This vapor does not remain in the evaporator. The
compressor is operating and the suction that it exerts (on the evaporator side of its circuit) pulls
the heat-laden vapor out of the evaporator, through the piping, and into the compressor. The
compressor, therefore, is the mechanism that keeps the Freon in circulation through the system.
In the compressor cylinders, the Freon is compressed from a low-pressure vapor to a high-pressure vapor and its temperature therefore rises.
8A5. Through the condenser. The Freon vapor, now at high pressure, passes next
into the condenser, where the vapor passes around the tubes through which sea water is
continuously pumped. Here the excess heat flows by conduction through the walls of the tubing
from the higher-temperature vapor to the relatively lower-temperature sea water, and here,
therefore, the unwanted heat leaves the primary refrigerating system and is finally carried away.
This excess heat thus
flowing out of the vapor is latent heat of vaporization and therefore, the vapor condenses back to
the liquid state. The liquid Freon is now at high pressure and high temperature.
8A6. Through the receiver. The liquid Freon passes next into the receiver, or tank.
The liquid in this receiver acts as a seal between the vapor in the condenser and the liquid as it
flows into the next element, the expansion valve, in order that the liquid Freon in the expansion
valve may be free of vapor. The whole system is a single circuit in which the fluid is circulated.
8A7. Through the expansion valve. The liquid Freon enters the expansion valve at
high pressure and high temperature. This valve regulates the flow of the refrigerant into the
evaporator. The liquid outlet from the expansion valve is a small opening, or orifice. In
passing through the orifice, the liquid is subjected to a throttling action, and is dispersed into a
finely divided form. The Freon now is again a vapor at low pressure
and low temperature, and is reentering the evaporator, its cycle completed, and ready to be
repeated. Every part of the cycle is, of course, taking place simultaneously throughout the circuit,
and continuously as long as the refrigeration is wanted. The entire operation is automatic.
8A8, The low-pressure side. That portion of the cycle from the orifice of the
expansion valve around through the evaporator to and including the intake side of the compressor
cylinders is called the low-pressure side. The dividing line between the low-pressure and the high-pressure sides is the discharge valve of the compressor.
8A9. The high-pressure side. The remainder of the cycle, that section from the
discharge valve of the compressor around through the condenser, receiver, and expansion valve to
its orifice is called the high-pressure side. The dividing line between the high-pressure and low-pressure sides is the thermostatic expansion valve.
B. MECHANICAL DETAILS OF AIR-CONDITIONING SYSTEM
8B1. The air-conditioning cycle. The air-conditioning cycle in the air-conditioning
system is the same as in the refrigeration system. In general, the mechanical circuit of equipment
is also similar, the main difference being that the air is brought by forced ventilation through ducts
to the evaporators and returned through ducts to the rooms.
8B2. The air-conditioning plant.The air-conditioning plant consists of the following
a. Two compressors, York-Navy Freon 12, enclosed single-acting vertical, two
cylinders, 4-inch bore x 4-inch stroke, rated at 4 refrigeration tons each.
b. Two condensers, York-Navy Freon 12, horizontal shell-and-tube 4-pass type.
c. Two receivers, York-Navy Freon 12 type.
d. Four evaporators, with finned cooling coils in two casings.
e. Two conning tower evaporators, in one casing.
8B3. Double system arrangement. The main
elements listed in Section 8B2 are connected as two separate systems, each containing all
necessary valves, gages, and controls for automatic operation. The cooling coils of these two
systems, however, are placed side by side in an evaporator casing, and though appearing to be a
single unit of coils, are, nevertheless, entirely separate. Thus, either of the two systems may be
operated alone, with its cooling action taking place in the evaporating casing.
8B4. Interconnection of double system. The double systems, while ordinarily set to
operate individually, are interconnected. On the 200 class submarines, the interconnecting pipes
run between a) the discharge lines of the condensers, b) the outlet lines of the condensers, and c)
the inlet or suction lines to the compressors. Shutoff valves in these interconnecting pipes permit
any of the main elements to be cut out of one system and put into the other, in case of necessity.
There would be no flow in the interconnecting pipes unless their shutoff valves were opened;
normally they are closed. On the 300 class
submarines, the interconnecting pipes run between a) the discharge lines of the compressors and b)
the outlet lines of the condensers. There is no interconnection between the suction lines of the
8B5. Capacity of the air-conditioning system. The capacity of the air-conditioning
system is 8.0 tons of refrigeration with the two compressors operating at 330 rpm.
8B6. Necessity for compressors of different capacities. The air conditioning system
and the refrigeration system aboard a submarine are designed as two separate and distinct
systems. Each is capable of performing its task independently of the other. However, in practice
it is desirable that these two systems be interconnected so that the air-conditioning compressor
can serve as a standby for the refrigeration system. This will insure continuous operation of the
refrigerating system in the event of a prolonged repair job on the refrigerating compressor, which
otherwise would result in the spoilage of the food stored in the refrigerating rooms.
In earlier references and explanations within this text, the rated capacity of the refrigeration
system compressor has been given as 1/2 refrigeration ton, while the rated capacity of each of the
air-conditioning system compressors is given as 4 refrigeration tons. This difference in rated
capacity of the two units is due to the fact that the air-conditioning system performs a greater
amount of work than does the refrigeration system. The refrigeration system has to perform only
sufficient work to remove heat from the comparatively small space of the cool and refrigerating
rooms, with the minor addition of the ice cuber. Since these two rooms are thoroughly insulated,
little or no heat enters them from the outside. The only source of heat, therefore, inside the
rooms is from the stowed foodstuffs and from persons entering for supplies. The air-conditioning
system, on the other hand, has to remove heat generated throughout the ship. This is heat which
passes into the air of the ship from the engines, crew, cooking, batteries, electric light bulbs,
equipment, and at times from the surrounding water outside the hull.
These requirements determine the work load of each system, and this work load, expressed in
refrigeration tons, determines in turn the capacity of the compressor needed for each system.
8B7. Relation of capacities. The capacity of the compressor is the amount of work,
expressed in refrigeration tons, that a compressor is capable of performing under a single set of
operating conditions. A change in the operating conditions will cause a corresponding change in
the rated capacity of the compressor. Therefore, the relation between the capacity of a
compressor on a refrigeration system and one on an air-conditioning system is a comparison of
the operating conditions of evaporator temperature, speed of the compressor, and temperature of
the cooling medium for each system, and not a comparison of the compressor or its maximum
work load under optimum conditions.
The misunderstanding of this relationship has often given rise to a question as to whether or
not there is difference between a ton of air-conditioning and a ton of refrigeration.
The cause of this question is the apparent increase in the capacity in refrigeration tons developed
by a compressor on an air-conditioning unit over the capacity developed by the same compressor
when operating on a refrigerating unit. Although it may appear that there is a difference between
a refrigeration ton and an air-conditioning ton, actually there is none and the term
air-conditioning ton is not in acceptable usage.
The basic rating of refrigeration ton or heat-removing capacity of a machine is exactly the
same whether the machine is used for removing heat from an icebox or lowering the humidity
and/or temperature of the air in a submarine. However, a compressor that is rated at 2.95
refrigeration tons when operating at a -5 degree Fahrenheit evaporator temperature, running at
600 rpm with the same temperature of cooling water in the condenser in both cases will have a
rating of 8,348 refrigeration tons if it is operated at a 35 degree Fahrenheit evaporator
temperature. Thus, the rating of a compressor may vary, depending upon the evaporator
temperature; also, the rating of a compressor may vary, depending upon
the speed of the compressor and the temperature of the cooling water flowing through the
condenser. The operating temperature of the evaporator (suction pressure) will have the greatest
effect on the number of refrigeration tons that the compressor will develop. The higher the
suction (and pressure), the smaller the pressure differential between the suction and discharge;
hence the compressor will handle more Freon with less work. In other words, the compressor
will handle approximately twice the gas at 40 degrees that it will at 0 degrees Fahrenheit.
Therefore, more refrigeration tons are developed at the higher evaporation temperatures (suction
8B8. Cross connection of air-conditioning and refrigeration system. In an emergency
it is possible to cross connect at least one of the air-conditioning compressors, condenser, and
receiver, to the refrigerating system evaporator and maintain the desired temperatures in the
On some classes of submarine, either of the air-conditioning compressors may be cross
connected to the refrigeration system; on other classes only the No. 1 air-conditioning compressor
can be used. As the arrangement and location of valves and lines vary on each installation, no
detailed description can be given here. It is never necessary nor desirable to cross-connect the
refrigerating compressor to the air-conditioning evaporators.
When cross-connecting the air-conditioning compressor to the refrigerating evaporator, there
are several major adjustments that must be made on all installations. The low-pressure cutout on
the air-conditioning compressor must be reset so that it will not stop the compressor until the
suction pressure drops down to 2 psi. Normally this cutout is set to stop the compressor when
the suction pressure on the air-conditioning evaporator reaches 32 psi. If the compressor is to
operate both the air-conditioning system and the refrigerating system, the bypass around the
suction pressure regulating valve should be closed, the stops opened, and the valve cut into the
system. With the suction regulating valve in operation, a 32-pound suction
pressure will be
maintained in the air-conditioning evaporator while the compressor is operating on the lower
suction pressure necessary on the refrigerating system. The operation of the two systems in this
manner is desirable because the capacity of the air-conditioning compressor is much greater than
is needed to maintain the refrigerating rooms at their desired temperatures.
The current supplied to the thermostatic control on the refrigeration system is another point
that must be checked, otherwise the solenoid valves will remain closed and no refrigerant will
flow through the system. On some ships, the thermostat circuits are energized from 110 volt d.c.
so that in this case the main thermostatic control circuit will still be energized. On some 300 class
submarines, the thermostat circuits are energized through the refrigerating control panel and when
the main switch is pulled on the refrigerating compressor, it interrupts the supply to the
thermostatic control circuits. In this case, the following procedure should be followed:
Leave in the main switch supplying current to the refrigerating compressor; with some
insulated material, lift the overload relay cutout located on the bottom left side of the half-ton
compressor control panel, to the OFF position, making sure that the overload relay cutout stays
up. Then turn the selector switch on the half-ton system to either MANUAL or AUTOMATIC.
This will insure a supply of current to the thermostatic controls.
8B9. Cross connection of air-conditioning systems. On some classes of submarines,
it is possible to operate the No. 1 compressor and condenser on the No. 2 evaporator and vice
versa. The air-conditioning systems on the 300 class submarines are cross-connected only by the
compressor discharge lines and the high-pressure liquid lines. There is no cross connection
between the suction lines. Because of this arrangement in the air-conditioning system, the No. 1
compressor can be connected to the No. 2 condenser, and the No. 2 compressor can be connected
to the No. 1 condenser. The No. 1 compressor cannot be connected to the No. 2 evaporator, nor
the No. 2 compressor to the No. 1 evaporator.
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Version 1.10, 22 Oct 04