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Survey
of Refrigeration Equipment
| Refrigeration equipment can be classified
as either self-contained or remote units. Self-contained equipment
houses both the insulated storage compartments (refrigerated),
in which the evaporator is located, and an uninsulated compartment
(nonrefrigerated), in which the condensing unit is located,
in the same cabinet. This type of equipment can be designed
with a hermetically sealed, semisealed, or an open condensing
unit. These units are completely assembled and charged at
the factory and come ready for use with little or no installation
work. Self-contained refrigerating equipment includes such
equipment as domestic refrigerators and freezers, water coolers,
reach-in and walk-in refrigerators, small cold-storage plants,
and ice plants.
Remote refrigerating equipment has the condensing unit
installed in a remote location from the main unit. These
types of units are used where the heat liberated from the
condenser cannot enter the space where the unit is installed
or space is limited for installation. |
Reach-In Refrigerators
 Reach-in
refrigerators have a storage capacity of 15 cubic feet or
greater. They are mainly used for storing perishable foods,
but they can be found in medical facilities for storing biologicals,
serums, and other medical supplies requiring temperatures
between 30°F and 45°F. Standard-size units most frequently
used are those with storage capacities between 15 and 85 cubic
feet.
Exterior finishes for reach-in refrigerators are usually
of stainless steel, aluminum, or vinyl, while the interior
finishes are usually metal or plastic, and the refrigerator
cabinet is insulated with board or batten type polystyrene
or urethane. Reach-in refrigerators are normally self-contained,
with an air-cooled condenser, but in larger refrigerators,
with remote condensers, water-cooled condensers are sometimes
used. The evaporator is mounted in the center of the upper
portion of the food compartment. In operation, warm air
is drawn by the fan into the upper part of the unit cooler,
where it passes over the evaporator coils, is cooled, and
then is discharged at the bottom of the cooler. The air
then passes up through the interior and around the contents
of the refrigerator. The cycle is completed when the air
again enters the evaporator.
The low-pressure control is set to operate the evaporator
on a self-defrosting cycle, and temperature is thus control
led. Another type of control system uses both temperature
and low-pressure control or defrost on each cycle. The evaporator
fan is wired for continuous operation within the cabinet.
Evaporators in reach-in refrigerators are generally the
unit cooler type with dry coils (Fig. 1). In smaller capacity
refrigerators, ice-making coils, similar to those used in
domestic refrigerators, are often used as well as straight
gravity coils. R-12 and R-502 are normally used in these
units.
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Walk-In Refrigerators
Walk-in refrigerators are normally larger than reach-in types
and are either built-in or prefabricated sectional walk-in
units. They are made in two types - one for bulk storage of
fresh meats, dairy products, vegetables, and fruits requiring
a temperature from 35°F to 38°F and the other for
the storage of frozen food at temperatures of 10°F or
below. The 35°F to 38°F refrigerators are built and
shipped in sections and assembled at the location they are
installed. They can be taken apart, moved, and reassembled
in another area if needed. Standard-size coolers can be from
24 square feet up to 120 square feet in floor area. A walk-in
refrigerator with reach-in doors is shown in figure 2.
The exterior and interiors of these units are normally
galvanized steel or aluminum. Vinyl, porcelain, and stainless
steel are also used. Most walk-in refrigerators use rigid
polyurethane board, batten, or foamed insulation between
the inner and outer walls. For storage temperatures between
35°F to 40°F, 3 to 4 inches of insulation is generally
used. For low-temperature applications, 5 inches or more
of insulation is used. These refrigerators are equipped
with meat racks and hooks to store meat carcasses.
Walk-in refrigerators also have a lighting system inside
the refrigerator compartment. Most systems have the compressor
and condenser outside the main structure and use either
a wall-mounted forced-air or gravity-type evaporator that
is separated from the main part of the cabinet interior
by a vertical baffle.
The operation of the walk-in refrigerator is similar to
that of the reach-in units. The evaporator must have sufficient
capacity (Btu per hour) to handle the heat load from infiltration
and product load.
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Domestic Refrigerators
Most domestic refrigerators are of two types—either
a single door fresh food refrigerator or a two-door refrigerator-freezer
combination, with the freezer compartment on the top portion
of the cabinet, or a vertically split cabinet (side-by-side),
with the freezer compartment on the left side of the cabinet.
They are completely self-contained units and are easy to install.
Most refrigerators use R-22 refrigerant, normally maintaining
temperatures of 0°F in the freezer compartment and about
35°F to 45°F in the refrigerator compartment. The
technician must be able to perform various duties in the maintenance
and repair of domestic refrigerators, water coolers, and ice
machines. This section provides information to aid you in
handling some of the more common types of troubles. But let
us remind you that the information given here is intended
as a general guide and should, therefore, be used with the
manufacturer's detailed instructions.
Single Door Fresh Food Refrigerator
 A
single door fresh food refrigerator (fig. 3) consists of
an evaporator placed either across the top or in one of
the upper corners of the cabinet. The condenser is on the
back of the cabinet or in the bottom of the cabinet below
the hermetic compressor. During operation, the cold air
from the evaporator flows by natural circulation through
the refrigerated space. The shelves inside the cabinet are
constructed so air can circulate freely past the ends and
sides, eliminating the need for a fan. This refrigerator
has a manual defrost, which requires that the refrigerator
be turned off periodically (usually overnight) to enable
the buildup of frost on the evaporator to melt. Both the
outside and inside finish is usually baked-on enamel. Porcelain
enamel is found on steel cabinet liners. The interior of
the unit contains the shelves, lights, thermostats, and
temperature controls.
Two-Door Refrigerator-Freezer Combination
 The
two-door refrigerator-freezer combination is the most popular
type of refrigerator. It is similar to the fresh food refrigerators
in construction and the location of components except it
sometimes has an evaporator for both the freezer compartment
and the refrigerator compartment. Also, if it is a frost-free
unit, the evaporators are on the outside of the cabinet.
Because of the two separate compartments (refrigerator-freezer)
and the larger capacity, these types of refrigerators use
forced air (fans) to circulate the air through the inside
of both compartments. The two-door refrigerator also has
one of the following three types of evaporator defrost systems:
manual defrost, automatic defrost, or frost-free.
There are two types of automatic defrosting: the hot gas
system or the electric heater system. The hot gas system,
through the use of solenoid valves, uses the heat in the
vapor from the compressor discharge line and the condenser
to defrost the evaporator. The other system uses electric
heaters to melt the ice on the evaporator surface.
A frost-free refrigerator-freezer (fig. 4) has the evaporator
located outside the refrigerated compartment. On the running
part of the cycle, air is drawn over the evaporator and
is forced into the freezer and refrigerator compartments
by a fan. On the off part of the cycle, the evaporators
automatically defrost.
Refrigerator-freezer cabinets are made of pressed steel
with a vinyl or plastic lining on the interior wall surfaces
and a lacquer exterior finish. Most domestic refrigerators
have urethane foam or fiber glass insulation in the cabinet
walls. The side-by-side refrigerator-freezer arrangement
has a number of features not found in other refrigerators.
In addition to the automatic icemaker in the freezer compartment,
it has an option for a cold water dispenser, a cube or crushed
ice dispenser, and a liquid dispenser built into the door.
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Water
Coolers and Ice Machines
Water coolers provide water for drinking at a temperature
under 50°F. Two types of water coolers are instantaneous
and storage. The instantaneous type only cools water when
it is being drawn; the storage type maintains a reservoir
of cooled water. One instantaneous method used places coils
in a flooded evaporator through which the water flows. A second
instantaneous method uses double coils with water flowing
through the inner coil with refrigerant flowing in the space
between the inner coil and the outer coil. A third instantaneous
method is to coil the tubing in a water storage tank. This
allows refrigerant to flow through it (fig. 5).
Water coolers are of two basic designs—wall mounted
or floor mounted. Both types are the same in construction
and operation; the only difference is in the method of installation.
Water cooler cabinets have a sheet metal housing attached
to a steel framework. The condenser and hermetic compressor
are located in the housing base, and the evaporator is located
in the cabinet depending on its type of evaporator, but
normally under the drain basin. Most water coolers use a
heat exchanger or pre-cooler, which pre-cools the fresh
water line to the evaporator, reducing cooling requirements
for the evaporator. A thermostat, which is manually set
and adjusted, is located in the cooler housing close to
the evaporator.
Ice machines are self-contained, automatic machines, ranging
from a small unit producing 50 pounds of ice per day to
a commercial unit producing 2,400 pounds of ice per day.
The primary difference in the design of these machines is
the evaporator. They automatically control water feed to
the evaporator, freeze the water in an ice cube mold, heat
the mold and empty the ice into a storage bin, and shut
down when the storage bin is full.
Floats and solenoids control water flow, and switches operate
the storing action when ice is made. Electrical heating
elements, hot water, hot gas defrosting, or mechanical devices
remove the ice from the freezing surfaces depending on the
unit. In recent years, many companies have begun to manufacture
their units to use HFC R-404a refrigerant instead of HCFC
R-22.
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