Common Refrigerants
Today, there are three specific types of refrigerants used in
refrigeration and air-conditioning systems:
- Chlorofluorocarbons or CFCs, such as R-11, R-12, and R-114
- Hydrochlorofluorocarbons or HCFCs, such as R-22 or R-123
- Hydrofluorocarbons or HFCs, such as R-134a. All these refrigerants
are "halogenated," which means they contain chlorine,
fluorine, bromine, astatine, or iodine.
Refrigerants, such as Dichlorodifluoromethane (R-12), Monochlorodifluoromethane
(R-22), and Refrigerant 502 (R-502), are called PRIMARY REFRIGERANTS
because each one changes its state upon the application or absorption
of heat, and, in this act of change, absorbs and extracts heat
from the area or substance.
The primary refrigerant is so termed because it acts directly
upon the area or substance, although it may be enclosed within
a system. For a primary refrigerant to cool, it must be placed
in a closed system in which it can be controlled by the pressure
imposed upon it. The refrigerant can then absorb at the temperature
ranges desired. If a primary refrigerant were used without being
controlled, it would absorb heat from most perishables and freeze
them solid.
SECONDARY REFRIGERANTS are substances, such as air,
water, or brine. Though hot refrigerants in themselves, they
have been cooled by the primary refrigeration system; they pass
over and around the areas and substances to be cooled; and they
are returned with their heat load to the primary refrigeration
system. Secondary refrigerants pay off where the cooling effect
must be moved over a long distance and gas-tight lines cost
too much.
Refrigerants are classified into groups. The National Refrigeration
Safety Code catalogs all refrigerants into three groups:
- Group I – safest of the refrigerants, such as R-12, R-22,
and R-502
- Group II – toxic and somewhat flammable, such as R-40
(Methyl chloride) and R-764 (Sulfur dioxide)
- Group III – flammable refrigerants, such as R-170 (Ethane)
and R-290 (Propane).
R-12 DICHLORODIFLUOROMETHANE (CC12 F2 ) Dichlorodifluoromethane,
commonly referred to as R-12, is colorless and odorless in concentrations
of less than 20 percent by volume in air. In higher concentrations,
its odor resembles that of carbon tetrachloride. It is nontoxic,
non-corrosive, nonflammable, and has a boiling point of -21.7°F
(-29°C) at atmospheric pressure.
WARNING - Because of its low-boiling point at atmospheric
pressure, it prevents liquid R12 from contacting the eyes because
of the possibility of freezing.
One hazard of R-12 as a refrigerant is the health risk should
leakage of the vapor come into contact with an open flame of
high temperature (about 1022°F) and be decomposed into phosgene
gas, which is highly toxic. R-12 has a relatively low latent
heat value, and, in smaller refrigerating machines, this is
an advantage.
R-12 is a stable compound capable of undergoing the physical
changes without decomposition to which it is 6-20.commonly subjected
in service.
The cylinder code color for R-12 is white.
R-22 MONOCHLORODIFLUOROME-THANE (CHCIF2 ) Monochlorodifluoromethane,
normally called R-22, is a synthetic refrigerant developed for
refrigeration systems that need a low-evaporating temperature,
which explains its extensive use in household refrigerators
and window air conditioners. R-22 is nontoxic, non-corrosive,
nonflammable, and has a boiling point of -41°F at atmospheric
pressure.
R-22 can be used with reciprocating or centrifugal compressors.
Water mixes readily with R-22, so larger amounts of desiccant
are needed in the filter-driers to dry the refrigerant.
The cylinder code color for R-22 is green.
R-502 REFRIGERANT (CHCIF2 /CCIF2 CF3 ) R-502 is an azeotropic
mixture of 48.8 percent R-22 and 51.2 percent R-115. Azeotropic
refrigerants are liquid mixtures of refrigerants that exhibit
a constant maximum and minimum boiling point. These mixtures
act as a single refrigerant. R-502 is non-corrosive, nonflammable,
practically nontoxic, and has a boiling point of -50°F at
atmospheric pressure. This refrigerant can only be used with
reciprocating compressors. It is most often used in refrigeration
applications for commercial frozen food equipment, such as frozen
food walk-in refrigerators, frozen food display cases, and frozen
food processing plants.
The cylinder color code for R-502 is orchid.
R-134a TETRAFLUOROETHANE (CH2 FCF3 ) R-134a, tetrafluoroethane,
is very similar to R-12, the major difference is that R-134a
has no harmful influence on the ozone layer of the earth's atmosphere
and is a replacement for R-12 applications. Non-corrosive, nonflammable,
and nontoxic, it has a boiling point of -15°F at atmospheric
pressure. Used for medium-temperature applications, such as
air conditioning and commercial refrigeration, this refrigerant
is now used in automobile air-conditioners.
The cylinder color code for R-134a is light (sky) blue.
Additional Refrigerants
In addition to the previously mentioned refrigerants, other
less common refrigerants are used in a variety of applications.
R-717 Ammonia (NH3 ) Ammonia, R-717, is commonly used
in industrial systems. It has a boiling point of -28°F at
atmospheric pressure. This property makes it possible to have
refrigeration at temperatures considerably below zero without
using pressure below atmospheric in the evaporator. Normally
it is a colorless gas, is slightly flammable, and, with proper
portions of air, it can form an explosive mixture, but accidents
are rare.
The cylinder color code for R-717 is silver.
R-125 Pentafluoroethane (CHCF5 ) Pentafluoroethane,
R-125, is a blend component used in low- and medium-temperature
applications. With a boiling point of -55.3°F at atmospheric
pressure, R-125 is nontoxic, nonflammable, and non-corrosive.
R-125 is one replacement refrigerant for R-502.
All refrigerants have their own characteristics. It is extremely
important to charge a system with the refrigerant specified.
Use of an incorrect refrigerant can lead to reduced efficiency,
mechanical problems, and dangerous conditions.
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