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
- 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.
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 gastight lines cost too much.
Refrigerants are classified into
groups. The National Refrigeration Safety Code catalogs all refrigerants into three
- 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, noncorrosive, nonflammable, and has a boiling point of
-21.7°F (-29°C) at atmospheric pressure.
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
(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, noncorrosive, 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
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 noncorrosive, 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
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. Noncorrosive, 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
The cylinder color code for R-134a is
light (sky) blue.
In addition to the previously
mentioned refrigerants, other less common refrigerants are used in a variety of
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
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
noncorrosive. 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.