Page 442 - Mechanical Engineers' Handbook (Volume 4)

4 Refrigerants 431

Table 2 ANSI/ASHRAE Toxicity and Flammability Rating
System 9
Flammability Group Group
High A3 B3
Moderate A2 B2
Non A1 B1
Threshold limit value 400 400
(parts per million)

extensively in refrigeration applications. Many CFCs are in the A1 group. With regulations
banning the production and restricting the sale of all CFCs, the CFCs will eventually cease
to be used. Common refrigerants in the A1 group include R-11, R-12, R-13, R-22, R-114,
R-134a, and R-502.
Refrigerant 11, trichlorofluoromethane, is a CFC. It has a low-pressure–high-volume
characteristic suitable for use in close-coupled centrifugal compressor systems for water or
brine cooling. Its temperature range extends no lower than 7 C.
Refrigerant 12, dichlorodifluoromethane, is a CFC. It was the most widely known and
used refrigerant for U.S. domestic refrigeration and automotive air-conditioning applications
until the early 1990s. It is ideal for close-coupled or remote systems ranging from small
reciprocating to large centrifugal units. It has been used for temperatures as low as 90 C,
although 85 C is a more practical lower limit because of the high gas volumes necessary
for attaining these temperatures. It is suited for single-stage or compound cycles using re-
ciprocating and centrifugal compressors.
Refrigerant 13, chlorotrifluoromethane, is a CFC. It is used in low-temperature appli-
cations to approximately 126 C. Because of its low volume, high condensing pressure, or
both, and because of its low critical pressure and temperature, R-13 is usually cascaded with
other refrigerants at a discharge pressure corresponding to a condensing temperature in the
range of 56 to 23 C.
Refrigerant 22, chlorodifluoromethane, is an HCFC. It is used in many of the same
applications as R-12, but its lower boiling point and higher latent heat permit the use of
smaller compressors and refrigerant lines than R-12. The higher pressure characteristics also
extend its use to lower temperatures in the range of 100 C.
Refrigerant 114, dichlorotetrafluoroethane, is a CFC. It is similar to R-11, but its slightly
higher pressure and lower volume characteristic than R-11 extend its use to 17 C and
higher capacities.
Refrigerant 123, dichlorotrifluoroethane, is an HCFC. It is a replacement refrigerant for
R-11 in low-pressure centrifugal chillers. New centrifugal equipment designed for R-123 can
provide exceptionally high energy efficiency. In retrofits of older existing centrifugal chillers,
modifications are often needed to increase capacity or avoid material incompatibility (es-
pecially elastomers).
Refrigerant 125, pentafluoroethane, is an HFC. It is used in some refrigerant mixtures,
including R-407C and R-410A.
Refrigerant 134a, 1,1,1,2-tetrafluoroethane, is an HFC. It is a replacement refrigerant
for R-12 in both refrigeration and air-conditioning applications. It has operating character-
istics similar to R-12. R-134a is commonly used in domestic refrigeration applications in
the United States.
Refrigerants 407C and 410A are both mixtures of HFCs. R-407C can be used in some
retrofit applications for R-22. Because of its much higher operating pressures, R-410A cannot