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Refrigerants

Types of Refrigerants
Background:
In refrigerating systems, such as air conditioners, the fluid that absorbs and releases the heat is called refrigerant.  The process starts in the evaporator component of the system. Under a lower pressure, the refrigerant liquid absorbs heat and changes to a vapor. The vapor then travels into the compressor component of the system. In the compressor, the temperature and pressure are increased, allowing the heat from the vapor to be released. The heat is released in the condenser component of the system. Then the refrigerant changes back into liquid form, and travels back into the evaporator. This cycle is repeated over and over with the same fluid.
There are many different types of refrigerants. They are grouped into Class A or B, depending on their toxicity level. Toxicity is the ability of a substance to be harmful or lethal to humans. They are also given a flammability classification, indicated by a 1 (no flammability), 2 (low flammability), or 3 (high flammability).  A listing of the toxicity and flammability of some of the most common refrigerants is shown in Table 1 below.

Table 1: ASHRAE Safety Classifications of Common Refrigerants [1]


Refrigerant Number

Toxicity Grouping

Flammability Number

R-11

A

1

R-12

A

1

R-22

A

1

R-123

B

1

R-124

A

1

R-125

A

1

R-134a

A

1

R-401A

A

1

R-406A

A

2

R-500

A

1

R-502

A

1

R-503

No rating listed

No rating listed

R-507A

A

1

R-717

B

2

R-744

A

1

As you can see from Table 1, only two Group B refrigerants are commonly used, compared to twelve Group A refrigerants.  Therefore, use of toxic refrigerants is uncommon.  A more detailed discussion of each refrigerant will follow.

Group A Refrigerants:
Refrigerants in Group A can be used in fairly large quantities. Allowable quantities are specified by the American Standard Safety Code for Mechanical Refrigeration. These amounts are as follows:

  • Up to 20 lbs. of refrigerant may be used in hospital kitchens.
  • Up to 20 lbs. may be used in residential air conditioning systems.
  • Up to 50 lbs. may be used in residential use if precautions are taken.
  • Up to 50 lbs. may be used in public assemblies.

 
Some refrigerants in Group A are chlorofluorocarbons (CFCs). These include R-11, 12, 13, 113, 114, 500, 502 and 503.  Due to the Environmental Protection Agency’s (EPA) rulings regarding the effects of CFCs on the ozone layer, the refrigerants that contain CFCs are being replaced by manufacturers. Some of the refrigerants in Group A are described in more detail below.

R-11 is Trichlorofluoromethane (CCl3F). It is synthetic, nonflammable and nontoxic. It is a low-pressure refrigerant that is used a lot in large centrifugal compressor systems. The low-side vacuum of R-11 is 24 in. Hg (610 mmHg) at 5oF. It has a high-side pressure of 18.3 psia (126 kPa) or 3.6 psig (94 kPa) at 86oF. The latent heat at 5oF is 84 BTU/lb (195 kJ/kg).  Up to 35 lbs. of R-11 can be used for every 1000 cubic feet of cooled space. The “cylinder code color” (the color of the cylinder it is stored in) of R-11 is orange. Because R-11 is a CFC, R-123 is used as a replacement for it.

R-12 is Dichlorodifluoromethane (CCl2F2). It was the most common domestic and automotive refrigerant until 1997, when production was stopped due to the suspected impact on the earth’s ozone layer. There is still a limited amount of R-12 left for service reasons. R-134a is the replacement for R-12. R-12 is nontoxic, noncorrosive, nonirritating and nonflammable. It is thermally stable to above 800oF. It has a pressure of 26.5 psia (183 kPa) or 11.8 psig (81 kPa) at 5oF, and a pressure of 108 psia (745 kPa) or 93.3 psig (644 kPa) at 86oF. The latent heat at 5oF is 68.2 BTU/lb. This is relatively low, which is an advantage in smaller refrigerating systems. The cylinder code color for R-12 is white.

R-22 is Chlorodifluoromethane (CHClF2). R-22 is stable, nontoxic, nonirritating, noncorrosive, and nonflammable. It has a pressure of 43 psia (297 kPa) or 28 psig (193 kPa) at 5oF, and a pressure of 173 psia (1194 kPa) or 158 psig (1090 kPa) at 86oF. The latent heat at 5oF is 93.2 BTU/lb. R-22 is three times more water soluble than R-12, so more desiccants (to dry up the water) should be used to remove the moisture from R-22. R-22 is used in residential refrigerators, air conditioners, nonindustrial heat pumps, positive displacement chillers, and in fast freezing units. The cylinder code color of R-22 is light green.

R-134a is Tetrafluoroethane (CF3CH2F). It is nontoxic, nonflammable and noncorrosive. Human exposure over 75,000 ppm may cause heart irregularities. The ozone depletion level of R-134a is zero. Although it is used as a replacement for R-12, it’s coefficient of performance is slightly lower than R-12. Due to the differences in R-12 and R-134a, design changes to systems had to be made to accommodate R-134a. These changes include an increase in condenser size, evaporator size, and in control pressure regulations. Also, smaller hoses and a different kind of desiccant are used for R-134a. The cylinder code color of R-134a is light blue. It is the standard refrigerant used in automobiles. It is also used in residential, commercial and industrial refrigeration and air conditioning systems.

R-500 is an azeotropic refrigerant, which means it is a mixture of two other refrigerants (26.2% R-152 + 73.8% R-12). The process of making an azeotropic refrigerant is complicated, and is done by manufacturers (should never be done by service technicians). R-500 is only used in systems with reciprocating compressors. It offers almost 20% more refrigerating capacity than R-12. It has a pressure of 31.1 psia (215 kPa) or 16.4 psig (113 kPa) at 5oF, and a pressure of 128 psia (883 kPa) or 113 psig (780 kPa) at 86oF. The latent heat at 5oF is 82.5 BTU/lb. The cylinder code color of R-500 is yellow.

R-502 is also an azeotropic refrigerant, consisting of 48.8% R-22 and 51.2% R-115. R-502 has many of the best properties of R-12 and R-22. It is practically nontoxic, is nonflammable, and noncorrosive. It can be used when temperatures of 0 to -60oF are needed (such as in frozen food lockers and display cases). R-502 is also only used in systems with reciprocating compressors. It has a pressure of 50.6 psia (349 kPa) or 35.9 psig (248 kPa) at 5oF, and a pressure of 191 psia (1318 kPa) or 177 psig (1221 kPa) at 86oF. The latent heat at 5oF is 67.3 BTU/lb. The cylinder code color of R-502 is orchid. R-507A and R-125 are used to replace R-502, since R-502 is a CFC.

R-507A is an azeotropic refrigerant, made up of 50% R-125 and 50% R-143a. It is nonflammable, but has a slight odor. The cylinder code color of R-507A is teal blue.

R-401A is a zerotropic refrigerant, meaning it is a mixture of two or more other refrigerants. R-401A consists of 53% HCFC-22, 13% HFC-152a, and 34% HCFC-124. It can be used as a replacement for CFC-12. It is used in walk-in coolers, food display cases, vending machines and other medium-temperature systems. The cylinder code color of R-401A is coral red.

R-406A is a zerotropic refrigerant, consisting of 55% R-22, 4% R-600a, and 41% R-142b. It is compatible with systems that utilize R-12, but using it may void the equipment warranty if the manufacturer does not approve its use for a specific system. R-406A is flammable (classification number 2). The cylinder code color for R-406A is light gray-green.

Group B Refrigerants:
Group B refrigerants are toxic, so users of these need to be more cautious. Some of the refrigerants in Group B are described in more detail below.

            R-123 is Dichlorotrifluorethane (CHCl2CF3). It is used as a replacement for R-11 (a Group A refrigerant that is a CFC). It has a higher coefficient of performance than R-11, and can be used in centrifugal compressors and in foam-blowing applications. It is nonflammable. The cylinder code color for R-123 is light grey.

            R-717 is Ammonia (NH3). It was one of the first refrigerants used. Because of its low boiling point (-28oF), it can be used in systems that need to operate well below zero, without using pressures below atmospheric pressure in the evaporator. It has a pressure of 34.3 psia (237 kPa) or 19.6 psig (135 kPa) at 5oF, and a pressure of 169 psia (1166 kPa) or 155 psig (1170 kPa) at 86oF. The latent heat of R-717 is 565 BTU/lb at 5oF. It is used in absorption refrigerators, and in large industrial compression machines. The cylinder code color for R-717 is silver. Ammonia affects the respiratory system, so exposure to 50 ppm is only allowed for a maximum of 5 minutes. It is flammable at 150,000-270,000 ppm. It has a noticeable odor, so leaks can be detected fairly easily.

Refrigerant Cylinders:
Service technicians use small refillable “service cylinders” to charge refrigeration systems. These are filled from larger storage cylinders located at either a wholesaler location, or at the technician’s shop. The valve on the cylinder is most commonly at ¼ in. male flare. It is important to never fill a cylinder completely full with liquid refrigerant. The refrigerant expands when temperature increases, so the cylinder could burst if it’s completely full and it gets hot out.  The general rule of thumb is to fill cylinders 80% full.

Detecting Leaks:
Leaks of refrigerant may be detected with a soap solution, halide torch, or an electronic leak detector that the service technician usually carries. R-12 leaks can also be detected by adding colored oil to the system. R-401A leaks can be detected by using leak detectors that are halogen-selective, compound-selective, or by using a fluorescent additive.

References:

  • Althouse, Turnquist, and Bracciano. Modern Refrigeration and Air Conditioning, 18th ed. Tinley Park, IL: The Goodheart-Willcox Company, Inc., 2004.
  • American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE Handbook. Atlanta, GA: The Society, 1998.
  • International Code Council. International Mechanical Code 2012. Country Club Hills, IL: International Code Council, Inc., 2011.
  • Miller, Rex. Refrigeration: Home and Commercial, 5th ed. Indianapolis, IN: Wiley Pub., 2004.

 

This content was written by Valerie Johnson and is copyrighted 2012.

E-mail: JHC@cooljohnson.com