Dinc Ibrahim. Refrigeration systems and applications 2th edition

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Refrigerants 81

. Thus, the GWP of CO

is deﬁned to be 1.0. CFC-12 has a GWP of 8500, while CFC-11

has a GWP of 5000. Various HCFCs and HFCs have GWPs ranging from 93 to 12,100. Water,

a substitute in numerous end uses, has a GWP of 0. GWP represents how much a given mass

of a chemical contributes to global warming, over a given time period, compared to the same

mass of CO

.CO

’s GWP is deﬁned as 1.0. These values are calculated over a 100-year time

horizon. HFCs are numbered according to the ASHRAE Standard 34 scheme. Table 2.2 lists many

ozone-depleting substances showing their ODPs, GWPs, and Chemical Abstract Service (CAS)

numbers.

As can be seen in Table 2.2, PFCs do not deplete stratospheric ozone, but the US Environmental

Protection Agency is concerned about their impact on global warming. Recent scientiﬁc studies,

however, indicate that the ODPs for halon 1301 and halon 1211 are at least 13 and 4, respectively.

Although HBFCs were not originally regulated under the “Clean Air Act (CAA),” subsequent

regulation added HBFCs to the list of class I substances. Although HCs are highly ﬂammable, they

may offer advantages as ODS substitutes because they are inexpensive to produce and have zero

ODP, very low GWP, and low toxicity. HCFCs have ODPs ranging from 0.01 to 0.1. Production

of HCFCs with the highest ODPs will be phased out ﬁrst, followed by other HCFCs. All HFCs

have an ODP of 0. Some HFCs have high GWPs.

2.8 Clean Air Act (CAA)

Scientists worldwide have concluded that R-12 and other CFCs deplete the ozone layer. As a result,

over 150 countries have signed a treaty called the Montreal Protocol to protect the earth’s ozone

layer as mentioned earlier. For example, the Protocol was implemented in the United States by

the CAA as the law amended by Congress in 1990 and regulations issued under the act ended the

production of R-12 for air conditioning and refrigeration uses on December 31, 1995. The CAA

directs the U.S. EPA to protect the ozone layer through several regulatory and voluntary programs

and covers the production of ODSs, the recycling and handling of ODSs, the evaluation of substi-

tutes, and efforts to educate the public. A detailed list of class I and class II substances with their

ODPs, GWPs, and CAS numbers has been given in Table 2.2. A class I substance is any chemical

with an ODP of 0.2 or greater. Class II substances include all of the HCFCs. These compounds are

numbered according to the ASHRAE Standard 34 scheme. In fact, CFCs are numbered according

to a standard scheme.

2.8.1 Signiﬁcant New Alternatives Policy (SNAP)

In 1994, EPA established the Signiﬁcant New Alternatives Policy (SNAP) Program to review

alternatives to ODSs like CFC-12. Under the authority of the 1990 CAA, EPA examines new

substitutes for their ozone depleting, global warming, ﬂammability, and toxicity characteristics. EPA

has determined that several refrigerants are acceptable for use as CFC-12 replacements, subject to

certain use conditions. This section lists the use conditions in detail and provides information about

the current crop of refrigerants.

It is important to understand the meaning of “acceptable subject to use conditions.” EPA believes

that such refrigerants, when used in accordance with the conditions, are safer for human health and

the environment than CFC-12. This designation does not mean that the refrigerant will work in any

speciﬁc system nor does it mean that the refrigerant is perfectly safe regardless of how it is used.

Finally, note that EPA does not approve or endorse any one refrigerant that is acceptable, subject

to use conditions, over others also in that category.

Also, note that EPA does not test refrigerants. Rather, it reviews information submitted to it by

manufacturers and various independent testing laboratories. Therefore, it is important to discuss any

82 Refrigeration Systems and Applications

new refrigerant before deciding to use it, and, in particular, to determine what the effects of using

a new refrigerant will be. Before choosing a new refrigerant, one should also consider whether it

is readily and widely available, and one should consider the cost of buying recovery equipment for

blends or recovery/recycling equipment for HFC-134a.

Many companies use the term drop-in to mean that a substitute refrigerant will perform identically

to CFC-12, that no modiﬁcations need to be made to the system, and that the alternative can be

used alone or mixed with CFC-12. However, EPA believes that the term confuses and obscures

several important regulatory and technical points. First, charging one refrigerant into a system

before extracting the old refrigerant is a violation of the SNAP use conditions and is, therefore,

illegal. Second, certain components may be required by law, such as hoses and compressor shut-

off switches. If these components are not present, they must be installed. Third, it is impossible

to test one refrigerant among the thousands of refrigeration systems in existence to demonstrate

identical performance. In addition, system performance is strongly affected by outside temperature,

humidity, driving conditions, etc., and it is impossible to ensure equal performance under all of

these conditions. Finally, it is very difﬁcult to demonstrate that system components will last as

long as they would have if CFC-12 were used. For all of these reasons, EPA does not use the term

“drop-in” to describe any alternative refrigerant.

Under the SNAP rule, each new refrigerant must be used in accordance with the conditions listed

below. If an alternative is chosen, one should make sure that the service shop meets these require-

ments and that it has dedicated recovery equipment for blends or recovery/recycling equipment for

HFC-134a.

The following (e.g., Table 2.3 and 2.4) is the SNAP glossary of the EPA (2009):

• Acceptable. This designation means that a substitute may be used, without restriction, to replace

the relevant ODS within the end use speciﬁed. For example, HCFC-22 is an acceptable substitute

for R-502 in industrial process refrigeration.

• Acceptable subject to use conditions. This designation means that a substitute would be unac-

ceptable unless it is used under certain conditions. An example is the set of use conditions placed

on the refrigerants, requiring the use of unique ﬁttings and labels and requiring that the original

refrigerant be removed before charging with an alternative. Use of the substitute in the end use

is legal, provided the conditions are fully met.

• Acceptable subject to narrowed use limits. This designation means that a substitute would

be unacceptable unless its use was restricted to speciﬁc applications within an end use. This

designation is generally used when the speciﬁc characteristics of different applications within an

end use result in differences in risk. Use of the substitute in the end use is legal only in those

applications included within the narrowed use limit.

• Application. This refers to the most speciﬁc category of equipment. This description is generally

used in sectors where the end uses are fairly broad. In order of increasing speciﬁcity, a particular

system is part of an industrial use sector, an end use, and an application.

• End use. Processes or classes of speciﬁc applications within major industrial sectors where a

substitute is used to replace an ODS. The speciﬁc deﬁnition varies by sector, but examples

are refrigeration, air conditioning, electronics cleaning, ﬂooding ﬁre extinguishing systems, and

polyurethane integral skin foam. Substitutes are listed by end use in the SNAP lists. In order of

increasing speciﬁcity, a particular system is part of an industrial use sector, an end use, and an

application.

• Industrial use sector. This refers to a user community that uses an ODS in similar ways.

SNAP reviews substitutes in nine sectors: (i) refrigerants, (ii) foam blowing, (iii) solvent cleaning,

(iv) ﬁre and explosion protection, (v) aerosols, (vi) sterilants, (vii) tobacco expansion, (viii) adhe-

sives, coatings, and inks, and (ix) pesticides. In order of increasing speciﬁcity, a particular system

is part of an industrial use sector, an end use, and an application.

Refrigerants 83

Table 2. 3 Acceptable substitutes for commercial refrigeration under SNAP program.

Substitutes Trade Name ODS Replaced CSW RT RFR IM VM WC LTR

HCFC-22 22 12; 502 R, N R, N R, N N R, N N –

HFC-23 23 12; 13; 13B1; 503 – – – – – – R, N

HFC-134a 134a 12 R, N R, N R, N N R, N R, N –

HFC-227ea – 12 N – N ––––

R-401A; R-401B MP39; MP66 12 R, N R, N R, N R, N R, N R, N –

R-402A; R-402B HP80; HP81 502 R, N R, N R, N R, N – – –

R-404A HP62; 404A 502 R, N R, N R, N R, N R, N – –

R-406A GHG 12; 500 R RRRRR –

R-407A; R-407B Klea407A; 407B 502 R, N R, N R, N R, N – – –

R-408A 408A 502 R R R R – – –

R-409A 409A 12 – RRRRR –

R-411A; R-411B 411A; 411B 12; 500; 502 R, N R, N R, N R, N R, N R, N –

R-507 AZ-50 502 R, N R, N R, N R, N R, N – –

R-508A KLE 5R3 13; 13BB1; 503 – – – – – – R, N

R-508B SUVA95 13; 13BB1; 503 – – – – – – R, N

FRIGC FRIGC FR-12 12; 500 R, N R, N R, N R, N R, N R, N –

Free Zone RB-276 12 R, N R, N R, N R, N R, N R, N –

Hot Shot Hot Shot 12; 500 R, N R, N R, N R, N R, N R, N –

GHG-X4 GHG-X4 12; 500 R, N R, N R, N R, N R, N R, N –

GHG-X5 GHG-X5 12; 500 R, N R, N R, N R, N R, N R, N –

GHG-HP GHG-HP 12 R, N R, N R, N R, N R, N R, N –

FREEZE 12 FREEZE 12 12 R, N R, N R, N R, N R, N R, N –

G2018C 411C 12; 500; 502 R, N R, N R, N R, N R, N R, N –

HCFC-22/

HCFC-142b

– 12 R,N R,N R,N R,N R,N R,N –

Ammonia Vapor

Compression

– ALL N –NN –––

Evaporative/

Desiccant Cooling

– ALL N ––––––

StirlingCycle – ALL –N–––––

Direct Nitrogen

Expansion

– ALL –N –––––

PressureStep-down– ALL N ––––––

(continued overleaf )

84 Refrigeration Systems and Applications

Table 2. 3 (continued)

Substitutes Trade Name ODS Replaced CSW RT RFR IM VM WC LTR

– 11; 12; 13; 113; 114;

115; 13B1; 502; 503

R, N R, N R, N R, N R, N R, N R, N

NARM-502 – 13;13B1;503 – –––––R,N

THR-04 THR-04 502 R, N R, N R, N R, N R, N R, N –

CSW, cold storage warehouses; RT, refrigerated transport; RFR, retail food refrigeration; IM, ice machines;

VM, vending machines; WC, water coolers; LTR, low-temperature refrigeration (cryogenics); R, retroﬁt uses;

N, new uses.

Source: US Environmental Protection Agency, EPA (2009).

• Unacceptable. This designation means that it is illegal to use a product as a substitute for an

ODS in a speciﬁc end use. For example, HCFC-141b is an unacceptable substitute for CFC-11

in building chillers.

• Use restriction. A general term that includes both use conditions and narrowed use limits.

2.8.2 Classiﬁcation of Substances

There are two signiﬁcant classes of substance as follows:

• Class I substance is one of several groups of chemicals with an ODP of 0.2 or higher. Class I

substances listed in the CAA include CFCs, halons, carbon tetrachloride, and methyl chloroform.

EPA later added HBFCs and methyl bromide to the list by regulation. Table 2.3 shows the ODPs,

GWPs, and CAS numbers of class I substances.

• Class II substance is a chemical with an ODP of less than 0.2. Currently, all of the HCFCs are

class II substances. Lists of class II substances with their ODPs are given in Table 2.2.

In addition to these lists, the Administrator may add, by rule, in accordance with the criteria set

forth, as the case may be, any substance to the list of class I or class II substances. Whenever a

substance is added to the list of class I substances, the Administrator, to the extent consistent with

the Montreal Protocol, assigns such substance to existing group I, II, III, IV, or V or places such

substance in a new group.

Regarding the regulations for production and consumption of class I substances, the Administrator

promulgated regulations within 10 months after the enactment of the Clean Air Act Amendments

of 1990 phasing out the production of class I substances in accordance with this section and other

applicable provisions of this title. The Administrator also promulgated regulations to ensure that the

consumption of class I substances in the United States is phased out and terminated in accordance

with the same schedule (subject to the same exceptions and other provisions) as is applicable to

the phaseout and termination of production of class I substances.

Regarding the regulations for production and consumption, as well as restriction of class I

substances, from January 1, 2015 it shall be unlawful for any person to introduce into interstate

commerce or use any class II substance unless such substance (i) has been used, recovered, and

recycled; (ii) is used and entirely consumed (except for trace quantities) in the production of other

chemicals; or (iii) is used as a refrigerant in appliances manufactured prior to January 1, 2020.

Refrigerants 85

Table 2. 4 Acceptable substitutes for noncommercial refrigeration under SNAP program.

Substitutes Trade Name ODS Replaced Industrial Ice Skating Household Household

Process Rinks Refrigerators Freezers

Refrigeration

HCFC-123 123 11 R, N – – –

HFC-22 22 12; 502 R, N R, N R, N R, N

HFC-23 134a 13; 13B1, 503 R, N – – –

HFC-134a 134a 12 R, N – R, N R, N

HFC-152a – 12 – – N N

HFC-227ea – 12 N – – –

HFC-236fa – 114 R,N – – –

R-401A; R-401B MP39; MP66 12 R, N R, R, N R, N

R-402A; R-402B HP80, HP81 502 R, N – – R, N

R-403B Isceon 69-L 13; 13B1; 503 R, N

–– –

R-404A HP62; 404A 502 R, N – – R, N

R-406A GHG 12; 500 R – R R

R-407A; R-407B Klea407A; 407B 502 R, N R, N – –

R-408A 408A 502 R – – –

R-409A 409A 12 – – R R

R-411A; R-411B 411A; 411B 12; 500; 502 R, N – – –

R-507 AZ-50 502 R, N – – –

R-508A KLE 5R3 13; 13BB1; 503 R, N – – –

R-508B SUVA95 13; 13BB1; 503 R, N – – –

FRIGC FRIGC FR-12 12; 500 R, N – R, N R, N

Free Zone RB-276 12 R, N R, N R, N R, N

Hot Shot Hot Shot 12; 500 R, N R, N R, N R, N

GHG-X4 GHG-X4 12; 500 R, N R, N R, N R, N

GHG-X5 GHG-X5 12; 500 R, N – R, N R, N

GHG-HP GHG-HP 12 R, N – R, N R, N

FREEZE 12 FREEZE 12 12 R, N R, N R, N R, N

G2018C 411C 12; 500; 502 R, N R, N – –

NARM-502 NARM-502 13; 503 R, N – – –

THR-01 THR-01 12 – – N N

THR-04 THR-04 502 R, N R, N R, N –

HCFC-22/

HCFC-142B

– 12 R,N – R,N R,N

(continued overleaf )

86 Refrigeration Systems and Applications

Table 2. 4 (continued)

Substitutes Trade Name ODS Replaced Industrial Ice Skating Household Household

Process Rinks Refrigerators Freezers

Refrigeration

– 12; 13; 13B1;

502; 503

R, N – R, N –

Ammonia Refriger-

ation

– 12; 502 R, N R, N – –

Ammonia Absorp-

tion

–12 ––NN

Propane; Propylene;

Butane; HC Blend

A, B

HC-12a; OZ-12 ALL R, N

–– –

Chlorine – ALL R, N – – –

Evaporative/

Desiccant Cooling

–ALLN–––

R, retroﬁt uses; N, new uses.

Prohibited for other end uses.

Source: US Environmental Protection Agency, EPA (2009).

As used, the term refrigerant means any class II substance used for heat transfer in a refrigerating

system. From January 1, 2015, it shall be unlawful for any person to produce any class II substance

in an annual quantity greater than the quantity of such substance produced by such person during

the baseline year. From January 1, 2030, it shall be unlawful for any person to produce any

class II substance, EPA (2009). Before December 31, 2002, the Administrator will promulgate

regulations phasing out the production, and restricting the use, of class II substances in accordance

with this section, subject to any acceleration of the phaseout of production. The Administrator also

promulgates regulations to insure that the consumption of class II substances in the United States

is phased out and terminated in accordance with the same schedule (subject to the same exceptions

and other provisions) as is applicable to the phaseout and termination of production of class II

substances under this title.

2.9 Alternative Refrigerants

New, alternative substances are required to replace the fully halogenated refrigerants that are believed

to contribute to atmospheric ozone depletion. In the past decade, many research and development

studies on the synthesis and characterization of alternative refrigerants were undertaken. The replace-

ment of restricted ODSs by any alternative may involve substantial changes in the design of various

components such as insulation, lubricants, heat exchangers, and motors. Tests must be done to

optimize the system performance and to ensure the reliability and safety of the system. Several

alternative refrigerants are already available on the market. Several people (e.g., Lorentzen, 1993)

have suggested natural refrigerants, that is, ammonia, propane, and CO

to replace ODSs. Here,

we present R-134a as the most common alternate as well as some other potential replacements,

including the natural substances, for ODSs, although there are so many alternates available ranging

from application to application.

Refrigerants 87

2.9.1 R-134a

R-134a is an HFC refrigerant which has a boiling temperature of −26.2

◦

C(−29.8

◦

C for R-12) and

a latent heat of 205 kJ/kg (159 kJ/kg for R-12) (Pearson, 1991). This is a nonﬂammable and nontoxic

substitute for R-12. R-134a has been widely used in household refrigerators and in automotive air

conditioning, but there appears to be little beneﬁt in using it in conventional air conditioning or

refrigeration where reasonable condensing temperatures can be speciﬁed. R-134a is suggested as

a potential replacement for R-22 in packaged systems. However, the volumetric displacement of a

compressor for R-134a must be about 50% larger than the displacement of an R-22 compressor of

the same cooling capacity. Pressure drops in refrigerant tubing can have a signiﬁcant effect on the

COP of an R-134a system, so larger tubing may be needed than in R-22 systems. R-134a packaged

systems will tend to be physically larger and more costly than their R-22 counterparts (Hickman,

1994). Currently, R-134a is not considered for wide use in reciprocating chillers; however, it is

offered by several manufacturers as an alternative to R-22 for screw and centrifugal chillers with

ﬂooded evaporators.

R-134a is also acceptable as a substitute for R-400 ((60/40)% by weight) and R-114 in new

industrial process air conditioning. EPA recommends that R-134a only be used where ambient

temperatures are lower than 70

◦

C because of very high system pressures. R-134a does not contribute

to ozone depletion. R-134a’s GWP and atmospheric lifetime are close to those of other alternatives

which are acceptable in this end use. While R-134a is compatible with most existing refrigeration

and air-conditioning equipment parts, it is not compatible with the mineral oils currently used in

such systems. An appropriate ester-based, polyalkylene glycol-based, or other type of lubricant

should be used.

2.9.1.1 Guidance on Retroﬁtting to R-134a

Some systems have a device that automatically releases refrigerant to the atmosphere to prevent

extremely high pressures. When retroﬁtting any system with such a device to use a new refrigerant,

a high-pressure shut-off switch must be installed. This switch will prevent the compressor from

increasing the pressure to the point where the refrigerant is vented.

The term retroﬁt describes special procedures required to convert an R-12 system to use an

alternative refrigerant. This section describes some facts about aftermarket options and procedures

for retroﬁtting air conditioning and refrigeration systems to R-134a. As known, R-134a is chosen

worldwide to be the long-term replacement for R-12 in air conditioning and refrigeration systems.

Manufacturers (also known as original equipment manufacturers) have developed retroﬁt kits or

guidelines for some of their models. These procedures were designed to provide the best level of

performance with the new R-134a system. Although using these kits and guidelines will provide

the greatest assurance that comparable system performance will be achieved, the costs of these

procedures will in many instances be relatively high. Procedures required for a least-cost retroﬁt

are simple and do not require major component changes. Generally, the process calls for removal

of the old refrigerant, installation of new ﬁttings and a new label, and the addition of either a

polyalkylene glycol (PAG) or polyester (POE or ester) lubricant as well as the R-134a refrigerant.

According to EPA regulations (EPA, 2009), the use of any alternative refrigerant to replace R-12

requires at a minimum that

• unique service ﬁttings be used in order to minimize the risk of cross-contamination of either the

refrigeration system or the service facility’s recycling equipment;

• the new refrigerant be identiﬁed by a uniquely colored label in order to identify the refrigerant

in the system;

• all R-12 be properly removed from the system before ﬁlling the system with an alternative

refrigerant;

88 Refrigeration Systems and Applications

• in order to prevent release of refrigerant to the atmosphere, a high-pressure compressor shut-off

switch be installed on any system equipped with a pressure relief device; and

• separate equipment be used to recover the R-12 from the system.

Also, alternative refrigerant blends that contain R-22 must be used with barrier hoses.

2.9.1.2 Technical Aspects on Retroﬁtting to R-134a

The following technical aspects are of practical importance in retroﬁtting applications and should

be taken into consideration wherever applicable.

• Toxicity, ﬂammability, corrosion. R-134a is regarded as one of the safest refrigerants yet

introduced, based on current toxicity data. The chemical industry’s program for Alternative

Fluorocarbon Toxicity Testing (PAFT) tested R-134a in a full battery of laboratory animal tox-

icity studies. The results indicate that R-134a does not pose cancer or birth defects hazard. In

addition, R-134a is being used in metered dose inhalers in Europe. The ﬂammability and corro-

sivity of each potential R-12 substitute has been examined by the chemical manufacturers and

various institutes. Like R-12, R-134a is not ﬂammable at ambient temperatures and atmospheric

pressures. Some mixtures of air and R-134a have been shown to be combustible at elevated pres-

sures. These mixtures may be potentially dangerous, causing injury or property damage. R-134a

is not corrosive on standard steel, aluminum, and copper samples.

• Handling. When handling R-134a, as with any other chemical, service staff should be sure to

work in a well-ventilated area. It is never a good idea to inhale any vapor to such an extent that

it replaces the oxygen in the lungs.

• Charging into the system. The amount of R-134a charged into the system should normally be

80–90% of the amount of R-12 in the system. Most system manufacturers provide guidelines

regarding the amount of R-134a to be used.

• Lubricants (PAGs versus esters). The mineral oil used with R-12 cannot be sufﬁciently

transported throughout the system by R-134a. Manufacturers tested both PAGs and esters for

refrigerant/lubricant miscibility, lubricity, chemical stability, and materials compatibility. In the

process of developing recommendations, they also considered the additives and conditioners

present in the oils. Most chose to use PAG lubricants in new systems equipped with R-134a, and

also recommended PAG lubricants for retroﬁts. Some compressor manufacturers are shipping

new compressors with PAGs, some with esters, and some are shipping them empty. PAGs

are hygroscopic, which means that they will draw water from the atmosphere when exposed.

Many aftermarket specialists are choosing to use ester lubricants because they believe that

the hygroscopic characteristics of PAGs may limit their lubricating ability and may introduce

corrosion into the system. Esters are also hygroscopic (although less so than PAGs), and care

must still be taken to ensure that excess moisture does not go into the system. It is good practice

to use PVC-coated gloves (or, if that is impractical, barrier creams) and safety goggles when

handling these lubricants, since prolonged skin contact and/or even brief eye contact can cause

irritations such as stinging and burning sensations. One should also avoid breathing vapors

produced by the lubricants, and make sure to use them in well-ventilated areas and keep both

PAGs and esters in tightly sealed containers, both so that humidity does not contaminate the oil

and so that vapors do not escape.

• Flushing. The amount of mineral oil that can safely remain in a system after retroﬁtting, without

affecting performance, is still being debated. It was originally thought that any mineral oil left

in the system might cause system failure. As long as the technical staff has removed as much of

the old mineral oil as possible, any residual R-12 left in the system should not have a signiﬁcant

effect on the performance of the system. Removing the mineral oil may require draining certain

components.

Refrigerants 89

• Hoses and O-rings. When R-134a was ﬁrst introduced, it was thought that all nonbarrier/nitrile

hoses would have to be replaced during a retroﬁt. Early laboratory tests showed that the small

R-134a molecules leaked through the walls of nonbarrier hoses more readily than the larger

R-12 molecules did. In the lab, this caused unacceptably high leakage rates. More recent testing,

however, has shown that oil used in automotive air-conditioning systems is absorbed into the hose

to create a natural barrier to R-134a permeation. In most cases, the R-12 system hoses will perform

well, provided they are in good condition. Cracked or damaged hoses should always be replaced

with barrier hoses. Unless a ﬁtting has been disturbed during the retroﬁt process, replacement

should not be necessary. Most retroﬁt instructions call for lubricating replaced O-rings with

mineral oil to provide this protection.

• Compressors. Industry experts once thought that a retroﬁt would require compressor replace-

ment. This belief helped create some of the horror stories about the expense of retroﬁtting. Now

it is routinely accepted that most compressors that are functioning well in R-12 systems will

continue to function after the systems have been retroﬁtted. When a compressor is ﬁrst run with

R-12, a thin ﬁlm of metal chloride forms on the bearing surfaces and acts as an excellent antiwear

agent. This ﬁlm continues to protect after the system has been converted to R-134a. This helps

explain why a new R-12 compressor may fail more quickly if it is installed in an R-134a system

without the beneﬁt of a break-in period on R-12. A few older compressors use seals that are not

compatible with either R-134a or the new lubricants. The compressor manufacturer can identify

which compressors need special attention.

• Condensers and pressure cutout switches. When retroﬁts were ﬁrst studied several years ago,

it was thought that the condenser and perhaps the evaporator would have to be replaced to

maintain an acceptable level of cooling performance on a retroﬁtted system. Now, it is generally

accepted that if an R-12 system is operating within the manufacturer’s speciﬁcations, there may

be no need to replace either part. It is true, however, that the higher vapor pressures associated

with R-134a may result in lost condenser capacity. When retroﬁtting, one should consider how

the airﬂow and condenser design on the particular vehicle will affect the success of the retroﬁt.

It should be noted that bent, misshapen, or improperly positioned airﬂow dams and directors

may affect performance. In addition, systems that are not equipped with a high-pressure cutout

switch should have one installed to prevent damage to system parts and to prevent refrigerant

emissions. It is recommended that the installation of a high-pressure cutout switch will shut

off the compressor when high pressures are encountered, reducing the possibility of venting the

refrigerant and overheating the engine cooling system.

• Control devices. Refrigerant controls (whether they are oriﬁce tubes or expansion valves that

meter refrigerant ﬂow, or pressure cycling switches or other pressure controls designed to protect

against freezing) may have to be changed during the course of a retroﬁt.

2.9.2 R-123

R-123 is an HCFC which has a boiling point of 27.1

◦

C (23.8

◦

C for R-11), a latent heat of

175 kJ/kg at 15

◦

C (194 kJ/kg for R-11), and a molecular weight of 153. It is suitable for use in

chiller systems with centrifugal compressors, air conditioning, refrigeration, and heat pump systems.

R-123’s environmental suitability as a replacement for R-11 is not in doubt. It has an ODP and a

GWP less than 0.02, compared with 1.0 for R-11, and does not present any ﬂammability problem.

About its toxicology, R-123 was assigned an allowable exposure limit of 100 ppm (Anon, 1991).

This means that a worker should not be continuously exposed to more than 100 ppm of R-123 during

any working day of 8–12 hours. Regarding the safety issue, the requirements for handling both

R-123 and R-11 refrigerants in charging and servicing equipment are the same. It was suggested

that the parafﬁnic oils which are used with R-11 could also be used with R-123.

90 Refrigeration Systems and Applications

Despite the concern that R-123 is not safe to use in centrifugal chillers and causes cancer in

rats, EPA lists it as acceptable. Although all refrigerants pose a certain amount of toxicity, R-123

actually poses less acute risk than R-11. In other words, in the event of a major leak, it is safer

with R-123 than with R-11. As for chronic toxicity, it is true that R-123 caused tumors in several

organs in rats, including the testes. However, the critical facts are that in all cases (i) the tumors

were benign, (ii) they only appeared after long exposures to very high concentrations, (iii) the

tumors were never life-threatening, and (iv) the exposed rats actually lived longer at these higher

concentrations. The acceptable exposure limit set by the R-123 manufacturers is 30 ppm. This

represents the concentration to which a worker could be exposed for 8 hours/day for a working

lifetime without effects. EPA conducted a study to determine the typical exposure level found in

actual equipment rooms. The study concluded that if appropriate measures are taken (for instance,

complying with ASHRAE 15), the concentration of R-123 can be kept below 1 ppm. EPA believes

that R-123 is a necessary transition refrigerant as the world phases out the CFCs and SNAP lists

it as acceptable for use in chillers. It is safe to be used in the long term, and is actually safer in

emergencies than R-11.

2.9.3 Nonazeotropic (Zeotropic) Mixtures

Table 2.5 shows refrigerant mixtures in the 400 series (zeotropic mixtures). Pederson 2001 calculated

their GWP values on the basis of the values in the table for single substances, weighting on the

basis of the mix ratio between the individual substances.

Table 2. 5 Some common zeotropic mixtures in the 400 series.

R-number Substances GWP Concentration (weight %)

R-401A HCFC-22/HFC-152a/HCFC-124 1082 53/13/34

R-402A HCFC-22/HFC-125/HC-290 2326 38/60/2

R-403A HCFC-22/PFC-218/HC-290 2675 75/20/5

R-403B HCFC-22/PFC-218/HC-290 3682 56/39/5

R-404A HFC-143a/HFC-125/HFC-134a 3260 52/44/4

R-406A HCFC-22/HC-600a/HCFC-142b 1755 55/4/41

R-407C HFC-32/HFC-125/HFC-134a 1526 23/25/52

R-408A HCFC-22/HFC-143a/HFC-125 2743 47/46/7

R-409A HCFC-22/HCFC-142b/HCFC-124 1440 60/15/25

R-410A HFC-32/HFC-125 1725 50/50

R-412A HCFC-22/HCFC-142b/PFC-218 2040 70/25/5

R-413A HFC-134a/PFC-218/HC-600a 1774 88/9/3

R-414A HCFC-22/HCFC-124/HCFC-142b/HC-600a 1329 51/28.5/16.5/4

R-415A HCFC-22/HFC-23/HFC-152a 1966 80/5/15

Source: Pederson (2001).