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ALTERNATIVE REFRIGERANT CHOICESLIMITED BUT PROMISING

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ALTERNATIVE REFRIGERANT CHOICESLIMITED BUT PROMISING Powered By Docstoc
					ALTERNATIVE
REFRIGERANT CHOICES:
LIMITED BUT PROMISING

A PRIMER FOR UNDERSTANDING
THE CHEMISTRY OF REFRIGERANT
SELECTION




        By: Jim Parsnow, Director
        Environmental Systems Marketing
        Carrier Corporation
 4/98
INTRODUCTION                                                        refrigeration. Since ammonia is moderately flammable
The current migration away from chlorofluorocarbon                  and toxic, it is not a viable solution for commercial
(CFC) refrigerants is in direct response to the need to             refrigeration. Sulfur dioxide (SO2) was also used as a
preserve Earth’s delicate, protective ozone layer. In               refrigerant, but its higher toxicity makes it a potential
fact, Earth is the only planet in the solar system with             liability in commercial applications (ASHRAE 15
an atmosphere that supports life. Preserving the                    Safety Code for Mechanical Refrigeration 2 currently
ozone is one of the many essential steps we must                    classifies SO2 as a B2 Class, higher-toxicity
take to protect life on our planet for future generations.          refrigerant).
Similarly, the spectrum of alternative refrigerant
choices is limited to the basic elements found on                   One of the most common compounds, water
Earth.                                                              (H2 0) is used as a refrigerant (Refrigerant Number 718)
                                                                    in absorption chillers. These systems use lithium
                                                                    bromide (salt solution) to quickly absorb and evaporate
THE BASIC ELEMENTS
                                                                    the water in a vacuum, creating a refrigeration effect.
The Periodic Table of The Elements shown below is a
                                                                    However, the application of water as a refrigerant is
compilation of the basic substances that comprise the
                                                                    limited by several factors: lower efficiency, equipment
planet Earth. Compounds are simply combinations of
                                                                    size, heat sources required, steam, gas-fired heat and
these basic elements. Not every elements can be
                                                                    first costs.
used to create a refrigerant compound, however.
Elements marked in purple below solidify at the
                                                                    The elements that hold potential for refrigerant
temperatures required for refrigeration. The red
                                                                    compounds are clearly limited; they are further
elements are toxic in compound form. Those marked
                                                                    narrowed by the choices for fluorocarbon refrigerants.
with blue are very rare, or radioactive. Elements
                                                                    Chlorine (CL) and Bromine (Br) have been eliminated
marked with violet at the edge are unstable
                                                                    as refrigerant elements as they have proven to be
compounds with boiling points too low for refrigeration
                                                                    catalysts that destroy ozone when discomposed from
applications.
                                                                    stable compounds.
                                                                    Nitrogen results in a reactive, increasing toxicity and is
                                                                    less stable. The same is true for sulfur.
 PERIODIC TABLE OF THE ELEMENTS
 Basic Elements & Refrigerant Compounds                             LIMITED CHOICES
                                                                    Clearly, the group of elements considered viable
                                   H                                presents a limited set of options when applied to
                   C     N    O    F                                refrigerant compounds. The matrix triangle depicted
                                                                    below shows the relationship of the elements
                              S    Cl                               Hydrogen, Chlorine and Fluorine combined with a base
    H                                                      H He
                                  Br                                element Carbon (not shown). This triangle - with each
    Li Be                                  B   C   N   O   F   Ne
                                                                    element at an extreme apex - represents all of the
   Na Mg                                  Al Si    P   S   Cl Ar
    K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Ar
                                                                    compounds that may be formed. Refrigerants located
    Rb Sr   Y   Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te     I Xe
                                                                    in the left side of the triangle contain either too much
    Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Ti Pb Bl Po At Rn            hydrogen, and are thus flammable, or too
    Fr Ra As                                                        much of both hydrogen and chlorine, and are thus
               Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
                                                                    toxic. Today’s common refrigerant compounds are
                 Th Pg U Np Pu AmCm Bk Ct Es Fm Md No Lw
                                                                    found in the right area of the triangle. In the figures
                                                                    below, the combinations are shown as both their
                                                                    ASHRAE refrigerant designations (i.e., R-11) and their
REFRIGERANT COMPOUNDS                                               chemical makeup (i.e., CFCL3 - one Carbon, one
By process of elimination, eight elements remain as                 Fluorine and three Chlorine).
candidates for refrigerant compounds: carbon,
nitrogen, oxygen, sulfur, hydrogen, fluorine, chlorine                         TRADE-OFFS AMONG THE
and bromine. Focusing on these eight elements,                                 PROPERTIES OF REFRIGERANTS
Thomas Migley, Jr. 1 formulated the first CFCs used for                                        CL
refrigeration in 1930. Prior to Migley’s discovery, the
elements used for refrigeration had serious drawbacks.                              Toxic
For example, ammonia (NH3) was (and still is) used for
isolated industrial process



                                                                                H                               F
                                                                                            Flammable
                                                                                         in smaller amounts than the CFCs. Global concern
    DERIVATIVES OF METHANE (CH4)                                                         over all chlorine-bearing refrigerants has produced
                                                                                         legislation mandating the phaseout of all HCFCs
                                            10                                           through gradual, stepped-down levels of production.
                                           CCl 4
                                     20    11                                            HCFC 123 is a close replacement for CFC 11 in
                                    CHCl 3CFCl 3                                         centrifugal chillers. However, HCFC borders on the
                           30     21     12                                              toxicity range, and so must be used with extreme
                          CH 2Cl CHFCl2 CF2Cl 2                                          precaution. This compound has undergone numerous
                40               31                22                 13                 toxicity tests in order to qualify for use (it is rated as
              CH 3Cl           CH2FCl            CHF 2Cl             CF3Cl               B1 Class in ASHRAE 15 2). Far from new, HCFC 123
      50              41                    32                23              14         is more than 20 years old, but until now has remained
     CH 4            CH3F                  CH2F2             CHF 3
                                                                              CF 4       in the shadows of CFC 11.
    R-50             R41                   R32               R23              R14
                                                                                         HCFC 22 is also more than 20 years old, and is
                                                                                         currently the most widely used fluorocarbon refrigerant
    DERIVATIVES OF ETHANE (C 2H6)                                                        in commercial refrigeration. It is also used in most
                                                                                         comfort cooling applications, from room air
                                           R110                                          conditioners to the largest chillers. The large volume
                                           C2Cl6
                                                                                         of installed HCFC 22 combined with legislation
                                      R120      R111
                                     C2 HCl 5   C FCl5
                                                 2
                                                                                         prohibiting HCFC 22 venting should ensure adequate
                                R130        R121     R112
                                                                                         amounts of this refrigerant for extended interim usage.
                               C2 H2 Cl4   C2 HFCl4 C2 F Cl4
                                                        2


                       R140           R131      R122      R113                           LONG-TERM SOLUTIONS: HFCS
                      C2 H3 Cl 3     C2H2 FCl3 C2 HF3 Cl C2 F 3Cl3
                                                       2
                                                                                         Given the realities of an accelerated CFC phaseout
                   R150          R141      R132         R123      R114                   and a somewhat less accelerated HCFC phaseout, the
                  C2 H Cl2
                      4
                                C2 H3 FCl C2 H2 F2 Cl2 C2 HF3Cl2 C2 F4 Cl2
                                                                                         search for long-term refrigerant solutions must focus
              R160          R151       R142b         R133        R124      R115          on the bottom of the matrix triangles. HFC 134a is the
              C2 H3 Cl1     C2 H4 FCl1 C2 H3 F2 Cl 1 C2 H2 F3 Cl C2 HF4 Cl C2 F 3Cl
                                                                                         leading choice for a variety of reasons. A close
     R170          R161          R152a      R143a        R134a       R125       R116
     C 2H 6
          F        C2H 3F        C H4F 2
                                  2         C 2H 3 3
                                                 F       C 2H 2F 4   C2HF 5     C2H 6F   replacement for CFC 12, HFC 134a will grow in
                                                                                         demand at a rate that will easily exceed even the
For years, chlorofluorocarbon refrigerants - CFC 11 (R-                                  quantities of HCFC 22. Given its chlorine-free,
11), CFC 12 (R-12), CFC 113 (R-113) and CFC 114 (R-                                      phaseout-free status and its extreme stability, HFC
114) - were preferred for their stability, non-toxicity,                                 134a is probably the next safest refrigerant to water.
non-flammability, thermodynamic properties (ability to                                   The lack of chlorine in HFC 134a did lead to the study
cool) and practical use in designing equipment. Now,                                     of its performance apart from thermodynamic
a new consideration, ozone protection, has forced the                                    applications. For example, HFC 134a does not mix
elimination of chlorine-bearing refrigerant compounds                                    with mineral oils, a feature that is essential in
from the already limited list of viable options.                                         refrigeration equipment so that lubricating oil can be
  Both international agreements (i.e., Montreal                                          reclaimed and returned to compression devices. This
Protocol) and the legislation of individual nations (i.e.,                               hurdle has been overcome by the introduction of
U.S. Clean Air Act) mandate the phaseout of all                                          synthetic refrigerant oils. Today, HFC 134a is being
chlorine-bearing or CFC refrigerants.                                                    applied in foam blowing, pharmaceuticals, auto air
                                                                                         conditioning, refrigeration chillers, residential air
                                                                                         conditioning, water fountains, domestic refrigerators
INTERIM SOLUTIONS: HCFCS                                                                 and supermarkets.
CFC refrigerants, with their long atmospheric life and
high chlorine content, are no longer choices for new
                                                                                         AZEOTROPES
equipment. The search for alternatives to CFC
                                                                                         Although HFC 134a will play a leading role in many
refrigerants has led to a new focus on the refrigerants
                                                                                         applications, other HFC refrigerants found at the
found toward the lower center and bottom of the matrix
                                                                                         bottom of the matrix triangle are also good
triangles. Hydrochlorofluorocarbons (HCFC)
                                                                                         replacements for CFCs and interim HCFCs. Excluding
refrigerants such as HCFC 123 (R-123) and HCFC 22
                                                                                         HFCs that are highly flammable, very high pressure or
(R-22) may be used as interim refrigerant solutions.
                                                                                         lack good application thermodynamics narrows the
                                                                                         field to five compounds. These compounds have
However, HCFCs are also subject to a phaseout
                                                                                         recently been commercialized as azeotropes and
schedule because they, too, contain Chlorine, though
zeotropes. Azeotropes are near-compounds - unique
mixtures of two or more compounds which have nearly          Since azeotropes perform without volumetric
or precisely the same composition in both liquid and         composition or saturated temperature change, they are
vapor states. ASHRAE Standard 344 defines                    promising as replacements for new designs.
azeotropes as “blends comprising multiple
components of different volatilities (evaporating quickly)   ZEOTROPES AND BLENDS
that, when used in refrigeration cycles, do not change       The remaining refrigerants on the manufacturers chart
volumetric composition (size) or saturation                  are either zeotropes or blends. Zeotropes are defined
temperatures as they evaporate (boil) or condense at         by ASHRAE 34 as “blends comprising multiple
constant pressure.”                                          components of different volatilities that, when used in
                                                             refrigeration cycles, change volumetric composition
Only four base compounds are being used to form              and saturation temperatures as they evaporate (boil) or
azeotropes and zeotropes for commerical refrigeration:       condense at constant pressure. The word is derived
HFC 32, 134a, 143a and 125. Other compounds using            from the Greek words zein (to boil) and tropos (to
HFCs R-23, 32, and 152a are being blended with               change).” Blends are defined by ASHRAE 34 as
HCFCs along with propane and butane to create                “refrigerants consisting of mixtures of two or more
limited offerings in niche applications. These blends        different chemical compounds, often used individually
are marketing under several different brand names.           as refrigerants for other applications.”
Understanding that there are limited compounds being         The refrigerants from DuPont, HP62 and AC9000, are
used is helpful in sorting through the various refrigerant   referred to as zeotropes, as is ICI’s refrigerant
brands for the future. A partial list of these newly-        KLEA66. As shown in fig. 4, all of the azeotropes and
created mixtures of existing compounds is shown              zeotropes are mixtures of the refrigerants from the
below.                                                       bottom of the matrix triangles.
                                                             Zeotropes may fit some limited drop-in applications as
             Examples Of HFC Blends,                         well as several replacement design applications. Each
              Zeotropes & Azeotropes                         application must be reviewed in light of the potential for
                                                             different boiling and condensing temperature ranges of
                                                             the zeotropes, commonly referred to as “guide.” Guide
Brand          Manufacture    Composition     ASHRAE 34      is defined by ASHRAE 34 as “the absolute value of the
Name                          Weight %        Number
                                                             difference between the starting and ending
AZ-20          Allied         R 32/ 125     R-410A           temperatures of a phase change process by a
               Signal         50 / 50%                       refrigerant within a component of a refrigerating
AZ-50          Allied         R-125 /143a R-507
                                                             system, exclusive of any sub-cooling or superheating.
               Signal         50 / 50%
                              125/143a/134a R-404A           This term usually describes condensation or
HP-62          DuPont
                              44/52/4 %                      evaporation of a zeotrope.” Simply put, the
AC-9000        DuPont         R-32/125/134a   R-407C         components of the blend each evaporate and
                              23/25/52 %                     condense at different rates. For this reason, zeotropes
Klea 66        ICI            R-32/125/134a   R-407c         will not be used in flooded chiller applications where
                              23/25/52 %                     the design requires a constant
                                                             evaporation/condensation rate.
Allied Signal’s AZ20 is a proposed replacement for
HCFC 22, although it may not be used as a drop-in            In addition, as a zeotrope refrigerant leaves a
due to its nominal 40% higher condensing pressure.           system, its composition may change, leaving behind a
AZ50, an azeotrope of HCFC 22, HFC 125 and 143a is           mixture that is different from the original virgin blend.
the replacement for R-502 which was used in the past         This change is called “fractionalization” and is defined
for low-temperature applications and is itself an            by ASHRAE 34 as “a change in composition of a blend
azeotrope of CFC 12 and HFC 152. Both AZ50 and               by preferential evaporation of the more volatile
AZ20 an azeotrope and a near azeotrope respectively          component(s) or condensation of the less volatile
that match a true compound very closely. Typically           components.” The following is an example of
azeotropes are assigned a R-500 series number where          fractionalization:
zeotropes and blends are assigned 400 series
numbers. AZ20 is somewhat an exception as it                 Refrigerant      HFC-134a + HFC 125 + HFC 32 -->LEAK
performs as a azeotrope in the wide temperature range        Nominal          -15.1°F    -55.3°F    -61.1°F
of refrigeration application however at extreme low and      Boiling Point:   -26.2°C    -48.5°C    -51.7°C
high temperatures it would perform as a blend. So
technically, AZ20 was assigned a 400 series number.
Note: One component of the blend would not leak out
singularly, but as a mixture of its next evaporating
components, as noted by the plus (+) marks.


FUTURE SOLUTIONS
Testing on azeotropes and zeotropes continues, and           REFERENCES
these refrigerants will ultimately supersede the HCFC        1) Thomas Migley, Jr. directed the research team that
refrigerants now used as interim solutions. A broad          developed the first CFC refrigerants in the General
range of these substances will be available. Reference       Motors research laboratory at the request of Frigidaire
White Paper "Three Important Questions to Answer on          Corporation of Dayton, Ohio. In 1937, Migley
Alternative Refrigerants” for questions and reference        published “From the Periodic Table to Production:
material to assist in sorting your choices.4                 Industrial and Engineering Chemistry.”

                                                             2) ASHRAE 15-1992 Safety Code For Mechanical
CONCLUSION                                                   Refrigeration, American Society of Heating,
By taking the mystery out of the subject, a basic            Refrigerating and Air-Conditioning Engineers, Inc.,
understanding of refrigerant chemistry can help              1791 Tullie Circle NE, Atlanta, GA, 30329.
decision-makers sort through complex and often
confusing claims. The migration away from CFC and            3) ASHRAE 34 (currently under change review for new
HCFC refrigerants makes it important to understand           refrigerants), Number Designation and Safety
that current options are limited by both the chemistry       Classification of Refrigerants, American Society of
and the application. Could a “miracle” refrigerant be        Heating, Refrigerating and Air-Conditioning Engineers,
developed in the future? Perhaps, but the substance          Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329.
will require elements beyond those found here on
Earth.                                                       4) “Three Important Questions to Answer on
                                                             Alternative Refrigerants”, written by Jim Parsnow,
Today’s choices are limited, but the HFCs and                Director, Environmental Systems Marketing, Carrier
specifically, HFC 134a, are excellent choices for a          Corporation.
future of chlorine-free, non-ozone depleting refrigerant
compounds. As HFCs are applied to new technology
and continuously improving efficiencies, it is unlikely
that they will present other environmental concerns,
such as global warming. At this point, any refrigerant
selected for long-term use must support an overall
system that is safe, environmentally sound, reflecting
considerations such as new technologies, waste
minimization, containment and energy efficiency. It is
clear that today’s refrigerant choices must be made
with an eye toward protecting and preserving the future
of our delicate planet Earth.

  Prime Replacements For CFCs & HCFCs

  Refrigerant          Made From          Primary Usage

   R-134a                               Autos to Chillers

                        R - 32         Residental
   R-410a               R - 125        Lt. Commerical
                        R   -   32
   R-407C               R   -   125    Commerical
                        R   -   134a
                        R   -   125
                                       Lo Temp. Commerical
   R-404A               R   -   143a
                        R   -   134a
                        R   -   125
   R-507                R   -   143a   Lo Temp. Commerical

				
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