Note: Descriptions are shown in the official language in which they were submitted.
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REFRIGERANT COMPOSITIONS AND USE THEREOF
IN LOW TEMPERATURE REFRIGERATION SYSTEMS
Field of the Invention
[0001] This invention relates to refrigerant compositions for replacement of
ozone-depleting refrigerant chlorodifluoromethane (HCFC-22 or R-22) for
heating
and cooling applications, especially in low temperature refrigerant systems,
and to a
process for retrofitting a low temperature refrigerant system containing HCFC-
22
io refrigerant with a refrigerant composition without the necessity for any
significant
modification of the refrigerant systems components or lubricants, yet still
being able
to obtain at least about 90%, preferably at least about 95%, of the operating
characteristics of the R-22 composition in such refrigerant systems. The
invention
also relates to a process for using such R-22 replacement refrigerant
compositions in
is other systems capable of using R-22 refrigerant compositions such as newly
designed systems.
Background to the Invention
[0002] Mechanical refrigeration systems, and related heat transfer devices
such as heat pumps and air conditioners, using refrigerant liquids are well
known in
the art for industrial, commercial and domestic uses. Chlorofluorocarbons
(CFCs)
were developed in the 1930s as refrigerants for such systems. However, since
the
1980s the effect of CFCs on the stratospheric ozone layer has become the focus
of
much attention. In 1987 a number of governments signed the Montreal Protocol
to
protect the global environment setting forth a timetable for phasing out the
CFC
products. CFC's were replaced with more environmentally acceptable materials
that
contain hydrogen or hydrochlorofluorocarbons (HCFC's). Subsequent amendments
3o to the Montreal protocol accelerated the phase-out of these CFCs and also
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scheduled the phase-out of HCFCs. Thus, there is a requirement for a non-
flammable, non-toxic alternative to replace these CFCs and HCFCs. In response
to
such demand industry has developed a number of hydrofluorocarbons (HFCs),
which have a zero ozone depletion potential.
[0003] The importance of refrigeration systems, especially low temperature
refrigeration systems, to the food manufacture, distribution and retail
industries is
fundamental. Such systems play a vital role in ensuring that food which
reaches the
consumer is both fresh and fit to eat. In such low temperature refrigeration
systems
to the popular refrigerant employed has been chlorodifluoromethane (R-22 or
HCFC-
22), which has an ozone-depleting potential and will be phased out completely.
[0004] A number of patent publications have suggested replacements for
HCFC-22. That is, these patent publications have suggested refrigerants or
refrigerant compositions that can be used instead of HCFC-22 in new
refrigeration
systems to be built or installed. Among such patent publications there may be
mentioned US Patent Nos. US 5,185,094, US 5,370,811, US 5,438,849, US
5,643,492, US 5,709,092, US 5,722,256, US 6,018,952, US 6,187,219 131, US
6,606,868 131, U 6,669,862 131, published US application no. US 2004/00691091
Al,
and published European application nos. EP 0 430169 Al, EP 0 509 673 Al and EP
0 811 670 Al. While all the mentioned US patents and published EP applications
disclose ternary mixtures of difluoromethane (HFC-32), pentafluoroethane (HFC-
125) and tetrafluoroethane (HFC134a) for use in refrigeration or air
conditioning
systems, they do not address the ability to replace HCFC-22 in existing R-22
refrigeration systems or systems suitable for use with R-22 refrigerant,
particularly in
low temperature refrigeration systems, while obtaining at least about 90%,
preferably
at least about 95%, of the operating characteristics of R-22 without the
necessity for
modification of the system, especially without the necessity for adjustment or
replacement of the expansion valve of the low temperature refrigeration
system.
Comparative examples provided later in the present specification of this
application
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show that tertiary compositions within the scope of the prior art disclosure
are not
suitable for use in low temperature R-22 refrigeration systems. Those prior
art
compositions do not obtain at least about 90% of the operating characteristics
of R-
22 so as to enable one to use such compositions in low temperature R-22
refrigeration systems over a wide range of low refrigeration temperatures and
ambient temperatures without the necessity for modification of the system.
[0005] US Patent No. 6,526,764 discloses refrigerant compositions that are
soluble in a solubilising agent selected from butane, isobutene, pentane,
dimethyl
io ether and mixtures thereof. These refrigerant compositions are stated to be
useful
as R-22 retrofit compositions. However, the R-22 retrofit compositions
disclosed in
this document are only disclosed as suitable for R-22 retrofit high
temperature
refrigeration systems such as air conditioning systems (see Examples 2-7). The
document neither discloses nor contemplates retrofitting of R-22 for low
temperature
refrigeration i.e., refrigeration that maintains an evaporator temperature of
below
32 F.
[0006] Replacement of R-22 in low temperature refrigeration conditions is
completely different and comprises a completely different set of conditions
and
problems than retrofit of R-22 in high temperature refrigeration, such as in
air
conditioning systems. Refrigerant compositions that have acceptable
performance
characteristics at high evaporation temperature (e.g. air conditioning)
systems will
not necessarily have adequate or acceptable performance characteristics in low
evaporation temperature systems. Refrigeration capacity may fall off and
expansion
valves may not operate satisfactorily. This is generally due to lower vapor
pressure
and lower density of the refrigerant composition vapor at the suction point of
the
compressor of the refrigeration system. For example, a composition whose
performance is acceptable in high evaporation temperature systems (e.g. air
conditioning systems) may have a significant drop-off in refrigeration
capacity and
the expansion valves may unacceptably allow liquid to pass through the
compressor
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due to the refrigeration composition having a steeper slope of vapor pressure
versus
temperature than R-22.
[0007] In order to retrofit an existing low temperature refrigeration system
employing HCFC-22 refrigerant with a replacement refrigerant, it is necessary
that
that the operating characteristics of the replacement refrigerant, such as
evaporator
superheat, cooling capacity, refrigerant mass flow rate, efficiency, pressure
and
energy consumption, are substantially identical to that of the HCFC-22
refrigerant
being replaced. This near match in properties of the replacement refrigerant
to those
io of HCFC-22 is essential for their use in such existing low temperature
refrigeration
systems or systems designed for using R-22 refrigerant, without requiring
equipment
replacement or modification, e.g. replacement or modification of expansion
valves of
the low temperature refrigeration system. The solutions suggested by the
industry
for R-22 replacements, such as R-407A and R-407C refrigerants, do not solve
this
i5 problem since they require modification of the systems in an attempt to
match R-22
operating characteristics.
Summary of the Invention
20 [0008] There is a need for a composition that overcomes all of the
disadvantages associated with the prior art compositions heretofore proposed
as
HCFC-22 replacements.
[0009] Accordingly, there is provided a composition comprising: (a) 25-35 %
25 weight difluoromethane (HFC-32); (b) 20-40 % weight pentafluoroethane (HFC-
125);
and (c) 35-45 % weight tetrafluoroethane.
[0010] It has been discovered that these compositions are especially useful to
retrofit existing low temperature refrigeration systems employing HCFC-22
3o refrigerant.
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[0011] In a further embodiment of the composition according to the invention,
the composition comprises: (a) 28-32 % weight difluoromethane (HFC-32); (b) 28-
32
% weight pentafluoroethane (HFC-125); and (c) 38-42 % weight
tetrafluoroethane.
[0012] It has been found that this composition is particularly suitable
alternative to HCFC-22 refrigerant and can be used as a direct replacement in
retrofitting low temperature refrigeration systems which traditionally
employed
HCFC-22 refrigerant.
[0013] In an alternative embodiment of the composition according to the
invention, the composition comprises a) 25-35 wt% difluoromethane (HFC-32), b)
25-35 wt% pentafluoroethane (HFC-125), and c) 40 wt% tetrafluoroethane (HFC-
134a).
[0014] The composition according to the invention optionally includes one or
more additional components other than difluoromethane (HFC-32),
pentafluoroethane (HFC-125), and tetrafluoroethane (HFC-134a), such as, for
example, refrigerants, lubricants, compatibilizers, surfactants or
solubilising agents.
The additional components are present in minor amounts such that performance
characteristics such as superheat and other operating characteristics are not
compromised.
In a still further embodiment of the composition according to the invention,
the
components a), b) and c) comprise at least 97 % by weight of the overall
weight of
the composition. Preferably, the components a), b) and c) comprise
substantially the
entire composition, i.e. the components a), b) and c) comprise substantially
100% by
weight of the overall weight of the composition.
[0015] In a still further embodiment of the composition according to the
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invention, the composition comprises: (a) about 30 % weight difluoromethane
(HFC-
32); (b) about 30 % weight pentafluoroethane (HFC-125); and (c) about 40 %
weight
tetrafluoroethane.
[0016] This is the preferred composition according to the invention. When
used as a refrigerant, this composition exhibits operating characteristics
that are
comparable to those of HCFC-22 refrigerant. This composition can be used as a
direct replacement in retrofitting low temperature refrigeration systems which
traditionally employed HCFC-22 refrigerant.
[0017] The refrigerant compositions of this invention may be employed in
systems suitable for or capable of use with R-22 refrigerant such as existing,
new or
newly designed low temperature refrigeration systems. The ternary refrigerant
compositions of this invention substantially match the operating
characteristics of
HCFC-22 refrigerant, especially in, desired evaporator superheat, cooling
capacity,
mass flow and efficiency, i.e., COP (coefficient of performance that is the
ratio of
refrigeration effect to the energy required) and thereby enable the ternary
compositions of this invention to replace HCFC-22 in existing low temperature
refrigeration systems or in refrigeration systems suitable for use with R-22
refrigerant, without requiring any significant system modification, such as
adjustment,
replacement or redesign of the R-22 system expansion valve. The values of the
operating characteristics of the ternary compositions of this invention will
generally
be at least 90 % or more, preferably at least 95% or more, of the
corresponding
values of the operating characteristics of HCFC-22 in the low temperature
refrigeration systems in which the ternary composition is to replace the HCFC-
22
refrigerant. Also, the compositions employed in this invention are essentially
non-
flammable when tested in accordance with ASTM E681-2001 at conditions
described
in ASHRAE Standard 34 addendum P (3rd public review, January 1998).
[0018] The compositions according to present invention are acceptable
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refrigerant compositions for replacing R-22 refrigerant compositions in both
moderate and low temperature refrigerant applications and systems. The reason
the
compositions of the present invention are acceptable for both moderate and low
temperature refrigeration systems is that they are able to maintain acceptable
superheat levels and acceptable refrigeration capacity over the entire range
of
moderate to low temperature refrigeration. There has been a significant need
for a
single refrigerant composition to function over a broad refrigeration range.
For
example, a supermarket does not want to have the need for two or more
refrigerant
compositions to serve the needs of a single store where food is kept at
temperatures
io of from 32 F down to -10 F or below. The prior art compositions heretofore
proposed as R-22 replacements do not possess the ability to provide acceptable
refrigeration at both moderate and low temperature refrigeration as they are
unable
to provide acceptable superheat levels and refrigeration capacity.
[0019] The three recited components (i.e., difluoromethane, pentafluoroethane
and tetrafluoroethane) in the compositions according to the invention are
present in
amounts such that the operating characteristics of the refrigerant composition
with
respect to superheat provided during refrigeration is provided at an
acceptable
superheat level, and the operating characteristics of cooling capacity, mass
flow
characteristics and efficiency (COP), when employed as the refrigerant in a
low
temperature refrigeration system are each at least 90%, preferably at least
95%, of
the operating characteristics of chlorodifluoromethane (HCFC-22) if HCFC-22
were
to be employed as the refrigerant in such low temperature refrigeration
systems.
[0020] In particular, when the compositions according to the invention are
employed in low temperature refrigeration systems, that is refrigeration
systems
wherein the evaporator temperature is below 32 F, about 14 F or below, about 5
F
or below, or about -22 F or below, the compositions according to the invention
have
an operating characteristic of superheat during refrigeration of at least 2 F.
Preferably, the compositions according to the invention have an operating
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characteristic of superheat during refrigeration in the range of from about 8
F to
about 16 F for an evaporator temperature range of about 15 F to about 30 F,
from
about 8 F to about 12 F for an evaporator temperature of about -15 F, or from
about
4 F to about 8 F for an evaporator temperature of about -30 F.
[0021] There is also provided a process for producing low temperature
refrigeration in a low temperature refrigeration system, said process
comprising the
steps of:
(a) condensing a composition according to the invention; and
(b) evaporating the composition in the vicinity of a body to be cooled,
wherein the evaporator temperature of the refrigeration system is below 32 F.
[0022] Preferably, the evaporator temperature of the refrigeration system is
about 14 F or below.
[0023] Preferably, the evaporator temperature of the refrigeration system is
about 5 F or below.
[0024] Preferably, the evaporator temperature of the refrigeration system is
about -22 F or below.
[0025] In a further embodiment of the process according to the invention, the
composition has an operating characteristic of superheat during refrigeration
of at
least 2 F. Preferably, the composition has an operating characteristic of
superheat
during refrigeration in the range of from about 8 F to about 16 F for an
evaporator
temperature range of about 15 F to about 30 F, from about 8 F to about 12 F
for an
3o evaporator temperature of about -15 F, or from about 4 F to about 8 F for
an
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evaporator temperature of about -30 F.
[0026] The operating characteristics of the refrigerant composition with
respect to cooling capacity, efficiency (COP), and mass flow, when employed as
the
refrigerant in the refrigeration system, are each at least about 90%,
preferably at
least about 95%, of those operating characteristics if chlorodifluoromethane
(HCFC-
22) were to be employed as the refrigerant in said refrigeration system at
identical
refrigeration conditions.
to [0027] The refrigeration system is suitable for use with
chlorodifluoromethane
(HFC-22) and the composition according to the invention can be used in place
of
HFC-22 in the system without requiring any adjustment of the system. In
particular,
no adjustment (including redesign) or replacement of the HCFC-22 expansion
valve
in the low temperature refrigeration system is required in order to achieve
the
is desired operating characteristics. The phrase "suitable to be used with
chlorodifluoromethane (HCFC-22)" means a system has used, or has been adapted
for use with chlorodifluoromethane (HCFC-22) refrigerant in the system to
obtain the
low temperature refrigeration.
20 [0028] In a further aspect of the process according to the invention, the
low
temperature refrigeration system contains HCFC-22 and the process further
comprises the step of replacing at least a portion of, and preferably
essentially totally
replacing, the chlorodifluoromethane (HCFC-22) refrigerant in the
refrigeration
system with a composition according to the invention. "Essentially totally
replacing"
25 means that some slight amount, generally less than about 5%, preferably
less than
about 3%, and more preferably less than about 1%, of HCFC-22
(chlorodifluoromethane) may inadvertently remain in the system upon
replacement
thereof.
30 [0029] There is also provided a low temperature refrigeration system
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comprising a condenser, an evaporator and a refrigerant composition according
to
the invention, wherein the evaporator temperature of the refrigeration system
is
below 32 F.
[0030] Preferably, the evaporator temperature of the refrigeration system is
about 14 F or below.
[0031] Preferably, the evaporator temperature of the refrigeration system is
about 5 F or below.
[0032] Preferably, the evaporator temperature of the refrigeration system is
about -22 F or below.
[0033] In a further embodiment of the system according to the invention, the
composition has an operating characteristic of superheat during refrigeration
of at
least 2 F. Preferably, the composition has an operating characteristic of
superheat
during refrigeration in the range of from about 8 F to about 16 F for an
evaporator
temperature range of about 15 F to about 30 F, from about 8 F to about 12 F
for an
evaporator temperature of about -15 F, or from about 4 F to about 8 F for an
evaporator temperature of about -30 F.
[0034] The operating characteristics of the refrigerant composition with
respect to cooling capacity, efficiency (COP), and mass flow, when employed as
the
refrigerant in the refrigeration system according to the invention, are each
at least
about 90%, preferably at least about 95%, of those operating characteristics
if
chlorodifluoromethane (HCFC-22) were to be employed as the refrigerant in said
refrigeration system at identical refrigeration conditions.
[0035] The refrigeration system according to the invention is suitable for use
with chlorodifluoromethane (HCFC-22) and the composition according to the
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invention can be used in place of HCFC-22 in the system without requiring any
adjustment of the system. In particular, no adjustment (including redesign) or
replacement of the HCFC-22 expansion valve in the low temperature
refrigeration
system is required in order to achieve the desired operating characteristics.
The
phrase "suitable to be used with chlorodifluoromethane (HCFC-22)" means a
system
has used, or has been adapted for use with chlorodifluoromethane (HCFC-22)
refrigerant in the system to obtain the low temperature refrigeration.
[0036] Although the refrigerant compositions of this invention have been
io formulated to be useful to replace HCFC-22 refrigerant in existing low
temperature
refrigeration systems and other low temperature refrigeration systems suitable
for
using chlorodifluoromethane (HCFC-22) refrigerant, it will be appreciated that
use of
such refrigerant compositions of this invention is not limited to such use but
will have
other refrigerant uses, such as, for example, in non-low temperature
refrigeration
systems. The compositions according to the invention are acceptable
refrigerant
compositions for replacing R-22 refrigerant compositions in both moderate and
low
temperature refrigerant applications and systems. The reason the compositions
of
the present invention are acceptable for both moderate and low temperature
refrigeration systems is that they are able to maintain acceptable superheat
levels
and acceptable refrigeration capacity over the entire range of moderate to low
temperature refrigeration.
Brief Description of the Drawing
[0037] In the drawings, Figure 1 is an illustration of a typical refrigeration
system.
Figure 2 is an illustration of suitable superheat measurement points in
a typical refrigeration system.
Figure 3 is an illustration of a compressor of a typical refrigeration
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system showing how suction line superheat is measured.
Figure 4 is a graph of the refrigerant compositions of this invention
outlining the proportions of the tertiary composition components, and showing
their
close proportional relationship to two comparative refrigerant compositions
examples
outside the scope of the invention that were tested in a low temperature
refrigeration
system and shown not to provide at least about 90%, preferably at least about
95%,
of the operating characteristics of R-22 over a wide range of low temperature
operating temperatures without the necessity for modification of the system.
Detailed Description of the Invention
[0038] It has been discovered that specific ternary refrigerant compositions
can be utilized in a process for producing low temperature refrigeration in a
low
temperature refrigeration system suitable for use with HCFC-22 refrigerant,
which
system achieves and maintains an evaporator temperature of below 32 F, or
about
14 F or below, or about 5 F or below, and even about -22 F or below. A
composition
according to the invention comprises (a) 25-35 % weight difluoromethane (HFC-
32);
(b) 20-40 % weight pentafluoroethane (HFC-125); and (c) 35-45 % weight
tetrafluoroethane. A composition comprising (a) 28-32 % weight difluoromethane
(HFC-32); (b) 28-32 % weight pentafluoroethane (HFC-125); and (c) 38-42 %
weight
tetrafluoroethane has been found to be particularly good. In one embodiment of
the
composition according to the invention, the components a), b) and c) comprise
at
least 97 % by weight of the overall weight of the composition. In a preferred
2s embodiment, the components a), b) and c) comprise substantially the entire
composition. A preferred composition according to the invention comprises (a)
about
% weight difluoromethane (HFC-32); (b) about 30 % weight pentafluoroethane
(HFC-125); and (c) about 40 % weight tetrafluoroethane.
30 [0039] The process for producing low temperature refrigeration in a low
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temperature refrigeration system comprises the steps of condensing a
composition
according to the invention and thereafter evaporating the refrigerant with an
evaporator in the vicinity of a body to be cooled, wherein an evaporator
temperature
of the refrigeration system is below 32 F, or about 14 F or below, or about 5
F or
below, and even about -22 F or below. The compositions according to the
invention
have an operating characteristic of superheat during refrigeration of at least
2 F. In
preferred embodiments, the compositions according to the invention have an
operating characteristic of superheat during refrigeration in the range of
from about
8 to about 16 F for an evaporator temperature range of about 15 to 30 F, in
the
io range of from about 8 to about 12 F for an evaporator temperature of about
-15 F,
or in the range of from about 4 to about 8 F for an evaporator temperature of
about
-30 F. The operating characteristics of the refrigerant composition with
respect to
cooling capacity, efficiency (COP), and mass flow, when employed as the
refrigerant
in the refrigeration system, are each at least about 90%, preferably at least
about
95%, of those operating characteristics if chlorodifluoromethane (HCFC-22)
were
employed as the refrigerant in said refrigeration system at identical
refrigeration
conditions.
[0040] The phrase "low temperature refrigeration system" means a
refrigeration system that achieves and maintains an evaporator temperature of
below
32 F, preferably about 14 F or below, and more particularly about 5 F or
below, and
especially a temperature of about -22 F or below.
[0041] The term "superheat" means the temperature rise of the refrigerant at
the exit of the evaporator above the saturated vapor temperature (or dew
temperature) of the refrigerant. This feature and its importance to
refrigeration
systems is best understood by briefly outlining the operation of a typical
refrigeration
system.
[0042] In a typical refrigeration system such as that illustrated in Figure 1,
a
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compressor sends hot gas to a condenser. The condensed liquid passes through
an
expansion valve into an evaporator where it evaporates and collects heat from
the
area to be cooled. The gaseous refrigerant then enters the compressor where
the
compression process raises the pressure and temperature. From the compressor,
the refrigerant is routed back to the condenser and the cycle is repeated.
Based on
the principle that heat flows from warmer areas to cooler areas, the
refrigeration
cycle consists of seven stages: (i) compression of hot gas; (ii) cooling;
(iii)
condensing; (iv) subcooling; (v) expansion; (vi) evaporation; and (vii) super
heating.
A basic vapor compression refrigeration system comprises four primary
components:
lo a metering device (e.g., a capillary tube, fixed orifice/piston, or a
thermostatic
expansion valve), evaporator, compressor, and condenser (see Figure 1).
[0043] Compression energy elevates the vapor pressure to a boiling point that
is below the condensing mediums' temperature. In other words, the compressor
elevates the boiling point of the refrigerant to a point at which the air (or
water)
moving across the condenser is low enough to condense the refrigerant to a
liquid.
Additional passes in the condenser coil cool the liquid refrigerant below its
boiling
point to ensure it remains a liquid as it experiences pressure drop in its
journey to the
evaporator. This cooling below the boiling point is known as subcooling. A
metering
2o device at the evaporator inlet acts as a "dam" to restrict flow and drop
the refrigerant
pressure to a new lower boiling point. This new boiling point is below the
evaporator
medium (air or water) temperature so that the air or water across the
evaporator will
cause the refrigerant to boil. After all of the refrigerant in the evaporator
has boiled
to a vapor, the vapor will pick up additional heat through extra passes in the
evaporator. The amount of vapor temperature increase above the boiling
temperature is known as superheat. The compressor reduces the gas to a high
pressure while simultaneously raising the temperature of the gas. The hot gas
is
then delivered to the condenser where it is cooled, dissipating the heat and
steadily
converting the gas back to a liquid state. When the liquid under high pressure
3o reaches the metering device, the cycle starts over.
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[0044] In the system's evaporator, conversion of liquid to vapor involves
adding heat to the liquid at its boiling temperature, commonly referred to as
the
saturation temperature. After all of the refrigerant has boiled to a vapor,
any
additional temperature increase above the boiling point is known as superheat.
The
temperature and pressure of the refrigeration system is measured in order to
assess
the system performance. The superheat of a refrigeration system can be
determined
in a number of ways. One such method is the superheat temperature/pressure
method and, as the name suggests, involves measurement of the suction pressure
lo and one temperature - the temperature of the refrigerant at the outlet of
the
evaporator on the suction line. The boiling temperature is determined by using
a
pressure-temperature (PT) chart. For single component refrigerants such as
tetrafluoroethane (R-134a), boiling temperature remains constant during the
saturation or boiling phase provided that the pressure remains the same within
the
evaporator. For refrigerant blends, the temperature changes during the boiling
or
saturation phase. This is referred to as glide. Refrigerants with a
temperature glide
use dew point (DP) temperature. This is the temperature of the refrigerant
when the
last of the liquid has boiled into a vapor. Any vapor temperature increase
above the
dew point temperature is called superheat (see Figure 2).
[0045] Figure 3 illustrates how the suction line superheat is determined using
the temperature-pressure method. The pressure is measured at the suction line
service valve. The evaporator boiling temperature is determined from a
temperature-
pressure chart using suction line pressure. The evaporator boiling temperature
is
subtracted from the suction line temperature measured by a digital
thermometer. The
difference is superheat. Pressure-temperature charts are very common tools for
refrigeration technicians and can be and have been generated for the
compositions
according to the invention.
[0046] When measuring superheat, the system must be running long enough
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for temperatures and pressures to stabilize while verifying normal airflow
cross the
evaporator. Using a clamp or other means of attachment, the suction line
temperature is determined by attaching the thermometer probe around a bare
section of the pipe, at the outlet of the evaporator. Best results are
obtained when
the pipe is free of oxides or other foreign material. Next, a pressure gauge
(usually
part of a manifold gauge set) is attached to the suction line service valve
and the
pipe temperature and pressure are noted. This pressure reading will be that of
the
boiling refrigerant inside the evaporator, assuming no abnormal restrictions
exist
within the suction line. Using this pressure value, the evaporator (or dew
point)
io boiling temperature is determined from a PT chart for the refrigerant type
being used.
The boiling/dew point temperature is subtracted from the suction line
temperature to
find the superheat. The suction line temperature may also be taken by
attaching a
bead thermocouple to the suction line. Care must be taken to insulate the
thermocouple and use heat-conducting compound to minimize errors due to heat
loss to ambient air.
[0047] The superheat value reflects the performance of the refrigerant
composition in the refrigerant system. In normal operation, the refrigerant
entering
the compressor must be sufficiently superheated above the evaporator boiling
temperature to ensure that the compressor draws only vapor and no liquid
refrigerant. A low or zero superheat reading indicates that the refrigerant
did not pick
up enough heat in the evaporator to completely boil into a vapor. Liquid
refrigerant
drawn into the compressor typically causes slugging, which can damage the
compressor valves and/or internal mechanical components. Additionally, liquid
refrigerant in the compressor, when mixed with oil, reduces lubrication and
increases
wear, causing premature failure.
[0048] On the other hand, if the superheat reading is excessive - above 20 F
to 30 F - it indicates that the refrigerant has picked too much heat, i.e. the
cooling
capacity and efficiency of the refrigeration system suffers leading to
reliability
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problems due to high compressor discharge temperatures. It is therefore
desirable
to use a refrigerant composition that has a superheat in the range of about 5
F to
about 15 F.
[0049] The term "COP" is a measure of energy efficiency and means the ratio
of refrigeration or cooling capacity to the energy requirement of the
refrigeration
system, i.e., energy to run the compressor. COP is the useful output of the
refrigeration system, in this case the refrigeration capacity or how much
cooling is
provided, divided by how much power it takes to get this output. Essentially,
it is a
lo measure of the efficiency of the system.
[0050] The term "mass flow rate" is the amount (pounds) of refrigerant flowing
through a conduit of a given size in a given amount of time. The mass flow
rate is
important when retrofitting an existing moderate or low temperature
refrigeration
system with a composition according to the invention. The mass flow rate of
the
replacement refrigerant composition must be close to that of the original
refrigerant,
in the present case, chlorodifluoromethane (R-22).
[0051] The term "capacity" refers to the amount of cooling provided, in BTUs
/hr, by the refrigerant in the refrigeration system. This is experimentally
determined
by multiplying the change in enthalpy, in BTU/Ib, of the refrigerant as it
passes
through the evaporator by the mass flow rate of the refrigerant. The enthalpy
can be
determined from a measurement of the pressure and temperature of the
refrigerant.
The capacity of the refrigeration system relates to the ability to maintain an
area to
be cooled at a specific temperature, for example, maintaining food at a
specified
temperature as required by various health and safety regulations. If a low
temperature refrigeration system has a lower capacity, the food in the display
cases
(both fresh and frozen) will rise in temperature and exceed specified limits.
[0052] Refrigerant compositions that do not meet both the evaporator
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superheat requirements and have values for their operating characteristics,
such as
capacity, COP and mass flow rate, in low temperature refrigeration systems
that will
be at least 90 %, preferably at least 95 %, of the corresponding values of the
operating characteristics of HCFC-22 in an identical low temperature
refrigeration
system are not suitable for use in replacing HCFC-22 refrigerant in such low
temperature refrigeration systems since the use of such compositions will
generally
require modification or replacement or redesign of the HCFC-22 refrigeration
system
components, such as expansion valve used in HCFC-22 refrigeration systems, and
thus lead to undesired expense and downtime for the systems. In contrast, the
1o ternary refrigerant compositions of this invention do have the ability to
substantially
match evaporator superheat requirements and meet at least 90 %, preferably at
least 95 %, or more of the value of, operating characteristics (such as,
cooling
capacity, efficiency and mass flow), of HCFC-22 in low temperature
refrigeration
systems across a wide range of refrigeration conditions, e.g., evaporator and
ambient temperatures,
[0053] The surprising ability of the ternary refrigerant compositions of this
invention to substantially match operating characteristics of HCFC-22 in low
temperature refrigeration systems across a wide range of refrigeration
conditions,
e.g., evaporator and ambient temperatures, and the inability of the
compositions
within the scope of the prior art and other comparative compositions to
substantially
match such operating characteristics of HCFC-22 in such systems is illustrated
by
the following non-limiting, examples.
[0054] Ternary compositions in accordance with this invention were prepared
by producing mixtures of the refrigerants HFC-32, HFC-125 and HFC-134a in the
amounts indicated in the following Table 1. The compositions were subjected to
thermodynamic analysis to determine their ability to match the operating
characteristics of HCFC-22 (R-22) in a low temperature refrigeration system.
This
3o analysis was performed using properties from the National Institute of
Science and
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H0005639 (4510)
Technology (NIST) Reference Fluid Thermodynamic and Transport Properties
Database (Refprop 7.0, NIST Std. Database, 2002). The assumptions used to
conduct the analysis are the following. All calculations were performed
assuming an
average evaporation temperature of -25 F (-31.7 C) and 25 F (13.9 C) total
super
heat including 10 F (5.5 C) useful (in evaporator). Average condensing
temperature is equal to ambient temperature plus 15 F (8.3 C). Capacity is
based
on 1 cubic foot/min (0.028m3/min) compressor displacement. COP assumes 65%
isentropic compressor efficiency.
[0055] The results of the performance prediction for the compositions of this
invention relative to HCFC-22 (R-22) are set forth in the following Table 1.
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Table 1
Composition Ambient Capacity Mass Flow COP
components temperature Btu/hr lb/min
(mass percent) F ( C) (watts) (kg/min)
Value % Value % Value %
Relative Relative Relative to
to HCFC- to HCFC- HCFC-22
22 22 value
value value
HCFC-22 60-(15.50) 1771 N/A 0.404 N/A 2.08 N/A
(519) (.184)
80-(26.6') 1662 N/A 0.404 N/A 1.74 N/A
(487) (.184)
95 (35 ) 1550 N/A 0.404 N/A 1.46 N/A
(454) (.184)
HFC-32 (30%) 60 (15.5 ) 1837 103.7% 0.419 103.7% 1.97 94.7%
HFC-125 (538) (.190)
(30%) 0 80 (26.6 ) 1662 101.4% 0.416 103.0% 1.62 93.1%
HFC-134a (494) (.189)
(40%) 95 (35 ) 1529 98.6% 0.413 102.2% 1.34 91.8%
(448) (.188)
HFC-32 (25%) 60 (15.5 ) 1776 100.3% 0.427 105.7% 1.96 94.2%
HFC-125 (520) (.194)
(35%) $0 (26.6 ) 1623 97.7% 0.424 105.0% 1.61 92.5%
HFC-134a (476) (.193)
(40%)
95 (35 ) 1466 94.6% 0.420 104.0% 1.33 91.1%
(430) (.191)
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[0056] The substantially identical match of the operating characteristics of
the
ternary refrigerant compositions of this invention to that of HCFC-22
demonstrates
that such ternary compositions can be used to retrofit existing low
temperature
HCFC-22 refrigerant-containing refrigeration systems without any significant
modification to the refrigeration system components. This match also
demonstrates
that the compositions of this invention can be used in any low temperature
refrigeration system suitable for use with HCFC-22.
[0057] A ternary composition in accordance with this invention, as well as two
comparative compositions in accordance with the disclosure in prior art
publication
EP 0 509 673 Al, comprising mixtures of the refrigerants HFC-32, HFC-125 and
HFC-134a in the amounts indicated in the following Table 2, were subjected to
thermodynamic analysis to determine their ability to substantially match the
operating characteristics of HCFC-22 in a low temperature refrigeration system
operating at -25 F (-31.7 C) evaporation temperature and 110 F (43 C)
condensing
temperature. This analysis was performed using properties from the National
Institute of Science and Technology (NIST) Reference Fluid Thermodynamic and
Transport Properties Database (Refprop 7.0, NIST Std. Database, 2002). The
assumptions used to conduct the analysis are the following. All calculations
were
performed assuming an average evaporation temperature of -25 F (-31.7 C, and
F (13.9 C) total super heat at the compressor which includes 10 F (5.5 C)
useful in the evaporator. Average condensing temperature is equal to ambient
25 temperature plus 15 F (8.3 C). Capacity is based on 1 cubic foot/min
(0.028m3/min) compressor displacement. COP assumes 65% isentropic
compressor efficiency.
The results of the thermodynamic analysis are reported in Table 2.
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Table 2
Composition Capacity Mass Flow
components Btu/hr lb/min
(wt percent) (watts) (kg/min)
Value % Relative Value % Relative
to HCFC-22 to HCFC-22
value value
HCFC-22 (100%) 1550 0.404
(454) (.184)
HFC-32 (35%) 1458 94.1% 0.350 86.7%
HFC-125 (10%) (427) (.159)
HFC-134a (55%)
Comparative composition
HFC-32 (30%) 1402 90.5% 0.355 88.0%
HFC-125 (15%) (411) (.161)
HFC-134a (55%)
Comparative composition
HFC-32 (30%) 1529 98.6% 0.413 102.2%
HFC-125 (30%) (448) (.188)
HFC-134a (40%)
Inventive composition
[0058] As can be seen from the data above, for the comparative compositions
of the prior art, their operating characteristics are not substantially
identical to the
operating characteristic of HCFC-22 in capacity and mass flow and therefore
are not
is considered suitable to replace HCFC-22 refrigerant in existing low
temperature
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refrigeration systems without the need to change other components of the
refrigeration system. In contrast thereto, the data for the compositions of
this
invention are substantially identical to the operating characteristics of the
HCFC-22
refrigerant and, therefore, are suitable to replace HCFC-22 refrigerant in
existing low
temperature refrigeration systems without the need to change components of the
refrigeration system. This match also demonstrates that the compositions of
this
invention can be used in any low temperature refrigeration system suitable for
use
with HCFC-22.
o [0059] The criticality of the proportions of the components of the ternary
composition of the present invention is demonstrated by the following
comparative
testing. The comparative testing, in relationship to an HCFC-22 (R-22)
composition,
is comparative testing of three ternary compositions of this invention
(designated
compositions LT, LT1 and LT2) with two closely related prior art ternary
compositions (designated R-407A and R-407C) having proportions of the three
components outside the ranges of the component proportions of this invention.
The
compositions are further identified in Table 3.
[0060] Comparison in a Typical Commercial Refrigeration System
The compositions were tested with the refrigerant the system was designed for,
HCFC-22, to serve as a baseline for subsequent tests. The performance of all
three
inventive compositions was nearly identical to that of the baseline HCFC-22 (R-
22).
There was no need to adjust the expansion valve much less replace it.
Refrigerant
mass flow rate, cooling capacity, and efficiency (COP) matched that of HCFC-22
within expected measurement error. Other refrigerants R-407A and R-407C did
not
perform adequately. Using these comparative refrigerants would require change
of
system components such as the expansion valve and possibly the evaporator.
[0061] The commercial refrigeration system equipment employed was a
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commercially available condensing unit and an evaporator for a walk-in
freezer/cooler. The following is a detailed description of the equipment:
Condensing Unit
Unit as manufactured by Keeprite Refrigeration, Brantford, Ontario
Model K350L2 outdoor, air cooled, low temperature, R-22 condensing unit
equipped
with:
460 volts / 60 Hz. / 3 phase electrical, 2DF-0300 Copeland compressor, with
demand cooling for low temperature conditions and
1o KAKA-020 Copeland compressor for higher temperature conditions suction
accumulator, oil separator with solenoid, receiver, two valve flooded head
pressure
control system, and standard operating controls.
Evaporator
Unit as manufactured by Keeprite Refrigeration.
Model KUCB204DED electric defrost, low profile DX fed evaporator with:
230 volts / 60 Hz. / 1 phase electrical, electric defrost heaters, 17,340 BTUH
@ -
F. SST, 10 degree TD, 3,200 CFM air flow, and Sporlan distributor and TXV.
2o The evaporator was installed in an environmentally controlled chamber that
served
as the walk-in freezer/cooler. The condenser unit was installed in another
chamber
to control temperature. Instrumentation was added to the system to measure
refrigerant mass flow rate, refrigerant pressure & temperature before and
after each
component, air temperature and flow in/out of evaporator and condenser, and
power
to condensing unit and evaporator. Tests were run at two typical freezer
temperatures (0 F and -15 F), two typical walk-in cooler temperatures (35 F
and
50 F) and a range of ambient temperatures from 55 F to 95 F. It should be
noted
that the refrigerant temperatures were typically 15 to 20 F lower than the
chamber
temperatures.
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A coriolis-type flow meter was installed in the liquid line after the liquid
receiver and
before the expansion valve in order to measure the refrigerant mass flow rate.
This
flow meter is a Micromotion CMF025 model with an accuracy of 0.1% of the
measured flow.
Pressures were measured using Honeywell TJE transducers with varied ranges
depending of the location (0-300 PSIA, 0-500 PSIA). The accuracy is of 0.1 %
of full
scale. The dew temperature of the refrigerant compositions was determined from
Refrop 7.0 - NIST using the pressure measured directly at the outlet of the
1o evaporator.
The temperature at the evaporator outlet was measured directly using Type T
Thermocouples made by Omega. The range of operation of these Type T
Thermocouples is from -40 C (-40 F) to 125 C (257 F) with an estimated
accuracy
of 0.2 C. The refrigerant superheat was then calculated using the following
equation:
Superheat = Temperature at evaporator Outlet - Dew Temperature
Many other devices known to the skilled person may be used to determine the
temperature and pressure values. Other suitable devices for measuring the
pressure at the suction line service valve include the TITAN 2-Valve and 4-
Valve
and BRUTE II 4-Valve Test and Charging Manifolds manufactured by Ritchie
Engineering. Suitable devices for measuring the suction line temperature
include the
digital thermometers in the 69200 range manufactured by Ritchie Engineering.
Power consumption of the different components of the refrigeration was
measured
using OHIO Semitronics power transducers. Due to the varied range a GW5-002X5
(0-1000 W) model was used for the condenser fan, a GW5-002X5-Y21 (0-500 W)
model was used for the evaporator fan and a GW5-023X5 (0-8000 W) model was
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used for the compressor. The accuracy of these transducers is 0.2% of full
scale.
The power consumption was calculated using the following equation:
Total Power = Evaporator-Fan Power + Condenser-Fan Power + Compressor
Power
The refrigerating capacity was calculated using the following equation:
Capacity = Mass Flow x (Enthalpy at Evaporator Outlet - Enthalpy at
Evaporator Inlet)
wherein, the mass flow is measured directly as indicated above, the enthalpy
at evaporator inlet is the saturated liquid enthalpy for the temperature at
the
inlet of the expansion valve (value extracted from Refprop 7.0 - NIST) and the
enthalpy at the outlet of the evaporator is obtained from Refprop 7.0 - NIST
using the direct measurements of temperature and pressure at the evaporator
outlet. The estimated accuracy is 3% of the reported value.
[0062] The tested compositions were as follows.
Table 3
Refrigerants Tested
by weight
Commercial Name R-32 R-125 R-134a
or Designation
LT 30 30 40
LT1 25 35 40
LT2 35 25 40
R-407A 20 40 40
R-407C 23 25 52
R-404a is composed of 44 wt % HFC-125, 52 wt % HFC-143A and 4 wt % HFC-
134a. It is a common low temperature refrigerant.
[0063] The results of the series of tests are shown in Tables 4 through 7.
Additional comparative tests were performed on the prior art compositions R-
407B,
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R-407D and R-407E. The results of these tests are shown in Tables 9 and 10.
Table 4 lists the superheat at the exit of the evaporator. In order for the
system to
operate reliably and efficiently, superheat should be in the 8 to 16 F (4.4 to
8.9 C)
range for moderate temperatures (e.g. 35 F and 50 F Cooler Temp.), 8 to 12 F
(4.4
s to 6.7 C) range for moderately low temperatures (e.g. 0 F Freezer Temp.) and
4 to 8
OF (2.2 to 4.4 C) range for very low temperatures (e.g. -15 F Freezer Temp.)
(Ref:
Sporlan Valve Company, Expansion Valve Bulletin). If the superheat is too low
or
negative, the refrigerant is in the two-phase region (liquid and vapor) and
liquid
refrigerant can be leaving the evaporator and potentially cause damage to the
to compressor. If the superheat is too high, the capacity and efficiency of
the system
suffers and could also cause reliability problems due to high compressor
discharge
temperatures.
Table 4
Evaporator Superheat ( F)
Refrigerant
Chamber Approx. Evap. Outdoor R-22 LT LTI LT2 R-407A R-407C R-404A
Temp. Temp. Temp. No Ad'. Ad' TXV No Ad'. Ad' TXV No Adj. Ad TXV
-15 F -30 F 55 F 6.78 7.39 6.99 5.06 2.18 - -0.51 - 19.43
75 F 6.80 4.42 6.32 5.63 0.20 - -1.53 - 17.30
95 F 4.94 2.92 1.90 5.06 -0.50 4.90 -1.25 15.48
0 F -20 F 55 F 11.44 11.57 11.56 10.49 7.76 - 5.88 25.04
75 F 11.99 11.05 9.70 11.22 8.67 - 4.84 10.50 24.32
95 F 9.95 8.97 9.14 11.48 7.48 10.00 4.15 8.50 21.52 12.50
35 F 15 F 55 F 11.66 13.78 12.21 14.55 11.39 - 6.88 - 23.36
80 F 10.78 11.54 10.93 12.59 10.12 - 6.52 - 21.48 -
95 F 9.08 10.39 10.01 11.78 9.11 5.55 19.78 9.77
50 F 30 F 55 F 12.06 16.85 15.08 16.58 14.93 - 9.53 - 27.11 -
80 F 12.13 13.09 13.11 14.89 12.16 - 8.65 - 23.86 -
95 F 10.43 11.86 12.00 13.52 10.69 - 7.41 - 21.89
15 From the results, it is clear that for refrigerants R-407A, R-407C, and R-
404A, the
expansion valve needs to be either adjusted or changed. R-407A and R-407C
allows
liquid to leave the evaporator at low temperature (noted by negative superheat
numbers). R-404A has too high a superheat, which leads to poor cooling
performance.
[0064] The refrigerant mass flow, cooling capacity, and efficiency (COP) are
shown relative to R-22 in the following three tables. LT, LT1, and LT2
consistently
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show performance comparable to that of the refrigerant the system was designed
to
operate with, R-22. This is especially true for the LT blend at the highest
ambient
temperature for both 0 F and -15 F freezer temperatures, where the match with
the
mass flow and capacity with R-22 is most critical (design point of the
system). LT1
and LT2 also show acceptable performance considering that no adjustment or
change of the expansion valve is needed.
Table 5
Refri Brant Mass Flow Relative to R-22
Refrigerant
Chamber Approx. Evap. Outdoor LT LT1 LT2 R407A R-407C R-404A
Temperature. Temp. Temperature No Ad). Ad TXV No Ad). Ad TXV No Ad . AdJ TXV
-15 F -30 F 55 F 99% 98% 97% 111% - 98% - 122%
75 F 101% 98% 97% 110% - 101% - 121%
95 F 101% 96% 100% 115% 90% 97% 124%
0 F -20 F 55 F 95% 100% 94% 103% - 95% 112%
75 F 100% 102% 88% 105% - 94% 86% 115% -
95 F 101% 103% 93% 108% 92% 97% 90% 121% 145%
35 F 15 F 55 F 98% 100% 93% 106% - 100% - 114% -
80 F 98% 99% 91% 104% - 98% - 113% -
95 F 97% 97% 90% 104% 97% 110% 135%
50 F 30 F 55 F 97% 99% 89% 104% - 99% - 109% -
80 F 99% 101% 90% 107% - 99% - 111% -
95 F 98% 100% 90% 107% 98% 113%
Average of All Conditions 99% 99% 93% 107% 91% 98% 88% 115% 140%
Table 6
Refrigeration Capacity Relative to R-22
Refrigerant
Chamber Approx. Evap. Outdoor LT LTI LT2 R-4TTXVNo 07C R-404A
Temperature Temp. Temperature No Adj. Adj TXV No Ad j. Adj TXV
-15 F -30 F 55 F 99% 90% 97% 95% 88%
75 F 103% 94% 104% 98% 87% 95 F 99% 89% 104% 99 % 83%
0 F -20 F 55 F 99% 96% 100% 92% 82%
75 F 101% 96% 93% 94% 85% 83%
95 F 99% 95% 97% 93% 80% 92% 88% 81% 91%
35 F 15 F 55 F 104% 99% 103% 100% - 101% - 90% -
80 F 99% 95% 97% 95% - 97% - 84%
95 F 97% 92% 95% 93% 94% 78% 92%
50 F 30 F 55 F 104% 100% 100% 100% - 100% - 89% -
80 F 99% 97% 96% 97% - 97% - 83% -
95 F 98% 96% 95% 96% - 97% - 81%
-
Average of All Conditions 100% 96% 9-7-9/6-
7 % 96% 80% 96% 87% 84% 92%
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Table 7
COP (Efficiency) Relative to R-22
Refrigerant
Chamber Approx. Evap. Outdoor LT LT7 LT2 R-407A R-407C R-404A
Temperature, Tamp . Temperature No Adj. Ad' TXV No Adj. Adj TXV No Adj. Ad TXV
-15 F -30 F 55 F 99% 94% 94% 95% - 95% - 90% -
75 F 101% 97% 101% 99% - 102% - 86% -
95 F 98% 94% 101% 99% 89% 100% 84%
0 F -20 F 55 F 100% 98% 98% 92% - 99% 83% -
75 F 100% 95% 92% 94% - 95% 92% 83% -
95 F 94% 95% 93% 93% 85% 96% 93% 80% 83%
35 F 15 F 55 F 106% 103% 105% 104% - 105% - 94%
80 F 98% 98% 96% 98% - 101% - 87% -
95 F 92% 91% 91% 92% - 95% - 78% 87%
50 F 30 F 56* F 105% 102% 102% 103% - 103% - 91% -
80 F 95% 94% 91% 95% - 98% - 81%
95 F 93% 93% 90% 93% 96% 80%
Average of All Conditions 98% 96% 96% 97% 87% 99% 92% 85% 85%
Table 8
Expansion Valve Adjustments
Impact on Performance
Refrigerant Condition Superheat Mass Flow Capacity COP
R-404A O F / 95 F 12.5 354.6 14846 0.96
145% 91% 83%
R-404A 35 F/95 F 9.8 253.2 12198 1.38
135% 92% 87%
R-407C O F / 95 F 8.5 221.4 14215 1.08
90% 88% 93%
R-407C O F / 75 F 10.5 213.8 15087 1.22
86% 85% 92%
R-407A -15 F / 95 F 4.9 153.0 9047 0.82
90% 80% 89%
R-407A 0 F / 95 F 10.0 225.0 13000 0.99
92% 80% 85%
Condition means chamber/outdoor temperature
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Table 9
Refrigerant Composition Superheat Capacity COP Mass Flow
name (wt%) 4 to 8 *F Relative to
32/125/134a (corresponding Relative to Relative to R-22 (%)
Except 404A range from R-22 (%) R-22 (%)
125/143a/134a claim
407B 10/70/20 10.8 82.0 88.8 114.8
407D 15/15/70 -7.4 98.3 107.0 101.2
407E 25/15/60 -3.9 97.0 104.9 92.3
i) Box Temperature = -15 F
ii) Evaporator Temperature = -30 F
iii) Outdoor Temperature = 95 F
Table 10
Refrigerant Composition Superheat Capacity COP Mass Flow
name (wt%) 8 to 12 OF Relative to R-
32/125/134a (corresponding Relative to Relative to 22 (%)
Except 404A range from R-22 (%) R-22 (%)
125/143a/134a claim
407B 10/70/20 17.3 80.2 82.9 114.1
407D 15/15/70 -3.1 91.9 102.2 96.5
407E 25/15/60 1.2 94.0 100.0 91.6
i) Box Temperature = 0 F
ii) Evaporator Temperature = -15 F
iii) Outdoor Temperature = 95 F
[0065] R-407A and R-407C's performance at first glance looks acceptable but
the R-22 expansion valve fails to operate satisfactorily over the operating
range
thereby not providing the required superheat (rise in temperature) without
modification of the refrigeration system. This necessitates, at a minimum, an
adjustment of this expansion valve component to increase the superheat. The
"Adj
TXV" columns and Table 8 shows the performance impact of such an adjustment.
Capacity and COP are affected resulting in significantly lower performance
than R-
22 and the LT blends. R-407C's capacity drops to only 88% of R-22's at the
critical
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design point. Likewise R-407A has significantly lower capacity. R-404A's
original
performance showed too great a superheat so the expansion valve was adjusted
to
lower the superheat. The performance improved but still remained considerably
below that of R-22 and the LT blends. It should be noted that the adjusted TXV
data
for R-407A at 0 F / 95 F was extrapolated from actual test data at lower
superheats
(5.2 to 6.6 F).
[0066] The test results in Table 9 measure the operating characteristic of
superheat, cooling capacity, COP and mass flow rate for the prior art
compositions
1o R-407B, R-407D and R-407E, wherein the box temperature is -15 F, the
evaporator
temperature is -30 F and the outdoor Temperature is 95 F. R-407B exhibits
significantly lower performance relative to R-22 (see capacity and COP
parameters).
R-407D and R-407E both allow liquid to leave the evaporator at low temperature
(noted by negative superheat numbers). Table 10 shows the measurement of the
same characteristics but in this instance the box temperature is 0 F and the
evaporator temperature is -15 F. Again, R-407B exhibits significantly lower
performance relative to R-22. R-407D and R-407E allows liquid to leave the
evaporator at low temperature (negative superheat value). The superheat value
of
R407E is positive in this instance but should be in the range of about 4 to
about 8 F
for moderately low temperatures (e.g. 0 F Box or Freezer Temperature). The
data in
Tables 9 and 10 shows that these prior art compositions are not able to
maintain
acceptable superheat levels and acceptable refrigeration capacity over the
entire
range of moderate to low temperature refrigeration.
[0067] Figure 4 shows the range of the components of the ternary
compositions of this invention in the diamond shaped area in the graph and
illustrates reasons why this range has considerable advantages over
compositions
outside this range designated by the dots for R-407A and R-407C. Moving up the
graph from the diamond shaped area of the invention results in too great an R-
32
concentration and can result in high pressures, high superheat, and
flammability
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issues. Moving down and to the left of the diamond shaped area of the
invention in
the graph results in low pressures, low capacity, and lack of superheat heat
using
expansion valves designed for R-22. Moving to the right of the diamond shaped
area
of the invention in the graph results in higher mass flows and higher pressure
and
the necessity to replace the expansion valve with a new one designed for these
conditions. The graph also illustrates the nearby prior art compositions (R-
407 A and
R-407C) that do not produce the required nearly identical match with the
operating
characteristics of R-22 that the compositions of this invention produce.
[0068] The compositions according to present invention are acceptable
refrigerant compositions for replacing R-22 refrigerant compositions in both
moderate and low temperature refrigerant applications and systems. These
compositions are able to maintain acceptable superheat levels and acceptable
refrigeration capacity over the entire range of moderate to low temperature
refrigeration. In contrast, the prior art compositions, including the R 404A,
R 407A
and R 407C compositions, do not possess the ability to provide acceptable
refrigeration at both moderate and low temperature refrigeration as they are
unable
to provide acceptable superheat levels and refrigeration capacity.
[0069] While the invention has been described herein with reference to the
specific embodiments thereof, it will be appreciated that changes,
modification and
variations can be made without departing from the spirit and scope of the
inventive
concept disclosed herein. Accordingly, it is intended to embrace all such
changes,
modification and variations that fall with the spirit and scope of the
appended claims.
Numbered Embodiments
[0070] Numbered Embodiment 1
3o A process for producing low temperature refrigeration in a low temperature
refrigeration system suitable for use with chiorodifluoromethane (HCFC-22)
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refrigerant that achieves and maintains an evaporator temperature of below 32
F
(0 C), about 14 F or below, about 5 F or below, or about -22 F or below, the
process comprising condensing a refrigerant and thereafter evaporating the
refrigerant in the vicinity of a body to be cooled, wherein the refrigerant
composition
comprises from about 25 to about 35 mass % difluoromethane (HFC-32), from
about
20 to about 40 mass % pentafluoroethane (HFC-125), and from about 35 to about
45
mass % tetrafluoroethane (HFC-134a) whereby these three components are present
in the refrigerant composition such that the operating characteristic of
superheat
provided during refrigeration is in the range of from about 8 to about 16 F
(about 4.4
1o to about 8.9 C) for an evaporation temperature range of about 15 to 30 F
(about -9
to -1 C), in the range of from about 8 to about 12 F (about 4.4 to about
6.7 C) for
an evaporation temperature of about -15 F (about -26 C), or in the range of
from
about 4 to about 8 F (about 2.2 to about 4.4 C) for an evaporation
temperature of
about -30 F (about -34 C), and the operating characteristics of the
refrigerant
composition in regard to cooling capacity, efficiency (COP), and mass flow,
when
employed as the refrigerant in the refrigeration system, are each at least
about 90%,
preferably at least about 95%, of those operating characteristics if
chlorodifluoromethane (HCFC-22) were to be employed as the refrigerant in said
refrigeration system at identical refrigeration conditions.
[0071] Numbered Embodiment 2
A low temperature refrigeration system suitable for use with
chlorodifluoromethane
(HCFC-22) refrigerant, the low temperature refrigeration system being capable
of
producing low temperature refrigeration achieving and maintaining an
evaporator
temperature of below 32 F (0 C), about 14 F or below, about 5 F or below, or
about
-22 F or below, the system comprising a condenser, an evaporator and a
refrigerant
composition, wherein the refrigerant composition comprises from about 25 to
about
mass % difluoromethane (HFC-32), from about 20 to about 40 mass %
30 pentafluoroethane (HFC-125), and from about 35 to about 45 mass %
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H0005639 (4510)
tetrafluoroethane (HFC-134a) whereby these three components are present in the
refrigerant composition such that the operating characteristic of superheat
provided
during refrigeration would be in the range of from about 8 to about 16 F
(about 4.4
to about 8.9 C) for an evaporation temperature range of about 15 to 30 F
(about -9
to -1 C), in the range of from about 8 to about 12 F (about 4.4 to about
6.7 C) for
an evaporation temperature of about -15 F (about -26 C), or in the range of
from
about 40 to about 8 F (about 2.2 to about 4.4 C) for an evaporation
temperature of
about -30 F (about -34 C), and the operating characteristics of the
refrigerant
composition in regard to cooling capacity, efficiency (COP), and mass flow,
when
to employed as the refrigerant in the refrigeration system, would each be at
least about
90%, preferably at least about 95%, of those operating characteristics if
chlorodifluoromethane (HCFC-22) were to be employed as the refrigerant in said
refrigeration system at identical refrigeration conditions.
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