INCORPORATING COLD CHAIN
FEATURE
Bitzer refrigerant report: Part 3
Published with permission of Bitzer
Stratospheric ozone depletion as well as atmospheric greenhouse effect due to refrigerant emissions have
led to drastic changes in refrigeration and air conditioning technologies since the beginning of the 1990s. For
reference to earlier information, please see Part 1 and 2 published in the previous issues of Cold Link Africa.
SUBSTITUTES FOR R22/R502
IN REFRIGERATION SYSTEMS:
R407A/407B/407F/407H
As an alternative to the earlier described
substitutes, additional mixtures have been
developed based on R32 which is chlorine
free (ODP = 0) and flammable like R143a.
The refrigerant R32 is also of the HFC type
and initially was regarded as a main
candidate for R22 alternatives.
However, due to extent of blend
variations comparable thermodynamic
characteristics to R404A/R507A can also be
obtained. These kinds of refrigerant were
marketed at first under the trade name
KLEA ® 60/61 (ICI) and are listed as R407A/
R407B* in the ASHRAE nomenclature.
Honeywell has developed another blend
with the trade name Performax ® LT (R407F
according to ASHRAE nomenclature) and
introduced it into the market, similar Daikin
Chemical with R407H. For both blends, the
R32 proportion is higher than for R407A,
while the R125 proportion is lower. With
R407H, this results in certain restrictions for
low temperature applications.
However, the necessary conditions
for alternatives containing R32 are
not quite as favourable compared to
the R143a based substitutes discussed
earlier. The boiling point of R32 is very
low at -52°C, in addition the isentropic
compression exponent is even higher
than with R22. Rather high proportions of
R125 and R134a are necessary to match
the characteristics at the level of R404A
and R507A.
The flammability of R32 is thus effectively
suppressed, but the large differences
in boiling points with a high proportion
of R134a lead to a larger temperature
glide. The main advantage of R32 is the
extraordinarily low global warming potential
(GWP = 675), so that even in combination
with R125 and R134a it is significantly lower
than with the R143a based alternatives
mentioned above (R407A: GWP = 2107,
R407F: GWP = 1825, R407H: GWP = 1490).
Thus, they also comply with the
requirement of the new EU F-Gas
Regulation which from 2020 will only allow
refrigerants of GWP < 2500. Measurements
made with R32 containing blends do show
certain capacity reductions compared to
R404A and R507A, with low evaporating
temperatures.
The COP however shows less deviation
and is even higher in medium temperature
applications (Figure 8).
Whether these favourable conditions
are confirmed in real applications is subject
to the system design. An important factor
is the significant temperature glide, which
can have a negative influence upon the
capacity/temperature difference of the
evaporator and condenser.
With regard to the material compatibility,
R32 blends can be assessed similarly to
R404A and R507A; the same applies to
the lubricants. Despite the relatively high
proportion of R125 and R134a in the R32
blends, the discharge gas temperature
is higher than with the R143a based
alternatives (especially for R407F and even
to a higher degree with R407H).
This results in certain limitations in
the application range as well as the
requirement for additional cooling of
compressors when operating at high
pressure ratios. 2-stage compressors can be
applied very efficiently
where especially large
lift conditions are
found. An important
advantage in this case
is the use of a liquid subcooler.
The experience with
R404A/R507A and R22
can be used for plant
technology in many
CONVERTING EXISTING R22 PLANTS
TO R407A/407B/407F/407H
Practical experiences show that qualified
conversions are possible. Compared to
R22 the volumetric refrigeration capacity is
nearly similar while the refrigerant mass flow
is only slightly higher. These are relatively
favourable conditions for the conversion of
medium and low temperature R22 systems.
The main components can remain in the
system provided that they are compatible
with HFC refrigerants and ester oils.
However, special requirements placed
on the heat exchanger with regard to
the significant temperature glide must
be considered. A conversion to ester oil is
also necessary, which leads to increased
dissolving of decomposition products and
dirt in the pipework. Therefore, generously
dimensioned suction clean-up filters must
be provided.
CONVERSION OF EXISTING
R404A/R507A SYSTEMS TO
R407A/407B/407F/407H
Larger differences in thermodynamic
properties (e.g. mass flow, discharge gas
temperature) and the temperature glide
of R407A/F/H may require the replacement
of control components and if necessary
retrofitting of additional compressor cooling
when existing systems are converted. For
newly built systems, a specific design of
components and system is necessary.
R422A as substitute for R22 and R502
Amongst other aims, R422A (ISCEON® MO79
– Chemours) was developed in order to
obtain a chlorine-free refrigerant (ODP = 0)
for the simple conversion of existing medium
and low temperature refrigeration systems
using R22 and R502. For this, it was necessary
to formulate a refrigerant with comparable
performance and energy efficiency to
that of R404A, R507A, and R22, which also
permits the use of conventional lubricants.
R422A is a zeotropic blend of the basic
components R125 and R134a with a small
addition of R600a. Due to its relatively
high R134a percentage, the temperature
glide lies higher than for R404A, but lower
than other refrigerants with the same
is comparable to the blends mentioned
previously, the same applies to the
lubricants. On account of the good
solubility of R600a, conventional lubricants
can also be used under favourable
circumstances. In particular, advantages
result during the conversion of existing R22
and R502 systems as mentioned above.
However, for plants with high oil circulation
rates and/or large liquid charge in the
receiver, oil migration might occur – for
example if no oil separator is installed.
If insufficient oil return to the
compressor is observed, the refrigerant
manufacturer recommends replacing
part of the original oil charge with ester oil.
But from the compressor manufacturer's
view, such a measure requires a very
careful examination of the lubrication
conditions. For example, if increased foam
formation in the compressor crankcase
is observed, a complete change to ester
oil** will be necessary.
Under the influence of the highly
polarised blend of ester oil and HFC, the
admixture of or conversion to ester oil leads
to increased dissolving of decomposition
products and dirt in the pipework.
Therefore, generously dimensioned
suction clean-up filters must be provided.
For further details, see the refrigerant
manufacturer's ‘Guidelines’.
From a thermodynamic point of view,
a heat exchanger between suction and
liquid line is recommended, improving
the refrigerating capacity and coefficient
of performance. Besides this the resulting
increase in operating temperatures leads
to more favourable lubricating conditions
(lower solubility). Due to the high global
warming potential (GWP ≥ 2500), R422A will
no longer be allowed for new installations
in the EU from 2020 onwards. The
requirements and restrictions are specified
in the F-Gas Regulation 517/2014.
* Meanwhile, R407B is no longer
available in the market. Due to the
historical development of HFC blends
this refrigerant will, however, still be
considered in this Report.
respects, although the
temperature glide as
well as the difference
in the thermodynamic
properties have to
be considered. This
especially concerns
the design and
construction of heat
exchangers and
expansion valves.
component blends – such as R417A and
R422D. The adiabatic exponent, and
therefore also the discharge gas and oil
temperatures of the compressor, are lower
than for R404A and R507A.
At extremely low temperatures, this
can be advantageous. However, in cases
of low pressure ratio and suction gas
superheat, this can be a disadvantage
due to increased refrigerant solution if
ester oil is used. The material compatibility
** General proposal for screw
compressors and liquid chillers when
used with DX evaporators with internally
structured heat exchanger tubes.
Furthermore, an individual check
regarding possible additional measures
will be necessary.
To be continued in the next issue of Cold
Link Africa
CLA
COLD LINK AFRICA • October 2020 www.coldlinkafrica.co.za 29