Technical
BITZER REFRIGERANT REPORT:
Republished with permission of Bitzer PART 3
Stratospheric ozone depletion as well as atmospheric greenhouse effect due
to refrigerant emissions have led to drastic changes in the refrigeration and air
conditioning technology since the beginning of the 1990s.
This is especially true for the area of commercial refrigeration
and air conditioning systems with their wide range of
applications. Please see part 1 and 2 in prior issues of RACA Journal
for other references.
R134A ALTERNATIVES
In addition to the flammable HFO refrigerants R1234yf and R1234ze(E)
already described, non-flammable mixtures are now also available as
R134a alternatives. As previously mentioned, the initial situation is most
favourable for these. They achieve GWP values of approx. 600 − less
than half of R134a (GWP = 1430). In addition, this type of blend can have
azeotropic properties, so that they can be used like pure refrigerants.
For quite some time a blend has been applied on a larger scale
in real systems – this was developed by Chemours and is called
OpteonTM XP-10. Results available today are promising. This is
also true for an R134a alternative designated Solstice® N-13 and
offered by Honeywell which, however, differs regarding the blend
composition.
The refrigerants are listed in the ASHRAE nomenclature under
R513A (Chemours) and R450A (Honeywell). The same category also
includes the refrigerant blends ARM-42 (ARKEMA) as well as R456A
(Mexichem AC5X). All options show refrigerating capacity, power input,
and pressure levels similar to R134a.
Thus, components and system technology can be taken over, only
minor changes like superheat adjustment of the expansion valves are
necessary. Polyolester oils are suitable lubricants which must meet
special requirements, e.g. for the utilisation of additives. Prospects
are especially favorable for supermarket applications in the medium
temperature range in a cascade with CO₂ for low temperature, just
as in liquid chillers with higher refrigerant charges where the use of
flammable or toxic refrigerants would require comprehensive safety
measures.
A special case is the refrigerant R515B: an azeotropic mixture
of R1234ze(E) and small amounts of R227ea. This combination,
declared by the manufacturer Honeywell as an R134a alternative,
is nonflammable (A1) despite the very low GWP of approx. 300.
However, as with the previously described R1234ze(E), this can
only be considered an alternative under certain restrictions. The
volumetric refrigerating capacity is also more than 20% lower than
that of R134a or R1234yf.
SUBSTITUTES FOR R404A/R507A AND R410A
Since the available HFO molecules (R1234yf und R1234ze) show
a considerably smaller volumetric refrigerating capacity than the
above mentioned HFC refrigerants, relatively large HFC proportions
with high volumetric refrigerating capacity must be added for the
particular alternatives. The potential list of candidates is rather
limited, one option is R32 with its relatively low GWP of 675.
However, one disadvantage is its flammability (A2L), resulting also
in a flammable blend upon adding fairly large proportions in order
to increase the volumetric refrigerating capacity while maintaining
a favorable GWP. For a non-flammable blend, on the other hand,
a fairly large proportion of refrigerants with high fluor content (for
example R125) must be added. A drawback here is the high GWP of
more than approx. 900 for non-flammable R22/R407C alternatives
and more than approx. 1300 with options for R404A/ R507A.
Compared to R404A/ R507A, however, this means a reduction
down to a third. The future drastic ‘phase-down’ of F-Gases, e.g.
as part of the EU F-Gas Regulation, already leads to a demand
for R404A/ R507A substitutes with GWP values clearly below 500.
Although this is possible with an adequate composition of the blend
(high proportions of HFO, R152a, possibly also hydrocarbons), the
disadvantage will be its flammability (safety groups A2L or A2).
In this case, the application will have higher safety requirements and
will need an adequately adjusted system technology. R410A currently
has no non-flammable alternatives for commercial applications. Either
R32 as pure substance or blends of R32 and HFO can be used. Due to its
high volumetric refrigerating capacity, this requires a very high proportion
of R32, which is why only GWP values from approx. 400 to 500 can be
achieved. With a higher HFO proportion, the GWP can be reduced even
further, but at the cost of a clearly reduced refrigerating capacity.
All blend options described with R1234yf and R1234ze(E) show
a more or less distinct temperature glide due to boiling point
differences of the individual components. The same criteria apply
as described in context with R407C. Beyond that, the discharge
gas temperature of most R404A/R507A alternatives is considerably
higher than for these HFC blends. In single stage low temperature
systems this may lead to restrictions in the compressor application
range or require special measures for additional cooling.
In transport applications or in low temperature systems with smaller
condensing units, the compressors used can often not meet the
www.hvacronline.co.za RACA Journal I October 2020 49