INCORPORATING COLD CHAIN
FEATURE
R143a and R125, with a relatively low
proportion of R134a, the temperature
glide with the ternary blend R404A
within the relevant application range is
less than one Kelvin. The characteristics
within the heat exchangers are therefore
not very different than with azeotropes.
The results obtained from heat transfer
measurements show favourable
conditions.
R507A is a binary substance
combination which even gives an
azeotropic characteristic over a relatively
wide range. The conditions therefore
tend to be even better. The performance
(Figure 6) gives hardly any difference
between the various substances and
is very similar to R502. This also explains
the high market penetration of these
refrigerants.
With regard to the thermodynamic
properties, they are particularly suitable
for commercial medium and low
temperature systems. Typical metallic
materials are compatible with HFC
refrigerants. Elastomers, however, must be
adapted to the changed characteristics.
Suitable lubricants are polyol esters. The
relatively high global warming potential
(GWP = 3922 .. 3985), which is mainly
determined by the R143a and R125, is
something of a hitch.
However, it is better than R502 and
with regard to the favourable energy
demand also leads to a reduction of
the TEWI value. Other improvements are
possible in this respect due to further developed system control.
Nevertheless, due to their high global warming potential (GWP),
the use of R404A and R507A will no longer be allowed in the EU
in new installations from 2020.
This has been settled in the F-Gas Regulation No. 517/2014
to be applied since 2015. However, the current requirement of
phase-down in connection with a strict quota system will lead to
an earlier phase-out in many applications. In the USA, Canada
and Australia there are also requirements to phase-out R404A
and R507A. For an international phase-down (starting in 2019) of
HCFC and HFC refrigerants, the so-called Kigali Amendment was
agreed upon in 2016 as part of the Montreal Protocol.
The system technology can be based on the experience with
R22 and R502 over a wide area. On the thermodynamic side, a
heat exchanger between the suction and liquid line is recommended
as this will improve the refrigerating capacity and COP. CLA
To be continued in the next issue of Cold Link Africa
COLD LINK AFRICA • September 2020 www.coldlinkafrica.co.za 31