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APPLICATIONS OF HFOS
HFOs are a range of synthetic refrigerants that promise to be a
part of solution to the environmental problems. They are found
in a number of applications. In refrigeration and heat pump
technology HFO-1234yf has been chosen to replace R134a in
systems; HFO-1234ze and HFO-1233zd are used in chillers. In the
automotive sector R1234yf is commonly used.
The application of new HFOs are further extended when
they are used as a component for lowering GWP in refrigerant
mixtures. When one considers that the industry is in a state of
flux with ongoing investigations in regard to the safe use of
HFOs and considering the previous generations of synthetic
refrigerants, it is still too early to tell whether HFOs represent
the long-term solution.
Stewart, you specifically asked about R1234yf, so let us look at
this refrigerant.
R1234yf is an HFO refrigerant. HFO refrigerants are
composed of hydrogen, fluorine and carbon atoms, but contain
at least one double bond between the carbon atoms. Due to its
composition, R1234yf does not damage the ozone layer and has
minimal global warming impact. R1234yf has similar operating
pressures to R134a.
Main characteristics of R1234yf:
• Low toxicity
• Low GWP; GWP = <1
• Zero ozone-depleting potential
• Class A2L Refrigerant - Lower flammability
Stewart, let us now look at this in context and compare the
characteristics of R1234yf to R134a.
As you can see, R1234yf compares very well with R134a.
The real difference lies in the flammability and acid forming
characteristics of R1234yf. This of course means one should
handle R1234yf with care.
EQUIPMENT NEEDED TO HANDLE R1234YF
As when dealing with any flammable refrigerant including
hydrocarbons R290 and R600a and HFOs, the general
requirement for tools is that they do not create an ignition source
and are used in an environment that has no ignition source and
has adequate ventilation. This is with particular reference to
power tools and single-phase switch gear (equipment on-off
switches, light switches and plug points). Particular precautions
apply to the use of open flames (brazing equipment).
EQUIPMENT REQUIREMENTS FOR R1234YF
For automotive applications a unique vehicle quick release
fitting is used.
• A R1234yf calibrated gauge set with dedicated R1234yf
couplers. Standards have been developed for hoses and
couplings.
Figure 1: Structural formula of HFO-1234yf.
• Red and blue service hoses, the fittings are 12mm O Ring
fittings male with a hexagon nut.
• Yellow service hose ½” LH thread (an adaptor is available to
fit a universal vacuum pump).
• Manifold gauge sets designed to take the male fittings
of the hose set and are calibrated to read R1234yf
temperatures.
• Electronic refrigerant leak detector (A2L compliant).
• Vacuum pump (A2L compliant).
• Recovery/reclamation equipment (A2L compliant).
Although it is not mandatory to recover R1234yf, it is still
good environmental practice and, due to the cost of this
refrigerant, it would be advisable to do so. Having said that,
recovery machines that meet these criteria are difficult to
obtain in South Africa at the moment.
• Dedicated cylinders for R1234yf have a left-hand valve
thread and require a suitable adaptor to connect to the
gauge set charge hose.
Stewart you asked, “is R1234yf compatible with existing R134a
systems?” The short answer is no, R1234yf system refrigerant
circuit is accessed using service couplers that are a different size
to those of a R134a system. The service coupler hose connection
also has a left-hand thread that requires a matching hose for
connection. Hence the need for an R1234yf gauge set.
R1234yf is classified as an A2L mildly flammable refrigerant
and requires the use of equipment designed for use with such a
refrigerant.
The exception is an electronic leak detector. Several
manufacturers produce detectors that are suited to both
refrigerants. Also, R134a systems were not designed to operate
using a flammable refrigerant. The standards lay down specific
requirements for system design. For example, the R1234yf
evaporator is significantly stronger than the one you would
commonly find in an R134a system.
Can a R134a system be converted to R1234yf? Aside from
the safety aspects, although the two refrigerants have similar
thermodynamic properties, they are not the same. Therefore,
compressor damage or system performance limitations may be
found when attempting to convert an R134a system to R1234yf.
www.hvacronline.co.za RACA Journal I August 2020 41