Hydro-Carbons (HCs)
 Hydrocarbons
were also used as refrigerants before, but were dropped when
CFC refrigerants were introduced, except for some industrial
applications such as refineries. Today, some are again used
as refrigerants, including: isobutane (R600a), propane (R290),
propylene (R1270) and some blends. HC refrigerants are good
substitutes for CFCs, HCFCs and HFCs without any major changes
because HCs are compatible with copper and they are miscible
with mineral oils. Their only drawback is their flammability
and this has limited their adoption beyond the domestic sector.
Isobutane (R600a)
Isobutane is an excellent alternative for R12 in domestic
refrigerators and small commercial units. Mass production
of domestic refrigerators with R600a started in Germany in
1992, and then spread globally except in USA where strict
regulations do not allow it. Energy efficiency is very good,
and generally better than R134a. Another advantage is the
smaller refrigerant charge (around 70 g), and the low price
of isobutane. Because of lower working pressures there is
little vibration and low noise. Since 1992, over 120 million
such refrigerators have been produced worldwide and we are
not aware of a single accident due to the flammability of
the refrigerant. Domestic refrigerators using isobutane are
at least as safe as those using halocarbons.
Propane (R290)
The thermodynamic properties of propane are similar to R22,
so it can be used as a substitute. The use of propane is increasing,
where local safety regulations allow. The highest usage is
now in small commercial units with refrigerant charges up
to 150 g. Important breakthroughs of propane applications
into commercial systems with indirect cooling are now occurring.
For example in supermarkets where the refrigerating unit is
isolated in a machine room and a secondary coolant circulates.
For lower temperatures (-80°C), cascade system with propane
in the upper cascade can be used. There are initiatives starting
to appear with propane in small air conditioning units.
Propane is an excellent refrigerant for vehicle air conditioning,
but here also the obstacle is safety of the passengers. Unofficially
in USA and Australia are present more than ten thousand vehicles
with propane / isobutane in their air conditioning units,
and there are still no negative reports of their application.
One of the possible options is a new concept with indirect
cooling, so in the passenger cabin there is no circulation
of propane.
Propylene (R1270)
Propylene has good thermodynamic properties and it can be
good replacement for R502. On the market are present refrigerating
units (liquid chillers) with Propylene, mostly for indirect
cooling. Propylene is one of the few refrigerants other than
ammonia to have a natural odour; this provides a useful safety
feature.
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