REFRIGERANTSFANS
Hydrocarbons are excellent refrigerants for Rankine technology. Technically, replacing HFCs with hydrocarbons would be simple to implement. Obviously, the overwhelming problem is the fl ammability hazard and consequent concern for product liability. Iso-butane is found in many modern European fridge freezers, but the quantities are small and safely contained in sealed circuits. Air is used in non-Rankine technology, such as air conditioning systems in aircraft, where compressed air from the jet engines can be exploited. However, generally, ‘air cycle’ systems are signifi cantly less energy effi cient than Rankine Cycle systems. Water is safe and cheap. Unfortunately, it has two signifi cant problems; it freezes at 00
C and boils at 1000 C. By elimination, carbon dioxide emerges as the only
fl uid that is non-fl ammable, has reasonably low toxicity, is environmentally acceptable and also cheap. Not surprisingly, other groups have reached the same conclusion. Compressor manufacturers are off ering carbon dioxide compressors for refrigeration. So why are carbon dioxide units not widely available? What’s the problem? The cooling equipment industry uses a range of fl uids, each of which is matched to a particular application; thus, 134a is fi ne for mobile air conditioning, and R410A is fi ne for room air conditioning. Now the expectation is that a single fl uid, carbon dioxide, will fi t all applications. However, carbon dioxide cannot be liquefi ed at all above 33°C and, in practice, is not easily liquefi ed above 20°C. In other words, carbon dioxide cannot be used in the traditional Rankine technology.
Even if it is accepted that carbon dioxide cannot be condensed, then it is still possible to remove heat from the compressed gas, although this is a less effi cient process than
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condensation. However, the operating pressure required is very high at >80 bar, which is four times greater than the maximum operating pressure for many present-day cooling units. Such high pressure requires heavy-duty equipment, which can reduce energy effi ciency and be expensive.
Next-generation refrigerants Producers would appear to be focused on replacing high GWP HFCs such as R134a, R410A, R507, R404A, etc., with A2L blends comprised predominantly of HFOs. Honeywell developed R466A to replace R410A, which is non-fl ammable, but was abandoned because of an inherent problem of stabilisation. Azeotropic blends R513A and R515A have been introduced to replace R134a but have signifi cantly lower cooling capacities (as well as GWPs in the range 200-400). Despite being a zeotropic blend with a signifi cant
temperature glide of ca. 5K, R407C was the fi rst widely adopted replacement for R22 in air-conditioning, both by OEMs in new equipment and also for retrofi t into existing installations operating at similar temperatures and pressures. Against a background of refrigerants with zero or near azeotropic properties, R407C was a new departure from the norm and demonstrated acceptance of new technology, which was supported by the subsequent take-up of higher pressure R410A, suitable only for specially designed equipment and a near azeotrope with glide <1 degree. The development and adoption of refrigerants with low GWPs below 10K, which are most preferably non-fl ammable, will require OEMs to redesign their equipment around the properties of the refrigerant(s) as has been the standard practice in the past. It is possible, even probable, that such refrigerant blends will be zeotropes with signifi cant temperature glides.
'Green activists
promote the so-called ‘natural
refrigerants’, ammonia, hydrocarbons (e.g.
propane and isobutane), carbon
dioxide, water and air. This is a ‘back to the future’ approach.'
www.acr-news.com • February 2026 21
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