Visteon says it will be ready to support the switch of refrigerants used in vehicle air conditioning by 2008. The company’s senior climate control engineers used a media briefing event to explain their approach to developing an air-conditioning system capable of meeting future European Union (EU) environmental legislation.
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Until recently, vehicle air-con engineering circles believed that their products were environmentally sound as during the 1990s they had replaced the conventional CFC refrigerant, R12 with the environmentally-friendly hydrofluorocarbon (HFC) refrigerant, R134a. The switch was necessary given the fact that one pound of R12 released into the atmosphere was equivalent to a whopping 15,000 tons of CO2 (carbon dioxide). The same amount of R134a releases just 1,300 tons of CO2 and being chlorine free has no affect whatsoever on the ozone layer.
However, as the installation of air-con permeates all new car segments as standard fitment, environmental lobbyists have raised concerns about the increasing use of R134a.
The EU has therefore been pushing for an even more environmentally-friendly cooling systems that use CO2 as alternative refrigerant. Legislation finally came to pass in August 2003 requiring that R134a be phased out from 2009, with a complete ban on its use from 2016.
Given that the days of R134a refrigerant are numbered, Visteon has been working at full tilt toward developing a solution using the natural refrigerant CO2, known as R744.
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By GlobalDataCompared with R134a, the thermodynamics of R744 allows for better cooling capacity as well as reduced fuel consumption. Because CO2 air-con systems use closed systems, they require smaller amounts of refrigerants compared to conventional systems. That means the system can be made smaller and squeezed into a tighter area beneath the cockpit, thereby freeing up space for multimedia systems and other electronic wizardry. CO2 air con systems also consume less power to deliver the same level of passenger comfort as R134a systems, thereby cutting fuel consumption by as much as 20%. They can also heat the passenger compartment quicker. To demonstrate the point, Visteon carried out winter trials in Scandinavia which proved that the integrated heat pump is capable of supplying additional heat almost instantaneously.
Engineering staff at the company’s technical centres in Germany and the Czech Republic have completely re-designed all the main components of the new R744 climate control system, including the compressor, heat exchanger, accumulators, refrigerant lines and all connections. In pointing out the rapid cooling output benefits of the new system, Nurdal Kuecuekkaya, director of Visteon’s climate control systems business, said: “By developing all the components in the R744 system, we have attained a level of system expertise which enables a very dynamic response, representing a real advance over conventional air conditioning systems.” To provide cooling capacity at very high ambient conditions, Visteon added an internal heat exchanger and incorporated it into the accumulator.
Visteon says it has already fitted out more than 20 prototype vehicles which are undergoing trials by ten carmakers. The company also operates its own fleet of ten test vehicles installed with the new air-con system, collectively clocking-up some 372,000 miles to date.
Matthew Beecham
Main differences between R744 and R134a | ||
R744 | R134a | |
Operational mode | Trans-critical (partly) | Sub-critical |
High pressure (bar) | -60 to 140 | -8 to 26 |
Low pressure (bar) | -35 to 50 | -2.8 to 4 |
Maximum gas temperature | Up to 180ºC | Up to 120ºC |
AC line diameters (mm) | 10 to 12 | 13 to 19 |
AC line fitting type | Axial Metal | Radial/Axial Polymer |
Flexible hose material | Steel | Polymer/Rubber |
Compressor Displacement (cm³) | -20 to 33 | -120 to 190 |
Compressor housing diameter (mm) | -100 | -120 |
Additional components | Internal heat exchanger | — |
Expansion device | Orifice or electronic valve | Orifice or TXV |
Front-end heat exchanger | ‘Gascooler’ | ‘Condenser’ |
 |
click image to enlarge |
Figure 1: Visteon’s R44 climate control system
