Long term tests prove high R744 efficiency

The use of highly sophisticated simulation tools that show the performance of R744 (CO₂) cooling and heating systems will further help to optimize efficient R744 Technology, Austrian researchers conclude after 3 years of testing.

According to a study by the Austrian research centre "Das Virtuelle Fahrzeug Forschungsgesellschaft" (vif) there would still be potential for improving already efficient R744 car air conditioning and heating if new simulation models and latest testing methods are applied.

Research content & phases

Running from October 2003 to June 2006, the VIRTUAL VEHICLE project focused on the

verification of component models for R744 air conditioning and heating systems: tubing, internal heat exchangers, gas coolers, evaporators, compressors, expansion devices
analysis of the cooling and heating mode on the overall vehicle performance: motor, additional fuel consumption, compartment temperature
comparison of different heating options: air/air, coolant/air heat pumps, and hot gas cycle

Main test results

High cooling performance: Test rig measurements have shown that even at a high ambient temperature of 40°C and a relatively low compressor speed of 600 rpm, a R744-based air conditioning system could achieve a cooling performance of 4 kW and a maximum Coefficient of Performance (COP) of 3.0. At an ambient temperature of 20°C, the COP will even be at 4.2.

Different heating options: Using a coolant/air heat pump (HPCA) will lead to a heating performance of 5 kW and a COP of 2.5 at an ambient temperature of -5°C and a compressor speed of 1400 rpm. The HPCA therefore emerges as the preferred option for R744 heating systems compared to an air/air heat pump (HPAA), and a hot gas cycle (HGC).

Low fuel consumption: The operation of a R744 car air conditioning will lead to 1.5 l/100 km additional fuel consumption. This has been proved by operating a R744-equipped Ford Galaxy on a roller dynamometer, based on the New European Driving Cycle (NEDC) and an ambient temperature of 35°C.*

Recommendations

The researchers recommend that the simulation tools provided by the project should be used in the future to constantly optimize R744 cooling and heating cycles. More specifically, they call on component suppliers to move away from the solely optimization of single components in benefit of a more integrated approach taking into account the components interaction within the system.