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Low Cost and High Efficiency CO2 Mobile Air Conditioning system for lower segment cars

Final Report Summary - B-COOL (Low Cost and High Efficiency CO2 Mobile Air Conditioning system for lower segment cars)

The B-COOL project was fully devoted to the development of a low cost and high efficiency air-conditioning system based on a vapour compression cycle using CO2 - referred to with the acronym R-744 when used as refrigerant fluid. Methods to assess performance, fuel annual consumption and environmental impact were identified, within the project, and constituted a first step towards EU new standards.

The EU, as greenhouse gas emission reduction measure, proposed the ban for mobile air conditioning systems of fluids having a global warming potential higher than 150 (i.e. R134a) with possible future complementary measures - e.g. measurement of the MAC fuel consumption – and this initiative represents a challenge and an opportunity for OEMs and mobile A/C suppliers to increase their competitiveness.

The project has been focused, at first, to the identification of the most appropriate testing procedures so to be able to qualify in realistic way a mobile air conditioning in terms of fuel consumption and performances (thermal comfort). A specific activity has also been launched to verify the safety-related issues. The major effort has been devoted to the development of the A/C systems for a Fiat Panda with automatic air conditioning and a Ford KA with manual control. The cars have been fully characterised following the identified procedures before and after the R-744 A/C system installation.

Equivalent thermal conditions without solar irradiation have been identified under the hypothesis that the solar cabin soaking can be represented by an air temperature increase. This hypothesis introduces an approximation but simplifies in a crucial way the testing procedure requirements making it applicable in almost all the existing facilities (climatic chamber with rolling benches and emission and consumption measurement systems).

The ambient testing conditions are as follows:
- 28 degrees Celsius and 50 % R. H for European summer: these conditions can be considered representative to classify the air conditioning system with regards to the fuel consumption and thermal comfort. The A/C system set point: 20 degrees Celsius.
- 35 degrees Celsius and 60 % R. H. for severe summer: representative of very high thermal load (non-European). The A/C system set point: 23 degrees Celsius.
- 15 degrees Celsius and 70 % R. H for dehumidification: to consider the use of the A/C as a dehumidifier. The A/C system set point: 20 degrees Celsius.

All tests are performed with the A/C in fresh air mode. A specific procedure has been defined to represent in a realistic way the use of manual A/C systems and thermal comfort.

The system efficiency will increase when right-sized compressors will be available. The 28 cc externally controlled variable capacity compressors, designed for C-segment cars, when used on small cars, as in this study, in partial load, have a lower efficiency. Those compressors can be used to validate the rest of the components, and in a first phase of R-744 system diffusion, but smaller displacement compressors (15 cc) guarantee better efficiency.

As it has been previously mentioned, on the short term the cost will be significantly higher than present R-134a. If all the OEMs were to switch to R-744 technology and production volumes were increase, the cost would likely decrease but would hardly reach the same level of R-134a system.

The technical developments within the B-COOL project have led to specific solutions for the use of this technology in small cars. The B-COOL project demonstrated that the R-744 technology for A-B segment cars seems technologically affordable even if reliability and system additional cost are still open issues that need to be further investigated.