Tech Briefs
Auto industry takes another look at keeping cool

EPA proposes formal partnership with SAE SAE has earned the Environmental Protection Agency's (EPA) support for their work in climate protection. In fact, during the 1999 SAE Automotive Alternate Refrigerant Systems Symposium held in Phoenix, Stephen O. Andersen, Ph.D., Director of Strategic Climate Projects, EPA Climate Protection Division, worked with SAE and other experts to design a formal partnership. Dr. Andersen pointed out during his presentation that the symposium had brought together a critical grouping of the world's leading air conditioning engineers to collaborate and seek common sense solutions. The four-day international SAE event explored and tested new air conditioning technologies and systems in conventional, hybrid, and electric-powered vehicles. The proposed Global Mobil Air Conditioning Climate Protection Partnership will be Co-Chaired by representatives from EPA, SAE, and the Mobile Air Conditioning Society. A team of "partnership advisors" will represent companies from France, USA, Germany, Japan, and Sweden. Dr. Andersen sees the ultimate mission of the partnership to "encourage and accelerate ultra-high vehicle air conditioning." It complements the new automobile industry vision of marketing vehicles with improved environmental performance that also satisfy consumer demands for safety, affordability, and driving performance. The overall objectives of the partnership include: The promotion of cost-effective design and service procedures to minimize emissions from HFCÐ134a systems. Cooperation on the development and testing of the next-generation air conditioning systems to satisfy customer acceptance, environmental, safety, and reliability concerns. The communication of technical progress to policy makers and the public. "The Environmental Protection Agency is honored to work with SAE International and other partners on this important project," said Dr. Kathleen Hogan, Director, EPA Climate Change Division. "Each partner will contribute to our ultimate success." It is expected that the partnership will be announced at the Plenary of the Earth Technologies Conference, Monday, Sep. 27, 1999.

SAE International has played a key role since the 1980s in the auto industry's transition from the ozone depleting CFC-12 refrigerant to HFC-134a. SAE has provided the mechanisms and platform to address industry issues and reach consensus through the development of SAE industry standards and recommended practices. HFC's, however, are included in the "basket of gases" covered by the Kyoto Protocol, an international attempt to exercise control over greenhouse gas emissions.

The inclusion of HFC's in the "basket of gases" obligates the auto industry to take another look at alternate refrigerant systems. It is important that as an industry, everyone understands that future mobile air conditioning systems should maintain comparable performance and be cost effective for the environment and the consumer.

SAE accommodated this industry review of refrigerants by hosting the four-day Automotive Alternate Refrigerant Systems Symposium June 28, 1999 in Scottsdale, Arizona. Sponsors of the event included the following: Automotive Engineering International magazine, Calsonic North America, Delphi Automotive Systems, Denso, Mobile Air Conditioning Society, Texas Instruments, Sanden International, Service Technicians Society, UOP MOLSIV Adsorbents, Uview Ultraviolet Systems, and Visteon.

Air conditioning experts from around the world met to test alternate refrigerant systems and to discuss latest technologies. Presentations addressed topics including educational needs to service new air conditioning systems, design issues in expanding CO₂, effects of air conditioning system loads on vehicle operation, safety issues, potential government requirements, and occupant comfort in the design of air-conditioning systems.

"Ultimately, vehicle makers will have to decide whether a change to a non-HFC air conditioning system provides a cost-effective means of achieving their emissions reduction goals for the total vehicle," said James A. Baker of Delphi Automotive Systems.

Attendees of the four day symposium test-rode demonstration vehicles to determine occupant comfort and system efficiencies. However, an efficient refrigerant cycle does not assure that the vehicle will provide an acceptable level of occupant comfort. The following companies provided the test vehicles: Audi, Behr, BMW, Cadillac, DaimlerChrysler, Delphi, Ford, General Motors, Nissan, Pontiac, Toyota, Volkswagen, Volvo, and Zexel.

A total of 24 cars were tested, including two electric vehicles and ten prototype refrigerant systems. Eight of the demonstration vehicles had CO₂ refrigerant systems and one had a secondary-cooling loop using two different cooling media. A glycol and water mixture provided the evaporator circuit cooling. The refrigerant used in the engine compartment circuit was not identified at the time of the rides. The secondary loop exchanger was added to a conventional HFC-134a refrigerant system. A brief synopsis of the results of the symposium and testing is described below.

System Comfort • In general, most demonstration CO₂ vehicles provided a comparable level of comfort to their respective HFC-134a vehicles.

It had been thought that a secondary cooling loop system would have reduced cooling performance during soak and cool down, and city traffic operation. However, the occupant-perceived comfort levels in the demonstration of the secondary cooling loop system were comparable to the base HFC-134a system. CO₂ System Performance • During the symposium, it was evident that the CO₂ systems required additional development. The system problems experienced during the 1998 and 1999 evaluations were related to refrigerant circuit. This included refrigerant control and the system's high pressures.

Refrigerant containment during normal customer use must be comparable (number of years of operation before adding refrigerant) to that of existing HFC-134a systems.

Management of the refrigerant high and low side circuit pressures is required to prevent accidental discharge. System design should ensure both occupant and service technician safety.

With the initial high cooling demand of soak and cool down, the refrigerant system performance at low-speed city traffic operation should be comparable HFC-134a. At road speeds, evaporator freeze protection is required to prevent coil surface freeze-up.

Data recorded during the road evaluations indicated that panel temperatures on one vehicle were below 2.8°C (37°F) and indication of potential evaporator freeze-up conditions. Since this temperature is most likely not achievable on a production system, the demonstrated level of comfort may not be obtainable.

Materials • Refrigerant circuit seal materials used for HFC-134a systems are not compatible with CO₂. Development of new seal designs for refrigerant circuit connections and compressor shaft seals are required. New designs including metal seals are being considered.

Existing flexible hose assemblies used for HFC-134a systems are not usable with CO₂. New smaller flexible hose assemblies with internal metal surfaces must be evaluated for long term durability and their effect on noise and vibration into the passenger compartment.

Ward Atkinson, Sun Test Engineering, summarized the conclusions of the symposium by saying that, "The SAE Automotive Alternate Refrigerant Systems Symposium again points out the fact that an alternate refrigerant for replacing HFC-134a is not in the immediate future. There are on-going issues to address pertaining to refrigerant containment, system reliability, occupant safety, and servicing personnel. All aspects of the mobile air-conditioning system need to be fully evaluated before any replacement for HFC-134-a can be implemented."

SAE intends to support the mobile air conditioning industry through the SAE Interior Climate Control Standards Committee, as well as in partnership with the Environmental Protection Agency. For more information about this committee, or to order a detailed copy of the proceedings and test results, please contact Wael Berrached at (248)273-2461 or by Email at waelb@sae.org.