Koichi Fukaya, managing director and worldwide head of Thermal Systems Division, DENSO Corporation, introduces the CO₂ refrigerant to journalists at DENSO's SAE 2002 World Congress press conference.

Concerns regarding global warming have been growing in recent years. For good reason. According to the Environmental Protection Agency, the Earth has warmed by 1 degree Fahrenheit in the last century. If you don't think that sounds like much, consider this: during the last Ice Age, the Earth was just 5-9 degrees Fahrenheit cooler than it is today.

The scientific community determined that R-12, the car air conditioning refrigerant, was contributing to global warming by depleting the ozone layer.That discovery led to a worldwide conversion from R-12 (commonly known as Freon) to R-134a for air conditioners. But that wasn't a perfect compromise. R-134a does not harm the ozone layer, but its global warming potential is still high. New technology was needed.

That need led industry researchers to find the next-generation refrigerant: CO₂.

During our press conference at the SAE 2002 World Congress, Koichi Fukaya, managing director in charge of the Thermal Group, DENSO Corporation, and Rick Smith, director of Climate Control III Engineering, DENSO International America, revealed DENSO's leadership role in the development of a CO₂ air conditioning system and how this system works.

Why CO₂ ?
Why use CO₂ as an air conditioning refrigerant? Several reasons.

• CO₂ is a refrigerant that exists in nature and has a negligible effect on the environment - in fact, if all the cars in the world used CO₂ refrigerant, there would be a 35 percent improvement in ozone-depleting global warming by 2005.
• CO₂ is a good working fluid for cooling and for heat pump systems.
• CO₂ does not damage the ozone layer.

How does the system work?
The fundamental cycle is the same as the R-134a and R-12 air conditioning cycle, known as a vapor compression cycle. However for CO₂ to be an effective refrigerant, the system needs to operate at pressures 10 times higher than an R-134a system. The compressor pumps the CO₂ to a high pressure gas condition. The gas is cooled by ambient air in the gas cooler located in the front end of the vehicle. The cooled gas is then expanded through an electronic expansion valve and enters the evaporator located in the passenger compartment. The evaporator cools the cabin air. The heated CO₂ then re-enters the compressor to complete the cycle.

CO₂ also is a good working fluid for a heat-pump system. A heat-pump system achieves cabin heating by utilizing the same components as the A/C system,however the flow is reversed.

"Basically, what we have with CO₂ is single-system operation for heating and cooling, as opposed to the dual-system operations required on current vehicles," Smith stated in his press conference speech.

The bottom line
"Because the operating pressure of a CO₂ system is so high, it requires different materials for hoses and gaskets," explained Smith."Every component needs to be re-engineered."

CO₂ air conditioning systems are ready for specialized applications. However, before the CO₂ air conditioning system can enter the mainstream mass production marketplace, the following issues must be resolved:

• Cost reduction
• Weight reduction
• Reliability improvement
• Provision of service and maintenance equipment
• Clear, standardized procedures for safely handling CO₂ systems during service and maintenance.

According to Smith, these issues are too difficult and far-reaching for just one company.

"In order to continue progress in this area, DENSO needs the assistance of other automakers, other air-conditioning system suppliers and other governments worldwide. This is a monumental task, but it is one that we believe is well worth the potential benefits to the industry, and most importantly, to the environment."