Purdue University researcher Eckhard Groll says manufacturers are close to developing carbon-dioxide (CO2) air-conditioning systems for vehicles.

“The main concern is not so much the technology as the service that is associated with it,” he says.

Groll, an associate professor of mechanical engineering at Purdue in Lafayette, IN, says a related technology, in which a new generation of heat pumps will provide instant heat instead of waiting for the engine to warm up, also is on auto makers’ drawing boards.

These were among the developments discussed in more than 250 papers delivered at the 16th International Compressor Engineering Conference and the Ninth International Refrigeration and Air Conditioning Conference at Purdue, July 16-19.

Schematic of automotive HVAC application using CO 2 refrigerant, courtesy of Visteon Corp. and Society of Automotive Engineers

Werner Soedel, Ray W. Herrick professor of Mechanical Engineering, says many papers discussed energy efficiency and innovative technologies. “There must be close to 300 million compressors in the U.S. alone,” Soedel says. They are one of the major energy users in the world.

Groll says almost all major auto makers have prototypeCO2 systems running in cars. “I have driven a BMW with a carbon dioxide air-conditioning system and it was very comfortable,” he says.

Carbon dioxide was the preferred refrigerant in the early 20th century, only to be replaced by man-made chemicals. Now CO2 appears poised for a comeback.

Hydrofluorocarbons produce about 1,400 times more global warming-related gases than the same amount of CO2. Groll says minuscule amounts of CO2released from AC units are insignificant compared to emissions from burning fossil fuels for energy and transportation.

A CO2infrastructure needs to be created, however. In addition to an all-new distribution network, mechanics would need to be trained on maintaining CO2AC systems.

But CO2systems must perform under pressures five times higher than in today’s AC systems. He forecasts that the introduction of CO2air conditioners will occur in Europe first.

Heat pumps that use CO2 as the working fluid will reverse the heat-exchange cycle used in air conditioners. The pumps would transfer outside heat to a vehicle’s interior. “I am convinced that in northern climates we will see this technology, not so much in the U.S. market, but in places like Scandinavia, Canada and countries that have long, tough winters,” Groll says.

But there are serious obstacles to designing suitable heat pumps for vehicles. The pump would need to maintain a temperature of about 75°F (24°C) when the outside temperature might hover around zero. The 75F° (42C°) difference is double that handled by air-conditioning, where interiors of vehicles need to be maintained at 75°F, about 40F° (22C°) lower than outdoor temperature.

Groll notes there are heat-pump reliability problems associated with freezing winter weather. “We’ve already broken two compressors because of lubrication problems,” he says. “So it’s going to be a challenge.”

Problems he has observed during testing include a dropoff in performance after several hours and piston wear.