But research beyond HFCs continues and CO2 remains the alternative getting the most attention. At the recent 18th International Compressor Engineering Conference and the 11th International Refrigeration and Air Conditioning Conference held jointly at Purdue University, at least 35 of the 225 papers had CO2 as their primary topic.
Engineers from Mitsubishi Electric said, "We have developed a new CO2 heat pump water-heater compressor with a single rotary mechanism." The engineers noted that the refrigerant had different characteristics than more typical refrigerants in regard to operating pressure, density, and the speed of sound in the refrigerant.