Heat-Generated Cooling Opportunities in Vehicles

Utilizing heat-generated cooling in vehicles offers the opportunity to reduce the amount of fuel used today for air conditioning. The U.S. uses approximately 7.1 billion gallons of gasoline each year for air conditioning in vehicles. By using waste heat as the primary energy source for heat-generated cooling, we have the potential to reduce the national fuel use by 7.1 billion gallons. An engine operating at a 30% thermal efficiency releases the remaining 70% of the fuel energy as waste heat through the coolant, exhaust gases, and engine compartment. Waste heat available for a representative 115-kW engine varies from 20 to 400 kW across the engine map, with an average value over the FTP cycle of 23 kW. Temperatures of the waste heat range from 200°C surface temperatures to 600°C gas temperatures. Therefore, the magnitude of energy currently wasted is significant, and a large opportunity exists to utilize this waste heat for productive purposes. This paper outlines the heat-generated cooling potential of metal hydride cooling systems, absorption heat pumps, zeolite heat pumps, and thermoacoustic cooling. System performance, material issues, advantages, disadvantages, and the current state of research is outlined for these technologies. All of these heat generated cooling systems offer great opportunities for utilizing waste heat and reducing fuel use in vehicles.