Balancing heating requirements and range in electric vehicles

Electric vehicles lack heat emissions from exhaust to warm their cabins. Inside heat is currently produced by either directly converting electricity to heat, using a heat pump, or a combination of both. Increased power consumption, reduced mileage, and the use of hydrofluorocarbon refrigerants have prompted the search for a more efficient and less harmful means of heating.

Using natural carbon dioxide as a refrigerant in electric vehicles is a promising alternative. Guo et al. investigated the use of CO₂ in the scaled-up heat pump systems of electric buses driven in cold-temperature regions.

“CO₂ is not only environmentally friendly but also possesses a wide temperature range of applications that hydrofluorocarbon refrigerants cannot reach,” said author Yang Guo.

The researchers focused their efforts on determining key problems that affect CO₂ heat pump operation. Multiple operating parameters were studied, including charge amount, ambient temperature, outlet temperature of the gas cooler, and compressor speed.

Study results showed the minimum value of the charge amount needed for highly efficient operation and indicated that system performance is more sensitive to the charge amount at low temperatures. A low-temperature performance test conducted at -22⁰C showed that the CO₂ heat pump system was able to meet the operation requirements of city buses.

“This research provides a best example for the subsequent product optimization and mass production and processing of the electric bus CO₂ pump,” said Guo.

Source: “Experimental study on refrigerant charge amount and optimal high pressure of a CO₂ heat pump system for an electric bus,” by Yang Guo, Wei Yang, Haimei Wu, Rongbin Deng, Tao Li, Shangmai Chen, and Zunlong Jin, Journal of Renewable and Sustainable Energy (2022). The article can be accessed at https://doi.org/10.1063/5.0117747 .