Natural refrigerant in public transport HVAC application.

In recent years, the HVAC&R (heating ventilation air-conditioning and refrigeration) industry has been actively investigating usage of natural refrigerants for many applications. Carbon dioxide (R744) is a potential candidate due to the low GWP, low toxicity and non-flammability. The R744 refrigerant use in public transport HVAC application (bus and rail) opens new challenges and opportunities if used in heat pump applications. Efficiency losses in air-conditioning operating mode at high ambient air temperatures could be offset by higher efficiency in heat pump operation. As a result, the overall HVAC systems energy consumption could reach similar or be even better to currently used hydrofluorocarbon (HFC) systems in the specific geographical areas where heating demands are a significant portion of energy use for the year. This paper will reveal a manufacturers experience in exploration of possible R744 heat pump solution for public transport HVAC applications (bus and rail). An overview of system design challenges, test findings, and outcomes from ongoing investigations will be presented in the paper.