Natural Five Mayekawa has long pursued natural refrigerant technology. Considering environmental issues such as ozone layer depletion and global warming, … NH3 as Refrigerant Ammonia has been used widely in industrial refrigeration in North America for many years. It is a natural refrigerant and widely available at an economical cost. CO2 as Refrigerant Due to its thermal characteristics CO2 offers a most effective refrigerant for middle to low temperature freezing needs. Air as Refrigerant From the early stage of developing “Natural Five,” Mayekawa has paid close attention to the air and its possibility as a refrigerant.