In Europe, meeting the requirements of the Kyoto Protocol has become increasingly important. CO2 has absolutely zero ozone depletion effect, and its global warming potential is negligible in the amounts used for industrial and commercial refrigeration. There is a decided trend away from artificial refrigerants in a number of applications.
HFCs are being used, but in restricted amounts, as well as requirements to refrigeration systems became much tougher. Heavy taxes on HFCs, add considerable urgency to the trend toward natural refrigerants. Natural refrigerants like CO2 (and the hydrocarbons), with no environmental consequences, are tax free, and they are increasingly being looked upon as a long-term solution.
Because CO2 is a high-pressure refrigerant, normal commercial and industrial refrigeration systems have to be of a cascade design, with another refrigerant being used in the high stage. Hydrocarbons have been evaluated for use as the high-stage refrigerant, but they are not currently being used in large supermarket installations.
Another solution is trans-critical refrigeration system. They could be quite efficient in cold climates, and are very popular in Nordic countries (Denmark, Sweden and Norway).
Danfoss can provide a variety of products for cascade applications, as well as working on trans-critical solutions. A Danfoss goal is to have a complete product portfolio for major CO2 applications.