The state of refrigeration science and technology are changing rapidly due to the internationally co-ordinated programme to phase out ozone depleting substances and greenhouse gases. The competitive position among the new systems is extremely complex, partly due to the willingness of some governments to legislate. This paper reports an investigation into the competitive position of systems for heating and cooling which make use of ambient air as the working fluid. A rationally-based system for choosing the suitable applications is described and used in the choice of a freezing application which was developed to the proof of concept by the construction of a pilot plant, the detail and performance of which are described. Computer-based design tools for plant components and complete cycles are part of the output of the project.