Technology alternatives to CFC/HCFC vapor compression

Phaseouts of CFCs and HCFCs to protect the stratospheric ozone layer have caused many developments in replacement or alternative technologies for heat pumping. Some of this effort has been of an ``evolutionary`` nature where the designs of conventional vapor compression systems were adapted to use chlorine-free refrigerants. Other alternatives are more radical departures from conventional practice such as operating above the critical point of an alternative refrigerant. Revolutionary changes in technology based on cycles sor principles not commonly associated with refrigeration have also attracted interest. Many of these technologies are being touted because they are ``ozone-safe`` or because they do not use greenhouse gases as refrigerants. Basic principles and some advantages and disadvantages of each technology are discussed in this paper