Stirling refrigeration system

An apparatus for cooling a space, the apparatus comprising:

• a Stirling refrigeration system configured to maintain temperature of the space below a first temperature, the Stirling refrigeration system comprising:
• a Stirling unit comprising a hot end and a cold end;
• a hot heat exchanger fluidically coupled to the hot end and configured to release the heat form the hot end, wherein the hot heat exchanger and the hot end defining a hot circuit for a first refrigerant to flow therein;
• a cold heat exchanger fluidically coupled to the cold end and configured to release the heat form the cold end, wherein the cold heat exchanger and the cold end defining a cold circuit for a second refrigerant to flow therein, wherein at least one of the first refrigerant and the second refrigerant comprises a two-phase low Global Warming Potential (GWP) refrigerant;
• and
• a vapour compression refrigeration system configured to maintain temperature of the space below a second temperature, wherein the second temperature is greater than the first temperature.