Refrigeration apparatus

A refrigeration system for cooling a space, said system having a refrigeration mode and having a defrost mode, said system comprising:

• a two-stage compressor to compress a refrigerant;
• a two-circuit condenser connected to said two-stage compressor, said condenser comprising a sub-condenser circuit and a main condenser circuit;
• an evaporator connected to said main condenser circuit of said two-circuit condenser, said evaporator absorbs heat from the space that is to be cooled during refrigeration mode;
• a sub-cooling heat exchanger having a first connection between said sub-condenser circuit of said two-circuit condenser and said two-stage compressor and a second connection that is between said main condenser and said evaporator;
• a first electric expansion valve connected between said sub-condenser circuit of said two-circuit condenser and said sub-cooling heat exchanger;
• a second electric expansion valve connected between said sub-cooling heat exchanger and said evaporator;
• a third electric expansion valve connected between main condenser circuit of said two-circuit condenser;
• said third electric expansion valve also controls head pressure of said main condenser circuit of said two-circuit condenser during refrigeration mode;
• means for electronic controlling said system wherein said controller means controls said first electric expansion valve to modulate the true superheat of said sub-cooling heat exchanger and wherein said controller means controls said second electric expansion valve to modulate the true superheat of said evaporator when said system is in the refrigeration mode and wherein said controller means controls said third electric expansion valve to modulate the suction pressure of said main condenser circuit of said two-circuit condenser when said system is in the defrost mode and modulates the head pressure when said system is in the refrigeration mode.