High performance refrigerator having passive sublimation defrost of evaporator

A refrigerator, comprising:

• a cabinet having a refrigerated interior;
• a refrigeration fluid circuit for circulating a refrigerant, the circuit including a compressor, a condenser, a first evaporator located within the cabinet, a second evaporator located within the cabinet, and a three-way valve enabling selective communication of refrigerant to one or both of the first and second evaporators;
• the first evaporator including a first evaporator coil, a first defrost heater, and a first evaporator cover separating a first evaporator compartment from the refrigerated interior, the first evaporator cover defining an inlet aperture communicating between the refrigerated interior and the first evaporator compartment, and an outlet aperture;
• the second evaporator including an air diffuser communicating with the first evaporator compartment at the outlet aperture so as to be configured to receive chilled air from the first evaporator compartment and pass the chilled air to the refrigerated interior, the air diffuser defining a second evaporator compartment separated from the refrigerated interior, and the air diffuser including air inlets communicating between the second evaporator compartment and the refrigerated interior, and an air outlet communicating between the refrigerated interior and the second evaporator compartment on an opposite side of the second evaporator from the air inlets;
• an evaporator fan producing air flow through at least one of the first and second evaporators;
• a first damper located at the inlet aperture and moveable between an open position that permits air flow into the first evaporator from the refrigerated interior, and a closed position that blocks air flow from flowing into the first evaporator via the inlet aperture;
• and
• a second damper located at the outlet aperture and moveable between an open position that blocks air flow through the air inlets but permits flow into the second evaporator compartment through the outlet aperture, and a closed position the blocks air flow from flowing out of the first evaporator via the outlet aperture but permits flow from the refrigerated interior through the air inlets into the second evaporator compartment,
• wherein the three-way valve directs refrigerant into only the first evaporator during normal operation such that chilled air from the first evaporator passively defrosts the second evaporator by sublimation, and
• wherein the evaporator fan is located in the air diffuser such that when the first and second dampers are open, the evaporator fan draws air flow from the refrigerated interior through the inlet aperture, the first evaporator, the outlet aperture, the second evaporator, and the air outlet in sequence, and such that when the first and second dampers are closed to isolate the first evaporator compartment from the refrigerated interior, the evaporator fan draws air flow from the refrigerated interior through the air inlets, the second evaporator, and the air outlet in sequence.