A reverse Brayton cycle refrigeration system uses air as the working fluid. The turbine and compressor operate ideally, and regeneration (recuperation) is used in the cycle. The pressure ratio is 5. Air enters the compressor at 12.5 psia, 70°F. After the compressor, the air is cooled to 120°F by rejecting heat to the atmosphere. The air is then cooled to -250°F by passing through a heat exchanger and rejecting heat to the air returning to the compressor. The air enters the turbine at -250°F. Determine the system COP and the lowest temperature of the system. Use constant specific heat at room temperature.