FDNY Operating Engineer Practice Test

In a two-stage centrifugal compressor with an economizer, the refrigerant pressure is greatest in the second stage. This is due to the design and operational principles of multi-stage compressors.

In this system, the first stage of the compressor compresses the refrigerant to an intermediate pressure. The refrigerant then moves to the economizer, where it is partially condensed and partially vaporized, taking on some heat exchange. After this stage, the refrigerant enters the second stage. Here, the refrigerant is further compressed to a much higher pressure, which is necessary for effective heat rejection and condensation in the condenser unit.

Therefore, the second stage is responsible for achieving the highest pressure of the refrigerant in this setup. The economizer stage assists in enhancing the efficiency of the overall process by making use of the energy that would otherwise be wasted during compression, but it does not reach higher pressures than what is achieved in the second stage.