An economizer can also be used in conjunction with multiple expansion devices to improve the efficiency of a multistage chiller. In a 2-stage compressor chiller, the expansion process can be separated in 2 steps, with an economizer between them.
Condenser refrigerant enters the first expansion device, which reduces the refrigerant pressure to the second stage suction pressure. This pressure drop causes part of the liquid refrigerant to vaporize (or flash), and the resulting mixture of liquid and vapor enters the economizer. In the economizer the vapor is separated from the mixture and sent directly to the suction of the second stage. The remaining refrigerant passes through a second expansion device and goes to the evaporator.
Just before entering the evaporator, the liquid refrigerant passes through the second expansion device and reduces its pressure to the evaporator pressure and temperature.
Vaporizing part of the refrigerant before the economizer reduces compressor consumption since refrigerant vapor generated in the economizer only needs to be compressed by the second stage.
