Steps to Design of Two-Stage Back-to-Back Centrifugal Compressor for Chiller Application

The project involves the design of a two-stage centrifugal compressor for chiller application. The refrigerant adopted is R1224yd(Z), which is a non-flammable (ASHRAE A1), low pressure, low GWP (under 1) refrigerant newly developed for chiller and heat pump applications. The capacity requirements include three operating modes: frequent operation, over load and low load operation. The compressor design aims to cover these operating points with different pressure ratio and under different massflow rate.

The deliverables are the detailed design of the two stage back-back compressor including the interconnection pipe that achieves high COP at frequent operation point and meets the off-design operation requirements.

Fig. 1. Two stages compression cycle.

The design of the compressor aims to cover a wide operation range. A ‘back-to-back’ configuration is therefore selected considering its advantage on performance range. Each stage of the compressor includes an impeller and a vaneless diffuser with a downstream volute.

The operating point with maximum capacity and pressure ratio will determine the maximum power needed from the motor. Both the shrouded and unshrouded impeller have been evaluated to provide information for rotor dynamics study and motor design.

Fig. 3.1. 1st Stage Compressor Fig. 2. 1st stage compressor.

To discover the initial cycle analysis, stage sizing, the 3D design and optimization of the compressor stage and the performance prediction, you can download the complete consultancy summary below.