Brand-New Consultancy Summary on the Design of Large 2-Stage Inline Chiller Compressor

For this consultancy summary, the customer, one of the world’s leading HVAC manufacturers, required the design of a new range of chillers using R1234ze(E) refrigerant. The chiller uses a 2-stage in-line compressor. Both compressors and the return channel need to be designed.

What are the design targets? The scope of this project is to design a 2-stage inline chiller compressor for HVAC application. The refrigerant adopted is R1234ze(E), which is a low GWP (~6) alternative to R134a. High-efficiency level is required in a range of flowrates (20% around design condition).

Fig. 1. Two stages compression cycle.

The deliverables are the design of a 2 stage inline compressor that achieves high COP at most frequent operating points, but also meets the partload conditions, with specially designed tandem return channel to be used as inlet guide vane for the second stage compressor.

Stage Impeller Loading - Inline Chiller Compressor Fig. 2. 1st Stage Impeller Loading (left) and 2nd Stage Impeller Loading (right).

TURBOdesign Pre (refrigeration cycle coupled with compressor meanline design) was used for the initial cycle analysis and compressor stage sizing. Both the cycle and the compressor performance were available from the simulation results. The compressor map could also be produced to evaluate the operating range. A parametric study was carried out to find the optimum rpm and pressure ratio split between 1st and 2nd stage compressor.

Based on the customer’s feedback from rotor dynamics, a proper design rpm was chosen to balance the requirement from aerodynamic performance and mechanical integrity.

Fig. 3.1 1st Stage Compressor Fig. 3. 1st stage compressor.