This payout time is considered too long to justify the additional investment. In such a case applying a VSDS may become economically justified. Another option for obtaining variable compressor speed is through a hydraulic torque converter instead of an electrical variable-speed system. The hydraulic torque converter is installed between a constant-speed electric motor and the compressor. Variable compressor speed is obtained through the hydraulic coupling and planetary gear in the converter.
Conversion involves power losses and thus, slightly less achievable energy savings.
However, the hydraulic torque converter requires less additional capital investment than the electrical variable-speed system. Rough calculation shows that the payout time for a hydraulic torque converter installed in the unit subject of investigation is certainly less than five years. Deleting the gearbox would open the possibility of using magnetic bearings in the compressor and motor, eliminating need for a lube oil system. The authors Cris Heijkers holds an MSc degree in mechanical engineering, specializing in process equipment, from the University of Technology, Delft, The Netherlands. As a student he performed a detailed study on the 10-MW refrigeration unit during his practical training period at Fluor Daniel in Haarlem.