Variable capacity screw compressor and method

Patent metadata

Field	Value
Publication number	US-11486396-B2
Application number	US-202117334147-A
Country	US
Kind code	B2
Filing date	May 28, 2021
Priority date	Jul 20, 2010
Publication date	Nov 1, 2022
Grant date	Nov 1, 2022

Abstract

A variable capacity screw compressor comprises a suction port, at least two screw rotors and a discharge port being configured in relation to a selected rotational speed that operates at least one screw rotor at an optimum peripheral velocity that is independent of a peripheral velocity of the at least one screw rotor at a synchronous motor rotational speed for a rated screw compressor capacity. A motor is configured to drive the at least one screw rotor at a rotational speed at a full-load capacity that is substantially greater than the synchronous motor rotational speed at the rated screw compressor capacity. A variable speed drive receives a command signal from a controller and generates a control signal that drives the motor at the selected rotational speed.

First claim

What is claimed is:

1. A method of operating a screw compressor, the screw compressor having a rated capacity, the method comprising:
operating a motor of the screw compressor at a selected rotational speed when the screw compressor is operated at a full load capacity,
wherein:
at the selected rotational speed, at least one rotor of the screw compressor rotates at an optimum tip velocity independent of the rated capacity of the screw compressor,
the selected rotational speed is greater than a synchronous motor speed for the rated capacity,
the motor is a permanent magnet motor, and
operating the permanent magnet motor includes receiving a command signal at a variable speed drive from a controller, and generating, at the variable speed drive, a control signal that drives the permanent magnet motor to operate at the selected rotational speed.

2. The method of claim 1 , wherein operating the screw compressor includes compressing R-134A.

3. The method of claim 2 , wherein the optimum tip velocity is between 141 feet per second and 164 feet per second.

4. The method of claim 2 , wherein the rated capacity is 100 tons and the selected rotational speed is 5800 revolutions per minute.

5. The method of claim 1 , wherein the screw compressor includes a male rotor including six lobes and having a wrap angle of 347.5 degrees, and a female rotor including seven lobes.

6. The method of claim 1 , wherein the screw compressor includes a male rotor and a female rotor, each of the male rotor and the female rotor having a size 20% to 30% smaller than conventionally sized male and female rotors, respectively, for a screw compressor having the rated capacity.

7. A method of operating a system including a plurality of screw compressors, including:
operating at least one screw compressor of the plurality of screw compressors by:
operating a motor of the at least one screw compressor at a selected rotational speed when the screw compressor is operated at a full load capacity,
wherein:
each of the plurality of screw compressors has a rated capacity,
at the selected rotational speed, at least one rotor of the at least one screw compressor rotates at an optimum tip velocity independent of the rated capacity of the screw compressor,
the selected rotational speed is greater than a synchronous motor speed for the rated capacity,
the motor is a permanent magnet motor, and
operating the permanent magnet motor includes receiving a command signal at a variable speed drive from a controller, and generating, at the variable speed drive, a control signal that drives the permanent magnet motor to operate at the selected rotational speed.

8. The method of claim 7 , wherein the rated capacity of each screw compressor of the plurality of screw compressors is different from the others of the plurality of screw compressors.

9. The method of claim 7 , wherein operating the screw compressor includes compressing R-134A.

10. The method of claim 9 , wherein the optimum tip velocity is between 141 feet per second and 164 feet per second.

11. The method of claim 9 , wherein the rated capacity is 100 tons and the selected rotational speed is 5800 revolutions per minute.

12. The method of claim 7 , wherein the screw compressor includes a male rotor including six lobes and having a wrap angle of 347.5 degrees, and a female rotor including seven lobes.

13. The method of claim 8 , wherein the screw compressor includes a male rotor and a female rotor, each of the male rotor and the female rotor having a size 20% to 30% smaller than conventionally sized male and female rotors, respectively, for a screw compressor having the rated capacity.

Assignees

• Trane Int Inc

Inventors

• Dorman Dennis R
• Sauls John R

Classifications

• F25B1/047

  of screw type · CPC title

• F25B49/025

  Motor control arrangements · CPC title

• F04C28/08

  characterised by varying the rotational speed · CPC title

• Y02B30/70

  Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating · CPC title

• F04C18/16 Primary

  with helical teeth, e.g. chevron-shaped, screw type {(for non-parallel axes of movement F04C18/48)} · CPC title