Variable volume ratio compressor

1. A compressor, comprising:

an intake passage;

a discharge passage;

a compression mechanism, the compression mechanism being positioned to receive vapor from the intake passage and provide compressed vapor to the discharge passage; and

at least one opening positioned in the compression mechanism to bypass a portion of the vapor in the compression mechanism to the discharge passage;

wherein the at least one opening being sized and positioned to automatically vary a volume ratio in the compressor in response to a varying pressure differential between the intake passage and the discharge passage, and wherein the at least one opening is configured to automatically vary the volume ratio in the compressor without a device that selectively opens the at least one opening, closes the at least one opening, or both.

2. The compressor of claim 1 , wherein the volume ratio is variable between a partial load and a full load.

3. The compressor of claim 2 , wherein the partial load is about twenty-five percent of the full load.

4. The compressor of claim 1 , wherein the compressor is a screw compressor.

5. The compressor of claim 4 , wherein the screw compressor includes a first rotor and a second rotor.

6. The compressor of claim 5 , wherein the at least one opening is positioned in fluid communication with at least one of the first rotor and the second rotor.

7. The compressor of claim 5 , wherein the at least one opening is positioned in fluid communication with each of the first rotor and the second rotor.

8. The compressor of claim 7 , wherein at least a portion of the at least one opening is positioned symmetric to a plane positioned between and parallel to an axis of rotation of the first rotor and the second rotor.

9. The compressor of claim 7 , wherein at least a portion of the at least one opening is positioned asymmetric to a plane positioned between and parallel to an axis of rotation of the first rotor and the second rotor.

10. The compressor of claim 1 , wherein at least a portion of the at least one opening is circular.

11. The compressor of claim 1 , wherein at least a portion of the at least one opening has an axis oriented non-perpendicularly to a point of tangency of the at least one opening with the compressor.

12. The compressor of claim 1 , wherein at least a portion of a surface defining the at least one opening is oriented non-perpendicularly to a point of tangency of the at least one opening with the compressor.

13. The compressor of claim 1 , wherein at least a portion of the at least one opening defines a passageway.

14. The compressor of claim 1 , wherein the at least one opening is formed on a selectably removable portion of the compressor.

15. A method for controlling a volume ratio of a compressor, the method comprising:

providing a compression mechanism, the compression mechanism being positioned to receive vapor from an intake passage and provide compressed vapor to a discharge passage;

forming at least one opening positioned in the compression mechanism to bypass a portion of the vapor in the compression mechanism to the discharge passage, the at least one opening being sized and positioned to automatically vary a volume ratio in the compressor in response to a varying pressure differential between the intake passage and the discharge passage, wherein the at least one opening is configured to automatically vary the volume ratio in the compressor without a device that selectively opens the at least one opening, closes the at least one opening, or both.

16. The method of claim 15 , further comprising operating the compressor at a variable speed.

17. The method of claim 16 , wherein operating the compressor at the variable speed is in response to a system load varying between a partial load and a full load.

18. The method of claim 15 , wherein the at least one opening positioned in the compression mechanism is formed on a selectably removable first portion of the compressor.

19. The method of claim 18 , further comprising removing the first portion;

and installing a second portion in the compressor.

20. The method of claim 15 , wherein the compression mechanism comprises a rotor.