FLUID EQUALISATION FOR MULTIPLE COMPRESSORS

Abstract

A method of manufacturing a suction pipe for a multi-compressor device having a plurality of inlets, the suction pipe comprising a primary portion and a plurality of secondary portions arranged to receive fluid from the primary portion for supplying fluid in parallel to the inlets of a multi-compressor device. The method includes designing the suction pipe by: selecting a first dimension for the primary portion of the suction pipe, calculating a first fluid velocity for fluid in the primary portion based on the first dimension, and comparing the first fluid velocity to a first predetermined threshold; selecting a second dimension for the secondary portions, calculating a second fluid velocity for fluid in the secondary portions based on the second dimension, and comparing the second fluid velocity to a second predetermined threshold; and calculating a ratio of the first fluid velocity to the second fluid velocity.

Claims

1. A method of manufacturing a suction pipe (100) for a multi-compressor device having a plurality of inlets, the suction pipe comprising a primary portion (110) and a plurality of secondary portions (120) arranged to receive fluid from the primary portion (110) for supplying fluid in parallel to the inlets of a multi-compressor device; the method comprising designing the suction pipe (100) by: selecting a first dimension for the primary portion (110) of the suction pipe (100), calculating a first fluid velocity for fluid in the primary portion (110) based on the first dimension, and comparing the first fluid velocity to a first predetermined threshold; selecting a second dimension for the secondary portions (120), calculating a second fluid velocity for fluid in the secondary portions (120) based on the second dimension, and comparing the second fluid velocity to a second predetermined threshold; and calculating a ratio of the first fluid velocity to the second fluid velocity; the method further comprising: manufacturing the suction pipe (100) according to the selected first dimension and second dimension if the first fluid velocity is greater than the first predetermined threshold, if the second fluid velocity is greater than the second predetermined threshold, and if the ratio of the first fluid velocity to the second fluid velocity is greater than 1.5.

2. A method as claimed in claim 1, wherein the first predetermined threshold is 18 meters per second.

3. A method as claimed in claim 1, wherein the second predetermined threshold is 12 meters per second.

4. A method as claimed in claim 1, wherein designing the suction pipe (100) comprises designing the suction pipe (100) to have three or more secondary portions (120).

5. A method as claimed in claim 1, wherein designing the suction pipe (100) comprises designing the suction pipe (100) to have four or more secondary portions (120).

6. A method as claimed in claim 1, wherein designing the suction pipe (100) comprises designing the suction pipe (100) to have five or more secondary portions (120).

7. A method as claimed in claim 1, wherein calculating the first and second fluid velocities is based on the full load rating conditions for a predetermined multi-compressor device.

8. A refrigeration system comprising a multi-compressor device and a suction pipe (100) manufactured according to claim 1.

9. A refrigeration system as claimed in claim 8, wherein the suction pipe (100) comprises five or more secondary portions (120), and wherein the multi-compressor device is a multi-scroll compressor comprising five or more compressors, each compressor arranged to receive fluid from a respective secondary portion (120) of the suction pipe (100).

10. A refrigeration system as claimed in claim 8, wherein the multi-compressor device is arranged to operate with a fluid temperature of less than 0 degrees Celsius, preferably less than 5 degrees Celsius, and more preferably less than 10 degrees Celsius.

11. A method of designing a suction pipe (100) comprising a primary portion (110) and a plurality of secondary portions (120) arranged to receive fluid from the primary portion (110) for supplying fluid in parallel to inlets of a multi-compressor device; the method comprising selecting dimensions of the suction pipe to ensure that: fluid velocity in the primary portion (110) during use is greater than a first predetermined threshold; fluid velocity in the secondary portions (120) during use is greater than a second predetermined threshold; and the ratio of the fluid velocity in the primary portion to fluid velocity in the secondary portions is greater than 1.5.

12. A method as claimed in claim 11, wherein the first predetermined threshold is 18 meters per second.

13. A method as claimed in claim 11, wherein the second predetermined threshold is 12 meters per second.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Certain preferred embodiments of the invention will be described below by way of example only and with reference to the drawing, in which:

[0042] FIG. 1 is a suction pipe for a compressor device; and

[0043] FIG. 2 shows a schematic of a method for manufacturing a suction pipe.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a suction pipe 100 for a compressor device (not shown) which is a multi-scroll compressor. The suction pipe 100 comprises a primary portion 110 and a plurality of secondary portions 120. Each secondary portion 120 is arranged to receive fluid from the primary portion 110, and connects to the primary portion at a predetermined angle. The secondary portions 120 are arranged in parallel to each and each other and each have an outlet 122 for providing fluid to parallel inlets of the compressor device.

[0045] The primary portion 110 therefore distributes fluid (e.g. oil, or a mixture of oil and refrigerant) to the four secondary portions 120 during use, and each secondary portion 120 is arranged to provide fluid during use to a respective inlet of the multi-scroll compressor. However, although the suction pipe of FIG. 1 is shown with four secondary portions 120, a suction pipe 100 may have three, four, five, six, or more secondary portions 120 as required for the corresponding compressor. The design method described herein enables suctions pipes with more than four secondary portions 120.

[0046] The secondary portions 120 shown in FIG. 1 are connected at an angle of 60° to the primary direction of fluid flow through the primary portion 110, but any suitable angle may be used. The primary portion 110 has substantially the same internal diameter along its entire length, though the width reduces near the fourth secondary portion 120, at the end of the suction pipe 100. Each secondary portion 120 has substantially the same internal diameter along its length, though it may curve if needed, as shown in FIG. 1. Each secondary portion 120 has substantially the same internal diameter as the others.

[0047] The suction pipe 100 is used to distribute fluid between the inlets of the compressor device. Each secondary 120 is therefore substantially the same as the others, in order to ensure that fluid is distributed evenly. However, geometric imperfections in suctions pipes 100 designed by known methods will lead to uneven fluid distribution between the inlets. For example, the first secondary portion 120 may receive a greater amount of fluid than the second, which in turn may receive more than the third, which in turn may receive more than the fourth.

[0048] The method of designing a suction pipe 100 described herein ensures that fluid velocities (e.g. oil velocities) in the portions of the suction pipe have minimum thresholds, and therefore the geometry imperfections in the portions have a negligible effect on the fluid distribution.

[0049] FIG. 2 shows a schematic of steps of a method of manufacturing a suction pipe. The method includes designing the suction pipe by ensuring that fluid velocities in the primary portion 110 and secondary portions 120 are greater than predetermined thresholds, and ensuring that the fluid velocity in the primary portion 110 is at least a minimum proportion greater than the fluid velocity in the secondary portions 120.

[0050] In contrast to known methods for designing a suction pipe 100, the method herein relies upon generating a sufficient pressure drop by requiring minimum velocity thresholds, in particular requiring minimum fluid velocity thresholds in the primary portion 110 and each secondary portion 120. Further, the method requires that the ratio between velocities is larger than a predetermined threshold.

[0051] At step 210, the method comprises designing the suction pipe, which comprises selecting dimensions of the suction pipe 100 e.g. based on a predetermined system, including selecting the internal pipe diameter for the primary portion 110, and the internal diameter of the secondary portions 120. The secondary portions 120 each have substantially the same internal diameter.

[0052] At step 220, the method comprises calculating the fluid velocity in the primary portion 110 of the suction pipe 100. The method may include calculating the fluid velocity for expected full load conditions for the suction pipe for a given multi-compressor in a predetermined system. The method then includes comparing the calculated fluid velocity in the primary portion 110 with a first predetermined threshold. The first predetermined threshold is 18 meters per second. Although alternative thresholds may be used for certain systems, the threshold of 18 meters per second for fluid velocity in the primary portion 110 has been found to provide particularly reliable results for a broad range of systems.

[0053] If the calculated fluid velocity is less than the first predetermined threshold, the method includes changing the selected dimensions of the primary portion 110 and recalculating the first fluid velocity. The method therefore comprises selecting dimensions of the primary portion 110 so that the expected fluid velocity therein is greater than the first predetermined threshold.

[0054] At step 230, the method includes calculating the fluid velocity in the secondary portions 110 of the suction pipe 100. The method may include calculating the fluid velocity for expected full load conditions for the suctions pipe for a given compressor in a predetermined system. The method then includes comparing the calculated fluid velocity in the secondary portions 120 with a second predetermined threshold. The second predetermined threshold is 12 meters per second. Although alternative thresholds may be used for certain systems, the threshold of 12 meters per second has been found to provide particularly reliable results for a broad range of systems, particularly in combination with the first predetermined threshold of 18 meters per second.

[0055] If the calculated fluid velocity in the secondary portions is less than the second predetermined threshold, the method includes changing the selected dimensions of the secondary portions 120 and recalculating the second fluid velocity. The method therefore comprises selecting dimensions of the secondary portions 120 so that the expected fluid velocity therein is greater than the second predetermined threshold.

[0056] At step 240 the method comprises calculating the ratio between the calculated fluid velocity in the primary portion 110 and the calculated fluid velocity in the secondary portions 120, and comparing that ratio to a third predetermined threshold. The third predetermined threshold is 1.5. Again, although different values may be used for the third predetermined threshold, the value of 1.5 has been found to be particularly effective and applicable to a wide range of systems, especially in combination with the first and second thresholds of 18 meters per second and 12 meters per second.

[0057] If the calculated ratio is smaller than the third predetermined threshold, then the method comprises changing the dimensions of the suction pipe 100 and recalculating the ratio. The method therefore comprises selecting dimensions for the suction pipe 100 to ensure that the fluid velocity in the primary portion 110 is at least 1.5 times greater than the fluid velocity in the secondary portions 120.

[0058] If all three calculated values are greater than the respective thresholds, then the method includes manufacturing the suction pipe 100 according to the design. If any one of the criteria is not satisfied, then the suction pipe 100 is not manufactured. The method may also include manufacturing an HVAC system comprising manufacturing a suction pipe as described herein.

[0059] The method described herein provides suction pipes that ensure substantially even fluid distribution between stages of a multi-compressor. As a result of the method, restrictor devices are not needed and systems may be less complicated. Further, efficiency of the design process is significantly increased because iterations of the design are not needed—there is a very high likelihood that the manufactured suction pipe will work first time. The method also enables refrigeration systems to operate with a wider range of parameters e.g. in a brine configuration with fluid temperature less than e.g. −10° C.

[0060] Moreover, the robust fluid distribution resulting from the design process allows suction pipes with five secondary portions and therefore systems with multi-scroll compressors with five compressors.