Centrifugal compressors, two-stage chillers and two-stage compressors

Abstract

A centrifugal compressor for a chiller includes an impeller, a motor, a diffuser, and at least one injection port. The impeller is mounted on a shaft rotatable about an axis of rotation. The motor is arranged and configured to rotate the shaft to rotate the impeller. The diffuser is disposed downstream of the impeller. The at least one injection port is disposed within the diffuser. The at least one injection port is constructed and arranged to deliver liquid refrigerant from a condenser or economizer of the chiller to the diffuser.

Description

[Technical Field]

[0001] The present invention relates generally to centrifugal compressors, and more particularly to centrifugal compressors that receive liquid injection. [Background technology]

[0002] A chiller system is a cooling machine or device that extracts heat from a medium. Typically, a liquid, such as water, is used as the medium, and chiller systems operate on a vapor-compression refrigeration cycle. The liquid is then circulated through a heat exchanger to cool air or equipment as needed. Cooling inevitably generates waste heat as a by-product, which can be released to the environment or recovered for heating purposes to increase efficiency. Traditional chiller systems often utilize centrifugal compressors, also known as turbo compressors. Therefore, such chiller systems can also be referred to as turbo chillers. Alternatively, other types of compressors, such as screw compressors, can be used.

[0003] In a conventional (turbo) chiller, the refrigerant is compressed in a centrifugal compressor and sent to a heat exchanger, where heat is exchanged between the refrigerant and a heat exchange medium (e.g., a liquid). This heat exchanger is called a condenser because the refrigerant condenses there. As a result, heat is transferred to the medium (e.g., liquid), which is heated. The refrigerant leaving the condenser is expanded through an expansion valve and sent to another heat exchanger, where heat is exchanged between the refrigerant and the exchange medium (e.g., liquid). This heat exchanger is called an evaporator because the refrigerant is heated (evaporated) there. As a result, heat is transferred from the medium (e.g., liquid) to the refrigerant, which is heated. The refrigerant from the evaporator is then returned to the centrifugal compressor, and the cycle repeats. The liquid used is often water.

[0004] A conventional centrifugal compressor basically includes a casing, inlet guide vanes, an impeller, a diffuser, a motor, various sensors, and a controller. Refrigerant flows through the inlet guide vanes, the impeller, and the diffuser in this order. Therefore, the inlet guide vanes are connected to the gas intake port of the centrifugal compressor, and the diffuser is connected to the gas outlet port of the impeller. The inlet guide vanes control the flow rate of gas refrigerant to the impeller. The impeller increases the velocity of the gas refrigerant. The diffuser functions to convert the velocity (dynamic pressure) of the gas refrigerant obtained from the impeller into (static) pressure. The motor rotates the impeller. The controller controls the motor, the inlet guide vanes, and the expansion valve. Thus, the refrigerant is compressed in a conventional centrifugal compressor. The inlet guide vanes are usually adjustable, and the motor speed is usually adjustable to adjust the capacity of the system. Furthermore, the diffuser is also adjustable to further adjust the capacity of the system. The controller controls the motor, the inlet guide vanes, and the expansion valve. The controller can further control further controllable elements. Summary of the Invention

[0005] In conventional centrifugal compressors, compression noise can be generated by flow separation and pressure waves at the trailing edge of the impeller. To suppress the compression noise, a separation cover or a micro girth liquid film is used.

[0006] An object of the present invention is to suppress noise in centrifugal compressors.

[0007] In view of the state of the known art, one aspect of the present disclosure provides a centrifugal compressor suitable for use in a chiller. The centrifugal compressor includes an impeller, a motor, and a diffuser. The impeller is mounted on a shaft rotatable about an axis of rotation. The motor is arranged and configured to rotate the shaft to rotate the impeller. The diffuser is located downstream of the impeller. At least one injection port is located in the diffuser. The at least one injection port is configured and arranged to supply liquid refrigerant from a condenser or an economizer of the chiller to the diffuser.

[0008] Another aspect of the present invention provides a two-stage chiller. The two-stage chiller includes a first centrifugal compressor and a second centrifugal compressor. The first centrifugal compressor includes a first impeller and a first diffuser. The first impeller is rotatable about a first rotational axis. The first diffuser is disposed downstream of the first impeller. The second centrifugal compressor includes a second impeller and a diffuser. The second impeller is rotatable about a second rotational axis. The second diffuser is disposed downstream of the second impeller. At least one motor is arranged and configured to rotate the first impeller and the second impeller. A return channel flow path connects the first diffuser to the second impeller. The two-stage chiller further includes a condenser and an economizer. An evaporator is connected in series with the first stage centrifugal compressor, the second stage centrifugal compressor, the condenser, and the economizer. At least one injection port is disposed within at least one of the first diffuser, the return channel passage, and the second diffuser, and at least one injection passage is connected to the at least one injection port, the at least one injection passage delivering liquid refrigerant from at least one of the condenser and the economizer.

[0009] Another aspect of the present invention provides a two-stage compressor configured for use in a chiller. The two-stage compressor includes a first stage centrifugal compressor, a second stage centrifugal compressor, at least one motor, and a plurality of injection ports. The first stage centrifugal compressor includes a first impeller and a first diffuser. The first impeller is rotatable about a first rotational axis. The first diffuser is disposed downstream of the first impeller. The first diffuser has a first upstream edge and a first downstream edge. The second stage centrifugal compressor includes a second impeller and a second diffuser. The second impeller is rotatable about a second rotational axis. The second diffuser is disposed downstream of the second impeller. The second diffuser has a second upstream edge and a second downstream edge. At least one motor is disposed and configured to rotate the first impeller and the second impeller. A plurality of injection ports are disposed in the second diffuser downstream of the second upstream edge of the second diffuser for delivering liquid refrigerant into the second diffuser.

[0010] These and other objects, features, aspects and advantages will become apparent to those skilled in the art from the following description, which, taken in conjunction with the accompany drawings, discloses preferred embodiments of the invention. [Brief explanation of the drawings]

[0011] The following description refers to the accompanying drawings, which form a part of this disclosure. [Figure 1] FIG. 1 depicts a chiller according to an embodiment of the present invention in which the compressor has an injection port. [Figure 2] FIG. 2 is a schematic diagram showing the impeller, diffuser, and motor of the compressor of FIG. 1, with the injection port located at the inlet side of the diffuser. [Figure 3] FIG. 3 shows the chiller of FIG. 1 in which the compressor has multiple injection ports. [Figure 4A] 4A is an elevational view of a section of the two-stage centrifugal compressor of the chiller of FIG. 1. FIG. [Figure 4B]FIG. 4B is a detailed view of FIG. 4A showing the first impeller, the first diffuser, the return channel, and the injection port located within the first diffuser. [Figure 4C] FIG. 4C is a detailed view of FIG. 4A showing the first diffuser located within the return channel, the return channel, and the injection port. [Figure 4D] FIG. 4D is a detailed view of FIG. 4A showing the second impeller, the second diffuser, and the injection port located within the second diffuser. [Figure 5] FIG. 5 is a front view of the impeller of the two-stage centrifugal compressor of FIG. 4A, with multiple injection ports located in the diffuser. [Figure 6] 6 is a top view of the first impeller of FIG. 5 with different injection port sizes. [Figure 7] FIG. 7 is a top view of the trailing edge of the first impeller, with the injection ports located along the axis of rotation of the impeller. [Figure 8] FIG. 8 is a top view of the trailing edge of the first impeller, with the injection ports positioned at an angle relative to the axis of rotation of the impeller. [Figure 9] FIG. 9 is a schematic diagram showing the impeller, diffuser, and motor of the compressor of FIG. 1, with the injection port located at the outlet side of the diffuser. [Figure 10] FIG. 10 is a schematic diagram showing the impeller, diffuser, and motor of the compressor of FIG. 1, with injection ports located on the inlet and outlet sides of the diffuser. DETAILED DESCRIPTION OF THE INVENTION

[0012] Selected embodiments are described with reference to the drawings. Those skilled in the art will appreciate from this disclosure that the following description of the embodiments is merely exemplary and does not limit the invention as defined by the appended claims and their equivalents.

[0013] Referring first to Figure 1, a chiller system 10 having at least one injection port according to an exemplary embodiment of the present invention is described. Chiller system 10 is preferably a water chiller that utilizes cooling water and chilled water in a conventional manner. The illustrated chiller system 10 is a two-stage chiller system. However, it will be apparent to those skilled in the art from this disclosure that chiller system 10 can be a single-stage chiller system or a multi-stage chiller system, such as three or more stages.

[0014] Chiller system 10 basically includes a refrigeration controller 14, a compressor 16, a condenser 18, an economizer 20, expansion valves 22 and 24, and an evaporator 26, all connected in series to form a loop refrigeration cycle. Additionally, various sensors S and T can be positioned throughout the circuit of chiller system 10. Chiller system 10 can also include orifices instead of expansion valves 22 and 24.

[0015] 1 and 4A, the compressor 16 is a two-stage centrifugal compressor in the illustrated embodiment. The illustrated compressor 16 is a two-stage centrifugal compressor having two impellers. However, the compressor 16 may also be a single-stage centrifugal compressor or a multi-stage centrifugal compressor having three or more impellers. Optionally, the compressor 16 may be a screw compressor. The illustrated two-stage centrifugal compressor 16 includes a first-stage impeller 28 and a second-stage impeller 30. The centrifugal compressor 16 further includes a first-stage inlet guide vane 32, a first diffuser / volute 34, a second-stage inlet guide vane 36, a second diffuser / volute 38, a compressor motor 40, a magnetic bearing assembly 42, and various sensors (only some of which are shown).

[0016] As described in detail below, the refrigeration controller 14 receives signals from various sensors to control the inlet guide vanes 32, 36, compressor motor 40, and magnetic bearing assembly 42. Refrigerant flows through the first-stage inlet guide vanes 32, first-stage impeller 28, first diffuser 34, return channel 48, second-stage inlet guide vanes 36, second-stage impeller 30, and second diffuser 38, in that order. The inlet guide vanes 32, 36 control the flow of gas refrigerant to the impellers 28, 30, respectively. The impellers 28, 30 increase the velocity of the gas refrigerant without substantially increasing its pressure. The motor speed determines the amount of velocity increase. The diffuser / volutes 34, 38 increase the refrigerant pressure. The diffuser / volutes 34, 38 are immovably fixed relative to the compressor housing 44. A compressor motor 40 rotates the impellers 28, 30 via a shaft 46. Optionally, a first motor can drive the first impeller 28, and a second motor 30 can drive the second impeller 30. A magnetic bearing assembly 42 magnetically supports the shaft 46. Optionally, the bearing system can include roller members, hydrodynamic bearings, hydrostatic bearings, oil bearings, and / or magnetic bearings, and / or any combination thereof. Refrigerant is thus compressed in the centrifugal compressor 16.

[0017] During operation of the chiller system 10, the first-stage impeller 28 and the second-stage impeller 30 of the compressor 16 rotate, and low-pressure refrigerant in the chiller system 10 is drawn in by the first-stage impeller 28. The refrigerant flow rate is regulated by the inlet guide vanes 32. The refrigerant drawn in by the first-stage impeller 28 is compressed to an intermediate pressure, and the refrigerant pressure is increased by the first diffuser / volute 34, and the refrigerant is introduced into the second-stage impeller 30. The refrigerant flow rate is regulated by the inlet guide vanes 36. The second-stage impeller 30 accelerates and compresses the refrigerant, and the refrigerant pressure is increased from the intermediate pressure to a high pressure by the second diffuser / volute 38. The high-pressure gas refrigerant is then discharged into the chiller system 10.

[0018] 3, chiller system 10 includes an economizer 20 according to the present invention. As described below, during normal operation, economizer 20 is connected to return channel 48 of compressor 16 to inject gas (vapor) refrigerant into return channel 48 of compressor 16. In chiller system 10, economizer 20 is positioned between condenser 18 and evaporator 26. As described below, under some conditions, the economizer can also be connected to first diffuser 34, return channel 48, and / or second diffuser 38 of compressor 16 to inject liquid refrigerant.

[0019] The economizer 20 has an inlet port 20a, a liquid outlet port 20b, and a gas outlet port 20c. The inlet port 20a is provided for introducing two-phase refrigerant from the condenser 18 into the economizer 20. The liquid outlet port 20b is provided for discharging liquid refrigerant separated from the two-phase refrigerant to the evaporator 26. The gas outlet port 20c is provided for discharging gas refrigerant separated from the two-phase refrigerant supplied to the economizer 20. The flow rate of the refrigerant flowing into the inlet port 20a is controlled by an expansion valve 22 arranged between the condenser 18 and the economizer 20.

[0020] In operation, the refrigerant cooled to condense in the condenser 18 is reduced in pressure to an intermediate pressure by the expansion valve 22 and introduced into the economizer 20. The two-phase refrigerant introduced into the economizer 20 through the inlet port 20a is separated into gas and liquid refrigerant by the economizer 20. Under some conditions, the gas refrigerant is injected through the gas outlet port 20c of the economizer 20 into the return channel 48 of the compressor 16 via a pipe. Under some conditions, the liquid refrigerant is guided through the liquid outlet port 20b to the evaporator 26, or can accumulate in the liquid accumulation section of the economizer 20, or can be injected through a pipe into the return channel 48 of the compressor 16.

[0021] The gas refrigerant injected into the return channel 48 of the compressor 16 is then mixed with refrigerant compressed to an intermediate pressure by the first stage impeller 28 of the compressor 16. The mixed refrigerant flows into the second stage impeller 30 for further compression.

[0022] In some embodiments, as shown in FIG. 4A , the housing 44 includes a first housing 50 and a second housing 52. The first housing 50 includes a first inlet section 50A and a first outlet section 50B. The first-stage impeller 28 is disposed in the first inlet section 50A of the first housing 50 and is rotatable about a first axis of rotation A1. The first diffuser 34 is disposed downstream of the first-stage impeller 28. The second housing 52 includes a second inlet section 52A and a second outlet section 52B. The second-stage impeller 30 can also be disposed in the second inlet section 52A of the second housing 52 and can be rotatable about a second axis of rotation A2. The first axis of rotation A1 and the second axis of rotation A2 can be collinear, as shown in FIG. 4A , or can be radially offset. The second diffuser 38 is disposed downstream of the second-stage impeller 30. A return channel 48 connects the first diffuser 34 to the inlet of the second impeller 30. The first housing 50 and the second housing 52 may be integrally formed as a single piece to form the housing 44, or the first housing 50 and the second housing 52 may be formed separately to form the housing 44.

[0023] The compressor 16 has at least one injection port 54 constructed and arranged to supply liquid refrigerant from a source (e.g., the condenser 18 or the economizer 20) to the compressor 16. As shown in Figures 1 and 2, the at least one injection port 54 may be located at various locations within the compressor 16, such as, but not limited to, the first stage diffuser 28, the return channel flow path 48, and the second stage diffuser 38. The liquid refrigerant may be supplied from any suitable source, such as, but not limited to, the condenser 18 and the economizer 20.

[0024] As shown in FIGS. 2, 4A, and 4B, the injection port 54 is located within the first diffuser 34. The injection port 54 can be located in any suitable location within the first diffuser 34. Preferably, the injection port 54 is located near the junction between the first stage impeller 28 and the first diffuser 34. The injection port 54 is located near the trailing edge of the first stage impeller 28, downstream of the junction between the first stage impeller 28 and the first diffuser 34. As the first stage impeller moves relative to the first diffuser 34, a leakage path can occur at the junction between the first stage impeller 28 and the first diffuser 34. By locating the injection port downstream of this junction, high-velocity refrigerant vapor emitted from the first stage impeller 28 can prevent the injected liquid refrigerant from traveling upstream toward the junction between the first stage impeller 28 and the first diffuser 34. The high velocity refrigerant vapor carries the injected liquid refrigerant downstream and can substantially prevent the injected liquid refrigerant from flowing upstream.

[0025] The injection port 54 is preferably located closest to the trailing edge of the first stage impeller 28 and downstream of the junction between the first impeller 28 and the first diffuser 34. Flow separation occurs within the rotating first stage impeller 28. By injecting high-pressure liquid refrigerant into the low-pressure vapor refrigerant from the impeller, the flow separation that occurs in the first stage impeller 28 is substantially prevented from propagating into the first diffuser 34. The closer the injection port 54 is to the trailing edge of the first stage impeller 28, the higher the velocity and lower the pressure of the emitted refrigerant vapor.

[0026] The refrigerant vapor entering the first diffuser 34 includes a high-velocity jet flowing toward the center of the flow path and a low-velocity separated flow near the walls of the first diffuser 34. The separated flow creates vortices in the flow path. Injecting liquid refrigerant into the first diffuser 34 adds energy to the flow, breaking down the distinction between the jet flow and the separated flow. The injected liquid refrigerant substantially suppresses the flow separation. The injected liquid refrigerant undergoes a phase change from liquid to vapor, slowing the flow of the refrigerant vapor.

[0027] As shown in Figure 5, multiple injection ports 54 may be circumferentially disposed around the first diffuser 34. Although the number of injection ports 54 is shown equal to the number of blades 56 on the first stage impeller 28, the diffuser may have any suitable number of injection ports 54. As shown in Figure 5, the first stage impeller 28 has 14 blades 56, and the first diffuser 34 has 14 injection ports 54.

[0028] As shown in FIG. 2, the first diffuser 34 has an inlet side, or upstream edge 34A, and an outlet side, or downstream edge 34B. The inlet side 34A is located closest to the first impeller 28 and upstream of the outlet side 34B. In other words, the outlet side 34B is located downstream of the inlet side 34A. Multiple injection ports 54 can be located on the inlet side 34A of the first diffuser 34. Alternatively, as shown in FIG. 9, multiple injection ports 54 can be located on the outlet side 34B of the first diffuser 34. Alternatively, as shown in FIG. 10, multiple injection ports 54 can be located on both the inlet side 34A and the outlet side 34B of the first diffuser 34. The injection ports 54 can be located as shown in FIG. 5, with the injection ports 54 located around the entire circumference of the first diffuser 34. Alternatively, the injection ports 54 may be located on only one side of the first diffuser 34, for example, only on the top.

[0029] As shown in Figure 7, the injection ports 54 are disposed in the first diffuser 34 and aligned along the axis of rotation A1 of the first stage impeller 28. As shown in Figure 8, the injection ports 254 are disposed in the first diffuser 234 such that the injection ports 254 are aligned along a direction angled relative to the axis of rotation A1 of the first stage impeller 28. Each injection port 254 is angled circumferentially.

[0030] As shown in FIG. 6, the injection port 154 is located in the first diffuser and has a diameter that varies as it approaches the injection passage 58. The injection passage 58 delivers liquid refrigerant from a source (e.g., the condenser 18 or the economizer 20) to the injection port 154. The pressure of the delivered liquid refrigerant is greatest closest to the point of arrival of the liquid refrigerant. The injection port 154A, closest to the point of arrival of the liquid refrigerant, has the smallest diameter of the injection ports. The diameter of the injection port 154 increases with the distance from the point of arrival of the liquid refrigerant. The diameter of the injection port 154A, farthest from the point of arrival of the liquid refrigerant, is the largest, and the diameter of the injection port 154B is between the diameter of the injection port 154A and the injection port 154C. The pressure of the delivered liquid refrigerant decreases with the distance from the point of arrival. By increasing the diameter of the injection ports 154 with increasing distance from the arrival point, the amount of liquid refrigerant injected from all of the injection ports 154A, 154B, 154C in the first diffuser can be kept approximately uniform. In other words, the injection port 154 subjected to the greatest operating pressure has the smallest diameter, and the injection port 154 subjected to the least operating pressure has the largest diameter.

[0031] As shown in Figure 4B, an injection port 54 can be formed in the first diffuser 34. As shown in Figure 4D, an injection port 56 can be formed in the second diffuser 38. The injection port 56 in the second diffuser 38 is configured substantially similarly to the injection port 54 formed in the first diffuser 34. As shown in Figure 4C, an injection port 54 can be formed in the return channel 48 to substantially prevent flow separation in the return channel 48. The injection port 54 formed in the return channel 48 is configured substantially similarly to the injection port 54 formed in the first diffuser 34.

[0032] An injection passage 58 is connected to at least one injection port 54 to supply liquid refrigerant. As shown in Figure 3, the liquid refrigerant is preferably supplied to at least one of the condenser 18 and the economizer 20. The liquid refrigerant is supplied to at least one of the first diffuser 34, the second diffuser 38, and the return channel 48. Each injection port 54 has an injection passage 58 that supplies liquid refrigerant from a source (e.g., the condenser 18 and the economizer 20).

[0033] As shown in FIGS. 3-5 , the condenser 18 and the economizer 20 supply liquid refrigerant to injection ports disposed in the first diffuser 34, the second diffuser 38, and the return channel 48. An injection passage 58 may connect the condenser 18 to the injection port 54 of the first diffuser 34. The injection passage 58 may connect the condenser 18 to the injection port 54 of the second diffuser 38. The injection passage 58 may connect the condenser 18 to the injection port 54 of the return channel 48. The injection passage 58 may connect the economizer 20 to the injection port 54 of the first diffuser 34. The injection passage 58 may connect the economizer 20 to the injection port 54 of the second diffuser 38. The injection passage 58 may connect the economizer 20 to the injection port 54 of the return channel 48. Any combination of sources, injection passages 58, and injection ports 54 may be used. In a preferred embodiment, for example, chiller 10 has an injection passage 58 connecting condenser 18 to the injection port 54 of first diffuser 34, an injection passage 58 connecting condenser 18 to the injection port 54 of second diffuser 38, and an injection passage 58 connecting economizer 20 to the injection port 54 of return channel 48.

[0034] In another embodiment, for example, liquid refrigerant from the economizer 20 is injected into the first diffuser 34, and liquid refrigerant from the condenser 18 is injected into the second diffuser 38. The economizer pressure is lower than the condenser pressure. The first diffuser pressure is lower than the second diffuser pressure. By injecting liquid refrigerant from the condenser 18 into the second diffuser 38 and from the economizer 20 into the first diffuser 34, a pressure differential is maintained at each injection port 54.

[0035] 1 and 2, each injection passage 58 has a valve 60 that is controllable to control the flow of liquid refrigerant to the injection port 54. The valve 60 is controlled in any suitable manner between a closed position, in which no liquid refrigerant is supplied to the injection port 54, and an open position, in which liquid refrigerant is supplied to the injection port 54. The valve 60 is connected to the controller 14, which is controlled to control the flow of liquid refrigerant through the injection passage 58. The valve 60 can be closed for fast flow conditions with little flow separation and open for slow flow conditions with more flow separation.

[0036] <General explanation of terms> In understanding the scope of the present invention, the term "comprises" and its derivatives are used herein to mean open-ended terms specifying the presence of stated features, elements, components, groups, entities, and / or steps, but do not exclude the presence of unstated features, elements, components, groups, entities, and / or steps. The same applies to words of similar meaning, such as "have," "include," and their derivatives. Additionally, the terms "part," "section," "portion," "member," or "element," when used in the singular, can have two meanings: a single part or multiple parts.

[0037] The term "detect" as used herein to describe an operation or function performed by a component, section, device, etc., includes components, sections, devices, etc. that do not require physical detection, but also includes determining, measuring, modeling, predicting, or calculating, etc., to perform such operation or function.

[0038] The term "configured" as used herein to describe a component, section, or part of an apparatus includes hardware and / or software that is constructed and / or programmed to achieve a desired function.

[0039] Terms indicating degree, such as "approximately," "approximately," and "about" are used herein to mean reasonable variations in the terms of variation that do not significantly alter the end result.

[0040] It will be apparent to those skilled in the art from this disclosure that several embodiments have been selected merely to illustrate the present invention, and that various modifications and variations can be made without departing from the scope of the present invention as defined by the appended claims. For example, the size, shape, location, and orientation of various components can be changed as needed and / or desired. Components shown to be directly connected or in contact with each other may have intermediate structures between them. The function of one element may be achieved by two, and vice versa. The structure and functionality of one embodiment may also be applied to other embodiments. Not all advantages necessarily accrue to a particular embodiment at the same time. Each feature distinguishing the present invention from the prior art, whether alone or in combination with other features, is to be considered as additional inventive content by the applicant that encompasses the structural or functional ideas embodied by such feature. Thus, it will be apparent to those skilled in the art from this disclosure that the foregoing description of the embodiments of the present invention is merely illustrative and does not limit the present invention, which is defined by the appended claims and their equivalents.

Claims

1. 1. A centrifugal compressor configured for use in a chiller, comprising: an impeller attached to a shaft rotatable about a rotation axis; a motor arranged and configured to rotate a shaft to thereby rotate the impeller; a diffuser disposed downstream of the impeller; at least one injection port disposed within the diffuser, the at least one injection port constructed and arranged to supply liquid refrigerant from an economizer of the chiller to the diffuser; A centrifugal compressor comprising:

2. the at least one injection port includes a plurality of injection ports circumferentially arranged around the diffuser. The centrifugal compressor according to claim 1 .

3. The number of the plurality of injection ports is the same as the number of blades of the impeller. The centrifugal compressor according to claim 2 .

4. the diffuser has an inlet side and an outlet side, the inlet side being located upstream of the outlet side, and the plurality of injection ports being located on the inlet side of the diffuser. The centrifugal compressor according to claim 2 .

5. the diffuser has an inlet side and an outlet side, the outlet side being located downstream of the inlet side, and the plurality of injection ports being located on the outlet side of the diffuser. The centrifugal compressor according to claim 2 .

6. the diffuser has an inlet side and an outlet side, the outlet side being disposed downstream of the inlet side; The plurality of injection ports are arranged on the inlet side and the outlet side of the diffuser. The centrifugal compressor according to claim 2 .

7. each of the plurality of injection ports is angled circumferentially; The centrifugal compressor according to claim 2 .

8. an injection passage connected to the at least one injection port, the injection passage having a controllable valve disposed therein to control the flow of liquid refrigerant to the at least one injection port; The centrifugal compressor according to claim 1 or 2.

9. a first stage centrifugal compressor including a first impeller rotatable about a first rotation axis and a first diffuser disposed downstream of the first impeller; a second stage centrifugal compressor including a second impeller rotatable about a second rotation axis and a second diffuser disposed downstream of the second impeller; at least one motor arranged and configured to rotate the first impeller and the second impeller; a return channel flow path connecting the first diffuser to the second impeller; A condenser; An economizer; an evaporator connected in series to the first stage centrifugal compressor, the second stage centrifugal compressor, the condenser, and the economizer; at least one injection port disposed within at least one of the first diffuser, the return channel flow path, and the second diffuser; at least one injection passage connected to the at least one injection port, the at least one injection passage delivering liquid refrigerant from the economizer; Two-stage chiller equipped with

10. the at least one injection port comprises a plurality of injection ports circumferentially arranged around at least one of the first diffuser and the second diffuser; The two-stage chiller of claim 9.

11. the at least one injection port is disposed within the return channel. The two-stage chiller of claim 9.

12. the injection passage having a controllable valve disposed therein to control the flow of liquid refrigerant to the at least one injection port. The two-stage chiller of claim 9.

13. 1. A two-stage compressor configured for use in a chiller, comprising: a first stage centrifugal compressor including: a first impeller rotatable about a first rotation axis; and a first diffuser disposed in a first outlet portion downstream of the first impeller, the first diffuser having a first upstream edge and a first downstream edge; a second stage centrifugal compressor including: a second impeller rotatable about a second rotation axis; and a second diffuser disposed downstream of the second impeller, the second diffuser having a second upstream edge and a second downstream edge; at least one motor arranged and configured to rotate the first impeller and the second impeller; a plurality of injection ports disposed in the second diffuser downstream of the second upstream edge of the second diffuser for delivering liquid refrigerant from the chiller economizer to the second diffuser; A two-stage compressor.

14. the second diffuser has a second inlet side and a second outlet side, the second inlet side being upstream of the second outlet side; the plurality of injection ports are arranged on one or both of the second inlet side and the second outlet side of the second diffuser; 14. The two-stage compressor according to claim 13.

15. an injection passage connected to the plurality of injection ports, the injection passage having a controllable valve disposed therein to control the flow of liquid refrigerant to the plurality of injection ports; 14. The two-stage compressor according to claim 13.

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