Patent Publication Number: US-2022220976-A1

Title: Cooling system for centrifugal compressor and refrigeration system including same

Description:
FIELD 
     The field relates generally to centrifugal compressors, and more particularly, to cooling and refrigeration systems for use with centrifugal compressors. 
     BACKGROUND 
     Centrifugal compressors have several advantages over positive displacement compressor designs, such as reciprocating, rotary, scroll, and screw compressors, but the incorporation of centrifugal compressors in lower-capacity cooling systems is limited due to the high rotation speed of the impeller of a centrifugal compressor and the associated challenges of providing a suitable operating environment for the impeller and associated motor. One particular challenge is providing sufficient cooling to the motor and bearings associated with the compressor driveshaft to maintain the motor and bearings within a suitable range of operating temperatures. 
     This background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     SUMMARY 
     In one aspect, a compressor system includes a centrifugal compressor and a cooling circuit. The compressor includes a housing, a shaft rotatably supported in the housing by at least one bearing, an impeller connected to the shaft, and a motor operably connected to the shaft. The housing has a plurality of coolant flow channels defined therein that delivers coolant to the bearing and the motor. The cooling circuit includes a coolant supply line connected to the compressor housing to deliver coolant to at least one of the plurality of coolant flow channels. The coolant supply line includes a coolant control valve to control coolant flow through the coolant supply line. The cooling circuit also includes a coolant return line connected to the compressor housing to receive coolant from the plurality of coolant flow channels and return coolant to a low-pressure side of the compressor, a temperature sensor connected to the coolant return line to detect at least one of a temperature of the coolant return line and a temperature of coolant within the coolant return line, and a controller connected to the temperature sensor and the coolant control valve. The controller is configured to control the coolant control valve based on the temperature detected by the temperature sensor to control the supply of coolant to the compressor housing. 
     In another aspect, a cooling system for a compressor includes a coolant supply line, a coolant return line, a temperature sensor connected to the coolant return line to detect at least one of a temperature of the coolant return line and a temperature of coolant within the coolant return line, and a controller. The coolant supply line includes a coolant control valve to control coolant flow therethrough, and is connectable to a housing of the compressor to deliver coolant to at least one of a plurality of coolant flow channels defined within the compressor housing. The coolant return line is connectable to the compressor housing to receive coolant from the plurality of coolant flow channels and return coolant to a low-pressure side of the compressor. The controller is connected to the temperature sensor and the coolant control valve, and is configured to control the coolant control valve based on the temperature detected by the temperature sensor to control the supply of coolant through the coolant supply line. 
     In yet another aspect, a refrigeration system includes a compressor, an evaporator, a condenser, an expansion device, and a cooling circuit. The compressor includes a housing, a shaft rotatably supported in the housing by at least one bearing, an impeller connected to the shaft, and a motor operably connected to the shaft. The housing has a plurality of coolant flow channels defined therein that delivers coolant to the at least one bearing and the motor. The cooling circuit includes a coolant supply line connected to the compressor housing to deliver coolant to at least one of the plurality of coolant flow channels, a coolant return line connected to the compressor housing to receive coolant from the plurality of coolant flow channels and return coolant to a low-pressure side of the compressor, a temperature sensor connected to the coolant return line to detect at least one of a temperature of the coolant return line and a temperature of coolant within the coolant return line, and a controller. The coolant supply line includes a coolant control valve to control coolant flow through the coolant supply line. The controller is connected to the temperature sensor and the coolant control valve, and is configured to control the coolant control valve based on the temperature detected by the temperature sensor to control the supply of coolant to the compressor housing. 
     Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures illustrate various aspects of the disclosure. 
         FIG. 1  is a schematic diagram of an example refrigeration system. 
         FIG. 2  is a schematic diagram of an example compressor cooling system suitable for use in the refrigeration system of  FIG. 1   
         FIG. 3  is a sectional view of a portion of the compressor cooling system shown in  FIG. 2 , showing a temperature sensor connected to a coolant return line. 
         FIG. 4  is a graph illustrating operation of a coolant control valve of the compressor cooling system shown in  FIG. 2  based on two temperature set points. 
         FIG. 5  is a schematic diagram of another example compressor cooling system suitable for use in the refrigeration system  100  of  FIG. 1 . 
         FIG. 6  is a graph illustrating operation of coolant control valves of the compressor cooling system shown in  FIG. 5  based on an example control scheme. 
         FIG. 7  is a perspective view of an assembled compressor suitable for use in the refrigeration system of  FIG. 1  and the compressor cooling systems of  FIGS. 2 and 5 . 
         FIG. 8  is a cross-sectional view of the compressor of  FIG. 7  taken along line  8 - 8 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic diagram of an example refrigeration system  100 . The refrigeration system  100  includes a centrifugal compressor  102 , a condenser  104 , an expansion device  106  (e.g., an expansion valve, orifice, capillary tube), and an evaporator  108 . The refrigeration system  100  may include additional components or other components than those shown and described with reference to  FIG. 1  without departing from the scope of the present disclosure. In operation, the compressor  102  receives a working fluid, such as a refrigerant, as a low pressure gas through a suction line  110 . The compressor  102  compresses the gas, thereby raising the temperature and pressure of the gas. The pressurized, high temperature gas then flows to the condenser  104 , where the high pressure gas is condensed to a high pressure liquid. The liquid then flows through an expansion device  106  that reduces the pressure of the liquid. The reduced pressure fluid, which may be a gas or a mixture of gas and liquid after passing through the expansion device  106 , then passes through the evaporator  108 . The evaporator  108  may include a heat exchanger, with a fluid circulating therethrough that is cooled by the reduced pressure refrigerant fluid as the refrigerant fluid evaporates to a gas in the evaporator  108 . The refrigerant gas is then directed back to the compressor  102  via the suction line  110 , where the working fluid is again compressed and the process repeats. 
     The example refrigeration system  100  includes a compressor cooling system  112  that draws working fluid from part of the refrigerant circuit (downstream of the condenser  104  in this example), and directs it to the compressor  102  to cool components of the compressor  102 , such as a motor and bearings of the compressor  102 . The working fluid used in the cooling system  112 , referred to as “coolant”, is returned to the refrigeration circuit by a coolant return line  114  that has an outlet connected to a low pressure side of the compressor  102  (e.g., the suction line  110 ). As described further herein, the pressure differential across the cooling circuit of the cooling system  112  drives coolant through the compressor  102 , and back into the refrigeration circuit. 
       FIG. 2  is a schematic diagram of an example compressor cooling system  200  suitable for use in the refrigeration system  100  of  FIG. 1 . The compressor cooling system  200  includes a compressor  202  (e.g., compressor  102 ) and a cooling circuit  204  configured to deliver coolant to components of the compressor  202  to facilitate cooling the compressor  202  and maintaining components of the compressor  202  within suitable operating temperature ranges. 
     The compressor  202  of the illustrated embodiment is a two-stage centrifugal compressor  202  that includes a first stage  206  and a second stage  208 . In other embodiments, the compressor  202  may include a single stage or may include more than two stages. In yet other embodiments, the compressor  202  may be a compressor other than a centrifugal compressor. The first stage  206  includes a first stage inlet  210  that is connected in fluid communication with an evaporator (e.g., evaporator  108 , shown in  FIG. 1 ) by a suction line  212 . The second stage  208  includes a second stage inlet  214  that is connected in fluid communication with a first stage outlet of the first stage  206  by a refrigerant transfer conduit (not shown in  FIG. 2 ) to receive compressed refrigerant from the first stage  206 . 
     The compressor  202  generally includes a housing  216 , a shaft  218  rotatably supported in the housing  216  by a plurality of bearings  220 ,  222 ,  224 , a first stage impeller  226  connected to a first end  228  of the shaft  218 , a second stage impeller  230  connected to a second end  232  of the shaft  218 , and a motor  234  operably connected to the shaft  218  to drive rotation thereof. The compressor  202  may include components in addition to those shown in  FIG. 2 . 
     The housing  216  encloses components of the compressor  202  within one or more sealed (e.g., hermetically or semi-hermitically) cavities. In some embodiments, for example, the housing  216  includes end caps at each stage of the compressor  202  that define volutes in which the first and second stage impellers  226 ,  230  are positioned. In some embodiments, the housing  216  is formed from a plurality of cast pieces that are assembled using suitable fasteners (e.g., screws, bolts, etc.) 
     The bearings  220 ,  222 ,  224  rotatably support the shaft  218  within the housing  216 . In the illustrated embodiment, the compressor  202  includes a first radial bearing  220 , a second radial bearing  222 , and a thrust bearing  224 . In other embodiments, the compressor  202  may include additional or fewer bearings. The bearings  220 ,  222 ,  224  may include any suitable type of bearings that enable the compressor  202  to function as described herein including, for example and without limitation, roller-type bearings, magnetic bearings, fluid film bearings, air foil bearings, and combinations thereof. In the illustrated embodiment, each of the bearings  220 ,  222 ,  224  comprises an air foil type bearing. 
     The motor  234  is operably connected to the shaft  218  to drive rotation thereof during operation of the compressor  202 . The motor  234  may generally include any suitable motor that enables the compressor  202  to function as described herein. In the illustrated embodiment, the motor  234  is an electric motor and includes suitable components (e.g., a stator and a rotor) to impart rotational motion to the shaft  218  during operation of the compressor  202 . 
     The housing  216  has a plurality of coolant flow channels  236 ,  238 ,  240 ,  242  defined therein that delivers coolant to the plurality of bearings  220 ,  222 ,  224  and the motor  234 . The plurality of coolant flow channels  236 ,  238 ,  240 ,  242  may be arranged and/or defined within the compressor housing  216  in any manner that enables the compressor cooling system  200  to function as described herein. For example, the coolant flow channels  236 ,  238 ,  240 ,  242  may be formed as passages in components (e.g., cast components, as by machining, for example) of the compressor housing  216 , as passages defined between two or more components of the compressor  202  (e.g., between the motor  234  and the compressor housing  216 ), and combinations thereof. 
     The example compressor  202  includes a first coolant flow channel  236 , a second coolant flow channel  238 , a third coolant flow channel  240 , and a fourth coolant flow channel  242 . The first coolant flow channel  236  delivers coolant to the thrust bearing  224 , the second coolant flow channel  238  delivers coolant to the first radial bearing  220 , the third coolant flow channel  240  delivers coolant to the second radial bearing  222 , and the fourth coolant flow channel  242  delivers coolant to the motor  234 . In some embodiments, the coolant flow channels  236 ,  238 ,  240 ,  242  may share common or overlapping portions. In the illustrated embodiment, for example, the first coolant flow channel  236  overlaps with and feeds into the second coolant flow channel  238  at the first radial bearing  220 , and the third coolant flow channel  240  overlaps with and feeds into the fourth coolant flow channel  242  at the motor  234 . 
     Each of coolant flow channels  236 ,  238 ,  240 ,  242  has a corresponding coolant inlet port  244  that connects to the cooling circuit  204  in the example embodiment. That is, the compressor housing  216  includes four external inlet connections for connecting the plurality of coolant flow channels  236 ,  238 ,  240 ,  242  to the cooling circuit  204 . In other embodiments, the compressor housing  216  may have fewer external inlet connections. For example, two or more of the coolant flow channels  236 ,  238 ,  240 ,  242  may share a common, single coolant inlet port (and a common connection point to the cooling circuit  204 ) that provides coolant to multiple of the coolant flow channels  236 ,  238 ,  240 ,  242 . In such embodiments, coolant flow delivered to the common coolant inlet port may be separated, divided, or otherwise routed within the compressor housing  216  to deliver coolant to two or more of the coolant flow channels  236 ,  238 ,  240 ,  242 . In some embodiments, for example, the bearing coolant flow channels (i.e., the first, second, and third coolant flow channels  236 ,  238 ,  240 ) may have a common coolant inlet port, and the coolant flow may be routed to the separate flow channels internally within the compressor housing  216 . 
     The compressor housing  216  also defines a common coolant outlet port  246  in the illustrated embodiment. The common coolant outlet port  246  receives coolant from each of the plurality of coolant flow channels  236 ,  238 ,  240 ,  242 . In other words, all of the coolant delivered to the compressor housing  216  and the coolant flow channels  236 ,  238 ,  240 ,  242  is returned to the common coolant outlet port  246 . In some embodiments, at least one of the plurality of coolant flow channels  236 ,  238 ,  240  is arranged such that coolant flows through at least one coolant flow channel, in series, across at least one of the bearings  220 ,  222 ,  224 , through the motor  234 , and to the common coolant outlet port  246 . In this way, coolant flowing through the at least one coolant flow channel absorbs heat from both the motor  234  and one of the bearings  220 ,  222 ,  224 . Coolant may flow through the motor  234 , for example, by flowing between a stator and a rotor of the motor  234 , through a portion of the shaft  218  around which the motor  234  is disposed, and/or through flow channels or holes defined in the rotor of the motor  234 . 
     The cooling circuit  204  delivers coolant to the compressor housing  216  (specifically, to the plurality of coolant flow channels  236 ,  238 ,  240 ,  242 ) and returns coolant to the refrigeration circuit (e.g., refrigeration system  100  shown in  FIG. 1 ) of which the compressor  202  is a part. The illustrated cooling circuit  204  includes a plurality of coolant supply lines  248 ,  250 ,  252 ,  254 , a coolant return line  256 , a temperature sensor  258 , and a controller  260 . 
     The coolant supply lines  248 ,  250 ,  252 ,  254  are connected in fluid communication with a coolant source  262 , and are connected to the compressor housing  216  to deliver coolant to the plurality of coolant flow channels  236 ,  238 ,  240 ,  242 . The coolant supply lines  248 ,  250 ,  252 ,  254  can include any suitable fluid conduit (rigid and/or flexible) that enables delivery of coolant to the compressor housing  216  including, for example and without limitation, pipes, hoses, tubes, and combinations thereof In some embodiments, the coolant supply lines  248 ,  250 ,  252 ,  254  are constructed of metal tubing, such as copper tubing. The illustrated cooling circuit  204  includes four coolant supply lines  248 ,  250 ,  252 ,  254 , one for each of the coolant flow channels  236 ,  238 ,  240 ,  242  defined within the compressor housing  216 . More specifically, the illustrated embodiment includes a plurality of bearing coolant supply lines  248 ,  250 ,  252  and a motor coolant supply line  254 . Each of the bearing coolant supply lines  248 ,  250 ,  252  is connected to one of the first, second, and third coolant flow channels  236 ,  238 ,  240  to channel or deliver coolant to at least one of compressor bearings  220 ,  222 ,  224 . The motor coolant supply line  254  is connected to the fourth coolant flow channel  242  to deliver coolant to the motor  234 . 
     The example coolant source  262  is the refrigeration circuit of which the compressor  202  is a part, specifically, coolant drawn from the refrigeration circuit downstream of a condenser (e.g., condenser  104 , shown in  FIG. 1 ) of the refrigeration circuit, such as between the condenser and an expansion device of the refrigeration system. The coolant is the same working fluid (e.g., refrigerant) used in the refrigerant system in the example. In other embodiments, the coolant source  262  may be a portion of the refrigeration system other than downstream of the condenser, such as the condenser, or any other suitable coolant source that enables the compressor cooling system  200  to function as described herein. In yet other embodiments, the coolant source  262  may be an auxiliary liquid cycle. 
     As explained further herein, coolant is drawn from the coolant source  262  and through the cooling circuit  204  using a pressure differential between the coolant source  262  and an outlet end of the return line  256 . In other embodiments, coolant may be directed through the cooling circuit  204  using additional or alternative means, such as a pump. 
     At least one of the coolant supply lines  248 ,  250 ,  252 ,  254  includes a coolant control valve  264  to control coolant flow through the corresponding coolant supply line. The control valve  264  includes an electrically-actuatable valve that is controllable by the controller  260  to vary or otherwise control the flow rate of coolant through the corresponding supply line. Suitable valves include, for example and without limitation, solenoid valves, electronic expansion valves, and modulating control valves. In the illustrated embodiment, the motor coolant supply line  254  includes the coolant control valve  264 . In other embodiments, one or more of the bearing coolant supply lines  248 ,  250 ,  252  may include a coolant control valve  264 . In yet other embodiments, the motor coolant supply line  254  and one or more of the bearing coolant supply lines  248 ,  250 ,  252  may include a coolant control valve  264 . 
     The motor coolant supply line  254  is configured as a primary or main coolant supply line in the illustrated embodiment, having an inlet  266  connected to the coolant source  262  and an outlet  268  connected to the compressor housing  216  to deliver coolant to the fourth coolant flow channel  242 . The bearing coolant supply lines  248 ,  250 ,  252  are configured as branch lines in the illustrated embodiment, each having an inlet  270  connected to the motor coolant supply line  254  upstream of the coolant control valve  264 , and an outlet  272  connected to the compressor housing  216  to deliver the coolant to the first, second, and third coolant flow channels  236 ,  238 ,  240 . In other embodiments, the inlet  270  of one or more of the bearing coolant supply lines  248 ,  250 ,  252  may be connected to the coolant source  262 . In yet other embodiments, the motor coolant supply line  254  may be configured as a branch circuit extending off of one of the bearing coolant supply lines  248 ,  250 ,  252 . 
     The illustrated cooling circuit  204  also includes a shutoff valve  274  on the main coolant supply line (i.e., the motor coolant supply line  254 ) to enable coolant flow to the entire cooling circuit to be shut off in order to isolate the compressor from the rest of the system, (e.g., for service). The shutoff valve  274  may be omitted in other embodiments. 
     In the illustrated embodiment, the bearing coolant supply lines  248 ,  250 ,  252  are free of shutoff valves or other devices that would cut the supply of coolant through the bearing coolant supply lines  248 ,  250 ,  252 . Thus, while the cooling circuit  204  is active, the bearing coolant supply lines  248 ,  250 ,  252  are configured to continuously supply coolant to the compressor housing  216 , irrespective of a position of the coolant control valve  264 . In this way, the bearings of the compressor  202  are continuously supplied with coolant during operation to facilitate maintaining bearings within a suitable range of operating temperatures. The bearing coolant flow paths—including the bearing coolant supply lines  248 ,  250 ,  252  and the associated coolant flow channels  236 ,  238 ,  240  defined within the compressor housing  216 —can include flow restrictors along the flow path to restrict or otherwise limit the flow of coolant therethrough. The flow restrictors may be included in the bearing coolant supply lines  248 ,  250 ,  252  and/or may be integrated into the compressor housing  216  (e.g., as metering orifices along the coolant flow channels). In some embodiments, for example, one or more of the coolant inlet ports  244  associated with the bearing coolant flow channels  236 ,  238 ,  240  includes a metering orifice to control the flow of coolant therethrough. 
     The coolant return line  256  is connected to the compressor housing  216  to receive coolant from the plurality of coolant flow channels  236 ,  238 ,  240 ,  242  and return coolant to a low-pressure side of the compressor  202 . The low pressure side of the compressor  202  generally refers to portions of the compressor  202  and the refrigeration circuit of which the compressor  202  is a part that precede the compression stages of the compressor  202  (i.e., the first stage  206  and the second stage  208 ). The low pressure side of the compressor  202  may include, for example and without limitation, a portion of the compressor  202  upstream of the first stage impeller  226 , an inlet to the first stage  206 , and the suction line  212  connected to the inlet of the first stage  206 . 
     The coolant return line  256  can include any suitable fluid conduit (rigid and/or flexible) that enables delivery of coolant from the compressor housing  216  to the lower pressure side of the compressor  202 . Suitable conduits include, for example and without limitation, pipes, hoses, tubes, and combinations thereof. In some embodiments, the coolant return line  256  is constructed of metal tubing, such as copper tubing. In other embodiments, the coolant return line  256  is constructed of other materials. Additionally, in some embodiments, the return line  256  may include a flat portion or section to facilitate mounting the temperature sensor  258 . 
     An inlet  276  of the coolant return line  256  is connected to the common coolant outlet port  246 , and an outlet  278  of the coolant return line  256  is connected to the low-pressure side of the compressor  202 . Coolant at the coolant source  262  (e.g., the condenser  104 ) is generally at a higher pressure than the low pressure side of the compressor  202 . As a result, a pressure differential exists between coolant at the coolant source  262  and the low pressure side of the compressor  202 , which facilitates driving coolant through the cooling circuit  204 . 
     The coolant return line  256  is connected to the common coolant outlet port  246 , and receives coolant from each of the plurality of coolant flow channels  236 ,  238 ,  240 ,  242  after the coolant absorbs heat from the motor  234  and/or the bearings  220 ,  222 ,  224 . As noted above, at least one of the plurality of coolant flow channels  236 ,  238 ,  240 ,  242  can be arranged such that coolant flows through the at least one coolant flow channel, in series, across at least one of the bearings  220 ,  222 ,  224 , through the motor  234 , and to the common coolant outlet port  246 . In the illustrated embodiment, for example, the third cooling flow channel  240  is arranged so the coolant flows, in series, across the second radial bearing  222 , through the motor  234 , and to the common coolant outlet port  246 . As a result, coolant that flows through the coolant return line  256  has absorbed heat from at least one of the bearings  220 ,  222 ,  224  and the motor  234 , even when the coolant control valve  264  is in an off position. 
     The temperature sensor  258  is connected to the coolant return line  256  to detect at least one of a temperature of the coolant return line  256  and a temperature of coolant within the coolant return line  256 . The temperature sensor  258  can include any suitable temperature sensor that enables the cooling circuit  204  to function as described herein, including, for example and without limitation, thermistors, thermocouples, resistance temperature detectors (RTDs), thermal switches, and combinations thereof. In some embodiments, the temperature sensor  258  includes a negative temperature coefficient thermistor. 
     The temperature sensor  258  of this embodiment is located completely external of the compressor housing  216  and the coolant return line  256 , and is configured to detect a temperature of the coolant return line  256 . As illustrated in  FIG. 3 , for example, the temperature sensor  258  is connected to an external surface  302  of the coolant return line  256 , and is configured to detect a temperature of the external surface  302 . In other embodiments, the temperature sensor  258  may include a probe  304  (shown in dashed lines in  FIG. 3 ) that extends within the coolant return line  256  to detect a temperature of coolant flowing through the coolant return line  256 . 
     The controller  260  is connected to the temperature sensor  258  and the coolant control valve  264 , and is configured to control operation of the coolant control valve  264  (e.g., by opening, closing, or varying a position of the coolant control valve  264 ). In some embodiments, for example, the controller  260  is configured to control the coolant control valve  264  based on the temperature detected by the temperature sensor  258  to control the supply of coolant to the compressor housing  216 . For example, the controller  260  may receive a signal from the temperature sensor  258  indicative of a temperature detected by the temperature sensor  258 , compare the detected temperature to one or more temperature set points, and control the coolant control valve  264  based on the detected temperature. 
     The controller  260  generally includes any suitable computer and/or other processing unit, including any suitable combination of computers, processing units and/or the like that may be communicatively connected to one another and that may be operated independently or in connection within one another (e.g., controller  260  may form all or part of a controller network). Controller  260  may include one or more modules or devices, one or more of which is enclosed within the compressor  202 , or may be located remote from the compressor  202 . The controller  260  may include one or more processor(s)  280  and associated memory device(s)  282  configured to perform a variety of computer-implemented functions (e.g., performing the calculations, determinations, and functions disclosed herein). As used herein, the term “processor” refers not only to integrated circuits, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, memory device(s)  282  of controller  260  may generally be or include memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s)  282  may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure or cause controller  260  to perform various functions described herein including, but not limited to, controlling the coolant control valve  264  and/or various other suitable computer-implemented functions. 
     Controller  260  and/or components of controller  260  may be integrated or incorporated within other components of the cooling circuit  204  and/or a refrigeration system within which the cooling circuit  204  is incorporated. For example, the controller  260  may be incorporated within the coolant control valve  264  and/or a system controller that controls other functions and operations of the compressor  202  and the refrigeration system. 
     The controller  260  can be configured to control the coolant control valve  264  based solely on temperatures detected by the temperature sensor  258 . As noted above, for example, the temperature sensor  258  is configured to detect a temperature of coolant within the coolant return line  256  or the coolant return line  256  itself, which receives coolant from each of the coolant flow channels  236 ,  238 ,  240 ,  242 . Further, at least one of the coolant flow channels (e.g., the third coolant flow channel  240 ) is arranged such that coolant flows across at least one of the bearings  220 ,  222 ,  224  and the motor  234  before reaching the common coolant outlet port  246 . Consequently, coolant flowing through the coolant return line  256  has absorbed heat from both the compressor bearings  220 ,  222 ,  224  and the motor  234 . Thus, the temperature of coolant within the coolant return line  256  and the temperature of the coolant return line  256  provides an indication of the temperature of the bearings  220 ,  222 ,  224  and the motor  234 , and can be used to determine when additional coolant at the motor  234  is needed (and thus the coolant control valve  264  should be opened), or when no additional coolant at the motor  234  is needed (and thus the coolant control valve  264  should be closed). 
     The controller  260  can be configured to receive a signal from the temperature sensor  258  indicative of a temperature detected by the temperature sensor  258 , and compare the detected temperature to one or more temperature set points (stored in the controller memory  282 , for example). Based on the comparison, the controller  260  can be configured to open the coolant control valve  264 , thereby permitting additional coolant flow through the motor coolant supply line  254  and to the motor  234 , or close the coolant control valve  264 , thereby reducing coolant flow through the motor coolant supply line  254  and to the motor  234 . “Opening” and “closing” the coolant control valve  264  can refer to absolute opening and closing (i.e., completely opening and closing of the valve), or relative opening and closing of the valve (e.g., opening the valve more than it already is, or closing the valve more than it already is). 
     The one or more temperature set points can be empirically determined prior to operation, for example, by comparing a measured temperature of the motor with the temperature detected by the temperature sensor  258 . In some embodiments, for example, a single temperature set point can be determined based on the temperature detected by the temperature sensor when the measured temperature of the motor  234  reaches a maximum allowable operating temperature. In this case, the temperature set point may be set as a temperature that is a certain number of degrees below the temperature detected by temperature sensor  258  (e.g., 10° C., 20° C., 30° C., etc.) when the measured temperature of the motor  234  is at the maximum allowable operating temperature. In embodiments that use a single temperature set point, the controller  260  can open the coolant control valve  264  when the temperature detected by the temperature sensor  258  is above the temperature set point, and close the coolant control valve  264  when the temperature detected by the temperature sensor  258  is below the temperature set point. 
     The controller  260  may alternatively, or additionally control the coolant control valve  264  based on more than a single temperature set point, such as two temperature set points. In such embodiments, two temperature set points may define a window or range of suitable temperatures. In such embodiments, the controller  260  can open the coolant control valve  264  when the temperature detected by the temperature sensor  258  is above a first, upper temperature set point, and close the coolant control valve  264  when the temperature detected by the temperature sensor  258  is below a second, lower temperature set point. 
       FIG. 4  is a graph  400  illustrating operation of the coolant control valve  264  based on two temperature set points, indicated by lines  402  and  404 . The first and second temperature set points  402  and  404  generally define a temperature range above which the coolant control valve  264  is opened, and below which the coolant control valve  264  is closed. The temperature range may be any suitable temperature range that enables the compressor  202  to function as described herein including, for example and without limitation, 2° F., 5° F., 10° F., 15° F., 20° F., 25° F., 30° F., 35° F., 40° F., 50° F., or greater. The temperature detected by the temperature sensor  258  is illustrated by curve  406  in  FIG. 4 . As shown by  FIG. 4 , when the detected temperature  406  exceeds the first temperature set point  402 , the controller  260  opens the coolant control valve  264  to supply additional coolant to the motor  234 . The additional coolant supplied to the motor  234  results in the temperature of coolant in the coolant return line  256  and the temperature of the coolant return line  256  initially increasing as additional heat is picked up from the motor  234  (e.g., from the stator), and subsequently decreasing, resulting in the detected temperature  406  decreasing. When the detected temperature  406  decreases to a temperature below the second temperature set point  404 , the controller  260  closes the coolant control valve  264 , reducing coolant flow to the motor  234 . The temperature of coolant at the coolant return line  256  increases as a result, as shown in  FIG. 4 . When the detected temperature  406  reaches a temperature that exceeds the first temperature set point  402  again, the controller  260  again opens the coolant control valve  264  to supply additional coolant to the motor  234  and the cycle repeats. 
       FIG. 5  is a schematic diagram of another example compressor cooling system  500  suitable for use in the refrigeration system  100  of  FIG. 1 . The compressor cooling system  500  includes a cooling circuit  502  that includes the first temperature sensor  258  connected to the coolant return line  256 . Additionally, the cooling circuit  502  includes a second temperature sensor  504  connected to the compressor housing  216  (e.g., a shell of the compressor housing  216 ) to detect a temperature of the compressor housing  216 . The second temperature sensor  504  is connected to an external surface of compressor housing  216  in this embodiment, and is configured to detect a temperature of the external surface. 
     Further, in this embodiment, the cooling circuit  502  includes a main bearing coolant supply line  506  that branches off of the motor coolant supply line  254 , and feeds into each of the plurality of bearing coolant supply lines  248 ,  250 ,  252 . The main bearing coolant supply line  506  includes a bearing coolant control valve  508  used to control a flow of additional or supplemental coolant flow to the compressor bearings  220 ,  222 ,  224 , and the motor coolant supply line  254  includes a motor coolant control valve  510  that controls a flow of additional or supplemental coolant flow to the motor  234 . More specifically, each of the motor coolant supply line  254  and the main bearing coolant supply line  506  includes a respective bypass line  512 ,  514 . The bypass lines  512 ,  514  allow coolant to bypass the respective motor coolant control valve  510  and the bearing coolant control valve  508  to provide a continuous flow of coolant to the motor  234  and compressor bearings  220 ,  222 ,  224 , respectively, irrespective of a position of the motor coolant control valve  510  and the bearing coolant control valve  508 . The bypass lines  512 ,  514  may include a metering orifice or other metering device to limit or regulate the flow of coolant therethrough. The motor coolant control valve  510  may be opened to provide additional or supplemental coolant flow to the motor  234 , and the bearing coolant control valve  508  may be opened to provide additional or supplemental coolant flow to the bearings  220 ,  222 ,  224 . 
     As shown in  FIG. 5 , the motor coolant control valve  510  and the bearing coolant control valve  508  are connected to the controller  260 . The controller  260  can be configured to control (i.e., open and close) the bearing coolant control valve  508  and the motor coolant control valve  510  based on temperatures detected by the first temperature sensor  258  and the second temperature sensor  504 . For example, the controller  260  can be configured to control the bearing coolant control valve  508  based on temperatures detected by the first temperature sensor  258 , and control the motor coolant control valve  510  based on temperatures detected by the second temperature sensor  504 . In particular, the controller  260  can compare a temperature detected by the first temperature sensor  258  to a first temperature set point associated with the first temperature sensor  258 , and open or close the bearing coolant control valve  508  based on the comparison. For example, the controller  260  can open the bearing coolant control valve  508  to provide supplemental coolant flow to the bearings  220 ,  222 ,  224  if the temperature detected by the first temperature sensor  258  is above the first temperature set point, and can close the bearing coolant control valve  508  to reduce coolant flow to the bearings  220 ,  222 ,  224  if the temperature detected by the first temperature sensor  258  is below the first temperature set point. Similarly, the controller  260  can open the motor coolant control valve  510  to provide supplemental coolant flow to the motor  234  if the temperature detected by the second temperature sensor  504  is above the second temperature set point, and can close the motor coolant control valve  510  to reduce coolant flow to the motor  234  if the temperature detected by the second temperature sensor  504  is below the first temperature set point. 
       FIG. 6  is a graph  600  illustrating operation of the bearing coolant control valve  508  and the motor coolant control valve  510  according to an example control scheme or algorithm. In this control scheme, the motor coolant control valve  510  is controlled based on a fixed or set motor temperature set point, indicated by line  602 , and the bearing coolant control valve  508  is controlled based on a variable bearing temperature set point, indicated by line  604 . The temperature detected by the first temperature sensor  258  is illustrated by curve  606  in  FIG. 6 , and the temperature detected by the second temperature sensor  504  is illustrated by curve  608  in  FIG. 6 . 
     In this embodiment, the bearing temperature set point  604  is determined on an ongoing or a continuous basis (e.g., periodically or in real-time) based on the detected temperature  608  of the compressor housing  216  detected by the second temperature sensor  504 . More specifically, the bearing temperature set point  604  is calculated or determined by subtracting an offset temperature  610  from the measured temperature  608  of the compressor housing  216 . As shown in  FIG. 6 , for example, as the measured temperature  608  of the compressor housing  216  increases, the bearing temperature set point  604  increases by the same amount, but remains offset from the measured temperature  608  by the offset temperature  610 . The offset temperature  610  can be any suitable offset temperature that enables the compressor  500  to function as described herein, including, for example and without limitation, in the range of 0° F. to 30° F., in the range of 0° F. to 25° F., in the range of 5° F. to 30° F., in the range of 5° F. to 20° F., in the range of 5° F. to 15° F., in the range of 10° F. to 25° F., and in the range of 10° F. to 20° F. 
     As shown in  FIG. 6 , when the detected temperature  608  of the compressor housing  216  exceeds the motor temperature set point  602 , the controller  260  opens the motor coolant control valve  510  to supply additional coolant to the motor  234 . The additional coolant supplied to the motor  234  results in the temperature of the compressor housing  216  decreasing after a period of time, resulting in the detected temperature  608  decreasing. When the detected temperature  608  of the compressor housing  216  decreases to a temperature below the motor temperature set point  602 , the controller  260  closes the motor coolant control valve  510 , reducing coolant flow to the motor  234 . The temperature of the motor  234  and the compressor housing  216  thereby increases, as shown in  FIG. 6 . 
     Additionally, when the detected temperature  606  of the coolant return line  256  exceeds the bearing temperature set point  604 , the controller  260  opens the bearing coolant control valve  508  to supply additional coolant to the bearings  220 ,  222 ,  224 . The additional coolant supplied to the bearings  220 ,  222 ,  224  results in the temperature of coolant in the coolant return line  256  and the temperature of the coolant return line  256  decreasing after a period of time, resulting in the detected temperature  606  decreasing. When the detected temperature  606  of the coolant return line  256  decreases to a temperature below the bearing temperature set point  604 , the controller  260  closes the bearing coolant control valve  508 , reducing coolant flow to the bearings  220 ,  222 ,  224  The temperature of coolant at the coolant return line  256  increases as a result, as shown in  FIG. 6 . This cycle repeats during operation of the compressor  500 . The motor temperature set point  602  and offset temperature  610  can be empirically determined prior to operation. 
       FIG. 7  is a perspective view of an example compressor  700  suitable for use in the refrigeration system  100  of  FIG. 1  and the compressor cooling systems  200 ,  500  of  FIGS. 2 and 5 .  FIG. 8  is a cross-sectional view of the compressor  700  of  FIG. 7  taken along line  8 - 8 . In the illustrated embodiment, the compressor  700  is a two-stage centrifugal compressor, although in other embodiments, the compressor  700  may include a single stage or more than two stages. In yet other embodiments, the compressor  700  may be a compressor other than a centrifugal compressor. 
     The compressor  700  generally includes a compressor housing  702  forming at least one sealed cavity within which each stage of refrigerant compression is accomplished. The compressor  700  includes a first refrigerant inlet  704  that receives refrigerant from a suction line  706  and introduces refrigerant vapor into a first compression stage  708 , a first refrigerant exit  710 , a refrigerant transfer conduit  712  to transfer compressed refrigerant from the first compression stage  708  to a second compression stage  714 , a second refrigerant inlet  716  to introduce refrigerant vapor into the second compression stage  714 , and a second refrigerant exit  718 . The refrigerant transfer conduit  712  is operatively connected at opposite ends to the first refrigerant exit  710  and the second refrigerant inlet  716 , respectively. The second refrigerant exit  718  delivers compressed refrigerant from the second compression stage  714  to a cooling system or refrigeration system (e.g., refrigeration system  100 ) in which the compressor  700  is incorporated. 
     With additional reference to  FIG. 8 , the compressor housing  702  includes a first housing end portion or cap  802  enclosing the first compression stage  708 , and a second housing end portion or cap  804  enclosing the second compression stage  714 . The first compression stage  708  and the second compression stage  714  are positioned at opposite ends of the compressor  700 , but can also be located at the same end of the compressor  700 . The first compression stage  708  includes a first impeller  806  configured to add kinetic energy to refrigerant entering via the first refrigerant inlet  704 . The kinetic energy imparted to the refrigerant by the first impeller  806  is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity is slowed upon transfer to a sealed cavity (e.g., a diffuser). Similarly, the second compression stage  714  includes a second impeller  810  configured to add kinetic energy to refrigerant transferred from the first compression stage  708  entering via the second refrigerant inlet  716 . The kinetic energy imparted to the refrigerant by the second impeller  810  is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity is slowed upon transfer to a sealed cavity (e.g., a diffuser). Compressed refrigerant exits the second compression stage  714  via the second refrigerant exit  718 . 
     The first impeller  806  and second impeller  810  are coupled at opposite ends of a driveshaft  814 . The driveshaft  814  is operatively coupled to a motor  816  positioned between the first impeller  806  and second impeller  810  such that the first impeller  806  and second impeller  810  are rotated at a rotation speed selected to compress the refrigerant to a pre-selected target (e.g., mass flow) exiting the second refrigerant exit  718 . Any suitable motor may be incorporated into the compressor  700  including, but not limited to, an electrical motor. The example compressor  700  includes an electrical motor having a stator  818  connected to the compressor housing  702 , and a rotor  820  connected to the driveshaft  814 . An air gap (not labeled in  FIG. 8 ) is defined between the stator  818  and the rotor  820  to allow coolant to flow therethrough. The driveshaft  814  is supported by first and second radial foil bearings  822 ,  824 , and a thrust foil bearing  826 . Additional details of the compressor  700 , such as additional components and operation of the compressor  700 , are described in U.S. Patent Application Publication No. 2020/0256347, the disclosure of which is incorporated herein by reference. 
     As shown in  FIG. 8 , the compressor housing  702  has a plurality of coolant flow channels  828 ,  830 ,  832 ,  834  defined therein that delivers coolant to the bearings  822 ,  824 ,  826  and the motor  816 . The example compressor  700  includes a first coolant flow channel  828 , a second coolant flow channel  830 , a third coolant flow channel  832 , and a fourth coolant flow channel  834 . The first coolant flow channel  828  delivers coolant to the thrust bearing  826 , the second coolant flow channel  830  delivers coolant to the first radial bearing  822 , the third coolant flow channel  832  delivers coolant to the second radial bearing  824 , and the fourth coolant flow channel  834  delivers coolant to the motor  816 . The compressor housing  702  also defines a common coolant outlet port  836  in the illustrated embodiment. The common coolant outlet port  836  receives coolant from each of the plurality of coolant flow channels  828 ,  830 ,  832 ,  834 . 
     The first coolant flow channel  828  extends radially inward through the first housing end portion  802 , around the thrust bearing  826 , axially along the driveshaft  814  between the first bearing housing  808  and the driveshaft  814 , and radially outward to the common coolant outlet port  836 . The second coolant flow channel  830  extends radially inward through the first bearing housing  808  to the first radial bearing  822 , axially along the first radial bearing  822  and the driveshaft  814 , and radially outward to the common coolant outlet port  836 . The third coolant flow channel  832  extends radially inward through the second bearing housing  812  to the second radial bearing  824 , axially along the second radial bearing  824  and the driveshaft  814 , radially outward toward the air gap defined between the stator  818  and the rotor  820 , axially through the air gap, and radially outward to the common coolant outlet port  836 . The fourth coolant flow channel  834  extends helically around the stator  818  through a spiral groove  838  defined by the compressor housing  702 . The fourth coolant flow channel  834  then extends radially inward to the air gap defined between the stator  818  and rotor  820 , axially through the air gap, and then radially outward to the common coolant outlet port  836 . 
     As shown in  FIG. 8 , the coolant flow channels  828 ,  830 ,  832 ,  834  can share common or overlapping portions of the compressor housing  702 . For example, the first coolant flow channel  828  overlaps with and feeds into the second coolant flow channel  238  at the first radial bearing  822 , and the third coolant flow channel  832  overlaps with and feeds into the fourth coolant flow channel  834  at the motor  816 . Moreover, as shown in  FIG. 8  and described above, the coolant flow channels  828 ,  830 ,  832 ,  834  within the example compressor housing  702  are arranged such that coolant flows through at least one of the coolant flow channels  828 ,  830 ,  832 ,  834 , in series, across at least one of the bearings  822 ,  824 ,  826 , through the motor  816 , and to the common coolant outlet port  836 . For example, the third coolant flow channel  832  delivers coolant to the second radial bearing  824  and the motor  816  (e.g., by flowing across the stator  818  and rotor  820 ), resulting in coolant absorbing heat from both the bearings  822 ,  824 ,  826  and the motor  816 . 
     A coolant return line  840  (shown schematically in  FIGS. 7 and 8 ) has an inlet  842  connected to the common coolant outlet port  836 , and an outlet  844  connected to the suction line  706  to return coolant to a low-pressure side of the compressor  700 . The suction line  706  is generally at a lower pressure than the coolant delivered to the compressor housing  702 , which can be supplied from a relatively high pressure side of a refrigeration system in which the compressor  700  is incorporated, such as downstream of the condenser. As a result, a pressure differential exists between coolant at the coolant source and the suction line  706 , and facilitates driving coolant through the plurality of coolant flow channels  828 ,  830 ,  832 ,  834 . 
     Embodiments of the systems and methods described achieve superior results as compared to prior systems and methods associated with centrifugal compressor cooling systems. For example, the cooling circuits and associated coolant control valves and schemes disclosed herein provide continuous coolant to the bearings of the compressor, thereby providing protection to the bearings, while also allowing additional coolant to be supplied to the motor for additional cooling based on temperature feedback. Additionally, the cooling systems disclosed herein do not require the use of an external or additional liquid pump, and require little or few additional components, thereby providing a relatively simple, reliable compressor cooling system. 
     Example embodiments of compressor systems and methods, such as refrigerant compressors, are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the system and methods may be used independently and separately from other components described herein. For example, the cooling circuits described herein may be used in compressors other than centrifugal compressors, including, for example and without limitation, scroll compressors, rotary compressors, and reciprocating compressors. 
     When introducing elements of the present disclosure or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” “containing” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., “top”, “bottom”, “side”, etc.) is for convenience of description and does not require any particular orientation of the item described. 
     As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawing(s) shall be interpreted as illustrative and not in a limiting sense.