Patent Application
20240085075
The field of the disclosure relates generally to heating, ventilation, and air conditioning (HVAC) systems, and more particularly, to control systems for HVAC systems.
Dynamic compressors, including centrifugal compressors, are commonly used in process industries and in heating, ventilation, and air conditioning (HVAC) systems. The compressor is typically connected to a motor via a shaft that supports multiple compression stages. A drive controls the motor to rotate the compression stages at a rotational speed and loading condition selected to compress a refrigerant to a specified demand. The motor speed and load can be controlled to operate the compressor under a wide range of operating conditions.
During operation, the drive, motor, and compressor bearings can reach high temperatures that, if left unaddressed, may increase the risk of mechanical failure due to overheating. Many existing cooling systems divert low-temperature refrigerant from the main flow path to the components needing cooling. However, using liquid refrigerant for cooling creates the opportunity for liquid to enter the bearings or the high-speed impeller, degrading the performance and longevity of the compressor. Thus, there is a need for a compressor cooling system that uses only gaseous refrigerant as a cooling fluid.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the 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.
One aspect of the disclosure is directed to a vapor compression system including a primary loop and a secondary loop. The primary loop includes a dynamic compressor operable to compress a refrigerant, a condenser fluidly connected to the dynamic compressor, a first expansion device fluidly connected to the condenser, and an evaporator fluidly connected to the first expansion device and the dynamic compressor. The dynamic compressor includes a housing, a shaft supported in the housing by a bearing, an impeller connected to the shaft, a motor operably connected to the shaft to drive rotation thereof, and a drive operable to control the motor. The secondary loop includes a second expansion device fluidly connected to the condenser, a heat exchanger fluidly connected to the second expansion device, the condenser, and the dynamic compressor, and a supply duct fluidly connected between the heat exchanger and the dynamic compressor to provide a flow of refrigerant to the bearing.
Another aspect of the disclosure is directed to a controller for a compressor system. The compressor system includes a dynamic compressor and a cooling apparatus, and the cooling apparatus includes a heat exchanger and a supply duct fluidly connected between the heat exchanger and the dynamic compressor. The controller includes a processor and a memory that stores instructions that program the processor to operate the dynamic compressor to compress a refrigerant, operate the cooling apparatus to provide a flow of refrigerant through the supply duct to a bearing of the dynamic compressor, determine if a condition is satisfied, and adjust a position of a valve in fluid communication between the dynamic compressor and the cooling apparatus when the condition is satisfied.
Another aspect of the disclosure is directed to a compressor system including a dynamic compressor operable to compress a refrigerant and a cooling apparatus. The dynamic compressor includes a housing, a shaft supported in the housing by a bearing, and an impeller connected to the shaft. The cooling apparatus includes a heat exchanger fluidly connected to the dynamic compressor, a supply duct fluidly connected between the heat exchanger and the dynamic compressor to provide a flow of refrigerant to the bearing, a valve fluidly connected to the supply duct and selectively positionable to permit refrigerant to flow therethrough, and a controller operable to control the valve.
Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure 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 of the present disclosure may be incorporated into any of the above-described aspects of the present disclosure, alone or in any combination.
Corresponding reference characters indicate corresponding parts throughout the drawings.
For conciseness, examples will be described with respect to a centrifugal compressor. However, the methods and systems described herein may be applied to any suitable compressor. The bearings, motor, and drive of a dynamic compressor can be cooled with vapor injection by diverting portions of the main flow through a supplemental loop with a heat exchanger or flash tank. The gaseous refrigerant exiting the heat exchanger or flash tank can be selectively provided to the bearings, motor, or drive based on the measured and desired temperatures of those components.
Referring to
Referring to
Similarly, the second compressor stage 126 includes a second compression mechanism 116 configured to add kinetic energy to refrigerant transferred from the first compressor stage 124 entering via the second refrigerant inlet 118. In some embodiments, the second compression mechanism 116 is an impeller. The kinetic energy imparted to the refrigerant by the second compression mechanism 116 is converted to increased refrigerant pressure as the refrigerant velocity is slowed upon transfer to a sealed cavity (e.g., a diffuser) formed within the volute 132. Compressed refrigerant exits the second compressor stage 126 via the second refrigerant exit 120 (not shown in
The first compression mechanism 106 and second compression mechanism 116 are connected at opposite ends of a shaft 104. The shaft 104 is operatively connected to a motor 108 positioned between the first compression mechanism 106 and second compression mechanism 116 such that the first compression mechanism 106 and second compression mechanism 116 are rotated at a rotation speed selected to compress the refrigerant to a pre-selected pressure exiting the second refrigerant exit 120 (not shown in
A controller 610 is operatively connected to the dynamic compressor 100 to control its operation based in part on the measured parameters described above. The controller 610 includes a processor 611, a memory 612, and an unloading interface 614. The memory 612 stores instructions that program the processor 611 to determine whether the bearing assembly(s) 200, motor 108, and/or drive 616 require cooling, which will be discussed in greater detail further below. The system 600 includes an interface for connection of the controller 610 to the drive 616 and a motor interface 613 for connection of the drive 616 to the motor 108. In certain embodiments, the drive 616 operates under the control of the controller 610. In further embodiments, the drive 616 is a part of the controller 610. The drive 616 may include a drive temperature sensor (not shown) operable to determine a temperature of the drive. The drive temperature sensor may be a thermocouple, thermistor, resistance temperature detector (RTD), or any other suitable sensor. The system 600 further includes an unloading interface 614 for connection of the controller 610 to the unloading device 601.
The controller 610 is operatively coupled to the unloading device 601 through the unloading interface 614, which removes and/or reduces the load on the compressor 100 during start-up and shut-down routines, during detected surge events, and when otherwise instructed by the controller 610 to do so. In the example embodiment, the unloading device 601 is a variable inlet guide vane (VIGV) at the inlet of each impeller stage (
The system 600 further includes a user interface 615 configured to output (e.g., display) and/or receive information (e.g., from a user) associated with the system 600. In some embodiments, the user interface 615 is configured to receive an activation and/or deactivation input from a user to activate and deactivate (i.e., turn on and off) or otherwise enable operation of the system 600. Moreover, in some embodiments, the user interface 615 is configured to output information associated with one or more operational characteristics of the system 600, including, for example and without limitation, warning indicators such as severity alerts, occurrence alerts, fault alerts, motor speed alerts, and any other suitable information.
The user interface 615 may include any suitable input devices and output devices that enable the user interface 615 to function as described herein. For example, the user interface 615 may include input devices including, but not limited to, a keyboard, mouse, touchscreen, joystick(s), throttle(s), buttons, switches, and/or other input devices. Moreover, the user interface 615 may include output devices including, for example and without limitation, a display (e.g., a liquid crystal display (LCD) or an organic light emitting diode (OLED) display), speakers, indicator lights, instruments, and/or other output devices. Furthermore, the user interface 615 may be part of a different component, such as a system controller (not shown). Other embodiments do not include a user interface 615.
The controller 610 is generally configured to control operation of the dynamic compressor 100. The controller 610 controls operation through programming and instructions from another device or controller or is integrated with the system 600 through a system controller. In some embodiments, for example, the controller 610 receives user input from the user interface 615, and controls one or more components of the system 600 in response to such user inputs. For example, the controller 610 may control the motor 108 based on user input received from the user interface 615. In some embodiments, the system 600 may be controlled by a remote control interface. For example, the system 600 may include a communication interface (not shown) configured for connection to a wireless control interface that enables remote control and activation of the system 600. The wireless control interface may be embodied on a portable computing device, such as a tablet or smartphone.
The controller 610 may generally include any suitable computer and/or other processing unit, including any suitable combination of computers, processing units and/or the like that may be communicatively coupled to one another and that may be operated independently or in connection within one another (e.g., controller 610 may form all or part of a controller network). Controller 610 may include one or more modules or devices, one or more of which is enclosed within system 600, or may be located remote from system 600. The controller 610 may be part of compressor 100 or separate and may be part of a system controller in an HVAC system. Controller 610 and/or components of controller 610 may be integrated or incorporated within other components of system 600. The controller 610 may include one or more processor(s) 611 and associated memory device(s) 612 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 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) 612 of controller 610 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) 612 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 611, configure or cause the controller 610 to perform various functions described herein including, but not limited to, controlling the system 600, controlling operation of the motor 108, receiving inputs from user interface 615, providing output to an operator via user interface 615, controlling the unloading device 601 and/or various other suitable computer-implemented functions.
The condenser 320 is fluidly connected to the first expansion device 330, which reduces the pressure of the refrigerant. In some embodiments, the pressure may be reduced until the liquid refrigerant's current temperature becomes the boiling point temperature at that pressure, and the refrigerant becomes a two-phase mixture as some of the liquid refrigerant boils and turns into a gas. The first expansion device 330 may be a fixed orifice, a thermal expansion valve, an electronic expansion valve, or any type of expansion device that allows the vapor compression system 700 to function as described herein. The first expansion device 330 is fluidly connected to the evaporator 340, which receives low-pressure, low-temperature liquid refrigerant or a two-phase mixture of liquid and gaseous refrigerant at its inlet. In the evaporator 340, the refrigerant absorbs heat Qin to change phase from a liquid to a gas. The evaporator 340 is fluidly connected to the compressor 100, and the cycle begins again.
The secondary refrigerant loop 460 includes the second expansion device 480, a second stream 494 of the heat exchanger 490, the economization valve 470, the second compressor stage 126 (
The economization valve 470 is controlled by the controller 610 to be fully open, partially open, or fully closed, and the economization valve's 470 status determines whether refrigerant will flow through the secondary refrigerant loop 460. That is, when the economization valve 470 is fully closed, all of the refrigerant will flow through the primary refrigerant loop 410, and the system 800 will operate in substantially the same way as the system 700 illustrated in
When the economization valve 470 is open, the condenser 320 is fluidly connected to the second expansion device 480, which reduces the pressure of the liquid economizer flow until the liquid refrigerant's current temperature becomes the boiling point temperature at that pressure. The refrigerant in the secondary refrigerant loop becomes a two-phase mixture as some of the liquid refrigerant boils and turns into a gas as it enters the heat exchanger 490. The second expansion device can be sized and selected to divert a particular amount of refrigerant through the secondary refrigerant loop 460 when the economization valve 470 is open, for example, 0 to 20 percent of the total mass flow, or any amount of refrigerant flow that allows the system 800 to function as described herein.
In some embodiments, the second expansion device 480 is a thermal expansion valve (TXV) that adjusts the amount of refrigerant flow through the secondary refrigerant loop 460 based on the thermal load of the heat exchanger 490. The TXV works in combination with a bulb 496 located downstream of the second stream 494 of the heat exchanger 490. A membrane inside the TXV is movable to balance the refrigerant pressure inside the bulb with the refrigerant pressure upstream of the heat exchanger 490. The movement of the membrane is coupled to a needle that sets the position of the valve, thereby controlling the amount of refrigerant that flows through the secondary refrigerant loop 460. In further embodiments, the second expansion device 480 can also be a fixed orifice, an electronic expansion valve, or any type of expansion device that allows the system 800 to function as described herein.
The refrigerant exits the second expansion device 480 and enters the second stream 494 of the heat exchanger 490 as a low-pressure liquid or two-phase mixture. The second stream 494 comes into thermal communication with the first stream 492, which carries high-pressure liquid refrigerant from the condenser 320 in the primary refrigerant loop 410. The thermal contact between the two streams 492, 494 cools the refrigerant in the first stream 492 and warms the refrigerant in the second stream 494, causing it to boil. The cooled refrigerant in the first stream 492 exits the heat exchanger 490 as a lower-temperature, high-pressure liquid, and the boiled refrigerant in the second stream 494 exits the heat exchanger 490 as a low-temperature, intermediate-pressure gas. The heat exchanger 490 may be a counterflow heat exchanger, a cross-flow heat exchanger, a parallel flow heat exchanger, a shell and tube heat exchanger, a mixing chamber, or any type of heat exchanger that allows the system 800 to function as described herein. In further embodiments, a flash tank may be used instead of or in addition to the heat exchanger 490. Such embodiments will be shown and described further below.
The low-temperature, intermediate-pressure gas exiting the second stream 494 of the heat exchanger 490 then flows through an economization duct 465 and is injected into the refrigerant transfer conduit 112 (
The first supply duct 565 includes a first valve 570 fluidly connected thereto. The first valve 570 is controlled by the controller 610 and is selectively positionable to permit refrigerant to flow therethrough. When the first valve 570 is fully closed, all of the refrigerant in the secondary refrigerant loop 460 will flow through the economization duct 465, and the system 900 will operate in substantially the same manner as the system 800 illustrated in
When the first valve 570 is open, the first supply duct 565 provides a first flow of refrigerant to facilitate cooling of at least one bearing assembly 200 of the dynamic compressor 100. In the illustrated embodiment, the first supply duct 565 diverges into first, second, and third streams 565a-c that respectively provide the first refrigerant flow to a first radial bearing 200a, a second radial bearing 200b, and a thrust bearing 200c of the dynamic compressor 100. In some embodiments, the first, second, and third streams 565a-c may each include a valve (not shown) operable to control the flow of refrigerant therethrough.
The cooling apparatus 560 further includes a return duct 520 that fluidly connects the first supply duct 565 to the dynamic compressor 100 to provide a return flow of refrigerant thereto. The return duct 520 collects refrigerant from downstream of the cooled bearings and returns the refrigerant to the inlet 110 of the first compressor stage 124. In the illustrated embodiment, each of the first, second, and third streams 565a-c of the first supply duct 565 converge downstream of their respective bearings 200a-c to form the return duct 520. The return flow is mixed with the refrigerant flow upstream of the inlet 110 such that the primary and secondary refrigerant loops 410, 460 converge. The return duct 520 may include a return temperature sensor (not shown) operable to measure a return flow temperature T r. The return temperature sensor may be a thermocouple, thermistor, or any suitable temperature sensor.
An alternate embodiment of the third example vapor compression system 900 is shown in
The second supply duct 665 includes a second valve 670 fluidly connected thereto. The second valve 670 is controlled by the controller 610 and selectively positionable to permit refrigerant to flow therethrough. When the second valve 670 is fully closed, and when at least one of the economization valve 470 and the first valve 570 are open, all of the refrigerant in the secondary refrigerant loop 460 will flow through the economization duct 465 and/or the first supply duct 565, and the system 1100 will operate in substantially the same manner as the system 900 illustrated in
When the second valve 670 is open, the second supply duct 665 provides a second flow of refrigerant to facilitate cooling of the motor 108. The second supply duct 665 is fluidly connected to the return duct 520, and the first and second flows combine to form the return flow that is mixed with the refrigerant flow upstream of the compressor inlet 110.
The third supply duct 765 includes a third valve 770 fluidly connected thereto. The third valve 770 is controlled by the controller 610 and selectively positionable to permit refrigerant to flow therethrough. When the third valve 770 is fully closed, and when at least one of the economization valve 470, the first valve 570, and the second valve 670 is open, all of the refrigerant in the secondary refrigerant loop 460 will flow through the economization duct 465, the first supply duct 565, and/or the second supply duct 665, and the system 1200 will operate in substantially the same manner as the system 1100 illustrated in
When the third valve 770 is open, the third supply duct 765 provides a third flow of refrigerant to facilitate cooling of the drive 616. The third supply duct 765 is fluidly connected to the return duct 520, and the first, second, and third flows combine to form the return flow that is mixed with the refrigerant flow upstream of the compressor inlet 110.
In further embodiments (not shown), vapor compression systems of the present disclosure may include any combination of the economization duct 465, first supply duct 565, second supply duct 665, third supply duct 765, and return duct 520 in any suitable configuration.
The memory 612 stores instructions that program the processor 611 to control the supply of refrigerant to the compressor 100, motor 108, and drive 616 based on operating parameters of each component. Example control algorithms are shown in
In some embodiments, and with reference to
P
set
=P
suction
+P
offset
The pressure offset Poffset may be 1 psi, 2 psi, or any other suitable pressure offset that creates a sufficient pressure differential to cause refrigerant to flow through the bearing assembly 200.
In embodiments in which the cooling apparatus 560 includes a second supply duct 665 and a second valve 670 fluidly connected thereto, the instructions stored in the memory 612 program the processor 611 to determine whether the motor 108 is overheating based on the measured temperature of the return flow or the motor 108. For example, and with reference to
When the condition is satisfied in either such case, the motor 108 is determined to be overheating and in need of cooling. Accordingly, adjusting a position of a valve in such embodiments includes opening the second valve 670 to provide the second flow of refrigerant to the motor 108. When the condition is not determined to be satisfied, and the motor 108 is not determined to be overheating, the instructions stored in the memory 612 program the processor 611 to continue to operate the dynamic compressor 100 without adjusting the position of the second valve 670.
In embodiments in which the cooling apparatus 560 includes a third supply duct 765 and a third valve fluidly connected thereto, the instructions stored in the memory 612 program the processor 611 to determine whether the drive 616 is overheating based on the temperature of the drive 616 measured by the drive temperature sensor. In such embodiments, and with reference to
When the condition is satisfied, the drive 616 is determined to be overheating and in need of cooling. Accordingly, adjusting a position of a valve in such embodiments includes opening the third valve 770 to provide the third flow of refrigerant to the drive 616. When the condition is not determined to be satisfied, and the drive 616 is not determined to be overheating, the instructions stored in the memory 612 program the processor 611 to continue to operate the dynamic compressor 100 without adjusting the position of the third valve 770.
In some embodiments, the condition is a first condition, and the instructions stored in the memory 612 further program the processor 611 to determine if a second condition is satisfied, and to adjust the position of a valve when the second condition is satisfied. For example, the instructions stored in the memory 612 program the processor 611 to determine whether the motor 108 and drive 616 have been sufficiently cooled after the second or third valve 670, 770 has been opened.
For example, and with reference to
T
r,low
=T
r,up
−T
r,db
Determining if the motor 108 is overcooling may also include determining the motor temperature T m and determining a motor temperature lower threshold value Tm,low. In some embodiments, the motor temperature lower threshold value Tm,low is the difference between the motor temperature upper threshold value Tm,up and a motor temperature deadband value Tm,db:
T
m,low
=T
m,up
−T
m,db
The motor temperature deadband may be, for example and without limitation, 10 or 15 degrees Fahrenheit. The second condition is determined to be satisfied when the temperature of the return flow Tr is less than the return temperature lower threshold value Tr,low, and/or the motor temperature Tm is less than the motor temperature lower threshold value Tm,low.
When the second condition is satisfied in either such case, the motor 108 is determined to be sufficiently cooled and no longer in need of cooling. Accordingly, adjusting a position of a valve in such embodiments includes closing the second valve 670 to terminate the second flow of refrigerant to the motor 108. When the second condition is not determined to be satisfied, and the motor 108 is not determined to be overcooling, the instructions stored in the memory 612 program the processor 611 to continue to operate the dynamic compressor 100 with the second valve 670 open.
Similarly, and with reference to
T
d,low
=T
d,up
−T
d,db
The second condition is determined to be satisfied when the measured drive temperature Td is less than the drive temperature lower threshold value Tm,low.
When the second condition is satisfied in such embodiments, the drive 616 is determined to be sufficiently cooled and no longer in need of cooling. Accordingly, adjusting a position of a valve in such embodiments includes closing the third valve 770 to terminate the third flow of refrigerant to the drive 616. When the second condition is not determined to be satisfied, and the drive 616 is not determined to be overcooling, the instructions stored in the memory 612 program the processor 611 to continue to operate the dynamic compressor 100 with the third valve 770 open.
Technical benefits of the methods and systems described include that the vapor compression system can use an existing vapor path from an economization system to provide vapor injection cooling to the bearings, motor, and drive of a dynamic compressor. In addition, the bearings, motor, and drive of a dynamic compressor can be cooled using vapor injection with no risk of flooding the bearings or compressor flow path with liquid. Vapor injection is also better suited for the small amount of cooling required by the bearings.
As used herein, the terms “about,” “substantially,” “essentially” and “approximately” when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.
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.
