Centrifugal compressors are known to provide certain benefits such as enhanced operating efficiency and economy of implementation, especially in oil free designs. However, centrifugal compressors are usually reserved for high capacity applications. The benefits of centrifugal compressors have not been realized in low capacity applications in part because centrifugal designs have been complicated (and expensive) to manufacture within smaller housings.
There is a large market for compressors capable of operating at low capacities. For example, many light commercial applications like roof-top air-conditioning include compressors that operate at relatively low capacities. Centrifugal compressors are uncommon in light commercial applications.
A compressor according to an exemplary aspect of the present disclosure operates within a system having a cooling capacity below 60 tons includes, among other things, a hermetically sealed housing and a drive module and aero module within the housing. The drive module includes a motor, a rotor, and oil free bearings. The aero module has a centrifugal impeller driven by the drive module to compress a working fluid. The compressor is arranged such that a flow path for the working fluid flows through the drive module before reaching the aero module.
In a further non-limiting embodiment of the foregoing compressor, the oil free bearings are magnetic bearings.
In a further non-limiting embodiment of the foregoing compressor, the oil free bearings are gas bearings configured to use a working fluid as lubricant.
In a further non-limiting embodiment of the foregoing compressor, the drive module is cooled by suction gas before the suction gas reaches the impeller inlet.
In a further non-limiting embodiment of the foregoing compressor, the drive module is driven by a variable frequency drive.
In a further non-limiting embodiment of the foregoing compressor, the variable frequency drive can drive the drive module to achieve system cooling capacities of between 15 and 60 tons.
In a further non-limiting embodiment of the foregoing compressor, the sealed housing acts as a heatsink for power components of the variable frequency drive, and the working fluid cools the sealed housing.
In a further non-limiting embodiment of the foregoing compressor, electronics are enclosed in an integrated electronics housing that is part of the hermetically sealed housing.
In a further non-limiting embodiment of the foregoing compressor, the integrated electronics housing is within an exterior housing defined by two end caps and a tube portion of the sealed housing.
A method of manufacturing a centrifugal compressor according to an exemplary aspect of the disclosure comprises disposing a drive module and aero module in a tube, and welding an end cap to one end of the tube to create a hermetically sealed housing.
In a further non-limiting embodiment of the foregoing method, end caps are welded to opposite ends of the tube to create a hermetically sealed housing.
In a further non-limiting embodiment of the foregoing method, the method further includes fastening the aero module to the drive module.
A compressor according to an exemplary aspect of the present disclosure includes, among other things, a drive module within a housing, and first and second aero modules located within the housing and about opposite ends of the rotor. The drive module includes a motor, a rotor, and bearings. The first and second aero modules each have a centrifugal impeller driven by the drive module to compress a working fluid. The compressor is arranged such that a flow path for working fluid flows through the first aero module.
In a further non-limiting embodiment of the foregoing compressor, the compressor is installed in a system having a cooling capacity of less than 60 tons.
In a further non-limiting embodiment of the foregoing compressor, the housing is hermetically sealed housing.
In a further non-limiting embodiment of the foregoing compressor, the bearings are oil free bearings.
In a further non-limiting embodiment of the foregoing compressor, the compressor includes a dedicated cooling circuit for cooling the drive module using a heat exchanger and a diverted portion of the working fluid that flows through the heat exchanger.
In a further non-limiting embodiment of the foregoing compressor, the heat exchanger includes a fluid passage coiled around the drive module.
In a further non-limiting embodiment of the foregoing compressor, the dedicated cooling circuit includes a temperature sensor mounted to the drive module, and a controller. The temperature sensor is configured to produce an output indicative of a temperature of the drive module. The controller is configured to receive an output from the temperature sensor, and to command an adjustment of a pressure regulator based on the output from the temperature sensor.
In a further non-limiting embodiment of the foregoing compressor, a flow path for the working fluid exits the compressor after flowing through the first aero module but before flowing through the second aero module.
The compressors 10 discussed herein are suitable for a wide range of applications. An application contemplated here is a refrigerant system 32, such as represented in
The compressor 10 of the present is hermetically sealed. The compressor 10 includes an exterior housing provided by a discharge end cap 17, a suction end cap 18, and a main housing 11. The main housing 11 is attached to the end caps 17, 18 by welds 22, thus rendering the compressor 10 hermetically sealed. In this example, the exterior housing is a three-piece housing and is provided exclusively by the end caps 17, 18, the main housing 11, and the welds 22.
The welds 22 allow one to quickly and economically assemble exterior housing of the compressor 10, especially compared to some prior compressors, which are assembled using fasteners such as bolts or screws.
In this example, the main housing 11 houses all working components of the compressor 10. For example, the main housing 11 includes a drive module 12 having a motor stator 13, rotor 19, radial bearings 14a, 14b, and a thrust bearing 15. In one embodiment, the drive module 12 is driven by a variable frequency drive.
The main housing 11 also includes an aero module 16, which is an in-line impeller 27 arrangement in the embodiment depicted by
The radial bearings 14a, 14b and thrust bearing 15 are magnetic or gas bearings, as example, and enable oil free operation of the compressor 10. The working fluid 23 is used as a coolant for the drive module 12. The drive module 12 is cooled as the working fluid 23 flow through fluid paths 26 throughout the drive module 12. If the radial bearings 14a, 14b or thrust bearing 15 are gas bearings, the working fluid 23 is also used as a lubricant.
In one example, the working fluid 23 flows from a suction port 40 to the aero module 16. Between the suction port 40 and the aero module 16, the fluid paths 26 are dispersed throughout the drive module 12 such that the working fluid passes near each drive module 12 component. In particular, some fluid passes outside the stator 13, while some fluid passes around the shaft 19. The proximity of the fluid paths 26 to components of the drive module 12 allows the working fluid 23 to convectively cool the components of the drive module 12.
Since only one fluid is used as the working fluid 23, coolant, and lubricant, separate distribution networks for each of the working fluid 23, and coolant, are not necessary. A single distribution network carrying working fluid 23, and coolant, further contributes to a compact and simple design. Example working fluids include for such purposes include low global warming potential (GWP) refrigerants, like HFO refrigerants R1234ze, R1233zd, blend refrigerants R513a, R515a, and HFC refrigerant R 134a.
Downstream of the drive module 12, the working fluid 23 reaches the aero module 16. In this example, the aero module 16 has two impellers 27 arranged in a serial arrangement such that fluid exiting the outlet of the first impeller is directed to the inlet of the second impeller. It should be noted, however, that a dual-impeller arrangement is not required in all example. Other centrifugal compressor design variants come within the scope of the disclosure.
For example, in another embodiment, which is shown in
With two stage compression, an extra flow can be introduced through the economizer port 38 to the second stage inlet to improve the total compressor efficiency.
In either illustrated embodiment, the aero module 16 compresses the working fluid 23 in a known manner. In the case of centrifugal impellers, the known manner of compression involves one or more impellers 27 rotationally accelerating the working fluid 23, then directing the accelerated working fluid 23 against stationary passages which bring the working fluid 23 to a state of relatively lesser velocity and relatively greater pressure. The compressed working fluid 23 exits the compressor 10 through a discharge port 42.
Referring jointly to
In a third embodiment illustrated in
In a fourth embodiment illustrated in
The two smaller aero modules 16a, 16b provide more design options for fitting around other components of the compressor 10 than the single aero module 16 of the above described embodiments. The distant back-to-back impeller 27 arrangement thus provides relative freedom in choosing diameters of the shaft 19 and impellers 27 compared to the embodiments described above.
The compressor 10 of
The expansion valve 30 and the pressure regulator 134 may be any type of device configured to regulate a flow of refrigerant, including mechanical valves, such as butterfly, gate or ball valves with electrical or pneumatic control (e.g., valves regulated by existing pressures). In the illustrated example, the control of the expansion valve 30 and pressure regulator 134 is regulated by a controller 138, which may be any known type of controller including memory, hardware, and software. The controller 138 is configured to store instructions, and to provide those instructions to the various components of the cooling circuit C, as will be discussed below.
During operation of the refrigerant loop 32, in one example, refrigerant enters the cooling circuit C from the condenser 129 through a diverted passage 124. At P1, the fluid is relatively high temperature, and in a liquid state. As fluid flows through the expansion valve 30, it becomes a mixture of vapor and liquid, at P2.
The cooling circuit C provides an appropriate amount of refrigerant to the drive module 12 without forming condensation in the drive module 12. Condensation of water (i.e., water droplets) may form within the drive module 12 if the temperature of the drive module 12 falls below a certain temperature. This condensation may cause damage to the various electrical components within the drive module 12. The pressure regulator 134 is controlled to control the pressure of refrigerant within the heat exchanger 132, which in turn controls the saturated temperature of that refrigerant, such that condensation does not form within the drive module 12. The expansion of refrigerant as it passes through the pressure regulator 134 is represented at P3 in
During operation of the refrigerant loop 32, the temperature of the drive module 12 is continually monitored by a first temperature sensor T1. In one example of this disclosure, the output of the first temperature sensor T1 is reported to the controller 138. The controller 138 compares the output from the first temperature sensor T1 to a target temperature TTARGET. The target temperature TTARGET is representative of a temperature at which there will be no (or extremely minimal) condensation within the drive module 12. That is, TTARGET is above a temperature at which condensation is known to begin to form. In one example TTARGET is a predetermined value. In other examples, the controller 138 is configured to determine TTARGET based on outside temperature and humidity.
The controller 138 is further in communication with the pressure regulator 134, and is configured to command an adjustment of the pressure regulator 134 based on the output from the first temperature sensor T1. The position of the pressure regulator 134 controls the temperature of the refrigerant within the heat exchanger 132. In general, during normal operation of the loop 32, the controller 138 maintains the position of the pressure regulator 134 such that the output from T1 is equal to TTARGET. However, if the output from T1 decreases and falls below TTARGET, the controller 138 commands the pressure regulator 134 to incrementally close (e.g., by 5%). Conversely, if the output from T1 increases, the controller 138 commands the pressure regulator 134 to incrementally open.
Incrementally closing the pressure regulator 134 raises the temperature of the refrigerant within the heat exchanger 132, and prevents condensation from forming within the drive module 12. In one example, the controller 138 commands adjustment of the pressure regulator 34 until the output from T1 returns to TTARGET. Closing the pressure regulator 134 raises the output from T1 and raises the pressure P2, as illustrated graphically in
Concurrent with the control of the pressure regulator 134, the controller 138 also controls the expansion valve 30 during operation. In this example the temperature and pressure of the refrigerant within the cooling circuit C downstream of the heat exchanger 132 are determined by a second temperature sensor T2 and a pressure sensor PS. In one example, the temperature sensor T2 and the pressure sensor PS are located downstream of the pressure regulator 134. However, T2 and PS could be located downstream of the heat exchanger 132 and upstream of the pressure regulator 134.
The outputs from the second temperature sensor T2 and the pressure sensor PS are reported to the controller 138. The controller 138 is configured to determine (e.g., by using a look-up table) a level of superheat within the refrigerant downstream of the heat exchanger (e.g., at P4). The controller 138 then compares the level of superheat within the refrigerant at P4 and a superheat target value SHTARGET. This comparison indicates whether an appropriate level of fluid was provided to the heat exchanger 132 by the expansion valve 30.
For example, the output from the second temperature sensor T2 is compared to a saturation temperature TSAT at the pressure sensor output from the pressure sensor PS. From this comparison, the controller 138 determines the level of superheat in the refrigerant. In one example, the controller 138 maintains the position of the expansion valve 30 such that the level of superheat exhibited by the refrigerant equals SHTARGET. If the level of superheat exhibited by the refrigerant falls below SHTARGET, the controller 138 will determine that too much fluid is provided to the heat exchanger 132 and will incrementally close the expansion valve 30. Conversely, the controller 138 will command the expansion valve 132 to incrementally open if the level of superheat exhibited by the refrigerant exceeds SHTARGET.
This disclosure references an “output” from a sensor in several instances. As is known in the art, sensor outputs are typically in the form of a change in some electrical signal (such as resistance or voltage), which is capable of being interpreted as a change in temperature or pressure, for example, by a controller (such as the controller 138). The disclosure extends to all types of temperature and pressure sensors.
Further, while a single controller 138 is illustrated, the expansion valve 30 and pressure regulator 134 could be in communication with separate controllers. Additionally, the cooling circuit C does not require a dedicated controller 138. The functions of the controller 138 described above could be performed by a controller having additional functions. Further, the example control logic discussed above is exemplary. For instance, whereas in some instances this disclosure references the term “equal” in the context of comparisons to TTARGET and SHTARGET, the term “equal” is only used for purposes of illustration. In practice, there may be an acceptable (although relatively minor) variation in values that would still constitute “equal” for purposes of the control logic of this disclosure.
The embodiments discussed above are simple enough to make oil free, centrifugal compressors economical for applications below 60 tons. Other known improvements of compressors, such as economizers 36 or variable speed drives, may be incorporated into the disclosed compressors 10 without causing the design to become prohibitively expensive to manufacture. It is to be noted that compressor housing 11a can be used as a heatsink for power components, like power semiconductors. Use of the compressor housing 11a as a heatsink further simplifies the structure and enhances reliability.
Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.
One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content.
This application claims priority to provisional application 62/458,761, filed on Feb. 14, 2017.
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