HK1119762A1 - Refrigerant system with variable speed scroll compressor and economizer circuit and operating method thereof - Google Patents

Description

Refrigeration system with variable speed scroll compressor and economizer circuit and method of operation

Technical Field

The present invention relates to a variable speed scroll compressor operating in a refrigeration system having an economizer function and other capacity adjustment means.

Background

Refrigerant systems are used in many fields to condition an environment. In particular, air conditioners and heat pumps are used to cool and/or heat a secondary fluid, such as air entering an environment. The cold or heat load of the environment may vary with ambient conditions, occupancy levels, apparent and potential load demands, and other changes, as the set point temperature and/or humidity may be adjusted by the building occupants.

In this way, the refrigeration system can have a complex controller and many optional components and features that can adjust the cooling and/or heating capacity. Known options include the function of bypassing the refrigerant, which is at least partially compressed by the compressor to return to the suction line. This function is also referred to as an unloader function. In operation, this additional step is taken to reduce the refrigeration capacity of the system.

Other options include the so-called economizer cycle. In the economizer cycle, refrigerant directed to the evaporator is subcooled in the economizer heat exchanger. The refrigerant is subcooled by a tapped refrigerant that is expanded and then passed through an economizer heat exchanger to subcool the main refrigerant. The tapped refrigerant is then returned to an intermediate point in the compression cycle. Thus, the economizer cycle provides a step in operation to change the capacity of the system by switching between economized and other modes or steps of operation.

In the prior art, the controller can be programmed to selectively perform any of these various functions. However, the capabilities provided by these functions are increased or decreased in synchrony. It is desirable to be able to vary this capability as the system continues to operate during any of the above-described operational steps (modes) to precisely match external load demands.

Variable speed drives are known for driving variable speed operation of compressors of refrigeration systems. By driving the compressor at a high or low speed, the amount of refrigerant that is compressed and circulated throughout the system varies, so that the capacity of the system can be varied accordingly.

Scroll compressors are an increasingly popular type of compressor. In a scroll compressor, a pair of scroll members rotate relative to each other to compress a sucked refrigerant. One design concept for a scroll compressor is to utilize both economizer and unloader functions. Also, such scroll compressors may employ separate ports to provide either or both of the above functions, optionally. Such a scroll compressor is disclosed in U.S. patent No. 5,996,364. However, this type of scroll compressor is not utilized in conjunction with a variable speed drive for its motor.

Disclosure of Invention

In a disclosed embodiment of the invention, a scroll compressor is provided in a refrigeration system having an economizer circuit. The scroll compressor has a motor driven by a variable speed drive. The controller can increase or decrease the capacity of the refrigerant system by selectively utilizing the economizer circuit and/or the optional unloader function. Moreover, by varying the speed of the motor, the capabilities of each mode of operation are again adjusted to provide substantially continuous stepless control.

The controller identifies a desired level of capability and then obtains such desired level of capability by: first, if increased capacity is desired, the economizer cycle is started, or if no additional capacity is needed, the economizer cycle is not started (or other means of unloading is provided to further reduce capacity), and then to obtain an accurate capacity level, the desired speed of the motor is determined. Because refrigerant compressors can only operate efficiently and reliably over a range of speeds, it would be desirable and equally desirable to employ an additional step of capacity reduction, such as an unloader function, with or without the use of an economizer circuit, which is applied simultaneously with the corresponding adjustment of the compressor motor speed to precisely control the capacity level or to achieve greater efficiency of the overall operation. In a simplified approach, the speed of change is adjusted incrementally in specific modes of operation (conventional, economical, unloaded, etc.) and the provided capacity is monitored. When the desired capacity is reached, the system then runs at the new speed. If the adjustment capability is still needed, the speed is adjusted in another incremental step. Similarly, the alternative unloading-type mode of operation can be used with either closed or open economizer circuits if reduced capacity is desired. In addition, the controller may monitor the efficiency level of the system, selecting the most appropriate operating mode and motor speed. In this case, the capacity and efficiency are taken into account in combination to establish the optimum overall operation. Other modes of unloading operation may be added to a system in which both the economizer circuit and the unloader have been operated simultaneously.

By providing a variable speed drive and the various alternatives to the adjustment capabilities described above, the present invention can allow the end user to fully tailor the capabilities and/or efficiency of the system, or a combination of both parameters, to a desired level. The above described modes of operation are particularly applicable to transport type refrigeration units, such as container refrigeration units, trailer type units or automotive type units, where a wide operating range of capacity is required, but at the same time a precise level of control over the capacity is required to maintain the cargo or cooling environment within a narrow temperature range. As is also common in these refrigeration applications, an additional throttling device, often referred to as a Suction Modulation Valve (SMV), is provided to further reduce the capacity level below that which can be achieved by the unloading mechanism and reduction in motor speed. The use of a variable speed drive can reduce or even eliminate the need for additional SMV in certain situations.

In other features, the scroll compressor is preferably provided with a separate inlet port into the compressor for injecting refrigerant into the intermediate compression port, and wherein the separate port is also used to direct refrigerant into the suction line when the unloader function is actuated.

In a second embodiment, the scroll compressor is a two-stage compressor with the intermediate port located between the two stages.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Drawings

Fig. 1A shows a refrigeration cycle of the first embodiment.

FIG. 1B shows the scroll compressor shown in FIG. 1A in greater detail.

Fig. 2 shows a refrigeration cycle of another embodiment.

Fig. 3A shows a graph of the provisioning capability provided in the prior art.

Fig. 3B shows a graph of the provisioning capability provided in the prior art.

FIG. 4A shows a graph of the delivery capabilities provided by the present invention.

FIG. 4B shows a graph of the delivery capabilities provided by the present invention.

FIG. 5 shows a detailed view of the actual capabilities offered by a typical prior art transmission controller.

Detailed Description

The refrigeration system 20 illustrated in fig. 1A has a single stage compressor 22, a controller 42, a variable speed drive 44, and other components illustrated in the figure. As is well known, the motor 24 of the compressor 22 can be driven at a variety of speeds such that the amount of refrigerant compressed by the compressor 22 can vary. The compressor 22 is a scroll compressor having a moving scroll member 26 and a fixed scroll member 28. As is well known, a plurality of compression chambers are defined between the two scroll members to compress the refrigerant drawn in as the orbiting scroll member 26 is driven in rotation by the motor 24. It can also be seen that the suction line 30 directs refrigerant into a suction chamber 31, which suction chamber 31 surrounds the motor and leads into the compression chamber. Once the refrigerant is compressed, the refrigerant is discharged into a discharge chamber 33 communicating with the discharge port 32. The construction of scroll compressors is known. Also shown is that the fill line 34 communicates with a port 51, the port 51 being located at an intermediate compression point, the fill line 34 being described in greater detail below. As shown in fig. 1B, port 51 may actually be a plurality of ports as disclosed in U.S. patent 5,996,364.

The refrigerant compressed by the compressor 22 is discharged through the discharge port 32 and then enters the outdoor heat exchanger 46, which will act as a condenser in the cooling mode. A fan 47 moves air through the heat exchanger 46. Downstream of the condenser 46 is an economizer heat exchanger 48. As is well known, the economizer heat exchanger 48 connects the tap refrigerant line 45 to the main refrigerant line 41, the tap refrigerant line 45 passing through an economizer expansion device 49. Although the two flow paths are shown in the same flow direction in fig. 1A, this is merely for the sake of simplifying the drawing. In practice, it is generally preferred that the two flow paths are in a counter-flow arrangement.

The tapped refrigerant in the tap line 45 subcools the refrigerant in the main line 41 so that the refrigerant has a higher cooling potential after passing through the expansion device 52 and before entering the evaporator 54. A fan 55 moves air through the evaporator 54. After exiting the evaporator 54, the refrigerant returns to the suction line 30, and the suction line 30 leads back to the compressor 22. As illustrated, a variable or fixed speed drive 110 is coupled to the fans 55 and 47, and it is known that the variable or fixed speed drive 110 can be used to vary the speed of these fans to achieve system control. An optional suction modulation valve 61 may be located in the suction line 30 between the compressor 22 and the evaporator 54. The tapped refrigerant from the tap line 45 flows through a return injection line 34 to enter an intermediate compression point or injection port (or ports) 51 of the compressor 22. When the bypass valve 40 is open, the bypass line 19 may selectively bypass the return refrigerant from the compressor 22 to the suction line 30. It should be understood that the economizer expansion device 49 also preferably has a shutoff feature, or a separate shutoff device 36 is provided. The shut-off device 36 is preferably closed when the bypass valve 40 is open, and the bypass valve 40 is closed when the shut-off device 36 is open; however, it is also possible that both the shut-off device 36 and the bypass valve 40 are open. As shown, the same port of the injection line 34 can be used to deliver refrigerant from the economizer heat exchanger and also to bypass refrigerant to return to the suction line. Of course, the bypass and refrigerant injection functions could utilize different ports rather than a common end point 51, if desired.

As is known, the bypass valve 40 is opened when the full capacity of the compressor 22 is not required. In this way, a portion of the compressed refrigerant is returned to the suction line 30, and the refrigeration capacity of the refrigeration system is reduced. If increased capacity is required, the bypass valve 40 is closed. If further capacity increase is desired, the bypass valve 40 is closed and the economizer expansion device 49 and/or shutoff device 36 are opened to provide the economizer function. In this way, increased capacity is obtained.

The contour 15 in fig. 1A is for clarity to show that the refrigeration system 20 may be combined with different devices, such as refrigerated containers, refrigeration suspension units, automotive air conditioners, and the like.

As shown in fig. 2, a refrigeration system 60 has two compression stages 62 and 64. The variable speed drive 66 can vary the speed of the motor of either or both of the compressors 62 and 64. A third compression stage 161 is shown which can also be controlled by the variable speed drive 66, so there can also be a fourth compression stage etc. The downstream discharge line 68 leads to a condenser 70 and then to an economizer heat exchanger 72. The tap line 74 passes through an economizer expansion device 76 and back to a return intermediate pressure line 78. As shown, the return line 78 enters an intermediate point 80 of the two compression stages 62 and 64. If the expansion valve 76 is not electronically controlled, additional flow devices (typically solenoid valves) may be installed to selectively connect and disconnect the economizer circuit. Bypass line 82 passes through a bypass valve 84 to return to a suction line 86. Downstream of the economizer heat exchanger 72, the main refrigerant passes through a main expansion device 88 and an evaporator 90 before returning to the suction line 86. Both compression stages 62 and 64 have scroll compressors.

An additional or alternative bypass valve 100 may connect the drain line 68 back to the intermediate line 78. Further control of unloading or bypass operation may also be permitted. Further, while two compression stages 62 and 64 are possible, additional compression stages would be provided within the scope of the present invention.

Also in this embodiment, a suction modulation valve 61 is placed downstream of the evaporator 55 to provide additional throttling in the suction flow path.

The controller for each refrigeration cycle 20 and 60 can determine the desired refrigeration capacity and operate the bypass function and/or the economizer function as necessary. Thus, as shown in FIG. 3A, the prior art system provides various stages A, B, C, D of capabilities. Phase a corresponds to the economized mode of operation, phase B corresponds to the economized mode of operation and the bypass mode of operation simultaneously, phase C corresponds to the non-economized mode of operation, and phase D corresponds to the bypass mode of operation. If there are additional SMVs, then the capacity can be adjusted between the modes by adjusting the SMV between the modes of operation as shown in FIG. 3B. However, the operation of the SMV is inefficient and should generally be avoided as much as possible.

When the system of fig. 1A and 2 includes a variable speed drive for the compressor motor, then continuous capacity control occurs between the base values of A, B, C, D, whether or not SMV is used. Thus, as shown in FIG. 4A, if the system is operating at maximum capacity at point E1 (which generally corresponds to using an economizer circuit and the compressor is operating at maximum speed), the capacity can be reduced to point E2 by reducing the speed of the compressor. If a further reduction is desired, the speed of the compressor is adjusted and switched to an economized mode using bypass. Additionally, by varying the speed of the compressor along the line connecting points EB1 and EB2, the system capacity can be adjusted. If further capacity reduction is required, the speed is again adjusted and the system will change to the next mode of operation, which will be a non-economized mode. Now, by varying the speed of the compressor along the line connecting points N1 and N2, the system capacity can be adjusted. If the capacity needs to be reduced again, the speed is changed again and the system will change to the next mode of operation, which will be the bypass mode. Now, by varying the speed of the compressor along the line connecting points B1 and B2, the system capacity can be adjusted. The system shown in fig. 4B operates as the system shown in fig. 4A except that sudden changes in speed are avoided by briefly introducing SMV before changing the mode of operation. Also, although fig. 3A, 3B, 4A and 4B show four main operation modes, the number of actual modes can be reduced. For example, the system may only operate in a single economy mode, and by introducing a variable speed drive, the capacity in that mode is changed. For another example, an economy/bypass type mode of operation may not be performed. The mode of operation may be expanded by selectively opening and closing an optional valve 100, which optional valve 100 is located between the discharge line and the intermediate compression line in fig. 1A and 2. It should be noted that additional modes of operation are possible in order to control the capacity of a two-stage compressor system in which each or all of the stages of the compressors may be driven by a variable speed drive. It should also be noted that the illustrations of fig. 4A and 4B are merely examples of how transitions between modes can be made, and the decision of when to transition, how to adjust speed, and how to introduce SMV will depend on specific operating conditions, load characteristics, efficiency, and power considerations. Other improvements to the operation of the system are condenser fans or evaporator fans (or both) having variable speed drives.

When varying the compressor speed to provide the desired benefit, there are upper and lower limits imposed on the actual operating speed range of the compressor that is available to the end user. Typically, the lower limit is defined by reliability requirements in order to maintain proper lubrication of compressor components such as bearings and compression elements. On the other hand, the upper limit is limited by undesirably high power consumption or excessive noise and consequent inefficient operation and safety concerns. These limits may be used in the design steps of the system to define the time desired for switching between operating modes. The upper and lower speed limits may also change when switching from one application to another, and depend on conditions during system operation.

Fig. 5 shows how the ramp shown in the figure is typically obtained. As shown in fig. 5, once a particular operating mode is selected, the speed can be varied within the mode and within the speed limits described above. This repeated change is how the prior art variable speed drive works. If the need for a speed change exceeds the speed limit, the system transitions to a different mode of operation.

In other respects, it is known to make the economizer and unloader functions continuously adjustable. Furthermore, providing a variable speed drive for the compressor will result in more flexible, reliable and efficient operation.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (26)

1. A refrigeration system comprising:

at least one scroll compressor having a variable speed drive for varying a speed of the scroll compressor, the scroll compressor having a suction port, an intermediate pressure port, and a discharge port;

a condenser downstream of said scroll compressor and an evaporator downstream of said condenser, an economizer heat exchanger between said condenser and said evaporator, said economizer heat exchanger selectively returning a tapped refrigerant to said scroll compressor;

at least one condenser fan for passing air through the condenser, at least one evaporator fan for passing air through the evaporator, and

a controller selectively operating the economizer heat exchanger to deliver a tapped refrigerant through the economizer heat exchanger and back to the compressor, the controller further operating to vary a speed of the scroll compressor to achieve a capacity level between a capacity level when the economizer heat exchanger is operating and a capacity level when the economizer heat exchanger is not operating;

a bypass port to selectively bypass refrigerant from the scroll compressor and return it to a suction line of the scroll compressor, the controller operating to vary a speed of the scroll compressor to provide a capacity level between a capacity level at which the bypass operating mode is enabled and a capacity level at which the bypass operating mode is not enabled;

the controller is operable to selectively operate the refrigerant system in a non-economized mode, an economized mode, a bypass mode, or a combined economized and bypass mode.

2. The refrigerant system as set forth in claim 1, wherein said bypass port and said intermediate pressure port are provided as the same port.

3. The refrigerant system as set forth in claim 1, wherein the delivery of said bypass refrigerant is controlled by a flow controller.

4. The refrigerant system as set forth in claim 1, wherein said scroll compressor is a single stage compressor, said intermediate pressure port in said scroll compressor also communicating with said bypass port.

5. The refrigerant system as set forth in claim 1, wherein said scroll compressor has at least two scroll compressor stages, said intermediate pressure port being located between two of said stages.

6. The refrigerant system as set forth in claim 1, wherein said control varies said speed of said scroll compressor in incremental steps.

7. The refrigerant system as set forth in claim 1, wherein said bypass port is selectively in communication with an intermediate pressure line, said intermediate pressure line receiving said tapped refrigerant to return it to a suction line, said suction line leading to said compressor.

8. The refrigerant system as set forth in claim 1, wherein said bypass is between a discharge line for compressed refrigerant and a line returning to said suction line.

9. The refrigerant system as set forth in claim 1, wherein said tapped refrigerant is returned to said intermediate compression port.

10. The refrigerant system as set forth in claim 1, wherein the delivery of said tapped refrigerant is controlled by a flow controller.

11. The refrigeration system of claim 1 wherein said system is part of a refrigerated transport unit.

12. The refrigeration system of claim 11 wherein said refrigerated transport unit is a refrigerated container unit.

13. The refrigeration system of claim 11 wherein said refrigerated transport unit is a tractor/trailer type unit.

14. The refrigerant system as set forth in claim 1, wherein at least one of said evaporator fans has a variable speed drive for varying the speed of said fan.

15. The refrigerant system as set forth in claim 1, wherein at least one of said condenser fans has a variable speed drive for varying the speed of said fan.

16. The refrigerant system as set forth in claim 1, having a suction modulation valve downstream of said evaporator.

17. The refrigerant system as set forth in claim 1, wherein said scroll compressor is a single stage compressor.

18. The refrigerant system as set forth in claim 1, wherein said scroll compressor has at least two stages.

19. The refrigerant system as set forth in claim 1, wherein said control varies said speed of said scroll compressor in incremental steps.

20. The refrigerant system as set forth in claim 1, wherein said scroll compressor has at least two scroll compressor stages, said intermediate pressure port being located between said stages.

21. The refrigerant system as set forth in claim 20, wherein there are more than two scroll compressor stages, said intermediate pressure port being located between two of said stages.

22. The refrigerant system as set forth in claim 20, wherein a variable speed drive controls said two scroll compressor stages.

23. The refrigerant system as set forth in claim 20, wherein at least one of said two scroll compressor stages is free of a variable speed drive.

24. A method of operating a refrigeration system having a scroll compressor and an economizer cycle, and having a variable speed drive for the compressor;

determining an expected load of the refrigeration system, determining whether to run the economizer cycle to meet the expected load, and

varying a speed of the scroll compressor to meet a desired load; and is

The scroll compressor further having an unloader function, the unloader and the economizer providing a pattern that meets an expected load;

selectively operating the refrigeration system in a non-economized mode, an economized mode, a bypass mode, or a combined economized and bypass mode.

25. The method of claim 24, wherein said speed of said scroll compressor is varied in incremental steps.

26. The method of claim 24 further comprising a suction modulation valve, wherein the suction modulation valve is actuated to change an operating function of the refrigerant system to meet a desired load.