Refrigerant system with pulse width modulated components and variable speed compressorTechnical Field
The present invention relates to a control for a refrigerant system having a variable speed compressor wherein pulse width modulation techniques are utilized to provide further control of the overall system.
Background
Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are used to cool and/or heat air entering an environment. The cooling or heating load of the environment may vary as the environmental conditions, occupancy level, other sensible and latent load demands change, and as the temperature and/or humidity set points are adjusted by the occupants of the environment.
A known solution for improving the efficiency of refrigeration systems is to drive the compressor motor at a variable speed. Typically, the compressor does not have to run at full speed, for example, when the cooling load on the refrigeration system is relatively low. In such a case, it may be desirable to reduce the compressor speed, thereby reducing the overall energy consumption of the refrigeration system. The use of variable speed drives is one of the most effective techniques to improve system performance and reduce life cycle costs of equipment in a wide range of operating environments and potential applications, particularly under part load conditions.
However, in view of the reliability requirements, a lower limit has to be set for an ideal compressor deceleration. For example, problems may arise at low operating speeds if the lubrication of the compressor elements is insufficient. In addition, certain types of compressors require a minimum operating speed to provide radial flexibility. For example, if a scroll compressor is operating below a minimum speed, the scroll compressor may have a significant performance penalty due to the loss of radial flexibility.
In addition to using a method of reducing the speed of the compressor, various other schemes are known for providing a change in system capacity. For example, an economizer cycle is known as an unloader cycle. However, even if these cycles are provided in a system having a variable speed drive for the compressor, it is desirable to provide greater variability in system capacity.
Another method that has been used in the prior art to vary the capacity of a refrigerant system is to use pulse width modulation to control valves, such as a block valve on the economizer cycle, and/or a block valve on the unloader line, and/or a block valve on the suction line. Additional capacity control is provided by rapidly cycling the valves using pulse width modulation techniques. Pulse width modulation of the inner scroll member may also be applied in conjunction with variable speed drive operation. In this case, the scroll elements are separated from each other in a pulse width manner, as is known in the art, to control the amount of refrigerant pumped by the compressor. However, these pulse width modulation techniques, which control valves or internal scroll compression elements, have not been used in refrigerant systems having variable speed driven compressors.
Disclosure of Invention
In a disclosed embodiment of the invention, a compressor is provided with a variable speed drive. Upon detection of a demand for low capacity, the compressor is turned to a low speed to maintain proper conditions in the environment without switching to a start-stop mode of operation. The compressor is incorporated into a refrigerant system having a pulse width modulation control for cyclically operating some of the components within the system in addition to cyclically starting and stopping the compressor motor. In the disclosed embodiment, the component being cycled is a valve and may be a suction valve, and/or an economizer cycle shut-off valve and/or an unloader valve, and/or the component being cycled is one of the scroll compressor suction elements. By cycling these components on and off, the amount of refrigerant delivered to various locations within the refrigeration cycle is reduced, thereby allowing capacity reduction without reducing the compressor motor speed beyond safety conditions.
Although the operation of the valve of the present invention is described below for illustrative purposes in terms of a refrigeration system including a scroll compressor, such operation may be used with any variable speed compressor.
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 is a schematic view of a refrigeration system incorporating the present invention;
FIG. 1B shows an alternative embodiment;
figure 2 shows another schematic diagram of a refrigeration system.
Detailed Description
In fig. 1, a refrigeration system 19 is shown having a scroll compressor 21, the scroll compressor 21 including a fixed scroll member 22 and an orbiting scroll member 24. As is known, the shaft 26 is driven by an electric motor 28 to cause the orbiting scroll member 24 to orbit. As shown, a variable speed drive 30 is schematically connected to drive the electric motor 28. As is known, an oil sump 32 and oil passages 34 in the shaft 26 supply oil to various moving elements within the compressor 21.
As is known, the condenser 36 is located downstream of the compressor 21, the expansion device 38 is located downstream of the condenser 36, and the evaporator 40 is located downstream of the expansion device 38. As is also known, the compressor 21 is driven by an electric motor 28 to compress and drive refrigerant vapor through the refrigeration system 19. Oil from the oil sump 32 is delivered to the compressor elements to provide proper lubrication of the compressor components, such as the crankcase bearing 100, orbiting scroll bearing 102, fixed scroll member 22, and orbiting scroll member 24, while some amount of oil will exit the compressor 21 with the refrigerant circulating through the refrigeration system 19. One of the most typical oil delivery systems for scroll compressors is also shown in FIG. 1, wherein oil from the oil sump 32 is picked up by the oil pickup tube 110 and delivered along the oil path 34 to the various compressor components as described above. Some of the oil can also be carried through the suction port 120 by the refrigerant entering the compressor. However, most of the oil transportation work is performed by transporting oil from the oil tank as described above. In the prior art, when a variable speed drive has been used in a refrigeration system, the designer is limited by the minimum operating speed of the shaft 26 of the compressor 21. If the speed falls below a certain level for a longer period of time, insufficient oil will be delivered through the oil circuit to the compressor components requiring lubrication. Thus, for low cooling load situations where only a small amount of compressed refrigerant mass flow needs to be circulated through the system, the minimum speed requirement (e.g., 45Hz) is often the limiting factor in ensuring that a sufficient amount of oil is provided to the compressor components. In addition, operation above the minimum speed also ensures that the radial flexibility required for efficient operation of the scroll compressor is not lost due to excessively low motor speeds. As is known, it is important to match the delivery capacity to the system load. Since compressor operating speeds often cannot be reduced below a certain threshold for capacity shedding, additional efficient means are needed to reduce the capacity delivered by the equipment without cycling the equipment on and off for cumbersome temperature control in a cooled environment. The following description provides additional means for effectively shedding capacity by combining variable speed operation of the compressor with pulse width modulation of the various system components.
Fig. 1 illustrates additional features that may be incorporated into the refrigeration system 19. For example, an economizer cycle is included and has an economizer heat exchanger 18. The main liquid line 13 has a tap line 11, the tap line 11 being tapped from the main liquid line and passed through an economizer expansion device 115. Both the tap line 11 and the main liquid line 13 pass through an economizer heat exchanger 18. In practice, in fact, the refrigerant flow in the tap line passes through the economizer heat exchanger in a generally countercurrent direction relative to the flow in the main liquid line 13. However, to simplify the illustration in this figure, the fluid in both lines is shown in the same direction. As is known, the economizer circuit subcools the refrigerant in the main liquid line, thereby enhancing the performance (capacity and/or efficiency) of the refrigeration system 19. The economizer injection line 20 is shown extending back to the compressor 21 and injecting refrigerant at an intermediate pressure into the compression chambers through passages, such as passage 23. The function and configuration of the economizer circuit is known, however, the economizer circuit including the motor controller 30 of the present invention provides greater flexibility to the refrigeration system to enhance operation of the refrigeration system 19.
The optional unloader line 17 includes an unloader valve 200. The unloader valve 200 is selectively opened to return partially compressed refrigerant from the compression chambers to the suction port 120 of the compressor 21 through the passage 23. The unloader function provides the refrigerant system designer with additional freedom to adjust and optimize performance. As is known, the unloader valve may be disposed inside or outside of the compressor.
Essentially, when more system capacity is required, the economizer function can be utilized by shutting off the unloader valve. Alternatively, if a lower capacity is desired, the economizer expansion device 115 (or a separate shut-off device) is turned off while the unloader valve 200 is opened. In this way, the amount of compressed refrigerant delivered to the condenser 36 is reduced. Also, if it is desired to provide another intermediate capacity level for the refrigeration system 19, the economizer function may be combined with the unloader function by opening the economizer expansion device 115 and the unloader valve 200. Another optional intermediate stage of capacity unloading can also be achieved by shutting off flow in the economizer injection line and closing the unloader valve 200.
These system configurations in combination with the variable speed motor controller disclosed below provide greater freedom and flexibility for refrigerant system designers to control delivered system capacity.
In this case, the controller 30 may not only include a variable speed drive, but may also be a microprocessor or other type of controller capable of providing pulse width modulation control for the economizer valve 115 (which in this case may be a stop valve), and/or the unloader valve 200, and/or the suction modulation valve 210.
As is also known in the art, pulse width modulation may also be used to pulse width modulate the scroll compression elements themselves, in which case the scroll elements will be separated from each other in a pulse width manner to control the amount of refrigerant pumped by the compressor.
Fig. 1B schematically shows an embodiment 301. It is known that orbiting scroll member 302 and fixed scroll member 304 may be biased together by gas within a chamber 306. By activating and closing the valve 310, the pressure within the chamber 306 can be controlled. As shown, the valve 310 is in communication via line 308 with another pressure source at a different pressure than the pressure within the chamber 306 when the valve 310 is closed. When the pressure within the chamber 306 decreases below a certain level, the scroll members separate from each other and the amount of refrigerant drawn by the compressor decreases. When the pressure in the chamber 306 increases above a certain level, the scroll members will contact each other, thus resuming the normal compression process. The valve may be controlled by a pulse width modulation controller 312. Thus, by regulating the pressure within the chamber 306, the two scroll members 302 and 304 may be allowed to periodically separate from and contact each other. It should be noted that the schematic shown in FIG. 1B is shown for illustrative purposes only. For example, instead of allowing the scroll member 304 to move axially into and out of contact with the scroll member 302, the scroll member 302 may be allowed to move axially while the scroll member 304 remains substantially stationary in the axial direction. The valve 310 may be located inside or outside the compressor.
While the schematic shows the controller providing pulse width modulation control for each of these valves and/or compressor elements, in other embodiments, a combination of these valves and/or compressors, or even other valves, may be utilized. By rapidly cycling these valves to the on and off positions (the shut off may be a partial or full shut off), the amount of refrigerant passing through either of the valves and the compressor can be varied to vary capacity. For example, once the compressor speed has been reduced, but additional capacity reduction is required, the valves or compressors may be cycled to further reduce system capacity. It should be noted that the compressor speed reduction will generally be implemented first to trim the capacity, as this is the most efficient means of trimming the capacity compared to other unloading methods.
The present invention provides an efficient means to effectively and accurately control the capacity of the refrigerant system 19 through various pulse width modulation methods using various system components that incorporate the use of a variable speed drive motor. The motor drive may vary in speed when capacity modulation is required. The economizer circuit can also be opened or closed to vary capacity. An unloader function may also be utilized. In addition, in combination with the above options for this control, the present invention also allows the controller to regulate refrigerant flow through any of the valves 115, 200, and 210 and/or adjustments to the compressor suction element itself. In this way, capacity may be further reduced without excessively reducing the speed of the compressor electric motor 28 beyond its safe threshold of operation.
Fig. 2 shows another embodiment 300 in which the valves 200 and 210 are in the flow path inside the compressor shell. It should be noted that although in fig. 2, the valves are all shown inside the compressor, the compressor designer may choose to place some of the valves inside and some of the valves outside. Additionally, the shut-off valve 220 of the economizer line is shown separate from the expansion valve. If the shut-off valve 220 is located externally, its function may be combined with the use of an expansion valve. Although the valves are shown as separate components, the functions of the valves may be combined into a single three-way valve as is known in the art. Each or some of the valves 220, 200, and 210 may be controlled by pulse width modulation techniques.
It should be understood that the motor controller 30 includes a program that takes input information from various locations within the refrigerant system and determines when a lower speed of the compressor motor is required and when pulse width modulation of the pulse width modulated components needs to be activated. The controller can also determine when the system needs to operate in an economy mode, a non-economy mode, a bypass dump mode, or any combination of the above. Controllers capable of implementing the present invention by such valves and compressors are known.
One of ordinary skill in the art will recognize when a lower speed is desirable and preferred over, or in addition to, other available options.
It should be understood that although the present invention is described with reference to a refrigeration system including a scroll compressor, the present invention may be used with any variable speed compressor, including scroll compressors, screw compressors, reciprocating compressors, rotary compressors, and the like. This technology is useful, for example, in refrigeration systems used in transport container units, truck/trailer applications, supermarket refrigeration applications, and in factory building and residential home cooling or heating applications, as well as in water heating applications. 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.
The claims (modification according to treaty clause 19)
1. A refrigeration system comprising:
a compressor and an electric motor for driving the compressor, a variable speed drive for varying an operating speed of the electric motor;
a condenser downstream of the compressor, an expansion device downstream of the condenser, and an evaporator downstream of the expansion device;
the variable speed drive turns the electric motor to a low speed operation and the variable speed drive operates the electric motor at a low speed level; and
a pulse width modulation controller for controlling at least one system component, the at least one system component being a component other than the electric motor.
2. The refrigeration system of claim 1, wherein: the pulse width modulation controller controls at least one valve.
3. The refrigeration system of claim 2, wherein: an economizer circuit is included in the refrigeration system.
4. The refrigeration system of claim 3, wherein: the at least one system component is a block valve associated with the economizer circuit.
5. The refrigeration system of claim 2, wherein: the compressor is provided with an unloader circuit.
6. The refrigeration system of claim 5, wherein: the at least one system component is a valve associated with the unloader circuit.
7. The refrigeration system of claim 2, wherein: a refrigeration system is provided with an economizer circuit and an unloader circuit.
8. The refrigeration system of claim 7, wherein: the at least one system component includes a valve associated with the economizer circuit and a valve associated with the unloader circuit.
9. The refrigeration system of claim 2, wherein: the at least one system component is a valve for controlling a mass flow of refrigerant delivered from the evaporator to the compressor.
10. The refrigeration system of claim 1, wherein: the at least one system component is external to a shell of the compressor.
11. The refrigeration system of claim 1, wherein: the at least one system component is internal to a shell of the compressor.
12. The refrigeration system of claim 1, wherein: the compressor is selected from the group consisting of scroll compressors, rotary compressors, reciprocating compressors, and screw compressors.
13. The refrigeration system of claim 1, wherein: the at least one system component is a pulse width modulated controller for holding the orbiting and non-orbiting scroll members together or allowing the orbiting and non-orbiting scroll members to be separated from each other within the scroll compressor.
14. The refrigeration system of claim 1, wherein: the refrigeration system is selected from the group consisting of a container refrigeration system, a truck/trailer system, a supermarket refrigeration system, a residential air conditioning system, a residential heat pump system, a commercial air conditioning system, a commercial heat pump system, and a water heating system.
15. A method of operating a refrigeration system comprising the steps of:
(1) providing a compressor having a variable speed drive and monitoring a load of a refrigeration system associated with the compressor;
(2) determining a low load condition and shifting said compressor to low speed operation when a low load condition has been determined; and
(3) pulse width modulation control is provided for other system components, other than those associated with the variable speed drive, to allow for variation in capacity from the refrigeration system by varying the speed of the compressor and varying the operation of the other components.
16. The method of claim 15, wherein: the pulse width modulation control controls at least one valve.
17. The method of claim 16, wherein: an economizer circuit is included in the refrigeration system and the at least one system component is a block valve associated with the economizer circuit.
18. The method of claim 16, wherein: the compressor is provided with an unloader circuit and the at least one system component is a valve associated with the unloader circuit.
19. The method of claim 16, wherein: a refrigeration system is provided with an economizer circuit and an unloader circuit, and the at least one system component includes a valve associated with the economizer circuit and a valve associated with the unloader circuit.
20. The method of claim 15, wherein: the at least one system component is external to a shell of the compressor.
21. The method of claim 15, wherein: the at least one system component is internal to a shell of the compressor.
22. The method of claim 15, wherein: the other system component is a valve for controlling the amount of refrigerant delivered from the evaporator to the compressor.
23. The method of claim 15, wherein: the at least one system component is a pulse width modulated controller for holding the orbiting and non-orbiting scroll members together or allowing the orbiting and non-orbiting scroll members to be separated from each other within the scroll compressor.