US20100011792A1

US20100011792A1 - Refrigerant system with pulse width modulation control in combination with expansion device control

Info

Publication number: US20100011792A1
Application number: US12/442,775
Authority: US
Inventors: Alexander Lifson; Michael F. Taras; Mark A. Lifson
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2006-11-07
Filing date: 2006-11-07
Publication date: 2010-01-21
Also published as: HK1135760A1; WO2008057079A1; CN101535741A; CN101535741B

Abstract

A refrigerant system is provided with pulse width modulation control to adjust the amount of refrigerant compressed by a compressor. In one embodiment, a pulse width modulation control controls a suction modulation valve cycled between open and closed positions. In a second embodiment, the compressor itself is cycled between a position at which it compresses refrigerant and a position at which the compression elements are disengaged. In either embodiment, the control also cycles the expansion device in concert with cycling the pulse width modulation valve or the compressor. In this manner, pressure fluctuations in the refrigerant system do not exceed desirable levels. Typical cycle time for pulse width modulation control is between 5 and 30 seconds, and typical offset (delay) time for an expansion device may be between 0 and 3 seconds.

Description

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system, wherein the capacity of the refrigerant system is adjusted by a pulse width modulation control, and a main expansion device of the refrigerant system is used to limit or eliminate refrigerant flow communication between an evaporator and a condenser when a pulse width modulation control is preventing compression of a refrigerant or blocking, at least partially, refrigerant flow from entering into a compressor.
One method that is known in the prior art to assist in the adjustment of capacity provided by a refrigerant system is the use of a pulse width modulation control. It is known in the prior art to apply a pulse width modulation control to rapidly cycle a valve between open and closed positions for controlling the flow of refrigerant through the refrigerant system to adjust capacity. Therefore, by limiting the amount of refrigerant flow passing through the system, the capacity can be reduced below a full-load capacity of the refrigerant system. There are many ways of applying pulse width modulation technique to various components to reduce refrigerant system capacity. For instance, a valve located at the compressor suction can be cycled in a pulse width modulation manner or compression elements themselves can be engaged and disengaged at a certain rate.
One challenge raised by the prior art use of pulse width modulation controls is that while this technique does provide control over refrigerant system capacity, the suction and discharge system pressures can experience undesirably large fluctuations, for instance, between the “on” and “off” positions of the pulse width modulation valve. Such pressure fluctuations are undesirable and may make it difficult to control the operation of various system components. Also, it may become harder to maintain constant parameters, such as temperature and humidity, within the environment to be conditioned. Furthermore, the overall system operation may become less efficient due to irreversible losses associated with these pressure fluctuations.
On the other hand, if the pulse width modulation valve is cycled too frequently to minimize the pressure fluctuations, there are additional cycling losses associated with a transition of certain system components from the state at which the valve is open to the state at which the valve is in a closed position. Further, the chances of valve failure increase due to the extensive cycling.
As was mentioned above, there is another known way of using pulse width modulation approach to engage and disengage the scroll compressor compression elements. This is done by rapidly changing refrigerant pressure in a scroll compressor back pressure chamber. When pressure is low in the back pressure chamber, then the scroll compressor members are allowed move out of contact with each other and there will be effectively no refrigerant compressed. On the other hand, when pressure is high in the back pressure chamber, the scroll elements are engaged with each other and provide full compression of the refrigerant flowing through the compressor. The abovementioned problem of the suction and/or discharge pressure fluctuations associated with this control may be undesirable and create problems with proper system operation.
In another control for an HVAC&R system, the pulse width modulation control can be provided for the pulse width modulation of scroll elements by separating the elements and bringing them back into contact with each other in a pulse width modulated manner where the control will monitor pressures or temperatures on the suction (low pressure) side, and adjust the pulse width modulation duty cycle accordingly. However, this disclosed control does not specifically seek to minimize fluctuations, associated conditioned space discomfort and efficiency losses, as well as it does not control a suction pulse width modulation valve, and also does not monitor conditions on the discharge (high pressure) side of the system.
It is known in the prior art to include an isolation valve between the evaporator and the condenser to block flow between the two components when it is used in conjunction with pulse width modulation of the scroll elements. In this case, the isolation valve is normally closed when the compressor is not compressing a refrigerant. This solution requires the inclusion of a separate additional isolation valve, which in combination with the requirement of the pulse width modulated compressor, increases the overall cost of the refrigerant system.

SUMMARY OF THE INVENTION

In disclosed embodiments of this invention, a compressor is provided with a pulse width modulation control. In one embodiment, a suction modulation valve is controlled in pulse width modulation manner to control the flow of refrigerant to the compressor. In a second embodiment, the pressure to a back pressure chamber of a scroll compressor is changed in a pulse width modulation manner to engage and disengage the scroll elements. With both embodiments, the expansion device positioned between the condenser and the evaporator is preferably an electronic expansion device, which can be rapidly cycled from an open position to a closed position. When the compressor is in an “off” position due to the pulse width modulation control, the expansion device is also predominantly closed. When the compressor is in an “on” position due to the pulse width modulation control, the expansion device is predominantly open. In this manner, refrigerant flow between the condenser and the evaporator is instantly interrupted. Therefore, the pressure fluctuation problem mentioned above is addressed without the requirement of having an isolation valve. Please note that, in the context of this invention, the compressor “off” position refers to a situation when the scroll elements are disengaged from each other and little or no compressor is taken place. Similarly, the “on” position refers to a situation where the compressor elements are engaged and the scroll compressor is compressing the refrigerant moving it from evaporator to condenser.
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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic refrigerant system incorporating the first embodiment of the present invention.

FIG. 2 shows a compressor, as utilized in a second embodiment of the present invention.

FIG. 2A shows a refrigerant system with the FIG. 2 compressor.

FIG. 3 is a graph showing pressure fluctuations for the prior art and the present invention system and control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A refrigerant system 20 is illustrated in FIG. 1 and includes a compressor 22 compressing a refrigerant and delivering it to a downstream heat exchanger 24. Heat exchanger 24 would act as a condenser in a cooling air conditioning mode of operation, and is an outdoor heat exchanger. While the present invention is illustrated as an air conditioning system, it should be understood that the invention would also extend to heat pumps, and other applications (e.g., refrigeration applications). Also, it has to be understood that a basic refrigerant system shown in FIG. 1 (and FIG. 2A) may have various options and features to enhance its operation and control (including vapor injection, bypass unloading, various dehumidification schemes, tandem compressors, multi-circuit arrangements, variable speed components, etc.). All these system design variations are within the scope and can equally benefit from the present invention.
An expansion device 26 is positioned downstream of the heat exchanger 24. The expansion device 26 may be an electronic expansion valve, which can be rapidly cycled between an open and closed position to control the amount of refrigerant flowing through the expansion device 26. A heat exchanger 28 is positioned downstream of the expansion device 26. The heat exchanger 28 is an indoor heat exchanger, and provides the function of an evaporator in a cooling air conditioning mode of operation. Refrigerant flowing from the heat exchanger 28 passes through a suction modulation valve 30, and back to the compressor 22. A control 32 provides a pulse width modulation control to both suction modulation valve 30 and electronic expansion valve 26. The suction modulation valve 30 is rapidly cycled between opened and closed positions to control the amount of refrigerant flowing to the compressor, when the control 32 determines that the refrigerant system 20 should operate in a reduced (part-load) capacity mode. The control logic and timing when such control would be actuated, and the detail of the control and design of the valve 30 are known in the art. What is inventive here is that the control 32 simultaneously controls the expansion valve 26 such that it is predominantly biased toward the closed position when the valve 30 is biased toward closed position. In this manner, the heat exchangers 24 and 28 may essentially have no flow communication when the mass flow of refrigerant reaching the compressor is reduced.
FIG. 2 shows another embodiment 301 wherein the compressor is a scroll compressor having a non-orbiting scroll member 304 and an orbiting scroll member 302. As known, a back pressure chamber 306 may receive a pressurized fluid from a source 308 and through a flow (e.g., solenoid) valve 310. The control 312 controls the opening and closing of the valve 310 using the pulse width modulation method. By rapidly opening and closing the valve 310 the pressure in the back pressure chamber 306 is cycled between high and low values. When the back pressure chamber is subjected to a high pressure, this pressure forces the non-orbiting scroll 304 against the orbiting scroll 302, essentially eliminating any leak bypass of compressed refrigerant through the compression elements. Thus, refrigerant is compressed in the compressor and delivered throughout the system. When the valve 310 blocks flow of high pressure refrigerant to the back pressure chamber 306, the lower force in the back pressure chamber 306 allows the scroll elements 304 and 302 to move away from each other, creating a significant gap between the orbiting scroll 302 and non-orbiting scroll 304, resulting in minimal or no refrigerant compression in the compressor 301. This structure is shown schematically, and is generally known in the art. Many of the variations of this concept (including a pulse width modulation technique applied to different compressor types) are known in the art and are within the scope of the present invention. The control 312 also communicates with the expansion device 26 in this embodiment in a manner similar to the FIG. 1 embodiment, and as shown in the circuit 120 in FIG. 2A.
By controlling the expansion device 26, in conjunction with the suction modulation valve 30 of the FIG. 1 embodiment or with the valve 310 of the FIG. 2 embodiment, the potential excessive pressure fluctuation problem, present in the prior art can be controlled and eliminated. FIG. 3 shows P_condand P_evap, as the fluctuating pressures in the condenser and evaporator accordingly without the pulse width modulation control of the expansion device 26. Further, the P′_condand P′_evapare the pressures in the condenser and evaporator accordingly, showing significant reduction in magnitude of pulsations, with the pulse width modulation control of the expansion device 26 provided by the present invention.
As stated above, the electronic expansion device 26 is cycled in a pulse width modulation manner between essentially open and closed positions, in synchronized relation with the opening and closing of the suction modulation valve 30 or valve 310, to reduce pressure fluctuations throughout the system and consequently improve operational efficiency and an occupant's comfort in the conditioned space. It should be noted that the open and closed positions for the expansion device 26 are not necessarily correspond to fully open and fully closed positions. For instance, a partially closed position for the electronic expansion device 26 may serve the purpose of reducing pressure fluctuations to an acceptable level. Furthermore, synchronization of the operation for the flow control devices 26 and 30 (or 310) is valuable, although it may be beneficial to slightly delay closing of the electronic expansion device 26 to allow some refrigerant flow generated by flow inertia to pass to a low pressure side of the refrigerant system. For the same reason, the cycle time interval for the expansion device 26 may be slightly different than for the flow control devices 30 or 310. In general, a typical cycle time for the flow control devices 26 and 30 (or 310) may range from 5 seconds to 30 seconds. A typical delay time may be on the order of 2-3 seconds and would largely depend on a refrigerant system size (or internal volume).
It should also be noted that the open and closed position of the suction modulation valve 30 (or the valve 310) may not necessarily correspond to the maximum possible opening or the minimum possible closure of this valve. The pressure fluctuations can be especially important on the high side of the refrigerant system (a condenser portion of the refrigerant system), where the refrigerant is at a higher pressure, than on the lower side, and thus the magnitude of the pressure fluctuations on the high side is normally higher then the magnitude of the pressure fluctuations on the low side (an evaporator portion of the refrigerant system). As known, pressure fluctuations can be detrimental in obtaining desired temperature and/or humidity control within the conditioned environment and need to be reduced to the acceptable level. The desired temperature and/or humidity control within the conditioned environment is achieved by reducing the pressure fluctuations as described above. Another potential problem associated with the pressure fluctuations in the refrigerant system is that these pressure fluctuations introduce unwanted, and sometimes excessive, vibrations of various system components, often leading to the failure of these components. A high vibration level can also generate undesirable noise. In this case, a reduction in the vibration level can be achieved by coupling feedback obtained from the operation of the valve 30 (or 310) and the electronic expansion valve 26. The feedback control can establish the most appropriate operation of these components relying on the input from a vibration sensor 44. This vibration sensor 44 can be installed at certain specific locations in the refrigerant system. As an example, the sensor 44 can be installed on the discharge line 42, and the electric signal of this sensor corresponding to the vibration level can be communicated to the control 32 (or 312).
Thus, the present invention without the requirement of any additional flow control devices, or other extra hardware, addresses the abovementioned problem of excessive pressure fluctuations on the high and low pressure sides of the refrigerant system.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill 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

1. A refrigerant system comprising:

a compressor for compressing a refrigerant and delivering the refrigerant to a first heat exchanger, refrigerant passing from said first heat exchanger through an expansion device, into a second heat exchanger, refrigerant passing from said second heat exchanger back to said compressor; and

a pulse width modulation control for rapidly modulating the flow of refrigerant from the compressor between high and low flow positions, said control also using pulse width modulation for moving said expansion device predominantly toward a closed position when the compressor is in said low flow position and moving said expansion device predominantly toward an open position when the compressor is in said high flow position.

2. The refrigerant system as set forth in claim 1, wherein said expansion device is an electronically controlled expansion device.

3. The refrigerant system as set forth in claim 1, wherein a suction modulation valve is positioned between said second heat exchanger and said compressor, and said suction modulation valve being controlled to rapidly open and close to adjust the flow of refrigerant to said compressor between the high and low flow positions.

4. The refrigerant system as set forth in claim 1, wherein said compressor being a scroll compressor, and having a back pressure chamber, which is rapidly cycled between high and low pressure conditions to move said compressor between the high and low flow positions.

5. The refrigerant system as set forth in claim 1, wherein said expansion device is moved to a fully closed position when the compressor is in said low flow position.

6. The refrigerant system as set forth in claim 1, wherein a pulse width modulation cycle time is between 2 and 30 seconds.

7. The refrigerant system as set forth in claim 1, wherein an expansion device time in said closed position is different from a compressor time in said low flow position.

8. The refrigerant system as set forth in claim 7, wherein said time difference is between 1 and 3 seconds.

9. The refrigerant system as set forth in claim 1, wherein the expansion device cycle is delayed with respect to the compressor cycle.

10. The refrigerant system as set forth in claim 9, wherein said delay is between 1 and 3 seconds.

11. The refrigerant system as set forth in claim 1, wherein vibration on at least one component in the refrigerant system is monitored, and the monitored vibration being utilized to adjust at least one operational parameter of at least one of the pulse width modulated expansion device and the pulse width modulated refrigerant flow from the compressor.

12. The refrigerant system as set forth in claim 1, wherein pressure fluctuation control is provided to tightly maintain at least one of temperature and humidity in an environment to be conditioned.

13. The refrigerant system as set forth in claim 1, wherein the pulse width modulation of the expansion device and the pulse width modulation of the refrigerant flow from the compressor are provided to control and limit pressure fluctuations within said first heat exchanger, within said second heat exchanger or within both said first and said second heat exchangers.

14.-25. (canceled)

26. A refrigerant system comprising:

a pulse width modulation control for a suction modulation valve positioned between said second heat exchanger and said compressor, and said suction modulation valve being rapidly modulated between open and close positions to adjust the flow of refrigerant to the compressor and said control also using pulse width modulation to move said expansion device predominantly toward a closed position when the suction modulation valve is moved toward a closed position and to move said expansion device predominantly toward an open position when the suction modulation valve is moved toward an open position.

27. A refrigerant system comprising:

a compressor for compressing a refrigerant and delivering the refrigerant to a first heat exchanger, refrigerant passing from said first heat exchanger through an expansion device, into a second heat exchanger, refrigerant passing from said second heat exchanger back to said compressor, and

said compressor being a scroll compressor, and having a back pressure chamber, which is rapidly cycled by a control using pulse width modulation, to move between high and low pressure conditions to move said compressor between high and low flow positions and said expansion device also being controlled by pulse width modulation and being moved predominantly toward a closed position when said compressor is in said low flow position and being moved predominantly toward an open position when said compressor is in said high flow position.