HK1138351B - Pulse width modulation with discharge to suction bypass - Google Patents

Description

Pulse width modulation with exhaust to intake bypass

Technical Field

The present application relates to a control for a refrigerant system that utilizes pulse width modulation techniques to improve the control of the refrigerant system by combining a discharge bypass with pulse width modulation to reduce the power consumption of the compressor.

Background

Refrigerant systems are used in many applications to condition a climate controlled environment. In particular, air conditioners and heat pumps are used to cool and/or heat air entering a climate controlled environment. Ambient conditions, degrees of use, changes in sensible latent load demands, and when an occupant of the environment adjusts temperature and/or humidity set points, may cause changes in the ambient cooling or heating load.

Various features are known for adjusting the capacity of a refrigerant system. One method that has been used in the art to reduce refrigerant system capacity is to use pulse width modulation techniques to control a fast-acting solenoid valve on the compressor suction line. Additional and precise capacity control is provided by rapidly cycling the valve using pulse width modulation techniques.

The goal of pulse width modulation control is to effectively compress the refrigerant with a reduced mass flow rate. This is done when the heat load demand of the refrigerant system is lower than that provided by a full capacity compressor.

However, this technique does not always achieve the desired efficiency improvement goal because even though the suction pressure is significantly reduced when the suction valve is closed (or nearly closed), the discharge pressure is still high, resulting in a compressor power consumption higher than desired. In addition, the compressed refrigerant on the discharge side may flow back into the compression pockets, which further increases compressor power consumption due to recompression of the returning refrigerant. This problem is particularly acute in compressors that are not equipped with a dynamic discharge valve, as is often the case for compressors used in standard air conditioning applications. The lack of a dynamic discharge valve causes the compressed refrigerant at the discharge pressure to flow back into the compression chambers of the compressor, thereby contributing to increased power consumption. However, the problem also exists in compressors having dynamic discharge valves where the refrigerant still needs to be compressed to a discharge pressure. Refrigeration type compressors are generally examples of compressors that use dynamic discharge valves.

Disclosure of Invention

In a disclosed embodiment of the invention, a compressor is associated with a refrigerant system. The refrigerant system has a valve that is capable of rapid cycling. The valve is mounted on the suction line and provides a pulse width modulation control for the suction valve. The pulse width modulation control is operable to rapidly cycle the valve from an open position to a closed position to vary the capacity of the refrigerant system by controlling the amount of refrigerant delivered to the compressor.

Providing a bypass line connecting the compressor discharge side to the suction side; the bypass line also includes a bypass valve. When the pulse width modulation control moves the suction valve to a closed position, the bypass valve is opened. In this manner, the compressed refrigerant is returned to the suction line of the compressor. In the disclosed embodiment, a bypass line returns refrigerant to a location downstream of the suction valve. Since the compressor discharge is now directly connected to the suction line, the refrigerant is not compressed to a high pressure and the compressor power consumption is greatly reduced.

Although the present invention is described with respect to a refrigerant system incorporating a scroll compressor for illustrative purposes, the present invention is equally applicable to other types of compressors.

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. 1 is a schematic diagram of a refrigerant system incorporating the present invention.

Figure 2 shows a pressure versus volume graph for a compressor.

Detailed Description

The refrigerant system 19 shown in fig. 1 has a scroll compressor 21 which includes a non-orbiting scroll member 22 and an orbiting scroll member 24. As is known, shaft 26 is driven by a motor 28 to rotate orbiting scroll member 24. It is also known that the oil sump 32 and the oil passage 34 in the shaft 26 supply oil to various moving elements in 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. It is also known for the compressor 21 to be driven by a motor 28 to compress refrigerant and drive the refrigerant through the entire refrigerant system 19.

The controller 30 may be a microprocessor or other type of controller that provides pulse width modulation control to the suction modulation valve 210 on the suction line 212. It should be understood that the controller 30 includes a routine that accepts inputs from various locations within the refrigerant system and determines when pulse width modulation of the suction modulation valve 210 needs to be initiated. Controllers for carrying out the invention with such suction modulation valves are known in the art. The valve itself may be a solenoid valve, which is also known.

Now, when the control 30 determines that it is desired to reduce the capacity of the refrigerant system 19, the suction modulation valve 210 is rapidly cycled from an open position to a closed position (the cycle rate is typically in the range of 3-30 seconds) using a pulse width modulation control. For this pulse width modulation cycle, the closed position of the suction modulation valve 210 need not be a fully closed position, and the open position of the suction modulation valve 210 need not be a fully open position.

As is known, the compressor housing is sealed such that when the compressor is in operation, suction pressure is generated in chamber 121 and discharge pressure is generated in chamber 123 after refrigerant is compressed by rotational movement of one of the scroll members 22 and 24 relative to the other.

As shown, the exhaust valve 200 is disposed in the exhaust pipe 202 (the valve may also be disposed in an exhaust line 206, the exhaust line 206 connecting the exhaust pipe 202 to the condenser 36). The exhaust valve 200 may be a solenoid valve or may be a mechanical check valve. In the illustrated embodiment, the exhaust valve 200 is a solenoid valve controlled by the controller 30. Notably, when the compressor is not operating in the pulse width modulation mode, this valve is normally open so that refrigerant can flow relatively unimpeded through the discharge tube 202 to the condenser 36. The bypass line 204 selectively bypasses refrigerant from the discharge tube 202 (or discharge line 206, or discharge pressure chamber 123) back to the suction chamber 121. A bypass valve 216 is disposed on the bypass line 204. The bypass valve 216 typically needs to be opened within a time interval of 0 to 0.2 seconds of (before or after) the pulse width modulation valve 210 being closed.

When the controller moves the suction valve 210 to the closed position, the discharge valve 200 is also closed and the bypass valve 216 is opened. In this manner, refrigerant is returned from the discharge chamber 123 to the suction chamber 121. At the same time, the closed discharge valve 200 prevents refrigerant from flowing back into the discharge chamber 123 from the discharge line 206. Therefore, the pressure in the exhaust chamber 123 can be maintained at the same or almost the same low pressure as the pressure in the suction chamber 121. This reduces the power consumption of the compressor motor 28 because the refrigerant no longer needs to be compressed to a pressure corresponding to the high pressure in the condenser 36. The exhaust valve 200 typically needs to be opened within a time interval of 0 to 0.2 seconds after (before or after) the pulse width modulated valve 210 is closed. If the exhaust valve 200 is a solenoid valve, it may typically close within a time interval of 0 to 0.2 seconds of the valve 210 closing. If the vent valve 200 is, for example, a mechanical check valve, it will automatically close because refrigerant from the condenser 36 will begin to enter the cavity 123, thereby closing the vent valve 200.

Fig. 2 shows a so-called PV diagram, which represents the compression process in the compressor 21. In the figure, P is the varying pressure within the scroll member of the compressor 21 and V is the varying compression volume within the scroll member. The area covered by the PV diagram represents the power consumed by the compressor 21. As shown in fig. 2, the cross-hatched Area (ABC) represents the power consumed by the compressor 21 incorporating the present invention when the pulse width modulation valve 210 is in the closed position and with the bypass arrangement of the present invention. The non-cross-hatched area (DEFG) represents the power consumed by the compressor 21 without the bypass line of the present invention when the pulse width modulation valve 210 is closed. It can be seen that the present invention can save a lot of energy, as shown by comparing the above two regions in fig. 2. It should be understood that the graph is an illustration and that the actual results will vary for any given compressor and operating conditions. Also as shown in FIG. 2, point G represents the pressure within the compressor suction chamber 121 without the bypass arrangement of the present invention when the suction modulation valve 210 is in the closed position. It is well known that for compressors with hermetic motors, this pressure needs to be maintained above a certain threshold (if the pressure decreases below a certain value, the so-called "corona discharge" effect can damage the motor terminal pins, which occur under near vacuum conditions of the compressor suction chamber 121). Typically, this pressure is maintained at a level of about 1 psia. Without the bypass arrangement, the pressure in the exhaust chamber 123 would be the exhaust pressure indicated at point F.

When a bypass arrangement is used, this pressure will be released to a pressure close to the suction pressure, as shown at point C. Since in the arrangement of the invention the discharge pressure is reduced from F to C, the motor can reduce the power consumption since the amount of work required to compress the refrigerant is reduced. Further, it should also be noted that with the bypass arrangement of the present invention, the suction pressure will increase slightly from the pressure indicated by point G to the pressure indicated by point C. This occurs because some of the refrigerant trapped on the discharge side re-expands back into the suction chamber 121, causing the pressure in the suction chamber 121 to rise above the pressure indicated by point G, which is the pressure level in the prior art pulse width modulation arrangement.

It should be understood that while the present invention is described with respect to a refrigerant system incorporating a scroll compressor, the present invention is applicable to a variety of compressor types including screw compressors, reciprocating compressors, rotary compressors, and the like. The present invention is also applicable to different refrigerant systems including residential air conditioning applications, container and truck trailer applications, heat pump applications, supermarket applications, rooftop applications, and the like. The refrigerant system may also include additional features such as an economizer circuit that employs a compressor with a vapor injection line. The compressor may also have a bypass line that bypasses refrigerant from an intermediate compression point to suction. If an intermediate point to suction line bypass line is employed, a connection between the discharge bypass and compressor suction described in this application may also be established via the intermediate point to suction bypass line. Of course, the present invention is also applicable to various types of refrigerants, such as R410A, R134a, R22, R407C, R744, and the like.

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 (16)

1. A refrigerant system comprising:

a compressor that compresses a refrigerant to a discharge pressure, and a motor that drives the compressor, the compressor being housed in a casing;

a condenser, an expansion device and an evaporator, the condenser being downstream of the compressor, the expansion device being downstream of the condenser, and the evaporator being downstream of the expansion device;

a suction valve located on a suction line leading from the evaporator into the compressor housing;

a controller that cycles the suction valve between an open position and a closed position using pulse width modulation, the suction valve in the closed position preventing refrigerant flow through the suction line; and

a bypass line selectively bypassing refrigerant compressed to a discharge pressure by the compressor to a location downstream of the suction valve, the bypass line including a bypass valve controlled by the controller, the bypass valve being open when the controller closes the suction valve.

2. The refrigerant system as set forth in claim 1, wherein: the compressor is selected from the group consisting of a rotary compressor and a reciprocating compressor.

3. The refrigerant system as set forth in claim 2, wherein: the compressor is selected from the group consisting of scroll compressors and screw compressors.

4. The refrigerant system as set forth in claim 1, wherein: a discharge valve is also arranged on the discharge side of the compressor, downstream of the bypass line.

5. The refrigerant system as set forth in claim 4, wherein: when the suction valve is controlled to be closed, the exhaust valve is closed, and the bypass valve is controlled to be opened.

6. The refrigerant system as set forth in claim 5, wherein: closing the exhaust valve within a time interval of between 0 and 0.2 seconds of the closing of the suction valve.

7. The refrigerant system as set forth in claim 5, wherein: opening the bypass valve in a time interval between 0 and 0.2 seconds of the suction valve closing.

8. The refrigerant system as set forth in claim 1, wherein: the bypass line returns refrigerant to the suction line at a location downstream of the suction valve.

9. The refrigerant system as set forth in claim 1, wherein: opening the bypass valve in a time interval between 0 and 0.2 seconds of the suction valve closing.

10. A method of operating a refrigerant system comprising the steps of:

(1) providing a compressor for compressing a refrigerant to a discharge pressure and a motor for driving the compressor, the compressor being housed within a housing;

(2) providing a condenser downstream of the compressor, an expansion device downstream of the condenser, and an evaporator downstream of the expansion device;

(3) providing a suction valve on a suction line leading from the evaporator into the compressor shell;

(4) providing a controller cycling said suction valve between an open position and a closed position using pulse width modulation, said suction valve in the closed position preventing refrigerant flow through the suction line; and

(5) selectively bypassing refrigerant compressed to a discharge pressure by the compressor to a location downstream of the suction valve through a bypass line, the bypass line including a bypass valve controlled by the controller, the bypass valve being open when the controller closes the suction valve.

11. The method of claim 10, wherein: a discharge valve is also arranged on the discharge side of the compressor, downstream of the bypass line.

12. The method of claim 11, wherein: when the suction valve is controlled to be closed, the exhaust valve is closed, and the bypass valve is controlled to be opened.

13. The method of claim 12, wherein: closing the exhaust valve within a time interval of between 0 and 0.2 seconds of the closing of the suction valve.

14. The method of claim 12, wherein: opening the bypass valve in a time interval between 0 and 0.2 seconds of the suction valve closing.

15. The method of claim 10, wherein: the bypass line returns refrigerant to the suction line at a location downstream of the suction valve.

16. The method of claim 10, wherein: opening the bypass valve in a time interval between 0 and 0.2 seconds of the suction valve closing.