HK1128045A - Refrigerant system unloading by-pass into evaporator inlet - Google Patents

Description

Refrigerant system unload bypass into evaporator inlet

Technical Field

The present invention relates to a unique arrangement for the connection between the unloader line valve and the low pressure refrigerant line.

Background

One type of compressor particularly suited for use with the present invention is a scroll compressor. Scroll compressors are increasingly being used in the compressor field. However, scroll compressors present some design challenges. One particular design challenge is how to achieve reduced load levels when full load operation is not required.

Thus, scroll compressors, as an example, are provided with a bypass unloader valve to return a portion of the compressed refrigerant to the compressor suction port. In this way, the amount of refrigerant compressed by the compressor can be reduced. Of course, other types of compressors may have a bypass valve for similar purposes, for example, a bypass valve in a screw compressor can bypass a portion of refrigerant from an intermediate compression chamber within the screw compressor back to the suction line.

In the system disclosed in us patent 5996364, the refrigerant system has a bypass line and an economizer circuit. A bypass line communicates the vapor directly from the economizer line to the suction line. The bypass line is provided with an unloader valve. When an unloading operation is desired, the unloading valve is opened and the economizer valve is closed. So that the refrigerant is returned directly from an intermediate point in the compression process to the suction portion.

Us patent 6883341 discloses an improvement to the above system in which the location where the economizer line is returned to connect with the main low pressure refrigerant line is not between the evaporator and the compressor, but upstream of the evaporator. Many beneficial effects can be achieved by this arrangement. These are all disclosed in U.S. patent 6883341, invented by the inventors of the present application and owned by the assignee of the present application. However, this application is limited to situations where the economizer circuit is also incorporated into the system. But also to the case where there is only a single bypass valve in the system. The present invention relates to a compressor wherein the unloader line is decoupled from the economizer circuit. The invention also discloses a method of operation in which there may be a plurality of unloader lines. In addition to the bypass line being either fully open or fully closed for an extended period of time, the present invention also discloses a bypass valve that can be operated in a pulse width modulation fashion: rapidly opened and closed to control the amount of refrigerant bypassing the evaporator at a location upstream thereof. The proportion of time that the valve is open determines the degree of bypass modulation achieved. The cycling rate of the pulse width modulation valve is selected to be shorter than the response time of the system. In this case, the system does not respond quickly to changes in refrigerant flow through the unloader line, creating a situation where the system responds as if the valve is partially opened rather than cycling between its open and closed positions.

While this prior art system has achieved many beneficial results, certain additional improvements would still be advantageous.

Disclosure of Invention

In a disclosed embodiment of the invention, the compressor is provided with at least one bypass line. An unloader valve is disposed on the bypass line and is operable to selectively communicate refrigerant from a compression location to a location upstream of the evaporator. The unloader line is connected to a point at an intermediate point in the compression process.

The present invention provides a number of advantages over the prior art in which refrigerant is returned directly to the suction line from an intermediate compression location. In the present invention, refrigerant from the intermediate compression point is returned upstream of the evaporator (preferably at a location between the main expansion valve and the evaporator inlet) rather than downstream of the evaporator (at a location between the evaporator outlet and the compressor suction port). This achieves a greater refrigerant mass flow through the evaporator during unloaded operation compared to the prior art. The increase in refrigerant mass flow rate improves the return flow of oil back to the compressor during unloaded operation, thereby increasing the efficiency of the evaporator by improving the heat exchange characteristics of the evaporator. The improved oil return also minimizes the risk of oil being pumped out of the compressor oil tank and stored in the evaporator. If oil is pumped out of the compressor, the compressor may be damaged because bearings and other compressor components may not receive sufficient lubrication for proper operation.

Additionally, it is known that a sensor is typically provided downstream of the evaporator to control the opening of the main expansion device to maintain a desired superheat of the refrigerant leaving the evaporator. By returning the refrigerant from the unloader line upstream of the sensor and evaporator, the temperature of the refrigerant entering the compressor will be lower than if the refrigerant were returned downstream of the evaporator inlet. The higher the temperature of the refrigerant entering the compressor as it is returned downstream of the evaporator is due to the refrigerant also carrying it from the additional hot bypass branch exiting the intermediate compression point. Excessive refrigerant temperature entering the compressor is undesirable because it can overheat the motor driving the internal compressor components, resulting in excessive discharge temperature and resulting degradation of the lubricant or damage to the internal compressor components due to overheating.

In another feature, the prior art has a bypass unloader valve just outside the compressor. Thus, the valve and its associated piping, etc. are often placed in a location where replacement of the compressor may be necessary. By moving the bypass line and the bypass unloader valve away from the compressor toward the evaporator inlet, more space around the compressor can be created, which simplifies compressor replacement. In yet another feature of the invention, the compressor is provided with more than one unloader line and associated bypass unloader valves. Each unloader line is connected at a different compression location. With this arrangement, one unloader line can be connected to return partially compressed refrigerant upstream of the evaporator and the other unloader line can return partially compressed refrigerant downstream of the evaporator. While in another arrangement both unloader lines can be connected such that they both return refrigerant upstream of the evaporator. In accordance with the above logic, even more than two unloader lines can be used in the present invention. Solenoid valves are one example of the type of bypass valves that may be used for these applications, in which a valve plunger moves to switch a valve opening between open and closed positions. The valve type of the bypass valve may be selected from the one described above as a rapid circulation valve, in addition to being fully open or fully closed for an extended period of time; wherein the valve is operated between open and closed positions by pulse width modulation control. The proportion of time the valve is open determines the degree of modulation achieved and the bypass flow through the valve. The valve cycling rate is typically selected to be shorter than the response time of the system. Thus, the system responds as if the valve is partially opened rather than cycling between its fully open and fully closed positions.

The invention thus provides a number of valuable and advantageous technical effects.

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 prior art schematic of a refrigerant cycle.

Figure 2 shows a refrigerant cycle of the present invention with a single unloader line.

Figure 3 shows a refrigerant cycle of the present invention having two unloader lines, both of which return refrigerant upstream of the evaporator.

Fig. 4 shows a refrigerant cycle of the present invention having two unloader lines, one of which returns refrigerant upstream of the evaporator and the other of which returns refrigerant downstream of the evaporator.

Fig. 5 shows the location of the compressor internal bypass port for a single unloader line.

Fig. 6 shows the location of the compressor internal bypass ports for the two unloader lines.

Fig. 7 shows another embodiment.

Fig. 8 shows yet another embodiment.

Detailed Description

As shown in fig. 1, which represents the prior art, there is provided a compressor 20 having a suction port 71, an intermediate compression port 72 and a discharge port 73. Line 40 establishes communication between intermediate compression port 72 and suction line 45 through line 44.

As shown, a sensor 61 senses the condition of the refrigerant in line 74 downstream of the evaporator 58 and communicates with the main expansion device 63. It should be noted that the sensor 61 may be a temperature sensor such as a temperature sensing bulb of a thermostatic expansion valve (TXV) or an electronic expansion valve (EXV). Regardless of the type of sensor or type of expansion device, however, the purpose of the sensor is to control the opening of the main expansion device to achieve the desired amount of expansion of refrigerant to the evaporator 58 so that the refrigerant leaving the evaporator 58 enters the compressor suction port 71 at the desired superheat. However, during unloading operation, the bypass line 44 returns relatively hot refrigerant to the suction line 45 downstream of the sensor 61. When the compressor is operating in the bypass mode, the sensor 61 is therefore unable to achieve the desired superheat of the refrigerant returning to the suction inlet 71 of the compressor 20 via the suction line 45. That is, since the warmer refrigerant returning from bypass line 44 mixes with the refrigerant from line 74, sensor 61 cannot detect an increase in the temperature of the refrigerant in line 45 and, therefore, cannot bring the refrigerant entering the compressor through port 71 to the desired superheat.

Preferably, the bypass line 44 and valve 42 are disposed outside of the scroll compressor housing, thus simplifying the control assembly of the valve 42 and simplifying the assembly of the scroll compressor. However, the bypass line 44 and valve 42 may also be disposed within the housing. Valve 42 is selectively opened and closed to control the amount of refrigerant flowing through line 44.

Figure 2 shows the system of the present invention. Components having substantially the same structure and location are identified with the same reference numerals in figure 1. The bypass line 144 and the unloader valve 142 are now set such that refrigerant is returned through the bypass line 144 upstream of the evaporator 58. When the refrigerant returns through bypass line 144 in the unloaded mode, the refrigerant will mix with the main refrigerant flowing in line 75 toward the evaporator 58. Temperature sensor 161, still downstream of evaporator 58, now senses the combined effect of the bypass refrigerant and the main refrigerant flow from line 144. However, at this point the sensor will control the degree of superheat of the refrigerant in the combined flow leaving the evaporator 58 and entering the compressor through the suction port 71. Thus, the temperature of the refrigerant entering the compressor through port 71 may be reduced as compared to prior art arrangements. This temperature reduction increases the reliability of the compressor by reducing the motor's coil temperature, prevents degradation of the compressor lubricant performance, and also reduces the compressor discharge temperature and potential risk of damage to internal compressor components due to overheating.

In addition, the mass flow of refrigerant through the evaporator 58 is greater in unloaded mode operation than in prior art systems because an additional amount of refrigerant is added to the main refrigerant flow prior to entering the evaporator. The increase in the amount of refrigerant flowing through the evaporator improves the return of oil through suction line 45 to compressor 20. The improved oil return in turn increases the heat transfer capacity of the evaporator, since less oil remains on the heat transfer surfaces of the evaporator. The improved return of oil to the compressor also minimizes the possibility of oil leaving the compressor, thereby preventing the potential risk of compressor damage due to lack of lubrication oil.

In addition, in the prior art, the bypass line and the bypass valve are disposed near the compressor to communicate the bypass refrigerant with the suction line, so that the replacement of the compressor is troublesome. The present invention simplifies compressor replacement by moving the bypass line and bypass valve further away from the compressor.

Fig. 3 shows another embodiment in which a second unloader line 150 having a separate unloader valve 152 is added to the refrigerant system. It can be seen that the second unloader line 150 communicates back to the refrigerant line 75 upstream of the evaporator 58. Note that as a variant of embodiment, the lines downstream of the valves 142 and 152, in addition to being both connected to the line 75, can also be connected to each other first downstream of the valves 142 and 152, and then this common connection downstream of these valves can be connected to the line 75.

Fig. 4 shows another embodiment, given the example where one of the unloader lines communicates downstream of the evaporator and the other unloader line communicates upstream of the evaporator. In this embodiment, the unloader line 180 and a separate valve 182 communicate with a location 184 downstream of the sensor 61. The options shown in fig. 3 and 4 allow the compressor designer to effect changes in the amount of refrigerant unloaded, as well as changes in the amount of refrigerant delivered upstream of the evaporator. The above-described embodiments further include a controller 60 capable of controlling the operation of the bypass valve 142 and/or the valve 152 and/or the valve 182. The controller is capable of keeping at least one of the valves open when bypass operation is desired or keeping at least one of the valves closed when bypass through at least one bypass line is not desired. If the valves are adapted for fast pulse width modulation, the controller can control the amount of time any of these valves remain open and closed to maintain the desired bypass flow through the valves.

Figure 5 illustrates the internal structure of an embodiment of a scroll compressor for implementing a single unloader line such as the embodiment shown in figure 2. As shown, fixed scroll member 200 and orbiting scroll member 202 cooperate. The internal unloader port 204 communicates back to the communication port 72 and then to the line 40. An internal exhaust port 206 is shown downstream of the internal bypass port 204.

Fig. 6 shows an embodiment suitable for use in the embodiments of fig. 3 and 4. An additional internal port 210 is provided downstream of the location of port 204. Line 180 communicates with port 210.

Fig. 7 illustrates another embodiment of a compressor 348 in which a compressor pumping unit 350 is disposed within a housing 351. An unloader line 352 and its valve 354 are also provided in the housing. A suction line 356 is shown in communication with line 352. Of course, this embodiment is only schematically illustrated with respect to features, but it is indeed clearly illustrated that one of the unloader lines that bypass refrigerant downstream of the evaporator can be housed inside the compressor housing 351.

Fig. 8 schematically illustrates another embodiment 300. In this embodiment, the compressor pumping unit 302, which is comprised of two rotors, is shown as being driven by a motor 308, with the unloader lines 304 and 306 axially spaced along the length of the compressor pumping unit 302. The unloader lines 304 and 306 communicate with the screw compressor pumping unit at different locations during compression. In this configuration, the connection of these unloader lines to the rest of the system can be made in a similar manner to the connection of lines 40 and 150 or 180 shown in FIGS. 3 and 4. Of course, instead of having two bypass lines as shown in fig. 8, the screw compressor pumping unit may also have more than two bypass lines or only one bypass line. In the case of only one bypass line, the connection of this bypass line to the rest of the system may be made in a similar manner to the connection of line 40 shown in FIG. 2. Of course, other types of compressors may be used with the present invention.

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 (17)

1. A refrigerant cycle system comprising:

a compressor;

the compressor having an outlet providing refrigerant to a condenser, the condenser providing refrigerant to a main expansion device, refrigerant moving from the main expansion device to an evaporator, and a compressor suction inlet downstream of the evaporator; and

at least one unloader valve for selectively communicating compressed refrigerant from the compressor from at least one intermediate compression location to a location upstream of the evaporator.

2. The refrigerant cycle system as set forth in claim 1, wherein said at least one unloader valve is a solenoid valve.

3. The refrigerant cycle system as set forth in claim 1, wherein said at least one unloader valve is a rapid cycle valve.

4. The refrigerant cycle system as set forth in claim 1, wherein there are two unloader valves communicating compressed refrigerant from said compressor from two intermediate compression locations to at least one location upstream of said evaporator.

5. A refrigerant cycle system as set forth in claim 1, wherein there are two unloader valves communicating compressed refrigerant from said compressor from two intermediate compression positions, with a first unloader valve communicating to a position upstream of said evaporator and a second unloader valve communicating to a position downstream of said evaporator.

6. The refrigerant cycle system as set forth in claim 1, wherein said compressor is a scroll compressor.

7. The refrigerant cycle system as set forth in claim 1, wherein said compressor is a screw compressor.

8. The refrigerant cycle system as set forth in claim 1, wherein said at least one unloader valve is disposed in a bypass passage mounted to an exterior of the compressor housing.

9. The refrigerant cycle system as set forth in claim 1, wherein said at least one unloader valve is disposed in a bypass passage mounted inside a compressor housing.

10. A refrigerant cycle system as set forth in claim 1, wherein a sensor is provided downstream of said evaporator and upstream of said suction inlet of said compressor, said sensor controlling said main expansion device to achieve a desired degree of superheat at the outlet of said evaporator.

11. A refrigerant cycle system as set forth in claim 1, wherein there is an unloader valve for returning refrigerant from an intermediate compression position to said position upstream of said evaporator.

12. A refrigerant cycle system comprising:

a scroll compressor pumping unit having a compression chamber;

at least one port into said compression chamber;

said compressor pumping unit having an outlet for providing refrigerant to a condenser, said condenser providing refrigerant to a main expansion device, and said refrigerant moving from said main expansion device to an evaporator, and a suction inlet disposed downstream of said evaporator back to said compressor; and

an unloader system selectively communicating a port to a location upstream of the evaporator, the unloader system including a bypass line connected to the location upstream of the evaporator and an unloader valve selectively opening the bypass line, when the unloader valve is open, compressed refrigerant from the compression pockets passing through the port and to the location upstream of the evaporator.

13. A refrigerant cycle system as set forth in claim 12, wherein a sensor is provided downstream of said evaporator and upstream of said suction inlet of said compressor, said sensor controlling said main expansion device to achieve a desired degree of superheat at the outlet of said evaporator.

14. The refrigerant cycle system as set forth in claim 12, wherein said unloader valve is disposed in a bypass passage mounted to an exterior of the compressor housing.

15. The refrigerant cycle system as set forth in claim 12, wherein said unloader valve returns refrigerant from an intermediate compression position to said position upstream of said evaporator.

16. A refrigerant cycle system as set forth in claim 12, wherein there are two unloader valves communicating compressed refrigerant from said compressor from two intermediate compression locations to at least one location upstream of said evaporator.

17. A refrigerant cycle system as set forth in claim 12, wherein there are two unloader valves communicating compressed refrigerant from said compressor from two intermediate compression positions, with a first unloader valve communicating to a position upstream of said evaporator and a second unloader valve communicating to a position downstream of said evaporator.