HK1147310B - Refrigerant system with bypass line and dedicated economized flow compression chamber - Google Patents

Description

Refrigerant system with bypass line and dedicated economized flow compression chamber

Technical Field

The present application relates to a refrigerant system having an economizer cycle and wherein an economizer flow is returned to an economizer compression chamber of a compression unit and a main refrigerant flow is returned to a main compression chamber of the compression unit, with a bypass refrigerant line providing communication between the two refrigerant flows upstream of their respective compression chambers.

Background

Refrigerant compressors compress and circulate refrigerant throughout a refrigerant system to condition a secondary fluid, which is typically delivered to a climate controlled space. In a basic refrigerant system, a compressor compresses a refrigerant and delivers it to a heat rejecting heat exchanger. The refrigerant from the heat rejecting heat exchanger may pass through an expansion device where the pressure and temperature of the refrigerant may drop. Downstream of the expansion device, the refrigerant passes through a heat exchanger that receives heat and then returns to the compressor. As is known, the heat exchanger receiving heat is usually an evaporator, while the heat rejecting heat exchanger is a condenser applied in subcritical conditions and a gas cooler applied in transcritical conditions.

An alternative refrigerant system design to enhance performance is to use economizers, or introduce vapor venting functionality. When the economizer function is activated, a portion of the refrigerant is tapped from the main refrigerant stream downstream of the heat rejecting heat exchanger. In one configuration, the tapped refrigerant is passed through an auxiliary expansion device to be expanded to an intermediate pressure and temperature, and then the tapped refrigerant, which has undergone partial expansion, is passed in an economizer heat exchanger in heat exchange relationship with the main refrigerant flow. In this way, the main refrigerant flow is cooled so that it will have a greater thermodynamic potential when it reaches the heat receiving heat exchanger. The tapped refrigerant is typically in a superheated thermodynamic state and returned to the compressor.

As is known, the economizer function can be implemented in a flash tank or in an economizer heat exchanger. For the purposes of this application, both of these devices will be referred to as "economizer heat exchangers".

As described in european patent application EP1498667, the vapor refrigerant is returned to a dedicated economizer compression chamber or compressor. The main refrigerant flow is returned from the heat exchanger receiving heat to its own dedicated compression chamber or compressor. The known system maintains the economizer and the suction refrigerant flow in complete isolation from each other. The purpose of the dedicated compression chamber is to obtain two separate, unmixed, incoming refrigerant streams, each stream compressing refrigerant from a particular thermodynamic state to a common discharge thermodynamic state.

Disclosure of Invention

In a disclosed embodiment of the invention, a refrigerant system with an economizer cycle is provided in which an economizer refrigerant stream is returned from an economizer line through an economizer line return line to a dedicated economizer compression chamber (or separate compressor). The main refrigerant stream is returned through a suction line to its own dedicated main compression chamber (or compressor). A bypass line connects the two refrigerant flow lines upstream of the respective inlets to the dedicated compression chamber (or compressor). In this arrangement, the two incoming refrigerant streams may be selectively communicated to and mixed with each other via the bypass line. In one embodiment, the bypass line may have a small orifice that always communicates the two refrigerant streams. In a second embodiment, the bypass line may comprise a control valve. In a third embodiment, the bypass line may comprise a combination of these two options.

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 illustrates a prior art system;

FIG. 2 shows a schematic view of a first embodiment;

FIG. 3 shows a schematic view of a second embodiment;

FIG. 4 shows a schematic view of a third embodiment; and

fig. 5 shows a schematic view of a fourth embodiment.

Detailed Description

Fig. 1 shows a prior art refrigerant system 20. As is known, the compression unit 22 includes at least two chambers, cylinders or compressors 24 and 26. Which compresses the refrigerant and delivers it downstream to a heat rejecting heat exchanger 28. The heat rejecting heat exchanger 28 may be a condenser (if the thermodynamic state of the refrigerant discharge is below the critical point) or a gas cooler (if the thermodynamic state of the refrigerant discharge is above the critical point). An expansion device 29 is positioned downstream of the heat rejecting heat exchanger and partially expands the refrigerant entering the flash tank 30 to an intermediate pressure. An expansion device 34 is positioned downstream of the flash tank 30 to control the amount of refrigerant reaching the evaporator 36 and to expand the refrigerant to a pressure of about the suction pressure. In the flash tank 30, liquid refrigerant is separated from vapor refrigerant. Liquid refrigerant from the flash tank 30 expands in an expansion device 34 to a two-phase thermodynamic state, flows through an evaporator 36, where it is evaporated and typically in a superheated state, through a suction line 38 and back to the dedicated main compression chamber 26. Vapor refrigerant separate from the liquid refrigerant passes through the economizer line return line 32 to its dedicated compression chamber 24. In this known prior art system, lines 32 and 38 are maintained in a strictly separated condition. The purpose of providing two separate lines to deliver refrigerant to the two dedicated compression chambers 24 and 26 is: the refrigerant in each compression chamber is closer to a homogeneous state than if the two refrigerant streams were allowed to mix.

Fig. 2 shows an embodiment 40 in which the compression unit 42 has a dedicated economizer compression chamber 44 and a dedicated main compression chamber 46. However, a bypass line 48 including a restriction device 49 is provided to communicate the economizer refrigerant flow with the main refrigerant flow. The restriction means may be in the form of an orifice; but it could also be a capillary tube or any other type of restriction throttling the refrigerant flow. The size of the orifice is typically selected to have a cross-sectional area of between 0.1 mm and 3 mm. Other types of restriction devices may have different cross-sectional areas; but its effective cross-sectional area is set so as to correspond to an equivalent orifice area within the above-mentioned range.

The purpose of this bypass line 48 is to allow pressure equalization at start-up. This will reduce the motor starting torque resulting in more efficient operation and will allow the use of smaller, less expensive motors. Furthermore, the orifice allows for the discharge of lubrication oil from the economizer line 32 to the suction line 38 after a shutdown. A shut-off valve 33 may be provided in the return line 32 of the economizer circuit.

Fig. 3 shows an embodiment 50 with a compression unit 52 having dedicated compression chambers 54 and 56. The bypass line 58 comprises an electrically controlled valve, which in this embodiment is disclosed as a controlled solenoid valve 59, which can be opened or closed. The solenoid valve may be opened to allow the main refrigerant stream to mix with the economized refrigerant stream during continuous operation, or may be opened prior to start-up for pressure equalization, or may be opened at or after shutdown to return oil. Furthermore, in some cases, valve 59 may be operated in a pulsed mode, for example, to facilitate oil return or unloading of compression unit 50. Further, the valve 59 may be a modulating type valve to adapt the opening of the valve to specific operating conditions (particularly operating pressures) and to achieve an exact match of the valve opening to the thermal load demand in the conditioned space.

As shown in fig. 4, just as in the previous embodiment, the refrigerant system 60 has a compression unit 62 with dedicated compression chambers 64 and 66. However, the bypass function in this embodiment includes both the solenoid valve 59 on the bypass line 58 and the orifice 68 on the branch bypass line 66. Embodiment 60 combines the advantages of the embodiment of fig. 2 with the embodiment of fig. 3 and allows control at shutdown or startup without opening valve 59. The bypass lines 58 and 66 may also be arranged in a parallel configuration between the economizer line return line 32 and the main line suction line 38.

Fig. 5 shows a further embodiment 80 having a compression unit 82 with separate compression chambers 84 and 86. In the embodiment 80, the economizer function is provided by the economizer heat exchanger 94 instead of the flash tank 30 as described in the previous embodiment. As is known, the tap line 90 taps a portion of the refrigerant from the main refrigerant flowing through the liquid line 88 and passes the refrigerant through an economizer expansion device 92, wherein the refrigerant is expanded to a lower intermediate pressure and temperature. This will allow the refrigerant in the tap line 90 to further cool the main refrigerant in the liquid line 88 while passing through the economizer heat exchanger 94. The economized refrigerant, typically in a vapor thermodynamic state, flows into the economizer circuit return line 96. The main line expansion device 34 is disposed downstream of the economizer heat exchanger 94 to control the amount of liquid refrigerant reaching the evaporator 36. Although the economizer refrigerant flow in the tap line 90 and the main refrigerant flow in the liquid line 88 are shown as flowing in the same direction through the economizer heat exchanger 94, in practice, the two refrigerant flows preferably flow in a counter-flow relationship. The two refrigerant streams flowing in the same direction are shown for simplicity only. Further, the shunt line 90 may be positioned downstream of the economizer heat exchanger 94.

Similar to the previous embodiment, the bypass line 58 is shown with the solenoid valve 50. Further, an economizer heat exchanger 94 may also be used in place of the flash tank 30 in the embodiment shown in FIG. 2 or FIG. 4.

As noted above, the flow control device 59 may have an adjustable orifice to control the amount of refrigerant circulated between the dedicated economizer and the main compression chamber, such as based on operating conditions and thermal load demands in the conditioned space. On the other hand, the solenoid valve 59 may be controlled by pulse width modulation techniques in order to obtain similar compressor unit unloading results or to facilitate oil return and ensure reliable operation of the compressor.

It should be noted that: many different types of compressors may be used in the present invention. For example, a scroll compressor, a screw compressor, a rotary compressor, or a reciprocating compressor may be employed. The economized flow chamber and the main flow chamber may be separate compressors, or the compression chambers may be positioned within a single compressor. In the context of the present invention, each compression chamber may be of the single-cylinder type or of the multi-cylinder type, as may be the case, for example, with reciprocating compressors. If the compression chambers are provided within a single compressor, the bypass line may be internal or external with respect to the compressor housing. If the compression chambers are separate compressors, the bypass line is preferably located outside these compressors. Further, each of the dedicated compression chambers may have a plurality of sequentially arranged compression stages, and the dedicated main compression chamber has a greater number of sequentially arranged compression stages than the dedicated economizer compression chambers, as it operates between higher pressure differentials.

The present invention is applicable to a variety of refrigerants including, but not limited to, R744, R22, R134a, R410A, R407C, R290, R600a, and combinations thereof.

Refrigerant systems employing the present invention may be used in a variety of different applications including, but not limited to, air conditioning systems, heat pump systems, marine container units, refrigerated vehicle-trailer units, and supermarket refrigeration systems. The refrigeration system of the present invention may be a subcritical system or a transcritical system.

Although embodiments of the present invention have been disclosed, those skilled in the art will appreciate that: several variations are possible within the scope of the invention. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims (25)

1. A refrigerant system, comprising:

at least two compression chambers for compressing refrigerant, a heat rejecting heat exchanger downstream, a refrigerant line extending from the heat rejecting heat exchanger into an economizer cycle, and a primary refrigerant line extending from the economizer cycle through a primary expansion device and to a heat receiving heat exchanger, a suction line downstream of the heat receiving heat exchanger and extending to at least one of the at least two compression chambers;

a return line from the economizer that circulates back to at least one other of the at least two compression chambers; and

a bypass line communicating the return line with the suction line,

wherein a main refrigerant flow is circulated from the economizer through the main expansion device to the heat accepting heat exchanger and then from the heat accepting heat exchanger back to the at least one compression chamber through the suction line;

an economized refrigerant flow is circulated from the economizer through a return line back to the at least one additional compression chamber; and

the bypass line is configured to allow the main refrigerant flow and the economized refrigerant flow to selectively communicate with each other and mix with each other.

2. The refrigerant system as set forth in claim 1, wherein said bypass line includes a restriction to enable continuous communication between said return line and said suction line.

3. The refrigerant system as set forth in claim 2, wherein said bypass line includes an electrically controlled valve to provide selective communication.

4. The refrigerant system as set forth in claim 3, wherein said electrically controlled valve is an electromagnetic on/off valve.

5. The refrigerant system as set forth in claim 3, wherein said electrically controlled valve is controlled by a pulse width modulation technique.

6. The refrigerant system as set forth in claim 3, wherein said electrically controlled valve is a modulating valve.

7. The refrigerant system as set forth in claim 3, wherein said electrically controlled valve is opened to equalize pressure at shutdown of the refrigerant system or prior to startup of the refrigerant system.

8. The refrigerant system as set forth in claim 2, wherein said restriction is an orifice.

9. The refrigerant system as set forth in claim 2, wherein said restriction has a cross-sectional area of between 0.1 and 3 square millimeters.

10. The refrigerant system as set forth in claim 2, wherein said restriction is a capillary tube.

11. The refrigerant system as set forth in claim 1, further comprising an electrically controlled valve mounted in parallel with said bypass line.

12. The refrigerant system as set forth in claim 1, wherein said economizer cycle includes a flash tank to separate liquid phase refrigerant from vapor phase refrigerant.

13. The refrigerant system as set forth in claim 1, wherein each of said at least two compression chambers is an independent compressor.

14. The refrigerant system as set forth in claim 1, wherein said at least two compression chambers are positioned within a single compressor.

15. The refrigerant system as set forth in claim 14, wherein said bypass line is located externally with respect to said compressor.

16. The refrigerant system as set forth in claim 14, wherein said bypass line is located internally with respect to said compressor.

17. The refrigerant system as set forth in claim 14, wherein said compressor is a reciprocating compressor and said at least two compression chambers are reciprocating compressor cylinders.

18. The refrigerant system as set forth in claim 1, wherein at least one of said at least two compression chambers is represented by a sequence of compression stages.

19. The refrigerant system as set forth in claim 1, wherein said economizer cycle includes an economizer heat exchanger having an economizer expansion device, said economizer expansion device expanding a tapped portion of refrigerant and passing it through said economizer heat exchanger to exchange heat with said main refrigerant, and said tapped refrigerant being returned through said return line.

20. The refrigerant system as set forth in claim 1, wherein at least one of said compression chambers is part of at least one reciprocating compressor cylinder.

21. The refrigerant system as set forth in claim 1, wherein said refrigerant streams in said return line and suction line are partially combined together at subcritical pressure.

22. The refrigerant system as set forth in claim 1, wherein said refrigerant is selected from the group of refrigerants consisting of R744, R22, R410A, R134a, R407C, R290, R600a refrigerant or combinations thereof.

23. A method of operating a refrigerant system, the method comprising:

providing at least two compression chambers compressing a refrigerant and delivering the refrigerant to a heat rejecting heat exchanger located downstream, the refrigerant passing from the heat rejecting heat exchanger into an economizer cycle, and a main refrigerant flow circulating from the economizer through a main expansion device and to a heat receiving heat exchanger, the refrigerant from the heat receiving heat exchanger passing through a suction line to at least one of the at least two compression chambers;

circulating an economized refrigerant flow from the economizer through a return line back to at least one other of the at least two compression chambers, and the economized refrigerant flow being at least mostly vapor; and is

Communicating the return line with the suction line through a bypass line,

wherein the bypass line is configured to allow the main refrigerant flow and the economized refrigerant flow to selectively communicate with each other and mix with each other.

24. The method as set forth in claim 23, wherein an electrically controlled valve on said bypass line is opened to unload said refrigerant system.

25. The method of claim 23, wherein an electrically controlled valve on the bypass line is opened to return oil.