REFRIGERANT SYSTEM WITH BYPASS LINE AND DEDICATED ECONOMIZED FLOW COMPRESSION CHAMBER

Abstract

A refrigerant system has an economizer cycle. A vapor refrigerant from the economizer loop is returned to a dedicated economizer compression chamber. A main refrigerant is returned to a dedicated main compressor chamber. A bypass line communicates the two refrigerant flows.

Description

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system having an economizer cycle, and wherein an economized refrigerant 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 a compression unit, wherein a bypass refrigerant line communicates the two refrigerant flows upstream of their corresponding compression chambers.

Refrigerant compressors compress and circulate a refrigerant throughout a refrigerant system to condition a secondary fluid, typically delivered to a climate-controlled space. In a basic refrigerant system, a compressor compresses a refrigerant and delivers it to a heat rejection heat exchanger. Refrigerant from the heat rejection heat exchanger passes through an expansion device, in which its pressure and temperature are reduced. Downstream of the expansion device, the refrigerant passes through a heat accepting heat exchanger, and then back to the compressor. As known, the heat accepting heat exchanger is typically an evaporator, and the heat rejecting heat exchanger is a condenser for subcritical applications and a gas cooler for transcritical applications.

One option in a refrigerant system design to enhance performance is the use of an economizer, or vapor injection function. When an economizer function is activated, a portion of refrigerant is tapped from a main refrigerant stream downstream of the heat rejection heat exchanger. In one configuration, this tapped refrigerant is passed through an auxiliary expansion device, to be expanded to an intermediate pressure and temperature, and then this partially expanded tapped refrigerant passes in heat exchange relationship with a main refrigerant flow in an economizer heat exchanger. In this manner, the main refrigerant flow is cooled such that it will have a greater thermodynamic potential when it reaches the heat accepting heat exchanger. The tapped refrigerant, typically in a superheated thermodynamic state, is returned to the compressor.

As known, an economizer function can be performed in either a flash tank or in an economizer heat exchanger. For purposes of this application, the two devices will be both known as an “economizer heat exchanger.”

As described in European Patent Application EP1498667, the vapor refrigerant is returned to a dedicated economizer compression chamber or a compressor. The main refrigerant flow is returned from the heat accepting heat exchanger back to its own dedicated compression chamber or compressor. This known system maintains the economizer and suction refrigerant flows completely isolated from each other. A purpose of the dedicated compression chambers is to have two separate non-mixing inlet refrigerant streams, each compressing refrigerant from a particular thermodynamic state to a common discharge thermodynamic state.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a refrigerant system is provided with an economizer cycle, where an economized refrigerant stream is returned from the economizer circuit back to a dedicated economizer compression chamber (or a separate compressor) through an economizer circuit return line. A main refrigerant stream is returned to its own dedicated main compression chamber (or a compressor) through a suction line. A bypass line communicates the two refrigerant flow lines upstream of their corresponding inlets to the dedicated compression chambers (or compressors). In this arrangement, the two inlet refrigerant streams are allowed to selectively communicate and mix with each other via the bypass line. In one embodiment, the bypass line may have a small orifice which always communicates the two refrigerant streams. In a second embodiment, the bypass line may include a controlled valve. In a third embodiment, the bypass line may include 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art system.

FIG. 2 shows a schematic of a first embodiment.

FIG. 3 shows a schematic of a second embodiment.

FIG. 4 shows a schematic of a third embodiment.

FIG. 5 shows a schematic of a fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a prior art refrigerant system 20. As known a compression unit 22 includes at least two chambers, cylinders, or compressors 24 and 26. The two compression chambers compress refrigerant and deliver it downstream to a heat rejection exchanger 28. The heat rejection exchanger 28 can be a condenser (if the refrigerant discharge thermodynamic state is below the critical point) or a gas cooler (if the refrigerant discharge thermodynamic state is above the critical point). An expansion device 29 is positioned downstream of the heat rejection heat exchanger, and partially expands refrigerant passing into a 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 an evaporator 36, and expands this refrigerant to a pressure approximating the suction pressure. In the flash tank 30, a liquid refrigerant is separated from a vapor refrigerant. The liquid refrigerant from the flash tank 30 is expanded to a two-phase thermodynamic state in the expansion device 34, flows through the evaporator 36, where it evaporates and is typically superheated, passes through a suction line 38 and is returned to the dedicated main compression chamber 26. The separated vapor refrigerant passes through a return line 32 of the economizer circuit to its dedicated compression chamber 24. In the known prior art system, the lines 32 and 38 are maintained strictly separate. A purpose of the two separate lines delivering refrigerant to two dedicated compression chambers 24 and 26 is to have refrigerant in each of the compression chambers be closer to homogeneous conditions than if the two refrigerant flows were allowed to mix.

FIG. 2 shows an embodiment 40 wherein 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 49 is provided to communicate an economizer refrigerant flow and a main refrigerant flow. This restriction can be in a form of an orifice; however it can also be a capillary tube or any other type of a restriction that throttles the refrigerant flow. Typically the size of the orifice is selected to have a cross-sectional area between 0.1 to 3 square millimeters. Other restriction types may have a different cross-sectional area; however their effective cross-sectional area is sized to correspond to an equivalent orifice area in the range mentioned above.

A purpose of this bypass line 48 is to allow pressure equalization on startup. This will allow reduce motor starting torque, resulting in a more efficient operation, and allow the use of smaller and less expensive motors. Also, the orifice allows drainage of lubricating oil from the economizer line 32 to the suction line 38 after shutdown. A shutoff valve 33 may be included on the economizer circuit return line 32.

FIG. 3 shows an embodiment 50 having a compression unit 52 having dedicated compression chambers 54 and 56. The bypass line 58 includes an electrically controlled valve, which in this embodiment is disclosed as a controlled solenoid valve 59, which may be opened or closed. The solenoid valve may be opened to allow mixing of main and economized refrigerant streams during continuous operation, or can be opened prior to startup for pressure equalization, or can be opened at or after shutdown for oil return. Also, in some circumstances, the valve 59 may be operated in a pulse mode such as, for instance, to facilitate oil return or unload the compression unit 50. Further, the valve 59 may be of a modulating type to tailor valve opening to specific operating conditions (operating pressures, in particular) and precisely match thermal load demands in the conditioned space.

As shown in FIG. 4, a refrigerant system 60 has a compression unit 62 with dedicated compression chambers 64 and 66, as in the prior embodiments. However, the bypass function now has both the solenoid valve 59 on the bypass line 58 and an orifice 68 on a branch bypass line 66. The embodiment 60 would achieve the benefits of each of the embodiments of FIGS. 2 and 3, and allow the control at shutdown or startup without the need to open the valve 59. The bypass lines 58 and 66 may be arranged in a parallel configuration, between the economizer circuit return line 32 and the main circuit suction line 38, as well.

FIG. 5 shows yet another embodiment 80 having a compression unit 82 with separate compression chambers 84 and 86. In the embodiment 80, the economizer function is provided by an economizer heat exchanger 94, rather than the flash tank 30 of previous embodiments. As known, a tap line 90 taps a portion of refrigerant from a main refrigerant flowing through a liquid line 88 and passes this refrigerant through an economizer expansion device 92, where it is expanded to a lower intermediate pressure and temperature. This would 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 the vapor thermodynamic state, flows into the return line 96 of the economizer circuit. A main circuit expansion device 34 is positioned downstream of the economizer heat exchanger 94 to control the amount of liquid refrigerant reaching the evaporator 36. While the economized refrigerant flow in the tap line 90 and the main refrigerant flow in the liquid line 88 are shown passing through the economizer heat exchanger 94 in the same direction, in practice, they are preferably flown in counterflow relationship. The two refrigerant streams are shown flowing in the same direction for illustration simplicity only. Furthermore, the tap line 90 may be positioned downstream of the economizer heat exchanger 94.

Similar to previous embodiments, the bypass line 58 is shown with the solenoid valve 59. Further, the economizer heat exchanger 94 may be utilized in the embodiments of FIG. 2 or 4 as well, instead of the flash tank 30.

As stated above, the flow control device 59 may have an adjustable orifice to control the amount of communicated refrigerant between the dedicated economizer and main compression chambers, based, for instance, on operating conditions and thermal load demand in the conditioned space. On the other hand, the solenoid valve 59 may be controlled by a pulse width modulation technique to achieve similar results for compressor unit unloading or to facilitate oil return and assure reliable compressor operation.

It should be pointed out that many different compressor types could be used in this invention. For example, scroll, screw, rotary, or reciprocating compressors can be employed. The economized flow and main flow chambers can be separate compressors, or these compression chambers can be positioned within a single compressor. In the context of this invention, each compression chamber can be represented by a single cylinder or multiple cylinders, as for example, may be the case for a reciprocating compressor. If the compression chambers are located within a single compressor, then the bypass line can be located internally or externally, in relation to the compressor shell. If the compression chambers are independent compressors then the preferable location for the bypass line would be external to these compressors. Further, each of the dedicated compression chambers may have a number of sequential compression stages, with the dedicated main compression chambers having a higher number of sequential compression stages then the dedicated economizer compression chambers, since they operate between higher pressure differentials.

This invention would apply to a broad range of refrigerants including, but not limited to, R744, R22, R134a, R410A, R407C, R290, R600a and their combinations.

The refrigerant systems that utilize this invention can be used in many different applications, including, but not limited to, air conditioning systems, heat pump systems, marine container units, refrigeration truck-trailer units, and supermarket refrigeration systems. The refrigerant system of this invention can be a subcritical of transcritical system.

Although an 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

1. A refrigerant system comprising:

at least two compression chambers, said at least two compression chambers for compressing a refrigerant, a downstream heat rejection heat exchanger, a refrigerant line passing from the heat rejection heat exchanger into an economizer cycle, and a main refrigerant line passing from the economizer cycle through a main expansion device and to a heat accepting heat exchanger, a suction line downstream of said heat accepting heat exchanger and extending to at least one of the at least two compression chambers;

a return line being returned from the economizer cycle to at least one other of the at least two compression chambers; and

a bypass line communicating the return line and the suction line.

2. The refrigerant system as set forth in claim 1, wherein said bypass line includes a restriction to allow continuous communication between the return line and the 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 a solenoid 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 upon refrigerant system shutdown or before startup.

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-section area between 0.1 square millimeter 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 installed 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 and vapor refrigerant phases.

13. The refrigerant system as set forth in claim 1, wherein said compression chambers are independent compressors.

14. The refrigerant system as set forth in claim 1, wherein said 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 in relation to the compressor.

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

17. The refrigerant system as set forth in claim 14, wherein said compressor is reciprocating compressor and said 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 sequential 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 expanding a tapped portion of refrigerant and passing it through the economizer heat exchanger to exchange heat with the main refrigerant, with said tapped refrigerant being returned through the return line.

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

21. The refrigerant system as set forth in claim 1, wherein the 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 a group consisting of R744, R22, R410A, R134a, R407C, R290, R600a refrigerants or their combinations.

23. A method of operating a refrigerant system comprising:

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

an economized flow of refrigerant, that is at least largely vapor, being returned from the economizer cycle to at least one other of the at least two compression chambers through a return line; and

communicating the return line and the suction line through a bypass line.

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

25. The method as set forth in claim 23, wherein an electrically controlled valve on said bypass line is opened to return oil.