BACKGROUND OF THE INVENTION
This application relates to economized refrigerant systems utilizing an expander as an expansion device, where at least a portion of refrigerant is tapped from a location in the expander at which it has been at least partially expanded, and is used to subcool a main refrigerant flow during heat transfer interaction in an economizer heat exchanger. In this manner, a single expander can provide both an expansion function for a main expansion device of the refrigerant system, and further, an expansion function for an auxiliary economizer circuit expansion device of the refrigerant system.
Refrigerant systems are known, and circulate a refrigerant through a refrigerant cycle to condition a secondary fluid. Typically, a compressor compresses a refrigerant and delivers it to a first heat exchanger. Refrigerant from that first heat exchanger passes through an expansion process, at which its pressure is lowered. Downstream of the expansion process, a refrigerant passes through a secondary heat exchanger, and then back to the compressor.
One additional option in a refrigerant system design is the use of an economizer function. In an economizer function, a refrigerant flow is tapped from a main refrigerant flow, typically downstream of the first heat exchanger. This tapped refrigerant is passed through an expansion device, and then the expanded tapped refrigerant passes in heat exchange relationship with a main refrigerant flow in an economizer heat exchanger. In this manner, the refrigerant in the main refrigerant flow line is sub-cooled such that it will have a greater heating capacity when it reaches the second heat exchanger. The tapped refrigerant is returned to an intermediate compression point downstream of the economizer heat exchanger.
SUMMARY OF THE INVENTION
This invention relates to economized refrigerant systems, where a single expander is utilized for refrigerant expansion, and further, where this single expander has at least one intermediate expansion port and provides an expansion function as a main expansion device and as at least one economizer circuit expansion device. The simplest economized refrigerant system configuration with a single economizer circuit has an expander with only one intermediate expansion port. However, for example, if a refrigerant system incorporates more than one economizer circuits, the number of serially located intermediate expander ports can be increased accordingly. A corresponding refrigerant system compressor can consist of multiple serially connected stages or can be a single internally economized compressor (this, for example, is a common arrangement for scroll or screw compressors). An electrical or mechanical connection between the expander and any of the individual compressors or compression stages can be arranged accordingly to recover at least a portion of energy released during the refrigerant expansion process. The expander can also be used to assist in driving any other components within or outside of the refrigerant system. A portion of refrigerant partially expanded by the expander is tapped at the intermediate expansion point and passed through an economizer heat exchanger in heat exchange relationship with a main refrigerant flow to provide additional subcooling to the main refrigerant flow and consequently enhance system performance.
In one embodiment, a single intermediate pressure tap is formed in the expander to tap at least a portion of the refrigerant for passage through a single economizer heat exchanger. In a second embodiment, there are two intermediate pressure taps and two economizer heat exchangers associated with these taps. Of course, a worker of ordinary skill in the art would recognize that even more taps and more corresponding economizer circuits can be formed and included into the refrigerant system design.
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 refrigerant system.
FIG. 2 shows a first schematic of an inventive refrigerant system.
FIG. 3 shows a second schematic inventive refrigerant system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An economized refrigerant system 20, as known in the prior art, is illustrated in FIG. 1. As shown, two compressors 22 and 24 arranged serially may operate to provide two sequential stages of compression. Alternatively, it is known to use a single compressor, where the refrigerant is injected at the intermediate compression point within the compression process.
A compressed refrigerant passes through a condenser 26, and eventually through a main expansion device 28. While the expansion device 28 is illustrated as a valve, as mentioned above, it is also known to use an expander instead of the valve 28. In the latter case, at least a portion of energy could be recovered during the refrigerant expansion process in the expander, for the main portion of the refrigerant passing to the evaporator 30, where additional thermal potential is also provided to increase the cooling capacity of the refrigerant system 20 due to more efficient isentropic expansion process in the expander. Downstream of the main expansion device 28, the refrigerant passes through an evaporator 30 and then back to the compressor 22. An economizer heat exchanger 32 is incorporated into the circuitry of the refrigerant system 20. As shown, a tap line 34 taps a portion of the refrigerant from a main liquid line and passes that refrigerant through an economizer expansion device 36. The partially expanded economizer circuit refrigerant is at a lower pressure and temperature, and thus cools the main refrigerant flow during heat transfer interaction in the economizer heat exchanger 32. While the tapped refrigerant is shown flowing in the same direction through the economizer heat exchanger 32, it is typical to arrange the refrigerant flows in a counterflow configuration. However, for illustration simplicity, the two refrigerant streams are shown flowing in the same direction in this FIG. 1. The tapped partially expanded portion of refrigerant is returned through a return line 38 to an intermediate compression point between the compression stages 22 and 24. While a multi-stage compressor is illustrated in the FIG. 1, and the economized refrigerant return line 38 is positioned between the two compression stages 22 and 24, it is also known to return the economized portion of refrigerant to an intermediate point in a single compressor.
As mentioned above, the prior art shown in FIG. 1 provides benefits from the inclusion of the economizer circuit. However, as a minimum it requires a second expansion device 36. Also, if the expander is used to substitute the main expansion valve 28, only a portion of the available expansion energy is recovered, since no energy recovery can be obtained from the economized portion of refrigerant passing through the tap line 34 and the economizer circuit expansion valve 36. The present invention is shown in one example in FIG. 2. The refrigerant system 40 in FIG. 2 also includes two sequential compressors 42 and 44. A condenser 46 is positioned upstream of an economizer heat exchanger 48, and an expander 50. As known, the expander 50 serves to expand a refrigerant and recover work of expansion, by electrical or mechanical means, as shown schematically at 54. This recovered energy can be utilized to assist in driving of at least one of the components within or outside of the refrigerant system 40. Also, the expansion of the refrigerant through an expander 50 produces additional thermal potential for the fully expanded refrigerant entering an evaporator 56 and partially expanded refrigerant entering the heat exchanger 48, due to a more efficient isentropic expansion process in the expander 50, thus enhancing performance of the refrigerant system 40. Further, while two compressors are shown in FIG. 2, the present invention would also extend to refrigerant systems having a single compressor incorporating vapor injection or more than two sequential compression stages.
A portion of the refrigerant is tapped from an intermediate pressure tap 51 in the expander 50 and passed through a line 52 and through the economizer heat exchanger 48. The intermediate pressure tap point 51 is at a thermodynamic state at which the refrigerant has been at least partially expanded in the expander 50. The refrigerant from the tap line 52 will subcool the refrigerant in the main liquid line passing through the economizer heat exchanger 48 during heat transfer interaction between these two refrigerant streams. Refrigerant is again returned through a line 53 to the mid-point between the stages 42 and 44. The main portion of the refrigerant that is not tapped off through the intermediate pressure tap 51 continues to flow through the expander, undergoing further expansion, and thus adding to the expansion process work recovery and providing additional thermal potential to the refrigerant entering the evaporator 56. As with the FIG. 1 refrigerant system 20, an evaporator 56 is positioned downstream of the expander 50, and the main portion of refrigerant passes through the evaporator 56 and to the compressor 42. The expander 50 is as known in the art, except it has an additional intermediate pressure tap point 51 to supply a portion of the partially expanded refrigerant to the economizer heat exchanger 48. The tap 51 may be an additional port in an expander housing that communicates with intermediate expansion point inside the expander. A worker of ordinary skill in the art would recognize what is required to provide the disclosed expander 50 and the intermediate pressure tap 51.
This embodiment achieves the inclusion of the economizer circuit without the need for a separate economizer expansion device (prior art element 36) and provides additional recovery of the expansion work benefiting the performance of the refrigerant system 40.
FIG. 3 shows yet another embodiment 140. In this embodiment, the expander 150 has two intermediate pressure tap points located serially with respect to the expansion process. Here, a first economizer circuit and an economizer heat exchanger 142 is supplied with a portion of partially expanded refrigerant from a corresponding tap point 164 leading to a line 144 and a first return line 143. This embodiment shows the return line 143 leading to a mid-point between the compression stages 42 and 44. A second economizer heat exchanger 146 is supplied with a portion of further, but not fully, expanded refrigerant form a corresponding tap point 165 leading to a line 148, and returned to a line 145.
This embodiment illustrates the return line 145 connecting to an intermediate compression point in the compressor 42. In all other aspects, the FIG. 3 embodiment is similar to the embodiment shown in FIG. 2.
Further, while only two circuits are shown in FIG. 2, additional economizer circuits and intermediate pressure corresponding tap ports in the expander 50 can be provided. The present invention thus provides at least partially expanded refrigerant for use in an economizer circuit without the need for a separate dedicated economizer expansion device and enhances capacity and efficiency of the refrigerant system.
It should be pointed out that many different compressor and expander types could be used in this invention. For example, scroll, screw, rotary or reciprocating compressors and expanders can be employed.
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.
Furthermore, it has to be understood that although this invention can be applied to any economized refrigerant systems, the refrigerant systems employing CO2 as a refrigerant would particularly benefit from this invention, since these systems have inherit deficiencies and require additional means for the performance enhancement.
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.