This invention relates generally to refrigerant vapor compression systems and, more particularly, to improving the energy efficiency and/or cooling capacity of a refrigerant vapor compression system incorporating a multi-stage compression device, for example a two-stage compressor, and more particularly to a refrigerant vapor compression system incorporating a two-stage compressor and an intercooler for cooling refrigerant passing between the compression stages.
Refrigerant vapor compression systems are well known in the art and commonly used for conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems are also commonly used in refrigerating air supplied to display cases, merchandisers, freezer cabinets, cold rooms or other perishable/frozen product storage area in commercial establishments. Refrigerant vapor compression systems are also commonly used in transport refrigeration systems for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable/frozen items by truck, rail, ship or intermodally.
Refrigerant vapor compression systems used in connection with transport refrigeration systems are generally subject to more stringent operating conditions due to the wide range of operating load conditions and the wide range of outdoor ambient conditions over which the refrigerant vapor compression system must operate to maintain product within the cargo space at a desired temperature. The desired temperature at which the cargo needs to be controlled can also vary over a wide range depending on the nature of cargo to be preserved. The refrigerant vapor compression system must not only have sufficient capacity to rapidly pull down the temperature of product loaded into the cargo space at ambient temperature, but also should operate energy efficiently over the entire load range, including at low load when maintaining a stable product temperature during transport.
A typical refrigerant vapor compression system includes a compression device, a refrigerant heat rejection heat exchanger, a refrigerant heat absorption heat exchanger, and an expansion device disposed upstream, with respect to refrigerant flow, of the refrigerant heat absorption heat exchanger and downstream of the refrigerant heat rejection heat exchanger. These basic refrigerant system components are interconnected by refrigerant lines in a closed refrigerant circuit, arranged in accord with known refrigerant vapor compression cycles. It is also known practice to incorporate an economizer into the refrigerant circuit for increasing the capacity of the refrigerant vapor compression system. For example, a refrigerant-to-refrigerant heat exchanger or a flash tank may be incorporated into the refrigerant circuit as an economizer. The economizer circuit includes a vapor injection line for conveying refrigerant vapor from the economizer into an intermediate pressure stage of the compression process.
Traditionally, most of these refrigerant vapor compression systems have been operated at subcritical refrigerant pressures. Refrigerant vapor compression systems operating in the subcritical range are commonly charged with fluorocarbon refrigerants such as, but not limited to, hydrochlorofluorocarbons (HCFCs), such as R22, and more commonly hydrofluorocarbons (HFCs), such as R134a, R410A, R404A and R407C. However, greater interest is being shown in “natural” refrigerants, such as carbon dioxide, for use in refrigeration systems instead of HFC refrigerants. Because carbon dioxide has a low critical temperature, most refrigerant vapor compression systems charged with carbon dioxide as the refrigerant are designed for operation in the transcritical pressure regime.
In refrigerant vapor compression systems operating in a subcritical cycle, both the refrigerant heat rejection heat exchanger, which functions in a subcritical cycle as a condenser, and the refrigerant heat absorption heat exchanger, which functions as an evaporator, operate at refrigerant temperatures and pressures below the refrigerant's critical point. However, in refrigerant vapor compression systems operating in a transcritical cycle, the refrigerant heat rejection heat exchanger operates at a refrigerant temperature and pressure in excess of the refrigerant's critical point, while the refrigerant heat absorption heat exchanger, i.e. the evaporator, operates at a refrigerant temperature and pressure in the subcritical range. Operating at refrigerant pressure and refrigerant temperature in excess of the refrigerant's critical point, the refrigerant heat rejection heat exchanger functions as a gas cooler rather than as a condenser.
In multi-stage compression systems it is known that the operational envelope of the compression device can often be extended by incorporating a refrigerant to secondary fluid heat exchanger into the refrigerant circuit between two compression stages. Commonly referred to as an intercooler, this heat exchanger provides for passing refrigerant flowing from one compression stage to another compression stage in heat exchange relationship with a cooler fluid whereby the refrigerant is cooled. Typically, the cooler fluid is a secondary fluid and the heat extracted from the refrigerant is carried away by the secondary fluid. However, incorporating an intercooler into a refrigerant vapor compression system in accord with previous practice may not be practical in some situations, for example due to physical space, weight and equipment cost considerations. Such considerations are particularly relevant in transport refrigeration applications where it is generally desirable to minimize weight, size and cost of the components of the refrigerant vapor compression system. The higher refrigerant pressures associated with operation in a transcritical refrigeration cycle, such as in refrigerant vapor compression systems using carbon dioxide as the refrigerant, complicates incorporation of an intercooler into the refrigerant circuit.
An intercooler is incorporated into a refrigeration vapor compression system having at least a two stage compression device in such a manner as to improve energy efficiency and cooling capacity of the refrigerant vapor compression system, particularly when the system is operating in a transcritical cycle with a refrigerant such as carbon dioxide.
In an aspect, the refrigerant vapor compression system includes a compression device having at least a first compression stage and a second compression stage, a refrigerant heat rejection heat exchanger disposed downstream with respect to refrigerant flow of the second compression stage, and a refrigerant intercooler disposed intermediate the first compression stage and the second compression stage. The refrigerant intercooler is disposed downstream of the refrigerant heat rejection heat exchanger with respect to the flow of a secondary fluid. In an embodiment, the secondary fluid comprises air and the refrigerant vapor compression system further includes at least one fan operatively associated with the refrigerant heat rejection heat exchanger and with the intercooler for moving the flow of air first through the refrigerant heat rejection heat exchanger and thence through the refrigerant intercooler.
In an aspect, the refrigerant vapor compression system includes a compression device having at least a first compression stage and a second compression stage, a first refrigerant heat rejection heat exchanger disposed downstream with respect to refrigerant flow of the second compression stage, a second refrigerant heat rejection heat exchanger disposed downstream with respect to refrigerant flow of the first refrigerant heat rejection heat exchanger, a first refrigerant intercooler disposed intermediate the first compression stage and the second compression stage, and a second refrigerant intercooler disposed intermediate the first compression stage and the second compression stage and downstream with respect to refrigerant flow of the first refrigerant intercooler. The refrigerant passing through the first refrigerant heat rejection heat exchanger and the first refrigerant intercooler passes in heat exchange relationship with a first secondary fluid and the refrigerant passing through the second refrigerant heat rejection heat exchanger and the second refrigerant intercooler passes in heat exchange relationship with a second secondary fluid. In an embodiment, the first secondary fluid comprises air and the refrigerant vapor compression system further includes at least one fan operatively associated with the first refrigerant heat rejection heat exchanger and with the first refrigerant intercooler for moving the flow of air first through the first refrigerant heat rejection heat exchanger and thence through the first refrigerant intercooler. In an embodiment, the second secondary fluid comprises at least one of water and glycol and the refrigerant vapor compression system further includes at least one pump operatively associated with the second refrigerant heat rejection heat exchanger and with the second refrigerant intercooler for moving the flow of water or glycol or mixture thereof first through the second refrigerant heat rejection heat exchanger and thence through the second refrigerant intercooler.
In another aspect, a refrigerant vapor compression system is provided that includes a compression device having at least a first compression stage and a second compression stage, and a refrigerant to secondary liquid heat exchanger including a first refrigerant flow passage, a second refrigerant flow passage and a secondary liquid flow passage in heat exchange relationship with each of the first refrigerant flow passage and the second refrigerant flow passage. The first refrigerant flow passage is disposed downstream with respect to refrigerant flow of the second compression stage and the second refrigerant flow passage is disposed intermediate the first compression stage and the second compression stage. In an embodiment, the refrigerant to secondary fluid heat exchanger includes a first refrigerant tube defining the first refrigerant flow passage, a second refrigerant tube defining the second refrigerant flow passage, and a cooling liquid tube defining the secondary liquid flow passage. In an embodiment, the first and second refrigerant tubes are disposed on opposite sides of the cooling liquid tube.
For a further understanding of the disclosure, reference will be made to the following detailed description which is to be read in connection with the accompanying drawing, wherein:
There is depicted in
Referring now to
The refrigerant vapor compression system 20 includes a multi-stage compression device 30, a refrigerant heat rejection heat exchanger 40, also referred to herein as a gas cooler, a refrigerant heat absorption heat exchanger 50, also referred to herein as an evaporator, and a primary expansion device 55, such as for example an electronic expansion valve or a thermostatic expansion valve, operatively associated with the evaporator 50, with various refrigerant lines 22, 2426 and 28 connecting the aforementioned components in a primary refrigerant circuit.
The compression device 30 functions to compress the refrigerant and to circulate refrigerant through the primary refrigerant circuit as will be discussed in further detail hereinafter. The compression device 30 may comprise a single, multiple-stage refrigerant compressor, for example a reciprocating compressor, having a first compression stage 30a and a second stage 30b, or may comprise a pair of compressors 30a and 30b, connected in series refrigerant flow relationship in the primary refrigerant circuit via a refrigerant line 28 connecting the discharge outlet port of the first compression stage compressor 30a in refrigerant flow communication with the suction inlet port of the second compression stage compressor 30b. The first and second compression stages 30a and 30b are disposed in series refrigerant flow relationship with the refrigerant leaving the first compression stage 30a passing to the second compression stage 30b for further compression. In the first compression stage the refrigerant vapor is compressed from a lower pressure to an intermediate pressure. In the second compression stage, the refrigerant vapor is compressed from an intermediate pressure to higher pressure. In a two compressor embodiment, the compressors may be scroll compressors, screw compressors, reciprocating compressors, rotary compressors or any other type of compressor or a combination of any such compressors.
The refrigerant heat rejection heat exchanger 40 may comprise a finned tube heat exchanger 42 through which hot, high pressure refrigerant discharged from the second compression stage 30b (i.e. the final compression charge) passes in heat exchange relationship with a secondary fluid, most commonly ambient air drawn through the heat exchanger 42 by the fan(s) 44. The finned tube heat exchanger 42 may comprise, for example, a fin and round tube heat exchange coil or a fin and flat mini-channel tube heat exchanger. If the pressure of the refrigerant discharging from the second compression stage 30b, commonly referred to as the compressor discharge pressure exceeds the critical point of the refrigerant, the refrigerant vapor compression system 20 operates in a transcritical cycle and the refrigerant heat rejection heat exchanger 40 functions as a gas cooler. If the compressor discharge pressure is below the critical point of the refrigerant, the refrigerant vapor compression system 20 operates in a subcritical cycle and the refrigerant heat rejection heat exchanger 40 functions as a condenser.
The refrigerant heat absorption heat exchanger 50 may also comprise a finned tube coil heat exchanger 52, such as a fin and round tube heat exchanger or a fin and flat, mini-channel tube heat exchanger. The refrigerant heat absorption heat exchanger 50 functions as a refrigerant evaporator whether the refrigerant vapor compression system is operating in a transcritical cycle or a subcritical cycle. Before entering the refrigerant heat absorption heat exchanger 50, the refrigerant passing through refrigerant line 24 traverses the expansion device 55, such as, for example, an electronic expansion valve or a thermostatic expansion valve, and expands to a lower pressure and a lower temperature to enter heat exchanger 52. As the liquid refrigerant traverses the heat exchanger 52, the liquid refrigerant passes in heat exchange relationship with a heating fluid whereby the liquid refrigerant is evaporated and typically superheated to a desired degree. The low pressure vapor refrigerant leaving heat exchanger 52 passes through refrigerant line 26 to the suction inlet of the first compression stage 30a. The heating fluid may be air drawn by an associated fan(s) 54 from a climate controlled environment, such as a perishable/frozen cargo storage zone associated with a transport refrigeration unit, or a food display or storage area of a commercial establishment, or a building comfort zone associated with an air conditioning system, to be cooled, and generally also dehumidified, and thence returned to a climate controlled environment.
In the embodiments depicted in
Referring now to
Referring now to
To improve the energy efficiency and cooling capacity of the refrigerant vapor compression system 20, particularly when operating in a transcritical cycle and charged with carbon dioxide or a mixture including carbon dioxide as the refrigerant, the refrigerant vapor compression system 20 includes an intercooler 80 interdisposed in refrigerant line 28 of the primary refrigerant circuit between the first compression stage 30a and the second compression stage 30b, as depicted in
In the depicted embodiments, the intercooler 80 is located in the air stream at the air outlet of the refrigerant heat rejection heat exchanger 40. In this arrangement, the ambient air drawn by the fan(s) 44 passes first through the refrigerant heat rejection heat exchanger 40 in heat exchange relationship with the hot, high pressure refrigerant vapor passing through the heat exchanger coil 42 and thereafter passes through the intercooler 80 in heat exchange relationship with the intermediate temperature and intermediate pressure refrigerant passing through the intercooler hear exchanger 82. In this arrangement, the refrigerant passing through the refrigerant heat rejection heat exchanger 40 will be cooled by the incoming ambient air stream, thereby more effectively reducing the temperature of the refrigerant leaving the refrigerant heat rejection heat exchanger 40, which is critical for the system cooling capacity and energy efficiency, particularly when the refrigerant vapor compression system 20 is operating in a transcritical cycle with carbon dioxide refrigerant.
The refrigerant vapor compression system 20 may also include a second refrigerant heat rejection heat exchanger 90 and a second intercooler 100, such as depicted in
The second intercooler 100 comprises a refrigerant-to-liquid heat exchanger having a secondary liquid pass 102 and a refrigerant pass 104 arranged in heat transfer relationship. The refrigerant pass 104 is interdisposed in refrigerant line 28 that interconnects the first compression stage 30a in refrigerant flow communication with the second compression stage 30b and forms part of the primary refrigerant circuit. In operation, refrigerant having traversed the heat exchanger 82 of the intercooler 80 passes through the refrigerant pass 104 of the second intercooler 100 in heat exchange relationship with the secondary fluid, for example water, passing through the secondary liquid pass 102 whereby the refrigerant is cooled interstage of the first compression stage 30a and the second compression stage 104. The secondary fluid pass 102 and the refrigerant pass 104 of the second intercooler 100 may be arranged in a parallel flow heat exchange relationship or in a counter flow heat exchange relationship, as desired. The second intercooler 100 may be a brazed plate heat exchanger, a tube-in-tube heat exchanger, a tube-on-tube heat exchanger or a shell-and-tube heat exchanger.
As depicted in
The second refrigerant heat rejection heat exchanger 90 and the second intercooler 100 may also be disposed in parallel flow relationship with respect to the flow of cooling water. For example, the second refrigerant heat rejection heat exchanger 90 and the second intercooler 100 may comprise a double tube-on-tube heat exchanger 110 having two refrigerant tubes disposed in close contact with a single cooling water tube. For example, referring now to
Refrigerant vapor compression systems used in transport refrigeration applications are subject to a wide range of outdoor ambient conditions over which the refrigerant vapor compression system must operate. Under some conditions, it may not be desirable to operate the refrigerant vapor compression system 20 with the refrigerant vapor passing from the first compression stage to the second compression stage passing through an intercooler. For example, under low ambient air temperature conditions, refrigerant vapor passing from the first compression stage to the second compression stage could actually condense, partially or even fully, to liquid refrigerant in traversing the intercooler. Such a situation is to be avoid as liquid refrigerant entering the compression device 30 would be detrimental to performance and could result in damage to the compression device 20.
Accordingly, referring now to
The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as basis for teaching one skilled in the art to employ the present invention. Those skilled in the art will also recognize the equivalents that may be substituted for elements described with reference to the exemplary embodiments disclosed herein without departing from the scope of the present invention.
While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be recognized by those skilled in the art that various modifications may be made without departing from the spirit and scope of the invention. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as, but that the disclosure will include all embodiments falling within the scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/329,332 entitled “Refrigerant Vapor Compression System with Intercooler” filed on Apr. 29, 2010, the content of which is incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US11/29936 | 3/25/2011 | WO | 00 | 8/28/2012 |
Number | Date | Country | |
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61329332 | Apr 2010 | US |