Refrigeration system employing multiple economizer circuits

[0002] The present invention relates generally to a refrigeration system employing multiple economizer circuits to increase capacity and efficiency of the refrigeration system.

[0003] System capacity can be increased by increasing the subcooling of the refrigerant leaving the condenser. In a standard (non-economized) refrigeration system, the amount of subcooling typically ranges from 0 to 15° F. An economizer can be employed to additionally subcool the liquid refrigerant exiting the condenser, increasing the capacity and efficiency of the refrigeration system.

[0004] In an economized system, the refrigerant is split into two flow paths after leaving the condenser. The first flow path is expanded to a low pressure by an expansion valve prior to passing into the economizer heat exchanger. The second flow path flows directly into the economizer heat exchanger and is cooled by the refrigerant in the first flow path. The refrigerant from the first path then flows along an economizer return path and is injected through economizer ports into the compressor. The vapor refrigerant in the second path is then expanded by a main expansion valve. By employing an economizer, both system capacity and efficiency is increased.

[0005] It would be beneficial to employ multiple economizer circuits to further increase the capacity of the refrigeration system. The benefits of employing multiple economizer circuits are especially pronounced for a refrigeration system operating with a high discharge to suction pressure ratio. Multiple economizers have not been employed in prior refrigeration systems as the refrigerant flow from each of the economizers mixes at the point of injection. For example, prior screw compressors include a pair of rotors. As only two rotors are employed, the rotational angle of the compression process is not large enough to prevent vapor communication among the suction port, the low pressure economizer port, the high pressure economizer port, and the discharge port.

[0006] The multiple stage economizer refrigeration system of the present invention includes a compressor, a condenser, a high pressure economizer circuit, a low pressure economizer circuit, expansion valves, and an evaporator. After the refrigerant exits the condenser, the refrigerant splits into two flow paths. The first path of refrigerant is expanded to a lower pressure in an expansion valve prior to flowing into the high pressure economizer heat exchanger. Refrigerant from the main path flows through the high pressure economizer heat exchanger and is cooled by the refrigerant in the first path. The refrigerant in the first path is returned to the compressor through the high pressure economizer port.

[0007] After being cooled in the high pressure economizer, the refrigerant from the main path again splits into two flow paths. Refrigerant in the second path is expanded to a low pressure in an expansion valve prior to flowing into the low pressure economizer heat exchanger. Refrigerant from the main path passes through the low pressure economizer heat exchanger and is cooled by the refrigerant in the second path. The refrigerant from the second path is returned to the compressor through the low pressure economizer port. Thus, additional subcooling of the main flow of the refrigerant is accomplished by subcooling in two stages. For even greater subcooling benefits, more than to stages can be implemented.

[0008] After being cooled in the low pressure economizer heat exchanger, the refrigerant is expanded in the main expansion valve, heated in the evaporator, and enters the compressor at the suction port. After compression, the refrigerant is discharged through the discharge port.

[0009] The multiple economizer refrigeration system can be employed in a screw compressor or a scroll compressor. The screw compressor includes a male rotor including a plurality of helical threads and a pair of opposing female rotors each including a plurality of helical threads. The helical threads of the male rotor engage the helical threads of the female rotors to create two sets of compression chambers. One set of compression chambers communicates with refrigerant from the high pressure economizer, and the other set of compression chambers communicates with refrigerant from the low pressure economizer.

[0010] Alternately, a scroll compressor is employed in the multiple economizer refrigeration system. Vapor refrigerant from the low pressure economizer is injected into the scroll compressor through a pair of low pressure injections ports. The low pressure ports are located such that vapor injection initiates shortly after the suction port is covered and the compression chambers are sealed from suction. Vapor refrigerant from the high pressure economizer is injected into the scroll compressor through a high pressure injection port. The high pressure injection port is located proximate to the discharge port. Refrigerant injection through the high pressure injection port and the low pressure injection ports occurs into separate scroll compressor pockets.

[0011] These and other features of the present invention will be best understood from the following specification and drawings.

[0012] The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

[0013] FIG. 1 illustrates a schematic diagram of a prior art refrigeration system employing a single economizer circuit;

[0014] FIG. 2 illustrates a graph relating pressure to enthalpy for the prior art refrigeration system of FIG. 1;

[0015] FIG. 3 illustrates a schematic diagram of the refrigeration system of the present invention employing dual economizer circuits;

[0016] FIG. 4 illustrates a graph relating pressure to enthalpy for the refrigeration system of FIG. 4;

[0017] FIG. 5 illustrates a cross sectional view of a screw compressor employed in a refrigerant system utilizing dual economizers taken along line 5—5 of FIG. 6;

[0018] FIG. 6 illustrates a top view of the screw compressor of FIG. 5;

[0019] FIG. 7 illustrates a scroll compressor employed in a refrigerant system utilizing dual economizers when injection of refrigerant begins; and

[0020] FIG. 8 illustrates the scroll compressor of FIG. 7 when injection of the refrigerant from the low pressure economizer is still in progress, and injection of refrigerant from the high pressure economizer is almost complete.

[0021] FIG. 1 illustrates a schematic diagram of a prior art single economizer refrigeration system 20. The system 20 includes a compressor 22, a condenser 24, a main expansion device 26, an evaporator 28, and an economizer heat exchanger 30. Refrigerant circulates though the closed circuit system 20. After the refrigerant exits the compressor 22 through the discharge port 42 at high pressure and enthalpy, the refrigerant loses heat in the condenser 24, exiting at lower enthalpy and high pressure. The refrigerant then splits into two flow paths 32 and 34. Refrigerant in path 34 is expanded to a low pressure in the expansion valve 36 prior to flowing through the economizer heat exchanger 30. As the refrigerant in the path 32 flows through the economizer heat exchanger 30, it is cooled by the refrigerant in path 34. Refrigerant in path 34 from the economizer heat exchanger 30 is returned along the economizer return path 56 to the compressor 22 through the economizer port 38 at a pressure between the suction pressure and the discharge pressure. The refrigerant in line 32 is expanded by the main expansion device 26 and then heated in the evaporator 28. The refrigerant enters the compressor 22 at the suction port 40. Downstream, this refrigerant mixes with the refrigerant from the return path 56. A graph relating enthalpy to pressure for the refrigeration system 20 is illustrated in FIG. 2. The length of the evaporation line 29 illustrates the cooling capacity of the system 20.

[0022] FIG. 3 illustrates a schematic diagram of the refrigeration system 120 of the present invention employing dual economizer heat exchangers 130aand 130b. The system 120 includes a compressor 122, a condenser 124, a high pressure economizer heat exchanger 130a, a low pressure economizer heat exchanger 130b, an expansion valve 126, and an evaporator 128. After the refrigerant exits the compressor 122 at high pressure and enthalpy through the discharge port 142, the refrigerant loses heat in the condenser 124, exiting the condenser 124 at low enthalpy and high pressure. The refrigerant then splits into two flow paths 132aand 134a. Refrigerant in path 134ais expanded to a low pressure by the low pressure expansion valve 136aprior to flowing through the economizer heat exchanger 130a. As the refrigerant in the path 132aflows through the high pressure economizer heat exchanger 130a, it is cooled by the refrigerant in path 134a. Refrigerant from the economizer heat exchanger 130ais returned along the economizer return path 156ato the compressor 122 through the high pressure economizer port 138afor compression in compression chambers 148a.

[0023] After being cooled in the high pressure economizer heat exchanger 130a, the refrigerant in path 132asplits into two flow paths 132band 134b. Refrigerant in path 134bis expanded to a low pressure by the low pressure expansion valve 136bprior to flowing through the low pressure economizer heat exchanger 130b. As the refrigerant in the path 132bflows through the low pressure economizer heat exchanger 130b, it is cooled by the refrigerant in path 134b. Refrigerant in path 134bfrom the economizer heat exchanger 130bis returned along the economizer return path 156bto the compressor 122 through the low pressure economizer port 138bfor compression in compression chambers 148b.

[0024] Refrigerant from path 132bis then expanded in the main expansion valve 126. The main expansion valve 126, as well as the high pressure and low pressure expansion valves 136aand 136b, can be electronic EXV (electric expansion vales) or TXV valves. After evaporation in the evaporator 128, the refrigerant enters the compressor 122 through the suction port 140. Refrigerant from the paths 134aand 134benters the compressor 122 through the high pressure economizer port 138aand the low pressure economizer port 138b, respectively, and mixes with the refrigerant in the compressor 122 for compression.

[0025] The economizer ports 138aand 138bcommunicate with the compression chambers 148aand 148b, respectively, which are each at a pressure which varies during the compression cycle of the compressor 122. To prevent high pressure to low pressure leak of refrigerant from line 156ato 156b, the refrigerant from the economizer heat exchangers 130aand 130bwhich flows in the compression chambers 148aand 148bmust remain separate at the point of injection in the compressor 122.

[0026] Multiple steps of compressor 122 unloading are also possible with the system 120 of the present invention. In one step, both of the economizer heat exchangers 130aand 130bare engaged. Alternatively, in additional steps, either of the economizer heat exchangers 130aand 130bcan be disengaged by shutting off the expansions valves 136aand 136b, respectively. Both of the economizer heat exchangers 130aand 130bcan be disengaged for non-economized operation by shutting off both of the expansion valves 136aand 136b.

[0027] To regulate capacity of the system 120, two additional solenoid valves 144aand 144bmay be employed. A first solenoid valve 144aregulates the flow of refrigerant between the high pressure economizer port 138aand the low pressure economizer port 138b. A second solenoid valve 144bregulates the flow of refrigerant between the low pressure economizer port 138band the compressor suction port 140.

[0028] The solenoid valves 144aand 144bcan be opened or closed depending on system 120 requirements to achieve steps of compressor 122 or system 120 unloading. By opening the solenoid valves 144aand 144, the refrigerant flow from both the high pressure and the low pressure economizer ports 138aand 138bcan be by-passed into the suction port 140 to reduce cooling. Alternately, by opening the solenoid valve 144aand closing the solenoid valve 144b, the refrigerant flow from the high pressure economizer port 138acan be by-passed into the economizer port 138b. Alternately, by closing the solenoid valve 144aand opening the solenoid valve 144b, the refrigerant flow from the low pressure economizer port 138bcan be bypassed into suction line 166.

[0029] By controlling the expansion valves 136aand 136band solenoid valves 144aand 144b, the operation of the compressor 122 and system 120 can be adjusted to meet the cooling demands and achieve optimum capacity and efficiency. A worker of ordinary skill in the art would know how to control these valves depending on the system 120 requirements.

[0030] FIG. 4 illustrates a graph relating enthalpy to pressure for the refrigeration system 120 of FIG. 3 employing dual economizer heat exchangers 130aand 130b. As shown, the evaporation line 129 of the refrigerant system 120 is longer than the evaporation line 29 of the refrigeration system 20 employing one economizer 30 (illustrated in FIG. 2). This indicates that the refrigeration system 120 employing dual economizers 130aand 130bhas a greater cooling capacity than the refrigeration system 20 employing a single economizer 30.

[0031] FIG. 5 illustrates a cross-sectional view of a tri-rotor screw compressor 222 employed in the dual economizer system 120 of the present invention. The screw compressor 222 includes a housing 244 having a central portion 246cand a pair of opposing portions 246aand 246b. The central portion 246chouses a male rotor 248cincluding a plurality of helical threads 250c. The opposing portions 246aand 246beach house a female rotor 248aand 248b, each including a plurality of helical threads 250aand 250b, respectively. The helical threads 250cof the male rotor 248cengage the helical threads 250bof the female rotors 248aand 248b, respectively, to create high pressure compression chambers 252aand low pressure compression chambers 252b, respectively. Refrigerant from the high pressure economizer 130aenters the compressor 222 through the high pressure economizer port 238aand is compressed in the high pressure compression chambers 252a. Refrigerant from the low pressure economizer 130benters the compressor 222 through the low pressure economizer port 238band is compressed in the low pressure compression chambers 252b. As the refrigerant from the economizer heat exchangers 130aand 130bis injected into the compressor 222 through separate economizer ports 238aand 238b, respectively, the refrigerant from the economizers 130aand 130bremains separate at the point of injection into the compressor 222.

[0032] After evaporation, the refrigerant splits into two streams. As shown in FIG. 6, one stream enters the suction port 254afor compression in the compression chambers 252awith the refrigerant from the high pressure economizer 130a, and the other stream enters suction port 254bfor compression in the compression chambers 252bwith refrigerant from the low pressure economizer 130b. After compression, the refrigerant in the compression chambers 252aand 252bis discharged through the discharge ports 242aand 242b, respectively, for condensation. As shown, the low pressure economizer port 238bis positioned closer to the suction ports 254aand 254b, and the high pressure economizer port 238ais positioned closer to the discharge ports 254aand 254b.

[0033] As the compression chambers 252aand 252bare separate and are on opposing sides of the housing 244, there is no communication between the refrigerant from the high pressure economizer 230aand the refrigerant from the low pressure economizer 230a. By optimizing the position and size of economizer ports 238aand 238b, vapor communication between the compression chambers 252aand 252b, the suction ports 240aand 240b, and the discharge ports 242aand 242bis prevented, allowing for control of the pressure in each economizer 130aand 130b.

[0034] FIG. 7 illustrates a scroll compressor 322 employed in the refrigeration system 120 employing dual economizer heat exchangers 130aand 130b. The scroll compressor 322 includes a non-orbiting scroll 344, an orbiting scroll 346, and a plurality of compression chambers 348aand 348bdefined therebetween.

[0035] As the refrigerant from the economizer heat exchangers 130aand 130bis injected into the compressor 322 through separate economizer ports 338aand 338b, respectively, and as long as solenoid valve 144aremains closed, the refrigerant in lines 156aand 156b, respectively, remains separate, and there is no communication between compression chambers 348aand 348b.

[0036] Vapor refrigerant from the low pressure economizer heat exchanger 130bis injected into a pair of compression chambers 348bof the scroll compressor 322 through a pair of low pressure injections ports 338b. Vapor refrigerant from the high pressure economizer heat exchanger 130ais injected into the compression chambers 348aof the scroll compressor 322 through a high pressure injection port 338a. The high pressure injection port 338ais located proximate to the discharge port 342. The injection ports 338aand 338btypically extend through the body of the fixed scrolls 344 and into the compression chambers 348aand 348b, respectively.

[0037] FIG. 7 illustrates the position of scroll compressor 322 when injection of refrigerant from the dual economizer heat exchangers 130aand 130bbegins. The injection ports 338aand 338bhave just opened to allow the vapor refrigerant from each economizer heat exchanger 130aand 130bto enter the compression chambers 348aand 348b, respectively.

[0038] FIG. 8 illustrates the position of the scroll compressor 322 when refrigerant injection from the low pressure economizer 130binto the compression chambers 348bis still in progress and refrigerant injection from the high pressure economizer 130ainto the compression chamber 348ais almost complete. At this stage, the high pressure injection port 338ais separated from the discharge port 342 as the high pressure injection port 338ais still covered by the orbiting scroll 346 prior to the initiation of the discharge process through a discharge valve that may cover the discharge port.

[0039] The scroll compressor 322 can alternatively include additional injection ports and compression chambers to allow for three ore more economizer heat exchangers. If three economizers are to be employed, the scroll compressor 322 will preferably have more than 2.5 turns.

[0040] There are several benefits to the refrigerant system 120 of the present invention. For one, a higher operating efficiency is possible employing multiple economizer heat exchangers 130aand 130b. Additionally, an increase in refrigeration capacity is possible. Compressor reliability is also improved due to a decrease in the discharge temperature. Control of system capacity is also increased by alternating the engagement of economizer circuits, as well as initiating bypass operation between the economizer circuits or between any of the economizer circuits and suction line.

[0041] The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.