Abstract:
A refrigerant cycle includes economized tandem compressors. The refrigerant cycle is also provided with a common economizer circuit for all tandem compressors. Common manifolds communicate discharge, suction and economizer return flows within the refrigerant cycle to each of the tandem compressors. Also, an optional unloader function is provided for each of the compressors. Various arrangements allow enhanced operation control, improved system reliability and reduced equipment life-cycle cost.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a refrigerant cycle having tandem compressors, wherein the tandem compressors are each provided with an economizer port and can operate within an economizer cycle.  
         [0002]     Tandem compressor refrigerant cycles are known, and have two or more compressors compressing refrigerant and delivering it to a common discharge manifold. Similarly, these compressors are drawing refrigerant from a common suction manifold. In some arrangements, oil equalization lines connecting oil sumps of tandem compressors for oil management, and suction pressure equalization lines connecting shells of the tandem compressors are employed. The tandem compressors provide flexibility to a refrigerant cycle designer, such as allowing additional levels of capacity control by turning off some of the compressors. Moreover, in some applications that would otherwise require a very large single compressor, the tandem compressors provide design options, availability and potential cost savings.  
         [0003]     In refrigerant cycles having a single compressor, it is also known to utilize an economizer cycle. An economizer provides system performance enhancement under certain conditions by tapping off a portion of a refrigerant flow downstream of a condenser. The tapped refrigerant is passed through a separate expansion device, and then passes through an economizer heat exchanger along with the main refrigerant flow. The tapped refrigerant cools the main refrigerant flow, such that the main refrigerant flow has a greater cooling capacity when it reaches the evaporator. The tapped refrigerant is returned to an intermediate point in the compression cycle. Furthermore, economizer cycles provide extra steps of unloading, closely matching capacity requirements, as well as enhancing operation control and reducing life-cycle cost of equipment. Additionally, when an economizer cycle is combined with various means of compressor unloading, even greater benefits can be achieved. Although economizer circuits provide additional benefits to a refrigerant cycle as described above, they have not been incorporated into refrigerant cycles having tandem compressors.  
       SUMMARY OF THE INVENTION  
       [0004]     In a disclosed embodiment of this invention, a refrigerant cycle has tandem compressors, and each compressor is provided with an economizer port connected to a common economizer circuit. In a first disclosed embodiment, an economizer return manifold communicates with two economizer lines leading to the economizer ports of the individual compressors. Shutoff valves may be placed on these individual return lines. Further, it is preferable that an unloader valve is placed on a line connecting the economizer return line to a suction line. As an alternative, if the two tandem compressors are also connected by a suction pressure equalization line, the unloader valve may communicate the economizer line back to this pressure equalization line. The refrigerant cycle can operate with either one or both compressors unloaded, either one or both compressors in non-economizer operation, either one or both compressors in economized operation, and either one or both compressors in unloaded economized operation. There are thus several additional levels of capacity available.  
         [0005]     In an alternative embodiment, it may be that only one of the two economizer return lines is provided with a shutoff valve, and a main economizer shutoff valve is placed on the common economizer manifold. In this embodiment, one of the two tandem compressors is selected to be initially moved out of economizer operation in a preferential manner. This would be the compressor with the shutoff valve on its individual economizer return line. In a lower cost alternative, only the economizer manifold includes the shutoff valve.  
         [0006]     Further, in a lower cost embodiment, a single unloader valve may communicate each of the economizer lines back to suction or pressure equalization line. By connecting the unloader line to the economizer line, refrigerant can be effectively tapped from the intermediate compression chambers back to suction when the economizer shutoff valves are closed.  
         [0007]     While the description above is given for only two compressors connected in the tandem arrangement, it can be extended to additional economized compressors connected to each other in the tandem arrangement.  
         [0008]     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  
       [0009]      FIG. 1  is a schematic view of a refrigerant cycle including tandem compressors.  
         [0010]      FIG. 2  shows design alternatives to the  FIG. 1  embodiment.  
         [0011]      FIG. 3  schematically shows another embodiment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]      FIG. 1  shows a refrigerant cycle  20  having tandem compressors  22  and  24 . Compressors  22  and  24  communicate compressed refrigerant into individual discharge lines  26  leading to a common discharge manifold  28 . Downstream of discharge manifold  28 , the refrigerant is delivered to a condenser  30 .  
         [0013]     An economizer tap  32  taps off of a main refrigerant line  33 , downstream of condenser  30 . As shown, an economizer expansion device  34  is placed on the tap line  32  upstream of an economizer heat exchanger  36 . The tap line  32  and the main refrigerant flow line  33  both pass through the economizer heat exchanger  36 , as known. In practice, it is preferred that the refrigerant in the tapped refrigerant line  32  move in a counter-flow relationship to the main refrigerant flow in line  33 , rather than moving in the same direction as illustrated. However, for simplicity of illustration, the flows are shown in the same direction. As is known, the main refrigerant flow  33  is cooled in the economizer heat exchanger  36  by the tapped refrigerant  32 . The tapped refrigerant is returned through a common economizer manifold  38  and individual economizer manifolds  52  to the individual economizer compressor ports  55  of the compressors  22  and  24 . Downstream of the economizer heat exchanger  36  is a main expansion device  40 , and an evaporator  42 . Refrigerant is delivered from the evaporator  42  into a common suction return manifold  44 . Suction return manifold  44  communicates with individual suction return lines  46  leading to both compressors  22  and  24 .  
         [0014]     Optional unloader lines  48  include unloader valves  50  communicating individual economizer return lines  52  to the individual suction lines  46  of both compressors  22  and  24 . It should be noted that an alternate connection to a common suction manifold  44  is also permitted. As shown, economizer shutoff valves  54  are placed on each of the economizer return lines  52 . As is known, the economizer flow is returned from manifold  38  through return line  52  and the valves  54  into economizer compressor ports  55 . As is known, this refrigerant is returned at an intermediate point in the compression cycle of the compressors  22  and  24 . If the valves  54  are closed and the unloader valves  50  are open, then refrigerant can move from the economizer ports  55 , outwardly of the compression chambers, through the lines  48 , and into the lines  46 . This allows either one or both of the compressors  22  and  24  to operate in an unloaded mode.  
         [0015]     Also, as is known, a pressure equalization line  56  can connect the low pressure side of the compressors  22  and  24  for proper oil management.  
         [0016]     Further, an oil equalization line  58  may separately connect the compressors to additionally improve oil management for the tandem compressors.  
         [0017]     When operating the refrigerant cycle  20 , the compressors can be operated in economized mode, non-economized mode, unloaded mode and economized unloaded mode. Either or both of the compressors can be operated in any of those modes, and thus, several levels of capacity control are provided.  
         [0018]      FIG. 2  shows an alternative embodiment wherein a first economizer shutoff valve  60  is placed on the common manifold  38 . A second economizer shutoff valve  62  remains on the return individual economizer line  64  for the compressor  22 , and controls refrigerant flow from the manifold  38  to the economizer port  63 . The other economizer return line  56  leading to the compressor  24  and the economizer injection port  67  does not have an individual shutoff valve. When control  100  controls the economized operation between the compressors  22  and  24 , it may close the valve  60  to turn both compressors off of economized operation. If only one compressor is to be in an economized operation, then valve  60  is open but valve  62  is closed. In this manner, only compressor  24  is being operated in economized mode.  
         [0019]     A unique placement of the unloader line is also shown in  FIG. 2 . As shown, an individual unloader connection line  68  communicates with the individual economizer return line  66  and an individual unloader connection line  72  communicates with the individual economizer return line  64 . Both lines  68  and  72  lead into common unloader return line  73  having an unloader valve  70 . While this type flow control may return the refrigerant to the suction line  46 , it is also a design option for this flow arrangement, or for the dual unloader valve arrangement of  FIG. 1 , to return the refrigerant to the compressor equalization line  56  as shown in  FIG. 2 .  
         [0020]     As shown in  FIG. 3 , the above invention could extend to more than two compressors. Here, manifolds  28 ,  33  and  44  communicate with three compressors  22 ,  24  and  90 . Of course, even greater numbers of compressors could be connected in this manner.  
         [0021]     Although preferred embodiments of this invention have 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.