Patent Publication Number: US-11378318-B2

Title: Cascade system for use in economizer compressor and related methods

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to cooling and/or refrigeration systems, and more particularly to a cascade system for use in an economizer compressor for cooling and/or refrigeration systems. 
     BACKGROUND OF THE INVENTION 
     Traditional cascade refrigeration systems use two kinds of refrigerant and generally are composed of a first refrigerant system using a first refrigerant and a second refrigerant system using a second refrigerant. The first refrigerant system is typically a low temperature system and operates with the first type of refrigerant. The second refrigerant system is typically a high temperature system and operates with the second type of refrigerant. The two refrigerant systems operate independently in the cascade refrigeration system with a cascade heat exchanger situated between the two refrigerant systems. At a high level, the high temperature refrigerant system is used to cool the condenser of the low temperature refrigerant system by way of the cascade heat exchanger. 
     The two refrigerant systems of a cascade refrigeration system are generally not located adjacent one another. In many instances, one of the refrigerant systems (usually the low temperature system) is located at a location distant (remote) from the area that is being cooled, such as on the roof of a building, while the other of the refrigerant systems is located near the area that is being cooled, such as in an engine room. The cascade heat exchanger is therefore located in the same vicinity as the remote refrigerant system. In instances in which the remote refrigerant system and cascade heat exchanger are located on a rooftop, it will be appreciated that the resulting system has a large rooftop footprint and the rooftop must therefore hold a significant amount of weight. 
     Integrating a cascade system with an existing single-system (non-cascade) refrigeration system can be difficult. When retro-fitting an existing refrigeration system with a second refrigerant system in a cascade arrangement, refrigerant from the cascade heat exchanger is sent to the suction side of the compressor of the existing system. While the cascade system, as a whole, improves the efficiency of the refrigeration system, the capacity of the existing compressor is lowered and the existing compressor uses more horsepower. For example,  FIG. 1  shows such an exemplary refrigeration system. 
       FIG. 1  is a process flow schematic of a prior art refrigeration system  1  using a cascade heat exchanger  2 . The refrigeration system  1  has a first refrigerant system  1   a  and a second refrigerant system  1   b.    
     Refrigerant in the first refrigerant system  1   a  is pulled from the evaporator  3   a  into the compressor  4   a  at the suction side of the compressor  4   a . The gaseous refrigerant is compressed and discharged to the cascade heat exchanger  2 . From the cascade heat exchanger  2 , the liquid refrigerant is collected in a liquid receiver  6   a  and passed through a first expansion valve  8   a  where it is turned into a liquid/vapor mix before re-entering the evaporator  3   a.    
     In some embodiments, the first refrigerant system  1   a  may also include a condenser and/or one or more secondary refrigerant loops which bypass the cascade heat exchanger  2  so as, for example, to adjust the pressure and/or temperature experienced by the cascade heat exchanger. 
     Refrigerant from the second refrigerant system  1   b  is pulled from the evaporator  3   b  into the suction side of the compressor  4   b . As shown in  FIG. 1 , an additional portion of the second refrigerant from the cascade heat exchanger  2  enters the compressor  4   b  at the suction side of the compressor  4   b . It will be appreciated that the additional portion of the second refrigerant therefore consumes some of the volume of the compressor which would otherwise be occupied by second refrigerant from the evaporator  3   b . The second refrigerant is compressed in the compressor  4   b  and discharged to the condenser  5 . In the condenser  5 , the compressed gas is cooled and condensed to a liquid which is temporarily stored in the liquid receiver  6   b . The liquid receiver has two outlets  7   a  and  7   b , with the first outlet  7   a  moving a first (majority) portion of the liquid refrigerant to a first expansion valve  8   b   1  before it re-enters the evaporator  3   b . The second outlet  7   b  moves a second (minor) amount of liquid refrigerant to a second expansion valve  8   b   2 , and then to the cascade heat exchanger  2  and re-enters the compressor  4   b  at the suction side of the compressor  4   b.    
     It would be desirable to provide a cascade refrigeration system which addresses one or more of the drawbacks associated with the system shown in  FIG. 1 . 
     SUMMARY OF THE INVENTION 
     In accordance with at least one aspect of the invention, a refrigeration apparatus is provided. The refrigeration apparatus comprises a first refrigerant system comprising a first compressor, a cascade heat exchanger, and a first evaporator; and a second refrigerant system comprising a second compressor, a second condenser, the cascade heat exchanger, and a second evaporator, wherein the second compressor comprises an economizer port and the cascade heat exchanger is connected to the economizer port. 
     In accordance with at least a further aspect of the invention, a refrigeration apparatus is provided. The refrigeration apparatus comprises a first refrigerant system comprising a first compressor, a cascade heat exchanger, and a first evaporator, wherein the first compressor is connected to the cascade heat exchanger, the cascade heat exchanger is further connected to the first evaporator, and the first evaporator is further connected to the first compressor; and a second refrigerant system comprising a second compressor having a suction side inlet and an economizer port inlet, a second condenser, the cascade heat exchanger, and a second evaporator, wherein the second compressor is connected to the second condenser, the second condenser is further connected to the cascade heat exchanger and the second evaporator, the second evaporator is further connected to the second compressor at the suction side inlet, and the cascade heat exchanger is further connected to the second compressor at the economizer port inlet. 
     In accordance with at least a further aspect of the invention, a method of providing a cooling effect is provided. The method comprises passing a first portion of a first refrigerant through a condenser side of a cascade heat exchanger; and passing a first portion of a second refrigerant through an evaporation side of the cascade heat exchanger and into an economizer port of a compressor. 
     Various other aspects, objects, features and embodiments of the invention are disclosed with reference to the following specification, including the drawings. 
     Notwithstanding the above examples, the present invention is intended to encompass a variety of other embodiments including for example other embodiments as are described in further detail below as well as other embodiments that are within the scope of the claims set forth herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure are disclosed with reference to the accompanying drawings and are for illustrative purposes only. The disclosure is not limited in its application to the details of construction or the arrangement of the components illustrated in the drawings. The disclosure is capable of other embodiments or of being practiced or carried out in other various ways. Like reference numerals are used to indicate like components. In the drawings: 
         FIG. 1  is a process flow schematic of an existing refrigeration system incorporating a cascade heat exchanger; 
         FIG. 2  is a process flow schematic of an exemplary refrigeration system in accordance with embodiments of the present disclosure; and 
         FIG. 3  is a schematic of the exemplary refrigeration system of  FIG. 2  in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a process flow schematic of a refrigeration system  100  in accordance with embodiments of the present disclosure. 
     In the embodiment shown, the refrigeration system  100  is a cascade system having a first refrigerant system  90  and a second refrigerant system  95  with an economizer circuit  95   b.    
     In the embodiment shown, the first refrigerant system  90  is a subcritical CO 2  system and the second refrigerant system  95  is a high pressure refrigeration system. 
     The first refrigerant system  90  comprises a first evaporator  10 , a first compressor  12 , and the cascade heat exchanger  20  in a single refrigerant loop. In an embodiment, the first evaporator  10  is connected to the first compressor  12 , the first compressor  12  is further connected to the cascade heat exchanger  20 , and the cascade heat exchanger  20  is further connected to the first evaporator  10 . 
     In an embodiment, a first refrigerant system  90  may include additional first evaporators  10  and/or first compressors  12 . 
     In an embodiment, the first refrigerant system  90  may additionally include one or more liquid receivers, tanks, expansion valves and/or fans. 
     As used herein, the term “connected” and similar terms and phrases means operably coupled with, whether directly or indirectly with one or more intervening structures or assemblies. 
     The first evaporator  10  is connected to the first compressor  12 . In the embodiment shown in  FIG. 2 , the first evaporator  10  directly connected to the first compressor  12 . 
     The first compressor  12  is connected to the cascade heat exchanger  20 . In an embodiment, such as shown in  FIG. 2 , the first compressor  12  is directly connected to the cascade heat exchanger  20 . In an embodiment, the first compressor  12  is directly connected to both the first evaporator  10  and cascade heat exchanger  20 . 
     The cascade heat exchanger  20  is further connected to the first evaporator. In an embodiment, the cascade heat exchanger  20  is indirectly connected to the first evaporator  10 . In the embodiment shown in  FIG. 2 , the cascade heat exchanger  20  is indirectly connected to the first evaporator  10  by way of an expansion valve  18  and/or a liquid receiver  16 . 
     As shown in  FIG. 2 , the second refrigerant system  95  comprises a second evaporator  30 , a second compressor  32  having a suction side inlet  31  and an economizer port  33 , a condenser  34 , and the cascade heat exchanger  20 . 
     In an embodiment, the second evaporator  30  is connected to the second compressor  32  at the suction side inlet  31  and the cascade heat exchanger  20  is connected to the second compressor  32  at the economizer port  33 , the second compressor  32  is further connected to the condenser  34 , and the condenser  34  is further connected to the cascade heat exchanger  20 . 
     In other words, in the embodiment shown, the second refrigerant system  95  includes a primary second refrigerant loop  95   a  which cycles refrigerant from the second compressor  32  to the condenser  34 , to the second evaporator  30 , and back to the second compressor  32 , and a secondary refrigerant loop (or economizer circuit)  95   b  which cycles refrigerant from the second compressor  32  to the condenser  34 , to the cascade heat exchanger  20 , and back to the second compressor  32 . As used herein, the term “connected” and similar terms and phrases means operably coupled with, whether directly or indirectly with one or more intervening structures or assemblies. 
     In further embodiments, the second refrigerant system  95  may additionally include one or more liquid receivers, tanks, expansion valves and/or fans. 
     The second evaporator  30  is connected to the second compressor  32 . In an embodiment, the second evaporator  30  is directly connected to the second compressor  32  at the suction side inlet  31 . 
     The cascade heat exchanger  20  is also connected to the second compressor  32 . In the embodiment shown in  FIG. 2 , the cascade heat exchanger  20  is directly connected to the second compressor  32  at the economizer port  33 . In a further embodiment, the cascade heat exchanger  20  is indirectly connected to the second compressor  32  at the economizer port  33 . 
     The second compressor  32  is also connected to the condenser  34 . In an embodiment, the second compressor  32  is directly connected to the condenser  34 . In an embodiment, the second compressor  32  is directly connected to both the second evaporator  30  and condenser  34 . 
     The condenser  34  is connected to the cascade heat exchanger  20 . In an embodiment, the condenser  34  is indirectly connected to the cascade heat exchanger  20 . In the particular embodiment shown in  FIG. 2 , the condenser  34  is indirectly connected to the cascade heat exchanger  20  by way of a liquid receiver  36  and an expansion valve  38   a.    
     The condenser  34  is also connected to the second evaporator  30 . In an embodiment, the condenser  34  is indirectly connected to the second evaporator  30 . More particularly, as shown in  FIG. 2 , the condenser  34  is indirectly connected to the second evaporator  30  by way of a liquid receiver  36  and expansion valve  38   b.    
     In an embodiment, the first refrigerant system  90  includes a first refrigerant. In an embodiment, the first refrigerant is carbon dioxide (CO 2 ). 
     In an embodiment, the second refrigerant system  95  includes a second refrigerant. In an embodiment, the second refrigerant is selected from ammonia (NH 3 ), hydrofluorocarbons (HFCs), and combinations thereof. 
     The passage of first and second refrigerants through the first refrigerant system  90  and second refrigerant system  95 , respectively, is now described. 
     In the embodiment shown in  FIG. 2 , in the first refrigerant system  90 , gaseous refrigerant, e.g., CO 2 , from the first evaporator  10  is pulled into the compressor  12 , compressed, and discharged to the cascade heat exchanger  20 . The liquid refrigerant is then temporarily stored in the liquid receiver  16  and passed through an expansion valve  18  before re-entering the evaporator  10 . 
     In the second refrigerant system  95  (shown in  FIG. 2 ), refrigerant gas, e.g., ammonia (NH 3 ), from the evaporator  30  is pulled into the compressor  32 . The compressor  32  includes an economizer port  33 . After a given compression chamber has been sealed for compression and, in some embodiments, at least partially compressed, an additional portion of refrigerant from the cascade heat exchanger  20  is added to the chamber via the economizer port  33 . 
     It will be appreciated that the portion of the second refrigerant added to the compressor  32  via the economizer port  33  is in an at least partially compressed state. The volume of refrigerant in the chamber is therefore increased relative to a refrigerant system which does not introduce refrigerant to a compressor via an economizer port, and the overall efficiency of the compressor  32  is improved. In an embodiment, the efficiency of the refrigerant system  95 , as a whole, is approximately 10-20% improved relative to a refrigerant system having just a “second refrigerant system”  95  as described herein or a refrigerant system in which all the second refrigerant is introduced to the second compressor  32  via the suction side  31  of the compressor, such as shown in  FIG. 1 . 
     The second refrigerant (comprising a main gaseous portion from the evaporator and a minor portion from the cascade heat exchanger  20 ) is compressed and discharged to the condenser  34 . In the condenser  34 , the compressed gas is cooled and condensed to a liquid which is temporarily stored in the liquid receiver  36 . The liquid receiver  36  has two outlets  37   a ,  37   b , with a first outlet  37   a  moving a first portion of the condensed and cooled liquid refrigerant through a first expansion valve  38   a  where it is turned into a liquid/vapor mix before entering the cascade heat exchanger  20 . A second outlet  37   b  moves a second portion of the condensed and cooled liquid refrigerant to a second expansion valve  38   b  where it is turned into a liquid/vapor mix before re-entering the evaporator  30 . In an embodiment, the first portion of the condensed and cooled liquid refrigerant is less than the second portion of the condensed and cooled liquid refrigerant. The first portion of the condensed and cooled liquid refrigerant may therefore be referred to as a minor amount, while the second portion of the condensed and cooled liquid refrigerant may be referred to as a majority amount. 
     It will be appreciated that the cascade heat exchanger  20  operates as a condenser for the first refrigerant system  90  and as an evaporator for the second refrigerant system  95 . Refrigerant from the first refrigerant system  90  is condensed by the cascade heat exchanger  20  with the refrigerant of the second refrigerant system  95  evaporating and being drawn off. 
     In the embodiment shown, the first refrigerant system  90  has suction temperature from −50° F. to −30° F. and a condensing temperature from 15° F. to 25° F. 
     In the embodiment shown, the second refrigerant system  95  has a suction temperature from −20° F. to 0° F. and a condensing temperature from 95° F. to 120° F. 
     In the embodiment shown, the second refrigerant system  95  has an economizer temperature range from 15° F. to 25° F. to match the condensing temperature of the first refrigerant system  90 . 
     In an embodiment, the first refrigerant is CO 2  and the first refrigerant system  90  is a subcritical CO 2  system. 
     In an embodiment, the second refrigerant is ammonia (NH 3 ) and the second refrigerant system  95  is a high pressure refrigeration system. 
       FIG. 3  is a schematic of the exemplary refrigeration system of  FIG. 2 , although not all of the system components shown in  FIG. 2  and shown in  FIG. 3 . As shown in  FIG. 3 , all or a portion of the first refrigerant system  90  may be provided at any suitable location such as on the roof  102  of a facility or other suitable location. The first refrigerant system  90  is operated and controlled in a conventional manner to provide a desired amount of cooling to the cold storage and the second refrigerant system  95  also provides the desired condensing pressure and temperature to the cascade heat exchanger  20  in order to control the pressure of the first refrigerant system  90  using the economizer port  33 . 
     In the particular embodiment shown in  FIG. 3 , the first refrigerant system  90  is provided on a rooftop  102  of a building  101  with the second refrigerant system  95  in an existing engine room  103  of the building  101 . While in the embodiment shown the cascade heat exchanger  20  is located on the rooftop  102 , it will be appreciated that the cascade heat exchanger  20  may be located in the building  101  or, more particularly, in the engine room  103 , depending on the design of the refrigeration system  100 . 
     By utilizing a cascade refrigeration system as shown and described, the system  100  is more efficient and less expensive than conventional cascade systems. Moreover, only the subcritical CO 2  unit need be located on a roof or other elevated location. The rooftop weight and footprint are therefore reduced. 
     For example, refrigerant systems consistent with the second refrigerant systems  95  disclosed herein take up a large area and are generally around 100-500 tons or more. In contrast, refrigerant systems consistent with the first refrigerant systems  90  disclosed herein take up a much smaller area and are generally around 30-60 tons. The present system  100  is therefore advantageous to increase cooling capabilities of refrigerant systems when space near the site to be cooled is limited and/or the weight capacity of a rooftop is limited. Similarly, when looking to increase the cooling capabilities of existing refrigerant systems, it may not be easy or practical to modify or add to the existing refrigerant system (e.g., there is not enough room in an engine room). Retrofitting existing refrigerant systems (“second refrigerant systems”  95 ) with a first refrigerant system  90  as disclosed herein will increase the cooling capabilities of the existing refrigerant systems without requiring significant modification to the existing refrigerant system and/or its existing location (e.g., the first refrigerant system  90  may, in some instances, be small enough to install local to the existing refrigerant system and/or of low enough weight to be installed on a rooftop or some other remote location otherwise unable to support the existing refrigerant system). 
     In an embodiment, a method of providing a cooling effect is provided. 
     In an embodiment, the method of providing a cooling effect includes passing a first portion of a first coolant through a condenser side of a cascade heat exchanger, and passing a first portion of a second coolant through an evaporation side of a cascade heat exchanger and into an economizer port of a compressor. 
     In an embodiment, the method of providing a cooling effect further includes passing the first portion of the first coolant through a first evaporator and a first compressor before passing the first portion of the first coolant through the condenser side of the cascade heat exchanger. 
     In an embodiment, the method further includes passing the first portion of the second coolant through a second compressor and a second condenser before passing the first portion of the second coolant through the evaporator side of the cascade heat exchanger. 
     In an embodiment, the method includes providing a first refrigerant system comprising the first evaporator, the first compressor, and the cascade heat exchanger, as described according to any one or more embodiments herein. 
     In an embodiment, the method includes providing a second refrigerant system comprising the second compressor and second condenser, as described according to any one or more embodiments herein. 
     In an embodiment, the first refrigerant system further includes at least one of a condenser, an expansion valve and a first liquid receiver. In an embodiment, the method further includes passing the first portion of the first refrigerant through the first evaporator, first compressor, a first condenser, the condenser side of the cascade heat exchanger, a first liquid receiver, and an expansion valve, and returning the at least a first portion of the first refrigerant to the first evaporator. 
     In an embodiment, the method further includes passing a second portion of the first refrigerant through the first evaporator and first compressor and returning the second portion of the first refrigerant to the first evaporator. In an embodiment, the process includes passing the second portion of the first refrigerant through the first evaporator, first compressor, first condenser, and an expansion valve before returning the second portion of the first refrigerant to the first evaporator. 
     In an embodiment, the second refrigerant system further includes at least one of an expansion valve, a second liquid receiver, and an economizer tank. In an embodiment, the method further includes passing the first portion of the second refrigerant through the second compressor, the second condenser, the second liquid receiver, the economizer tank, an expansion valve, the evaporator side of the cascade heat exchanger and the economizer port of the second compressor. 
     In an embodiment, the method further includes passing a second portion of the second refrigerant through the second evaporator, the second compressor and the second condenser before returning the second portion of the second refrigerant to the second evaporator. In an embodiment, the process includes passing the second portion of the second refrigerant through the second evaporator, the second compressor, the second condenser, a second liquid receiver, and an expansion valve before returning the second portion of the second refrigerant to the second evaporator. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.