Patent Publication Number: US-2022235979-A1

Title: Refrigeration system with separate feedstreams to multiple evaporator zones

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/710,566, entitled “Refrigeration System with Separate Feedstreams to Multiple Evaporator Zones,” filed Sep. 20, 2017, which is a continuation of U.S. patent application Ser. No. 14/614,693, now U.S. Pat. No. 9,791,188, entitled, “REFRIGERATION SYSTEM WITH SEPARATE FEEDSTREAMS TO MULTIPLE EVAPORATOR ZONES,” filed Feb. 5, 2015, which claims priority from U.S. Patent Application Ser. No. 61/937,033 entitled “REFRIGERATION SYSTEM WITH SEPARATE FEEDSTREAMS TO MULTIPLE EXPANDING EVAPORATOR ZONES,” filed Feb. 7, 2014, and from U.S. Patent Application Ser. No. 61/993,865 entitled “REFRIGERATION SYSTEM WITH WARMING FEATURE,” filed May 15, 2014, the entireties of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Refrigeration systems comprising a compressor, a condenser and an evaporator come in a wide variety of configurations. The most common of these configurations is generally termed a “direct expansion system.” In a direct expansion system, a refrigerant vapor is pressurized in the compressor, liquefied in the condenser and allowed to revaporize in the evaporator and then flowed back to the compressor. 
     In direct expansion systems, the amount of superheat in the refrigerant vapor exiting the evaporator is almost exclusively used as a control parameter. Direct expansion systems operate with approximately 20% to 30% of the evaporator in the dry condition to develop superheat. 
     A problem with this control method is that superheat control is negatively effected by close temperature differences, wide fin spacing or pitch, light loads and water content. The evaporator must be 20% to 30% larger for equivalent surface to be available. Also, superheat control does not perform well in low-temperature systems, such as systems using ammonia or similar refrigerant, wherein the evaporator temperatures are about 0° F. 
     An additional disadvantage of the superheat control method is that it tends to result in excessive inlet flashing. Such inlet flashing results in pressure drop and instability transfer within the evaporator, and results in the forcible expansion of liquid out of the distal ends of the evaporator coils. Also, this control method is especially problematic when the refrigerant is ammonia or other low-temperature refrigerant, because so much liquid refrigerant is typically expelled from the evaporator to require the use of large liquid traps downstream of the evaporator. 
     Thus, in all superheat controlled expansion systems, negative compromises are necessarily made in efficiency and capacity. 
     The aforementioned problems have largely been overcome by the recent development of a refrigeration system control method wherein evaporator feed rate is controlled in response to refrigerant condition measured within the system evaporator. (See in U.S. patent application Ser. No. 13/312,706, entitled “REFRIGERATION SYSTEM CONTROLLED BY REFRIGERANT QUALITY WITHIN EVAPORATOR,” filed Dec. 6, 2011.) However, there remains a strong incentive for even greater efficiencies. 
     SUMMARY OF THE INVENTION 
     The invention provides a refrigeration system with such greater efficiencies. In one aspect, the invention is a refrigeration system comprising: (a) a fluid tight circulation loop including a compressor, a condenser and an evaporator, the circulating loop being configured to continuously circulate a refrigerant which is capable of existing in a liquefied state, a gaseous state and a two-phase state comprising both refrigerant in the liquefied state and refrigerant in the gaseous state, the evaporator having an outlet port and at least three evaporator zones, each evaporator zone having an inlet port, the circulation loop being further configured to (i) compress refrigerant in a gaseous state within the compressor and cool the refrigerant within the condenser to yield refrigerant in the liquefied state; (ii) flow refrigerant from the condenser into the evaporator via the inlet ports of each evaporator zone, wherein the refrigerant partially exists in a two-phase state; (iii) flow refrigerant from the evaporator to the compressor; (iv) repeat steps (i)-(iii); (v) measure the condition of the refrigerant with a refrigerant condition sensor disposed within the evaporator upstream of the evaporator outlet port; and (vi) control the flow of refrigerant to the evaporator in step (ii) based upon the measured condition of the refrigerant within the evaporator from step (v); and (b) a controller for controlling the flow rate of refrigerant to the evaporator based upon the measured condition of the refrigerant within the evaporator upstream of the evaporator outlet port. 
     In another aspect, the invention is a method of employing the refrigeration system, comprising the steps of: (a) compressing refrigerant in a gaseous state within the compressor and cooling the refrigerant within the condenser to yield refrigerant in the liquefied state; (b) flowing refrigerant from the condenser into the evaporator via the inlet ports of each evaporator zone, wherein the refrigerant partially exists in a two-phase state; (c) flowing refrigerant from the evaporator to the compressor; (d) repeating steps (a)-(c); (e) measuring the condition of the refrigerant with a refrigerant condition sensor disposed within the evaporator upstream of the outlet port; and (f) controlling the flow rate of refrigerant to the evaporator in step (b) based upon the measured condition of the refrigerant condition of the refrigerant from step (e). 
    
    
     
       DRAWINGS 
       Features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  is a flow diagram illustrating a first refrigeration system having features of the invention; 
         FIG. 2  is a flow diagram illustrating a second refrigeration system having features of the invention; 
         FIG. 3  is a flow diagram illustrating a third refrigeration system having features of the invention; is a first refrigeration system having features of the invention; 
         FIG. 4  is a flow diagram illustrating a fourth refrigeration system having features of the invention; is a first refrigeration system having features of the invention; 
         FIG. 5  is a diagrammatic representation of a continuously expanding continuous tube within an evaporator useable in the invention; 
         FIG. 6  is a flow diagram illustrating a fifth refrigeration system having features of the invention; is a first refrigeration system having features of the invention; and 
         FIG. 7  is a flow diagram illustrating a sixth refrigeration system having features of the invention; is a first refrigeration system having features of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following discussion describes in detail one embodiment of the invention and several variations of that embodiment. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. 
     Definitions 
     As used herein, the following terms and variations thereof have the meanings given below, unless a different meaning is clearly intended by the context in which such term is used. 
     The terms “a,” “an,” and “the” and similar referents used herein are to be construed to cover both the singular and the plural unless their usage in context indicates otherwise. 
     As used in this disclosure, the term “comprise” and variations of the term, such as “comprising” and “comprises,” are not intended to exclude other additives, components, integers, ingredients or steps. 
     The Invention 
     The invention is a refrigeration system  10  and a method for controlling the operation of the refrigeration system  10 . The refrigeration system  10  comprises a fluid tight circulation loop  11  including a compressor  12 , a condenser  14  and an evaporator  18 . 
     The compressor  12  has a discharge side  56  and a suction side  57 . The condenser  14  has at least one condenser input port  92  and a condenser outlet port  94 . The evaporator  18  has at least three evaporator input ports  36  and an evaporator outlet port  34 . 
     The circulating loop  11  is configured to continuously circulate a refrigerant which is capable of existing in a liquefied state, a gaseous state and a two-phase state comprising both refrigerant in the liquefied state and refrigerant in the gaseous state. 
     The evaporator  18  preferably comprises at least one continuous length of tubing  22  having an inlet opening  32 —which constitutes one of the evaporator inlet ports  36 —and a discharge opening  33 —which constitutes the evaporator outlet port  34 . In such embodiments the at least one continuous length of tubing  22  comprises the least three evaporator zones, an upstream-most evaporator zone, a downstream-most evaporator zone and one or more intermediate evaporator zones. Each evaporator zone has one or more evaporator input ports  36 . The evaporator inlet port  36   a  for the upstream-most evaporator zone is the inlet opening  32  of the at least one continuous length of tubing  22 . 
     In the invention, refrigerant from the condenser  14  is divided into separate feed streams, one feed stream being in fluid tight communication with the refrigerant inlet port  36  of each of the evaporator zones. 
     The circulation loop  11  is further configured to (i) compress refrigerant in a gaseous state within the compressor  12  and cool the refrigerant within the condenser  14  to yield refrigerant in the liquefied state; (ii) flow refrigerant from the condenser  14  into the evaporator  18  via the inlet port  36  of each evaporator zone, wherein the refrigerant partially exists in a two-phase state; (iii) flow refrigerant from the evaporator  18  to the compressor  12 ; (iv) repeat steps (i)-(iii); (v) measure the condition of the refrigerant with a refrigerant condition sensor  44  disposed within the evaporator  18  upstream of the evaporator outlet port  34 ; and (vi) control the flow of refrigerant to the evaporator  18  in step (ii) based upon the measured condition of the refrigerant within the evaporator  18  from step (v). 
     Control of the refrigerant flow to the evaporator  18  in step (ii) is provided by an evaporator feed rate controller  40 . The evaporator feed rate controller  40  controls the flow rate of refrigerant to the evaporator  18  based upon the measured condition of the refrigerant within the evaporator  18  upstream of the evaporator outlet port  34 . 
     In the invention, the cross-sectional area of the tubing  22  within each evaporator zone is preferably less than the cross-sectional area of the tubing  22  within the next downstream evaporator zone. Also, it is preferable that the cross-sectional areas of the tubing  22  within the upstream-most evaporator zone and within each intermediate evaporator zone smoothly and continuously expands from its inlet port  36  to the inlet port  36  of the next downstream evaporator zone. Typically, the continuous length of tubing  22  continually and smoothly expands from the inlet port  36   a  of the most upstream evaporator zone to the evaporator outlet port  34 . 
     It is also typical for the at least one continuous length of tubing  22  to have a circular cross-section with a cross-sectional diameter at its inlet opening  32  of between about 0.375″ and 0.75″ with a cross-sectional diameter at its discharge opening of between about 0.5″ and 0.875″. 
     The condenser  14  can also be divided into multiple condenser zones—with each condenser zone having one or more condenser inlet ports  92 . In the embodiments illustrated in the drawings, the condenser  14  comprises three condenser zones, an upstream condenser zone, an intermediate condenser zone and a downstream condenser zone. In these embodiments, pressurized refrigerant from the compressor  12  is divided into separate pressurized refrigerant feed lines  16 , one pressurized refrigerant feed lines  16  being in fluid tight communication with a condenser inlet port  92  of each of the condenser zones. 
       FIGS. 1-4  illustrate four embodiments of the refrigeration system  10  of the invention. In the embodiment illustrated in  FIG. 1 , gaseous refrigerant is pressurized in a compressor  12  and flowed to a condenser  14  via a pressurized refrigerant line  16 . In the condenser  14 , the refrigerant is brought into thermal contact with a coolant, such as cooling water, and is thereby condensed to a liquid state. From the condenser  14 , the refrigerant is flowed to an evaporator  18  via an evaporator feed line  20 . In the at least one continuous length of tubing  22  within the evaporator  18 , the refrigerant is converted to its gaseous state through the absorption of heat. From the evaporator  18 , the refrigerant flows via an evaporator discharge line  24  back to the compressor  12 . 
     In the embodiments illustrated in  FIGS. 1-4 , a drop leg  26  is disposed within the evaporator discharge line  24 . During normal operation, trace amounts of refrigerant liquid and lubricating exiting the evaporator  18  travel at comparatively high velocity directly to the suction side  57  of the compressor  12 . During abnormal operation, for example at very light load or during start up after a power failure, refrigerant liquid and lubricating oil collect at the low point of the drop leg  26 . Heat added to the bottom of the drop leg  26  and/or heat provided by a drop leg heater  28  evaporates the small amounts of refrigerant liquid and warms high viscosity liquids. Thereafter, the refrigerant liquid and oil separated into the low point of the drop leg  26  is returned to the compressor  12  through a drop leg heater return line  30 . 
     In the embodiment illustrated in the drawings, the at least one continuous length of tubing  22  is divided into four zones. Zone A is the upstream-most evaporator zone, zone B is a first intermediate evaporator zone, zone C is a second intermediate evaporator zone and zone D is the downstream-most evaporator zone. Each evaporator zone has a refrigerant input port, input ports  36   a - 36   d , respectively. The refrigerant inlet port  36   a  for evaporator zone A is the inlet opening  32  of the at least one continuous length of tubing  22 . 
     In the embodiment illustrated in the  FIG. 1 , refrigerant from an evaporator feed line  20  is divided into four separate evaporator feed streams  38 , one evaporator feed stream being in fluid tight communication with a refrigerant inlet port  36  of each of the evaporator zones. In the embodiment illustrated in  FIG. 1 , the division of incoming refrigerant from the evaporator feed line  20  is made so that the flow of refrigerant to each of the four evaporator zones is substantially equal. 
     The total incoming refrigerant from the evaporator feed line  20  is controlled by an evaporator feed rate controller  40  which sends signals to an evaporator feed input control valve or injector  42 . The evaporator feed rate controller  40  receives signals concerning the condition of the refrigerant within the evaporator  18  from one or more refrigerant quality sensors  44  disposed within the evaporator  18  upstream of, the discharge opening  34  of the evaporator. Preferably, one such refrigerant condition sensor  44  is disposed within the evaporator  18  proximate to the discharge opening  34  of the evaporator. Use and operation of refrigerant condition sensors disposed within a refrigeration evaporator  18  is discussed in detail in U.S. patent application Ser. No. 13/312,706, entitled “REFRIGERATION SYSTEM CONTROLLED BY REFRIGERANT QUALITY WITHIN EVAPORATOR,” filed Dec. 6, 2011, the entirety of which is incorporated herein by reference. 
     In the embodiment illustrated in the  FIG. 1 , the condenser  14  is divided into three condenser zones. Condenser zone X is the upstream-most condenser zone, condenser zone Y is an intermediate condenser zone and condenser zone Z is the downstream-most condenser zone. Each condenser zone has a condenser input port, condenser input ports  92   a - 92   c , respectively. 
     In the embodiment illustrated in the  FIG. 1 , refrigerant from a pressurized refrigeration line  16  is divided into three separate condenser feed streams, one evaporator feed stream being in fluid tight communication with the condenser inlet port  92  of each condenser zone. In the embodiment illustrated in  FIG. 1 , the division of incoming refrigerant from the pressurized refrigerant line  16  is made so that the flow of refrigerant to each of the three condenser zones is substantially equal. 
       FIG. 2  illustrates an embodiment of the refrigeration system  10  similar to the embodiment illustrated in  FIG. 1 , except that each of the evaporator feed streams  38  to the four evaporator zones are separately controlled by the evaporator feed rate controller  40  which sends signals to separate feed input control valves or injectors  42 . The evaporator feed rate controller  40  for each of the evaporator zones receives input signals from one or more refrigerant condition sensors  44  disposed within each evaporator zone. 
       FIG. 3  illustrates an embodiment of the refrigeration system  10  similar to the embodiment illustrated in  FIG. 2 , except that the separate evaporator feed streams  38  to the four evaporator zones are first precooled by thermal contact with evaporating refrigerant in an evaporator feed precooler  46 . Use and operation of an evaporator feed precooler  46  is also discussed in detail in U.S. patent application Ser. No. 13/312,706. 
       FIG. 4  illustrates an embodiment of the refrigeration system  10  similar to the embodiment illustrated in  FIG. 1 , with the addition of an evaporator discharge vapor recycle line  48  for recycling some of the refrigerant vapor from the evaporator discharge line  24 , through an evaporator discharge vapor pressure booster  50  and into evaporator discharge vapor injectors  52  for injecting refrigerant vapor into each of the refrigerant input ports  36 . In this embodiment, the evaporator feed rate controller  40  again modulates the flow of refrigerant evaporator feed with the evaporator feed input control valve or injector  42  based on refrigerant quality within the evaporator  18  as sensed by the refrigerant condition sensors  44 . The evaporator discharge vapor pressure booster  50  is operated to maintain two phase refrigerant volume in the evaporator  18  at equilibrium under all loading conditions. 
       FIG. 5  illustrates an example of a continuous length of tubing  22  within a refrigeration system evaporator  18  which smoothly and continuously expands from an inlet port to a discharge port. Use and operation of a continuous length of tubing  22  within a refrigeration system evaporator  18  which smoothly and continuously expands from an inlet port to a discharge port is also discussed in detail in U.S. patent application Ser. No. 13/312,706. 
     In operation, the above described refrigeration system  10  can be employed to perform the following steps: (a) compress refrigerant in a gaseous state within the compressor  12  and cooling the refrigerant within the condenser  14  to yield refrigerant in the liquefied state; (b) flow refrigerant from the condenser  14  into the evaporator via the inlet ports  36  of each evaporator zone, wherein the refrigerant partially exists in a two-phase state; (c) flow refrigerant from the evaporator  18  to the compressor  12 ; (d) repeat steps (a)-(c); (e) measure the condition of the refrigerant with a refrigerant condition sensor disposed within the evaporator  18  upstream of the evaporator outlet port  34 ; and (f) control the flow rate of refrigerant to the evaporator  18  in step (b) based upon the measured condition of the refrigerant from step (e). 
     The refrigeration system  10  of the invention can further comprise alternative vapor flow paths to periodically route warm refrigerant vapor to either the evaporator  18  or the condenser  14 , or to both the evaporator  18  and the condenser  14 —to warm unduly chilled portions of the evaporator  18  and/or the condenser  14 .  FIGS. 6 and 7  illustrate an embodiment having such alternative vapor flow paths. 
       FIGS. 6 and 7  illustrate an embodiment of a refrigeration system  10  similar to the refrigeration system  10  illustrated in  FIG. 1  with respect to evaporator feed controls. In the embodiments illustrated in  FIGS. 6 and 7 , the refrigeration system  10  further comprises reversing conduits and valves  54  for alternatively (i) flowing refrigerant from the discharge side  56  of the compressor  12  to the evaporator inlet ports  36  without first flowing the refrigerant to the condenser  14 , (ii) flowing refrigerant exiting the evaporator  18  to the outlet port  94  of the condenser  14 , (iii) flowing refrigerant from the condenser outlet port  94 , through the condenser  14  to the condenser inlet ports  92  and (iii) flowing refrigerant from the condenser inlet ports  92  to the suction side  57  of the compressor  12 . 
     In the embodiment illustrated in  FIGS. 6 and 7 , refrigerant liquid and oil separated into the low point of the drop leg  26  and heated in the drop leg heater  28  is directed via a drop leg heater return line  30  to a 3-way valve  58 —from where it is alternatively directed to a first heated separates line  60  or to a second heated separates line  62 . The first heated separates line  60  is connected to a compressor inlet line  64 . The second heated separates line  62  is connected to a first condenser discharge line  66  via a condenser warming line  68  having a condenser warming line valve  70 . The operation of the condenser warming line valve  70  is controlled by a condenser warming line controller  90  which responds to the temperature of refrigerant in the pressurized refrigerant line  16 . 
     Reduced pressure refrigerant vapor from the top of the drop leg  26  is removed to a 4-way valve  76  via a reduced refrigerant vapor header  72 , having a reduced refrigerant vapor header block valve  74 . From the 4-way valve  76 , reduced pressure refrigerant vapor can be directed to the compressor inlet line  64  via a reduced pressure refrigerant vapor feed line  78 . 
     High pressure refrigerant vapor exiting the compressor  12  via a compressor discharge line  80  is directed to the 4-way valve  76 . From the 4-way valve  76 , high pressure refrigerant vapor can be alternatively directed to the pressurized refrigerant line  16  or to the evaporator  18  via an evaporator warming line  82 , having evaporator warming line block valve  84 . 
     Condensed refrigerant exiting the condenser  14  in the first condenser discharge line  66  is directed to the evaporator feed line  20  via a second condenser discharge line  86 , having a second condenser discharge line block valve  88 . 
       FIG. 6  illustrates the refrigeration system  10  in normal refrigeration mode. In such normal refrigeration mode, the 3-way valve  58  is set to direct refrigerant liquid and oil separated into the low point of the drop leg  26  and heated in the drop leg heater  28  to the first heated separates line  60 . The 4-way valve  76  is set to direct reduced pressure refrigerant vapor from the top of the drop leg  26  to the compressor inlet line  64  via the reduced pressure refrigerant vapor feed line  78 , and to direct high pressure refrigerant vapor from the compressor discharge line  80  to the condenser inlet line pressurized refrigerant line  16 . The condenser warming line valve  70  is closed as is the evaporator warming line block valve  84 . As can be readily seen, such normal refrigeration mode is adapted to repeatedly (a) compress refrigerant in a gaseous state within the compressor  12  and cool the refrigerant within the condenser  14  to yield refrigerant in a liquefied state; (b) flow refrigerant from the condenser  14  into the evaporator  18  wherein refrigerant is converted to a gaseous state; and (c) flow refrigerant from the evaporator  18  to the compressor  12 . 
       FIG. 7  illustrates how the refrigeration system  10  can be quickly and easily converted periodically to a warm-up mode—to warm portions of the condenser  14  and the evaporator  18  which have become unduly chilled. In such heat-up mode, the 3-way valve  58  is set to direct refrigerant liquid and oil heated in the drop leg heater  28  to the second heated separates line  62 . The condenser warming line valve  70  is opened and the second condenser discharge line block valve  88  is closed. As noted above, the operation of the condenser warming line valve  70  is controlled by the condenser warming line controller  90  which responds to the temperature of refrigerant in the pressurized refrigerant line  16 . The 4-way valve  76  is set to direct high pressure refrigerant vapor exiting the compressor  12  to the evaporator  18  via the evaporator warming line  82 . The evaporator warming line block valve  84  is opened. The 4-way valve  76  is also set to direct refrigerant from the pressurized refrigerant line  16  to the compressor inlet line  64 . 
     Thus in this warm-up mode, the condenser  14  tends to function as an evaporator and the evaporator  18  tends to function as a condenser. In the warm-up mode, high pressure refrigerant is directed to the evaporator  18  via the compressor discharge line  80 , the 4-way valve  76  and the evaporator warming line  82 . Refrigerant flowing out of the evaporator  18  is directed to the condenser  14  via the drop leg  26 , the drop leg heater  28 , the 3-way valve  58 , the second heated separates line  62  and the condenser warming line  68 . Refrigerant flowing out of the condenser  14  is directed back to the compressor inlet line  64  via the pressurized refrigerant line  16 , the 4-way valve  76  and the reduced pressure refrigerant vapor feed  78 . 
     The embodiments of the invention illustrated in  FIGS. 6 and 7  provide the refrigeration system with simple and effective capabilities to warm unduly cooled portions of the evaporator  18  and the condenser  14 . 
     When compared to similar capacity refrigeration systems of the prior art, refrigeration systems of the invention uses markedly less refrigerant. In the embodiment illustrated in  FIG. 4 , for example, approximately 50% less refrigerant is required compared to similar capacity systems of the prior art. Refrigerant residence time within the evaporator  18  in the embodiment illustrated in  FIG. 4  is approximately only 1% of the residence time required by similar capacity systems of the prior art. 
     Having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth herein above and described herein below by the claims.