Abstract:
A defrost refrigeration system of the type having a main refrigeration circuit comprising a first line extending from the compression stage to the evaporator stage and adapted to receive a portion of refrigerant in a high-pressure gas state. A valve system stops a flow of the refrigerant in a low-pressure liquid state to an evaporator of the evaporator stage and for conveying a flow of the refrigerant in the high-pressure gas state from the first line to release heat to defrost the at least one evaporator. A second line conveys the refrigerant having released heat directly to the condensing stage.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally relates to refrigeration systems and, more particularly, to a refrigeration system having a defrost cycle in parallel to the refrigeration cycle, with refrigerant of the refrigeration system being circulated in the evaporators to perform the defrost cycle.  
       BACKGROUND ART  
       [0002]     Energy costs are an increasing concern for industries operating refrigeration systems, such as the food retailing industry. Due to the increasing costs of energy, refrigeration systems are evolving to provide refrigeration system solutions that optimize the use of energy.  
         [0003]     Defrost cycles are common place in refrigeration systems, and are used to remove frost build-ups on evaporators. Frost build-ups typically result from the relatively high humidity content of the air to which the evaporators are exposed.  
         [0004]     One type of defrost cycle consists in circulating hot refrigerant in the evaporators, such that the hot refrigerant releases heat to the frost build-up, which melts away. Such defrost cycles are operated in relatively short time spans, so as not to expose the foodstuff being refrigerated to unsuitable temperatures.  
         [0005]     The overall installation costs of the defrost loops (e.g., piping, valves, controls) are being compared to the energy consumption of operating such defrost loops. It would therefore be desirable to optimize the consumption of energy for defrost cycles of refrigeration systems.  
       SUMMARY OF INVENTION  
       [0006]     Therefore, it is a feature of the present invention to provide a novel defrost circuit for a refrigeration system.  
         [0007]     It is a further feature of the present invention to provide a defrost circuit optimizing energy consumption.  
         [0008]     It is a still further feature of the present invention to provide a novel method for defrosting evaporators of a refrigeration system.  
         [0009]     Therefore, in accordance with the present invention there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compression stage, wherein said refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein said refrigerant in said high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein said refrigerant in said high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein said refrigerant in said first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to said compression stage, said defrost refrigeration system comprising: a first line extending from the compression stage to the evaporator stage and adapted to receive a portion of said refrigerant in said high-pressure gas state; a valve system for stopping a flow of said refrigerant in said first low-pressure liquid state to at least one evaporator of the evaporator stage and for conveying a flow of said refrigerant in said high-pressure gas state from the first line to release heat to defrost the at least one evaporator; and a second line to convey said refrigerant having released heat directly to the condensing stage.  
         [0010]     Further in accordance with the present invention, there is provided a method for defrosting evaporators in a refrigeration system operating a refrigeration cycle, comprising the steps of: providing a first line extending from a compression stage of the refrigeration system to an evaporation stage of the refrigeration system, a second line extending from the evaporation stage of the refrigeration system directly to a condensing stage of the refrigeration system; stopping a flow of cooling refrigerant to at least one evaporator; conveying hot gas refrigerant from the compressing stage to the at least one evaporator through said first line so as to defrost the at least one evaporator; and conveying the hot gas refrigerant from the at evaporator directly to the condensing stage by the second line so as to return the refrigerant to the refrigeration cycle. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:  
         [0012]      FIG. 1  is a schematic view of a defrost refrigeration system in accordance with a first embodiment of the present invention;  
         [0013]      FIG. 2  is a schematic view of a defrost refrigeration system in accordance with a second embodiment of the present invention; and  
         [0014]      FIG. 3  is a schematic plan view of the defrost refrigeration system of  FIG. 1 . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     Referring to the drawings, and more particularly to  FIG. 1 , a refrigeration system in accordance with the present invention is generally shown at  10 . The refrigeration system  10  comprises the stages found on typical refrigeration systems, such as the compression stage  12 , the condensation stage  14 , the expansion stage  16 , and the evaporation stage  18 .  
         [0016]     Refrigerant circulates from one stage to another in a refrigeration cycle. The refrigerant is compressed to a high pressure gas state in the compression stage  12 . The compression stage  12  is connected to the condensation stage  14  by line  13  (i.e., a hot gas line). The refrigerant then releases heat in the condensation stage  14 , to reach a high pressure liquid state. The refrigerant is expanded in the expansion stage  16  to reach the evaporation stage  18  in a low pressure liquid/gas state. In the evaporators of the evaporation stage  18 , the refrigerant absorbs heat to reach a low pressure gas state, to then reach the compression stage  12  and complete the refrigeration cycle.  
         [0017]     For the purposes of illustrating the defrost system of the present invention, the evaporation stage  18  is shown having evaporators  20 A and  20 B. Sub-lines  21 A and  21 B of line  21  relate the expansion stage  16  to the evaporators  20 A and  20 B, respectively. Sub-lines  22 A and  22 B of line  22  relate the evaporators  20 A and  20 B, respectively, to the compression stage  12 .  
         [0018]     In known refrigeration systems having defrost loops, hot refrigerant is directed to one or more of the evaporators of the evaporation stage, so as to release heat to melt the frost build-up on the evaporators. In some systems, the lines extending between the evaporators of the evaporation stage and the compressors of the compression stage are then used, with appropriate valves, to direct the defrosting refrigerant exiting from the evaporators to a subsequent portion of the refrigeration system, such as a suction header, a suction accumulator, a pressure regulator device, or the like.  
         [0019]     The suction lines relating the evaporators of the evaporation stage to the compression stage in multi-evaporator refrigeration systems are known to have relatively large diameters, so as to prevent suction pressure loss between the evaporation stage and the compression stage.  
         [0020]     Accordingly, in order for the defrost cycle to operate rapidly, a substantial amount of defrost refrigerant must be used to fill the suction line, and effectively defrost the evaporators of the evaporation stage.  
         [0021]     Non-negligible volumes of hot refrigerant are therefore used in known defrost loops in order to fill suction lines of relatively large diameters after the defrost. This hot refrigerant must thereafter be reconditioned so as to be re-injected in the refrigeration cycle. Therefore, the ratio of volume of refrigerant per defrosted evaporator is not optimized, for instance due to the use of the suction lines for conveying the refrigeration after defrost. Moreover, some components have been added to refrigeration systems to accommodate this hot refrigerant during reconditioning, such as accumulators and flushing systems.  
         [0022]     Therefore, the defrost system in accordance with the present invention aims at reducing the ratio of volume of refrigerant per defrosted evaporator. Referring to  FIG. 1 , the defrost system in accordance with the preferred embodiment of the present invention is generally shown at  30 . The defrost system  30  has a line  31  that directs refrigerant from line  13  to the evaporation stage  18 , so as to direct hot refrigerant exiting from the compression stage  12 . The line  31  diverges into a plurality of sub-lines to feed each of the evaporators  20  of the evaporation stage  18 . The line  31  has a sub-line  31 A connecting into the line  22 A, and has a sub-line  31 B connecting into the line  22 B.  
         [0023]     The defrost system  30  also has a line  32  that returns the defrost refrigerant in the line  13 , upstream of the condensation stage  14 , but downstream of the branching between the line  13  and the line  31 . The line  32  has sub-lines  32 A and  32 B, which are respectively connected to the lines  21 A and  21 B.  
         [0024]     This network of pipes is provided with a suitable valve system, so as to control the switch between refrigeration cycle and defrost cycle for each of the evaporators. As an example, the refrigeration system  10  has valve A 1  on sub-line  31 A, valve A 2  on sub-line  22 A, valve A 3  on sub-line  32 A, and valve A 4  on sub-line  21 A, to control the feed of refrigerant to the evaporator  20 A. Similarly, the refrigeration system  10  has valve B 1  on sub-line  31 B, valve B 2  on sub-line  22 B, valve B 3  on sub-line  32 B, and valve B 4  on sub-line  21 B, to control the feed of refrigerant to the evaporator  20 B. These valves are any suitable valve, such as solenoid valves, EPR valves (e.g., electronic EPR valves), pulse valves or the like.  
         [0025]     A pressure regulating valve  40  is provided in the line  13  between the branching of line  13  and line  31 , and the branching of line  13  and line  32 . The valve  40  causes a pressure differential between upstream end and downstream end of line  13 .  
         [0026]     These valves are typically remotely operated valves, such as solenoid valves, wired to a controller  41  that operates the switch sequence between refrigeration cycle and defrost cycle for each of the evaporators.  
         [0027]     A switch from refrigeration cycle to defrost cycle is operated as follows.  
         [0028]     The evaporator  20 A is in a refrigeration cycle, whereby valves A 2  and A 4  are opened, and valves A 1  and A 3  are closed, so as to allow cooling refrigerant to circulate through the evaporator  20 A. It is required to put the evaporator  20 A in a defrost cycle, whereby the valve positions are reversed. Valves A 2  and A 4  are closed, and valves A 1  and A 3  are opened.  
         [0029]     The pressure differential across the pressure regulating valve  40  causes circulation of some of the hot gas refrigerant, compressed at the compression stage  12 , through the evaporator  20 A once the valves A 1  and A 3  are opened. Accordingly, the hot gas refrigerant flowing through the evaporator  20 A releases heat to the build-up on the evaporator  20 A, to then return directly to the refrigeration cycle at the condensation stage  14 .  
         [0030]     Therefore, the hot gas refrigerant is exposed to defrosting temperatures for a short time span, as the arrangement of the defrost system induces a rapid flow of refrigerant in the evaporator  20 A. Moreover, the use of lines  31  and  32 , which divert and return refrigerant to and from line  13 , minimizes the amount of defrosting refrigerant. More specifically, the line  22  operates in suction, and therefore has a relatively large diameter.  
         [0031]     As the lines  31  and  32  convey high pressure refrigerant through the evaporation stage  18  in the defrost cycle, they can have smaller diameters without significantly affecting the flow of refrigerant therethrough. For instance, the diameter of the lines  32  may typically be a third of the diameter of the suction lines  22 .  
         [0032]     Accordingly, a smaller volume of refrigerant is required using the defrost system  30  of the present invention, as opposed to systems using a greater portion of the suction lines connecting the evaporation stage  18  to the compression stage  12 . Considering that the ratio of volume of refrigerant per defrosted evaporator is relatively lower than other defrost systems, more evaporators of the evaporation stage  18  may thus be defrosted simultaneously with the defrost system  30  of the present invention.  
         [0033]     Referring to  FIG. 2 , a refrigeration system in accordance with another embodiment of the present invention is shown at  10 ′. The refrigeration system  10 ′ is similar to the refrigeration system  10  of  FIG. 1 , whereby like elements will bear like reference numerals.  
         [0034]     The refrigeration system  10 ′ has a defrost system  30 ′. The defrost system  30 ′ has a dedicated compression stage (i.e., one or more dedicated compressors), illustrated as  12 A, parallel to the compression stage  12 . The high pressure gas refrigerant at the outlet of the dedicated compression stage  12 A is selectively directed to the evaporator stage  18 , so as to defrost the evaporators  20 A and  20 B from frost build-up thereon.  
         [0035]     More specifically, a line  31 ′ extends from the dedicated compression stage  12 A to the evaporators  20 A and  20 B, by way of sub-lines  31 A′ and  31 B′. The sub-lines  31 A′ and  31 B′ respectively connect to sub-lines  22 A and  22 B.  
         [0036]     Similarly to the defrost system  30  of  FIG. 1 , the defrost system  30 ′ has a line  32  that returns the defrost refrigerant in the line  13 , upstream of the condensation stage  14 . The line  32  has sub-lines  32 A and  32 B, which are respectively connected to the lines  21 A and  21 B.  
         [0037]     This network of pipes is provided with a suitable valve system, so as to control the switch between refrigeration cycle and defrost cycle for each of the evaporators. As an example, the refrigeration system  10 ′ has valve A 1  on sub-line  31 A′, valve A 2  on sub-line  22 A, valve A 3  on sub-line  32 A, and valve A 4  on sub-line  21 A, to control the feed of refrigerant to the evaporator  20 A. Similarly, the refrigeration system  10 ′ has valve B 1  on sub-line  31 B′, valve B 2  on sub-line  22 B, valve B 3  on sub-line  32 B, and valve B 4  on sub-line  21 B, to control the feed of refrigerant to the evaporator  20 B.  
         [0038]     These valves are typically remotely operated valves, such as solenoid valves, wired to a controller  41  that operates the switch sequence between refrigeration cycle and defrost cycle for each of the evaporators.  
         [0039]     Additionally, the dedicated compression stage  12 A may be used to feed the refrigeration cycle, by way of line  50  and valve  51 , as a function of the demand for defrost refrigerant for defrost cycles.  
         [0040]     A switch from refrigeration cycle to defrost cycle for the refrigeration system  10 ′ is similar to that of the refrigeration system  10  and is operated as follows.  
         [0041]     The evaporator  20 A is in a refrigeration cycle, whereby valves A 2  and A 4  are opened, and valves A 1  and A 3  are closed, so as to allow cooling refrigerant to circulate through the evaporator  20 A. It is required to put the evaporator  20 A in a defrost cycle, whereby the valve positions are reversed. Valves A 2  and A 4  are closed, and valves A 1  and A 3  are opened.  
         [0042]     Therefore, the hot gas refrigerant output from the compression stage  12 A is directed through sub-line  31 A′ to the evaporator  20 A, so as to release heat to the build-up on the evaporator  20 A, to then return directly to the refrigeration cycle at the condensation stage  14 . The output pressure at the dedicated compression stage  12 A is preferably higher than the output pressure at the compression stage  12 , such that the refrigerant flows to the condensation stage  14 , through line  32 , after the defrost cycle. Alternatively, pumps and other devices could be used to re-inject the defrost refrigerant in the refrigeration cycle.  
         [0043]     Therefore, the hot gas refrigerant is exposed to defrosting temperatures for a short time span, as the arrangement of the defrost system  30 ′ induces a rapid flow of refrigerant in the evaporator  20 A. Moreover, the use of lines  31 ′ and  32 , which divert and return refrigerant to and from line  13 , minimizes the amount of defrosting refrigerant. More specifically, the line  22  operates in suction, and therefore has a relatively large diameter.  
         [0044]     As the lines  31 ′ and  32  convey high pressure refrigerant through the evaporation stage  18  in the defrost cycle, they can have smaller diameters without significantly affecting the flow of refrigerant therethrough. For instance, the diameter of the lines  32  may typically be a third of the diameter of the suction lines  22 .  
         [0045]     Accordingly, a smaller volume of refrigerant is required using the defrost system  30 ′ of the present invention, as opposed to systems using a greater portion of the suction lines connecting the evaporation stage  18  to the compression stage  12 . Considering that the ratio of volume of refrigerant per defrosted evaporator is relatively lower than other defrost systems, more evaporators of the evaporation stage  18  may thus be defrosted simultaneously with the defrost system  30 ′ of the present invention.  
         [0046]     Additionally, the suction line  22  in both refrigeration systems  10  and  10 ′ is only used for the defrost cycle. Accordingly, the conditions of the refrigerant in the suction line  22  are generally constant, as opposed to refrigeration systems in which the suction line between the evaporation stage and the compression stage is used to convey defrost refrigerant as well as refrigerant from a refrigeration cycle. This latter use results in non-negligible thermal expansion/contraction of the suction pipes. Thermal expansion/contraction may cause pipe ruptures, may cause damages to insulation jackets onto the pipes, and results in energy losses.  
         [0047]     Referring to  FIG. 3 , the refrigeration system  10  of  FIG. 1  is shown as schematically laid out in a refrigeration plan, illustrating the use of known components, such as an oil separator  100 , refrigerant tanks  101 , a heat reclaim loop  102 , and headers. It is pointed out that the evaporator stage  18  is illustrated as having a single bank of evaporators for simplicity purposes. Moreover, the evaporator stage  18  is shown having display cabinets  120 A.  
         [0048]     It is within the ambit of the present invention to cover any obvious modifications of the embodiments described herein, provided such modifications fall within the scope of the appended claims.