Abstract:
A refrigeration system having a main refrigeration circuit having a condensing stage, wherein a first refrigerant in a high pressure gas state is condensed at least partially to a liquid state. The condensing stage has a pair of  stand-alone condensing stage closed loops  in heat exchange relation with the main refrigeration circuit. The stand-alone condensing stage closed loops are  is in parallel one to another  with a condenser of the condensing stage and each comprise  comprises a second refrigerant circulating between at least a heat absorption stage, wherein the second refrigerant absorbs heat from the first refrigerant in the main refrigeration circuit so as to condense the first refrigerant to the liquid state, and a heat release stage, wherein the second refrigerant releases the absorbed heat. The condensing stage has modulating valves for selectively and quantitatively modulating the temperature of said first refrigerant and compressor head pressure.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to refrigeration systems, and more particularly, to modulate closed condensing loops for use therewith. 
     BACKGROUND OF THE INVENTION 
     In a typical refrigeration system, particularly those found in supermarkets, a plurality of evaporators are used to refrigerate foodstuff in refrigerated display cases. Such systems basically comprise a closed circuit having a compressor stage, a condenser stage, an expansion stage and an evaporator stage. Other stages may be added to the above described basic refrigeration circuit in order to recuperate heat, or to provide refrigeration systems with defrosting loops for high speed defrosting of the evaporators. For instance, U.S. Pat. No. 5,673,567, issued on Oct. 7, 1997 to the present assignee, discloses a refrigeration system with a heat reclaim loop for recuperating heat from hot high pressure refrigerant gas outletting from the compressor stage, rather than evacuating the heat through the condensers, where the heat would be lost to the atmosphere. Thus, the heat reclaim loop is provided in parallel to the condenser stage in order to recuperate heat in heat exchange devices rather than rejecting it to the atmosphere. Preferably, in the cooler seasons, the heat is used for heating the entrance area and other specific colder areas of supermarkets. In the warmer months, the heat may be recuperated for heating water. 
     U.S. Pat. No. 5,826,433, issued on Oct. 27, 1998 to the present assignee, discloses modification to the above described patent, whereby a modulating valve is provided for efficiently controlling the rate of heat reclaim versus the heat rejection through the condenser stage. 
     Finally, U.S. Pat. No. 6,089,033, issued on Jul. 18, 2000 to the present assignee discloses a refrigeration system configuration in order to defrost evaporator units at higher speeds. 
     These refrigeration systems, and generally most refrigeration systems used in supermarkets, have roof top condensers in order to reject heat at the outlet of the compressor stage, whereby the refrigerant is condensed at least partially to a liquid state. Unfortunately, the loops to the roof top condensers extend the piping length of the refrigeration system. Accordingly, the piping networks of refrigeration systems are filled with refrigerant to provide every stage with the necessary conditions for refrigeration. Furthermore, with the advent of heat reclaim loops and high speed defrost cycles, even more refrigerant is used. 
     Unfortunately, the refrigerants typically used in such refrigeration systems (i.e. refrigerants 404, 408, 507, AZ-20 and the like) are expensive and are often volatile, whereby they may be hazardous to human health and to the environment. The more these refrigerants are used, the higher is the risk of polluting the environment. 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to provide a refrigeration systems having reduced amounts of the above stated refrigerants. 
     It is a further feature of the present invention to provide a refrigeration system optimizing heat reclaim with respect to compressor operation. 
     According to the above feature of the present invention, and from a broad aspect thereof, the present invention provides a refrigeration system having a main refrigeration circuit having a condensing stage, wherein a first refrigerant in a high pressure gas state is condensed at least partially to a liquid state. The condensing stage ha a pair of stand-alone condensing stage closed loops in heat exchange relation with the main refrigeration circuit. The stand-alone condensing stage closed loops are parallel one to another and each comprise a second refrigerant circulating between at least a heat absorption stage, wherein the second refrigerant absorbs heat from the first refrigerant in the main refrigeration circuit so as to condense the first refrigerant to the liquid state, and a heat release stage, wherein the second refrigerant releases the absorbed heat. The condensing stage has modulating valves for selectively and quantitatively modulating the temperature of said first refrigerant and compressor head pressure. 
     Therefore, in accordance with the present invention, there is provided a refrigeration system having a main refrigeration circuit, wherein a first refrigerant goes through at least a compressing stage, wherein said first refrigerant is compressed to a high pressure gas state to then reach a condensing stage, wherein said high pressure gas refrigerant is condensed at least partially to a liquid state to then reach an expansion stage, wherein said high pressure liquid refrigerant is expanded to a low pressure liquid state to then reach an evaporator stage, wherein said low pressure liquid refrigerant is evaporated at least partially to a low pressure gas state by absorbing heat, to then return to said compressing stage, said condensing stage having at least one stand- alone condensing stage closed loop in heat exchange relation with said main refrigeration circuit, said stand - alone condensing stage closed loop being in parallel with a condenser of the condensing stage and comprising a second refrigerant circulating between at least a heat absorption stage, wherein said second refrigerant absorbs heat from a portion of said first refrigerant in said main refrigeration circuit so as to condense said first refrigerant to said liquid state, and a heat release stage, wherein said second refrigerant releases said absorbed heat, said condensing stage having modulating valve means for selectively and quantitatively modulating the temperature of said first refrigerant and compressor head pressure.    
       Further in accordance with the present invention, there is provided a refrigeration system having a main refrigeration circuit, wherein a first refrigerant goes through at least a compressing stage, wherein said first refrigerant is compressed to a high pressure gas state to then reach a condensing stage, wherein said high pressure gas refrigerant is condensed at least partially to a liquid state to then reach an expansion stage, wherein said high pressure liquid refrigerant is expanded to a low pressure liquid state to then reach an evaporator stage, wherein said low pressure liquid refrigerant is evaporated at least partially to a low pressure gas state by absorbing heat, to then return to said compressing stage, said condensing stage having at least a pair of stand - alone condensing stage closed loops in heat exchange relation with said main refrigeration circuit, said stand - alone condensing stage closed loops being parallel one to another and each comprising a second refrigerant circulating between at least a heat absorption stage, wherein said second refrigerant absorbs heat from said first refrigerant in said main refrigeration circuit so as to condense said first refrigerant to said liquid state, and a heat release stage, wherein said second refrigerant releases said absorbed heat, said condensing stage having modulating valve means for selectively and quantitatively modulating the temperature of said first refrigerant and compressor head pressure as a function of at least one of an outdoor temperature and an indoor ambient temperature.   
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described in detail having reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram illustrating a stand-alone evaporative condenser loop of the present invention; 
         FIG. 2  is a schematic diagram depicting a stand-alone heat reclaim loop of the present invention; and 
         FIG. 3  is a schematic diagram illustrating a refrigeration system having the stand-alone evaporative condenser loop and heat reclaim loop. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , there is generally shown at  10  a stand-alone evaporative condenser loop of the present invention. The loop  10  comprises a plate heat exchanger  12  for the heat exchange between a refrigerant A in a refrigeration system and a refrigerant B in the evaporative condenser loop  10 . Refrigerant A of the refrigeration system entering the heat exchanger  12  is from the output of compressors in a high pressure hot gas state, and goes through the heat exchanger  12  to release latent heat by condensing, to then exit therefrom at least partially in a high pressure liquid state. Thus, a gas refrigerant line from the refrigeration system is shown entering the heat exchanger  12  through inlet line  1 , whereas a liquid refrigerant line exits the heat exchanger  12  at outlet line O. The refrigeration system will be described in further detail hereinafter. 
     The condensing loop  10  has an evaporative condenser  14 . The evaporative condenser  14  typically comprises a coiling system therein, across which a fluid flows in order for refrigerant within the coiling system to release heat it has previously absorbed in the heat exchanger  12 . For instance, the fluid may be air or a spray of water flowing over the coiling system. A condenser feedline  16  connects the heat exchanger  12  to the evaporative condenser  14 . It is pointed out that the condensing loop  10  may be provided with a plurality of evaporative condensers  14 , wherefore a branch line  18  is shown diverging from the condenser feedline  16  to add similar evaporative condensers  14  in parallel to the first one. The condenser feedline  16  is provided with valves and control devices to ensure the flow direction and the proper refrigerant conditions. For instance, a manometer  20  is shown mounted in the condenser feedline  16 , as well as a plurality of check valves  22 . 
     A condenser return line is generally shown at  24  and connects the evaporative condenser  14  to the heat exchanger  12 , so as ensure the flow of cooled refrigerant from the evaporative condenser  14  to the heat exchanger  12 . A pump  26  is provided in the condenser return line  24  to ensure the flow of the refrigerant B in the condensing loop  10 . A filter  28  in the condenser return line  24  filters out the refrigerant. Further check valves  22  and manometer  20  are provided in the condenser return line  24 . Furthermore, parallel loops (not shown) along with manually operated valves (e.g. three-way valves, ball valves, butterfly valves) may also be provided in order to isolate the various components of the condensing loop  10  for maintenance or for servicing purposes. A branch line  30  is shown connecting to the condenser return line  24  in the event where more than one evaporative condenser  14  are part of the condensing loop  10 . 
     Referring now to  FIG. 2 , a stand-alone heat reclaim loop in accordance with the present invention is generally shown at  50 . The heat reclaim loop  50  comprises a plate heat exchanger  52 , provided for absorbing heat from a refrigerant A in a refrigeration system. The refrigerant A in the refrigeration system is in a high pressure hot gas state when entering the heat exchanger  52  and is condensed to a liquid state to then exit the heat exchanger  52 . The inlet line of hot pressure gas refrigerant A is shown at  12 , whereas the outlet of condensed liquid refrigerant A is shown at outlet line O 2 . 
     The heat reclaim loop  50  has a heat reclaim coil  54  and a air heating unit  56 . The heat reclaim coil  54  is typically installed in a ventilation duct through which air circulates, so as to warm up the air. The air heating unit  56  is typically provided for heating areas where ventilation is not required (e.g. shipping dock, entrance). It is pointed out that the heat reclaim loop  50  may be limited to either one of the heat reclaim coil  54  and the heating unit  56 , or may even have a plurality of both. A heat reclaim feedline  58  connects the heat exchanger  52  to the heat reclaim coil  54  and to the air heating unit  56  to ensure the flow of a refrigerant B therebetween. An accumulation tank  60  is connected in the heat reclaim feedline  58  for accumulating refrigerant B having absorbed heat in the heat exchanger  52 . A pump  62  is also mounted in the heat reclaim feedline  58 , downstream from the accumulation tank  60  to ensure the flow of refrigerant B from the accumulation tank  60  to the heat reclaim coil  54  and the air heating unit  56 . A heat reclaim return line  64  connects the heat reclaim coil  54  and the air heating unit  56  to the heat exchanger  52 , thereby ensuring the flow of refrigerant B from the formers to the latter. 
     The heat reclaim coil  54  has an inlet line  66  separated from the heat reclaim feedline  58  by a three-way valve  68 . A by-pass line  70  is connected to the free port of the three-way valve  68  and converges with an outlet line  72  of the heat reclaim coil  54  to reach the heat reclaim return line  64 . Thus, the three-way valve  68  controls the flow of refrigerant B from the heat reclaim feedline  58  to the heat reclaim coil  54 . The three-way valve  68  may be fully closed to the inlet line  66  of the heat reclaim coil  54 , whereby refrigerant B flows through the by-pass line  70  to reach the heat reclaim return line  64 . It is pointed out that the outlet line  72  comprises a check valve  74  such that refrigerant by-passing the heat reclaim coil  54  is prevented from entering same through the outlet line  72  thereof. 
     The air heating unit  56  is connected to the heat reclaim loop  50  in parallel to the heat reclaim coil  54 . The heating unit  56  has an inlet line  76  connected to the heat reclaim feedline  58  through a three-way valve  78 . The free port of the three-way valve  78  is connected to a by-pass line  80  which converges with an outlet line  82  of the heating unit  56  to connect to the heat reclaim return line  64 . Similarly to the heat reclaim coil  54 , the flow of refrigerant B to the heating unit  56  is controlled by the three-way valve  78 . Once more, the heating unit  56  may be by-passed by the refrigerant B, whereby refrigerant B circulates through the by-pass line  80  and is prevented from entering the heating unit  56  by the check valve  84  mounted therein. 
     The pump  62  and the accumulation tank  60  allow storage of refrigerant B, having absorbed heat in the heat exchanger  52 . If the heat reclaim coil  54  and the air heating unit  56  are in standby (by being by-passed) as the demand for heating air is low, the tank  60  accumulates the heated refrigerant B such that the heat reclaim loop  50  is able to sustain sudden and rapid increases in demand of heating air. The pump  62  may stop operating beyond certain levels of refrigerant B. It is pointed out that the accumulation tank  60  may be insulated to keep the refrigerant therein in given states. The pump  62  may be automated in order to operate automatically according to factors such as outdoor and indoor temperatures, as well as refrigerant B temperature. Increased refrigerant B demand may thus be anticipated and fulfilled by the pump  62  and the accumulation tank  60 . 
     The heat reclaim loop  50  comprises various devices for the control of the refrigerant parameters, such as the direction of flow, the pressure and the filtering. For instance, filter  86 , check valves  88  and manometers  90  are provided in the heat reclaim loop  50  for the above described reasons. 
     Now that both the stand-alone evaporative condenser loop  10  and heat reclaim loop  50  have been described in detail, a typical refrigeration system in which the formers may be used will now be described. Because the stand-alone condensing loops use non-polluting refrigerants such as glycol, there is a reduction in the quantity of refrigerant required in the conventional portion of the refrigeration system. 
     Referring now to  FIG. 3 , a refrigeration system  100  is typically adapted for receiving the stand-alone evaporative condenser loop  10  described in FIG.  1  and the heat reclaim loop  50  described in FIG.  2 . The evaporative loop  10  and the heat reclaim loop  50  are shown connected to the refrigeration system  100  parallel one to another. Similarly to the description of the loops  10  and  50 , for clarity purposes, a refrigerant, identified as refrigerant A, which will be discussed hereinafter, flows in the refrigeration system  100 , whereas a refrigerant, referred to as refrigerant B, flows in the loops  10  and  50 . Furthermore, as the invention resides in the portion of the refrigeration system involving the stand-alone evaporative condenser loop  10  and the stand-alone heat reclaim loop  50 , which have been described extensively above, the refrigeration system  100  will only be described schematically. For instance, the refrigeration system  100  shown in  FIG. 3  comprises high speed defrost loops which will not be described herein. 
     As shown in  FIG. 3 , the refrigeration system  100  comprises a plurality of compressors  102 . Refrigerant A from compressors  102  is in a high pressure gas state. A header  106  and a high pressure gas line  108  are connected to the outlets of the compressors  102  so as to convey the high pressure gas refrigerant A exiting therefrom to a three-way control valve  104  and modulating valves  105  and  107 , which separates the high pressure gas line  108  into an evaporative condenser line  110  and a heat reclaim line  112 . Both the evaporative condenser line  110  and the heat reclaim line  112  will converge to a liquid refrigerant reservoir  114 , after having high pressure gas refrigerant A gone through heat exchangers  12  and  52  of the evaporator condenser loop  10  and the heat reclaim loop  50 , respectively. Therefore, as the evaporative condenser line  110  and the heat reclaim line  112  diverge at the valves  104 ,  105  and  107  and converge at the refrigeration reservoir  114 , these lines are parallel one to another. It is pointed out that the evaporative condenser line  112  was referred to as input line I and output line O in  FIG. 1 , wherefore reference letters I and O have been added to FIG.  3 . Similarly, the heat reclaim line  112  was referred to in  FIG. 2  as inlet line  12  and outlet line O 2 , wherefore reference letters for the latters have been added to FIG.  3 . 
     The three-way control valve  104  and the modulating valves  105  and  107  are adapted to control the amounts of refrigerant A flowing to the evaporative condenser line  110  and the heat reclaim line  112 . A main objective of the refrigeration system  100  is to recuperate as much heat as possible from the refrigerant A requiring to be condensed at least partially to a liquid state. However, in order to keep the operation costs low for such a refrigeration system, the compressor  102  must operate with the head pressures as low as possible, yet by fulfilling the compression needs of the system. By the use of parallel condenser line  110  and heat reclaim line  112 , it is possible to optimize the head pressure of the refrigerant A in the main refrigeration system  100 . According to a plurality of factors which will be described hereinafter, the three-way control valve  104  and the modulating valves  105  and  207  can completely shut the feeding of high pressure gas refrigerant A to either one of the heat exchanger  12  and heat exchanger  52 , as well as modulate and control the output pressure of the compressor  102 . As mentioned in the description of the evaporative condenser loop  10  and the heat reclaim loop  50 , the high pressure gas refrigerant A exiting the heat exchangers  12  and  52 , respectively, through outlet lines O and O 2 , is in a high pressure liquid state. 
     Typically, the head pressure in the condenser line  110  floats in order to maintain the pressure of refrigerant A in this portion of the refrigeration system at a relatively low pressure. As the evaporative condenser loop  10  has great cooling capacities due to the use of water to cool refrigerant B, which then cools refrigerant A through heat exchanger  12 , the condenser line  110  allows lowering of the output refrigerant A pressure of the compressors  102 , thereby resulting in energy savings. Modulating valves  105  and  107  modulate the output pressure of the compressors  102 . One, for instance, may operate at lower pressures, whereas the other works at higher pressures. The pressure of refrigerant A varies according to a few factors. The compressors must operate as little as possible, as they increasingly consume electricity as a function of their pressure output. On the other hand, the refrigerant released from the compressors  102  must be at a temperature above that of the cooling fluid, usually a predetermined constant pressure differential (e.g., +15° C.). In the present invention, the cooling fluid is refrigerant B, which is actually cooled by the ventilation air in the heat reclaim coil  54  or the heating unit  56  in the case of the heat reclaim line  112 , and by water in the evaporative condenser  14  in the case of the evaporative condenser line  10 . Therefore, the temperature and pressure of the refrigerant A are modulated in accordance with the heat reclaim demand, the indoor air temperature and the outdoor air temperature. 
     Thereafter, high pressure liquid refrigerant A accumulated in the liquid refrigerant reservoir  114  flows through a liquid refrigerant line  116  and liquid refrigerant header  118  to reach the expansion valves  120  of the refrigeration system  100 . High pressure liquid refrigerant A flowing across the expansion valves  120  expands to be lowered in pressure. Therefore, refrigerant A, in a low pressure liquid state, flows to evaporators  122  through evaporator inlet lines  124 , which extend between the expansion valves  120  and the evaporators  122 . The low pressure liquid A is at a temperature well below the desired temperature of the refrigerator units (not shown). The refrigerant A absorbs heat in the evaporators  122 , whereby it exits the evaporators  122  in a gas state. The low pressure liquid refrigerant A exists the evaporators  122  in evaporator outlet lines  126  to reach a suction header  128  to then return to the compressors  102 . 
     Typical refrigerants used as refrigerant A are refrigerants  404 ,  408 ,  507 , AZ- 20 . The typical refrigerants used as refrigerant A may be volatile, whereby they are a threat to the environment as they evaporate at ambient conditions. Furthermore, they are toxic and are likely hazardous to health. The evaporative condenser loop  10  and the heat reclaim loop  50  allow for the reduction of size of the refrigeration system  100 . Typically, the evaporative condenser line  110  and the heat reclaim line  112  extend from the compressors  102  to the roof top of the building to reach condensers of the condenser stage, wherein heat is released to the environment. Accordingly, these lengthy networks of piping must be filled with refrigerant A for the proper functioning thereof. 
     The stand-alone evaporative condenser loop  10  and heat reclaim loop  50  extend from adjacent the compressors  102  to the various condensing units thereof, namely the evaporative condenser  14 , the heat reclaim coil  54  and the air heating unit  56 . Therefore, the evaporative condenser line  110  and the heat reclaim line  112  are substantially shortened, whereby the amount of refrigerant A in the refrigeration system  100  is greatly reduced. As the refrigerant B must not sustain great variations in temperature as compared to the refrigerant A which must rise above the outdoor temperature to condense and drop below the refrigerator temperature to evaporate, the sole purpose of the refrigerant B is to absorb heat to condense the refrigerant A. Therefore, refrigerant B may be any of the following: ethylic acetate, acetic acid, sulfuric acid, ammoniac, calcium chloride, hydrogen chloride, methylene chloride, sodium chloride, vinyl chloride, carbon dioxide, ethanol, ethylene glycol, acetate formiate, potassium formiate, iso-butane, Pekasol 50, propane, propylene glycol, toluene, trichloroethylene. In any event, refrigerant B is chosen amongst safer fluids than refrigerant A. As the piping of the refrigeration system  100  is greatly reduced, the compressors  102  are not required to outlet compressed refrigerant at pressures as high as for longer refrigeration lines. The compressors can operate at head pressures of about 120 psi instead of 220 psi, thereby reducing their operating time and increasing their life-span. Therefore, substantial savings are achieved in electricity consumption of the compressors  102 , and the life of the compressors  102  is increased. 
     The three-way control valve  104  and the modulating valves  105  and  107  redirect the flow of refrigerant A towards heat exchanger  12  or heat exchanger  52  according to the seasonal heat requirements of the building in which the refrigeration system  100  is. The stand-alone heat reclaim loop  50  advantageously recuperates the heat produced by the compressors  102 . The evaporative condenser  14  of the stand-alone evaporative condenser loop  10  may either release the heat outdoors, or recover the heat by, for instance, spraying a liquid such as water on the coils of the evaporative condenser  14  to absorb the excess heat. Thus, in the fall, winter and spring seasons, a greater amount of refrigerant is circulated in the heat exchanger  52 , whereby the heat absorbed from refrigerant A will serve for heating the building. It is pointed out that the refrigeration system  100  may be provided with only one of the evaporative condenser loop  10  or the heat reclaim loop  50 . 
     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.