Abstract:
A method for controlling a temperature-related refrigeration parameter of parallel evaporators of an evaporation stage of a refrigeration system within an operational range of the refrigeration parameter for the evaporators, with a control valve positioned between the evaporators and a compression stage in the refrigeration system to vary a suction effect of the compression stage on the evaporation stage and a sensors associated with each of the evaporators. The method comprises the steps of monitoring the temperature-related refrigeration parameter for each evaporator individually with their respective sensors; and modulating the control valve to vary the suction effect of the compression stage on the evaporators of the evaporator stage, as a response to a signal from any sensor detecting a refrigeration parameter value out of the operational range for any one of the evaporators, so as to return the refrigeration parameter value to the operational range.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to a refrigeration system for foodstuff refrigerators and, more particularly, to a method for controlling an evaporation temperature in a refrigeration system having multiple evaporators.  
         BACKGROUND ART  
         [0002]    In an evaporation stage of a refrigeration system utilized, for instance, in supermarkets, a refrigerant is circulated in evaporators so as to absorb heat from air blown through the evaporators. The air thus cooled is used to maintain refrigerated display enclosures/cases at temperatures suitable for preservation of foodstuff. The refrigeration systems found in supermarkets typically have a plurality of refrigerated enclosures, and hence evaporators, in accordance with the types of foodstuff that must be preserved: fruit, dairy products, meats.  
           [0003]    A compression stage is found subsequent to the evaporation stage in the refrigeration systems. Refrigerant is compressed in the compression stage by compressors to reinitiate a refrigeration cycle. Compressors in operation create a suction at their inlet, which suction causes the refrigerant to flow from the evaporation stage to the compression stage. A regulating control valve is provided in the line between the evaporation stage and the compression stage. The control valve is modulated to control the magnitude of the suction on the evaporation stage. The pressure, and hence the temperature, of the refrigerant in the evaporators of the evaporation stage are thus controlled by the modulation of the control valve.  
           [0004]    The modulation of the control valve is actuated by a controller as a function of the reading of sensors at the evaporation stage. Whether the sensors measure the temperature of the refrigerant in the evaporators, the outlet temperature of air blown on the evaporators, or the display cabinet temperature, these measurements will be used by the controller to modulate the control valve. The controller is programmed with an operational range of values of temperature at which the evaporators must be kept. If the sensors wired to the controller detect temperatures out of the operational range of values, the controller will modulate the control valve to return the evaporator temperature within the operational range of values of temperature.  
           [0005]    One of the drawbacks of such modulation of the control valve occurs in instances where a plurality of sensors is provided for a refrigeration system having a plurality of evaporators. The evaporators are often all controlled by a single control valve, which receives the sensor measurements and calculates an average evaporation temperature from all the measurements. The average evaporation temperature is used as the reference value that must be kept within the operational range of values of temperature. Because the reference value is an average of temperatures of all evaporators, the controller can be slow to react to an abnormal increase in the temperature of a single one of the evaporators, as the increase in temperature of the single evaporator must be substantially out of the operational range to bring the average out of the operational range. Moreover, dysfunctional evaporators having opposite of normal reactions (e.g., one of the evaporators having a temperature above the operational range, and another evaporator having a temperature below the operational range) will cancel each other out. Such situations will result in the foodstuff in a refrigerated enclosure being exposed to inadequate temperatures. Exposure of the foodstuff to inadequate temperatures may reduce the life of the foodstuff, as well as foul or freeze temperature-sensitive foodstuff.  
           [0006]    Also, some refrigerators having a plurality of evaporators are often equipped with a single sensor. The sensor monitors the refrigerator locally, not globally. Accordingly, one of the evaporators of the refrigerator can be dysfunctional, thereby exposing foodstuff to fouling temperatures, yet a distally positioned sensor will not detect a temperature variation.  
           [0007]    In order to increase the precision in the control of the temperature at the evaporation stage, there have been provided refrigeration systems having a plurality of control valves, each related to one evaporator group and each controlled individually as a function of a sensor reading of the respective evaporator groups. This represents, however, a costly solution. The additional number of control valves amounts to nonnegligible expenses. The controller must treat each control valve individually, thereby increasing the wiring and installation costs.  
         SUMMARY OF INVENTION  
         [0008]    Therefore, it is a feature of the present invention to provide a method of controlling an evaporator output temperature that substantially overcomes the disadvantages of the prior art.  
           [0009]    It is a further feature of the present invention that the method reacts rapidly to abnormal changes of temperature of evaporators.  
           [0010]    It is a still further feature of the present invention that the method reduces the risks of fouling foodstuff due to an exposure to an abnormal temperature.  
           [0011]    It is a still further feature of the present invention to provide a system operating with the above described method.  
           [0012]    According to a feature of the present invention, from a broad aspect, there is provided a method for controlling a temperature-related refrigeration parameter of at least two parallel evaporators of an evaporation stage of a refrigeration system within an operational range of the refrigeration parameter for the evaporators, with a control valve positioned between the at least two evaporators and a compression stage in the refrigeration system to vary a suction effect of the compression stage on the evaporation stage and a sensors associated with each of the evaporators, comprising the steps of: monitoring the temperature-related refrigeration parameter for each one of the evaporators individually with respective ones of the sensors; and modulating the control valve to vary the suction effect of the compression stage on the evaporators of the evaporator stage, as a response to a signal from any one of the sensors detecting a refrigeration parameter value out of said operational range for any one of the evaporators, so as to return said refrigeration parameter value to said operational range.  
           [0013]    According to a further broad feature of the present invention, there is provided a system for controlling a temperature-related refrigeration parameter of a first group of at least two parallel evaporators of an evaporation stage of a refrigeration system, comprising: a first control valve positioned between the evaporation stage and a compression stage of the refrigeration system, the at least one control valve being modulable to vary a suction effect of the compression stage on the evaporation stage; sensors associated with each one of the evaporators of the first group of evaporators; and a controller having a first operational range of the refrigeration parameter for the first group of evaporators and being connected to the first control valve and to each one of the sensors, so as to monitor the refrigeration parameter of each one of the evaporators individually through respective ones of the sensors, and to modulate the first control valve as a response to a refrigeration parameter value of any one of the evaporators of the first group of evaporators being out of said first operational range so as to return said refrigeration parameter value to said first operational range.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:  
         [0015]    [0015]FIG. 1 is a plan schematic view of a refrigeration system operated with a method for controlling an evaporator output temperature in accordance with the present invention;  
         [0016]    [0016]FIG. 2 is a plan schematic view of another refrigeration system operating with the method of the present invention;  
         [0017]    [0017]FIG. 3 is a flowchart illustrating steps of the method of the present invention;  
         [0018]    [0018]FIG. 4 is a table illustrating a reaction time of controller as a function of the method used for monitoring sensors; and  
         [0019]    [0019]FIG. 5 is a graph illustrating a reaction time of controller as a function of the method used for monitoring sensors. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    A typical refrigeration cycle consists of, sequentially, a compression stage, a condensation stage, an expansion stage and an evaporation stage. The present invention is concerned with the interrelation between the evaporation stage and the compression stage. In the evaporation stage, low-pressure liquid refrigerant is circulated into evaporators to absorb heat from a fluid that comes into contact with the evaporators. For instance, in commercial refrigerators of supermarkets, fans force air through the evaporators for the evaporators to cool the air. This heat exchange between the air and the refrigerant in the evaporators causes the refrigerant to change phase and increase in temperature. The cooled air is circulated in the refrigerator to preserve foodstuff in the refrigerator at suitable temperatures.  
         [0021]    In the compression stage, compressors collect the gaseous refrigerant from the evaporators to reinitiate a refrigeration cycle. The low pressure at the compressor inlets will exert a suction on the evaporators of the evaporation stage, thereby causing the flow of refrigerant from the evaporators to the compressors.  
         [0022]    Referring to the drawings, and more particularly to FIG. 1, a portion of a refrigeration system consisting of an evaporation stage and a compression stage is illustrated. The evaporation stage is generally shown at  10  and includes evaporator groups  11 ,  12 ,  13  and  14 . The evaporator groups  11  to  14  differentiate from one another by the type of refrigerator they are part of, or by the products that they refrigerate. For instance, the evaporator group  11  is a self-service refrigerated display cabinet (e.g., open case refrigerator) or enclosure for dairy products having evaporators  11 A,  11 B and  11 C. The evaporator group  12  is also a self-service refrigerated display cabinet or enclosure, but refrigerating meat. The evaporator group  12  consists of evaporators  12 A,  12 B,  12 C and  12 D. The evaporator group  13  is also a self-service open-ended refrigerated display cabinet, but refrigerates fruits and vegetables. The evaporator group  13  has evaporators  13 A,  13 B,  13 C,  13 D and  13 E. Finally, the evaporator group  14  is a closed refrigerated enclosure hosting beverages such as beer and soft drinks. The evaporator group  14  has evaporators  14 A and  14 B, each in a respective closed refrigeration cabinet.  
         [0023]    The compression stage is generally shown at  20  and includes compressors  20 A,  20 B and  20 C. The compression stage  20  is connected at a compressor inlet  21  to the evaporation stage  10  by a refrigerant line network  30  collecting the refrigerant from every evaporator of the evaporation stage  10  to convey the refrigerant to the compression stage  20 . The refrigerant line network  30  consists of piping of appropriate sizing for the proper conveying of the refrigerant from the evaporation stage  10  to the compression stage  20 . As mentioned previously, the suction at the inlet  21  will cause refrigerant in the refrigerant line network  30  to flow toward the compression stage  20 .  
         [0024]    A control valve  31  is provided in the refrigerant line network  30  upstream of the compressor inlet  21 . The control valve  31  is also known as an evaporator pressure regulator (EPR) valve. For instance, the control valve  31  may be a Sporland electric evaporator control valve of the CDS series. The control valve  31  is wired to a controller  40 , via connection  32 . The controller  40  is a processor unit, for instance from Micro-Thermo™, model MT-EEPR. Therefore, the controller  40  sends actuation signals to the control valve  31  to modulate the control valve  31 .  
         [0025]    Each of the evaporators of the evaporator groups,  11 ,  12 ,  13  and  14  is provided with a temperature sensor. More specifically, evaporators  11 A to  11 C of the evaporator group  11  are provided with sensors  41 A to  41 C, respectively. The evaporators  12 A to  12 D of the evaporator group  12  are provided with the sensors  42 A to  42 D, respectively. The evaporators  13 A to  13 E of the evaporator group  13  are provided with the sensors  43 A to  43 E, respectively. Finally, the evaporators  14 A and  14 B of the evaporator group  14  are provided with the sensors  44 A and  44 B. The temperature sensors are, for instance, Micro-Thermo™, model 23-0073 sensors. The temperature sensors are all wired to the controller  40 , as illustrated at  33 , such that the controller  40  can obtain a temperature reading for any one of the evaporators of the evaporator groups  11  to  14 .  
         [0026]    The control valve  31  is positioned in a line of the refrigerant line network  30  that is common to all the evaporator groups of the evaporation stage  10 . Being positioned upstream of the compression stage  20 , the control valve  31  can be modulated to vary the effect of the suction at the inlet  21  on the refrigerant line network  30 . For instance, the control valve  31  may be fully opened to fully expose the refrigerant line network  30  to the suction at the compressor inlet  21 , whereby the refrigerant will pass rapidly through the evaporators of the evaporator stage  10 . Such action will cause a decrease in temperature of the fluid blown across the evaporators of the evaporation stage  10 . On the other hand, the control valve  31  may substantially block the refrigerant line network  30  to reduce the effect of suction of the compression stage  20  on the refrigerant line network  30 , thereby causing an increase in pressure of refrigerant in the evaporators of the evaporation stage  10 . This will have the effect of increasing the outlet temperature of the air blown across the evaporators of the evaporation stage  10 .  
         [0027]    Referring to FIGS. 1 and 3, the evaporator temperature is controlled according to the method illustrated at  50 . The controller  40  has been programmed beforehand with an operational range of temperature (i.e., a minimum and a maximum value) at which the refrigeration cabinets of the evaporation stage  10  must be kept. For instance, for typical refrigerators, such as that described for the evaporation stage  10 , the operational range is between 32.0° F. and 34.0° F. According to Step  52 , the controller  40  will monitor each sensor of the evaporation stage  10 . According to decision  54 , if, during the monitoring of temperature through the sensors, any one of the sensor readings falls out of the operational range of values, the controller  40  will perform Step  56 . In Step  56 , the controller  40  modulates the control valve  31  while monitoring the sensors to return the measured out-of-range temperature to the operational range. As mentioned previously, the modulation of the control valve  31  will have an effect on the pressure upstream of the control valve  31  in the refrigerant line network  30 . The controller  40  will then return to a monitoring mode, as in Step  52 , in the wait of further interventions in modulating the control valve  31  as in Step  56 .  
         [0028]    Referring to FIG. 4, a table is generally shown at  60 , and shows the output temperature of four evaporators (i.e., evaporators  1 ,  2 ,  3  and  4 ) over a five-minute period, as well as an average of the output temperature of all evaporators. Assuming that the operational range of temperatures is between 32.0° F. and 34.0° F., the evaporators  1  to  3  have constant temperature values within the operational range of temperature during the five-minute period. Evaporator  4 , on the other hand, reaches 34.1° F. at 0.75 minute.  
         [0029]    Using the above-described prior-art method of monitoring the average temperature of the evaporators  1  to  4 , the controller will modulate the valve after 4.50 minutes, for a temperature of 38.0° F. for the evaporator  4 . Therefore, the foodstuff cooled by evaporator  4  would have been exposed to out-of-range temperatures during 3.75 minutes before a reaction of the controller.  
         [0030]    Using the method  50  of the present invention as illustrated in FIG. 3, as soon as the evaporator  4  goes above 34.0° F., the controller reacts to modulate the control valve to correct the abnormal temperature.  
         [0031]    [0031]FIG. 5 shows a graph  70  that illustrates the reaction time of the practical case of FIG. 4. More specifically, the minimum of the operational range, i.e., 32.0° F., is illustrated at  71 , whereas the maximum of the operational range, i.e., 34.0° F., is illustrated at  72 . The average temperature  73  goes over the maximum  72  at about 4.5 minutes, even though the temperature of evaporator  4 , as illustrated at  74 , has been above the maximum  72  starting at about 0.75 minute. Therefore, the method  50  illustrated in FIG. 3 accelerates the time of reaction of the controller  20  (FIG. 1), thereby reducing the risk of exposure of foodstuff to out-of-range temperature.  
         [0032]    The method  50  of the present invention may be applied to refrigeration systems having multiple zones of evaporators, which are independent from one another with regard to temperature requirements. Referring to FIG. 2, a portion of a refrigeration system consisting of an evaporation stage and a compression stage, and having independent zones of evaporators, is illustrated. The evaporation stage is generally shown at  100  and includes zones  101 ,  102  and  103 . As an example, zone  101  is provided with evaporators  101 A to  101 E. The evaporators  101 A to  101 E are used to refrigerate fruits and vegetables, which must be kept between 34.0° F. and 36.0° F. Zone  102  is provided with evaporators  102 A to  102 G, which are used to refrigerate meats and dairy products, which must be kept between 32.0° F. and 34.0° F. Finally, zone  103  is provided with evaporators  103 A to  103 D, which are used to refrigerate frozen foods, which must be kept between 24.0° F. and 26.0° F.  
         [0033]    The compression stage is generally shown at  110  and includes compressors  110 A,  110 B and  110 C. The compression stage  110  is connected at a compressor inlet  111  to the evaporation stage  100  by a refrigerant line network  120  collecting the refrigerant from every evaporator of the evaporation stage  100  to convey the refrigerant to the compression stage  110 . More specifically, the refrigerant line network  120  is separated in lines  121 ,  122  and  123 , respectively connected to the zones  101 ,  102  and  103 . The lines  121 ,  122  and  123  merge at common line  124 . The suction at the inlet  111  will cause refrigerant in the refrigerant line network  120  to flow toward the compression stage  110 .  
         [0034]    Control valves  131 ,  132  and  133  are respectively provided in the lines  121 ,  122  and  123 . As in the refrigeration system of FIG. 1, the control valves  131  to  133  are evaporator pressure-regulator valves. The control valves  131 ,  132  and  133  are all wired to the controller  140 , as shown respectively by  141 ,  142  and  143 . The controller  140  sends actuation signals to the control valves  131 ,  132  and  133  to modulate each independently.  
         [0035]    Each evaporator of the zones  101 ,  102  and  103  is provided with a temperature sensor. More specifically, evaporators  101 A to  101 E of the zone  101  are provided with sensors  151 A to  151 E, respectively. The evaporators  102 A to  102 G of the zone  102  are provided with the sensors  152 A to  152 G, respectively. The evaporators  103 A to  103 D of the zone  103  are provided with the sensors  153 A to  153 D, respectively. The temperature sensors are all wired to the controller  140 , as shown by wire network  170 , such that the controller  140  can obtain a temperature reading for any one of the evaporators of the zones  101  to  103 .  
         [0036]    The control valves  131  to  133  are modulated to vary the effect of the suction at the inlet  111  on their respective zones  101 ,  102  and  103  of the refrigerant line network  120 . For instance, the control valve  131  may be fully opened to fully expose the line  121  to the suction at the compressor inlet  111 , whereby the refrigerant will pass rapidly through the evaporators of the zone  101 . Such action will cause a decrease in temperature of the fluid blown across the evaporators of the zone  101 . Simultaneously, the control valve  132  may substantially block the line  122  to reduce the effect of suction of the compression stage  110  on the refrigerant line network  30 , thereby causing an increase in pressure of refrigerant in the evaporators of the zone  102 . This will have the effect of increasing the outlet temperature of the air blown across the evaporators of the zone  102 . Each of the control valves  131 ,  132  and  133  is controlled individually by the controller  140  according to the method  50  described in FIG. 3.  
         [0037]    Although reference is made throughout the above description and in the ensuing claims to temperature control, it is obvious that the various members of the present invention may be provided with pressure sensing means, and may operate with respect to operational ranges of pressure, due to the direct relation between the pressure and temperature in refrigeration systems. Considering that the end result is to preserve foodstuff at adequate temperatures, and to simplify the present specification, reference is made to temperature-driven operation, although the above described system and method may be indirectly pressure-driven.  
         [0038]    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.