US20040226308A1

US20040226308A1 - Method for controlling evaporation temperature in a multi-evaporator refrigeration system

Info

Publication number: US20040226308A1
Application number: US10/439,117
Authority: US
Inventors: Serge Dube
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-05-16
Filing date: 2003-05-16
Publication date: 2004-11-18
Also published as: CA2428861A1

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

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

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.

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.

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.

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.

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.

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

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.

It is a further feature of the present invention that the method reacts rapidly to abnormal changes of temperature of evaporators.

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.

It is a still further feature of the present invention to provide a system operating with the above described method.

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.

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

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: [0014]
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; [0015]
FIG. 2 is a plan schematic view of another refrigeration system operating with the method of the present invention; [0016]
FIG. 3 is a flowchart illustrating steps of the method of the present invention; [0017]
FIG. 4 is a table illustrating a reaction time of controller as a function of the method used for monitoring sensors; and [0018]
FIG. 5 is a graph illustrating a reaction time of controller as a function of the method used for monitoring sensors.[0019]

DESCRIPTION OF PREFERRED EMBODIMENTS

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. [0020]
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. [0021]
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 [0022] 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 11A, 11B and 11C. The evaporator group 12 is also a self-service refrigerated display cabinet or enclosure, but refrigerating meat. The evaporator group 12 consists of evaporators 12A, 12B, 12C and 12D. 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 13A, 13B, 13C, 13D and 13E. Finally, the evaporator group 14 is a closed refrigerated enclosure hosting beverages such as beer and soft drinks. The evaporator group 14 has evaporators 14A and 14B, each in a respective closed refrigeration cabinet.
The compression stage is generally shown at [0023] 20 and includes compressors 20A, 20B and 20C. 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.
A [0024] 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.
Each of the evaporators of the evaporator groups, [0025] 11, 12, 13 and 14 is provided with a temperature sensor. More specifically, evaporators 11A to 11C of the evaporator group 11 are provided with sensors 41A to 41C, respectively. The evaporators 12A to 12D of the evaporator group 12 are provided with the sensors 42A to 42D, respectively. The evaporators 13A to 13E of the evaporator group 13 are provided with the sensors 43A to 43E, respectively. Finally, the evaporators 14A and 14B of the evaporator group 14 are provided with the sensors 44A and 44B. 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.
The [0026] 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.
Referring to FIGS. 1 and 3, the evaporator temperature is controlled according to the method illustrated at [0027] 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.
Referring to FIG. 4, a table is generally shown at [0028] 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.
Using the above-described prior-art method of monitoring the average temperature of the evaporators [0029] 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.
Using the [0030] 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.
FIG. 5 shows a graph [0031] 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.
The [0032] 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 101A to 101E. The evaporators 101A to 101E 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 102A to 102G, 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 103A to 103D, which are used to refrigerate frozen foods, which must be kept between 24.0° F. and 26.0° F.
The compression stage is generally shown at [0033] 110 and includes compressors 110A, 110B and 110C. 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.
Each evaporator of the [0035] zones 101, 102 and 103 is provided with a temperature sensor. More specifically, evaporators 101A to 101E of the zone 101 are provided with sensors 151A to 151E, respectively. The evaporators 102A to 102G of the zone 102 are provided with the sensors 152A to 152G, respectively. The evaporators 103A to 103D of the zone 103 are provided with the sensors 153A to 153D, 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.
The control valves [0036] 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.
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. [0037]
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. [0038]

Claims

1. 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.

2. The method according to claim 1, wherein the temperature-related refrigeration parameter is a temperature in refrigerators cooled by the evaporators of the evaporation stage.

3. The method according to claim 1, wherein the temperature-related refrigeration parameter is a refrigerant pressure in the evaporators.

4. 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.

5. The system according to claim 4, further comprising at least a second group of evaporators and a second control valve for the second group of evaporators, with each of the evaporators of the second group of evaporators being associated with a sensor, said controller having a second operational range of the refrigeration parameter for the second group so as to modulate the second control valve as a response to a refrigeration parameter value of any one of the evaporators of the second group of evaporators being out of said second operational range so as to return said refrigeration parameter value to said second operational range, independently of a control of the first group of actuators.

6. The system according to claim 4, wherein the temperature-related refrigeration parameter is a temperature in refrigerators cooled by the evaporators of the evaporation stage.

7. The system according to claim 4, wherein the temperature-related refrigeration parameter is a refrigerant pressure in the evaporators.