EP0412474B1 - Refrigeration system and method of operating such a system - Google Patents

Description

The invention relates to a method for operating a refrigeration system in which a refrigerant compresses, liquefies, is supplied to various refrigeration consumers, is expanded and evaporated there and is then returned to compression, with the temperature in the room to be cooled being controlled by a manipulated variable for each refrigeration consumer is regulated, the instantaneous value of this manipulated variable serves as a measure of the refrigeration requirement of the respective refrigeration consumer and the performance of the refrigeration system is set as a function of a weighted average of the instantaneous refrigeration requirement values of the connected refrigeration consumers. In addition, an apparatus for performing this method is the subject of the invention.

Such refrigeration systems, also referred to as composite refrigeration systems, are used wherever several devices have to be supplied with cold at different points and / or at different temperatures. For example, in a supermarket, several refrigerators and freezers as well as, for example, an additional cold room as a cold consumer are connected to such a system. The refrigeration system supplies every refrigeration consumer with pressurized, liquefied refrigerant. This is released by the respective cooling consumers and evaporated in indirect heat exchange with cooling air, which is then introduced into the room to be cooled. The evaporated and low-pressure refrigerant is returned to the refrigeration system. In general, the cooling output currently output at the evaporator is controlled by an individual regulation of the temperature in the room to be cooled by each cooling consumer. A method for such a regulation is, for example, the subject of a patent application filed simultaneously with the present application (published as EP-A-0412473).

For economic reasons, it is also necessary to limit the total cooling capacity of the composite system by means of a regulation in order to save energy. The performance during compression and / or liquefaction is reduced by switching off individual compressors or condenser fans operating in parallel or reducing their speed. The suction pressure, i.e. the pressure of the gaseous refrigerant before compression. Although this variable is very easy to determine, the known type of regulation is quite coarse and insensitive. The cooling capacity of the system must therefore be chosen to be relatively high for safety reasons, in order to prevent undersupply of the cold consumers and the associated spoilage of fresh goods. Other regulations are also known, for example depending on one of the deviations from the target temperature (US-4487028) or on the cooling demand of a single consumer (US-4084388) found in the individual cooling consumers. The increase in economy which can be achieved with the previously known method is therefore unsatisfactory.

The present invention is therefore based on the object of developing a method of the type mentioned at the outset which works particularly economically by keeping the energy consumed by the refrigeration system as low as possible.

This object is achieved in that the volume throughput of the refrigerant expanded and evaporated at the respective refrigeration consumer is used as a measure of the refrigeration requirement of the respective refrigeration consumer.

The control circuits of the individual refrigeration consumers control the throughput of refrigerant through the evaporator as a manipulated variable, depending on a control variable, generally the instantaneous temperature in the room to be cooled respective cooling consumer (interior temperature). This manipulated variable is a very direct measure of the cooling consumer's current cooling requirements. According to the invention, the control loops of the individual refrigeration consumers are now coupled with those of the composite refrigeration system and the instantaneous refrigeration demand values of the individual refrigeration consumers are forwarded to the composite control system. The entirety of the refrigeration requirement values then represents a very realistic and also practically manageable control variable for controlling the performance of the refrigeration system.

The performance of the refrigeration system is preferably set essentially proportional to the arithmetic mean of the determined refrigeration demand values of all refrigeration consumers connected to the refrigeration system. When averaging, the values of the individual cooling consumers can be weighted if necessary.

An apparatus for carrying out the method according to the invention comprises means for compressing and liquefying refrigerant, a composite liquid line for guiding liquefied refrigerant to various refrigeration consumers, means for the expansion and evaporation of refrigerant assigned to the individual refrigeration consumers, a composite suction line via which the evaporated refrigerant returns to Compression is fed back, one microprocessor-controlled refrigeration consumer controller per refrigeration consumer, by means of which the temperature in the room to be cooled is regulated by controlling a manipulated variable and which is connected to a temperature measurement input and a control output and also to a data line via which the current value of this manipulated variable can be output, and a microprocessor-controlled compound controller, which is also connected to the data line and also has control outputs which to the Lead aggregates of the refrigeration system, the compound controller being designed so that the performance of the aggregates is set as a function of a weighted average of the instantaneous values of the manipulated variables of the connected refrigeration consumers, and is characterized in that the refrigeration consumer controllers relax the volume flow rate of the respective refrigeration consumer and adjust the evaporated refrigerant.

Figur 1

ein Ausführungsbeispiel einer erfindungsgemäßen Kälteanlage mit drei Kälteverbrauchern und den zugehörigen Regeleinrichtungen in schematischer Darstellung und

Figur 2

ein Flußdiagramm, welches ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens beschreibt.

The invention and further details of the invention are explained below with reference to a drawing and a flow chart. Show here

Figure 1

an embodiment of a refrigeration system according to the invention with three refrigeration consumers and the associated control devices in a schematic representation and

Figure 2

a flowchart describing an embodiment of the method according to the invention.

The refrigeration system has a plurality of compressors 2 connected in parallel, which draw in refrigerant from a composite suction line 1. The number of compressors is generally 2 to 10, preferably 2 to 8. The compressed refrigerant is led to a condenser 3, in which it is condensed in indirect heat exchange with air. The condenser is generally outdoors. Its outer surfaces are supplied with outside air by condenser fans 4. The largely liquefied refrigerant is introduced into a collector 5, from which only the liquid portion reaches the composite liquid line 6, which leads the liquid and pressurized refrigerant to the refrigeration consumers 7a, 7b, 7c. The compressors 2 and condenser fans 4 represent the units of the refrigeration system.

The number of connected cooling consumers 7a, 7b, 7c is in principle unlimited; the maximum cooling capacity of the composite system must of course be designed accordingly.

Liquid refrigerant is supplied to each refrigeration consumer 7a, 7b, 7c separately via individual liquid lines 8a, 8b, 8c. There it is expanded in each case by an expansion valve 9, introduced into an evaporator 10 and evaporated there against cooling air conducted over the outer surfaces of the evaporator 10. The cooling air duct within the cooling consumers 7a, 7b, 7c is not shown in FIG. 1 for the sake of simplicity. Relaxed and evaporated refrigerant is introduced into the compound suction line 1 via the individual suction lines 11a, 11b, 11c and is thus returned to the refrigerant circuit.

For the individual control of the cooling capacity for each cooling consumer 7a, 7b, 7c, the throughput of refrigerant through the evaporator 10 or the pressure difference when relaxing 9 is generally set. In the example in FIG. 1, the throughput of refrigerant is controlled. Basically, one valve per cooling consumer 7a, 7b, 7c is sufficient. In the example in FIG. 1, a solenoid valve 12 or 13 is provided for each liquid line 8a, 8b, 8c and for each suction line 11a, 11b, 11c. The valves are set by an individual microprocessor-controlled refrigeration consumer controller 14a, 14b, 14c depending on the respective interior temperature (temperature sensor 15) (see above-mentioned patent application EP-A-0412473).

A likewise microprocessor-controlled compound controller 17 controls the compressors 2 and, in the present example, one of the two condenser fans 4. According to the invention, the refrigeration consumer controllers 14a, 14b, 14c of the individual refrigeration consumers 7a, 7b, 7c are connected via a data line 16, here a common data and address bus connected to the compound controller 17.

In the exemplary embodiment, the compound controller 17 has further inputs and outputs 18, 19. Line 18 represents a safety chain which is interrupted in the event of failure of an assembly, for example one of the compressors 2. A warning can optionally be given to the operating personnel via line 19. In addition, both the compound controller 17 and the refrigeration consumer controller 14a, 14b, 14c can be connected via further data lines to a central monitoring device, for example a computer, which performs additional tasks such as controlling lighting or heating.

An example of the practical functioning of a program which controls the compound controller 17 can be seen from the flow chart in FIG. After switching on or resetting (reset) the device (step 1.1), the configuration is first checked in step 1.2 (for example, type and structure of the combined system and the connected cooling consumers, etc.) and the corresponding default setting of the control device. In addition, internal processes of the microprocessor are started, for example the time measurement and the initialization of the input / output channels.

In the following step 1.3, certain parameters are preset. This applies above all to the initially assumed cooling demand values, for which no current data are available yet. The program then enters an endless loop from which only switching off or resetting the device results.

• Anzahl der Verdichter und Verflüssigerventilatoren
• alle Arten von Verzögerungszeiten
• Anzahl der angeschlossenen Kälteverbraucher
• bisherige Laufzeit der einzelnen Verdichter
• Anzahl der laufenden Verdichter und Ventilatoren
• von einen Kälteverbraucher übermitteltes Warnsignal

As the first step 2.1 of the loop, the current control parameters are read from the EEPROM. These are, for example, the setting and setpoints of the refrigeration system or also more specific parameters, such as the delay time between the request for additional cooling capacity and the output of corresponding switching signals to the compressor or condenser fan. In the following step 2.2, the keyboard and the digital inputs are queried. If parameters are requested to be changed using the keyboard, this is done in 2.3. Step 2.4 enables the output of specially selected data, such as, if desired

• Number of compressors and condenser fans
• all kinds of delay times
• Number of connected cooling consumers
• previous runtime of the individual compressors
• Number of compressors and fans running
• warning signal transmitted by a cold consumer

The device also communicates the request for output via the keyboard.

Then (2.5) the data are called up by the refrigeration consumer controllers, especially the current values of the refrigeration demand. In addition, other signals can be exchanged between the compound controller and the refrigeration consumer controller, for example warning messages in the event of faults, overloading or insufficient supply. The data is buffered in the working memory of the network controller. In step 2.6, an average is calculated from the current cooling demand values of the individual cooling consumers, which may be weighted with parameters that depend on the size and importance of individual cooling consumers.

The performance of the composite system is now set according to this mean value, i.e. exactly according to the current requirements of the refrigeration consumers. This is done by outputting control signals to relays that switch the compressors or the motors of the condenser fans (2.7). Speed controls can also be provided to refine the setting of the power. The control of the compressors is preferably carried out as part of a base load switchover, as described, for example, in DE-A-35 43 707.

In the last step 2.8 before returning to the start of the loop, additional services are processed, for example the determination of the warning state (possibly issuing a warning to the operating personnel, for example in the event of a unit failure) or the monitoring of the start of frost on the condenser and the corresponding defrosting processes.

Claims (4)

1. A process for operating a refrigerating apparatus in which a refrigerating medium is compressed (2), condensed (3), conveyed to different cold consumers (7a, 7b, 7c), expanded (9) and evaporated (10a, 10b, 10c) therein, and then returned (11a, 11b, 11c; 1) to the compression stage (2), wherein in each cold consumer (7a,7b, 7c) the temperature in the chamber which is to be refrigerated is regulated by the adjustment of a manipulated variable, the instantaneous value of this manipulated variable serves as a gauge for the cold requirement of the respective cold consumer (7a, 7b, 7c), and wherein the output of the refrigerating apparatus is adjusted in dependente upon a weighted mean value of the instantaneous cold requirement values of the connected cold consumers (7a, 7b, 7c), characterised in that the volume throughout of the refrigerating medium expanded and evaporated in the respective cold consumer (7a, 7b, 7c) is used as a gauge for the cold requirement of the respective cold consumer (7a, 7b, 7c).
2. A prpcess as claimed in Claim 1, characterised in that the mean value of the instantaneous cold requirement values is weighted with parameters which are a function of the size and importance of individual cold consumers.
3. A refrigerating apparatus for the implementation of the process claimed in Claim 1 or 2, with means for the compression (2) and condensation (3) of refrigerating medium, with a composite liquid line (6) for the conveyance of condensed refrigerating medium to different cold consumers (7a, 7b, 7c), with means assigned to the individual cold consumers for the expansion (9) and evaporation (10a, 10b, 10c) of refrigerating medium, with a composite suction line (1) via which the evaporated refrigerating medium is returned to the compression stage (2), with a respective, microprocessor-controlled cold consumed controller (14a, 14b, 14c) in respect of each cold consumer (7a, 7b, 7c) by which the temperature in the chamber which is to be refrigerated is regulated by the control of a manipulated variable and which is in each case connected to a temperature measuring input (20) and a control output (21) and is also connected to a data line (16) via which the instantaneous value of this manipulated variable can be output, and with a microprocessor-controlled composite controller (17) which is likewise connected to the data line (16) and also possesses control outputs (22, 23) which lead to the assemblies (compressor 2, condenser fans 4) of the refrigerating apparatus, where the composite controller (17) is designed such that the output of the assemblies (2, 4) is adjusted in dependence upon a weighted mean value of the instantaneous values of the manipulated variables of the connected cold consumers (7a, 7b, 7c), characterised in that the cold consumer controllers (14a, 14b, 14c) adjust the volume throughput of the refrigerating medium expanded and evaporated in the respective cold consumer (7a, 7b, 7c).
4. A refrigerating apparatus as claimed in Claim 3, characterized in that the composite controller (17) is designed such that the mean value of the instantaneous values of the manipulated variables is weighted with parameters which are a function of the size and importance of individual cold consumers.

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