EP0325163A1 - Operating method for a refrigeration system and refrigeration system for carrying out the method - Google Patents

Operating method for a refrigeration system and refrigeration system for carrying out the method Download PDF

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Publication number
EP0325163A1
EP0325163A1 EP89100468A EP89100468A EP0325163A1 EP 0325163 A1 EP0325163 A1 EP 0325163A1 EP 89100468 A EP89100468 A EP 89100468A EP 89100468 A EP89100468 A EP 89100468A EP 0325163 A1 EP0325163 A1 EP 0325163A1
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Prior art keywords
refrigerant
temperature
pressure
refrigeration system
expansion
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EP89100468A
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German (de)
French (fr)
Inventor
Franz Gruber
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Linde GmbH
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Linde GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/027—Condenser control arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/22—Refrigeration systems for supermarkets
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/19—Refrigerant outlet condenser temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B40/00—Subcoolers, desuperheaters or superheaters

Definitions

  • the invention relates to a method for operating a refrigeration system and a refrigeration system for carrying out the method with a refrigerant circuit in which a refrigerant compresses, liquefies, expands, evaporates and is then fed back to the compression.
  • Refrigeration systems are used where the temperature in a room has to be kept at a lower level than in the environment, e.g. for refrigeration units in supermarkets or for cold rooms in warehouses.
  • the gaseous refrigerant is compressed in a compressor and then condensed in a condenser.
  • outside air is used to remove the heat of condensation.
  • the pressure in the condenser is set so that the corresponding condensing temperature of the refrigerant is higher than the temperature of the air used for cooling.
  • the refrigerant In order to ensure a trouble-free refrigerant circuit, the refrigerant must be undercooled prior to expansion, ie it must be in a liquid state.
  • the throughput of a commonly used expansion valve is in fact not sufficient to maintain sufficient cooling capacity if part of the refrigerant is in vapor form before the expansion.
  • refrigeration systems In order to ensure that the refrigerant is always in a liquid state between liquefaction and expansion, refrigeration systems have previously been operated at relatively high pressures, which correspond, for example, to liquefaction temperatures of 20 to 27 ° C (when using R12, R22 or R502 as refrigerant). As a rule, the condensing temperature of the refrigerant is then higher than the temperatures of the rooms through which the refrigerant lines are laid.
  • the present invention has for its object to develop a method for operating a refrigeration system that works economically, in particular by saving work in compression.
  • This object is achieved in that the temperature and pressure of the refrigerant are measured before the expansion and that, depending on this measurement, the pressure of the refrigerant before the expansion is adjusted by regulating the power during liquefaction so that the refrigerant is in a liquid state before expansion is present.
  • the condensing pressure can be reduced to surprisingly low values, corresponding to a condensing temperature of, for example, -10 ° C., without disturbances in the refrigerant circulation. With correspondingly low outside temperatures, very little energy is required for compression. If the pressure during the liquefaction is smoothly adapted to the outside temperatures, a refrigeration system operated according to the method of the invention works extremely economically.
  • the cooling capacity is the ratio of the cooling capacity Q0 to the drive power P supplied during compression. The smaller the difference between the temperatures during liquefaction and evaporation, the better the cooling capacity e k .
  • the sliding adjustment of the temperature during the liquefaction to the outside air temperature which is possible with the method according to the invention, also makes economic operation possible by the fact that the cooling capacity Q0 increases as the outside air temperature falls and at the same time the drive power P supplied decreases and the cooling capacity coefficient e k increases.
  • the refrigerant has a temperature before the expansion which is slightly below the condensing temperature.
  • the slight subcooling ensures that the refrigerant remains liquid before the expansion process and that the refrigerant circulation is not disturbed.
  • the invention also relates to a refrigeration system for carrying out the method according to the invention, which is characterized by a measuring device for pressure and temperature of the refrigerant attached to the pipe in front of the expansion device, a control device connected to it and a control line which connects the control device and the liquefaction device.
  • the refrigeration system shown in the figure contains a refrigeration unit, consisting of a compressor 6, an air-cooled condenser 7 and a refrigerant collector 10, and a cooling device, consisting of a heat exchanger 13, an expansion valve 14 and an evaporator 12.
  • the refrigeration unit is installed outdoors, while the cooling device in or on the cooled space, for example a refrigerator.
  • the refrigeration device and the cooling device are connected by a liquid line 3 and a suction line 4, which generally lead through heated rooms.
  • the two lines 3, 4 are insulated against condensation.
  • R22 or R502 is preferably used as the refrigerant.
  • the refrigerant in the liquid line 3 can heat up considerably.
  • the refrigerant in the evaporator 12 also has a relatively high temperature. Therefore, the performance of the heat exchanger 13 is not sufficient to ensure subcooling of the refrigerant upstream of the expansion valve 14. The refrigerant thus boils upstream of the expansion valve 14.
  • the pressure in the condenser can be set to a condensing temperature t c of approximately 2K.
  • the condensed refrigerant for example, has a temperature of 0 ° C and is thus subcooled by 2K. In continuous operation, this subcooling and the cooling in the heat exchanger 13 are generally sufficient to keep the liquid free of bubbles up to the expansion valve 14. However, during an interruption in operation or when starting up for the first time, the refrigerant can heat up well above the condensing temperature t c , in extreme cases up to room temperature.
  • the throughput of the expansion valve 14 is then, however, much too small to supply the evaporator with sufficient refrigerant in the event of a larger vapor content.
  • the pressure in the evaporator drops and the compressor 6 is switched off by the usual suction pressure control (not shown in the figure) and the refrigeration is thereby interrupted.
  • the pressure in the liquid line 4 drops further, so that the condensing temperature t c .
  • the compressor 6 is switched on and off again and again until finally a steady state is reached after a long time.
  • the refrigeration system outlined in the figure has sensors 18 for the temperature and pressure of the refrigerant upstream of the expansion valve 14 and a control device 16, which is connected to the condenser 7 via a control line 17.
  • the supercooling of the refrigerant is maintained by these devices: as soon as the temperature of the refrigerant exceeds a certain limit value t 1 below the condensing temperature t c of the refrigerant at the measured pressure, the control device 16 throttles the performance during the liquefaction 7. This increases the pressure in the liquid line 3. As soon as the pressure in front of the expansion valve 14 has risen to such an extent that the condensing temperature t c of the refrigerant has reached a further limit value t 2, the performance during the condensing 7 is increased again.
  • t c depends on the vapor pressure curve on the pressure of the refrigerant, which is measured together with the temperature of the refrigerant.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Compression-Type Refrigeration Machines With Reversible Cycles (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)

Abstract

In a refrigeration system, pressure and temperature of the refrigerant are measured before the expansion device (14). With the aid of these measured values, the pressure of the refrigerant is adjusted before expansion (14) by control of the capacity on liquefaction (7) in such a manner that the refrigerant is always in liquid state before expansion (14). As a result, the temperature on liquefaction (7) can, within a wide range, be adapted variably to the temperature of the external air used for leading off the liquefaction heat. <IMAGE>

Description

Die Erfindung betrifft ein Verfahren zum Betreiben einer Kälteanlage und eine Kälteanlage zur Durchführung des Verfah­rens mit einem Kältemittelkreislauf, in dem ein Kältemittel verdichtet, verflüssigt, entspannt, verdampft und anschließend wieder der Verdichtung zugeführt wird.The invention relates to a method for operating a refrigeration system and a refrigeration system for carrying out the method with a refrigerant circuit in which a refrigerant compresses, liquefies, expands, evaporates and is then fed back to the compression.

Kälteanlagen werden dort eingesetzt, wo die Temperatur in einem Raum auf niedrigerem Niveau als in der Umgebung gehalten werden muß, z.B. für Kühlmöbel in Supermärkten oder für Kühlräume in Lagerhäusern.Refrigeration systems are used where the temperature in a room has to be kept at a lower level than in the environment, e.g. for refrigeration units in supermarkets or for cold rooms in warehouses.

In einer Kälteanlage mit Kältemittelkreislauf wird das gasför­mige Kältemittel in einem Verdichter komprimiert und danach in einem Verflüssiger kondensiert. In der Regel wird Außenluft zum Abführen der Verflüssigungswärme verwendet. Der Druck im Verflüssiger wird so eingestellt, daß die entsprechende Verflüssigungstemperatur des Kältemittels höher als die Temperatur der zur Kühlung eingesetzten Luft ist. Damit ein störungsfreier Kältemittelkreislauf gewährleistet ist, muß das Kältemittel vor der Entspannung unterkühlt sein, d.h. in flüssigem Zustand vorliegen. Die Durchsatzleistung eines üblicherweise verwendeten Expansionsventils reicht nämlich nicht aus, um eine genügende Kühlleistung aufrecht zu erhal­ten, wenn ein Teil des Kältemittels vor der Entspannung dampfförmig vorliegt.In a refrigeration system with a refrigerant circuit, the gaseous refrigerant is compressed in a compressor and then condensed in a condenser. As a rule, outside air is used to remove the heat of condensation. The pressure in the condenser is set so that the corresponding condensing temperature of the refrigerant is higher than the temperature of the air used for cooling. In order to ensure a trouble-free refrigerant circuit, the refrigerant must be undercooled prior to expansion, ie it must be in a liquid state. The throughput of a commonly used expansion valve is in fact not sufficient to maintain sufficient cooling capacity if part of the refrigerant is in vapor form before the expansion.

Um zu gewähleisten, daß sich das Kältemittel zwischen Verflüssigen und Entspannen immer in flüssigen Zustand befindet, wurden Kälteanlagen bisher bei relativ hohen Drücken betrieben, die beispielsweise Verflüssigungstemperaturen von 20 bis 27°C entsprechen (bei Verwendung von R12, R22 oder R502 als Kältemittel). In der Regel liegt dann die Verflüssigungs­temperatur des Kältemittels höher als die Temperaturen der Räume, durch die die Kältemittelleitungen verlegt sind.In order to ensure that the refrigerant is always in a liquid state between liquefaction and expansion, refrigeration systems have previously been operated at relatively high pressures, which correspond, for example, to liquefaction temperatures of 20 to 27 ° C (when using R12, R22 or R502 as refrigerant). As a rule, the condensing temperature of the refrigerant is then higher than the temperatures of the rooms through which the refrigerant lines are laid.

Die hohe Temperatur beim Verflüssigen bedingt ein hohe Druckdifferenz im Kältemittelkreislauf zwischen Verdampfen und Verflüssigen. Es muß also viel Verdichtungsarbeit geleistet werden. Daher weisen die bisher angewandeten Verfahren den Nachteil auf, daß ihre Wirtschaftlichkeit nicht zufriedenstel­lend ist.The high temperature during liquefaction results in a high pressure difference in the refrigerant circuit between evaporation and liquefaction. So a lot of compaction work has to be done. Therefore, the processes used hitherto have the disadvantage that their economy is unsatisfactory.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Betreiben einer Kälteanlage zu entwickeln, das wirtschaftlich arbeitet, insbesondere dadurch, daß Arbeit beim Verdichten eingespart wird.The present invention has for its object to develop a method for operating a refrigeration system that works economically, in particular by saving work in compression.

Diese Aufgabe wird dadurch gelöst, daß vor dem Entspannen Temperatur und Druck des Kältemittels gemessen werden und daß in Abhängigkeit von dieser Messung der Druck des Kältemittels vor dem Entspannen durch Regelung der Leistung beim Verflüs­sigen so eingestellt wird, daß das Kältemittel vor dem Entspannen in flüssigem Zustand vorliegt.This object is achieved in that the temperature and pressure of the refrigerant are measured before the expansion and that, depending on this measurement, the pressure of the refrigerant before the expansion is adjusted by regulating the power during liquefaction so that the refrigerant is in a liquid state before expansion is present.

Mit den gemessenen Werten von Druck und Temperatur kann zusammen mit der Dampfdruckkurve es Kältemittels festgestellt werden, ob der Druck des Kältemittels oberhalb des Dampfdrucks liegt und sich damit das Kältemittel im gewünschten flüssigen Zustand befindet. Sollte dies nicht der Fall sein, kann durch Drosselung der Leistung beim Verflüssigen der Druck in der Flüssigkeitsleitung zwischen Verflüssigungsund Entspannungs­einrichtung erhöht werden. Versuche haben ergeben, daß mit Hilfe des erfindungsgemäßen Verfahrens der Verflüssigungsdruck bis zu überraschend niedrigen Werten abgesenkt werden kann, entsprechend einer Verflüssigungstemperatur von beispielsweise -10°C, ohne daß Störungen im Kältemittelumlauf entstehen. Damit braucht bei entsprechend niedrigen Außentemperaturen sehr wenig Energie zum Verdichten aufgewendet werden. Wird der Druck beim Verflüssigen gleitend an die Außentemperaturen angepaßt, arbeitet eine nach dem erfindungsgemäßen Verfahren betriebene Kälteanlage äußerst wirtschaftlich.With the measured values of pressure and temperature, together with the vapor pressure curve of the refrigerant, it can be determined whether the pressure of the refrigerant is above the vapor pressure and thus the refrigerant is in the desired liquid state. If this is not the case, throttling the power during liquefaction can increase the pressure in the liquid line between the liquefaction and expansion device. Experiments have shown that with With the aid of the method according to the invention, the condensing pressure can be reduced to surprisingly low values, corresponding to a condensing temperature of, for example, -10 ° C., without disturbances in the refrigerant circulation. With correspondingly low outside temperatures, very little energy is required for compression. If the pressure during the liquefaction is smoothly adapted to the outside temperatures, a refrigeration system operated according to the method of the invention works extremely economically.

Darüberhinaus wird die Wirtschaftlichkeit einer Kälteanlage durch die Kälteleistungszahl ek bestimmt. Die Kälteleistungszahl ist das Verhältnis der Kälteleistung Q₀ zur beim Verdichten zugeführten Antriebsleistung P. Je geringer der Unterschied zwischen den Temperaturen beim Verflüssigen und beim Verdampfen ist, umso besser wird die Kälteleistungszahl ek. Durch die beim erfindungsgemäßen Verfahren mögliche gleitende Anpassung der Temperatur beim Verflüssigen an die Außenlufttemperatur wird also auch dadurch ein wirtschaftlicher Betrieb ermöglicht, daß mit sinkender Außenlufttemperatur die Kälteleistung Q₀ größer und gleich­zeitig die zugeführte Antriebsleistung P kleiner wird und sich damit die Kälteleistungszahl ek erhöht.In addition, the economic efficiency of a refrigeration system is determined by the refrigeration coefficient e k . The cooling capacity is the ratio of the cooling capacity Q₀ to the drive power P supplied during compression. The smaller the difference between the temperatures during liquefaction and evaporation, the better the cooling capacity e k . The sliding adjustment of the temperature during the liquefaction to the outside air temperature, which is possible with the method according to the invention, also makes economic operation possible by the fact that the cooling capacity Q₀ increases as the outside air temperature falls and at the same time the drive power P supplied decreases and the cooling capacity coefficient e k increases.

In einer besonders vorteilhaften Weiterbildung des erfindungs­gemäßen Verfahrens weist das Kältemittel vor dem Entspannen eine Temperatur auf, die geringfügig unterhalb der Verflüssi­gungstemperatur liegt. Durch die leichte Unterkühlung wird sichergestellt, daß auch vor dem Entspannungsvorgang das Kältemittel mit Sicherheit flüssig bleibt und damit der Kältemittelumlauf nicht gestört wird.In a particularly advantageous development of the method according to the invention, the refrigerant has a temperature before the expansion which is slightly below the condensing temperature. The slight subcooling ensures that the refrigerant remains liquid before the expansion process and that the refrigerant circulation is not disturbed.

Die Erfindung betrifft außerdem eine Kälteanlage zur Durch­führung des erfindungsgemäßen Verfahrens, die gekennzeichnet ist durch eine an der Rohrleitung vor der Entspannungseinrich­tung angebrachte Meßeinrichtung für Druck und Temperatur des Kältemittels, eine daran angeschlossene Regeleinrichtung und eine Steuerleitung, die Regeleinrichtung und Verflüssigungs­einrichtung verbindet.The invention also relates to a refrigeration system for carrying out the method according to the invention, which is characterized by a measuring device for pressure and temperature of the refrigerant attached to the pipe in front of the expansion device, a control device connected to it and a control line which connects the control device and the liquefaction device.

Das erfindungsgemäße Verfahren und weitere Einzelheiten des erfindungsgemäßen Verfahrens werden im folgenden anhand eines in der Figur skizzierten Ausführungsbeispiels näher erläutert.The method according to the invention and further details of the method according to the invention are explained in more detail below with reference to an exemplary embodiment sketched in the figure.

Die in der Figur dargestellte Kälteanlage enthält einen Kälteerzeuger, bestehend aus einem Verdichter 6, einem luftgekühlten Verflüssiger 7 und einem Kältemittelsammler 10, und eine Kühleinrichtung, bestehend aus einem Wärmetauscher 13, einem Expansionsventil 14 und einem Verdampfer 12. Der Kälteerzeuger ist im Freien aufgestellt, während sich die Kühleinrichtung in bzw. an dem gekühlten Raum, z.B. einem Kühlmöbel, befindet. Kälteerzeuger und Kühleinrichtung sind durch eine Flüssigkeitsleitung 3 und eine Saugleitung 4 verbunden, die im allgemeinen durch beheizte Räume führen. Die beiden Leitungen 3, 4 sind gegen Schwitzwasserbildung isoliert. Als Kältemittel wird vorzugsweise R22 oder R502 verwendet.The refrigeration system shown in the figure contains a refrigeration unit, consisting of a compressor 6, an air-cooled condenser 7 and a refrigerant collector 10, and a cooling device, consisting of a heat exchanger 13, an expansion valve 14 and an evaporator 12. The refrigeration unit is installed outdoors, while the cooling device in or on the cooled space, for example a refrigerator. The refrigeration device and the cooling device are connected by a liquid line 3 and a suction line 4, which generally lead through heated rooms. The two lines 3, 4 are insulated against condensation. R22 or R502 is preferably used as the refrigerant.

Bisher wurden solche Anlagen mit einem Druck im Verflüssiger 7, der einer Verflüssigungstemperatur von 20°C oder höher entspricht, betrieben, da man bei noch niedrigeren Drücken Störungen im Betriebsverhalten der Expansionsventile und damit Störungen des Kältemittelumlaufs erwartete. In Versuchen, die im Rahmen der Erfindung durchgeführt wurden, wurde jedoch ermittelt, daß der Verflüssigungsdruck je nach Temperatur der zur Kühlung eingesetzten Außenluft erheblich unter das bisher als Grenzwert betrachtete Niveau gleitend abgesenkt werden kann, ohne daß Störungen des Kältemittelkreislaufs auftreten. Dadurch besteht die Möglichkeit, die Kälteanlage auf besonders wirtschaftliche Weise zu betreiben.So far, such systems have been operated at a pressure in the condenser 7, which corresponds to a condensing temperature of 20 ° C. or higher, since at lower pressures, malfunctions in the operating behavior of the expansion valves and thus malfunctions in the refrigerant circulation were expected. In experiments that were carried out in the context of the invention, however, it was found that the condensing pressure depends on the temperature of the outside air used for cooling can be slid down considerably below the level previously regarded as the limit value, without disturbances in the refrigerant circuit occurring. This makes it possible to operate the refrigeration system in a particularly economical manner.

Die Versuchsergebnisse zeigen, daß Werte für den Verflüssi­gungsdruck erreicht werden können, die einer Verflüssigungs­temperatur tc von etwa 10°C bei Normalkühlanlagen (ca. -10°C im gekühlten Raum) bzw. einem tc von etwa -10°C bei Tiefkühlanlagen (ca. -40°C im gekühlten Raum) entsprechen. Dabei muß allerdings sichergestellt werden, daß das Kältemittel vor dem Expansionsventil geringfügig unterkühlt und damit blasenfrei vorliegt. Diese Bedingung ist im normalen Dauerbetrieb im allgemeinen erfüllt, da die Kühlung des flüssigen Kältemittels 3 mittels Wärmetausch 13 mit verdampftem Kältemittel 4 aus dem Verdampfer 12 in der Regel die notwendige Unterkühlung vor dem Expansionsventil 14 gewährleistet. Des öfteren wird jedoch der Normalbetrieb einer Kälteanlage unterbrochen, etwa aufgrund von niedrigerem Kältebedarf während Zeiten, in denen z.B. der Warenraum des zu kühlenden Kühlmöbels abgedeckt ist, oder aufgrund eines Stillstands der Anlage zum Abtauen. Bei solchen längeren Betriebsunterbrechungen können sich bei niedriger Verflüssigungstemperatur tc Schwierigkeiten beim Wiederanfahren der Kälteanlage ergeben:The test results show that values for the condensing pressure can be achieved which include a condensing temperature t c of around 10 ° C in normal cooling systems (around -10 ° C in a refrigerated room) or a t c of around -10 ° C in freezing systems ( approx. -40 ° C in the cooled room). However, it must be ensured that the refrigerant is slightly undercooled in front of the expansion valve and is therefore free of bubbles. This condition is generally met in normal continuous operation, since the cooling of the liquid refrigerant 3 by means of heat exchange 13 with evaporated refrigerant 4 from the evaporator 12 generally ensures the necessary subcooling in front of the expansion valve 14. However, the normal operation of a refrigeration system is often interrupted, for example due to a lower cooling requirement during times in which, for example, the goods area of the refrigerated cabinet to be cooled is covered or because the system for defrosting has stopped. With such long interruptions in operation, difficulties can arise when restarting the refrigeration system at low condensing temperature t c :

Da die Kältemittelleitungen 3,4 im allgemeinen durch warme Räume geführt werden, kann sich das Kältemittel in der Flüssigkeitsleitung 3 stark erwärmen. Bei Wiederinbetriebnahme der Kälteanlage besitzt auch das Kältemittel im Verdampfer 12 eine relativ hohe Temperatur. Deshalb reicht reicht die Leistung des Wärmetauschers 13 nicht aus, um eine Unterkühlung des Kältemittels vor dem Expansionsventil 14 sicherzustellen. Das Kältemittel siedet also vor dem Expansionsventil 14.Since the refrigerant lines 3, 4 are generally led through warm rooms, the refrigerant in the liquid line 3 can heat up considerably. When the refrigeration system is restarted, the refrigerant in the evaporator 12 also has a relatively high temperature. Therefore, the performance of the heat exchanger 13 is not sufficient to ensure subcooling of the refrigerant upstream of the expansion valve 14. The refrigerant thus boils upstream of the expansion valve 14.

Wenn z.B. die Außenlufttemperatur -5°C beträgt, kann der Druck im Verflüssiger auf eine Verflüssigungstemperatur tc von etwa 2K eingestellt werden. Das kondensierte Kältemittel hat beispielsweise eine Temperatur von 0°C und ist damit um 2K unterkühlt. Im Dauerbetrieb reichen diese Unterkühlung und die Kühlung im Wärmetauscher 13 im allgemeinen aus, um die Flüssigkeit bis zum Expansionsventil 14 blasenfrei zu halten. Während einer Betriebsunterbrechung oder bei erstmaliger Inbetriebnahme kann sich jedoch das Kältemittel weit über die Verflüssigungstemperatur tc erwärmen, im Extremfall bis auf Raumtemperatur.For example, if the outside air temperature is -5 ° C, the pressure in the condenser can be set to a condensing temperature t c of approximately 2K. The condensed refrigerant, for example, has a temperature of 0 ° C and is thus subcooled by 2K. In continuous operation, this subcooling and the cooling in the heat exchanger 13 are generally sufficient to keep the liquid free of bubbles up to the expansion valve 14. However, during an interruption in operation or when starting up for the first time, the refrigerant can heat up well above the condensing temperature t c , in extreme cases up to room temperature.

Die Durchsatzleistung des Expansionsventils 14 ist dann jedoch viel zu klein, um bei größerem Dampfanteil dem Verdampfer genügend Kältemittel zu liefern. Als Folge fällt der Druck im Verdampfer ab und durch die übliche Saugdruckregelung (in der Figur nicht eingezeichnet) wird der Verdichter 6 abgeschaltet und dadurch die Kälteerzeugung unterbrochen.The throughput of the expansion valve 14 is then, however, much too small to supply the evaporator with sufficient refrigerant in the event of a larger vapor content. As a result, the pressure in the evaporator drops and the compressor 6 is switched off by the usual suction pressure control (not shown in the figure) and the refrigeration is thereby interrupted.

Der Druck in der Flüssigkeitsleitung 4 sinkt weiter, damit auch die Verflüssigungstemperatur tc. Der Verdichter 6 wird immer wieder an- und abgeschaltet, bis endlich nach längerer Zeit ein stationärer Zustand erreicht wird.The pressure in the liquid line 4 drops further, so that the condensing temperature t c . The compressor 6 is switched on and off again and again until finally a steady state is reached after a long time.

Um diese Störungen zu vermeiden, weist die in der Figur skizzierte Kälteanlage erfindungsgemäß Meßfühler 18 für Temperatur und Druck des Kältemittels vor dem Expansionsventil 14 und ein Regelgerät 16 auf, das über eine Steuerleitung 17 dem Verflüssiger 7 verbunden ist.In order to avoid these faults, the refrigeration system outlined in the figure has sensors 18 for the temperature and pressure of the refrigerant upstream of the expansion valve 14 and a control device 16, which is connected to the condenser 7 via a control line 17.

Durch diese Einrichtungen wird erfindungsgemäß die Unterkühlung des Kältemittels aufrechterhalten: Sobald die Temperatur des Kältemittels einen bestimmten Grenzwert t₁ unterhalb der Verflüssigungstemperatur tc des Kältemittels beim gemessenen Druck überschreitet, drosselt das Regelgerät 16 die Leistung beim Verflüssigen 7. Dadurch erhöht sich der Druck in der Flüssigkeitsleitung 3. Sobald vor dem Expansionsventil 14 der Druck soweit gestiegen ist, daß die Verflüssigungstemperatur tc des Kältemittels einen weiteren Grenzwert t₂ erreicht hat, wird die Leistung beim Verflüssigen 7 wieder erhöht. Die Werte für die beiden Grenztemperaturen t₁ und t₂ betragen vorzugsweise
t₁ = tc - 3K
t₂ = tc - 6K.
tc hängt dabei über die Dampfdruckkurve vom Druck des Kältemittels ab, der zusammen mit der Temperatur des Kältemittels gemessen wird.According to the invention, the supercooling of the refrigerant is maintained by these devices: as soon as the temperature of the refrigerant exceeds a certain limit value t 1 below the condensing temperature t c of the refrigerant at the measured pressure, the control device 16 throttles the performance during the liquefaction 7. This increases the pressure in the liquid line 3. As soon as the pressure in front of the expansion valve 14 has risen to such an extent that the condensing temperature t c of the refrigerant has reached a further limit value t 2, the performance during the condensing 7 is increased again. The values for the two limit temperatures t 1 and t 2 are preferably
t₁ = t c - 3K
t₂ = t c - 6K.
t c depends on the vapor pressure curve on the pressure of the refrigerant, which is measured together with the temperature of the refrigerant.

Auf diese Weise wird durch eine Regelung, die unabhängig von äußeren Einflüssen wie z.B. der Raumtemperatur arbeitet, einem Sieden des Kältemittels vor dem Expansionsventil 14 während des laufenden Betriebs wirksam vorgebeugt und eine sehr kurze Anlaufzeit nach längerem Stillstand der Kälteanlage erreicht.In this way, a regulation that is independent of external influences such as the room temperature works, effectively prevents boiling of the refrigerant upstream of the expansion valve 14 during operation, and achieves a very short start-up time after the refrigeration system has been idle for a long time.

Claims (3)

1. Verfahren zum Betreiben einer Kälteanlage mit einem Kältemittelkreislauf, in dem ein Kältemittel verdichtet, verflüssigt, entspannt, verdampft und anschließend wieder der Verdichtung zugeführt wird, dadurch gekennzeichnet, daß vor dem Entspannen (14) Temperatur und Druck des Kältemittels gemessen werden und daß in Abhängigkeit von dieser Messung der Druck des Kältemittels vor dem Entspan­nen (14) durch Regelung der Leistung beim Verflüssigen (7) so eingestellt wird, daß das Kältemittel vor dem Entspan­nen (14) in flüssigem Zustand vorliegt.1. A method of operating a refrigeration system with a refrigerant circuit in which a refrigerant compresses, liquefies, expanded, evaporated and then fed back to the compression, characterized in that the temperature and pressure of the refrigerant are measured before the expansion (14) and that in Depending on this measurement, the pressure of the refrigerant before the expansion (14) is adjusted by regulating the power during liquefaction (7) so that the refrigerant is in a liquid state before the expansion (14). 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Kältemittel vor dem Entspannen eine Temperatur aufweist, die geringfügig unterhalb der Verflüssigungstemperatur liegt.2. The method according to claim 1, characterized in that the refrigerant has a temperature before the expansion, which is slightly below the condensing temperature. 3. Kälteanlage zur Durchführung des Verfahrens nach Anspruch 1 oder 2, gekennzeichnet durch eine an der Rohrleitung (4) für flüssiges Kältemittel vor der Entspannungseinrichtung (14) angebrachte Meßeinrichtung (18) für Druck und Temperatur des Kältemittels, eine daran angeschlossene Regeleinrichtung (16) und eine Steuerleitung (17), die Regeleinrichtung (16) und Verflüssigungseinrichtung (7) verbindet.3. Refrigeration system for performing the method according to claim 1 or 2, characterized by a on the pipe (4) for liquid refrigerant in front of the expansion device (14) attached measuring device (18) for pressure and temperature of the refrigerant, a control device connected to it (16) and a control line (17) connecting the control device (16) and the liquefaction device (7).
EP89100468A 1988-01-21 1989-01-12 Operating method for a refrigeration system and refrigeration system for carrying out the method Withdrawn EP0325163A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19883801711 DE3801711A1 (en) 1988-01-21 1988-01-21 METHOD FOR OPERATING A REFRIGERATION SYSTEM AND REFRIGERATION SYSTEM FOR IMPLEMENTING THE PROCESS
DE3801711 1988-01-21

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NL1000899C2 (en) * 1994-12-09 1996-08-28 Kempen Koudetechniek B V Van Cooling system e.g. for refrigerated storage - uses under-cooled refrigerant whose pressure is held constant by regulating pump and valves irrespective of ambient temperature and pressure
EP0762064A1 (en) * 1995-09-08 1997-03-12 Fritz Ing. Weider Refrigerant flow control for a heat pump and method
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EP0762064A1 (en) * 1995-09-08 1997-03-12 Fritz Ing. Weider Refrigerant flow control for a heat pump and method
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US9759468B2 (en) 2014-03-21 2017-09-12 Lennox Industries Inc. System for controlling operation of an HVAC system having tandem compressors

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