EP1771689B1 - Refrigeration machine and method for operating a refrigeration machine - Google Patents

Refrigeration machine and method for operating a refrigeration machine Download PDF

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Publication number
EP1771689B1
EP1771689B1 EP05748140.0A EP05748140A EP1771689B1 EP 1771689 B1 EP1771689 B1 EP 1771689B1 EP 05748140 A EP05748140 A EP 05748140A EP 1771689 B1 EP1771689 B1 EP 1771689B1
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EP
European Patent Office
Prior art keywords
refrigerant
temperature
compressor
overheating
evaporator
Prior art date
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Application number
EP05748140.0A
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German (de)
French (fr)
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EP1771689A1 (en
Inventor
Ali R. Nejad
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Copeland Europe GmbH
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Emerson Climate Technologies GmbH
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Publication of EP1771689A1 publication Critical patent/EP1771689A1/en
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Classifications

    • 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
    • F25B31/00—Compressor arrangements
    • F25B31/006—Cooling of compressor or motor
    • 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
    • F25B49/022—Compressor 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
    • F25B13/00—Compression machines, plants or systems, with reversible cycle
    • 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
    • F25B2500/00—Problems to be solved
    • F25B2500/08—Exceeding a certain temperature value in a refrigeration component or cycle
    • 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
    • F25B2600/21—Refrigerant outlet evaporator 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
    • F25B2600/00—Control issues
    • F25B2600/25—Control of valves
    • F25B2600/2501—Bypass valves
    • 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
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/19—Pressures
    • F25B2700/193—Pressures of the compressor
    • F25B2700/1933—Suction pressures
    • 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
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2106—Temperatures of fresh outdoor air
    • 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
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2115—Temperatures of a compressor or the drive means therefor
    • F25B2700/21151—Temperatures of a compressor or the drive means therefor at the suction side of the compressor
    • 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
    • F25B43/00—Arrangements for separating or purifying gases or liquids; Arrangements for vaporising the residuum of liquid refrigerant, e.g. by heat
    • F25B43/006—Accumulators

Definitions

  • the invention relates to a refrigerating machine, in particular a heat pump, with a refrigerant having a closed circuit in which successively an evaporator, a compressor, a condenser and a, in particular electrically operated, expansion valve are arranged. Furthermore, the invention relates to a method for operating such a refrigerator.
  • chillers of the type mentioned are known.
  • the refrigerant In the evaporator, the refrigerant is vaporized and overheated, i. heated beyond its saturation temperature. Overheating of the refrigerant thus means an increase in the refrigerant temperature at a constant pressure beyond its saturation temperature. Overheating is defined as the difference between the actual temperature of the refrigerant, e.g. in the area of the evaporator outlet, and the evaporation temperature or saturation temperature of the refrigerant.
  • a predetermined value for the superheating of the refrigerant is set and the superheat controlled so that it - regardless of other operating conditions - does not differ significantly from the predetermined value, on the one hand to achieve optimum efficiency of the refrigerator and on the other hand, a complete Ensure evaporation of the refrigerant.
  • a typical value for overheating is, for example, 6K to 10K.
  • a chiller in which by a temperature sensor, the refrigerant temperature is measured in the region of the output of a compressor.
  • the temperature sensor is connected to a valve, through which liquid refrigerant in the suction line can be introduced.
  • the valve is controlled by the temperature sensor so that the refrigerant temperature at the compressor outlet does not exceed a critical upper temperature limit.
  • US-B-6185949 discloses a refrigerator in which the compressor temperature is controlled by adding liquid refrigerant to the suction line. The addition of the liquid refrigerant is controlled by a microprocessor-controlled valve.
  • US-A-2004/0134206 discloses a refrigerator in which the opening degree of the expansion valve is controlled between a minimum and a maximum value, thereby preventing overheating of the compressor.
  • the US-A-2004/0134206 discloses a refrigerator according to the preamble of claim 1 and a method according to the preamble of claim 5 for operating a refrigerator. From the EP-A-1146299 It is known to reduce the refrigerant pressure at the compressor outlet or reduce the power consumption of the compressor by closing the expansion valve, the compressor end temperature and the outside temperature are used as parameters in an algorithm by which the overheating of the refrigerant to be set in the evaporator is limited.
  • the invention has for its object to provide a refrigeration machine with improved efficiency and a method for operating such a refrigerator.
  • a method according to claim 1 and a refrigerator according to claim 5 are provided.
  • Advantageous embodiments of the invention are described in the subclaims.
  • the method according to the invention is characterized inter alia by the fact that the temperature of the refrigerant in the region of the compressor, in particular the compression end temperature, is at least temporarily regulated by means of an overheating control unit such that it does not exceed a critical upper temperature limit.
  • the critical upper temperature limit is meant a temperature at which there is a risk of damage to the compressor, e.g. by a decomposition of lubricating oil provided in the compressor and / or by a mechanical wear of the compressor.
  • the refrigerant temperature in the region of the compressor in particular the compression end temperature, can always be kept below the critical upper temperature limit. In this way, damage to the compressor and a previously required to protect the compressor shutdown of the chiller are effectively avoided. Service life of the chiller resulting from the shutdown of the chiller or from damage result in the compressor, and the associated loss of cooling or heating power are thus minimized.
  • the refrigerant temperature can be regulated by means of the superheat control unit so that it is as close as possible to the upper temperature limit, that is as high as possible.
  • the superheat control unit fulfills a dual function: it not only serves to control the overheating to a predetermined value, but at the same time also to control the refrigerant temperature in the region of the compressor.
  • the regulation of the refrigerant temperature in the area of the compressor, in particular the compression end temperature, does not have to be permanent. For example, it may be sufficient to maintain the refrigerant temperature only at particularly low outside temperatures, e.g. during the winter months, because under these conditions there is a high risk that the final discharge temperature will reach levels that will damage the compressor.
  • the ambient temperature of the refrigerator and in particular the outside temperature is measured. If no permanent, for example year-round, regulation of the refrigerant temperature provided is, the control is activated when measuring the ambient or outdoor temperature when the ambient or outdoor temperature falls below a predetermined lower temperature limit. The activation of the control of the refrigerant temperature is thus thus weather-dependent.
  • the refrigerant temperature is measured downstream of the compressor and in particular in the region of the compressor outlet. In this way, it can be directly determined whether the refrigerant temperature at the compressor outlet, where the refrigerant temperature is highest, exceeds the predetermined target temperature.
  • the refrigerant temperature can be regulated down accordingly by taking measures, which are explained in more detail below. As soon as the refrigerant temperature is within the range of the target temperature, the measures taken can be reversed or stopped.
  • the refrigerant temperature is regulated by a change in the overheating of the refrigerant in the evaporator.
  • An increase in the overheating of the refrigerant leads to an increase in the refrigerant temperature in the region of the compressor, in particular the compression end temperature, while, conversely, a reduction in overheating leads to a reduction in the refrigerant temperature.
  • the overheating is not regulated to a value that always remains constant, but the overheating value to be set is variable, wherein the variable control of overheating is particularly weather-dependent.
  • the refrigerant temperature in the region of the compressor, in particular the compression end temperature, within certain limits can be controlled so that it is always in the range of the predetermined target temperature.
  • the superheat is just controlled so that the refrigerant temperature in the range of the compressor output is as close as possible to the critical upper temperature limit, but this does not exceed, in order to achieve optimum heating performance.
  • the refrigerant temperature in the area of the compressor thus forms the control variable, while the overheating represents a manipulated variable and the expansion valve is the corresponding actuator.
  • the overheating is regulated as a function of the ambient temperature of the chiller, in particular the outside temperature.
  • the overheating is determined by the saturation pressure and / or the saturation temperature of the refrigerant.
  • a decrease in the saturation temperature or the saturation pressure e.g. due to a reduced outside temperature leads to an increase in overheating and thus an increase in the refrigerant temperature in the compressor, while conversely, an increase in the saturation temperature or the saturation pressure, e.g. due to an increase in the outside temperature, resulting in a reduction in overheating and thus in a reduction in the refrigerant temperature in the compressor.
  • the overheating is changed by a corresponding control of the expansion valve.
  • An increase in refrigerant flow through the expansion valve i. an opening of the expansion valve leads to a reduction in overheating, while conversely, closing the expansion valve reduces the refrigerant flow and results in an increase in overheating.
  • the refrigerant temperature in the region of the compressor can be reduced according to the invention by separate cooling of the refrigerant in the compressor. In this way, the refrigerant temperature in the compressor can still be kept below the critical upper temperature limit even if a reduction in overheating to reduce the refrigerant temperature in the compressor is insufficient or not possible.
  • the compressor can be cooled by introducing liquid refrigerant into the compressor.
  • Liquid refrigerant is used because it has a lower temperature than the compressed refrigerant in the compressor.
  • liquid refrigerant in particular in the outlet region of the compressor, is introduced into the compressed refrigerant.
  • the refrigerant is cooled directly and thus indirectly reduces the temperature of the compressor.
  • the liquid refrigerant is branched out of the circuit downstream of the condenser and directed to the compressor. After passing through the condenser, the refrigerant has a temperature at which the refrigerant is condensed, which is thus lower than the compression end temperature, but at the same time is above the temperature of the refrigerant at the compressor inlet.
  • the liquid refrigerant can therefore be injected into the vaporized refrigerant without damaging the compressor.
  • Fig. 1 illustrated refrigerating machine according to the invention which is described here in the function of a heat pump, comprises a closed circuit 10 having a refrigerant.
  • a refrigerant circuit 10 In the refrigerant circuit 10, an evaporator 12, a compressor 14, a condenser 16 and an electrically operated expansion valve 18 are sequentially arranged.
  • the evaporator 12 and the compressor 14 are interconnected by a suction gas line 20. Since the compressor 14 is designed for compression exclusively of vaporized refrigerant and by a Accidental penetration of liquid refrigerant would be damaged, the compressor 14 is preceded by a arranged in the suction line 20 liquid separator 22, which not completely evaporated and / or condensed in the suction gas 20 liquid refrigerant removed from the refrigerant flow in the evaporator 12 and collects.
  • the liquid separator 22 is preceded by a four-way switching valve 24 arranged in the suction gas line 20, which is arranged simultaneously in a hot gas line 26 leading from the compressor 14 to the condenser 16.
  • a four-way switching valve 24 arranged in the suction gas line 20, which is arranged simultaneously in a hot gas line 26 leading from the compressor 14 to the condenser 16.
  • the chiller - as described herein - is used as a heat pump, i. operated in heating mode
  • the refrigerant flow heated in the compressor 14 can be switched to defrost the evaporator 12 during a corresponding actuation of the reversing valve 24 and completely fed to the evaporator 12.
  • the switching valve 24 allows switching of the refrigerant flow so that the refrigerator can operate in the cooling mode.
  • a bypass line 28 Downstream of the condenser 16 branches off a bypass line 28 from the cooling circuit 10, which is connected to a connected to the compressor 14 injection line 29.
  • the bypass line 28 and the injection line 29 enable the supply of liquid refrigerant to the compressor 14.
  • a solenoid valve 30 arranged in the bypass line 28 is provided.
  • a throttle member 31 may further be arranged, for example, a nozzle or a capillary tube, through which the refrigerant to be injected into the compressor 14 can be expanded and thereby additionally cooled.
  • the liquid refrigerant supplied to the compressor 14 through the bypass pipe 28 and the injection pipe 29 is injected into the compressed refrigerant to thereby lower the temperature of the compressed refrigerant, particularly in the area of the compressor outlet. This allows the compressor 14 to be protected from excessive temperatures that would damage the compressor 14.
  • the solenoid valve 30 is connected to and controllable by an overheating control unit 32.
  • the superheat control unit 32 may be a separate unit or integrated into a central heat pump controller.
  • the superheat control unit 32 for controlling the expansion valve 18 is also connected thereto.
  • the expansion valve 18 is an electrically operated expansion valve.
  • a pressure transmitter or pressure sensor 34 connected to the superheat control unit 32 and a temperature sensor 36 connected to the superheat control unit 32 are further arranged on the suction gas line 20.
  • the pressure sensor 34 By the pressure sensor 34, the evaporation pressure of the vaporized refrigerant in the evaporator can be measured. With knowledge of the thermodynamic and physical properties of the refrigerant can be calculated from the measured evaporation pressure, the saturation temperature of the refrigerant.
  • the temperature sensor 36 determines the actual temperature of the superheated refrigerant flowing through the suction gas line 20 or the suction gas temperature. From the difference between the suction gas temperature and the saturation temperature, the superheat control unit 32 determines the superheat of the refrigerant.
  • a temperature sensor 38 for measuring the ambient temperature of the heat pump and in particular the outside temperature is connected to the superheat control unit 32.
  • a temperature sensor 40 connected to the superheat control unit 32 is also provided in the area of the compressor outlet.
  • Fig. 2 shows a log p, H diagram of one in the heat pump of Fig. 1 used refrigerant, wherein the pressure p of the refrigerant is plotted logarithmically as a function of enthalpy H. Shown are the boundaries of saturated liquid 42 and saturated gas 44 and curves 46 of constant temperature.
  • the point E indicates the state of the refrigerant after expansion by the expansion valve 18.
  • evaporation E-A and overheating A-B of the refrigerant take place.
  • the compressor 14 provides a compression B-C of the refrigerant, which is accompanied by a corresponding increase in temperature.
  • the temperature of the refrigerant is increased from + 10 ° C at the outlet of the evaporator 12 through the compressor 14 up to + 90 ° C.
  • the condenser 16 is a liquefaction C-D of the refrigerant, wherein the liquefaction temperature in the example shown + 50 ° C.
  • the now liquid and only 50 ° C warm refrigerant is then expanded through the expansion valve 18 (D-E), where it cools down to 0 ° C.
  • the overheating is 10 K, namely just the difference between the temperatures at point B (+ 10 ° C) and at point A (0 ° C).
  • the temperature at point B corresponds to the actual temperature of the refrigerant in the suction gas line and is measured by the temperature sensor 36.
  • the temperature at point A corresponds to the evaporation temperature of the refrigerant, which is determined from the evaporation pressure of the refrigerant measured by the pressure sensor 34.
  • a situation is shown in which the evaporation temperature of the refrigerant due to a reduced evaporation pressure compared to the in Fig. 2 situation is reduced by 10 K, ie only -10 ° C.
  • Such a reduction of the evaporation pressure may for example result from a lower outside temperature.
  • the reduced evaporation temperature of the refrigerant leads to an increase in the superheat AB, which in turn causes an increase in the refrigerant temperature at the outlet of the compressor 14 (point C).
  • the increased refrigerant temperature at the compressor outlet is + 120 ° C.
  • an increase in the liquefaction temperature at which the refrigerant in the condenser 16 liquefies, CD leads to an increase in the refrigerant temperature at the compressor outlet C.
  • Fig. 4 is exemplified results in an increase in the liquefaction temperature of 50 ° C to 60 ° C compared to the in Fig. 2 shown situation at a constant evaporation temperature of 0 ° C in an increase in the refrigerant temperature at the compressor outlet C from 90 ° C to 120 ° C.
  • a regulation of the refrigerant temperature at the compressor outlet by the superheat control unit 32 is provided such that the refrigerant temperature at the compressor outlet does not exceed the above-mentioned critical upper temperature limit.
  • the refrigerant temperature at the compressor outlet is set to a specified value Target temperature regulated, which is slightly below the critical upper temperature limit.
  • the manipulated variable is the overheating AB of the refrigerant, which can be varied by changing the opening degree of the expansion valve 18, and alternatively or additionally, the injection of liquid refrigerant into the compressor 14 is provided.
  • the refrigerant temperature at the compressor outlet C or the final compression temperature within certain limits can be regulated so that it assumes a maximum value, but does not exceed the critical upper temperature limit. This optimizes the heat output of the heat pump and prevents damage to the compressor or shutdown of the heat pump. Service life of the heat pump are therefore minimized. As a result, an improved economy of the heat pump is achieved.
  • the adjustment of the required overheating is made by a corresponding control of the expansion valve 18 by the superheat control unit 32.
  • the superheat control unit 32 starts to monitor the refrigerant temperature at the compressor outlet with the aid of the temperature sensor 40. If the refrigerant temperature at the compressor outlet exceeds or threatens to exceed the predetermined target temperature below the critical upper temperature limit, the superheat control unit 32 controls the expansion valve 18 such that the flow of the refrigerant through the expansion valve 18 increases. This reduces overheating and, as a result, reduces the refrigerant temperature at the compressor outlet to the target temperature. To reduce the refrigerant temperature at the compressor outlet, the expansion valve 18 is thus opened further.
  • the superheat control unit 32 will activate the solenoid valve 30 to supply liquid refrigerant to the compressor 14 for cooling the compressed refrigerant.
  • the actuation of the solenoid valve 30 takes place in dependence on the refrigerant temperature at the compressor outlet.
  • the solenoid valve becomes 30 closed again by the superheat control unit 32 and the supply of liquid refrigerant to the compressor 14 stopped.
  • the superheat control unit 32 causes a reduction of the refrigerant flow through the expansion valve 18 by a corresponding control of the expansion valve 18 in order to bring the overheating of the refrigerant back to the original, recommended value.
  • the inventive regulation of the refrigerant temperature at the compressor outlet the efficiency of the heat pump is increased during particularly cold outdoor temperatures and extended the working range of the heat pump to higher condensing temperatures and higher heat capacity.
  • the risk of damaging the compressor 14 by exceeding a critical upper temperature limit and the risk of icing of the evaporator 12 are reduced.
  • Shutdown and defrost phases of the heat pump are thereby minimized.
  • the inventive variable and in particular weather-dependent control of overheating and the control of the refrigerant temperature at the compressor output, in particular the compression end temperature results in improved efficiency of the heat pump.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Air Conditioning Control Device (AREA)
  • Compression-Type Refrigeration Machines With Reversible Cycles (AREA)
  • Control Of Positive-Displacement Pumps (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)

Description

Die Erfindung betrifft eine Kältemaschine, insbesondere eine Wärmepumpe, mit einem ein Kältemittel aufweisenden geschlossenen Kreislauf, in dem nacheinander ein Verdampfer, ein Verdichter, ein Verflüssiger und ein, insbesondere elektrisch betriebenes, Expansionsventil angeordnet sind. Ferner betrifft die Erfindung ein Verfahren zum Betreiben einer solchen Kältemaschine.The invention relates to a refrigerating machine, in particular a heat pump, with a refrigerant having a closed circuit in which successively an evaporator, a compressor, a condenser and a, in particular electrically operated, expansion valve are arranged. Furthermore, the invention relates to a method for operating such a refrigerator.

Grundsätzlich sind Kältemaschinen der eingangs genannten Art bekannt. In dem Verdampfer wird das Kältemittel verdampft und überhitzt, d.h. über seine Sättigungstemperatur hinaus erwärmt. Überhitzung des Kältemittels bedeutet also eine Erhöhung der Kältemitteltemperatur bei konstantem Druck über seine Sättigungstemperatur hinaus. Die Überhitzung ist definiert als die Differenz zwischen der tatsächlichen Temperatur des Kältemittels, z.B. im Bereich des Verdampferausgangs, und der Verdampfungstemperatur bzw. Sättigungstemperatur des Kältemittels.Basically, chillers of the type mentioned are known. In the evaporator, the refrigerant is vaporized and overheated, i. heated beyond its saturation temperature. Overheating of the refrigerant thus means an increase in the refrigerant temperature at a constant pressure beyond its saturation temperature. Overheating is defined as the difference between the actual temperature of the refrigerant, e.g. in the area of the evaporator outlet, and the evaporation temperature or saturation temperature of the refrigerant.

Üblicherweise wird bei einer herkömmlichen Kältemaschine ein vorbestimmter Wert für die Überhitzung des Kältemittels vorgegeben und die Überhitzung so geregelt, dass sie - unabhängig von anderen Betriebsbedingungen - von dem vorgegebenen Wert nicht wesentlich abweicht, um einerseits einen optimalen Wirkungsgrad der Kältemaschine zu erreichen und andererseits eine vollständige Verdampfung des Kältemittels sicherzustellen. Ein typischer Wert für die Überhitzung beträgt beispielsweise 6 K bis 10 K.Usually, in a conventional refrigerator, a predetermined value for the superheating of the refrigerant is set and the superheat controlled so that it - regardless of other operating conditions - does not differ significantly from the predetermined value, on the one hand to achieve optimum efficiency of the refrigerator and on the other hand, a complete Ensure evaporation of the refrigerant. A typical value for overheating is, for example, 6K to 10K.

Bei bekannten Wärmepumpen hat es sich als problematisch herausgestellt, dass die Temperatur des verdampften Kältemittels unter bestimmten Betriebsbedingungen, beispielsweise bei besonders tiefen Außentemperaturen, am Ausgang des Verdichters so hohe Werte erreicht, dass eine Zersetzung von in dem Verdichter befindlichem Öl, z.B. Schmieröl, stattfindet und/oder ein mechanischer Verschleiß des Verdichters verursacht wird. Dies kann zu einer Beschädigung des Verdichters führen und das Abschalten der Wärmepumpe bzw. des Verdichters erfordern. Daneben besteht bei besonders tiefen Außentemperaturen die Gefahr einer Vereisung des Verdampfers, die ebenfalls ein Abschalten der Wärmepumpe oder ein Umschalten eines zu diesem Zweck zwischen dem Verdichter und dem Verflüssiger bzw. Verdampfer angeordneten Umschaltventils, insbesondere Vierwegeumschaltventils, zur Enteisung des Verdampfers erforderlich machen kann.In known heat pumps, it has proven to be problematic that the temperature of the vaporized refrigerant under certain operating conditions, for example at particularly low outside temperatures, reaches such high levels at the outlet of the compressor that decomposition of oil in the compressor, e.g. Lubricating oil, takes place and / or a mechanical wear of the compressor is caused. This can damage the compressor and require the heat pump or compressor to shut down. In addition, there is the risk of icing of the evaporator at particularly low outside temperatures, which can also make a shutdown of the heat pump or switching a arranged for this purpose between the compressor and the condenser or evaporator switching valve, in particular Vierwegeumschaltventils required for deicing the evaporator.

Sowohl das Abschalten der Wärmepumpe zur Vermeidung einer erhöhten Verdichtungsendtemperatur am Ausgang des Verdichters als auch das Abschalten der Wärmepumpe oder Umschalten des Umschaltventils zur Enteisung des Verdampfers bedeuten Standzeiten der Wärmepumpe, welche die Wirtschaftlichkeit der Wärmepumpe beeinträchtigen.Both switching off the heat pump to avoid an increased compression end temperature at the output of the compressor as well as switching off the heat pump or switching the switching valve to defrost the evaporator mean service life of the heat pump, which affect the efficiency of the heat pump.

Aus der FR-A-2679987 ist eine Kältemaschine bekannt, bei welcher durch einen Temperaturfühler die Kältemitteltemperatur im Bereich des Ausgangs eines Verdichters gemessen wird. Der Temperaturfühler ist mit einem Ventil verbunden, durch welches flüssiges Kältemittel in die Saugleitung einleitbar ist. Das Ventil wird durch den Temperaturfühler so gesteuert, dass die Kältemitteltemperatur am Verdichterausgang eine kritische Temperaturobergrenze nicht übersteigt.From the FR-A-2679987 a chiller is known in which by a temperature sensor, the refrigerant temperature is measured in the region of the output of a compressor. The temperature sensor is connected to a valve, through which liquid refrigerant in the suction line can be introduced. The valve is controlled by the temperature sensor so that the refrigerant temperature at the compressor outlet does not exceed a critical upper temperature limit.

Auch die US-B-6185949 offenbart eine Kältemaschine, bei welcher die Verdichtertemperatur durch Zugabe von flüssigem Kältemittel in die Saugleitung gesteuert wird. Die Zugabe des flüssigen Kältemittels wird dabei über ein mikroprozessorgesteuertes Ventil geregelt.Also the US-B-6185949 discloses a refrigerator in which the compressor temperature is controlled by adding liquid refrigerant to the suction line. The addition of the liquid refrigerant is controlled by a microprocessor-controlled valve.

In der US-A-2003/0094007 ist eine Kältemaschine beschrieben, bei welcher ein Motor des Verdichters durch flüssiges Kältemittel gekühlt wird, welches nach dem Verflüssiger abgezweigt und dem Verdichter über eine Leitung zugeführt wird. Die Einleitung des flüssigen Kältemittels in den Verdichter erfolgt über ein durch eine Steuerung gesteuertes Ventil.In the US-A-2003/0094007 a refrigerating machine is described in which a motor of the compressor is cooled by liquid refrigerant, which is branched off after the condenser and fed to the compressor via a line. The introduction of the liquid refrigerant into the compressor via a controlled by a control valve.

In der US-A-2004/0134206 ist eine Kältemaschine offenbart, bei welcher der Öffnungsgrad des Expansionsventils zwischen einem minimalen und einem maximalen Wert geregelt wird, um dadurch eine Überhitzung des Verdichters zu verhindern. Die US-A-2004/0134206 offenbart eine Kältemaschine gemäß dem Oberbegriff des Anspruchs 1 und ein Verfahren gemäß dem Oberbegriff des Anspruchs 5 zum Betreiben einer Kältemaschine. Aus der EP-A-1146299 ist es bekannt, durch Schließung des Expansionsventils den Kältemitteldruck am Verdichterausgang zu reduzieren oder die Stromaufnahme des Verdichters zu reduzieren, wobei die Verdichterendtemperatur und die Außentemperatur als Parameter in einen Algorithmus einfließen, durch welchen die im Verdampfer einzustellende Überhitzung des Kältemittels begrenzt wird.In the US-A-2004/0134206 discloses a refrigerator in which the opening degree of the expansion valve is controlled between a minimum and a maximum value, thereby preventing overheating of the compressor. The US-A-2004/0134206 discloses a refrigerator according to the preamble of claim 1 and a method according to the preamble of claim 5 for operating a refrigerator. From the EP-A-1146299 It is known to reduce the refrigerant pressure at the compressor outlet or reduce the power consumption of the compressor by closing the expansion valve, the compressor end temperature and the outside temperature are used as parameters in an algorithm by which the overheating of the refrigerant to be set in the evaporator is limited.

Der Erfindung liegt die Aufgabe zugrunde, eine Kältemaschine mit einer verbesserten Wirtschaftlichkeit und ein Verfahren zum Betreiben einer solchen Kältemaschine zu schaffen.The invention has for its object to provide a refrigeration machine with improved efficiency and a method for operating such a refrigerator.

Zur Lösung der Aufgabe sind ein Verfahren nach Anspruch 1 und eine Kältemaschine nach Anspruch 5 vorgesehen. Vorteilhafte Ausführungsformen der Erfindung sind in den Unteransprüchen beschrieben. Das erfindungsgemäße Verfahren zeichnet sich unter anderem dadurch aus, dass die Temperatur des Kältemittels im Bereich des Verdichters, insbesondere die Verdichtungsendtemperatur, mittels einer Überhitzungsregeleinheit zumindest zeitweise so geregelt wird, dass sie eine kritische Temperaturobergrenze nicht übersteigt.To solve the problem, a method according to claim 1 and a refrigerator according to claim 5 are provided. Advantageous embodiments of the invention are described in the subclaims. The method according to the invention is characterized inter alia by the fact that the temperature of the refrigerant in the region of the compressor, in particular the compression end temperature, is at least temporarily regulated by means of an overheating control unit such that it does not exceed a critical upper temperature limit.

Unter der kritischen Temperaturobergrenze wird hier eine Temperatur verstanden, bei welcher die Gefahr einer Beschädigung des Verdichters besteht, z.B. durch eine Zersetzung von in dem Verdichter vorgesehenem Schmieröl und/oder durch einen mechanischen Verschleiß des Verdichters.By the critical upper temperature limit is meant a temperature at which there is a risk of damage to the compressor, e.g. by a decomposition of lubricating oil provided in the compressor and / or by a mechanical wear of the compressor.

Durch die Regelung der Kältemitteltemperatur auf eine vorgegebene Zieltemperatur, die zur Berücksichtigung eines Überschwingverhaltens der Kältemitteltemperatur vorzugsweise um einen gewissen Betrag unterhalb der kritischen Temperaturobergrenze gewählt wird, kann die Kältemitteltemperatur im Bereich des Verdichters, insbesondere die Verdichtungsendtemperatur, stets unterhalb der kritischen Temperaturobergrenze gehalten werden. Auf diese Weise werden eine Beschädigung des Verdichters und ein bisher zum Schutz des Verdichters erforderliches Abschalten der Kältemaschine wirksam vermieden. Standzeiten der Kältemaschine, die aus dem Abschalten der Kältemaschine oder aus einer Beschädigung des Verdichters resultieren, und der damit verbundene Verlust an Kälte- bzw. Heizleistung werden folglich minimiert.By controlling the refrigerant temperature to a predetermined target temperature, which is preferably selected to account for an overshoot of the refrigerant temperature by a certain amount below the critical upper temperature limit, the refrigerant temperature in the region of the compressor, in particular the compression end temperature, can always be kept below the critical upper temperature limit. In this way, damage to the compressor and a previously required to protect the compressor shutdown of the chiller are effectively avoided. Service life of the chiller resulting from the shutdown of the chiller or from damage result in the compressor, and the associated loss of cooling or heating power are thus minimized.

Gleichzeitig kann die Kältemitteltemperatur mittels der Überhitzungsregeleinheit so geregelt werden, dass sie möglichst dicht an der Temperaturobergrenze liegt, also möglichst hoch ist. Dadurch wird eine optimale Heizleistung einer als Wärmepumpe arbeitenden Kältemaschine erreicht. Dabei erfüllt die Überhitzungsregeleinheit eine Doppelfunktion: sie dient nicht nur der Regelung der Überhitzung auf einen vorbestimmten Wert, sondern gleichzeitig auch der Regelung der Kältemitteltemperatur im Bereich des Verdichters.At the same time, the refrigerant temperature can be regulated by means of the superheat control unit so that it is as close as possible to the upper temperature limit, that is as high as possible. As a result, an optimal heating capacity of a working as a heat pump chiller is achieved. In this case, the superheat control unit fulfills a dual function: it not only serves to control the overheating to a predetermined value, but at the same time also to control the refrigerant temperature in the region of the compressor.

Sowohl die minimierten Standzeiten als auch die optimierte Heizleistung der Kältemaschine führen zu einem erhöhten Gesamtwirkungsgrad der Kältemaschine über das Jahr gesehen und somit zu einer verbesserten Wirtschaftlichkeit der Kältemaschine.Both the minimized service life and the optimized heating power of the chiller lead to an increased overall efficiency of the chiller over the year and thus to an improved economy of the chiller.

Die Regelung der Kältemitteltemperatur im Bereich des Verdichters, insbesondere der Verdichtungsendtemperatur, muss nicht dauerhaft erfolgen. Es kann beispielsweise ausreichend sein, die Kältemitteltemperatur lediglich bei besonders tiefen Außentemperaturen, z.B. während der Wintermonate, zu regeln, da unter diesen Bedingungen die Gefahr besonders hoch ist, dass die Verdichtungsendtemperatur Werte erreicht, die zu einer Beschädigung des Verdichters führen.The regulation of the refrigerant temperature in the area of the compressor, in particular the compression end temperature, does not have to be permanent. For example, it may be sufficient to maintain the refrigerant temperature only at particularly low outside temperatures, e.g. during the winter months, because under these conditions there is a high risk that the final discharge temperature will reach levels that will damage the compressor.

Erfindungsgemäß wird die Umgebungstemperatur der Kältemaschine und insbesondere die Außentemperatur gemessen. Sofern keine dauerhafte, beispielsweise ganzjährige, Regelung der Kältemitteltemperatur vorgesehen ist, wird die Regelung bei Messung der Umgebungs- bzw. Außentemperatur aktiviert, wenn die Umgebungs- bzw. Außentemperatur eine vorgegebene Temperaturuntergrenze unterschreitet. Die Aktivierung der Regelung der Kältemitteltemperatur erfolgt somit also witterungsabhängig. Erfindungsgemäß wird die Kältemitteltemperatur stromabwärts von dem Verdichter und insbesondere im Bereich des Verdichterausgangs gemessen. Auf diese Weise kann direkt festgestellt werden, ob die Kältemitteltemperatur am Verdichterausgang, wo die Kältemitteltemperatur am höchsten ist, die vorgegebene Zieltemperatur überschreitet. Überschreitet die Kältemitteltemperatur diese Zieltemperatur oder droht dieser Fall einzutreten, kann die Kältemitteltemperatur durch Ergreifen von Maßnahmen, die weiter unten näher erläutert werden, entsprechend heruntergeregelt werden. Sobald die Kältemitteltemperatur wieder im Bereich der Zieltemperatur liegt, können die ergriffenen Maßnahmen wieder rückgängig gemacht oder gestoppt werden.According to the invention, the ambient temperature of the refrigerator and in particular the outside temperature is measured. If no permanent, for example year-round, regulation of the refrigerant temperature provided is, the control is activated when measuring the ambient or outdoor temperature when the ambient or outdoor temperature falls below a predetermined lower temperature limit. The activation of the control of the refrigerant temperature is thus thus weather-dependent. According to the invention, the refrigerant temperature is measured downstream of the compressor and in particular in the region of the compressor outlet. In this way, it can be directly determined whether the refrigerant temperature at the compressor outlet, where the refrigerant temperature is highest, exceeds the predetermined target temperature. If the refrigerant temperature exceeds this target temperature or if this situation threatens to occur, the refrigerant temperature can be regulated down accordingly by taking measures, which are explained in more detail below. As soon as the refrigerant temperature is within the range of the target temperature, the measures taken can be reversed or stopped.

Erfindungsgemäß wird die Kältemitteltemperatur durch eine Veränderung der Überhitzung des Kältemittels in dem Verdampfer geregelt. Eine Erhöhung der Überhitzung des Kältemittels führt zu einer Erhöhung der Kältemitteltemperatur im Bereich des Verdichters, insbesondere der Verdichtungsendtemperatur, während umgekehrt eine Verringerung der Überhitzung eine Reduzierung der Kältemitteltemperatur nach sich zieht. Die Überhitzung wird mit anderen Worten nicht auf einen stets konstant bleibenden Wert geregelt, sondern der einzustellende Überhitzungswert ist variabel, wobei die variable Regelung der Überhitzung insbesondere witterungsabhängig erfolgt.According to the invention, the refrigerant temperature is regulated by a change in the overheating of the refrigerant in the evaporator. An increase in the overheating of the refrigerant leads to an increase in the refrigerant temperature in the region of the compressor, in particular the compression end temperature, while, conversely, a reduction in overheating leads to a reduction in the refrigerant temperature. In other words, the overheating is not regulated to a value that always remains constant, but the overheating value to be set is variable, wherein the variable control of overheating is particularly weather-dependent.

Durch eine entsprechende Veränderung der Überhitzung kann die Kältemitteltemperatur im Bereich des Verdichters, insbesondere die Verdichtungsendtemperatur, innerhalb gewisser Grenzen so geregelt werden, dass sie stets im Bereich der vorgegebenen Zieltemperatur liegt. Bevorzugt wird die Überhitzung gerade so gesteuert, dass die Kältemitteltemperatur im Bereich des Verdichterausgangs möglichst dicht an der kritischen Temperaturobergrenze liegt, diese aber nicht übersteigt, um eine optimale Heizleistung zu erreichen. Die Kältemitteltemperatur im Bereich des Verdichters bildet also die Regelgröße, während die Überhitzung eine Stellgröße und das Expansionsventil das entsprechende Stellglied darstellt.By a corresponding change in overheating, the refrigerant temperature in the region of the compressor, in particular the compression end temperature, within certain limits can be controlled so that it is always in the range of the predetermined target temperature. Preferably, the superheat is just controlled so that the refrigerant temperature in the range of the compressor output is as close as possible to the critical upper temperature limit, but this does not exceed, in order to achieve optimum heating performance. The refrigerant temperature in the area of the compressor thus forms the control variable, while the overheating represents a manipulated variable and the expansion valve is the corresponding actuator.

Durch eine Verringerung der Überhitzung kann ferner die Gefahr einer Vereisung des Verdampfers vermindert werden. Auf diese Weise werden die Standzeiten noch weiter verkürzt und die Wirtschaftlichkeit der Kältemaschine noch weiter verbessert.By reducing the overheating, the risk of icing of the evaporator can be further reduced. In this way, the downtime is further reduced and the cost of the chiller even further improved.

Die Überhitzung wird verringert, wenn die im Bereich des Verdichters, gemessene Kältemitteltemperatur eine vorgegebene Zieltemperatur übersteigt oder zu übersteigen droht. Zur Regelung der Kältemitteltemperatur wird in diesem Fall also eine direkte Überwachung der Kältemitteltemperatur, vorzugsweise am Verdichterausgang, herangezogen.Overheating is reduced if the refrigerant temperature measured in the area of the compressor exceeds or threatens to exceed a specified target temperature. To control the refrigerant temperature in this case, therefore, a direct monitoring of the refrigerant temperature, preferably at the compressor output, used.

Vorteilhafterweise wird die Überhitzung in Abhängigkeit von der Umgebungstemperatur der Kältemaschine, insbesondere der Außentemperatur, geregelt.Advantageously, the overheating is regulated as a function of the ambient temperature of the chiller, in particular the outside temperature.

Die Überhitzung wird durch den Sättigungsdruck und/oder die Sättigungstemperatur des Kältemittels bestimmt. Ein Absinken der Sättigungstemperatur bzw. des Sättigungsdrucks, z.B. aufgrund einer reduzierten Außentemperatur, führt zu einem Anstieg der Überhitzung und somit zu einem Anstieg der Kältemitteltemperatur im Verdichter, während umgekehrt ein Anstieg der Sättigungstemperatur bzw. des Sättigungsdrucks, z.B. aufgrund eines Anstiegs der Außentemperatur, in einer Verringerung der Überhitzung und somit in einer Reduzierung der Kältemitteltemperatur im Verdichter resultiert. Durch eine entsprechende Regelung der Überhitzung unter Berücksichtigung der Umgebungs- bzw. Außentemperatur kann einem Anstieg oder einer Reduzierung der Kältemitteltemperatur im Verdichter entgegen gewirkt werden. Erfindungsgemäß wird die Überhitzung durch eine entsprechende Steuerung des Expansionsventils verändert. Eine Erhöhung der Kältemittelströmung durch das Expansionsventil, d.h. eine Öffnung des Expansionsventils, führt zu einer Verringerung der Überhitzung, während umgekehrt das Schließen des Expansionsventils die Kältemittelströmung verringert und in einer Erhöhung der Überhitzung resultiert.The overheating is determined by the saturation pressure and / or the saturation temperature of the refrigerant. A decrease in the saturation temperature or the saturation pressure, e.g. due to a reduced outside temperature leads to an increase in overheating and thus an increase in the refrigerant temperature in the compressor, while conversely, an increase in the saturation temperature or the saturation pressure, e.g. due to an increase in the outside temperature, resulting in a reduction in overheating and thus in a reduction in the refrigerant temperature in the compressor. By controlling the overheating accordingly, taking into account the ambient or outside temperature, an increase or a reduction in the refrigerant temperature in the compressor can be counteracted. According to the invention the overheating is changed by a corresponding control of the expansion valve. An increase in refrigerant flow through the expansion valve, i. an opening of the expansion valve leads to a reduction in overheating, while conversely, closing the expansion valve reduces the refrigerant flow and results in an increase in overheating.

Zusätzlich zu einer Verringerung der Überhitzung kann die Kältemitteltemperatur im Bereich des Verdichters erfindungsgemäß durch eine separate Kühlung des Kältemittels im Verdichter reduziert werden. Auf diese Weise kann die Kältemitteltemperatur im Verdichter selbst dann noch unterhalb der kritischen Temperaturobergrenze gehalten werden, wenn eine Verringerung der Überhitzung zur Reduzierung der Kältemitteltemperatur im Verdichter nicht ausreicht oder nicht möglich ist.In addition to a reduction in overheating, the refrigerant temperature in the region of the compressor can be reduced according to the invention by separate cooling of the refrigerant in the compressor. In this way, the refrigerant temperature in the compressor can still be kept below the critical upper temperature limit even if a reduction in overheating to reduce the refrigerant temperature in the compressor is insufficient or not possible.

Der Verdichter kann durch Einleiten von flüssigem Kältemittel in den Verdichter gekühlt werden. Flüssiges Kältemittel wird verwendet, da dieses eine niedrigere Temperatur aufweist als das im Verdichter verdichtete gasförmige Kältemittel.The compressor can be cooled by introducing liquid refrigerant into the compressor. Liquid refrigerant is used because it has a lower temperature than the compressed refrigerant in the compressor.

Bevorzugt wird flüssiges Kältemittel, insbesondere im Ausgangsbereich des Verdichters, in das verdichtete Kältemittel eingeleitet. Dadurch wird direkt das Kältemittel abgekühlt und somit indirekt die Temperatur des Verdichters reduziert.Preferably, liquid refrigerant, in particular in the outlet region of the compressor, is introduced into the compressed refrigerant. As a result, the refrigerant is cooled directly and thus indirectly reduces the temperature of the compressor.

Erfindungsgemäß wird das flüssige Kältemittel stromabwärts von dem Verflüssiger aus dem Kreislauf abgezweigt und zu dem Verdichter geleitet. Nach dem Durchgang durch den Verflüssiger weist das Kältemittel eine Temperatur auf, bei der das Kältemittel zwar kondensiert ist, die also niedriger als die Verdichtungsendtemperatur ist, die aber gleichzeitig über der Temperatur des Kältemittels am Verdichtereingang liegt. Das flüssige Kältemittel kann deshalb in das verdampfte Kältemittel eingespritzt werden, ohne den Verdichter zu beschädigen.According to the invention, the liquid refrigerant is branched out of the circuit downstream of the condenser and directed to the compressor. After passing through the condenser, the refrigerant has a temperature at which the refrigerant is condensed, which is thus lower than the compression end temperature, but at the same time is above the temperature of the refrigerant at the compressor inlet. The liquid refrigerant can therefore be injected into the vaporized refrigerant without damaging the compressor.

Durch die erfindungsgemäße Kältemaschine nach Anspruch 8 und ihre vorteilhaften Ausbildungen werden die voranstehend genannten Vorteile entsprechend erreicht.By the refrigerator according to the invention according to claim 8 and its advantageous embodiments, the advantages mentioned above are achieved accordingly.

Nachfolgend wird die Erfindung rein beispielhaft unter Bezugnahme auf die beigefügte Zeichnung beschrieben. Es zeigen:

Fig. 1
eine schematische Darstellung einer erfindungsgemäßen Kältemaschine;
Fig. 2
ein Log p, H - Diagramm des Kältemittels der Kältemaschine von Fig. 1 und einen zugehörigen Kreisprozess;
Fig. 3
das Log p, H - Diagramm von Fig. 2 bei reduzierter Sättigungstemperatur bzw. reduziertem Sättigungsdruck des Kältemittels;
Fig. 4
das Log p, H - Diagramm von Fig. 2 bei erhöhter Verflüssigungstemperatur des Kältemittels;
Fig. 5
das Log p, H - Diagramm von Fig. 3 bei reduzierter Überhitzung; und
Fig. 6
das Log p, H - Diagramm von Fig. 3 bei erhöhter Verflüssigungstemperatur, reduzierter Überhitzung und einer Zufuhr von flüssigem Kältemittel zum Verdichter.
Hereinafter, the invention will be described purely by way of example with reference to the accompanying drawings. Show it:
Fig. 1
a schematic representation of a refrigerator according to the invention;
Fig. 2
a log p, H - diagram of the refrigerant of the chiller of Fig. 1 and an associated cycle process;
Fig. 3
the log p, H diagram of Fig. 2 at reduced saturation temperature or reduced saturation pressure of the refrigerant;
Fig. 4
the log p, H diagram of Fig. 2 at increased condensing temperature of the refrigerant;
Fig. 5
the log p, H diagram of Fig. 3 at reduced overheating; and
Fig. 6
the log p, H diagram of Fig. 3 with increased condensing temperature, reduced overheating and a supply of liquid refrigerant to the compressor.

Die in Fig. 1 dargestellte erfindungsgemäße Kältemaschine, die hier in der Funktion einer Wärmepumpe beschrieben wird, umfasst einen geschlossenen Kreislauf 10, der ein Kältemittel aufweist. In dem Kältemittelkreislauf 10 sind nacheinander ein Verdampfer 12, ein Verdichter 14, ein Verflüssiger 16 und ein elektrisch betriebenes Expansionsventil 18 angeordnet.In the Fig. 1 illustrated refrigerating machine according to the invention, which is described here in the function of a heat pump, comprises a closed circuit 10 having a refrigerant. In the refrigerant circuit 10, an evaporator 12, a compressor 14, a condenser 16 and an electrically operated expansion valve 18 are sequentially arranged.

Der Verdampfer 12 und der Verdichter 14 sind durch eine Sauggasleitung 20 miteinander verbunden. Da der Verdichter 14 für eine Verdichtung ausschließlich von verdampftem Kältemittel ausgelegt ist und durch ein unbeabsichtigtes Eindringen von flüssigem Kältemittel beschädigt würde, ist dem Verdichter 14 ein in der Sauggasleitung 20 angeordneter Flüssigkeitsabscheider 22 vorgeschaltet, der im Verdampfer 12 nicht vollständig verdampftes und/oder in der Sauggasleitung 20 kondensiertes flüssiges Kältemittel aus dem Kältemittelstrom entfernt und sammelt.The evaporator 12 and the compressor 14 are interconnected by a suction gas line 20. Since the compressor 14 is designed for compression exclusively of vaporized refrigerant and by a Accidental penetration of liquid refrigerant would be damaged, the compressor 14 is preceded by a arranged in the suction line 20 liquid separator 22, which not completely evaporated and / or condensed in the suction gas 20 liquid refrigerant removed from the refrigerant flow in the evaporator 12 and collects.

Dem Flüssigkeitsabscheider 22 ist ein in der Sauggasleitung 20 angeordnetes Vierwegeumschaltventil 24 vorgeschaltet, das gleichzeitig in einer von dem Verdichter 14 zu dem Verflüssiger 16 führenden Heißgasleitung 26 angeordnet ist. Wird die Kältemaschine - wie es hier beschrieben ist - als Wärmepumpe, d.h. im Heizbetrieb, betrieben, so kann der im Verdichter 14 erhitzte Kältemittelstrom bei einer entsprechenden Betätigung des Umschaltventils 24 zum Abtauen des Verdampfers 12 umgeschaltet und vollständig dem Verdampfer 12 zugeführt werden. Alternativ ermöglicht das Umschaltventil 24 ein Umschalten des Kältemittelstroms derart, dass die Kältemaschine im Kühlungsbetrieb arbeiten kann.The liquid separator 22 is preceded by a four-way switching valve 24 arranged in the suction gas line 20, which is arranged simultaneously in a hot gas line 26 leading from the compressor 14 to the condenser 16. If the chiller - as described herein - is used as a heat pump, i. operated in heating mode, the refrigerant flow heated in the compressor 14 can be switched to defrost the evaporator 12 during a corresponding actuation of the reversing valve 24 and completely fed to the evaporator 12. Alternatively, the switching valve 24 allows switching of the refrigerant flow so that the refrigerator can operate in the cooling mode.

Stromabwärts von dem Verflüssiger 16 zweigt eine Bypassleitung 28 aus dem Kühlkreislauf 10 ab, die mit einer an den Verdichter 14 angeschlossene Einspritzleitung 29 verbunden ist. Die Bypassleitung 28 und die Einspritzleitung 29 ermöglichen die Zufuhr von flüssigem Kältemittel zu dem Verdichter 14. Zur Steuerung dieser Kältemittelzufuhr ist ein in der Bypassleitung 28 angeordnetes Magnetventil 30 vorgesehen. In der Einspritzleitung 29 kann ferner ein Drosselorgan 31 angeordnet sein, beispielsweise eine Düse oder ein Kapillarrohr, durch welches das in den Verdichter 14 einzuspritzende Kältemittel entspannt und dadurch zusätzlich abgekühlt werden kann.Downstream of the condenser 16 branches off a bypass line 28 from the cooling circuit 10, which is connected to a connected to the compressor 14 injection line 29. The bypass line 28 and the injection line 29 enable the supply of liquid refrigerant to the compressor 14. To control this refrigerant supply, a solenoid valve 30 arranged in the bypass line 28 is provided. In the injection line 29, a throttle member 31 may further be arranged, for example, a nozzle or a capillary tube, through which the refrigerant to be injected into the compressor 14 can be expanded and thereby additionally cooled.

Das dem Verdichter 14 durch die Bypassleitung 28 und die Einspritzleitung 29 zugeführte flüssige Kältemittel wird in das verdichtete Kältemittel eingespritzt, um auf diese Weise die Temperatur des verdichteten Kältemittels, insbesondere im Bereich des Verdichterausgangs, zu senken. Dadurch kann der Verdichter 14 vor übermäßigen Temperaturen geschützt werden, die den Verdichter 14 beschädigen würden.The liquid refrigerant supplied to the compressor 14 through the bypass pipe 28 and the injection pipe 29 is injected into the compressed refrigerant to thereby lower the temperature of the compressed refrigerant, particularly in the area of the compressor outlet. This allows the compressor 14 to be protected from excessive temperatures that would damage the compressor 14.

Alternativ oder zusätzlich ist es auch möglich, das dem Verdichter 14 zugeführte flüssige Kältemittel durch in dem Verdichter 14 entsprechend vorgesehene Kühlleitungen zu zirkulieren. Dies bewirkt eine Kühlung des Verdichters 14 selbst, über den dann auch das verdichtete Kältemittel gekühlt wird.Alternatively or additionally, it is also possible to circulate the liquid refrigerant supplied to the compressor 14 by cooling lines provided correspondingly in the compressor 14. This causes a cooling of the compressor 14 itself, via which then the compressed refrigerant is cooled.

Das Magnetventil 30 ist mit einer Überhitzungsregeleinheit 32 verbunden und durch diese steuerbar. Die Überhitzungsregeleinheit 32 kann eine separate Einheit sein oder in eine zentrale Wärmepumpensteuerung integriert sein.The solenoid valve 30 is connected to and controllable by an overheating control unit 32. The superheat control unit 32 may be a separate unit or integrated into a central heat pump controller.

Darüber hinaus ist die Überhitzungsregeleinheit 32 zur Steuerung des Expansionsventils 18 auch mit diesem verbunden. Das Expansionsventil 18 ist ein elektrisch betriebenes Expansionsventil.In addition, the superheat control unit 32 for controlling the expansion valve 18 is also connected thereto. The expansion valve 18 is an electrically operated expansion valve.

Dem Flüssigkeitsabscheider 22 vorgeschaltet sind an der Sauggasleitung 20 ferner ein mit der Überhitzungsregeleinheit 32 verbundener Drucktransmitter oder Drucksensor 34 und ein mit der Überhitzungsregeleinheit 32 verbundener Temperatursensor 36 angeordnet.Upstream of the liquid separator 22, a pressure transmitter or pressure sensor 34 connected to the superheat control unit 32 and a temperature sensor 36 connected to the superheat control unit 32 are further arranged on the suction gas line 20.

Durch den Drucksensor 34 ist der Verdampfungsdruck des im Verdampfer verdampften Kältemittels messbar. Bei Kenntnis der thermodynamischen und physikalischen Eigenschaften des Kältemittels lässt sich aus dem gemessenen Verdampfungsdruck die Sättigungstemperatur des Kältemittels errechnen. Durch den Temperatursensor 36 wird die tatsächliche Temperatur des durch die Sauggasleitung 20 strömenden überhitzten Kältemittels bzw. die Sauggastemperatur bestimmt. Aus der Differenz zwischen Sauggastemperatur und Sättigungstemperatur ermittelt die Überhitzungsregeleinheit 32 die Überhitzung des Kältemittels.By the pressure sensor 34, the evaporation pressure of the vaporized refrigerant in the evaporator can be measured. With knowledge of the thermodynamic and physical properties of the refrigerant can be calculated from the measured evaporation pressure, the saturation temperature of the refrigerant. The temperature sensor 36 determines the actual temperature of the superheated refrigerant flowing through the suction gas line 20 or the suction gas temperature. From the difference between the suction gas temperature and the saturation temperature, the superheat control unit 32 determines the superheat of the refrigerant.

Darüber hinaus ist ein Temperatursensor 38 zur Messung der Umgebungstemperatur der Wärmepumpe und insbesondere der Außentemperatur mit der Überhitzungsregeleinheit 32 verbunden.In addition, a temperature sensor 38 for measuring the ambient temperature of the heat pump and in particular the outside temperature is connected to the superheat control unit 32.

Zur Messung der Temperatur des durch den Verdichter 14 verdichteten Kältemittels ist im Bereich des Verdichterausgangs außerdem ein mit der Überhitzungsregeleinheit 32 verbundener Temperatursensor 40 vorgesehen.For measuring the temperature of the refrigerant compressed by the compressor 14, a temperature sensor 40 connected to the superheat control unit 32 is also provided in the area of the compressor outlet.

Nachfolgend wird der Kälteprozess der Wärmepumpe von Fig. 1 beschrieben.Below is the cooling process of the heat pump of Fig. 1 described.

Fig. 2 zeigt ein Log p, H - Diagramm eines in der Wärmepumpe von Fig. 1 verwendeten Kältemittels, wobei der Druck p des Kältemittels logarithmisch als Funktion der Enthalpie H aufgetragen ist. Eingezeichnet sind die Grenzen gesättigter Flüssigkeit 42 und gesättigten Gases 44 sowie Kurven 46 konstanter Temperatur. Fig. 2 shows a log p, H diagram of one in the heat pump of Fig. 1 used refrigerant, wherein the pressure p of the refrigerant is plotted logarithmically as a function of enthalpy H. Shown are the boundaries of saturated liquid 42 and saturated gas 44 and curves 46 of constant temperature.

Der Punkt E bezeichnet den Zustand des Kältemittels nach der Expansion durch das Expansionsventil 18. In dem Verdampfer 12 findet eine Verdampfung E-A und Überhitzung A-B des Kältemittels statt.The point E indicates the state of the refrigerant after expansion by the expansion valve 18. In the evaporator 12, evaporation E-A and overheating A-B of the refrigerant take place.

Der Verdichter 14 sorgt für eine Verdichtung B-C des Kältemittels, die mit einer entsprechenden Temperaturerhöhung einhergeht. Im dargestellten Ausführungsbeispiel wird die Temperatur des Kältemittels von +10°C am Ausgang des Verdampfers 12 durch den Verdichter 14 bis auf +90°C erhöht.The compressor 14 provides a compression B-C of the refrigerant, which is accompanied by a corresponding increase in temperature. In the illustrated embodiment, the temperature of the refrigerant is increased from + 10 ° C at the outlet of the evaporator 12 through the compressor 14 up to + 90 ° C.

Im Verflüssiger 16 erfolgt eine Verflüssigung C-D des Kältemittels, wobei die Verflüssigungstemperatur im dargestellten Beispiel +50°C beträgt. Das nunmehr flüssige und nur noch 50°C warme Kältemittel wird anschließend durch das Expansionsventil 18 entspannt (D-E), wobei es bis auf 0°C abkühlt.In the condenser 16 is a liquefaction C-D of the refrigerant, wherein the liquefaction temperature in the example shown + 50 ° C. The now liquid and only 50 ° C warm refrigerant is then expanded through the expansion valve 18 (D-E), where it cools down to 0 ° C.

Im in Fig. 2 dargestellten Ausführungsbeispiel beträgt die Überhitzung 10 K, nämlich gerade die Differenz zwischen den Temperaturen am Punkt B (+10°C) und am Punkt A (0°C). Die Temperatur am Punkt B entspricht der tatsächlichen Temperatur des Kältemittels in der Sauggasleitung und wird durch den Temperatursensor 36 gemessen. Die Temperatur am Punkt A entspricht dagegen der Verdampfungstemperatur des Kältemittels, die aus dem durch den Drucksensor 34 gemessenen Verdampfungsdruck des Kältemittels ermittelt wird.Im in Fig. 2 illustrated embodiment, the overheating is 10 K, namely just the difference between the temperatures at point B (+ 10 ° C) and at point A (0 ° C). The temperature at point B corresponds to the actual temperature of the refrigerant in the suction gas line and is measured by the temperature sensor 36. In contrast, the temperature at point A corresponds to the evaporation temperature of the refrigerant, which is determined from the evaporation pressure of the refrigerant measured by the pressure sensor 34.

In Fig. 3 ist eine Situation dargestellt, bei der die Verdampfungstemperatur des Kältemittels aufgrund eines reduzierten Verdampfungsdrucks im Vergleich zu der in Fig. 2 dargestellten Situation um 10 K reduziert ist, d.h. nur noch -10°C beträgt. Eine solche Verringerung der Verdampfungsdrucks kann beispielsweise aus einer niedrigeren Außentemperatur resultieren. Die reduzierte Verdampfungstemperatur des Kältemittels führt zu einer Erhöhung der Überhitzung A-B, die ihrerseits eine Erhöhung der Kältemitteltemperatur am Ausgang des Verdichters 14 (Punkt C) bewirkt. Im dargestellten Ausführungsbeispiel beträgt die erhöhte Kältemitteltemperatur am Verdichterausgang +120°C.In Fig. 3 a situation is shown in which the evaporation temperature of the refrigerant due to a reduced evaporation pressure compared to the in Fig. 2 situation is reduced by 10 K, ie only -10 ° C. Such a reduction of the evaporation pressure may for example result from a lower outside temperature. The reduced evaporation temperature of the refrigerant leads to an increase in the superheat AB, which in turn causes an increase in the refrigerant temperature at the outlet of the compressor 14 (point C). In the illustrated embodiment, the increased refrigerant temperature at the compressor outlet is + 120 ° C.

Auch eine Erhöhung der Verflüssigungstemperatur, bei welcher das Kältemittel in dem Verflüssiger 16 verflüssigt wird, C-D, führt zu einer Erhöhung der Kältemitteltemperatur am Verdichterausgang C. Wie in Fig. 4 beispielhaft dargestellt ist, resultiert eine Erhöhung der Verflüssigungstemperatur von 50°C auf 60°C verglichen mit der in Fig. 2 gezeigten Situation bei einer gleich bleibenden Verdampfungstemperatur von 0°C in einem Anstieg der Kältemitteltemperatur am Verdichterausgang C von 90°C auf 120°C.Also, an increase in the liquefaction temperature at which the refrigerant in the condenser 16 liquefies, CD, leads to an increase in the refrigerant temperature at the compressor outlet C. As in Fig. 4 is exemplified results in an increase in the liquefaction temperature of 50 ° C to 60 ° C compared to the in Fig. 2 shown situation at a constant evaporation temperature of 0 ° C in an increase in the refrigerant temperature at the compressor outlet C from 90 ° C to 120 ° C.

Eine Erhöhung der Kältemitteltemperatur am Verdichterausgang erweist sich dann als problematisch, wenn die erhöhte Kältemitteltemperatur eine kritische Temperaturobergrenze überschreitet, oberhalb der eine Beschädigung des Verdichters 14 zu erwarten ist, beispielsweise aufgrund einer Zersetzung von im Verdichter 14 vorgesehenen Schmierölen.An increase in the refrigerant temperature at the compressor outlet proves to be problematic if the increased refrigerant temperature exceeds a critical upper temperature limit above which damage to the compressor 14 is to be expected, for example due to decomposition of provided in the compressor 14 lubricating oils.

Erfindungsgemäß ist eine Regelung der Kältemitteltemperatur am Verdichterausgang durch die Überhitzungsregeleinheit 32 derart vorgesehen, dass die Kältemitteltemperatur am Verdichterausgang die voranstehend genannte kritische Temperaturobergrenze nicht überschreitet. Dazu wird die Kältemitteltemperatur am Verdichterausgang auf eine vorgegebene Zieltemperatur geregelt, die etwas unterhalb der kritischen Temperaturobergrenze liegt. Als Stellgröße ist dabei die Überhitzung A-B des Kältemittels, die durch eine Änderung des Öffnungsgrades des Expansionsventils 18 variierbar ist, und alternativ oder zusätzlich die Einspritzung von flüssigem Kältemittel in den Verdichter 14 vorgesehen.According to the invention, a regulation of the refrigerant temperature at the compressor outlet by the superheat control unit 32 is provided such that the refrigerant temperature at the compressor outlet does not exceed the above-mentioned critical upper temperature limit. For this purpose, the refrigerant temperature at the compressor outlet is set to a specified value Target temperature regulated, which is slightly below the critical upper temperature limit. The manipulated variable is the overheating AB of the refrigerant, which can be varied by changing the opening degree of the expansion valve 18, and alternatively or additionally, the injection of liquid refrigerant into the compressor 14 is provided.

Wie dem in Fig. 5 gezeigten Diagramm zu entnehmen ist, das von der in Fig. 3 dargestellten Situation, d.h. von einer reduzierten Verdampfungstemperatur von -10°C, ausgeht, lässt sich durch eine Verringerung der Überhitzung des Kältemittels die Kältemitteltemperatur am Verdichterausgang C reduzieren. Umgekehrt ist durch eine Erhöhung der Überhitzung die Kältemitteltemperatur am Verdichterausgang C anhebbar.Like the one in Fig. 5 shown in the diagram shown in the Fig. 3 assumed situation, ie starting from a reduced evaporation temperature of -10 ° C, can be reduced by reducing the superheat of the refrigerant, the refrigerant temperature at the compressor outlet C. Conversely, by increasing the overheating, the refrigerant temperature at the compressor outlet C can be raised.

Durch eine entsprechende Einstellung der Überhitzung ist die Kältemitteltemperatur am Verdichterausgang C bzw. die Verdichtungsendtemperatur innerhalb bestimmter Grenzen so regelbar, dass diese einen maximalen Wert einnimmt, aber die kritische Temperaturobergrenze gerade nicht überschreitet. Dadurch wird die Heizleistung der Wärmepumpe optimiert und eine Beschädigung des Verdichters bzw. Abschaltung der Wärmepumpe vermieden. Standzeiten der Wärmepumpe werden folglich minimiert. Im Ergebnis wird eine verbesserte Wirtschaftlichkeit der Wärmepumpe erreicht.By setting the overheating accordingly, the refrigerant temperature at the compressor outlet C or the final compression temperature within certain limits can be regulated so that it assumes a maximum value, but does not exceed the critical upper temperature limit. This optimizes the heat output of the heat pump and prevents damage to the compressor or shutdown of the heat pump. Service life of the heat pump are therefore minimized. As a result, an improved economy of the heat pump is achieved.

Die Einstellung der erforderlichen Überhitzung erfolgt durch eine entsprechende Ansteuerung des Expansionsventils 18 durch die Überhitzungsregeleinheit 32. Eine Öffnung des Expansionsventils 18, d.h. eine Erhöhung der Kältemittelströmung durch das Expansionsventil 18, führt zu einer Reduzierung der Überhitzung, während eine Drosselung des Expansionsventils 18, d.h. eine Reduzierung des Kältemittelstroms durch das Expansionsventils 18, die Überhitzung erhöht.The adjustment of the required overheating is made by a corresponding control of the expansion valve 18 by the superheat control unit 32. An opening of the expansion valve 18, ie an increase of the refrigerant flow through the expansion valve 18, leads to a reduction of overheating, while a throttling of the expansion valve 18, that is, a reduction of the refrigerant flow through the expansion valve 18, which increases overheating.

Sollte die Verringerung der Überhitzung des Kältemittels zur Reduzierung der Kältemitteltemperatur am Verdichterausgang C nicht ausreichend sein, beispielsweise weil neben einer reduzierten Verdampfungstemperatur von -10°C auch noch eine erhöhte Verflüssigungstemperatur von +60°C vorliegt, wie es in Fig. 6 dargestellt ist, so besteht erfindungsgemäß zusätzlich die Möglichkeit, das Kältemittel im Verdichter 14 zu kühlen, wie es bereits im Zusammenhang mit Fig. 1 beschrieben wurde. Die Zufuhr von flüssigem Kältemittel zu dem Verdichter 14 am Punkt B1 bewirkt eine Reduzierung der Enthalpie des Kältemittels, wodurch die Verdichterendtemperatur am Verdichterausgang C von etwa 140°C auf 90°C reduziert werden kann.If the reduction in the refrigerant overheating to reduce the refrigerant temperature at the compressor outlet C is insufficient, for example because, in addition to a reduced evaporation temperature of -10 ° C, there is also an increased condensing temperature of + 60 ° C, as in Fig. 6 is shown, it is according to the invention in addition the possibility of cooling the refrigerant in the compressor 14, as already associated with Fig. 1 has been described. The supply of liquid refrigerant to the compressor 14 at the point B1 causes a reduction in the enthalpy of the refrigerant, whereby the compressor discharge temperature at the compressor outlet C can be reduced from about 140 ° C to 90 ° C.

Die Regelung der Kältemitteltemperatur am Verdichterausgang wird bei der in Fig. 1 dargestellten Wärmepumpe folgendermaßen durchgeführt:

  • Während des Betriebs der Wärmepumpe überwacht die Überhitzungsregeleinheit 32 kontinuierlich die Außentemperatur über den Temperatursensor 38. Ferner überwacht die Überhitzungsregeleinheit 32 über den Temperatursensor 36 die tatsächliche Kältemitteltemperatur in der Sauggasleitung 20 und über den Drucksensor 34 den Verdampfungsdruck des Kältemittels in der Sauggasleitung 20. Aus der gemessenen tatsächlichen Kältemitteltemperatur und dem gemessenen Verdampfungsdruck des Kältemittels ermittelt die Überhitzungsregeleinheit 32 die aktuell vorliegende Überhitzung des Kältemittels. Ggf. betätigt die Überhitzungsregeleinheit 32 das Expansionsventil 18, um einen für den Normalbetrieb der Wärmepumpe empfohlenen Überhitzungswert einzuhalten.
The regulation of the refrigerant temperature at the compressor outlet is performed at the in Fig. 1 shown heat pump carried out as follows:
  • During operation of the heat pump, the superheat control unit 32 continuously monitors the outside temperature via the temperature sensor 38. Further, the superheat control unit 32 monitors the actual refrigerant temperature in the suction gas line 20 via the temperature sensor 36 and the evaporating pressure of the refrigerant in the suction gas line 20 via the pressure sensor 34 actual refrigerant temperature and the measured evaporation pressure of the refrigerant, the superheat control unit 32 determines the currently existing overheating of the refrigerant. Possibly. operates the superheat control unit 32, the expansion valve 18 to maintain a recommended for normal operation of the heat pump overheating value.

Sobald die Außentemperatur einen vorbestimmten Wert unterschreitet, beginnt die Überhitzungsregeleinheit 32 mit Hilfe des Temperatursensors 40 die Kältemitteltemperatur am Verdichterausgang zu überwachen. Falls die Kältemitteltemperatur am Verdichterausgang die unterhalb der kritischen Temperaturobergrenze liegende vorgegebene Zieltemperatur überschreitet oder zu überschreiten droht, steuert die Überhitzungsregeleinheit 32 das Expansionsventil 18 derart, dass sich die Strömung des Kältemittels durch das Expansionsventil 18 erhöht. Dadurch wird die Überhitzung verringert und in der Folge die Kältemitteltemperatur am Verdichterausgang auf die Zieltemperatur reduziert. Zur Verringerung der Kältemitteltemperatur am Verdichterausgang wird das Expansionsventil 18 also weiter geöffnet.As soon as the outside temperature falls below a predetermined value, the superheat control unit 32 starts to monitor the refrigerant temperature at the compressor outlet with the aid of the temperature sensor 40. If the refrigerant temperature at the compressor outlet exceeds or threatens to exceed the predetermined target temperature below the critical upper temperature limit, the superheat control unit 32 controls the expansion valve 18 such that the flow of the refrigerant through the expansion valve 18 increases. This reduces overheating and, as a result, reduces the refrigerant temperature at the compressor outlet to the target temperature. To reduce the refrigerant temperature at the compressor outlet, the expansion valve 18 is thus opened further.

Wenn es nicht möglich ist, die Kältemitteltemperatur am Verdichterausgang durch eine Verringerung der Überhitzung im Bereich der vorgegebenen Zieltemperatur zu halten, aktiviert die Überhitzungsregeleinheit 32 zusätzlich das Magnetventil 30, um dem Verdichter 14 flüssiges Kältemittel zur Kühlung des verdichteten Kältemittels zuzuführen. Die Betätigung des Magnetventils 30 erfolgt in Abhängigkeit von der Kältemitteltemperatur am Verdichterausgang.In addition, if it is not possible to keep the refrigerant temperature at the compressor output within the range of the predetermined target temperature by reducing overheating, the superheat control unit 32 will activate the solenoid valve 30 to supply liquid refrigerant to the compressor 14 for cooling the compressed refrigerant. The actuation of the solenoid valve 30 takes place in dependence on the refrigerant temperature at the compressor outlet.

Sinkt die Kältemitteltemperatur am Verdichterausgang unter die vorgegebene Zieltemperatur, beispielsweise aufgrund einer erfolgten Kühlung, aufgrund eines Absinkens der Verflüssigungstemperatur und/oder eines erhöhten Verdampfungsdrucks des Kältemittels, so wird das Magnetventil 30 durch die Überhitzungsregeleinheit 32 wieder geschlossen und die Zufuhr von flüssigem Kältemittel zum Verdichter 14 gestoppt.If the refrigerant temperature at the compressor outlet falls below the predetermined target temperature, for example because of cooling, due to a drop in the liquefaction temperature and / or an increased evaporation pressure of the refrigerant, the solenoid valve becomes 30 closed again by the superheat control unit 32 and the supply of liquid refrigerant to the compressor 14 stopped.

Sinkt die Kältemitteltemperatur am Verdichterausgang noch weiter ab, so bewirkt die Überhitzungsregeleinheit 32 durch eine entsprechende Ansteuerung des Expansionsventils 18 eine Verringerung der Kältemittelströmung durch das Expansionsventil 18, um die Überhitzung des Kältemittels wieder auf den ursprünglichen, empfohlenen Wert zu bringen.If the refrigerant temperature at the compressor outlet decreases further, the superheat control unit 32 causes a reduction of the refrigerant flow through the expansion valve 18 by a corresponding control of the expansion valve 18 in order to bring the overheating of the refrigerant back to the original, recommended value.

Durch die erfindungsgemäße Regelung der Kältemitteltemperatur am Verdichterausgang wird der Wirkungsgrad der Wärmepumpe während besonders kalter Außentemperaturen erhöht und der Arbeitsbereich der Wärmepumpe auf höhere Verflüssigungstemperaturen und höhere Wärmekapazitäten ausgedehnt. Gleichzeitig werden die Gefahr einer Beschädigung des Verdichters 14 durch Überschreitung einer kritischen Temperaturobergrenze und die Gefahr einer Vereisung des Verdampfers 12 verringert. Abschalt- und Abtauphasen der Wärmepumpe werden dadurch minimiert. Im Ergebnis resultiert die erfindungsgemäße variable und insbesondere witterungsabhängige Regelung der Überhitzung sowie die Regelung der Kältemitteltemperatur am Verdichterausgang, insbesondere der Verdichtungsendtemperatur, in einer verbesserten Wirtschaftlichkeit der Wärmepumpe.The inventive regulation of the refrigerant temperature at the compressor outlet, the efficiency of the heat pump is increased during particularly cold outdoor temperatures and extended the working range of the heat pump to higher condensing temperatures and higher heat capacity. At the same time the risk of damaging the compressor 14 by exceeding a critical upper temperature limit and the risk of icing of the evaporator 12 are reduced. Shutdown and defrost phases of the heat pump are thereby minimized. As a result, the inventive variable and in particular weather-dependent control of overheating and the control of the refrigerant temperature at the compressor output, in particular the compression end temperature results in improved efficiency of the heat pump.

BezugszeichenlisteLIST OF REFERENCE NUMBERS

1010
KältemittelkreislaufRefrigerant circulation
1212
VerdampferEvaporator
1414
Verdichtercompressor
1616
Verflüssigercondenser
1818
Expansionsventilexpansion valve
2020
SauggasleitungSuction
2222
Flüssigkeitsabscheiderliquid separator
2424
Umschaltventilswitching valve
2626
HeißgasleitungHot gas line
2828
Bypassleitungbypass line
2929
EinspritzleitungInjection line
3030
Magnetventilmagnetic valve
3131
Drosselorganthrottle member
3232
ÜberhitzungsregeleinheitOverheating control unit
3434
Drucksensorpressure sensor
3636
Temperatursensortemperature sensor
3838
Temperatursensortemperature sensor
4040
Temperatursensortemperature sensor
4242
Grenze gesättigter FlüssigkeitLimit of saturated liquid
4444
Grenze gesättigten GasesLimit of saturated gas
4646
Kurven konstanter TemperaturCurves of constant temperature

Claims (7)

  1. A method of operating a heat extraction machine, in particular a heat pump, comprising a closed circuit (10) which has a refrigerant and in which an evaporator (12), a compressor (14), a condenser (16) and an expansion valve (18), in particular an electrically operated expansion valve, are arranged one after the other;
    and comprising an overheating regulation unit (32) for the refrigerant which is connected to a pressure sensor (34) and to a temperature sensor (36) to determine an overheating of the refrigerant, said pressure sensor and temperature sensor each being arranged at a suction gas line (20) which connects the evaporator (12) and the compressor (14), wherein the overheating is changed by a corresponding control of the expansion valve (18), characterized in that
    the ambient temperature of the heat extraction machine is measured and, if the ambient temperature falls below a predetermined lower temperature limit, the overheating regulation unit (32) monitors the temperature of the refrigerant at the compressor outlet, in particular the end compression temperature, with the help of a temperature sensor (40) and regulates said temperature of the refrigerant at least at times by a change in the overheating of the refrigerant in the evaporator (12) so that it does not exceed a critical upper temperature limit and, if it is not possible to maintain the refrigerant temperature in the region of the compressor (14) at or below the critical upper temperature limit by a reduction of the overheating of the refrigerant in the evaporator (12), a solenoid valve (30) is activated by the overheating regulation unit (32) to supply liquid refrigerant to the compressor (14) for the cooling of the compressed refrigerant, wherein the solenoid valve (30) is arranged in a bypass line (28) which branches off from the refrigerant circuit (10) downstream of the condenser (16) and which is connected to an injection line (29) connected to the compressor (14).
  2. A method in accordance with one of the preceding claims,
    characterized in that
    the overheating is regulated in dependence on the ambient temperature of the heat extraction machine, in particular on the external temperature.
  3. A method in accordance with one of the preceding claims,
    characterized in that
    the refrigerant temperature in the region of the compressor is lowered by a cooling of the compressor (14), in particular in its outlet region.
  4. A method in accordance with any one of the preceding claims,
    characterized in that
    liquid refrigerant, in particular in the outlet region of the compressor (14), is introduced into the compressed refrigerant.
  5. A heat extraction machine, in particular a heat pump, comprising a closed circuit (10) which has a refrigerant and in which an evaporator (12), a compressor (14), a condenser (16) and an expansion valve (18), in particular an electrically operated expansion valve, are arranged one after the other; and comprising an overheating regulation unit (32) for the refrigerant which is connected to a pressure sensor (34) and to a temperature sensor (36) to determine an overheating of the refrigerant, said pressure sensor and temperature sensor each being arranged at a suction gas line (20) which connects the evaporator (12) and the compressor (14), wherein the expansion valve (18) is controllable for the variable control, in particular the weather-dependent control, of the overheating of the refrigerant by the overheating regulation unit (32), characterized by a second temperature sensor (40) connected to the overheating regulation unit (32) for the measurement of the refrigerant temperature downstream of the compressor (14), in particular of the end compression temperature; by a third temperature sensor (38) connected to the overheating regulation unit (32) for the measurement of the ambient temperature of the heat extraction machine; and by a solenoid valve (30) which can be activated by the overheating regulation unit (32) to supply liquid refrigerant to the compressor (14), wherein the solenoid valve (30) is arranged in a bypass line (28) which branches off from the refrigerant circuit (10) downstream of the condenser (16) and which is connected to an injection line (29) connected to the compressor (14), wherein the overheating regulation unit (32) is configured
    to regulate the temperature of the refrigerant in the region of the compressor, in particular the end compression temperature, at least at times by a change in the overheating of the refrigerant in the evaporator (12) if the ambient temperature falls below a predetermined lower temperature limit such that the refrigerant temperature in the region of the compressor (14) does not exceed a critical upper temperature limit; and
    to activate the solenoid valve (30) to supply liquid refrigerant to the compressor (14) for the cooling of the compressed refrigerant if it is not possible to maintain the refrigerant temperature in the region of the compressor (14) at or below the critical upper temperature limit by a reduction of the overheating of the refrigerant in the evaporator (12).
  6. A heat extraction machine in accordance with claim 5,
    characterized in that
    the second temperature sensor (40) is arranged in the region of the compressor outlet.
  7. A heat extraction machine in accordance with one of the claims 5 and 6,
    characterized in that
    a restrictor member (31) is arranged in the injection line (29).
EP05748140.0A 2004-07-27 2005-04-20 Refrigeration machine and method for operating a refrigeration machine Active EP1771689B1 (en)

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EP1771689A1 (en) 2007-04-11
WO2006010391A1 (en) 2006-02-02
JP2008508495A (en) 2008-03-21
DE102004036301A1 (en) 2006-03-23
CN1989378B (en) 2013-12-18
US7870752B2 (en) 2011-01-18
CN1989378A (en) 2007-06-27
US20080289345A1 (en) 2008-11-27
JP5150253B2 (en) 2013-02-20

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