DE102020129539A1 - Air conditioning system and method for controlling such - Google Patents

Abstract

The invention relates to an air conditioning system (10), in particular for a motor vehicle, with a refrigeration circuit (11) having a compressor (15), a condenser (16), an expansion valve (17) and an evaporator (18), which are arranged in series. wherein a droplet separator (14) with the liquid refrigerant can be removed from the refrigeration circuit (13), and a collector (19) in which the liquid refrigerant removed from the droplet separator (14) can be stored. The invention also relates to a method for controlling such an air conditioning system (10) and a motor vehicle with such an air conditioning system (10).

Description

The invention relates to an air conditioning system with a refrigeration circuit and a method for controlling such an air conditioning system.

Air conditioning systems are often installed in vehicles and are used there for air conditioning the interior, ie the passenger compartment, of the vehicle. In this context, heat pumps are known which absorb heat via an evaporator or chiller and release it via a condenser for heating. Such a heat pump is, for example, from DE 10 2016 213 619 A1 famous. The basic principle of such heat pumps is that thermal energy is absorbed, for example, from the ambient air at the evaporator. In addition, the drive power of a compressor introduces drive energy into the refrigeration circuit, with the heat energy absorbed at the evaporator being a multiple of the drive energy of the compressor. The sum of this energy is available as useful heat at the condenser.

In 2 a pressure-enthalpy diagram of a refrigerant is shown schematically. This diagram explains the basic functionality of normal heat pump operation from the prior art. In the diagram, the specific enthalpy is plotted on the abscissa and the pressure of the refrigerant is plotted on the ordinate. Along the route from point 4 to point 1, thermal energy is absorbed from the environment via the evaporator, more precisely the difference between the value on the abscissa at point 1 and the value on the abscissa at point 4. Along the route from point 1 to point 2, energy is introduced isentropically into the refrigerant by means of the compressor, which is converted by dissipation from electrical to hydraulic and finally to thermal and potential energy. The energy that is absorbed corresponds to the difference between the value on the abscissa at point 2 and the value on the abscissa at point 1. The sum of these values, i.e. the distance from 2 to 3, is then available at the condenser as useful heat, for example to heat the interior of the vehicle.

The current state of the art usually envisages the need for superheating of the refrigerant after the evaporator and before the compressor in order to prevent liquid refrigerant droplets from entering the compressor, which could otherwise damage the compressor. This usually requires a superheat of 10°K. The overheating is graphically in 2 represented as the amount by which point 1 is to the right of the wet steam line. Overheating of the refrigerant ensures that drops are safely evaporated and it is ensured that all refrigerant is in gaseous form when it enters the compressor.

However, this need for overheating comes at the expense of efficiency. To be more precise, the compression in the refrigeration circuit is always isentropic. Since the distance between the isentropes increases in a fan shape with increasing pressures, the energy required to compress the refrigerant also increases as the entropy increases. Since entropy always increases with overheating, overheating results in a reduction in efficiency.

It is therefore an object of the present invention to provide an air conditioning system with more efficient heat pump operation. This object is achieved by an air conditioning system according to claim 1, a method according to claim 6 and a motor vehicle according to claim 11. Advantageous developments of the invention are the subject matter of the dependent claims.

According to an exemplary embodiment of the invention, an air conditioning system, in particular for a motor vehicle, is provided with a refrigeration circuit having a compressor, a condenser, an expansion valve and an evaporator, in particular a chiller, which are arranged in series. Furthermore, the air conditioning system has a droplet separator with which liquid refrigerant can be removed from the refrigeration cycle, and a collector in which the liquid refrigerant removed from the droplet separator can be stored. By using a droplet separator, in particular after the evaporator (particularly a chiller) and before the compressor, it is ensured that only gaseous refrigerant gets into the compressor by removing existing droplets. As a result, the previously necessary overheating is no longer required to the extent that was previously necessary, which increases the efficiency of the refrigeration cycle. The aim of the approach is to reduce overheating of the refrigerant to a minimum after the evaporator and before the compressor and to place the start of compression, i.e. point 1 of the pressure-enthalpy diagram, ideally on the wet vapor line, as indicated by point 1 in 3 illustrated, so that in this way the efficiency of the air conditioning system, in particular the refrigeration cycle, is increased, both in a cooling mode and in a heating mode.

According to a further exemplary embodiment of the invention, the liquid refrigerant removed from the collector can be fed back to the refrigeration circuit, in particular via the droplet separator. In this way, if a certain amount of liquid refrigerant has collected in the collector, part of the collected liquid refrigerant can be returned to be returned to the refrigeration circuit, so that, figuratively speaking, point 1 of the pressure-enthalpy diagram can be shifted in both directions, ie the refrigeration circuit can be controlled in both directions, namely at point 1 in the direction of greater overheating and in the direction of lesser overheating.

According to a further exemplary embodiment of the invention, the refrigeration circuit, in particular the compressor and/or the expansion valve, can be controlled as a function of the filling level of the collector. This provides a relatively good and reliably measurable parameter for controlling the refrigeration circuit.

According to a further exemplary embodiment of the invention, the air conditioning system also has a control unit which controls the refrigeration circuit in such a way that a refrigerant volume flow through the compressor is reduced when the filling level falls below a lower limit value, and that a refrigerant volume flow through the compressor is increased when an upper filling level limit value is exceeded will.

According to a further exemplary embodiment of the invention, the air-conditioning system has a control unit which controls the expansion valve in such a way that the expansion valve is opened further when the fill level falls below a lower limit value and that the expansion valve is closed further when the fill level exceeds an upper limit value.

The invention also relates to a method for controlling an air conditioning system, in particular for a motor vehicle, with the step of conducting a refrigerant through a refrigeration circuit in which a compressor, a condenser, an expansion valve and an evaporator, in particular a chiller, are arranged in series. In addition, the method includes the steps of separating liquid refrigerant from the refrigeration cycle by means of a droplet separator, and storing the liquid refrigerant removed from the droplet separator in a collector. The advantages already described in connection with the air conditioning system can be achieved with this method.

According to a further exemplary embodiment, the method includes the step of returning the liquid, removed refrigerant to the refrigeration circuit from the collector, in particular via the droplet separator.

According to a further exemplary embodiment, the method includes the step of controlling the refrigeration circuit, in particular the compressor and/or the expansion valve, as a function of a filling level in the collector.

According to a further exemplary embodiment, the method includes the step of controlling the refrigeration circuit by means of a control unit in such a way that a refrigerant volume flow through the compressor is reduced when the filling level falls below a lower limit value, and that a refrigerant volume flow through the compressor is increased when an upper filling level limit value is exceeded .

According to a further exemplary embodiment, the method includes the step of controlling the expansion valve by means of a control unit in such a way that the expansion valve is opened further when the fill level falls below a lower limit value and that the expansion valve is closed further when the fill level exceeds an upper limit value.

In the context of this invention, the chiller is to be understood as meaning a fluid-fluid heat exchanger through which a first fluid, in particular refrigerant, can flow and, fluidically separate from this, a second fluid, in particular coolant, can flow through, the chiller being adapted such that Thermal energy is transferred between the first and second fluid.

The condenser is in particular a water-cooled condenser through which a first fluid, in particular refrigerant, can flow and through which a second fluid, particularly coolant, can flow fluidically separately, the condenser being adapted so that thermal energy is transferred between the first and second fluid . However, the condenser can also be a condenser through which fluid flows, around which air flows and heat energy is transferred between the fluid and the air.

• 1 zeigt schematisch ein Klimasystem gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;
• 2 zeigt schematisch ein Druck-Enthalpie-Diagramm eines Kältekreislaufs zu Erklärungszwecken der vorliegenden Erfindung;
• 3 zeigt schematisch ein Druck-Enthalpie-Diagramm des Kältekreislaufs der vorliegenden Erfindung.

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. These drawings show the following:

• 1 shows schematically an air conditioning system according to an embodiment of the present invention;
• 2 schematically shows a pressure-enthalpy diagram of a refrigeration cycle for the purpose of explaining the present invention;
• 3 Fig. 12 schematically shows a pressure-enthalpy diagram of the refrigeration cycle of the present invention.

This in 1 Air conditioning system 10 shown includes a refrigeration circuit 11 and a coolant circuit 12. The air conditioning system 10 is installed in particular in a motor vehicle (not shown). This is in particular an electrified motor vehicle, such as a purely battery-powered motor vehicle or a hybrid vehicle. For example, this is a passenger car.

The refrigeration cycle 11 is adapted to be flown through by a refrigerant and to circulate this refrigerant in a closed circuit. This is for example 1234yf, R744, CO ₂ or the like. The cooling circuit 12 is adapted to be flowed through by a coolant. This is, for example, water mixed with additives (eg glycol).

The refrigeration circuit 11 includes a compressor 15, a condenser 16, an expansion valve 17, an evaporator 18 and a droplet separator 14. The evaporator 18 is in particular a chiller. The coolant circuit 12 has a coolant pump 20 , a heating heat exchanger 21 , the condenser 16 and the evaporator 18 . Thermal energy generated in the refrigeration circuit 13 can be introduced via the condenser 16 from the refrigeration circuit 13 into the coolant circuit 12, where it is then available as thermal energy at the heating heat exchanger 21, so that air that can be supplied to a vehicle interior can be heated for heating purposes. Alternatively, the air that can be supplied to the vehicle interior can also flow directly around the condenser 16, so that the thermal energy is introduced directly into this air.

The elements mentioned are connected to one another in the circuits mentioned in each case by means of lines in the form of pipes and/or hoses. In addition, the elements mentioned are connected to one another in series in the circuits mentioned in each case, in particular in the order mentioned above.

The droplet separator 14 according to the invention is used to separate liquid refrigerant from the refrigeration circuit 13. Refrigerant, which is present in the droplet separator 14 in the liquid aggregate state, is removed from the refrigeration circuit 13 by means of the droplet separator 14 and fed to a collector 19. The liquid refrigerant stored in the collector 19, which was previously removed from the refrigeration circuit 13 via the droplet separator 14, can be fed back to the refrigeration circuit 13 under certain conditions (as explained later). The collector 19 is connected to the mist eliminator 14 and is in the form of a container for collecting liquid refrigerant. The droplet separator 14 can be, for example, a metal plate or perforated plate, by means of which the liquid refrigerant is captured and discharged into the collector 19 by gravity. The droplet separator 14 is connected to the collector 19 by means of a line in the form of a pipe and/or a hose, or both are connected directly to one another. The droplet separator 14 is considered to be part of the closed refrigeration circuit 13, whereas the collector 19 is not considered to be part of the closed refrigeration circuit 13, since the refrigerant flow does not flow through it.

Furthermore, a control unit 22 is provided, which is electrically connected at least to the compressor 15, the expansion valve 17 and the pump 20 in order to control these elements accordingly. In addition, the control unit 22 is electrically connected to one or more level sensors 23, 24 of the collector 19 in order to receive a level value of the collector 19 from them. For example, an upper filling level sensor 23 can be provided with which an upper filling level limit value can be measured, i.e. it could emit a signal which indicates whether this upper filling level limit value has been reached and/or exceeded, which would mean that a level of the liquid refrigerant collected in the accumulator 19 has reached or exceeded this upper level limit. In addition, a lower level sensor 24 can be provided with which a lower level limit can be measured, i.e. it could output a signal indicating whether this lower level limit has been reached or fallen below, which would mean that a level , the liquid refrigerant collected in the collector 19 has reached or fallen below this lower filling level limit. Alternatively, a fill level sensor could also be provided, which measures the exact fill level of the collector 19 and sends it to the control unit 22, which then compares the measured fill level with a stored upper and lower fill level limit value.

As already described in the introduction, liquid refrigerant can be removed from the refrigerant circuit 13 through the droplet separator, so that it is ensured that even with, compared to the prior art, low overheating, no refrigerant in liquid form at the inlet of the compressor 15, but exclusively gaseous refrigerant is present.

In order to be able to control the start of compression, i.e. point 1 of the pressure-enthalpy diagram, even more precisely, the air conditioning system is adapted as follows or the following procedure is provided.

The control unit 22 can control the refrigeration circuit 13 in such a way, for example by activating the compressor 15 and/or by activating the expansion valve 17, that when the filling level falls below the lower limit value, a refrigerant volume flow through the compressor 15 is reduced and/or the expansion valve is opened further , and that when the upper filling level limit value is exceeded, the volume flow of refrigerant through the compressor 15 is increased and/or the expansion valve 17 is closed further.

• In einem Zustand relativ hoher Überhitzung, wird kein flüssiges Kältemittel im Sammler 19 gesammelt, d.h. der untere Füllstands-Grenzwert wird unterschritten. Die Temperatur im Tropfenabscheider 14 bzw. im Sammler 19 liegt dann über der Nassdampftemperatur. In diesem Fall kann das Expansionsventil 17 weiter geöffnet werden und/oder der Kühlmittelvolumenstrom durch den Verdichter 15 weiter verringert werden. Dadurch steigen der Druck und damit die Temperatur im Verdampfer 18. In der Folge kann das Kältemittel nicht mehr so viel Wärme aus der Umgebung aufnehmen, da das treibende Temperaturdelta abnimmt, die Überhitzung geht zurück, und es können sich im Topfenabscheider 14 Tropfen bilden, die sich im Sammler 19 sammeln. Die Temperatur stromaufwärts des Verdichters 15 könnte sogar unter die Nassdampftemperatur absinken. Durch das Öffnen des Expansionsventils 17 und/oder die Erhöhung des Kühlmittelvolumenstroms durch den Verdichter 15 sinkt auch die Temperatur im Sammler 19, wo sich flüssiges Kältemittel befindet, in Richtung der Nassdampftem peratur.

In other words, the control of the air conditioning system by the control unit 22 has the following effects:

• In a state of relatively high overheating, no liquid refrigerant is collected in the collector 19, ie the level falls below the lower limit value. The temperature in the droplet separator 14 or in the collector 19 is then above the wet steam temperature. In this case, the expansion valve 17 can be opened further and/or the coolant volume flow through the compressor 15 can be further reduced. This increases the pressure and thus the temperature in the evaporator 18. As a result, the refrigerant can no longer absorb as much heat from the environment, since the driving temperature delta decreases, the overheating decreases, and drops can form in the pot separator 14 collect in collector 19. The temperature upstream of the compressor 15 could even drop below the wet steam temperature. By opening the expansion valve 17 and/or increasing the coolant volume flow through the compressor 15, the temperature in the collector 19, where liquid coolant is located, also decreases in the direction of the wet steam temperature.

If a certain amount of liquid refrigerant has collected in the collector 19, the expansion valve 17 must be closed further, i.e. a flow cross section of the expansion valve 17 must be reduced and/or the coolant volume flow through the compressor 15 must be increased. As a result, both the pressure and the temperature in the two-phase region fall in the evaporator, more heat can be absorbed from the environment again and the liquid refrigerant in the collector 19 can evaporate and be fed back to the refrigeration circuit 13 via the droplet separator 14 . On average, the temperature in front of the evaporator is then at the wet steam temperature, so that the overheating that was previously necessary can be reduced or even completely eliminated.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, this illustration and description is to be considered in the form of illustration and not limitation, and the invention is not intended to be limited to the precise form disclosed. The mere fact that certain features are recited in different dependent claims is not intended to imply that a combination of these features could not also be used to advantage.

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102016213619 A1 [0002]

Claims (11)

Air conditioning system (10), in particular for a motor vehicle, with a refrigeration circuit (11) having a compressor (15), a condenser (16), an expansion valve (17) and an evaporator (18), which are arranged in series, characterized by a droplet separator (14) with which the liquid refrigerant can be removed from the refrigeration circuit (13), and a collector (19) in which the liquid refrigerant removed from the droplet separator (14) can be stored. Air conditioning system (10) according to claim 1 , wherein the liquid, removed refrigerant from the collector (19) can be fed back to the refrigeration circuit (13). Air conditioning system (10) according to any one of the preceding claims, wherein the refrigeration circuit (13), in particular the compressor (15) and / or the expansion valve (17), depending on a filling level of the collector (19) is controllable. Air conditioning system (10) according to claim 3 , further with a control unit (22), which controls the refrigeration circuit (13) in such a way that a refrigerant volume flow through the compressor (15) is reduced when the filling level falls below a lower limit value, and that a refrigerant volume flow through the compressor (15) when an upper filling level limit value is exceeded Compressor (15) is increased. Air conditioning system (10) according to claim 3 , furthermore with a control unit (22) which controls the expansion valve (17) in such a way that the expansion valve (17) is opened further when the fill level falls below a lower limit value, and that the expansion valve (17) opens further when the fill level exceeds an upper limit value is closed. Method for controlling an air conditioning system (10), in particular for a motor vehicle, with the steps: conducting a refrigerant through a refrigeration cycle (11) in which a compressor (15), a condenser (16), an expansion valve (17) and an evaporator (18) are arranged in series, characterized by separating liquid refrigerant from the refrigeration circuit (13) by means of a droplet separator (14), and storing the liquid refrigerant removed from the droplet separator (14) in a collector (19). procedure according to claim 6 , further with the step: returning the liquid, removed refrigerant in the refrigeration circuit (13) from the collector (19). procedure according to claim 6 or 7 , also with the step: controlling the refrigeration circuit (13), in particular the compressor (15) and/or the expansion valve (17), depending on a filling level in the collector (19). procedure according to claim 8 , further with the step: controlling the refrigeration circuit (13) by means of a control unit (22) in such a way that a refrigerant volume flow through the compressor (15) is reduced when the filling level falls below a lower limit value, and that a refrigerant volume flow is reduced when an upper filling level limit value is exceeded is increased by the compressor (15). procedure according to claim 8 , further with the step: controlling the expansion valve (17) by means of a control unit (22) in such a way that the expansion valve (17) is opened further when the filling level falls below a lower limit value, and that the expansion valve (17 ) will continue to be closed. Motor vehicle with an air conditioning system (10) according to one of Claims 1 until 5 .

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