EP3816543A1 - Procédé de régulation d'un détendeur - Google Patents

Procédé de régulation d'un détendeur Download PDF

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Publication number
EP3816543A1
EP3816543A1 EP20200553.4A EP20200553A EP3816543A1 EP 3816543 A1 EP3816543 A1 EP 3816543A1 EP 20200553 A EP20200553 A EP 20200553A EP 3816543 A1 EP3816543 A1 EP 3816543A1
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EP
European Patent Office
Prior art keywords
refrigerant
temperature
heat source
compressor
control device
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Granted
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EP20200553.4A
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German (de)
English (en)
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EP3816543B1 (fr
Inventor
Florian ENTLEITNER
Florian Fuchs
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Lambda Waermepumpen GmbH
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Lambda Waermepumpen GmbH
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Publication of EP3816543A1 publication Critical patent/EP3816543A1/fr
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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
    • F25B40/00—Subcoolers, desuperheaters or superheaters
    • F25B40/06—Superheaters
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/05—Compression system with heat exchange between particular parts of the system
    • F25B2400/054—Compression system with heat exchange between particular parts of the system between the suction tube of the compressor and another part of the 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
    • F25B2500/28—Means for preventing liquid refrigerant entering into 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
    • 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
    • F25B2600/2513—Expansion 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
    • F25B2700/21—Temperatures
    • F25B2700/2117—Temperatures of an evaporator
    • F25B2700/21174—Temperatures of an evaporator of the refrigerant at the inlet of the evaporator
    • 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
    • F25B2700/2117—Temperatures of an evaporator
    • F25B2700/21175—Temperatures of an evaporator of the refrigerant at the outlet of the evaporator

Definitions

  • the present invention relates to a method for regulating an expansion valve of a refrigerant circuit with the features of the preamble of claim 1, a refrigerant circuit with the features of the preamble of claim 10 and a device with at least one such refrigerant circuit.
  • Refrigerant circuits known in the prior art for example for heat pumps, refrigeration systems or air conditioning units, comprise an evaporator, a compressor, a condenser, an expansion valve and a control device connected to the expansion valve in a signal-conducting manner for controlling the expansion valve.
  • Evaporator, compressor, condenser and expansion valve are arranged one behind the other in series in a direction of circulation of the refrigerant circuit and a refrigerant flows through them, which circulates in the closed refrigerant circuit.
  • a heat source acts in a known manner on the evaporator and causes a heat input to the refrigerant in the evaporator and thus leads to an increase in the enthalpy of the refrigerant, so that the refrigerant evaporates in the evaporator.
  • the heat source can be the surroundings of the evaporator, the ambient air of which surrounds the evaporator or is supplied to the evaporator (for example in the case of an air heat pump).
  • a heat source is water or another fluid, which is supplied to the evaporator in a known manner via its own heat medium circuit, which is hydraulically decoupled from the refrigerant circuit and thus materially separated from it, in order to heat the refrigerant of the refrigerant circuit in the evaporator .
  • the heat source is thermally connected to the evaporator and in the evaporator heat is supplied to the refrigerant from the heat source thermally connected to the evaporator (or its heat source medium, e.g. air or water) and the refrigerant evaporates while absorbing heat.
  • the compressor connected in the direction of circulation (often also as The refrigerant that has evaporated (i.e.
  • the condenser (often also referred to as a liquefier), the gaseous, superheated refrigerant is cooled to a temperature at which the refrigerant liquefies, and thereby liquefied with the release of heat. As it continues to flow through the refrigerant circuit, the liquefied refrigerant passes the expansion valve, which is a bottleneck in the refrigerant circuit.
  • the refrigerant which was previously brought to a low pressure level by the expansion valve, absorbs heat from the heat source (e.g. surroundings).
  • the refrigerant is (mostly completely) evaporated and "overheated” by 5 to 15 K (degrees Kelvin).
  • This so-called suction gas overheating i.e. the increase in the gas temperature of the evaporated refrigerant above the saturation temperature
  • the suction gas overheating is the temperature difference between the gas temperature of the evaporated refrigerant when entering the compressor (so-called suction gas temperature) and the evaporation temperature.
  • the evaporation temperature is the temperature at which the refrigerant can exist both as a liquid and as a gas and depends on the prevailing pressure.
  • the evaporation temperature can be determined from the pressure at a point between the valve outlet of the expansion valve and the Compressor input of the compressor can be calculated, or alternatively measured as the temperature after the expansion valve.
  • the refrigerant is continuously expanded in the expansion valve, which means that it partially evaporates.
  • the liquid-gas mixture then flows through the evaporator, in which the refrigerant is supplied with heat from the heat source (or its heat source medium) acting on the evaporator.
  • the refrigerant initially evaporates essentially completely at constant pressure. After the refrigerant has reached the dew line, the gaseous refrigerant is heated further to approx. 5 to 15 K above the boiling point (suction gas overheating so that the downstream compressor does not suffer any damage from the entry of liquid).
  • the expansion valve regulates the refrigerant mass flow and the pressure, so that the refrigerant at the compressor inlet has a certain suction gas overheating at all times. Too little or no suction gas overheating can damage the compressor. In this case, the evaporation pressure must be reduced (ie the expansion valve closed). Too much suction gas overheating, on the other hand, has a bad effect on the refrigeration circuit efficiency, since the evaporation pressure is lower than necessary.
  • known control methods regulate to a fixed suction gas superheat (eg 5 K). The control variable is the difference between the suction gas temperature (gas temperature of the evaporated refrigerant when entering the compressor) and the evaporation temperature.
  • refrigerant circuits with so-called internal heat exchangers or suction gas heat exchangers, which are also operated with dry evaporation.
  • a first fluid line of the internal heat exchanger is arranged between the condenser and the expansion valve (that is, it connects the condenser outlet to the valve inlet of the expansion valve) and a second fluid line of the internal heat exchanger is arranged between the evaporator and the compressor (that is, it connects the evaporator outlet to the compressor inlet).
  • the refrigerant flowing through the first fluid line gives off heat to the refrigerant flowing through the second fluid line and thus heats the refrigerant before it enters the compressor.
  • the liquid refrigerant exiting the condenser at a high temperature level is routed via the internal heat exchanger (in its first fluid line) and is cooled down a few Kelvin in the process. This heat is used to further heat the already completely evaporated and slightly overheated refrigerant from the evaporator by passing it through the second fluid line of the internal heat exchanger. This means that the evaporation process can be operated with less overheating ( ⁇ 5 K) without damaging the compressor.
  • the regulation of the expansion valve corresponds to that of the simple dry evaporation described above.
  • the opening width of the expansion valve is in turn regulated in order to maintain a certain suction gas overheating (difference in suction gas temperature between evaporator and internal heat exchanger and evaporation temperature).
  • the disadvantage of the known concept is that it still requires (albeit less) suction gas overheating in the evaporator. This means that only small amounts of energy can be transferred in the internal heat exchanger.
  • the suction gas temperature cannot be regulated upstream of the compressor, whereby excessively high suction gas temperatures at the compressor inlet can lead to damage and overheating of the compressor.
  • the temperature changes in the internal heat exchanger are heavily dependent on the operating conditions (e.g. partial load operation and pressure difference). For this reason, internal heat exchangers are usually only used in practice for low temperature increases in the refrigerant and the transfer surface is correspondingly small. So-called tube-in-tube heat exchangers or tube spindles in liquid separators as a combination device are typical.
  • a refrigerant circuit can also each comprise more than one evaporator, internal heat exchanger, compressor or condenser.
  • the term “at least one” in connection with these components means that one instance or several instances of the respective component - arranged in parallel or one behind the other - is or are present.
  • the components are often referred to in the singular to make them easier to read. In these cases, too, it is meant that at least one instance of the designated component is present and also several instances - arranged in parallel or one behind the other - can be present.
  • a refrigerant circuit comprises several instances of a component (for example a refrigerant circuit with three evaporators and two compressors), the instances of the respective component are usually arranged in parallel (the three evaporators arranged in parallel would represent the at least one evaporator here and the two compressors arranged in parallel would represent the at least one compressor).
  • the instances of the respective component are arranged one behind the other or mixed (some instances in parallel and some instances behind one another).
  • a refrigerant circuit comprises more than one expansion valve. It can thus be provided that there are two or more expansion valves which are arranged in parallel, at least one of which is regulated.
  • the object of the invention is to avoid the disadvantages described above and to provide a method for regulating an expansion valve of a refrigerant circuit which is improved compared to the prior art and a refrigerant circuit which is improved compared to the prior art.
  • the expansion valve is regulated as a function of a temperature difference between a heat source temperature of the heat source and the evaporation temperature of the refrigerant, which prevails in the area between the valve outlet of the expansion valve and the compressor inlet of the at least one compressor.
  • the suction gas overheating is not used as a control variable for controlling the expansion valve, but rather the temperature difference between a heat source temperature of the heat source and the evaporation temperature of the refrigerant, which prevails in the area between the valve outlet of the expansion valve and the compressor inlet of the at least one compressor, is used as the control variable. used. This ensures that the control system can react much more quickly.
  • the heat source temperature of the heat source can be the temperature of a heat source medium (eg air or water) of the heat source.
  • the heat source temperature can, however, also be a temperature that is dependent on a temperature of the heat source (or its heat source medium).
  • it can be a Act surface temperature of the at least one evaporator, which changes depending on the temperature of the heat source or its heat source medium (eg ambient air that is supplied to the evaporator or water of a heating medium circuit that is supplied to the evaporator).
  • the heat source temperature is therefore a value that reflects the temperature of the heat source on the evaporator.
  • the inlet or outlet temperatures e.g. if the heat source is water that is fed to the evaporator via its own circuit
  • surface temperatures on the evaporator e.g. if the heat source is ambient air
  • averaged or weighted values can be used as the heat source temperature.
  • the refrigerant In the area between the valve outlet and the compressor inlet, the refrigerant has essentially a constant pressure, as a result of which the evaporation temperature of the refrigerant, which is directly related to the pressure, is also essentially constant in this area.
  • the evaporation temperature of the refrigerant can be measured after the refrigerant exits the valve outlet of the expansion valve or calculated from the pressure of the refrigerant at a point between the valve outlet and the compressor inlet with the aid of the vapor pressure curve (also known as the boiling curve).
  • compressors can have different output levels or output-variable control.
  • the proposed control concept is independent of the heat source used (which acts on the evaporator) or heat sink (which the Refrigerant removes heat in or on the condenser) and the refrigerant circuit can also contain other parts and components that have no significant influence on the functioning of the control strategy. Examples of this are sight glasses, collectors, filters, check valves, additional expansion valves, additional subcoolers, intermediate steam injection systems or components that enable switching to reversible operation.
  • the refrigerant can exit the at least one evaporator partially evaporated, saturated or superheated.
  • the refrigerant circuit comprises at least one internal heat exchanger.
  • This heat exchanger is often referred to as a suction gas heat exchanger.
  • a condenser outlet of the at least one condenser is connected to a first internal heat exchanger inlet of the at least one internal heat exchanger and a first internal heat exchanger outlet of the at least one internal heat exchanger is connected to a valve inlet of the expansion valve.
  • the first fluid line runs between the first internal heat exchanger inlet and the first internal heat exchanger outlet.
  • An evaporator outlet of the at least one evaporator is connected to a second internal heat exchanger inlet of the at least one internal heat exchanger and a second internal heat exchanger outlet of the at least one internal heat exchanger is connected to a compressor inlet of the at least one compressor.
  • the second fluid line runs between the second internal heat exchanger inlet and the second internal heat exchanger outlet.
  • the second fluid line is materially separated from the first fluid line, but thermally coupled or connected to the first fluid line so that heat can be given off in a manner known per se from the refrigerant flowing through the first fluid line to the refrigerant flowing through the second fluid line.
  • the at least one internal heat exchanger can be designed as a tube-in-tube heat exchanger, a plate heat exchanger, a tube bundle heat exchanger or the like.
  • the refrigerant flows through the refrigerant circuit as follows: starting from the valve outlet of the expansion valve, the refrigerant is introduced into the evaporator, in which it evaporates completely or partially due to the effect of heat from the heat source thermally connected to the evaporator or acting on the evaporator becomes. After exiting the evaporator, the refrigerant flows through the second fluid line of the internal heat exchanger, in which the refrigerant is further completely evaporated and heated. After exiting the internal heat exchanger or its second fluid line, the refrigerant flows into the compressor, in which it is compressed and further heated. After exiting the compressor, the refrigerant flows through the condenser, in which it liquefies while giving off heat.
  • the refrigerant After exiting the condenser, the refrigerant flows completely or in a partial flow through the first fluid line of the internal heat exchanger and, in the process, ensures that the refrigerant flowing through the second fluid line is heated in the internal heat exchanger. After exiting the internal heat exchanger or its first fluid line, the refrigerant flows to a valve inlet of the expansion valve and after the refrigerant exits the valve outlet of the expansion valve, the cycle begins again.
  • the evaporation of the refrigerant in a tube runs through several phases, the tube wall temperature being indirectly proportional to the heat transfer coefficient.
  • a completely liquid refrigerant what is known as nucleate boiling takes place first and then film evaporation.
  • the heat transfer coefficient is generally high high.
  • the refrigerant flow heats up, which also reduces the driving force of heat transport (the temperature difference).
  • the position of the dryout point depends on the flow velocity, geometry / orientation and heat flow density, but is usually between approx. 70% and 90% gas mass fraction.
  • the heat transfer coefficient is reduced by one to two orders of magnitude compared to film evaporation.
  • the limitation of the heat transfer coefficient means that a large part of the evaporator's heat exchanger surface is necessary for complete evaporation after the dryout point and, above all, for overheating the refrigerant.
  • these two process steps only contribute to a fraction of the total energy input.
  • Around 80% to 90% of the heat is transferred to the refrigerant in the area of nucleate boiling and film evaporation.
  • only about 5% to 15% of the heat is transferred during aerosol evaporation and less than 5% of the heat is transferred through suction gas superheating.
  • the proposed method for regulating the expansion valve enables optimal utilization of the internal heat exchanger, while at the same time the regulating system can be kept stable. It is possible to increase the liquid content of the refrigerant in the evaporator and to move the dryout point from the evaporator to the internal heat exchanger. The overheating process is completely shifted and parts of the evaporation process are shifted to the internal heat exchanger. As a result, the entire heat exchanger surface of the evaporator can be used for the evaporation process, which leads to an increase in the evaporation temperature (and thus to an increase in efficiency).
  • the internal heat exchanger can not only raise the temperature of the suction gas (the gaseous refrigerant when it enters the compressor), but also allow the wet steam to evaporate after the actual evaporator. This improves the heat transfer in the evaporator, which greatly increases the efficiency of the system.
  • the refrigerant circuit comprises a first temperature sensor, the first temperature sensor preferably being arranged in a heat source medium of the heat source or on the at least one evaporator, the first temperature sensor measuring the heat source temperature and reporting it to the control device.
  • the first temperature sensor can for example be arranged on the at least one evaporator and measure the temperature of the ambient air as a heat source medium. It is also conceivable that the first temperature sensor measures a surface temperature of the at least one evaporator, which is dependent on the temperature of the heat source medium.
  • the first temperature sensor can also be arranged in a circulation line of a heating medium circuit, via which, for example, water or an anti-freeze mixture is fed into the evaporator as a heat source medium.
  • the refrigerant circuit comprises a second temperature sensor, which measures a refrigerant temperature of the refrigerant after the refrigerant has exited the valve outlet of the expansion valve and before the refrigerant enters the at least one evaporator and reports it to the control device, the one from the second Temperature sensor measured refrigerant temperature corresponds to the evaporation temperature.
  • the refrigerant In the area between the valve outlet and the compressor inlet, the refrigerant has essentially a constant pressure, as a result of which the evaporation temperature of the refrigerant, which is directly related to the pressure, is also essentially constant in this area.
  • the temperature of the refrigerant at the valve outlet of the expansion valve therefore reflects the evaporation temperature of the refrigerant.
  • the refrigerant has the evaporation temperature in the entire area between the valve outlet and the inlet to the evaporator. Only in the evaporator and the internal heat exchanger connected to it does the temperature of the refrigerant rise above its evaporation temperature. If the second temperature sensor is thus arranged between the valve outlet and the at least one evaporator, then it can measure the evaporation temperature of the refrigerant directly. In other words, the refrigerant temperature measured in the area between the valve outlet and the inlet into the evaporator corresponds to the evaporation temperature of the refrigerant at the pressure conditions in this area.
  • the refrigerant circuit comprises a pressure sensor, the pressure sensor measuring a refrigerant pressure of the refrigerant at a point between the valve outlet and the compressor inlet and reporting it to the control device, the control device preferably determining the evaporation temperature from the refrigerant pressure.
  • the evaporation temperature is the temperature at which the refrigerant changes from the liquid phase to the gaseous phase.
  • the evaporation temperature is pressure-dependent and can be determined from the refrigerant pressure using the vapor pressure curve (also called the boiling curve) be determined.
  • the proposed control is significantly faster than the conventional suction gas superheat control, since the measurement of the pressure, in contrast to the measurement of the suction gas temperature upstream of the compressor, does not have any significant dead time.
  • the heat source temperature of the heat source acting on the at least one evaporator and the evaporation temperature of the refrigerant in the area between the valve outlet and the compressor inlet are determined, an actual heat source degree being determined from the temperature difference between the heat source temperature and the evaporation temperature, the actual heat source degree being determined by Regulation of an opening width of the expansion valve is tracked to a predefined or predefinable target heat source graduation. It can also be provided that there are two or more expansion valves which are arranged in parallel, at least one of which is regulated. It can also be that all expansion valves are regulated or that these are regulated in stages depending on the desired refrigerant mass flow.
  • only one of the expansion valves can be regulated up to a first predetermined or predeterminable refrigerant mass flow, with the further expansion valves initially remaining closed.
  • a further expansion valve can be regulated in order to be able to further increase the throughput of refrigerant.
  • further threshold values for the refrigerant mass flow can be predefined or predefinable in order to achieve a desired graduation of the refrigerant mass flow by using further regulated expansion valves.
  • the so-called heat source grading between the heat source temperature of the heat source and the evaporation temperature e.g.
  • evaporator inlet temperature of the refrigerant after the refrigerant has emerged from the valve outlet of the Expansion valve or determination via evaporation pressure is used as a control variable.
  • the current actual value of the heat source graduation is determined and a predefined or specifiable setpoint value (target heat source graduation) is tracked.
  • the heat source temperature can be measured in the heat source medium or at the evaporator (e.g. a surface temperature of the evaporator, an air temperature of the ambient air in the area of the evaporator or the water temperature of a water supplied to the evaporator in a heat medium circuit when entering or exiting the evaporator).
  • the evaporation temperature of the refrigerant can, for example, be measured at the evaporator inlet or calculated from a measured refrigerant pressure of the refrigerant before the refrigerant enters the at least one compressor.
  • the opening width of the expansion valve is changed continuously (continuously or discrete in time) in such a way that the actual heat source gradation matches the target heat source graduation.
  • the opening width of the expansion valve is regulated in order to achieve and / or maintain a predefinable or predefined setpoint heat source gradation.
  • control device comprises a first control device, the first control device determining a valve control value on the basis of a first control deviation between the setpoint heat source scale and the actual heat source scale and reports it to the expansion valve, the expansion valve setting the opening width as a function of the valve control value.
  • the expansion valve can be a thermal valve or an electric or electronic valve, for example in the form of a stepper motor valve that changes the opening width with the help of an electromagnet.
  • the first control device can be a PID, PI, PD controller or the like.
  • the new control value for the expansion valve is generated from the comparison between the setpoint (target heat source scale) and the actual value (actual heat source scale).
  • the opening width of the expansion valve controls the amount of refrigerant injected into the evaporator and thus has a direct influence on the evaporation pressure.
  • the target heat source gradation can be continuously (continuously or time-discrete) adjusted or set or specified so that, on the one hand, the compressor does not suffer any liquid hammer and, on the other hand, high suction gas temperatures upstream of the compressor are prevented.
  • control device comprises a further control device for preventing the entry of liquid refrigerant into the at least one compressor, with at least one measured or determined temperature of the refrigerant in the refrigerant circuit and / or at least one measured or determined pressure of the refrigerant in the refrigerant circuit the overheating state of the refrigerant is determined before or after the actual control value characterizing at least one compressor, and the actual control value is tracked to a predefined or predefinable setpoint control value by controlling the setpoint heat source graduation.
  • the target heat source scale can be adjusted, for example, in that an actual suction gas overheating of the refrigerant is determined after the internal heat exchanger and before entering the at least one compressor, the target heat source scale being adjusted or set or set depending on the actual suction gas overheating . is specified. It can therefore preferably be provided that a suction gas temperature of the refrigerant is determined after the internal heat exchanger and before entry into the at least one compressor, an actual suction gas overheating being determined from a temperature difference between the suction gas temperature and the evaporation temperature, the actual suction gas overheating being determined by regulating the target -Wärmeuzegrädung a specified or specifiable target suction gas superheat is tracked.
  • the refrigerant circuit comprises a third temperature sensor, which measures the suction gas temperature of the refrigerant after the internal heat exchanger and before entering the at least one compressor and reports it to the control device, the control device comprising a second control device, the control device for determining the Actual suction gas superheat calculates the difference between the suction gas temperature and the evaporation temperature, the second control device specifying the setpoint heat source scale on the basis of a second control deviation between the setpoint suction gas superheat and the actual suction gas superheat.
  • the second control device can in turn be a PID, PI, PD controller or the like.
  • the actual suction gas superheat is the difference between the suction gas temperature and the evaporation temperature.
  • the target suction gas superheat can be a fixed value (e.g. 5 K) or it can be dynamically specified depending on the operating conditions (e.g. 5 K for low evaporation temperatures and 10 K for high evaporation temperatures).
  • the second control device determines the setpoint heat source graduation and reports this to the first control device.
  • For the first control device is thus the setpoint heat source graduation reported by the second control device, the setpoint for the control.
  • the second control device can ensure that the difference between the suction gas temperature and the evaporation temperature (evaporator inlet temperature) is regulated to the setpoint for superheating (setpoint suction gas superheat) and thus the setpoint for the heat source graduation (setpoint heat source graduation) is continuously or discontinuously is adjusted.
  • the first control device can also be referred to as an inner cascade and the second control device can be referred to as an outer cascade.
  • the basic principle of this control cascading is the division of the control system into an inner, very fast and precise control circuit (first control device) and an outer, slower control circuit (second control device).
  • the inner control circuit regulates the expansion valve by comparing the heat source graduation (comparison of the actual heat source gradation with the target heat source graduation).
  • the external control circuit adapts the setpoint of the heat source scale (target heat source scale) to the operating conditions by comparing the overheating state of the refrigerant upstream of the compressor.
  • target suction gas overheating It regulates the desired overheating state of the gas upstream of the compressor (target suction gas overheating) and dynamically specifies the target value in the form of the target heat source graduation for the inner control circuit. In principle, this results in “approaching” the optimal operating conditions and, at the same time, stable regulation for the inner control circuit, which reacts quickly to short-term changes in operation.
  • suction gas overheating control instead of or in addition to suction gas overheating control as an external cascade, other concepts that fulfill the same task (preventing liquid refrigerant from entering the compressor) can be used as the actual value, e.g. a further control device to control the hot gas overheating.
  • the hot gas overheating results from the temperature difference between the hot gas temperature (temperature at the outlet of the compressor) and the condensation temperature (liquefaction temperature of the refrigerant, which is calculated, among other things, via the pressure, measured at a point between the compressor outlet and the expansion valve inlet, using the vapor pressure curve of the refrigerant can be).
  • High hot gas overheating is synonymous with high suction gas overheating.
  • the control tries to adjust a fixed or variable target hot gas overheating by adjusting the actual hot gas overheating.
  • the target hot gas overheating can be made dependent, for example, on the pressure difference (condensation pressure - evaporation pressure) and the compressor speed.
  • Another concept that can be used as an alternative to the suction gas overheating control is the control of the "minimally most stable signal". Only the suction gas temperature (temperature before the compressor inlet) is measured. As soon as this can no longer be kept stable, the minimum stable signal is reached. Any further increase in the refrigerant flow through the expansion valve would lead to liquid hammers in the compressor.
  • the outer cascade which is used to determine the target heat source graduation, does not necessarily have to consist of a classic control system.
  • values for the overheating state of the refrigerant upstream of the compressor i.e. the actual suction gas overheating
  • the target heat source graduation is adjusted from the deviation.
  • further measured variables can optionally be implemented in the overall system (by supplementing the control device with further controller modules), for example, to take into account the influence of various disturbance variables, such as compressor speed or power or subcooling temperature, by means of a pilot control.
  • various disturbance variables such as compressor speed or power or subcooling temperature
  • the subcooling temperature temperature of the Refrigerant upstream of the expansion valve
  • the compressor speed / compressor output or the fan speed can also be implemented in the form of a feed-forward control system or a feed-forward control system or another standard control method.
  • a heat source motor is understood as the device that transports the heat source medium from the heat source and brings it into thermal contact with the refrigerant in the evaporator (e.g. a fan for the heat source medium air or a pump with the heat source medium water).
  • the specified or specifiable target heat source graduation is changed by at least one change value, the at least one change value depending on a temperature of the refrigerant upstream of the expansion valve and / or a compressor speed of the at least one compressor and / or a compressor output of the at least one compressor and / or a heat source motor speed of a heat source motor is determined.
  • the heat source motor can generally be a flow machine for the heat source medium of the heat source.
  • the heat source motor can be a fan that supplies ambient air to the evaporator as a heat source medium.
  • the brine motor can also be a pump that supplies water or an anti-freeze mixture to the evaporator as a heat source medium.
  • the refrigerant is only partially evaporated in the at least one evaporator, the refrigerant being completely evaporated in the internal heat exchanger.
  • the refrigerant which is only partially evaporated in the evaporator, flows after exiting the evaporator through the second fluid line of the internal heat exchanger, in which the refrigerant is further completely evaporated and heated. This enables optimal utilization of the internal heat exchanger, while at the same time keeping the control system stable.
  • the liquid content of the refrigerant in the evaporator is increased and the dryout point is moved from the evaporator to the internal heat exchanger. So parts of the evaporation process and the overheating process are completely relocated to the internal heat exchanger.
  • the entire heat exchanger surface of the evaporator can be used for the evaporation process before the dryout point, which leads to an increase in the evaporation temperature (and thus an increase in efficiency).
  • the internal heat exchanger should not only raise the temperature of the suction gas, but also allow the wet steam to evaporate after the actual evaporator. This improves the heat transfer in the evaporator, which greatly increases the efficiency of the system.
  • the described refrigeration circuit structure with internal heat exchanger is required, whereby the internal heat exchanger, in contrast to internal heat exchangers or suction gas heat exchangers customary in practice, is designed for a comparatively high transmission capacity should be.
  • a plate heat exchanger is preferably used for this.
  • the control strategy described is required, which ensures a stable overheating state directly before or (alternatively) directly after the compressor. The lower the overheating condition of the refrigerant, the higher the proportion of liquid in the refrigerant at the evaporator outlet.
  • the refrigerant circuit comprises at least one evaporator, at least one internal heat exchanger, at least one compressor, at least one condenser, an expansion valve and a control device connected to the expansion valve in a signal-conducting manner for controlling the expansion valve, in particular according to a method according to one of claims 1 to 9, wherein a first Fluid line of the at least one internal heat exchanger is arranged between the at least one condenser and the expansion valve and a second fluid line of the at least one internal heat exchanger is arranged between the at least one evaporator and the at least one compressor, the at least one evaporator, the second fluid line, the at least a compressor, the at least one condenser, the first fluid line and the expansion valve arranged one behind the other in series in a direction of circulation of the refrigerant circuit and through which a refrigerant can flow .
  • the refrigerant circuit comprises a first temperature sensor connected to the control device in a signal-conducting manner, wherein the first temperature sensor can measure a heat source temperature of a heat source acting on the at least one evaporator and can be reported to the control device, wherein the first temperature sensor is preferably arranged in a heat source medium of the heat source or on the at least one evaporator, the refrigerant circuit having a temperature detection device connected to the control device in a signal-conducting manner for determining the evaporation temperature of the refrigerant, which prevails in the area between the valve outlet of the expansion valve and the compressor inlet of the at least one compressor , wherein the regulating device regulates an opening width of the expansion valve as a function of a temperature difference between the heat source temperature and the evaporation temperature of the refrigerant in the area between the valve outlet and the compressor inlet.
  • the evaporation temperature can either be calculated using the evaporation pressure at
  • the heat source acting on the at least one evaporator can be the environment that surrounds the evaporator or whose air is supplied to the evaporator (e.g. in the case of an air heat pump).
  • a heat source is water or another fluid, which is supplied to the evaporator in a known manner via its own heat medium circuit, which is hydraulically decoupled from the refrigerant circuit and thus materially separated from it, in order to heat the refrigerant of the refrigerant circuit in the evaporator .
  • the heat source is thermally connected to the evaporator and in the evaporator heat is supplied to the refrigerant from the heat source thermally connected to the evaporator and the refrigerant evaporates while absorbing heat.
  • the refrigerant circuit comprises at least one internal heat exchanger, with heat flowing from the refrigerant flowing through the first fluid line of the at least one internal heat exchanger to the refrigerant flowing through the second Fluid line of the at least one internal heat exchanger flowing refrigerant can be emitted.
  • the at least one internal heat exchanger - also referred to as a suction gas heat exchanger - can not only raise the temperature of the suction gas (the gaseous refrigerant when it enters the compressor), but also allow the wet steam to evaporate after the actual evaporator. This improves the heat transfer in the evaporator, which greatly increases the efficiency of the system.
  • the temperature determination device comprises a second temperature sensor arranged between the valve outlet and the at least one evaporator, the evaporation temperature being measurable by the second temperature sensor and being able to be reported to the control device.
  • the second temperature sensor thus measures a refrigerant temperature of the refrigerant after the refrigerant emerges from the valve outlet of the expansion valve and before the refrigerant enters the at least one evaporator. In this range, the measured refrigerant temperature corresponds to the evaporation temperature of the refrigerant.
  • the temperature determination device comprises a pressure sensor arranged between the valve outlet and the compressor inlet, a refrigerant pressure of the refrigerant being measurable by the pressure sensor and being able to be reported to the control device, with the control device being able to determine the evaporation temperature from the refrigerant pressure.
  • control device determines an actual heat source scale from the temperature difference between the heat source temperature and the evaporation temperature and the actual heat source scale by regulating the opening width of the expansion valve to a predetermined or tracks the predefinable target heat source graduation. It is also provided that the control device continuously adjusts the setpoint heat source graduation.
  • control device comprises a further control device for preventing the entry of liquid refrigerant into the at least one compressor, the control device consisting of at least one measured or determined temperature of the refrigerant in the refrigerant circuit and / or at least one measured or determined pressure of the refrigerant In the refrigerant circuit, an actual control value characterizing the overheating state of the refrigerant before or after the at least one compressor is determined and the actual control value tracks a predetermined or predeterminable control setpoint by controlling the target heat source graduation.
  • control device comprises a first control device which, on the basis of a first control deviation between the target heat source scale and the actual heat source scale, determines a valve control value in relation to the opening width and reports it to the expansion valve.
  • the expansion valve adjusts the opening width depending on the valve control value.
  • the expansion valve can be a thermal valve or an electric or electronic valve, e.g. in the form of a stepper motor valve that changes the opening width with the help of an electromagnet.
  • the first control device can be a PID, PI, PD controller or the like.
  • the refrigerant circuit comprises a third temperature sensor, a suction gas temperature of the refrigerant from the third temperature sensor after the internal heat exchanger and before entering the at least one compressor can be measured and reported to the control device, the control device determining an actual suction gas overheating from a temperature difference between the suction gas temperature and the evaporation temperature, and the actual suction gas overheating by regulating the target heat source gradient of a predetermined or specifiable target -Suction gas overheating tracks.
  • control device calculates the difference between the suction gas temperature and the evaporation temperature.
  • control device comprises a second control device, which determines the target heat source degree on the basis of a second control deviation between target suction gas overheating and actual suction gas overheating and reports it to the first control device.
  • the second control device can be a PID, PI, PD controller or the like.
  • the proposed device can be, for example, a heat pump, a refrigeration system or an air conditioner.
  • Figure 1 shows a schematic representation of a device 19 with a refrigerant circuit 2 according to the prior art and Figure 2 shows a cycle carried out in the refrigerant circuit 2 in a pressure-enthalpy diagram or log-ph diagram.
  • the device 19 can be, for example, a heat pump, a refrigeration system or an air conditioner.
  • the refrigerant circuit 2 comprises an evaporator 3, a compressor 4, a condenser 5, an expansion valve 1 and a control device 6 for controlling the expansion valve 1, which is connected in a signal-conducting manner to the expansion valve 1 via a signal line 20.
  • the evaporator 3, the compressor 4, the condenser 5 and the expansion valve 1 are arranged one behind the other in series in a circulation direction Z of the refrigerant circuit 2 and a refrigerant K flows through them, which circulates in the closed refrigerant circuit 2 in the circulation direction Z.
  • a heat source 8 acts in a known manner on the evaporator 3 and leads to an increase in the enthalpy of the refrigerant K in the evaporator 3, so that the refrigerant K is at least partially evaporated in the evaporator 3.
  • the heat source 8 can be ambient air which surrounds the evaporator 3 or is supplied to the evaporator 3 (for example in the case of a device in the form of an air heat pump).
  • a heat source 8 is water or another fluid, which is supplied to the evaporator 3 in a manner known per se via its own heat medium circuit, which is hydraulically decoupled from the refrigerant circuit 2 and thus materially separated from it, in order to reduce the refrigerant K of the refrigerant circuit 2 to be heated in the evaporator 3.
  • the heat source 8 is thermally connected to the evaporator 3 and in the evaporator 3 heat is supplied to the refrigerant K from the heat source 8 thermally connected to the evaporator 3 and the refrigerant K evaporates while absorbing heat.
  • the heated and at least partially evaporated (i.e. gaseous) refrigerant K is compressed, whereby the refrigerant K is raised to a higher pressure and temperature level.
  • the gaseous refrigerant K is then passed on in the direction of the condenser 5 with a correspondingly increased pressure and correspondingly increased temperature.
  • the condenser 5 (often also referred to as a condenser), the gaseous, superheated refrigerant K is cooled to a temperature at which the refrigerant K liquefies and thereby dissipates heat to a heat sink (not shown in detail) (e.g.
  • the liquefied refrigerant K passes the expansion valve 1, which is a bottleneck in the Represents refrigerant circuit 2. With the passage of this constriction in the form of the expansion valve 1, there is a rapid pressure drop in the refrigerant K, since the refrigerant K can relax after passing through the expansion valve 1. The pressure drop is also accompanied by a cooling of the refrigerant K, which is fed back to the evaporator 3 after the expansion valve 1 and the described cycle starts again with at least partial evaporation of the refrigerant K in the evaporator 3.
  • the refrigerant K is continuously expanded in the expansion valve 1, whereby it partially evaporates.
  • the refrigerant K in the form of a liquid-gas mixture then flows through the evaporator 3, whereby the remaining liquid is first completely evaporated and finally 5 to 15 K is superheated (so-called suction gas superheating) before the gaseous refrigerant K enters the compressor 4.
  • the compressor 4 increases the pressure of the gaseous refrigerant K.
  • the refrigerant K is liquefied by removing heat.
  • FIG. 2 shows an example of a cycle C in the refrigerant circuit 2 according to FIG Figure 1 in the well-known log-ph diagram.
  • the specific enthalpy E energy content of the refrigerant K
  • P logarithmically scaled pressure
  • the refrigerant K is liquid, to the right of it (i.e. to the right of the dew line T) it is completely gaseous. In between, the gas content increases continuously from left to right.
  • the cycle C is indicated by dashed lines and comprises the process steps C1, C2, C3 and C4.
  • the refrigerant K initially evaporates completely at constant pressure in the evaporator 3 (process step C1). After reaching the dew line T, the then completely gaseous refrigerant K is heated further by approx. 5 to 15 K above the boiling point. This so-called suction gas overheating is necessary so that the compressor 4 does not Suffers liquid hammer.
  • the compressor 4 there is an increase in pressure and temperature of the refrigerant K (process step C2).
  • the condenser 5 the refrigerant K condenses at constant pressure while giving off heat (process step C3). There is a pressure drop in the refrigerant K in the expansion valve 1 (process step C4) and the cycle process C begins again with the process step C1.
  • the expansion valve 1 is controlled in order to achieve a predetermined setpoint value for the suction gas overheating.
  • a second temperature sensor 13 and a third temperature sensor 16 are provided, which are connected to the control device 6 in a signal-conducting manner.
  • the second temperature sensor 13 detects the temperature of the refrigerant K before it enters the evaporator 3 and reports this temperature to the control device 6 via a second sensor line 22.
  • the third temperature sensor 16 detects the temperature of the refrigerant K at the evaporator outlet before it enters the compressor 4 and reports this temperature to the control device 6 via a third sensor line 23.
  • the control device 6 determines the actual value of the suction gas overheating by calculating the temperature difference between the temperature of the refrigerant K before it enters the compressor 4 (suction gas temperature) and the evaporation temperature (e.g. measured by the temperature of the Refrigerant K is calculated before entering the evaporator 3).
  • the expansion valve 1 is controlled via the signal line 20 in such a way that an opening width of the expansion valve 1 is adjusted so that the actual value of the suction gas superheat is regulated to the target value for the suction gas superheat.
  • an (eg electronic or thermal) expansion valve 1 a fixed suction gas overheating (eg 5 K) can be regulated.
  • the difference between the suction gas temperature and the evaporation temperature is used as the control variable.
  • the expansion valve 1 regulates the refrigerant mass flow and the pressure, so that the refrigerant K has a certain suction gas overheating at the compressor inlet. Too little or no suction gas overheating can cause damage to compressor 4. In this case, the evaporation pressure must be reduced (ie the expansion valve 1 closed). Too much suction gas overheating, on the other hand, has a bad effect on the refrigeration circuit efficiency, since the evaporation pressure is lower than necessary.
  • FIG 3 shows a device 19 according to Figure 1 , wherein the refrigerant circuit 2 additionally comprises a heat exchanger 9 in the form of a so-called internal heat exchanger or suction gas heat exchanger and the third temperature sensor 16 is arranged between the evaporator 3 and the internal heat exchanger 9 and thus measures the suction gas temperature of the refrigerant K at the evaporator outlet.
  • a first fluid line 10 of the internal heat exchanger 9 is arranged between the condenser 5 and the expansion valve 1 and a second fluid line 11 of the internal heat exchanger 9 is arranged between the evaporator 3 and the compressor 4, with heat from the refrigerant K flowing through the first fluid line 10 can be delivered to the refrigerant K flowing through the second fluid line 11.
  • a condenser outlet 24 of the condenser 5 is connected to a first internal heat exchanger inlet 25 of the internal heat exchanger 9 and a first internal heat exchanger outlet 26 of the internal heat exchanger 9 is connected to a valve inlet 27 of the expansion valve 1.
  • the first fluid line 10 runs between the first internal heat exchanger inlet 25 and the first internal heat exchanger outlet 26.
  • An evaporator outlet 28 of the evaporator 3 is connected to a second internal heat exchanger inlet 29 of the internal heat exchanger 9 and a second internal heat exchanger outlet 30 of the internal heat exchanger 9 is connected to a compressor inlet 31 of the Compressor 4 connected.
  • the second fluid line 11 runs between the second internal heat exchanger inlet 29 and the second internal heat exchanger outlet 30.
  • the second fluid line 11 is materially separated from the first fluid line 10, however thermally coupled or connected to the first fluid line 10, so that heat can be given off in a manner known per se from the refrigerant K flowing through the first fluid line 10 to the refrigerant K flowing through the second fluid line 11.
  • the liquid refrigerant K exiting from the condenser 5 at a high temperature level is passed over the internal heat exchanger 9 and is cooled by a few Kelvin in the process. This heat is used to further heat the already completely evaporated and slightly overheated refrigerant K from the evaporator 3.
  • the evaporation process can thus be operated with less overheating ( ⁇ 5 K) without damaging the compressor 4.
  • the suction gas temperature of the refrigerant K is measured with the third temperature sensor 16 between the evaporator 3 and the internal heat exchanger 9.
  • the evaporation temperature of the refrigerant K can be measured at the inlet of the evaporator 3 with the second temperature sensor 13.
  • the regulation of the expansion valve 1 corresponds to that of the simple dry evaporation (see Figure 1 ).
  • the opening width of the expansion valve 1 is therefore again regulated in order to maintain a certain suction gas overheating (temperature difference between the suction gas temperature and the evaporation temperature).
  • FIG. 4 shows an example of a cycle C in the refrigerant circuit 2 according to FIG Figure 3 in the log-ph diagram.
  • the overheating of the completely gaseous refrigerant K takes place after reaching the dew line T in the internal heat exchanger 9 (in its second fluid line 11) and accordingly the last cooling of the refrigerant in process step C3 K also takes place in the internal heat exchanger 9 before the subsequent entry into the expansion valve 1 (in its first fluid line 10).
  • FIG. 5 shows a device 19 with an exemplary embodiment of a proposed refrigerant circuit 2.
  • the structure and interconnection of expansion valve 1, evaporator 3, internal heat exchanger 9, compressor 4 and condenser 5 correspond to that in FIG Figure 3
  • the refrigerant circuit 2 comprises a temperature determination device 18 connected to the control device 6 in a signal-conducting manner for determining an evaporator inlet temperature of the refrigerant K after the refrigerant K has emerged from a valve outlet 7 of the expansion valve 1.
  • the temperature determination device 18 comprises a second temperature sensor 13 , whereby the evaporation temperature (corresponds to the evaporator inlet temperature) can be measured by the second temperature sensor 13 and can be reported to the control device 6 via a second sensor line 22.
  • the proposed refrigerant circuit 2 also includes a first temperature sensor 12 which is connected in a signal-conducting manner to the control device 6 and which is arranged in a heat source medium of the heat source 8 or on at least one evaporator 3, with the first temperature sensor 12 showing a heat source temperature of a heat source 8 acting on the at least one evaporator 3 can be measured and reported to the control device 6 via a first sensor line 21.
  • the regulating device 6 is configured to regulate an opening width of the expansion valve 1 as a function of a temperature difference between the heat source temperature and the evaporation temperature.
  • the control device 6 determines an actual heat source graduation IW from the temperature difference between the heat source temperature and the evaporation temperature and tracks the actual heat source graduation IW by regulating the opening width of the expansion valve 1 to a predetermined or specifiable target heat source graduation SW.
  • the control device 6 comprises a first control device 15, not shown here, which is configured to determine a valve control value in relation to the opening width on the basis of a first control deviation between the setpoint heat source scale SW and the actual heat source scale IW and the expansion valve 1 via a signal line 20 to report.
  • FIG Figure 6 shows schematically the control scheme for regulating the expansion valve 1 of the refrigerant circuit 2 according to FIG Figure 5 .
  • the heat source gradation difference between heat source temperature and evaporation temperature
  • the first control device 15 determines a valve control value V in relation to the opening width of the expansion valve 1 and reports this via the signal line 20 to the expansion valve 1, which represents the controlled system in the control diagram.
  • a new actual heat source graduation IW results from a changed opening width of the expansion valve 1, which is fed back in the control scheme to determine the first control deviation.
  • the target heat source graduation SW can be specified as a fixed value (fixed value).
  • the actual heat source graduation IW is determined by the control device 6 by calculating the temperature difference between the heat source temperature reported by the first temperature sensor 12 and the evaporator inlet temperature reported by the second temperature sensor 13 (corresponds to the evaporation temperature).
  • the target heat source graduation SW should have a value of 5 K, the evaporation temperature should be -5 ° C, the heat source temperature (e.g. air temperature) should be 1 ° C and the actual value of the opening width of expansion valve 1 should be 40% at the beginning of the control .
  • the actual heat source graduation IW has a value of 6 K (heat source temperature minus evaporation temperature), ie the evaporation temperature could be increased by 1 K, thereby increasing the refrigeration circuit efficiency.
  • the deviation between the set heat source graduation SW and the actual heat source graduation IW is processed, for example in a PID controller, and a new valve control value V for the expansion valve 1 is generated therefrom.
  • the expansion valve 1 opens to 42%, for example, so that more refrigerant K flows into the evaporator 3 and the pressure and thus the evaporation temperature rise.
  • the actual heat source graduation IW is thereby reduced to 5.8 K and a new control cycle begins.
  • FIG. 7 shows an example of a cycle C in the refrigerant circuit 2 according to FIG Figure 5 in the log-ph diagram.
  • the cycle C of the Figure 4 it can be seen that significantly larger proportions of process steps C1 and C3 take place in the internal heat exchanger 9. Since the dryout point in the proposed refrigerant circuit 2 is strongly shifted in the direction of the internal heat exchanger 9, the internal heat exchanger 9 not only increases the temperature of the suction gas, but also enables the wet steam to evaporate after the actual evaporator 3. Overall, this allows the refrigerant circuit 2 operate much more efficiently.
  • FIG. 8 shows a device 19 with a further embodiment of a proposed refrigerant circuit 2.
  • the temperature determining device 18 comprises a pressure sensor 14, whereby the pressure sensor 14 can measure a refrigerant pressure of the refrigerant K at a point between the valve outlet 7 and the compressor inlet 31 and can be reported to the control device 6 via a pressure sensor line 32, the control device 6 determining the evaporation temperature from the refrigerant pressure is.
  • the regulation of the expansion valve 1 takes place in the same way as in the exemplary embodiment according to FIG Figures 5 and 6 .
  • FIG Figure 9 shows a device 19 with a further exemplary embodiment of a proposed refrigerant circuit 2.
  • the refrigerant circuit 2 corresponds to the refrigerant circuit 2 of FIG Figure 8 , supplemented by further sensors and controller modules.
  • the refrigerant circuit 2 shown additionally comprises a third temperature sensor 16, which is located between the internal heat exchanger 9 and the compressor 4 and thus measures the suction gas temperature of the refrigerant K after the internal heat exchanger 9 and before entering the compressor 4 and reports it to the control device 6 via a third sensor line 23.
  • the temperature determination device 18 can also comprise a second temperature sensor 13 for determining the evaporation temperature directly from the evaporator inlet temperature (see FIG Figure 5 ).
  • the control device 6 comprises a second control device 17, not shown here.
  • the control device 6 calculates the difference between the suction gas temperature reported by the third temperature sensor 16 and the evaporation temperature determined by the temperature determination device 18, and the second control device 17 provides the basis a second control deviation between a predefined or predefinable setpoint suction gas superheat SS and the actual suction gas superheat IS, the setpoint heat source graduation SW, which is fed to the first control device 15 as a reference variable.
  • the actual suction gas superheating IS is tracked to a predetermined or predeterminable desired suction gas superheating SS by regulating the setpoint heat source graduation SW.
  • FIG Figure 10 shows schematically the control scheme for regulating the expansion valve 1 of the refrigerant circuit 2 according to FIG Figure 9 .
  • the control scheme shows a 2-stage control cascade, in which the first control device 15 represents the inner cascade (inner control circuit) and the second control device 17 represents the outer cascade (outer control circuit).
  • the inner cascade corresponds to the control scheme of Figure 6 .
  • the second control device 17 specifies the target heat source graduation SW, which is fed to the first control device 15 as a reference variable.
  • the first control device 15 determines a valve control value V in relation to the opening width of the Expansion valve 1 and reports this via the signal line 20 to the expansion valve 1, which represents the controlled system in the inner cascade.
  • a new actual heat source graduation IW results from a changed opening width of the expansion valve 1, which is fed back in the inner cascade to determine the first control deviation.
  • a change in the opening width of the expansion valve 1 causes a changed refrigerant mass flow and thus a changed pressure and a changed temperature of the refrigerant K when it enters the evaporator 3, which, together with the connected internal heat exchanger 9, represents the controlled system of the outer cascade.
  • the refrigerant K After the refrigerant K emerges from the internal heat exchanger 9, it has a new actual suction gas overheating IS, which is fed back in the outer cascade to determine the second control deviation.
  • the basic principle of this control cascading is the division of the control system into an inner, very fast and precise control circuit (first control device 15) and an outer, slower control circuit (second control device 17).
  • the inner control circuit regulates the expansion valve 1 by comparing the heat source graduation (comparison of the actual heat source graduation IW with the set heat source graduation SW).
  • the external control circuit adjusts the setpoint of the heat source gradation (setpoint heat source gradation SW) to the existing operating conditions by comparing the overheating state of the refrigerant K upstream of the compressor 4. It regulates the desired overheating state of the gas upstream of the compressor 4 (target suction gas overheating SS) and dynamically specifies the target value in the form of the target heat source graduation SW to the inner control circuit.
  • the input setpoint for the outer cascade in the form of the setpoint suction gas superheat SS is intended to ensure, on the one hand, that the compressor 4 does not suffer any liquid hammer and, on the other hand, high suction gas temperatures in front of the compressor 4.
  • the target suction gas superheat SS can be a permanently stored value or can be dynamically specified as a function of the operating conditions.
  • FIG 11 shows a device 19 with a further exemplary embodiment of a proposed refrigerant circuit 2.
  • the refrigerant circuit 2 corresponds to the refrigerant circuit 2 of FIG Figure 9 , although here the temperature determination device 18 comprises a second temperature sensor 13 for direct measurement of the evaporation temperature and wherein the refrigerant circuit 2 comprises further sensors. Specifically, there is a second pressure sensor 33 for determining the pressure of the refrigerant K after it leaves the compressor 4 and before it enters the expansion valve 1 and a fourth temperature sensor 34 for determining the temperature of the refrigerant K after it leaves the compressor 4 and before it enters the condenser 5 provided.
  • a second pressure sensor 33 for determining the pressure of the refrigerant K after it leaves the compressor 4 and before it enters the expansion valve 1
  • a fourth temperature sensor 34 for determining the temperature of the refrigerant K after it leaves the compressor 4 and before it enters the condenser 5 provided.
  • the signals from the second pressure sensor 33 are fed to the control device 6 via a second pressure sensor line 35 and the signals from the fourth temperature sensor 34 are fed to the control device 6 via a fourth sensor line 36.
  • the hot gas overheating can be regulated on the basis of the hot gas temperature (determined by the fourth temperature sensor 34) versus the condensation temperature (determined from the vapor pressure curve by measuring the pressure from the second pressure sensor 33) to specify the target heat source graduation.
  • the hot gas superheat control behaves similarly to the suction gas superheat control. A slight overheating of the hot gas leads to Liquid hammer in the compressor 3, excessive hot gas overheating leads to a loss of efficiency.
  • the hot gas overheating is adapted to a fixed or changeable target hot gas overheating.
  • a variable target hot gas overheating can be dependent, for example, on the evaporation pressure, the condensation pressure and the compressor speed.
  • Figure 12 shows a device 19 according to Figure 11 , supplemented by a further valuation procedure and further controller modules. Specifically, a further sensor 37 is provided for determining the power and / or speed of the compressor 4. The signals from the sensor 37 are fed to the control device 6 via a further sensor line 38.
  • the opposite of the rule scheme of the Figure 10 further controller modules are shown in the schematic control diagram of Figure 13 shown.
  • the supplemented controller modules are a first pilot control 39 and a second pilot control 40.
  • the first pilot control 39 can take into account the temperature of the refrigerant K at the inlet to the expansion valve 1 and the second pilot control 40 can set a compressor speed and / or Compressor output of the compressor 4 (determined by the further sensor 37) must be taken into account.
  • a proposed refrigerant circuit can also each comprise more than one evaporator, internal heat exchanger, compressor or condenser.
  • a proposed refrigerant circuit comprises several instances of a component (for example a refrigerant circuit with three evaporators and two compressors), the instances of the respective component are usually arranged in parallel.
  • a proposed refrigerant circuit comprises more than one expansion valve. So it can be provided that two or more expansion valves are present that run in parallel are arranged, at least one of which is controlled as proposed. It can also be that all expansion valves are regulated as proposed or that these are regulated in a staggered manner as proposed, depending on the desired refrigerant mass flow.

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EP20200553.4A 2019-10-30 2020-10-07 Procédé de régulation d'un détendeur Active EP3816543B1 (fr)

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EP2647928A2 (fr) * 2007-11-30 2013-10-09 Mitsubishi Electric Corporation Appareil de circuit de réfrigération
EP3282209A1 (fr) * 2016-07-26 2018-02-14 LG Electronics Inc. Appareil de cycle de réfrigération supercritique et procédé de commande d'un appareil de cycle de réfrigération supercritique
WO2019020952A1 (fr) * 2017-07-28 2019-01-31 Valeo Systemes Thermiques Procede de gestion d'un circuit de climatisation de vehicule automobile

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Publication number Priority date Publication date Assignee Title
IT202100018296A1 (it) * 2021-07-12 2023-01-12 Irinox S P A Macchina frigorifera per prodotti alimentari
EP4119868A1 (fr) * 2021-07-12 2023-01-18 Irinox S.p.A. Machine à réfrigérer les denrées alimentaires
EP4170266A1 (fr) * 2021-10-20 2023-04-26 Lauda Dr. R. Wobser GmbH & Co. KG Installation frigorifique et procédé de fonctionnement d'une installation frigorifique

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AT522875B1 (de) 2021-03-15
AT522875A4 (de) 2021-03-15
EP3816543B1 (fr) 2022-11-30

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