CN105627643B

CN105627643B - Refrigeration system with fill level monitoring

Info

Publication number: CN105627643B
Application number: CN201510830465.4A
Authority: CN
Inventors: 米歇尔·宗内卡尔布; 哈特穆特·贡佩尔; 邦雅曼·黑尔维希; 塞巴斯蒂安·芬克; 菲利普·梅尔
Original assignee: Convoy Ag
Current assignee: Convoy Ag
Priority date: 2014-11-25
Filing date: 2015-11-25
Publication date: 2021-06-18
Anticipated expiration: 2035-11-25
Also published as: DE102014223956B4; JP2016102647A; DE102014223956A1; CN113465200A; CN105627643A

Abstract

The invention relates to a method and a device for monitoring a refrigerant charge in a refrigerant circuit (46) of a refrigeration system (10), the refrigeration system (10) having a compressor (12), a condenser or gas cooler (14), an expansion device (16) and an evaporator device (18). When the compressor (12) is off, the method comprises the steps of: measuring at least one temperature, measuring a refrigerant pressure in the refrigeration system (10); determining a refrigerant charge error, in particular a refrigerant deficiency, if the measured pressure is outside a nominal pressure range, wherein the nominal pressure of the refrigerant is determined on the basis of the measured temperature and the nominal pressure range comprises pressure values which deviate at most from the nominal pressure by a specified tolerance. When the compressor (12) is turned on, the method comprises the steps of: measuring at least one temperature; measuring the refrigerant pressure at the outlet of the condenser or gas cooler (14); a refrigerant charge error, in particular a refrigerant deficiency, is established if the measured pressure is outside a nominal pressure range, wherein the nominal pressure of the refrigerant is determined on the basis of the measured temperature, and the nominal pressure range comprises pressure values at which the pressure values deviate at most from the nominal pressure by a specified tolerance. The device according to the invention also comprises a storage container (22) which stores a refrigerant, and a refrigerant, in particular CO₂Operating in a transcritical range depending on the operating point, wherein at least one refrigerant temperature sensor (32) and at least one refrigerant pressure sensor (34) are provided for measuring the temperature and pressure of the refrigerant, wherein the temperature and pressure of the refrigerant can be evaluated in the control unit (30) in such a way that a refrigerant charge error is detectable, and if an under-run is detected, the control unit (30) causes a charging by means of a control intervention on the refrigerant circuit (46).

Description

Refrigeration system with fill level monitoring

Technical Field

The present invention relates to a method for monitoring the refrigerant charge of a refrigerant circuit of a refrigeration system for filling such a refrigeration system with refrigerant, and to a device, in particular for a vehicle, for monitoring the refrigerant charge of a refrigeration system.

Background

Compression refrigeration systems or air conditioning systems are used as air conditioning systems, for example, for air conditioning vehicles, such as automobiles or buses, in order to reduce the temperature in the interior of the vehicle. Compression refrigeration systems of the above type include a refrigerant delivery system having a condenser unit including at least one condenser or at least one gas cooler, in addition to an expansion device, an evaporator unit and a compressor, connected together by a refrigerant delivery line. Refrigerant circulates in the closed circuit.

Carbon dioxide (CO) according to environmental compatibility₂) As a refrigerant, as a replacement medium for compression refrigeration systems. The naturally occurring substance carbon dioxide has a very low climate damaging global warming potential compared to other refrigerants. CO 2₂One of its disadvantages is its very low critical temperature of only 31 c, for which reason the heat release must be carried out above the critical pressure and not condense/liquefy. CO 2₂The critical pressure of (a) is about 74 bar. In the presence of CO₂In known compression refrigeration systems that are refrigerants, the system charge, also referred to as the fill level, relative to the system volume is 50% to 100% of the critical density. The high pressure portion does not condense because the high pressure is above the critical pressure.

When such a compression refrigeration system is in operation, a relatively high operating pressure prevails downstream of the compressor, while a relatively low pressure prevails upstream of the compressor. Pressure equalization occurs when the system is at rest and still a relatively high rest pressure builds up in the circuit of the compression refrigeration system. The compressor must be designed for this relatively high static pressure and provide adequate protection. At a system temperature of 40 deg.c and a fill level of about 50% of the critical density of the refrigerant carbon dioxide, the system pressure is about 75 bar, and at the fill level of the region of critical density of the refrigerant it is about 89 bar. At a system temperature of 60 c and a fill level of about 50% of the critical density of the refrigerant carbon dioxide, the system pressure is about 89 bar, and at a fill level of 100% of the critical density of the refrigerant it is about 124 bar.

It is necessary to reliably determine the degree of filling of the refrigerant circuit, i.e. the amount of refrigerant present in the refrigerant circuit, in particular in order to identify a shortage of refrigerant. The refrigerant charge defined for a particular air conditioning or refrigeration system must be maintained within very tight tolerances, as any excess or deficiency in the system can result in reduced refrigeration performance, or even damage to the system. In particular, if there is a deficiency, an unstable situation may occur, which in some cases may even lead to a temporary failure of the circuit. The degree of filling of a compression refrigeration system is generally determined during an idle state analysis, the pressure of the refrigerant being measured by a pressure sensor and related to the temperature of the refrigerant.

In a further development of the known compression refrigeration system using carbon dioxide as refrigerant, which is a non-flammable, combustion inert, non-toxic and harmless medium of gaseous state under standard conditions, carbon dioxide from the compression refrigeration system can be used as extinguishing medium in a suitable vehicle fire extinguishing system. Refrigerant CO₂And thus have proven to be suitable fire extinguishing agents for extinguishing any fire source that may occur or result from a traffic accident. Extinguishing medium CO₂Has advantages over cooling water used in a similar manner.

US5481884 discloses a method for refrigerant charge monitoring during standstill and also during operation of air conditioning and heat pump systems. During operation of the continuously operating system, the temperature and pressure of the refrigerant are measured on the suction side of the compressor. At the measured pressure, an associated saturation temperature is established and used as a reference temperature, which is compared to the measured refrigerant temperature. If the measured temperature is higher than the reference temperature, it is assumed to be insufficient.

DE10061545a1 discloses a method for monitoring the refrigerant charge in a refrigerant circuit of an air-conditioning or heat pump system with a compressor and a refrigerant, which operates in the supercritical range depending on the operating point, at standstill and/or during operation. During operation of charge monitoring, refrigerant superheat, i.e., a temperature rise at the system evaporator, is detected and the detected superheat is compared to a limit. If the superheat exceeds a specified maximum, then an insufficiency is assumed and a corresponding alarm indication is generated.

The known methods from US5481884 and DE10061545a1 are indeed applicable in principle to any refrigerant and thus also to CO₂However, the method only identifies an erroneous refrigerant condition at the compressor inlet, i.e., on the low pressure side. However, error conditions can also occur, for example, due to a defective expansion element or a blockage of the refrigerant circuit. Both possible failures constitute a serious risk for the compressor.

DE4411281B4 discloses a motor vehicle air conditioning system using CO₂As a circulating medium, among which the circulating medium CO of the air-conditioning system₂Intended to act as a fire extinguishing agent in the event of a fire. In an air conditioning system, the circulating medium circulates in a pressure line, from which a fire extinguishing line, which has a solenoid valve arranged thereon and is controlled by a control unit and which terminates in a fire extinguishing nozzle, branches off. CO supplied to fire extinguishing apparatus₂Typically contain a lubricant for use in a circulating medium for lubricating moving parts.

Brief description of the invention

The invention relates to a method for monitoring the refrigerant charge of a refrigerant circuit of a refrigeration system and for filling such a refrigeration system with a refrigerant, and to a device for monitoring the refrigerant charge of a refrigeration system, wherein the refrigerant can be used as a fire extinguishing medium. In particular, the present invention enables reliable monitoring during continuous operation of the refrigeration system. The method proposed for monitoring the refrigerant charge in the refrigerant circuit is for a refrigeration system in the form of a compression refrigeration system.

A monitored compression refrigeration system for regulating the temperature of air within a vehicle includes a refrigerant delivery system having a condenser unit including at least one condenser or at least one gas cooler, an expansion device, an evaporator unit, and a compressor connected together by a refrigerant delivery line. A separate expansion tank can be connected to the refrigerant circuit by means of a valve, wherein the expansion tank is arranged in particular downstream of the expansion device on the low-pressure side. For example, temperature sensors for detecting temperature and pressure are required to monitor conditions in the circuit. Refrigerant circulates in the closed circuit. Such a system takes the form of a transcritical system, i.e. it is of a transcritical design, with carbon dioxide as the refrigerant.

When the refrigerant charge present in the refrigerant circuit changes, different parameter values change at different locations of the refrigerant circuit, wherein these parameters are charge-sensitive measurement variables. In transcritical compression refrigeration systems, a change in refrigerant charge is related to a change in pressure at a given location in the refrigerant circuit, such that the pressure can be considered a charge sensitive parameter. A change in refrigerant temperature at a given location in the refrigerant circuit is also associated with a change in refrigerant charge. The change in refrigerant subcooling at the outlet of the condenser unit can also be considered a charge sensitive parameter. A suitably placed pressure sensor is provided in the refrigeration system for detecting pressure and a suitably placed temperature sensor is provided for detecting temperature. According to the solution proposed by the present invention, a temperature sensor may be provided within the refrigeration system between the outlet of the condenser or gas cooler and the inlet of the expansion means.

If an insufficiency is clearly identified, it is advantageous to determine the state of the degree of filling on the high-pressure side. It is particularly advantageous to take these two states into account, i.e. on the high-pressure side and on the low-pressure side, in particular in connection with the method described in DE10061545a 1.

The value of each charge-sensitive parameter makes it possible to evaluate the refrigerant charge present in the refrigerant circuit. The refrigerant charge, which can also be expressed in terms of filling degree, should vary within strict limits if good refrigeration performance is to be achieved. The refrigerant charge level is defined as the quotient of the refrigerant charge and the total system volume.

Charge monitoring continues while the compressor is off. The equalized system pressure tracks the evaporating pressure, providing refrigerant that is still liquid and not evaporated. The reference temperature is the lowest temperature in the system.

p(T)＝p_crit·((T/T_crit+a)·b)^c+d

Substitution corresponding to those for refrigerant CO₂The values of (a) yield the following:

p(T)＝73.834·(((T+273.15)/304.21–0.350042)·1.54159)^4.31458–0.810014.

t should be substituted here in units of ℃ and p in bar_AbsoluteIs obtained in units.

Once evaporation is complete, the pressure follows an isochoric line corresponding to the degree of filling as the temperature increases. For this purpose, appropriate values have to be substituted into the thermal state equation. This pressure is lower than the evaporation pressure at the same temperature. Simple thermal state equations are, for example, the van der Waals equation and Redlich-Kwong equation.

The van der Waals equation is:

p(T)＝R*T/(v-b)–a/v²

wherein a is 27/64 (R T)_crit)²/p_crit，b＝R*T_crit/(8*p_crit)

If substituted into CO₂And 260kg/m³The following filling degree values were obtained:

p(T)＝189*T/((1/260)-0.0009732)–188.81/(1/260)²

wherein p is Pa, T is K,

or

p(T)＝((T+273.15)*65773–12763586)/100000

Wherein P is Ieba_AbsoluteIn units, and T is in units of deg.C.

Redlich-Kwong equation is:

p(T)＝R*T/(v-b)–a(T)/(v²+bv)

wherein a 0.42748 (T)/T_crit)^-0.5*(R*T_crit)²/p_crit，b＝0.08664*R*T_crit/p_crit

If substituted into CO₂Value of (d) and 260kg/m³The filling degree of (c) was obtained as follows:

p(T)＝189*T/((1/260)-0.00067454)-191.32*(T/304.21)^-0.5/((1/260)²+0.00067454/260)

wherein p is in Pa and T is in K

Or

p(T)＝((T+273.15)*59580–191916760*(T+273.15)^-0.5)/100000

Wherein P is Ieba_AbsoluteIn units, and T is in units of deg.C.

The temperature outside the refrigerant circuit, for example the interior temperature or the exterior temperature of the vehicle, may be used as the reference temperature. However, it is also possible to use the temperature measured in the refrigerant circuit, for example the evaporator temperature measured by an icing sensor. If a plurality of temperatures are measured, the lowest measured temperature is advantageously used.

In particular, the compressor is switched on for further charge monitoring, i.e. during continuous operation by means of suitable sensor devices, wherein a measured variable dependent on the refrigerant charge is determined. In this case, the pressure and temperature of the refrigerant are detected by pressure and temperature sensors suitably positioned on the high pressure side of the refrigerant circuit (i.e. downstream of the compressor and condenser unit, in particular the gas cooler, and upstream of the expansion device). If the measured refrigerant pressure is outside of a specified nominal pressure range associated with the detected temperature, the detected value is evaluated by an assumed charge error. If the measured pressure is below a specified nominal pressure range, or below a minimum pressure specified on the basis of the nominal pressure, which minimum pressure corresponds to a specified minimum pressure and thus to a specified minimum charge of refrigerant and depends on the current refrigerant temperature, it is assumed that there is insufficient refrigerant in the system and a corresponding signal is generated, which sets a further step in the operation. For example, a warning signal is output, which may be output in acoustic and/or visual form as service information.

In a preferred embodiment, a further step of the method proposed according to the invention comprises automatically filling the refrigerant system with refrigerant, wherein the refrigerant is stored, for example, in a storage container integrated in the system and is supplied by means of a controlled distributor. The distributor comprises in particular a controlled valve unit with a solenoid valve and a check valve which remain open until a pressure sensor installed downstream of the condenser unit or the gas cooler or the condenser detects that the pressure of the refrigerant is within a nominal pressure range, which corresponds to a nominal pressure based on the temperature detected at the outlet of the condenser unit.

For the purposes of the present invention, the term nominal pressure range refers to a pressure range that includes pressure values that deviate from the nominal pressure by at most, for example, a +/-10% tolerance, as well as specified extreme pressure values, which are determined on a temperature basis to achieve maximum efficiency. Said nominal pressure is obtained by optimizing the refrigeration capacity in relation to the compressor shaft power. One parameter in the optimization is the refrigerant temperature at the outlet of the heat-dissipating gas cooler, wherein the nominal pressure required to achieve maximum efficiency is determined by thermodynamic data of the refrigerant used or by suitable measurement of the nominal pressure.

The nominal pressure of the refrigerant is determined approximately on the basis of the temperature established at the outlet of the condenser or gas cooler. The nominal pressure can in the simplest case be determined, for example, by a linear equation or a partially linear equation according to the following relationship:

p (T) 90+2 (T-35), where p is substituted in bar, T is in c,

or

P (T) 74+2 (T-31 +5), where P is substituted in bar and T is in ° c.

When substituting the critical pressure of 74 bar, the critical temperature of 31 c and assuming a supercooling degree of 5 c, a slightly higher nominal pressure is obtained.

Another method for determining and producing better results involves using a vapor pressure curve and extrapolating it above the critical temperature, where a particular degree of supercooling, e.g., on the order of 5K, is specified. The actual relationship of steam pressure is:

p(T)＝p_crit·((T/T_crit+a)·b)^c+d

substitution for refrigerant CO₂The corresponding values of (a) were obtained as follows:

p(T)＝73.834·(((T+273.15)/304.21-0.350042)·1.54159)^4.31458–0.810014。

t should be substituted here in units of ℃ and p in bar_AbsoluteIs obtained as a unit. The nominal pressure obtained by using the supercooling degree of 5 ℃ is as follows:

p(T)＝73.834x(((T+278.15)/304.21-0.350042)·1.54159)^4.31458-0.810014。

accurately determining the optimum nominal pressure will require determining the refrigeration performance achieved and the compressor power used for this purpose. However, this would require additional pressure and temperature sensors at the compressor inlet and outlet, which would require considerable additional expenditure. For the reasons stated, simple, approximate determination by linear equations or by vapor pressure extrapolation is preferred in the present case. On the high pressure side of the transcritical compression refrigeration system, good vapor pressure extrapolation can be achieved with 5K subcooling downstream of the gas cooler. A pressure of about 80 bar prevails at a temperature of 30 c, a pressure of about 90 bar prevails at a temperature of 35 c and a pressure of about 100 bar prevails at a temperature of 40 c.

A nominal pressure value, which can be compared with the measured pressure, can be defined on the basis of a limit pressure curve plotted on a temperature/pressure diagram and the determined temperature value. On the basis of a comparison of the measured pressure with the nominal pressure, a refrigerant charge error in the refrigerant circuit is assumed. In particular, a deficiency is assumed if the measured pressure is outside a specified nominal pressure range, which is determined by a specified tolerance within the nominal pressure and the sensed temperature.

In the event of a detected deficiency, the compression refrigeration system is operated to fill in a controlled manner from the storage container via a filling opening provided on the suction side of the compressor. In an alternative embodiment, the refrigerant system is filled by an external source, such as during a shop visit.

In one embodiment, the storage container integrated in the system, for example in the form of a fill-up (top-up) cylinder, is fixedly arranged in the vehicle, for example in the trunk or a trough of the vehicle, so as not to be in the region of the engine compartment, in which the elevated temperature prevails. In particular, a filling port having an electromagnetic valve and a check valve may be provided on the suction side of the compressor, through which a prescribed amount of refrigerant is introduced into the refrigerant circuit. If gaseous refrigerant is provided, the fill port of the storage vessel is located on the low pressure side, either upstream or downstream of the evaporator unit. However, if liquid refrigerant is provided, the fill port is located upstream of the evaporator unit.

In the event that an insufficiency is detected in the refrigeration system, the pressure of the refrigerant is too low, and the refrigeration system is replenished with refrigerant, wherein the replenishment continues until a specified nominal pressure is reached, for example with the compressor turned on.

However, it may also be the case that the pressure in the refrigeration system is so low that the compressor has been switched off by the low-pressure switch. When the compression refrigeration system is at rest, a pressure equalization occurs between the high-pressure side and the low-pressure side of the refrigeration system, said equalization comprising the expansion device, the evaporator device up to the region of the compressor inlet, and an equalization pressure is built up in the refrigerant circuit of the system. In this case, the refrigerant system is initially replenished with refrigerant from the storage vessel without turning on the compressor until the pressure between the system and the storage vessel equalizes or until the opening pressure of the low pressure switch of the compressor is reached, and further filling continues after the compressor is turned on until the pressure is within the nominal pressure range.

The degree of filling of the refrigerant circuit is evaluated on the basis of the relationship between the pressure of the refrigerant and the temperature of the refrigerant or a comparable temperature in such a way that a filling error is established. The evaluation of the filling is based on the relation between pressure, temperature and filling. The evaluation result from the charging error can serve as a trigger event for filling the refrigerant circuit by the integrated storage container, wherein verification of the filling is possible. The compressor is switched on by a line controlled by the valve unit, and filling and therefore filling error compensation is continued, wherein the filling sensitive parameters pressure and temperature are measured by means of corresponding sensors. When the filling-sensitive parameters pressure and temperature return to within the specified nominal pressure range, the feed of refrigerant from the storage container is stopped and any output warning is cancelled, for example by a corresponding control signal to the valve unit. In this way, a defined filling can be maintained, which is a prerequisite for a refrigeration system with a maximum loss-free refrigeration performance.

The storage vessel is connected to the refrigerant circuit, wherein it is arranged on the low-pressure side of the compression refrigeration system on a line downstream of the evaporator device and upstream of the suction side of the compressor by means of a valve unit. In one embodiment, the storage vessel in which the refrigerant is stored includes a heating device to increase the temperature and thereby the pressure within the storage vessel so that the refrigerant system charging operation can be greatly accelerated and shortened.

In addition, the refrigerant, in particular CO, stored in the storage container₂Can be used as the fire extinguishing medium of the vehicle fire extinguishing system. Providing on demand refrigerant CO₂Fire extinguishing devices as fire extinguishing media are used in fire sources that may occur in vehicles or as a result of traffic accidents, in particular in the engine compartment. According to the invention, the refrigerant can be stored in a storage container and can be used for filling a refrigeration system and for extinguishing a fire. The fire suppression apparatus includes a fire suppressant line and a nozzle that terminates at a potential fire source in a sensitive area of the vehicle. In the event of a collision and/or fire, the automatic fire extinguishing process can be carried out by means of a suitable sensor system, in which the stored CO is₂In particular oil-free, in such a way that atmospheric oxygen is discharged from the fire hazard area in order to implement a precaution against fire. In particular, the carbon dioxide stored in the storage container is oil-free, unlike the refrigerant transported in the refrigerant circuit, being entrained on the high-pressure side due to the increased solubility of the lubricating oil used in the compressorWith oil.

In the event of a collision and/or fire, an automatic fire extinguishing sequence is triggered, in which the refrigerant present expels oxygen from the atmosphere involved in the fire without delivering any oil that would further increase the fire risk at the location of overheating.

Brief Description of Drawings

Exemplary embodiments of the present invention will be explained in more detail with reference to the accompanying drawings.

In the drawings:

FIG. 1 shows a refrigerant CO₂A schematic block diagram of a refrigeration system and fire suppression device that monitors refrigerant charge;

figure 2 shows a flow chart for monitoring refrigerant charge during ongoing operation of the refrigeration system of figure 1 with controlled charging,

figure 3 shows a graph of the relationship between the temperature of the refrigerant after emerging from the gas cooler at different evaporation temperatures and the associated nominal pressure,

fig. 4 shows a graph of the relationship between temperature and pressure of the refrigerant emerging from the gas cooler with a 5K supercooling degree, compared to a vapour pressure curve extrapolated above the critical point of the refrigerant,

figure 5 shows a graph of the relationship between the temperature of the refrigerant and the coefficient of refrigeration performance after emerging from the gas cooler with a 5K supercooling degree at different evaporation temperatures,

figure 6 shows a graph of the relationship between the temperature of the refrigerant and the degree of filling after the optimum refrigeration coefficient of performance emerges from the gas cooler,

FIG. 7 shows a pressure gauge with a temperature scale for measuring the pressure and temperature of the refrigerant when the compressor is off, an

Fig. 8 shows a pressure gauge with a temperature scale for measuring the pressure and temperature of the refrigerant when the compressor is turned on.

Various embodiments

FIG. 1 is a schematic diagram of a refrigeration system 10 utilizing a refrigerant CO₂And the system runs and can be used on a vehicle. CO 2₂Also known as carbon dioxide and R-744. Refrigeration system10 comprises a closed refrigerant circuit 46 with a compressor 12 downstream of which a gas cooler 14 is arranged on the high-pressure side. The latter is followed by an expansion device 16 through which the circulating refrigerant passing therethrough is provided in expanded and cooled form to an evaporator device 18 which is connected on a suction side 20 to the compressor 12. The

various components

12, 14, 16, and 18 of the refrigeration system 10 are connected together by pressure lines 19.

A storage vessel 22, in which a specific amount of refrigerant is stored, is connected to the suction side 20 or to the respective pressure line 19 between the output side of the evaporator device 18 and the inlet or suction side 20 of the compressor 12. The storage container 22 is connected to the pressure line 19 by a valve unit 24, the valve unit 24 including, for example, a solenoid valve and a check valve (not shown). Further, the storage vessel 22 may include a heating device 48, wherein an elevated temperature increases the pressure of the refrigerant stored in the storage vessel 22, which helps to speed up filling.

An air flow 26 to be cooled, which is blown into the interior of the vehicle, for example, is conveyed through the evaporator device 18. The gas cooler 14 is cooled by an air flow 28 conveyed away by the cooler. Further, at least one control unit 30 is shown that controls the operation of the refrigeration system 10 in a conventional manner. Furthermore, at least one control unit 30 controls the monitoring of the refrigerant charge in conjunction with the detection device, as will be explained further.

As can be inferred from fig. 1, if a refrigerant charge error is detected in the refrigeration system 10, a signal is sent from the at least one control unit 30 to the warning device 31, wherein the information output to the warning device 31 provides information about the charge error of the refrigeration system 10.

The detection means comprise a refrigerant temperature sensor 32 and a refrigerant pressure sensor 34, which are arranged on the output side 35 of the gas cooler 14. The at least one control unit 30 receives the measurement signals from the

sensors

32 and 34 and evaluates them in a manner that monitors the refrigerant charge, which is performed during continuous operation of the refrigeration system.

FIG. 1 shows a fire suppression circuit 36, representing a plurality of such circuits, beginning with the storage container 22 and ending with a vehicleFire risk point of the vehicle engine compartment. The fire suppression nozzles 38 are disposed at the end of the fire suppression circuit 36. A solenoid valve 40 connected to at least one control unit 30 via a control line 42 is arranged in the fire extinguishing line 36. At least one control unit 30 processes signals from sensors 44, which detect collisions and/or fires. For example, the sensor 44 may be a crash sensor, which may take the form of a seat belt tensioner and/or an air bag or a separate crash sensor. Alternatively or additionally, the respective sensors 44 may also include temperature sensors disposed at the potential fire location as fire sensors. A deformation sensor capable of detecting damage may additionally be included. In case of a fire caused by an accident or damage, the solenoid valve 40 in the fire extinguishing line 36 is driven by at least one control unit 30 and opens so that refrigerant CO from the storage container 22 comes out₂In a controlled manner from the extinguishing nozzle 38 through the extinguishing line 36 and purposefully extinguishing the fire or preventively exposing highly combustible areas to CO₂。

Fig. 2 shows a flow chart for monitoring the refrigerant charge of the refrigeration system 10 of fig. 1 during ongoing operation with controlled charging.

At the start 99 of monitoring the refrigerant charge of the refrigeration system 10, in a first step 100, the refrigerant temperature T_KMmessIs transmitted to the control unit 30 via a refrigerant temperature sensor 32 arranged on the output side 35 of the gas cooler 14, and the refrigerant pressure p_KMmessIs transmitted to the control unit 30 through a refrigerant pressure sensor 34 also provided at the same position. Then, it is checked in step 102 whether the compressor 12 of the refrigeration system 10 is on. The following relates to the case where the compressor 12 is turned on.

If the compressor 12 is switched off, for example because the measured pressure is so low, the compressor 12 is automatically switched off by means of a low-pressure switch, and pressure equalization between the high-pressure side and the low-pressure side takes place in step 101. In this case, the control unit 30 may open the valve unit 24, whereby refrigerant flows out of the storage vessel 22 into the refrigerant circuit 46 to a certain extent. Further filling of the refrigerant circuit 46 then continues with the compressor 12 on, as described below.

With the compressor 12 on, a measurable refrigerant temperature T is established in step 104_KMmessRelative nominal pressure p_soll(T), where various approximations may be used. The refrigerant charge error may be verified from the established refrigerant temperature and the established refrigerant pressure and based on a comparison of a limit pressure value or a nominal pressure related to the temperature. Here, the measured pressure and temperature values are compared to a limit pressure curve, which represents the limit pressure value of the associated reference temperature value and is therefore used as a basis for verifying the refrigerant charge error.

In step 106, the control unit 30 determines whether the measured refrigerant pressure p is present_KMmessOutside the nominal pressure range, which lies at the minimum pressure p_minAnd maximum pressure p_maxIn the meantime. In particular, the minimum pressure p_minBy nominal pressure p_soll(T) and determination of Δ P from which it deviates by a tolerance, e.g. allowable from nominal pressure P_soll(T) +/-10% tolerance. Nominal pressure p_soll(T) corresponds to a prescribed minimum pressure of refrigerant and thus to a prescribed minimum charge, and depends on the current refrigerant temperature T_KMmess。

If the measured refrigerant pressure p_KMmessWithin the covered tolerance range, the monitoring process is at an end state 115 and terminated. If the measured refrigerant pressure p_KMmessBelow a low specified minimum pressure p_minThe control unit 30 identifies that this is a refrigerant charge error or a deficiency in the refrigerant circuit 46 and generates further steps. A step 108 generates an alert which is output in a suitable manner.

A further step 110 involves automatically and controllably filling the refrigeration system 10 while refrigerant is stored in the storage container 22.

The control unit 30 opens the valve unit 24 so that refrigerant from the storage vessel 22 is fed through the pressure line 19 to the refrigerant circuit 46 on the suction side 20 of the compressor 12 until a shortage of refrigerant in the refrigeration system 10 is compensated for. Filling of the refrigeration system 10 is accompanied by steps112 measured refrigerant pressure p_KMmessWith nominal pressure p_soll(T) comparison. If the measured refrigerant pressure deviates from the nominal pressure by a +/-determined tolerance, e.g., 2%, within the nominal pressure range, the control unit 30 outputs a signal to terminate the filling and to cancel the warning in step 114. The filling process then ends at the end state 115.

FIG. 3 is a graph showing the measured refrigerant temperature T in degrees Celsius after emerging from the gas cooler 14_KMmessAnd the relative nominal pressure p of the refrigerant carbon dioxide in bar_soll(T) a graph of the relationship between. The first curve K1 shows here the prescribed relationship for the evaporation temperature t0 at +10 ℃ and the second curve K2 shows the prescribed relationship for the evaporation temperature t0 at-10 ℃.

Fig. 4 shows the measured refrigerant temperature T in ° c of the refrigerant carbon dioxide emerging from the gas cooler 14 of the constantly filled refrigerant circuit 46 with a supercooling degree of 5K with a third curve K3_KMmessAnd a graph of the relationship between pressure p in bar. By way of comparison, an extrapolated vapor pressure curve K4 is also plotted on the graph, above the critical point PC of the refrigerant carbon dioxide.

FIG. 5 is a graph showing the measured refrigerant temperature T in degrees Celsius of the refrigerant carbon dioxide after emerging from the gas cooler 14_KMmessAnd by way of example a diagram of the relationship between the coefficient of refrigeration performance epsilon with 5K subcooling. The fifth curve K5 shows here the prescribed relationship for the evaporation temperature t0 at +10 ℃ and the sixth curve K6 shows the prescribed relationship for the evaporation temperature t0 at-10 ℃.

FIG. 6 is a graph showing, by way of example, the measured refrigerant temperature T in degrees Celsius of the refrigerant carbon dioxide after emerging from the gas cooler 14_KMmessAnd a graph of the relationship between the filling degree F at the optimum refrigeration performance coefficient epsilon in g/liter. In the selected example, the evaporating temperature T0 amounts to 0 ℃, the compressor 12 has an efficiency of 0.8, and the volume of the gas cooler 14 is about twice the volume of the evaporator unit 18.

FIG. 7 shows a press with temperature scaleAn example of a force meter for measuring the refrigerant pressure p in bar when the compressor 12 is off_KMmessAnd a refrigerant temperature T of refrigerant carbon dioxide in units of DEG C_KMmess. In the example shown, the filling level amounts to about 260 g/L. In this case, the refrigerant carbon dioxide is in a liquid state.

Fig. 8 shows an example of a pressure gauge with a temperature scale for measuring the refrigerant pressure p in bar when the compressor 12 is turned on_KMmessAnd a refrigerant temperature T of refrigerant carbon dioxide in units of DEG C_KMmess. In the example shown, the supercooling degree is about 5K. In this case, the refrigerant carbon dioxide is in a supercritical state.

The invention is not limited to the exemplary embodiments described and aspects emphasized herein. On the contrary, many modifications are possible within the abilities of the person skilled in the art, within the scope defined by the claims.

List of reference numerals

10 refrigeration system

12 compressor

14 gas cooler

16 expansion device

18 evaporator device

19 pressure line

20 suction side

22 storage container

24 controlled valve unit

26 air flow to be cooled

28 air flow conveyed away by a gas cooler

30 control unit

31 alarm device

32 refrigerant temperature sensor

34 refrigerant pressure sensor

35 output side of gas cooler

36 fire extinguishing line

38 fire extinguishing nozzle

40 solenoid valve

42 control circuit

44 sensor for detecting a collision and/or a fire

46 refrigerant circuit

48 heating device

99 start of

100 … 114 step

115 end state

Degree of filling of F

p pressure

Critical point of PC

p_KMmessPressure of refrigerant

p_soll(T) nominal pressure

t0 Evaporation temperature

T_KMmessTemperature of refrigerant

Coefficient of performance of epsilon refrigeration

First curve of K1

Second curve of K2

Third curve of K3

K4 vapor pressure curve

Fifth curve of K5

K6 sixth curve.

Claims

1. Method for monitoring a refrigerant charge in a refrigerant circuit (46) of a refrigeration system (10), the refrigeration system (10) having a compressor (12), a gas cooler (14), an expansion device (16) and an evaporator device (18), wherein the charge monitoring when the compressor (12) is switched off comprises the steps of:

-measuring at least one temperature of refrigerant in the refrigerant circuit (46) at the evaporator device (18), and a second refrigerant temperature in the refrigerant circuit (46) at the gas cooler (14);

-measuring a refrigerant pressure in the refrigeration system (10);

-calculating a nominal pressure by using the minimum of the at least two measured temperatures, and the nominal pressure is the minimum of the evaporation pressure at that temperature and the gas pressure of the refrigerant at that temperature and at a prescribed fixed density;

-establishing a refrigerant charge error if the measured pressure is outside a nominal pressure range, and the nominal pressure range comprises pressure values deviating at most from the nominal pressure by a specified tolerance.

2. Method according to claim 1, characterized in that the temperature outside the refrigerant circuit (46) is measured.

3. The method according to claim 1, characterized in that the specified gas density amounts to 260 g/l.

4. A method according to one of claims 1 to 3, characterized in that if the pressure is more than 10% below the nominal pressure, it is indicative of a shortage of refrigerant.

5. Method according to one of claims 1 to 3, characterized in that the refrigerant is CO₂。