EP4248151B1 - Method for detecting leaks in a refrigerating circuit of a compression refrigeration machine, and leak detection system - Google Patents

Description

A method for detecting leaks in a refrigeration circuit of a compression refrigeration machine and a leak detection system for detecting the leakage of a refrigerant in a refrigeration circuit of a compression refrigeration machine are described, wherein the refrigeration circuit has at least one evaporator, one compressor, one condenser, one pressure reducer and one internal heat exchanger, which are connected to one another via lines, wherein a refrigerant is guided in the lines and the internal heat exchanger is arranged between the evaporator and the compressor and between the condenser and the pressure reducer.

background

Compression refrigeration machines use the heat of vaporization when the state of a refrigerant changes to cool a room or another device or coolant, whereby the refrigerant is circulated in the compression refrigeration machines.

Refrigerants are distinguished from conventional coolants (brine, etc.) in that they can transfer heat energy along the temperature gradient, which is not possible with a conventional coolant.

Often, refrigerants are used that are hazardous to health or the environment and therefore must not escape from the refrigeration circuit.

In addition, refrigerants are known that are not hazardous to health or the environment. With these refrigerants, the cooling circuit and thus the amount of refrigerant in the cooling circuit should also be kept to a minimum.

State of the art

In order to keep the leakage of refrigerant from a refrigeration circuit to a minimum, various solutions have been proposed in the prior art, whereby the known solutions comprise additional devices and/or are complex.

For example, EN 10 2006 039 925 A1 a method for determining the loss of refrigerant in refrigeration systems is known, whereby in systems with suction circuits, suction is carried out up to a predetermined pressure on the suction side of the compressor, whereby the high pressure that occurs on the pressure side of the compressor is measured and the measured high pressure is compared with the reference high pressure resulting from the target filling quantity of the refrigerant and evaluated. In a further embodiment, the condenser is switched off and the pressure on the pressure side of the compressor is increased up to a reference pressure, whereby the suction pressure that occurs on the suction side of the compressor is measured and is compared with a reference suction pressure resulting from the target filling quantity of the refrigerant.

DE 39 13 521 A1 discloses a method for detecting leaks in the refrigerant circuit of refrigeration systems, which detects a refrigerant leak, whereby the pressure and temperature of the evaporated refrigerant (suction gas) on the suction side of the compressor are measured and the difference between the actual values of suction gas pressure and suction gas temperature is compared with a setpoint value. The setpoint value is determined by the difference between suction gas pressure and suction gas temperature, which usually exists when the refrigeration system is intact. A deviation between the actual and setpoint difference is interpreted as a leak.

The known methods require pressure measuring devices in order to be able to measure the pressure in the refrigeration circuit in addition to temperatures. The known methods and systems are therefore complex, which means that in addition to increased costs, they also require a lot of maintenance. This can also lead to misinterpretations or late detection of leaks, so that, for example, a relatively large amount of coolant has to escape before the leak is detected and interpreted as such.

In EP 1 013 738 A1 A method for detecting leaks in a refrigeration circuit of a compression machine is disclosed. The refrigeration circuit has at least one evaporator, one compressor, one gas cooler, one pressure reducer and one internal heat exchanger, which are connected to one another via lines, with a coolant being carried in the lines. The disclosed method is based on the fact that an odor and/or colorant is added to the carbon dioxide as a coolant, whereby the leakage of the CO2 can be perceived and/or seen by humans through their sense of smell. Accordingly, only a solution for rapid detection of a leak through human sensory perception is proposed.

In WO 2020/067296 A1 A device for detecting leaks in cooling circuits is disclosed, which has a calculation unit and a detection unit. A leak in a cooling circuit is determined via the temperature ratio between the measured and estimated temperature at the compressor outlet. The amount of leaking coolant correlates with the degree of deviation between the actual value and the estimated value.

In GB 2 576 644 A discloses a control system that has a leak detection and a supply control system. Based on the temperature at the outlet of the condenser, the temperature at the outlet of the economizer, the outside temperature and the injection temperature in the compressor, a leak is detected and the supply control device causes a leak detection agent to be fed into the refrigeration circuit. The leak detection agent is designed as a fluorescent agent. This allows a maintenance employee to locate a leak by shining the ultraviolet rays of an ultraviolet lamp onto a specific location.

Task

In contrast, the task is to provide a solution for detecting leaks in a refrigeration circuit, which is simple, provides reliable detection of leaks, and continuously monitors the refrigeration circuit is monitored and even small leaks can be detected.

Solution

• mindestens im Bereich des inneren Wärmeübertragers
  1. a) in der Leitung vom inneren Wärmeübertrager zum Druckminderer ein erster Messpunkt,
  2. b) in der Leitung vom Verdampfer zum inneren Wärmeübertrager ein zweiter Messpunkt,
  3. c) in der Leitung vom Verflüssiger zum inneren Wärmeübertrager ein dritter Messpunkt, und
  4. d) in der Leitung vom inneren Wärmeübertrager zum Verdichter ein vierter Messpunkt
  für mindestens eine thermodynamische Zustandsgröße des Kältemittels zur Bestimmung der Temperatur des Kältemittels definiert sind, wobei die Temperatur direkt gemessen oder durch Messung des Drucks in Verbindung mit einem Stoffwert des Kältemittels indirekt erfasst wird,
• von der am dritten Messpunkt bestimmten Temperatur die am ersten Messpunkt bestimmte Temperatur des Kältemittels subtrahiert wird und daraus ein erster Wert ermittelt wird,
• von der am vierten Messpunkt bestimmten Temperatur die am zweiten Messpunkt bestimmte Temperatur des Kältemittels subtrahiert wird und daraus ein zweiter Wert ermittelt wird,
• der erste Wert und der zweite Wert in ein Verhältnis gesetzt werden,
• ein daraus gebildeter dritter Wert mit einer Referenz verglichen wird, und
• eine Leckage erkannt wird, wenn der dritte Wert von der Referenz abweicht.

The above-mentioned object is achieved by a method according to claim 1 for detecting leaks in a refrigeration circuit of a compression refrigeration machine, wherein the refrigeration circuit has at least one evaporator, one compressor, one condenser, one pressure reducer and one internal heat exchanger, which are connected to one another via lines, wherein a refrigerant is guided in the lines, wherein the internal heat exchanger is arranged between the evaporator and the compressor and between the condenser and the pressure reducer, wherein

• at least in the area of the internal heat exchanger
  1. a) a first measuring point in the line from the internal heat exchanger to the pressure reducer,
  2. b) a second measuring point in the line from the evaporator to the internal heat exchanger,
  3. c) a third measuring point in the line from the condenser to the internal heat exchanger, and
  4. d) a fourth measuring point in the line from the internal heat exchanger to the compressor
  are defined for at least one thermodynamic state variable of the refrigerant for determining the temperature of the refrigerant, whereby the temperature is measured directly or indirectly by measuring the pressure in conjunction with a material value of the refrigerant,
• the temperature of the refrigerant determined at the first measuring point is subtracted from the temperature determined at the third measuring point and a first value is determined from this,
• the temperature of the refrigerant determined at the second measuring point is subtracted from the temperature determined at the fourth measuring point and a second value is determined from this,
• the first value and the second value are put into a ratio,
• a third value formed from this is compared with a reference, and
• a leak is detected if the third value deviates from the reference.

The method provides a way of monitoring the refrigeration circuit and detecting leaks using a simple structure. Once the leak has been detected, technical measures, organizational measures or behavioral measures can be initiated. For example, the affected section of the line can be disconnected from the refrigeration circuit. Warning messages can be issued, e.g. acoustically and visually. Warning messages can also be sent (via SMS, email, messenger, etc.). For example, employees and/or service staff can be informed. Doors can also be locked, for example to block access to the room in which the refrigeration machine is located. Windows can also be opened to ventilate the room. Media-carrying ducts can also be regulated accordingly so that, for example, no coolant or the like is fed into a system. Ventilation systems can also be controlled accordingly. Once a leak has been detected, a wide variety of measures can therefore be initiated. In particular, several measures can be initiated simultaneously or in a fixed sequence.

In further embodiments, the recorded values can also be used to determine the extent of a leak, so that measures can be initiated depending on this, whereby, for example, a certain sequence of measures is observed depending on the extent of the leak and/or definable measures must be initiated immediately.

In other versions, for example, the temperature at the measuring points can be determined at set intervals, e.g. every time the compressor switches off, or continuously, whereby in other versions it is then also possible to immediately detect a leak.

For this purpose, temperature or pressure recording devices are required at at least 4 measuring points, which are located in the area of the internal heat exchanger. The evaluation is carried out by a control system, which calculates the recorded temperatures at the 4 measuring points using the specified calculation and thus generates a third value. This third value enables a conclusion to be drawn as to whether there is a leak in the cooling circuit.

The method is based on the determination of a leak based on the temperatures recorded. To do this, the temperatures can either be measured directly at the measuring points, or the pressures are measured at the measuring points and the temperature is determined based on the measured pressures using the material properties of the refrigerant. In this way, a leak can be determined using the thermodynamic state variables.

In further versions, the measured or determined temperatures and/or the measured pressures and material values as well as the first, second and third values can be offset against correction factors. The correction factors can refine the result and, for example, prevent misinterpretations. In further versions, correction factors can be, for example, the material values of the corresponding refrigerant itself, so that the temperature is determined via the pressure as a thermodynamic state variable and the material value. In addition to material values, other correction factors can also include, for example, pressures or the outside temperature.

In further embodiments, the internal heat exchanger can be defined by a section where the line between the evaporator and the compressor and the line between the condenser and the pressure reducer for internal heat transfer run together. The distance between these line sections is very small so that heat transfer can occur. The distance between these line sections can also approach zero or be "zero", so that the line between the evaporator and the compressor and the line between the condenser and the pressure reducer are also in direct contact. It is also possible for a heat transfer element to be provided between these line sections. This means that a relatively high heat transfer is achieved even when there is a distance between these line sections. For example, internal heat transfer devices can be used, with one line section surrounding the other line section and the coolants carried in it flowing through the line sections in countercurrent or cocurrent.

The internal heat exchanger can therefore be, for example, a short section in the refrigeration circuit in which the flow and return of the refrigerant run alongside each other in order to mutually influence the temperature of the refrigerant. However, other heat transfer devices can also be used for the internal heat exchanger, which serves to mutually influence the temperature in the flow and return.

The internal heat exchanger is generally used to transfer energy from the refrigerant that is fed from the condenser to the evaporator to the refrigerant (suction gas) that is sucked out of the evaporator via the compressor. This results in a higher subcooling of the refrigerant and thus a higher usable cooling capacity.

The determined third value is compared with a reference, whereby both the third value and the reference are dimensionless.

The method takes advantage of the fact that a leak in the refrigeration circuit inevitably leads to a change in temperature in the refrigeration circuit. To ensure that a change in temperature does not automatically lead to an interpretation as a leak, although temperature fluctuations can occur permanently in a refrigeration circuit due to various circumstances, the temperatures on the inner heat exchanger are put into a ratio according to the calculation described above and the third value is determined from this. The third value is independent of normal fluctuations (e.g. temperature increase along pipes, etc.). In the case of normal fluctuations, the temperatures at the 4 measuring points change accordingly, so that the third value essentially hardly changes or that the third value remains remains less than or equal to a reference. If a leak causes a temperature change at one of the 4 measuring points, this results in a change in the third value, which then deviates from the reference. This means that there is a leak and the control system can initiate appropriate measures to reduce the leak to a minimum and initiate further measures.

If the first or second value becomes "0", the controller can replace the corresponding value with a substitute value of, for example, 0.0001, so that the calculation can continue and no mathematical error occurs. This is intended in particular to prevent division by "0". Other substitute values can also be used within the scope of the calculation specified by the controller. This depends in particular on the accuracy to be achieved.

In the method, the first value can be divided by the second value, whereby a leak is then detected if the resulting third value is above a reference.

However, the method can also involve dividing the second value by the first value, whereby a leak is then detected if the resulting third value is below a reference.

The deviation from the reference is defined in the methods described here for determining leaks by either falling below a reference or exceeding a reference. The deviation should therefore not be understood in such a way that both exceeding and falling below a reference indicate a leak. The Determining whether a leak is present or not depends, as explained below, on the calculation method chosen. With one calculation method, a leak can only be determined if a specified reference is exceeded or not met.

The third value can be calculated according to the first alternative and then inverted, whereby a leak is then detected if the third value is below the reference. From a mathematical point of view, the method described here can therefore also be used in a corresponding manner if the third value is inverted or the second value is divided by the first value.

Overall, a leak can be concluded if the third value deviates from the reference, whereby, depending on the calculation, either values above the reference or below the reference indicate a leak.

The corresponding calculations are therefore to be regarded as equivalent and can mathematically result in a third value using different calculation methods, which in turn is representative of a leakage if the reference is not reached or exceeded, depending on the calculation method chosen.

In further embodiments, at least one additional measuring point can be defined in the refrigeration circuit, which is used to calculate the first value, the second value and/or the third value. In particular, the (measurement) result can be refined by using additional measuring points.

The determination of the values and the comparison with the reference can be carried out continuously or at specified intervals The intervals that can be set can, for example, be several seconds or minutes. The intervals can also be set by the components of the refrigeration circuit, whereby, for example, a leakage check is carried out using a method described herein whenever the compressor switches off.

Continuous measurement has the advantage that a leak can be detected immediately and measures can be taken immediately.

The reference can be a pre-determined reference value or a reference function.

A third value determined in advance through tests can be stored as a reference value in a control system or a memory connected to it and can be used as a reference for subsequent calculations. The compression refrigeration machine or a system comprising the compression refrigeration machine can be designed to be capable of learning or have a control system capable of learning, so that third values determined through tests can be stored as reference values in a memory and/or adjusted.

The reference value can be determined when the compression refrigeration machine is in operation, whereby the temperatures of the refrigerant are recorded at the 4 measuring points until the refrigerant reaches a specified target value at a defined point in the refrigeration circuit. The third value that prevails when the target value of the refrigerant is reached is then saved as the reference value. The generated third values are then continuously or at intervals compared with the reference value while the compression refrigeration machine is in operation.

The reference function can be formed from several values of the determined first, second, third and/or fourth temperatures and the position of the subsequently determined third values relative to the reference function can be determined, whereby a leak is detected if the third value deviates from the reference function as described above and, for example, is above or below the reference function.

In particular, the reference function can be generated from the values for several target temperatures of the refrigerant.

A reference function can be created by determining the corresponding third values for different target temperatures of the refrigerant. The reference function is then created from these third values. The behavior of a leak shows a pattern that can be represented as a function. This reference function represents a separation in the coordinate system. Depending on the calculation, all values above or below the reference function correspond to a leak, and the other values do not.

Furthermore, the reference function can also be formed from pressures and material values of the refrigerant for setpoint values of the refrigerant.

This allows for simple and reliable monitoring of a refrigeration circuit.

After calibrating the compression refrigeration machine and a related system, measured values can be continuously recorded at the 4 measuring points for each compressor cycle and compared with the reference value. The resulting number (third value) can be compared with the pre-stored reference or reference function.

For example, there is a leak if the comparison value is above or below the reference function. Once a leak has been detected, the evaporator can be separated from the cooling circuit. The compressor can then be switched off and shut-off valves that enclose the evaporator, for example, can be activated. This allows a cooling cell (on the evaporator) to be separated from the cooling circuit, for example, and prevents further refrigerant leakage. After that, only the refrigerant that is still contained in the shut-off area can leak out.

To isolate the evaporator as a critical point in the refrigeration circuit, valves arranged in the flow and return lines of the evaporator in the refrigeration circuit can be closed if the third value is above the reference.

In addition, further measures can be taken after a leak is detected, as described above.

The above-mentioned object is also achieved by a leak detection system according to claim 10 for detecting the leakage of a coolant in a refrigeration circuit of a compression refrigeration machine, comprising a refrigeration circuit with at least one evaporator, one compressor, one condenser, one pressure reducer and one internal heat exchanger, which are connected to one another via lines, wherein a coolant is guided in the lines, wherein the internal heat exchanger is arranged between the evaporator and the compressor and between the condenser and the pressure reducer, wherein the

1. a) in der Leitung vom inneren Wärmeübertrager zum Druckminderer einen ersten Messpunkt,
2. b) in der Leitung vom Verdampfer zum inneren Wärmeübertrager einen zweiten Messpunkt,
3. c) in der Leitung vom Verflüssiger zum inneren Wärmeübertrager einen dritten Messpunkt, und
4. d) in der Leitung vom inneren Wärmeübertrager zum Verdichter einen vierten Messpunkt

für die Erfassung mindestens einer thermodynamischen Zustandsgröße des Kältemittels zur Bestimmung der Temperatur des Kältemittels aufweist, wobei die Temperatur direkt messbar oder durch Messung des Drucks in Verbindung mit einem Stoffwert des Kältemittels indirekt erfassbar ist,
ferner aufweisend eine Steuerung, die nach Maßgabe eines der vorstehend beschriebenen Verfahren

• von der am dritten Messpunkt bestimmten Temperatur die am ersten Messpunkt bestimmte Temperatur des Kältemittels subtrahiert und daraus einen ersten Wert ermittelt,
• von der am vierten Messpunkt bestimmten Temperatur die am zweiten Messpunkt bestimmte Temperatur des Kältemittels subtrahiert und daraus einen zweiten Wert ermittelt,
• den ersten Wert und den zweiten Wert in ein Verhältnis setzt,
• daraus einen dritten Wert bildet und diesen mit einer Referenz vergleicht,
• eine Leckage erkennt, wenn der dritte Wert von der Referenz abweicht, und
• im Vorlauf und im Rücklauf des Verdampfers im Kältekreis angeordnete Ventile schließt, wenn der dritte Wert über oder unter der Referenz liegt.

Compression refrigeration machine at least in the area of the internal heat exchanger

1. a) a first measuring point in the line from the internal heat exchanger to the pressure reducer,
2. b) a second measuring point in the line from the evaporator to the internal heat exchanger,
3. c) a third measuring point in the line from the condenser to the internal heat exchanger, and
4. d) a fourth measuring point in the line from the internal heat exchanger to the compressor

for detecting at least one thermodynamic state variable of the refrigerant to determine the temperature of the refrigerant, wherein the temperature can be measured directly or indirectly by measuring the pressure in conjunction with a material value of the refrigerant,
further comprising a controller which, in accordance with one of the methods described above,

• the temperature of the refrigerant determined at the first measuring point is subtracted from the temperature determined at the third measuring point and a first value is determined from this,
• the temperature of the refrigerant determined at the second measuring point is subtracted from the temperature determined at the fourth measuring point and a second value is determined from this,
• the first value and the second value are related,
• creates a third value and compares it with a reference,
• detects a leak if the third value deviates from the reference, and
• valves arranged in the flow and return of the evaporator in the refrigeration circuit close when the third value is above or below the reference.

The leak detection system is simple in design and therefore neither maintenance-intensive nor prone to failure. The leak detection system is therefore advantageous for detecting leaks because it provides reliable leak detection, with interval or continuous checking possible.

With the leak detection system, the measuring points can be located in the immediate vicinity or inside the internal heat exchanger.

The measuring points can, for example, be located inside the internal heat exchanger and in adjacent pipe sections or in pipe sections that are located immediately after or before the adjacent pipe sections.

The leak detection system has suitable measuring devices for recording the temperature at the measuring points. For this purpose, temperature or pressure sensors can be arranged at the measuring points to record the temperature or pressure of the refrigerant in the lines, whereby the temperature can be determined directly or indirectly with the aid of the material value of the refrigerant, as already stated above for the method.

The leak detection system and the compression refrigeration machine can, for example, be part of a refrigerated cabinet, a cold storage room or a refrigeration system. The determined reference values or the reference function can be adopted for refrigerated cabinets, cold storage rooms or refrigeration systems of the same construction, so that for identical units a one-time calibration of a unit is sufficient to determine the references. This ensures that for identical units not for each unit a calibration must be carried out separately according to the procedures described above and a reference value or a reference function can be adopted.

Further advantages, features and design options emerge from the following description of figures of non-limiting embodiments.

Short description of the drawings

Fig. 1

eine schematische Darstellung eines Kältekreises einer Kompressionskältemaschine mit einer Einrichtung zur Erfassung von Leckagen; und

Fig. 2

eine weitere schematische Darstellung eines Kältekreises einer Kompressionskältemaschine.

In the drawings shows:

Fig.1

a schematic representation of a refrigeration circuit of a compression refrigeration machine with a device for detecting leaks; and

Fig. 2

another schematic representation of a refrigeration circuit of a compression refrigeration machine.

In the drawings, elements provided with the same reference symbols correspond essentially to one another, unless otherwise stated. Furthermore, we refrain from showing and describing components that are not essential to understanding the technical teaching disclosed herein. In the following, the reference symbols are not repeated for all elements already introduced and shown, provided that the elements themselves and their function have already been described or are known to a person skilled in the art.

Detailed description of implementation examples

The figures show exemplary designs of refrigeration circuits 100 of a compression refrigeration machine and described below, which are part of a refrigerated cabinet, a cold storage room or a cooling system. Refrigerated cabinets are, for example, those that are used in food retail to present chilled goods. In relation to the various types of refrigerated cabinets, cold storage rooms or cooling systems, the term refrigeration systems is also used below.

A refrigerant is included in the refrigeration circuits 100. Various refrigerants that are available on the market can be used as refrigerants, whereby the refrigerants used depend on the properties and the target values to be achieved, i.e. cooling performance. For example, R134a or R1234ze can be used as refrigerants. Other refrigerants can also be used.

Fig.1 shows a schematic representation of a refrigeration circuit 100 of a compression refrigeration machine with a device for detecting leaks, and Fig.2 shows a further schematic representation of a refrigeration circuit 100, wherein shut-off valves 200 are shown.

The refrigeration circuits 100 of Fig.1 and 2 each have an evaporator 120, a compressor 130, a condenser 140, a throttle element 150 as a pressure reducer and a line arrangement 100. In addition, the refrigeration circuits 100 each have an internal heat exchanger 160, which in the refrigeration circuit 100 of Fig.2 is not shown. For the refrigeration circuit 100 of Fig.2 Two shut-off valves 200 are shown, which are also used in the refrigeration circuit 100 of Fig.1 are provided in order to be able to separate the evaporator 120 from the rest of the refrigeration circuit 100. In addition, a control is provided which regulates the operation of the components of the respective refrigeration circuit 100. The Refrigeration circuits 100 may include additional components that are not shown for reasons of clarity and for a better understanding of the technical teaching disclosed herein.

The refrigeration circuit 100 of Fig.1 For example, it additionally has a dryer 180, which is designed as a filter dryer and filters the coolant from impurities.

In the cooling circuit 100 of Fig.1 A high-pressure monitor 190 and a low-pressure monitor 192 are also arranged. The high-pressure monitor 190 is used to control the condenser 140 and protects it from excessive pressures, for which purpose the output of the compressor 130 can be regulated. The low-pressure monitor 192 is used to control the compressor 130 and regulates it in accordance with the pressure prevailing in the corresponding line section of the line arrangement 110.

The compressor 130 serves to convey the coolant in the refrigeration circuit 100 and in particular in the line arrangement 110. The compressor 130 can be, for example, a piston compressor or a speed-controlled pump. Speed-controlled pumps have the advantage that their delivery capacity can be continuously adjusted. This allows very fine adjustments of the delivery volume to be achieved. In this case, coolant is sucked in from the evaporator 120 via the compressor 130. The coolant sucked in by the compressor 130 reaches the condenser 140, wherein the coolant in the condenser 140 is cooled with the aid of a heat exchanger and a fan or the like, for example with ambient air. The cooled coolant then reaches the evaporator 120 via the line arrangement, wherein the coolant flows into the evaporator 120 through a corresponding control of the throttle element 150 and through the Change of state during phase change absorbs heat from the environment and thus cools the environment. For this purpose, the evaporator 120 can have a heat exchanger and a fan. The throttle element 150 can be an expansion valve, for example.

The internal heat exchanger 160 is arranged between the compressor 130 and the evaporator 120 in the suction gas line of the line arrangement 110 and between the condenser 140 and the throttle element 150 in the corresponding high-pressure line section of the line arrangement 110 of the refrigeration circuit 100. In the exemplary embodiment, the internal heat exchanger 160 is formed by line sections of the line arrangement 110 which run along one another in such a way that the temperature of the refrigerant is mutually influenced. Energy is thus transferred from the refrigerant which is led from the condenser 140 to the evaporator 120 to the refrigerant (suction gas) which is sucked out of the evaporator 120 via the compressor 130. This results in a higher subcooling of the refrigerant and a higher usable cooling capacity.

The inner heat exchanger 160 is located in the Fig.1 shown section 170.

In section 170 of the refrigeration circuit 100 Fig.1 4 temperatures are measured at corresponding measuring points 172, 174, 176 and 178. At the first measuring point 172 a temperature (1) of the refrigerant is measured, at the second measuring point 174 a temperature (2) of the refrigerant is measured, at the third measuring point 176 a temperature (3 ) of the refrigerant and at the fourth measuring point a temperature (4) is measured.

Instead of a direct temperature measurement, the temperatures (1), (2), (3), (4) can also be determined by measuring pressures via pressure measuring devices at the measuring points 172, 174, 176, 178, whereby the temperatures of the refrigerant are calculated using the respective material value of the refrigerant for the measured pressures, so that the temperatures (1), (2), (3), (4) can also be determined in this way and the following procedures can be applied accordingly to detect leaks.

The measuring points 172, 174, 176, 178 can each be located in the immediate vicinity of the inner heat exchanger 160, but without measuring the temperature of the coolant in the inner heat exchanger 160. At the measuring points 172, 174, 176, 178, the temperature of the coolant is then no longer influenced by the coolant in the other line section of the inner heat exchanger 160. However, the temperatures or pressures in the inner heat exchanger 160 can also be measured to determine the temperatures (1), (2), (3), (4).

The heat exchanger 160 can be designed in different ways. For example, line sections can be provided that run next to each other or one line section can surround the other. In further embodiments, heat exchangers designed in other ways can also be provided.

1. (1) die am ersten Messpunkt (172) gemessene Temperatur ist,
2. (2) die am zweiten Messpunkt (174) gemessene Temperatur ist,
3. (3) die am dritten Messpunkt (176) gemessene Temperatur ist,
4. (4) die am vierten Messpunkt (178) gemessene Temperatur ist, R3 ein dritter Wert ist: $$\frac{\left(\left(3\right)-\left(1\right)\right)}{\left(\left(4\right)-\left(2\right)\right)}=\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}3$$
   

Temperature sensors are provided in the corresponding line sections of the line arrangement 110 to measure the temperatures (1), (2), (3) and (4). The measured temperatures are transmitted to the controller via signal lines. The controller continuously calculates the temperatures (1), (2), (3) and (4) according to the following equation (1), where

1. (1) is the temperature measured at the first measuring point (172),
2. (2) is the temperature measured at the second measuring point (174),
3. (3) is the temperature measured at the third measuring point (176),
4. (4) is the temperature measured at the fourth measuring point (178), R3 is a third value: $$\frac{\left(\left(3\right)-\left(1\right)\right)}{\left(\left(4\right)-\left(2\right)\right)}=\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}3$$
   

ein erster Wert R1 gebildet. Aus $$\left(\left(4\right)-\left(2\right)\right)=R2$$

wird ein zweiter Wert R2 gebildet. Damit kann Gleichung (1) auch durch $$\frac{R1}{R2}=R3$$

dargestellt werden.This involves $$\left(\left(3\right)-\left(1\right)\right)=R1$$

a first value R1 is formed. $$\left(\left(4\right)-\left(2\right)\right)=R2$$

a second value R2 is formed. This means that equation (1) can also be $$\frac{R1}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}2}=\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">R</figure-callout>}3$$

are displayed.

The calculated value R3 is then compared with a reference value R0. If the value R3 is greater than the reference value R0, there is a leak in the refrigeration circuit 100. The control then activates the shut-off valves 200 (see Fig.2 ), whereby the evaporator 120 is separated from the refrigeration circuit 100. In addition, at least the compressor 130 is switched off. This ensures that in the event of a leak, only the refrigerant that is still contained in the shut-off area can escape.

The reference value R0 is specified in advance or determined by calibration.

In the first example mentioned above, the temperature of the refrigerant after the condenser 140 is measured. As soon as the temperature of the refrigerant after the condenser 140 has reached a predetermined value, the compressor 130 is switched off. The temperature of the refrigerant after the condenser 140 is then still measured. If this temperature falls below a limit value, the compressor 130 is switched on again and cooling of the refrigerant begins again.

After a definable number of cycles, the temperatures (1), (2), (3), (4) at the measuring points 172, 174, 176 and 178 can be used to calculate a reference value R0. The temperatures (1), (2), (3), (4) at the measuring points 172, 174, 176 and 178 are recorded when the refrigerant has reached the setpoint at the test point after the condenser 140.

The measured temperatures (1), (2), (3), (4) are then offset against each other according to equation (1), whereby, for example, the value R3 calculated for the first time can be used as the reference value R0. The reference value R0 is stored in the control or an associated memory. Subsequently, all other values R3 calculated after calibration are compared with the stored reference value R0. If the measured values R3 exceed the reference value R0, there is a leak and the control initiates the above-mentioned measures. Additional measures can also be initiated by the control, whereby, for example, components of the evaporator 120 and the Condenser 140 can be switched off. In addition, the throttle element 150 and other valves can also be switched off or closed in order to prevent the flow of refrigerant.

Since a leak in the refrigeration circuit 100 can be ruled out during initial commissioning because the components are checked before assembly and the refrigeration system is checked before, for example, a coolant is introduced into the lines, there is no leak. Therefore, the values recorded during initial commissioning can be used as reference values.

Instead of a setpoint at a defined point, for example in the flow direction according to the arrows in the Fig.1 and 2 behind the condenser 140, the corresponding temperatures (1), (2), (3), (4) are recorded for several different setpoints and several reference values R0 are calculated from them. These reference values R0 are then used to create a function. The function then forms a reference function RF0. In the coordinate system, all values R3 determined afterwards are either below the reference function RF0, on the reference function RF0 or above the reference function RF0. If the values R3 determined are above the reference function RF0, there is a leak and the control system can initiate appropriate measures.

The compressor 130 can then be switched off and the shut-off valves 200 (see Fig. 2 ) that surround the evaporator 120 are activated. This separates the cooling cell (on the evaporator 120) from the refrigeration circuit 100 and prevents further leakage of coolant. After this, only the coolant that is in the sealed area can escape. of the refrigeration circuit 100 or the line arrangement 110 is still contained.

In particular, in refrigeration systems, the structure is chosen such that essential components of the refrigeration circuit 100 are accommodated within a housing or a tray is provided which can collect escaping coolant. Only the evaporator 120 represents a critical point, since it is connected to the room to be cooled, so that, for example, escaping coolant could enter this room. In the event of a leak, regardless of whether this occurs between the shut-off valves 200 or in the rest of the line arrangement 110, shutting off the evaporator 120 is therefore a sufficient measure to prevent coolant from escaping into the environment. Of course, further shut-off devices can be provided, so that, for example, the line arrangement 110 can be divided into many smaller sections, so that the amount of escaping coolant is always reduced to a minimum.

The exemplary design shown with the two shut-off valves 200 in the flow and return of the evaporator 120 enables the reduction of refrigerant leakage to an absolute minimum with regard to the interface that is hazardous to the environment and health.

In further embodiments, instead of the calculation given above, equation (3) can be divided by equation (2), whereby the third value R3 is then inverted compared to equation (4). A leak is then concluded if the third value R3 is smaller than an associated inverse reference value R0 ^-1 . This applies analogously to a reference function.

In further versions, the temperatures (1), (2), (3), (4) can be multiplied by correction factors to refine the measurement result and to ensure that natural fluctuations in the refrigeration circuit do not distort the monitoring of leaks.

List of reference symbols

100

Refrigeration circuit

110

Line arrangement

120

Evaporator

130

compressor

140

Condenser

150

Throttle organ

160

internal heat exchanger

170

Section

172

first measuring point

174

second measuring point

176

third measuring point

178

fourth measuring point

180

dryer

190

High pressure monitor

192

Low pressure switch

200

Shut-off valve

Claims (11)

1. Method for identifying leaks in a refrigeration circuit (100) of a compression refrigerating machine, wherein the refrigeration circuit (100) comprises at least an evaporator (120), a compressor (130), a condenser (140), a pressure-reducing valve and an internal heat exchanger (160), which are interconnected by means of lines, wherein a refrigerant is conducted in the lines, wherein the internal heat exchanger (160) is arranged between the evaporator (120) and the compressor (130) and between the condenser (140) and the pressure-reducing valve, wherein

   - there are defined, at least in the region of the internal heat exchanger (160):

   a) a first measurement point (172) in the line from the internal heat exchanger (160) to the pressure-reducing valve,

   b) a second measurement point (174) in the line from the evaporator (120) to the internal heat exchanger (160),

   c) a third measurement point (176) in the line from the condenser (140) to the internal heat exchanger (160) and

   d) a fourth measurement point (178) in the line from the internal heat exchanger (160) to the compressor (130)

   for at least one thermodynamic state variable of the refrigerant for the purposes of determining the temperature of the refrigerant,

   - the temperature is either measured directly or acquired indirectly by measuring the pressure in conjunction with a physical characteristic of the refrigerant,

   - the refrigerant temperature determined at the first measurement point (172) is subtracted from the temperature determined at the third measurement point (176), and a first value is established therefrom,

   - the refrigerant temperature determined at the second measurement point (174) is subtracted from the temperature determined at the fourth measurement point (178), and a second value is established therefrom,

   - a ratio between the first value and the second value is established,

   - a third value created therefrom is compared with a reference and

   - a leak is identified if the third value deviates from the reference.
2. Method according to claim 1, wherein

   - the first value is divided by the second value and then a leak is identified if the third value created therefrom as the result is above the reference, or

   - the second value is divided by the first value and then a leak is identified if the third value created therefrom as the result is below a reference.
3. Method according to claim 1 or claim 2, wherein at least one further measurement point is defined in the refrigeration circuit and is used for calculating the first value, the second value and/or the third value.
4. Method according to any of claims 1 to 3, wherein the establishment of the values and the comparison with the reference are carried out continually or at definable intervals.
5. Method according to any of claims 1 to 4, wherein the reference is a pre-established reference value or a reference function.
6. Method according to claim 5, wherein the reference function is created from a plurality of values of the determined first, second, third and/or fourth temperatures, and the position of the subsequently established third values relative to the reference function is determined, wherein a leak is identified if the third value deviates from the reference function.
7. Method according to claim 6, wherein the reference function is generated from the values for a plurality of target temperatures, pressures and/or physical characteristics of the refrigerant.
8. Method according to any of claims 1 to 6, wherein the evaporator (120) is disconnected from the refrigeration circuit (100) after a leak is identified.
9. Method according to claim 8, wherein valves (200) arranged in the flow pipe and return pipe of the evaporator (120) in the refrigeration circuit (100) are closed if the third value deviates from the reference.
10. Leak detection system for identifying the escape of a refrigerant in a refrigeration circuit (100) of a compression refrigerating machine, comprising a refrigeration circuit (100) having at least an evaporator (120), a compressor (130), a condenser (140), a pressure-reducing valve and an internal heat exchanger (160), which are interconnected by means of lines, wherein a refrigerant is conducted in the lines, wherein the internal heat exchanger (160) is arranged between the evaporator (120) and the compressor (130) and between the condenser (140) and the pressure-reducing valve, wherein the compression refrigerating machine comprises, at least in the region of the internal heat exchanger (160):

    a) a first measurement point (172) in the line from the internal heat exchanger (160) to the pressure-reducing valve,

    b) a second measurement point (174) in the line from the evaporator (120) to the internal heat exchanger (160),

    c) a third measurement point (176) in the line from the condenser (140) to the internal heat exchanger (160) and

    d) a fourth measurement point (178) in the line from the internal heat exchanger (160) to the compressor (130)

    for acquiring at least one thermodynamic state variable of the refrigerant for the purposes of determining the temperature of the refrigerant, wherein the temperature can be either measured directly or acquired indirectly by measuring the pressure in conjunction with a physical characteristic of the refrigerant,

    further comprising a controller which, according to one of the methods of claims 1 to 9,

    - subtracts the refrigerant temperature determined at the first measurement point (172) from the temperature determined at the third measurement point (176) and establishes a first value therefrom,

    - subtracts the refrigerant temperature determined at the second measurement point (174) from the temperature determined at the fourth measurement point (178) and establishes a second value therefrom,

    - establishes a ratio between the first value and the second value,

    - creates a third value therefrom and compares it with a reference,

    - identifies a leak if the third value deviates from the reference and

    - closes valves (200) arranged in the flow pipe and return pipe of the evaporator (120) in the refrigeration circuit (100) if the third value is above or below the reference.
11. System according to claim 10, wherein the measurement points (172; 174; 176; 178) are located in the immediate vicinity of the internal heat exchanger (160) or within the internal heat exchanger (160).

Images