LEAKAGE DETECTION

Description

[0001] The invention relates to a detection system for gas leakage. Specifically, it concerns a leak of a flammable gas used as a working fluid in a refrigeration circuit, which could escape from the circuit under irregular conditions. Such leaks are usually gradual and extremely minor; however, in very rare cases, significant leaks are conceivable, for example, if the refrigeration circuit is shaken or damaged by external influences.

[0002] One problem is that the speed, location, and magnitude of such gaseous refrigerant leaks are not known in advance. In the event of a leak, however, one would like to know what to expect before opening a device containing such a refrigeration circuit. While the corresponding gas concentrations within a housing are relatively easy to measure, the leakage location, velocity, and quantity are difficult to measure or estimate.

[0003] A desirable measuring system would therefore consist of a large number of inexpensive measuring points that can be easily placed near typical leakage points, such as pipe connections and compressor bearings, heat exchanger connections and fittings, and whose temporal sequence during measurement in the event of a leak would provide indications of where the leak has occurred and how large it is likely to be.

[0004] Various technologies are used for the measuring points. For example, EP 3 477 274 A1 describes a system for leak detection in a closed thermodynamic cycle, in which vibrations are analyzed and evaluated using a large number of accelerometers, and a sound or vibration pattern typical of leaks is filtered out.

[0005] EP 3 486 583 A1 describes a system in which a fluorescent agent is added to the refrigeration circuit, which glows fluorescently at leakage points, with the leakage being detected by means of a camera.

[0006] German patent DE 44 34 814 A1 describes an infrared spectroscopic sensor for gases. In this system, gases are selectively detected in the infrared spectral range using a spectrometer based on their gas-specific absorption.

[0007] German patent DE 10 2013 007 872 B4 describes an electrochemical gas sensor. In this sensor, a reversible chemical reaction with the gas is carried out within a sensor housing. For this purpose, the gas is brought into contact with an electrolyte, preferably an ionic liquid that is neither hygroscopic nor prone to evaporation. This electrolyte is contained in a measuring cell, which also includes a working or measuring electrode and a counter or auxiliary electrode. The measuring cell can be open on the gas side or sealed with a gas-permeable membrane. The concentration of the respective gas can be determined from the characteristic potential difference between the electrodes.

[0008] German patent applications DE 44 28 155 C2 and DE 10 2009 054 435 A1 describe gas sensors based on inorganic metal oxide semiconductors (MOX). When such gas sensors, designed as porous solids, come into contact with reducing substances, such as propane from R290, the electrical conductivity of the MOX changes at its surface. This change in conductivity is measured and used to detect or determine the concentration of such reducing gases. Systems are also known whose gas detection capability is based not on a change in electrical conductivity, but on the thermal conductivity of MOX or activated carbon following adsorption. This is particularly true at low temperatures.

[0009] Catalytically active and / or catalytically passive measuring elements in catalytic gas sensors or thermal conductivity sensors, so-called pellistors, are also known and are described, for example, in DE 35 13 033 A1. Field-effect transistors with gaseous semiconductor elements, for example, gas-type-sensitive gate substrates in semiconductor gas sensors, are also known.

[0010] US 2020 / 011560 A1 describes a system in which a chiller comprises an outdoor unit and an indoor unit. The indoor and outdoor units are connected by refrigerant lines. Air flows through the housing of the indoor unit; this air is to be heated or cooled as desired, coming into direct contact with a refrigerant-carrying heat exchanger. In the event of a leak, the refrigerant thus flows directly into the installation room, where further measures are taken to detect it. US 2019 / 170602 A1 describes a similar system.

[0011] All these measuring systems are expensive and can only measure the concentration of the gaseous refrigerant at a specific location. To measure the spatial distribution of the leaked gas component and its temporal evolution, it would be necessary to deploy a large number of these expensive measuring systems, record their measurement results and responses over time, and determine the spatial concentration development using a spatial model. Only when the temporal sequence of the concentration increase is discernible, taking the spatial distribution into account, can the location of the leak be determined.

[0012] During the adsorption of gas in solids, adsorption enthalpy is released, leading to a temperature increase in the adsorbent as the adsorbate is absorbed. DE 1 079 860 B describes a thermocouple coated with a suitable adsorbent selected for its selective adsorption of the gas component to be measured. In a gas stream, this allows for the adsorption of adsorbates such as water vapor or propane, and the corresponding gas concentration can be determined from the heat generated by the adsorbate measured by the thermocouple. However, once the adsorbent is saturated with the adsorbate, the heat generation decreases, and the temperature of the adsorbate drops again, approaching the ambient temperature. Therefore, the system is designed to regenerate the adsorbent by purging with inert gas and to operate alternately with at least one other identical system.In this way, quasi-continuous concentration measurement is possible.

[0013] Similarly, US Patent 7,338,640 B2 describes a sensor cell coated with an adsorbent and connected to an uncoated reference cell. Both are mounted on a sensor substrate. The sensor is configured to first adsorb a defined quantity of gas and then desorb it upon heating. The system apparently oscillates between adsorption and desorption. A thermopile is placed on top of the sensor cell to measure the heat flow between the coated sensor cell and the reference cell. The thermopile has a poorly conductive layer and a sacrificial layer; material is etched away between them, creating a variety of thermal connections that can withstand temperature differences. This allows for continuous concentration measurement.

[0014] The EP 3 604 980 A1 addresses the problem in a freezer in a different way. As a first step, it measures the concentration of the refrigerant that has leaked out and routinely compares this to a predefined refrigerant concentration. If this measurement indicates a possible leak, it issues a corresponding message and then performs an oxygen measurement. If the oxygen level reaches a predefined concentration, a message is issued indicating a potential ignition hazard. A powerful fan is then activated at full speed to purge the interior. Next, an infrared test is performed to check the air temperature, and if it exceeds a predefined value, a message is issued indicating a high probability of ignition. The refrigeration circuit is then shut down.

[0015] The object of the invention is therefore to provide an improved device for detecting a leak of a flammable refrigerant in a refrigeration circuit, as well as providing information on the location and size of the leak.

[0016] The invention solves this problem by means of a gas leak detection system according to the attached claims.

[0017] Thermocouples deserve special attention. This is a general term for thermocouples, resistance thermometers, thermistors, thermoelectric pyrometers, and all other measuring elements based on the Seebeck effect. What they all have in common is that an electrical voltage arises at the junction of two different metal parts or semiconductors, which depends on and changes with the temperature at the junction.

[0018] If one of these thermoconverters is coated with an adsorbent, the junction heats up precisely when heat of adsorption occurs, generated by an adsorbate. Once an adsorption equilibrium is reached between the adsorbate and the surrounding gas, no further adsorption or heating takes place, and heat conduction causes the adsorbate to return to ambient temperature. If the concentration of the adsorbate in the surrounding gas were to decrease again, desorption would occur, leading to cooling of the adsorbate.

[0019] Subtracting the resulting thermoelectric voltage of the coated thermocouple from that of an uncoated thermocouple of the same design yields the difference as a measure of the increase in the rising gas concentration.

[0020] In one embodiment, each coated thermocouple is directly connected to an uncoated thermocouple. This creates a coupled thermocouple which, while no longer able to display an accurate temperature, emits a voltage signal from the voltage difference during the heating process of the adsorbate, indicating a leakage.

[0021] According to the invention, the voltage difference causes a current flow that operates an RFID chip, which transmits the voltage signal wirelessly to the central signal acquisition unit. The RFID chip is directly connected to the thermal converters. As soon as an adsorbate comes into contact with the adsorbent and is adsorbed, the adsorbate heats up, generating a current flow that causes the RFID chip to transmit a corresponding signal to the central signal acquisition unit.

[0022] The invention is explained in more detail below with reference to five schematic diagrams. These show: Fig. 1 two coupled thermoconverters with sheathed thermocouples, Fig. 2 two coupled thermoconverters with semiconductor thermocouples, Fig. 3 a simplified design of a thermoconverter, Fig. 4 a simplified design with an RFID chip, Fig. 5 An exemplary arrangement in a heat pump housing.

[0023] Fig. 1 Figure 1 shows two conventional thermoelectric converters, 1 and 2, one of which is coated with an adsorbent 3. The two metal wires 4 and 5 of thermoelectric converter 1 and 6 and 7 of thermoelectric converter 2 are made of different metals and are welded together at connection points 8 and 9. Both thermoelectric converters, 1 and 2, have protective sheaths 10 and 11 to shield the sensitive wires. These wires typically extend from the housing in which they are used for temperature measurement; the housing wall is symbolically represented by 12. Outside the housing, there is a reference junction 13 and 14, respectively, with measurement compensation for comparison with a reference temperature. The respective thermoelectric voltages are then measured using voltage measuring devices 15 and 16, respectively, from which the temperatures at the measuring point are determined.In this way, during a loading process, the difference in voltages in the comparator 17 results in a temperature difference at the measured temperatures, from which a leakage-related gas escape can be inferred.

[0024] Fig. 2 Figure 1 shows another device in which the two thermocouples 21 and 22 are constructed using semiconductors instead of wires. This allows for higher thermoelectric voltages, but such thermocouples are more sensitive. The thermocouple 21 consists of a conductive measuring surface 24 onto which an adsorbate 23 is applied, as well as an n-type semiconductor 26 and a p-type semiconductor 28 connected to the measuring surface. These semiconductors are connected on the side opposite the measuring surface 24 to conductive measuring surfaces 27 and 29, respectively. A thermoelectric voltage is generated between these measuring surfaces 27 and 29, which is measured in the voltmeter 35.

[0025] The two measuring surfaces 27 and 29 must be cooled, as indicated by arrows. This can be achieved, for example, by ensuring good thermal contact with the ambient temperature or by using a cooling device. The cooling system must be dimensioned to dissipate the heat of adsorption, which is conducted through the measuring surfaces and the semiconductors. A small latent heat storage device can also fulfill this function, since only a relatively small heat flow needs to be dissipated over a short period of time due to the heat of adsorption.

[0026] Similarly, the thermocouple 22 consists of a conductive measuring surface 25, on which no adsorbate is applied, as well as an n-type semiconductor 30 and a p-type semiconductor 32 connected to the measuring surface. These semiconductors are connected on the side opposite the measuring surface 25 to a conductive measuring surface 31 and 33, respectively. A thermoelectric voltage is generated between these measuring surfaces 27 and 29, which is measured in the voltage measuring device 36.

[0027] Since only the difference between the voltages is of interest, a temperature difference at the measured temperatures results from the difference in voltages in the comparator 37 during a loading process, from which a leakage-related gas escape can be inferred.

[0028] Since adsorptive loading and the associated heat generation are dynamic processes superimposed with heat dissipation, the measured temperature difference cannot be used to directly determine the gas concentration in the housing. This, as is well known, leads to further complications, as already described in DE 1 079 860 B. However, if one only wants to detect the propagation of a gas cloud in a closed housing, knowledge of the absolute concentration is not required; it is sufficient if the various detectors each emit only one signal pulse and then remain silent.

[0029] Since the absolute temperatures are also irrelevant, standardized comparative measurements and thermocouple compensation can be dispensed with. This allows the [missing information - likely a specific measurement or parameter] to be [missing information - likely a specific measurement or parameter]. Fig. 1 Simplify the setup shown. Fig. 3 illustrates using the example of the in Fig. 1 The illustrated thermocouples demonstrate how a simplified measuring apparatus is constructed. Inside the housing, the two thermocouples are directly connected; the metal wires 5 and 7 become a single common conductor made of the same material, effectively short-circuiting them. The thermocouple 2 from Fig. 1 For this purpose, the diagram was mirrored, and the two identical materials 5 and 7 were connected. This results in the voltage of thermocouple 2 being subtracted from that of thermocouple 1. Only the uncompensated voltage difference is displayed. This is determined within the housing itself, and only the result needs to be output as a signal from the housing. The temporary occurrence of a thermoelectric voltage indicates a gas leak. This can also be applied analogously to the [unclear text - possibly referring to a specific component or component]. Fig. 2 The execution variants shown are carried out as follows.

[0030] Fig. 4 Figure 4 shows another design variant in which the thermocouple signal is transmitted from the housing via a radio device. An RFID 40 is used for this purpose. Such RFIDs can be passive or active; the latter require a power supply. Instead of generating a thermoelectric voltage, the thermoelectric current is used, which, when it occurs briefly, powers an active RFID that then transmits the signal wirelessly. Such a thermocouple 39 requires only a common enclosure 41 and can be completely integrated into the housing.

[0031] To transmit a sufficiently strong signal even at low currents or voltages, a thermopile can be used, depending on the device, in which several components are connected in parallel or in series. The 39 thermocouple can be miniaturized effectively, and transmitting signals within metal housings using RFID has now become state of the art.

[0032] Fig. 5 Figure 1 shows a simplified representation of a refrigeration circuit of a heat pump 100 with a large number of correspondingly miniaturized sensors 101 to 113, all of which transmit a signal to the outside at time intervals when a leakage cloud occurs. The casing walls of the heat pump 100 have been removed for illustrative purposes. The externally mounted signal acquisition / processing unit 200 receives these signals, evaluates them, integrates them, and determines the spatiotemporal propagation.

[0033] In this context, it may be useful to also provide a concentration measurement at a point in the room using a different measuring method in order to additionally obtain an absolute value of the concentration, from which one can conclude the extent of the entire escaped refrigerant cloud.

[0034] Of course, the signal acquisition unit / signal processing unit 200 can also receive and process the signals using conventional wiring. Reference symbol list

[0035] 1, 2, 21, 22, 39 Thermocouple 3 Adsorbent 4, 5, 6, 7 Metal wire 8, 9 Connection point 10, 11 Protective cover 11 Outer housing part 12, 34 Housing wall 13, 14 Reference junction 15, 16, 35, 36 Voltage meter 17, 37 Comparator 24, 25, 27, 29, 31, 33 Measuring surface 26, 30 n-type semiconductor 28, 32 p-type semiconductor 40 RFID 41 Enclosure 100 Heat pump 101 to 113 Sensor 200 Signal acquisition unit / Signal processing unit

Claims

1. Gas leak detection system with a measuring device comprising - a closed housing (100) with a refrigeration machine, with a refrigerant circuit and a flammable or hazardous refrigerant in the refrigerant circuit - with a measuring device in a closed housing characterised in that the measuring device comprises the following features: a plurality of thermal transducers (1, 21, 39) coated with an adsorbent matched to the refrigerant gas to be measured as an adsorbate and placed inside the housing (100), - and which are suitable for detecting the respective thermoelectric voltage of the adsorbate in parallel and simultaneously, and - further comprising at least one thermoconductor (2, 22) which, uncoated, measures the thermoelectric voltage of the ambient temperature of the thermoconductors (1, 21, 39) coated with adsorbent, - wherein each pair of thermal transducers (1, 2, 21, 22, 39) is connected to an RFID (40) and the voltage difference between the thermal transducers (1, 2, 21, 22, 39) causes a current to flow, which supplies the RFID (40) with electrical energy, whereby the voltage signal can be transmitted by radio to the central signal acquisition unit (200).

2. . Detection system according to claim 1, characterised in that an uncoated thermal transducer (2, 2) is directly connected to each of the coated thermal transducers (1, 21, 39).