Leakage sensor for a heat pump to detect a propane leak in a fluid circuit

Abstract

Leakage sensor (1) for a heat pump (2) for detecting a leak leading to the ingress of gas into a fluid circuit (3), wherein the leakage sensor (1) includes a sound transmitter (11) for coupling a sound signal into a fluid flowing along the fluid circuit (3), and a sound sensor (12) for detecting a sound reflected by gas bubbles (P, L) present in the fluid. and has an evaluation unit (13) which is designed, to evaluate the backsound to detect all gas bubbles (P, L) detectable in the fluid, to determine a number (N) of detected gas bubbles (P, L) and to evaluate a trend (V) of the number (N) of detected gas bubbles over time to detect the leakage.

Description

[0001] The invention relates to a leakage sensor for a heat pump for detecting a propane leak in a fluid circuit, wherein the fluid circuit is in particular a hot water circuit connected to the heat pump, preferably a heating and / or a domestic hot water circuit.

[0002] The heat pump market is increasingly shifting towards the use of propane (R290) as a refrigerant. While propane has advantageous thermodynamic properties, it is flammable, necessitating special safety requirements for leak detection when used indoors. Future generations of heat pumps will operate with comparatively small refrigerant charges of 150 g or less, thus reducing the legal and regulatory safety requirements for indoor installation. However, this necessitates the implementation of suitable measures for detecting potential propane leaks to ensure the safety of users and the surrounding environment.

[0003] It is known in the prior art that leaks can occur in the refrigerant circuit. To detect these leaks, sensors for propane gas are sometimes installed in the floor area below the heat pump, since propane is heavier than air and accumulates near the floor in the event of a leak.

[0004] However, it is insufficiently taken into account that in the event of a leak, propane can enter a hot water circuit from the actual refrigerant circuit, for example the heating circuit or the hot water circuit for domestic hot water.

[0005] This is particularly true within the condenser if a hot water circuit running through it has leaks. Due to the pressure conditions prevailing in the condenser – propane pressure in the range of 10 to 20 bar compared to 1 to 4 bar in the hot water circuit – propane can enter the hot water circuit in the event of a leak.

[0006] This means that, on the one hand, the leak cannot be detected by known systems, and on the other hand, the propane escaping via the hot water circuit also poses a significant safety risk that is not adequately addressed by the solutions known in the prior art.

[0007] Against this background, the object of the invention is to overcome the aforementioned disadvantages and to provide a sensor for heat pumps for the reliable detection of propane leaks affecting a hot water circuit, which can detect such leaks and thereby increase operational reliability, especially when installing heat pumps indoors.

[0008] This problem is solved by the combination of features according to the main claim and the dependent claim.

[0009] According to the invention, a leakage sensor for a heat pump is proposed for detecting a leak that leads to the ingress of gas, in particular propane, into a fluid circuit, thereby forming gas bubbles or propane bubbles in the fluid of the fluid circuit. The fluid circuit is preferably a hot water circuit connected to the heat pump, i.e., a heating circuit or a domestic hot water circuit. The leakage sensor according to the invention comprises a sound transmitter, a sound transducer, and an evaluation unit. The sound transmitter is designed and preferably configured to couple a preferably not arbitrary, but predetermined sound signal into a fluid flowing along the fluid circuit, wherein the sound signal particularly comprises sound waves and / or ultrasonic waves, and wherein the fluid is preferably water.Similarly, the sound transducer is provided and preferably designed to detect the backsound of the sound signal, which is reflected by gas bubbles present in the fluid (in addition to propane bubbles, especially air bubbles). Although the sound transducer can also generate the sound signal independently of the evaluation unit and couple it into the fluid, it is preferably provided that the sound transducer and the evaluation unit are connected via signal technology and that the sound transducer generates and / or couples the sound signal into the fluid under the control of the evaluation unit. Furthermore, the sound transducer is preferably connected to the evaluation unit via signal technology for the transmission of data representing the backsound. It is essential to the invention that the evaluation unit is designed according to the invention to use the backsound to detect all gas bubbles detectable in the fluid, i.e., not only propane bubbles, but also, for example,The system analyzes both propane and air bubbles and uses this analysis to determine the number of gas bubbles detected in the fluid. Based on this, the evaluation unit is designed to track the number of detected gas bubbles over time.

[0010] The detection always refers to the sensor's detection range and thus, in particular, to the measuring distance between the sound transmitter and the sound transducer, so that, of course, it is not the number of all gas bubbles in the fluid, but rather the number of gas bubbles in the sensor's detection range that is determined and evaluated.

[0011] Regarding the technical background, it should be noted that gas bubbles in fluids reflect sound waves differently depending on the specific gas, as these gases possess different resonant frequencies. This phenomenon is also known as Minnaert resonance and can be described by the Minnaert equation.

[0012] Assuming a closed fluid circuit, as is the case with a heating circuit, it can be assumed that there are no air bubbles or other gas bubbles in the fluid, so that all gas bubbles detected by the backsound can be assumed to be propane bubbles, i.e. gas bubbles formed by propane.

[0013] If the leakage sensor or the detection of propane bubbles is to be designed to be fail-safe and / or also suitable for use in non-closed or open fluid circuits, e.g. a domestic hot water circuit, it must be taken into account that other gas bubbles, especially air bubbles, may also be present in the fluid.

[0014] Propane bubbles of the same size and other gas bubbles, especially air bubbles, can be distinguished in a fluid under otherwise identical conditions based on their resonance frequency.

[0015] However, starting from the air bubbles relevant for heat pumps, which may be present in the fluid circuit, the problem arises that propane bubbles, whose radius is about 10% smaller than the radius of air bubbles present in the fluid, can no longer be reliably distinguished from them solely by their resonance frequency.

[0016] The leakage sensor proposed here solves this problem by not distinguishing between different gas bubbles, but by generally determining their number and then evaluating the development of the number, i.e. the course of the number.

[0017] To excite the gas bubbles, the sound transmitter, according to an advantageous embodiment, is designed to generate a predetermined broadband sound signal, encompassing not just a single frequency, and in particular not just a resonant frequency, but a frequency spectrum. Alternatively, the sound transmitter can also be designed to generate a single-frequency signal instead of a broadband sound signal, the frequency of which is, however, predetermined. To effectively detect gas bubbles in the fluid, the single frequency should lie within the range of the gas bubbles' resonant frequency, although the single frequency does not necessarily have to correspond exactly to the gas bubbles' resonant frequency to excite them.

[0018] For example, an average propane bubble size in the event of leaks can be determined using known statistical distributions, and the resonance frequency of an average-sized propane bubble can be chosen as the single frequency.

[0019] In principle, it is possible to evaluate the backsound in the time domain, which will be explained in more detail below. However, in order to enable a reliable determination of the number of bubbles, especially small ones, an advantageous embodiment provides that the evaluation unit is designed to transform the backsound into the frequency domain and / or to determine the frequency responses of the gas bubbles to the sound signal.

[0020] Building on this, the evaluation unit can additionally determine the number of detected gas bubbles based on typical acoustic frequency responses of gas bubbles. For this purpose, the frequency responses can either be counted or compared beforehand with typical frequency responses in order to exclude atypical frequency responses, which are not attributable to gas bubbles, from the count.

[0021] For clarification, it may be provided that the evaluation unit is designed to decompose the frequency response of the system, i.e., the fluid in the detection area, into individual curves or profiles, each attributable to a gas bubble, so that these can be counted.

[0022] Because the proposed detection principle records and evaluates not the type but the number of gas bubbles, it is not necessary to distinguish between propane bubbles and other gas bubbles.

[0023] As mentioned previously, determining the number of gas bubbles does not necessarily have to be done in the frequency domain, as the evaluation unit can alternatively or additionally be designed to analyze the backsound to determine the number of gas bubbles in the time domain. For this to work, it is important to consider that each gas bubble generates a scattering or an echo, i.e., backsound. In the time domain, the gas bubbles appear as pulses or amplitude fluctuations in the backsound detected by the signal sensor. If the gas bubbles are sufficiently spaced and generate short sound pulses as echoes or as their respective backsound, the individual echoes are temporally separable, allowing them, and thus the number of gas bubbles, to be directly detected in the time domain.

[0024] For both time-domain and frequency-domain evaluations, the evaluation unit can be designed to perform the evaluation of the backsound for counting or determining the number of gas bubbles by means of nonlinear analysis and / or machine learning.

[0025] In this context, it should be noted that while it is advantageous to integrate the evaluation unit into the housing of the leakage sensor and thus to locate it directly in the area of ​​the sound transmitter and transducer, an alternative control unit can also be provided in the leakage sensor or its housing, which connects at least the transducer and optionally also the sound transmitter to an evaluation unit located outside the housing, which can, for example, also be formed by a system optimized for machine learning, i.e., also artificial intelligence.

[0026] Assuming that all detectable gas bubbles in the detection range have been detected as proposed and their number recorded, it is preferably provided that the evaluation unit is designed to compare the trend of the number of detected gas bubbles with an associated limit value and / or boundary curve and, based on the comparison, especially if the number or trend exceeds the associated limit value or boundary curve, to generate a signal by which a leak detected thereby can be forwarded to a higher-level system.

[0027] Consequently, the number of all gas bubbles in the fluid is recorded and a leak is detected as soon as the number exceeds the predetermined limit and / or limit curve, for example, by sudden changes.

[0028] It should be noted that the evaluation of the trend can be implemented by comparing the slope of the trend with a corresponding threshold value for the slope. In this case, a slow increase in the number, i.e., a low slope, can lead to a leakage going undetected.

[0029] However, this is unlikely because, due to the pressure conditions in heat pumps (propane approx. 10-20 bar, water approx. 1-4 bar), even a small leak would result in a rapid increase in the number of bubbles. Furthermore, a leak that only leads to a predetermined, slow increase can be classified as harmless, since even over long periods only small amounts of propane enter the fluid circuit.

[0030] Starting with a heating circuit as a fluid circuit, which is a closed circuit, gas bubbles forming in the fluid circuit can in principle be either propane bubbles or air bubbles. However, it must be taken into account that air bubbles do not form quickly in a closed circuit. Therefore, if the number of gas bubbles increases rapidly, causing the curve or its steepness to exceed the corresponding limit value for the steepness, there is a very high probability of a leak, which can be reported accordingly.

[0031] If the fluid circuit is an open circuit, for example a domestic hot water circuit, air bubbles can also enter the fluid from the outside, so that in closed circuits with identical limit values ​​and / or limit curves, leaks would be incorrectly detected or alarm signals would be generated.

[0032] Therefore, the limit values ​​and / or limit curves for open circuits can be chosen to be higher compared to closed circuits.

[0033] For this purpose, the evaluation unit is designed to store several limit values ​​and / or limit profiles specific to each fluid circuit, which can then be selected by an operator or automatically. For example, the limit values ​​and / or limit profiles can be stored in the evaluation unit during commissioning of the leakage sensor, or the set of limit values ​​and / or limit profiles to be used can be configured.

[0034] To provide a multifunctional sensor, the sound transmitter and the sound transducer can be positioned between them, spanning a measuring section through the fluid and offset from each other in the direction of fluid flow. This allows the sound propagation time of the sound signal from the transmitter along the measuring section to the sound transducer through the fluid and / or the fluid flow velocity to be determined. The evaluation unit can then be configured to determine the fluid flow velocity from the sound propagation time from the transmitter to the sound transducer and the offset.

[0035] Another aspect of the invention relates to a heat pump with a leakage sensor according to the invention. The heat pump has a heat exchanger, which is arranged, in particular, on or in a condenser of the heat pump. The heat exchanger is designed to transfer heat from a cooling circuit through which coolant flows to a fluid circuit through which fluid flows, wherein the heat exchanger has a fluid channel through which the fluid flows or the fluid channel is connected to the heat exchanger. The fluid channel has a flow inlet and a flow outlet downstream of it and defines the fluid circuit section by section. The leakage sensor is arranged along the fluid channel and / or directly at the flow outlet of the fluid channel, so that propane flowing into the area of ​​the heat exchanger can be detected directly at the flow outlet.

[0036] Assuming that the heat pump has a condenser, the leakage sensor is preferably located outside, but fluidically directly after the condenser.

[0037] Depending on the specific design of the heat pump, it may have a leakage sensor for each fluid circuit.

[0038] It should be noted that in the context of the invention or in the context of the present disclosure, “heat” is also to be understood as “cold” and “heating circuit” is also to be understood as “cooling circuit”, for example when the heat pump is used in reverse for cooling instead of heating.

[0039] All the characteristics described for the leakage sensor also apply analogously to the heat pump.

[0040] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0041] Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show: Fig. 1 heat pump with leakage sensor; Fig. 2 Frequency response of two gas bubbles; Fig. 3. Change in the number of gas bubbles over time.

[0042] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0043] In Fig. Figure 1 schematically shows a heat pump 2 with a leakage sensor 1 according to the invention, whereby heat pumps and their operation are assumed to be known and are therefore not described in detail below.

[0044] In principle, heat pumps 2 define a coolant circuit 20, along which a coolant, at the time of registration in particular also propane gas, or propane for short, is pumped.

[0045] Along the refrigerant circuit 20, the propane flows from an evaporator 21 through a compressor 22, a condenser 23 and an expansion valve 28 back into the evaporator 21, whereby the propane compressed and thereby heated in the compressor 22 transfers heat in or at the condenser 23 via a heat exchanger 24 to a fluid circuit 3, which can be, for example, a heating circuit or a domestic hot water circuit of a building, so that the fluid is water.

[0046] Due to leaks along the coolant circuit 20, propane can escape from it and collect below the heat pump 2, which can be detected by gas sensors known in the prior art.

[0047] However, if the leak is located in the condenser 23 and / or the heat exchanger 24, propane from the coolant circuit 20 may not flow into the environment of the heat pump, but into a fluid channel 25 of the heat exchanger 24 and thus into the fluid circuit 3, causing propane bubbles to form within the fluid.

[0048] To detect such an inflow of propane gas into the fluid circuit, a leakage sensor 1 is proposed according to the invention, which, according to the embodiment shown here, is arranged directly at a flow outlet 27 of a fluid channel 25 of the heat exchanger 24. When propane penetrates and propane bubbles form in the fluid flowing through the fluid channel 25 from a flow inlet 26 to the flow outlet 27, a jump or a rapid increase in gas bubbles in the fluid can therefore be detected immediately, without the propane bubbles being able to collect or escape along the fluid circuit 3 before the fluid re-enters the heat exchanger 24 through the flow inlet 26.

[0049] Although the leakage sensor 1 and its functionality in the context of the in Fig. As described in section 1, the following applies regardless of the heat pump 2 shown, so that the Fig. The leakage sensor shown can also be considered independently of the heat pump.

[0050] Basically, the leakage sensor 1 has a sound transmitter 11 and a sound transducer 12, which - as shown - can be arranged on a fluid channel 10 of the leakage sensor 1 through which the fluid flows.

[0051] In addition to the sound transmitter 11 and the sound transducer 12, the leakage sensor 1 has as an essential component an evaluation unit 13, which is connected to at least the sound transducer 12 in terms of signal technology and can also be connected to the sound transmitter 11 for the purpose of controlling the sound transmitter 11.

[0052] To detect a leak, and in the given context of the heat pump, thus to detect propane bubbles in the fluid, it is provided that a predetermined sound signal is coupled into the fluid by the sound transmitter 11, which is reflected back by all gas bubbles in the fluid, regardless of whether they are propane bubbles or other gas bubbles, specifically for the gas bubbles, and thereby generates a backsound.

[0053] The sound waves are detected by the sound transducer 12 and evaluated by the evaluation unit 13 to detect all gas bubbles in the fluid, so that the number of all gas bubbles, in particular propane and air bubbles, within the sensor's detection range can be determined. Once the number has been determined, the development of the number of gas bubbles, i.e., the trend V of the number N of gas bubbles over time, is displayed, as for example in Fig. 3 shown, evaluated in order to detect a leak.

[0054] The feedback sound is preferably transformed into the frequency domain by the evaluation unit, and individual frequency responses of gas bubbles are isolated so that they can be counted easily and reliably. Alternatively, the evaluation can also be performed in the time domain.

[0055] In Fig. Figure 2 shows an example of a typical acoustic frequency response of a propane bubble P and an air bubble L of the same size, where the frequency f in kHz is given over the abscissa and the relative amplitude A is given over the ordinate.

[0056] The problem here is that the fluid contains gas bubbles of different sizes, so that a propane bubble and an air bubble can no longer be reliably distinguished solely by their resonance frequency if the bubbles are of different sizes.

[0057] This problem is solved by the leakage sensor 1 according to the invention in that no distinction is made between the gas bubbles, but only the temporal development of the number of all gas bubbles is observed or evaluated.

[0058] For example, in Fig. Figure 3 shows the curve V of the number N of all gas bubbles detected in the fluid within the detection range of the leakage sensor 1 over time t. The curve V, or rather its development, i.e., its slope, is monitored, and a leakage-indicating signal is generated as soon as and if the slope of the curve V is greater than the slope of a predetermined limit curve Y stored in the evaluation unit 13.

[0059] Although it is unlikely that the development of the number of gas bubbles will not increase abruptly, i.e., the curve will rise steeply, due to the pressure differences between the propane gas entering from heat pump 2 and the fluid, an additional comparison of the number N or the curve V with a limit value X, also shown as an example, can be provided, so that if the curve V exceeds the limit value X, a leak can also be assumed and a warning signal can be generated.

Claims

[1] Leakage sensor (1) for a heat pump (2) for detecting a leak leading to the ingress of gas into a fluid circuit (3), wherein the leakage sensor (1) includes a sound transmitter (11) for coupling a sound signal into a fluid flowing along the fluid circuit (3), and a sound sensor (12) for detecting a sound reflected by gas bubbles (P, L) present in the fluid. and has an evaluation unit (13) which is designed, to evaluate the backsound to detect all gas bubbles (P, L) detectable in the fluid, to determine a number (N) of detected gas bubbles (P, L) and to evaluate a trend (V) of the number (N) of detected gas bubbles over time to detect the leakage. [2] Leakage sensor according to claim 1, wherein the sound transmitter (11) is configured to generate a predetermined broadband signal or a predetermined single-frequency signal as a sound signal. [3] Leakage sensor according to claim 1 or 2, wherein the evaluation unit (13) is designed, to transform the backsound into the frequency domain and / or to determine the frequency responses of the gas bubbles (P, L) to the sound signal. [4] Leakage sensor according to claim 3, wherein the evaluation unit (13) is formed, to determine the number (N) of detected gas bubbles (P, L) according to the number (N) of typical acoustic frequency responses of gas bubbles (P, L). [5] Leakage sensor according to any one of the preceding claims, wherein the evaluation unit (13) is formed, to evaluate the backsound to determine the number (N) of gas bubbles (P, L) in the time domain. [6] Leakage sensor according to any one of the preceding claims, wherein the evaluation unit (13) is designed, to compare the trend (V) of the number (N) of detected gas bubbles with an associated limit value (X) and / or limit curve (Y) and to generate a notification signal based on the comparison. [7] Leakage sensor according to the preceding claim, wherein several limit values ​​(X) and / or limit profiles (Y) specific to a fluid circuit are stored in the evaluation unit (13). [8] Leakage sensor according to one of the preceding claims, wherein the sound transmitter (11) and the sound receiver (12) span a measuring section through the fluid between them and are arranged offset from each other in the direction of flow of the fluid, so that a sound travel time of the sound signal from the sound transmitter (11) along the measuring section to the sound receiver (12) through the fluid and / or the flow velocity of the fluid can be determined. [9] Heat pump (2) with a leakage sensor (1) according to one of the preceding claims, wherein the heat pump has a heat exchanger (24) which is designed to transfer heat from a cooling circuit (20) through which coolant flows to a fluid circuit (3) through which fluid flows, wherein the heat exchanger (24) has a fluid channel (25) through which the fluid flows, or the fluid channel (25) is connected to the heat exchanger (24), wherein the fluid channel (25) has a flow inlet (26) and a downstream flow outlet (27) and determines the fluid circuit (3) section by section, wherein the leakage sensor (1) is arranged along the fluid channel (25) and / or directly at the flow outlet (27) of the fluid channel (25).

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