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

Abstract

Propane bubble sensor (1) for a heat pump (2) for detecting propane bubbles (P) in a fluid circuit (3), wherein the propane bubble 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 includes an evaluation unit (13), wherein the evaluation unit (13) is designed, to evaluate the backsound for the detection of propane bubbles (P) on acoustic frequency responses typical for propane bubbles (P) and to determine an indicative value of the number and / or size and / or probability of propane bubbles (P) in the fluid through evaluation.

Description

[0001] The invention relates to a propane bubble 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 propane bubble sensor for a heat pump is proposed for detecting propane bubbles in a fluid circuit, wherein 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 propane bubble 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 particularly water.Similarly, the sound transducer is designed and preferably configured to detect the reflected sound of the sound signal, which is reflected by gas bubbles (especially air bubbles, in addition to propane bubbles) present in the fluid. Although the transducer can also generate the sound signal independently of the evaluation unit and couple it into the fluid, it is preferably provided that the transducer and the evaluation unit are connected via a signal transmission system, and that the transducer, controlled by the evaluation unit, generates the sound signal and / or couples it into the fluid. Furthermore, the sound transducer is preferably connected via a signal transmission system to the evaluation unit for transmitting data representing the reflected sound.The essential aspect of the invention is that the evaluation unit is designed to evaluate the backsound for the detection of propane bubbles based on acoustic frequency responses typical for propane bubbles and to determine an indicative value of the number and / or size and / or probability of propane bubbles in the fluid through the evaluation.

[0010] For clarity, such a value always refers to the detection range of the sensor and thus, in particular, to the measuring distance between the sound transmitter and the sound transducer.

[0011] The evaluation allows for the precise determination of a value for the number of detected propane bubbles, or values ​​for the sizes of propane bubbles or their size distribution, or precisely a value for the probability of propane gas bubbles being present in the fluid.

[0012] Alternatively, several values ​​can be determined, which then indicate, for example, the number of propane bubbles and a probability thereof.

[0013] 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.

[0014] 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.

[0015] If the propane bubble sensor or the detection of propane bubbles is to be designed to be fault-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.

[0016] 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.

[0017] 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.

[0018] To excite the gas bubbles, the sound generator is therefore designed, according to an advantageous variant, to generate a predetermined broadband signal as a sound signal, such that this signal does not merely comprise a frequency and, in particular, not merely a resonance frequency, but a frequency spectrum.

[0019] Furthermore, according to an advantageous embodiment, the evaluation unit is designed to transform the backsound into the frequency domain and / or to determine the frequency responses, in particular the total frequency response, of the gas bubbles to the sound signal.

[0020] Building on this, it can additionally be provided that the evaluation unit determines the indicative value(s) from or by means of an evaluation of the frequency response to typical acoustic frequency responses of propane bubbles.

[0021] By evaluating the frequency response and not just a single resonance frequency, further properties of frequency responses typical for propane bubbles can be taken into account, thereby differentiating between different types of gas bubbles or categorizing the detected gas bubbles.

[0022] A particularly advantageous advanced training is one in which the evaluation unit is trained to decompose the frequency response into individual curves or profiles, each attributable to a gas bubble, to determine the associated curve properties, which can also be referred to as parameters, such as width and / or slope and / or curvature and / or smoothing and / or their shape and / or their spectral envelope, and to identify gas bubbles as propane bubbles using the curve properties of the associated curves and, in particular, by curve shape analysis.

[0023] By evaluating not only the behavior of the gas bubbles at a resonance frequency for propane bubbles, but in particular the entire frequency response to the sound signal exciting the gas bubbles, the curve properties of the frequency responses of individual gas bubbles can be evaluated and thus propane bubbles can be identified.

[0024] If no further information is used, it is advantageous if typical curve properties of propane bubbles are known and stored in the evaluation unit.

[0025] Based on this, it can be further stipulated that the evaluation unit is designed to categorize gas bubbles into propane bubbles and other gas bubbles, particularly air bubbles, using the curve properties of corresponding curves. It is not necessary to know all typical curve properties of propane bubbles, as the detected gas bubbles only need to be categorized so that their typical curve properties merely need to differ.

[0026] Furthermore, a categorization into propane bubbles and one type of other gas bubbles, especially air bubbles, is sufficient, as the presence of other gases that can form gas bubbles in the fluid can be ruled out.

[0027] Furthermore, the evaluation unit can take into account, particularly for categorization, a statistically known distribution for the sizes of the gas bubbles forming in the fluid or statistically known distributions for the sizes of the propane bubbles and other gas or air bubbles forming in the fluid.

[0028] For such an analysis, the evaluation unit can be designed to perform the evaluation of the backsound for the detection of propane bubbles by nonlinear analysis and / or by machine learning.

[0029] In this context, it should be noted that while it is advantageous to integrate the evaluation unit into a housing of the propane bubble sensor and thus arrange it directly in the area of ​​the sound transmitter and sound transducer, alternatively a control unit can also be provided in the propane bubble sensor or in its housing, which connects at least the sound 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.

[0030] Assuming that propane bubbles are identified as proposed and, in particular, the indicative value for the number of propane bubbles is determined, it is preferably provided that the evaluation unit is designed to compare the indicative value with an associated limit value, or, in the case of several indicative values, each with a respective limit value, and, based on the comparison, especially if a respective indicative value exceeds the associated limit value, to generate a signal by which the indicative value or, for example, a leak detected therein can be transmitted to a higher-level system.

[0031] Additionally or alternatively, the evaluation unit can also be configured to determine the trend of the indicative value, or at least one of the indicative values, over time, compare this trend with a corresponding limit value, and generate a further signal or the alert signal based on this comparison. For example, if a sudden increase or a steeper rise in propane bubbles compared to the limit value is detected, this can be transmitted via the alert signal.

[0032] 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.

[0033] Another aspect of the invention relates to a heat pump with a propane bubble 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 propane bubble 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.

[0034] Assuming that the heat pump has a condenser, the propane bubble sensor is preferably located outside, but fluidically directly after the condenser.

[0035] Depending on the specific design of the heat pump, it may have a propane bubble sensor for each fluid circuit.

[0036] 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.

[0037] All the characteristics described for the propane bubble sensor also apply analogously to the heat pump.

[0038] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0039] 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 propane bubble sensor; Fig. 2 Frequency response of two gas bubbles; Fig. 3. Categorization of gas bubbles.

[0040] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0041] In Fig. Figure 1 schematically shows a heat pump 2 with a propane bubble 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] To detect such an inflow of propane gas into the fluid circuit, a propane bubble 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 enters and propane bubbles form in the fluid flowing through the fluid channel 25 from a flow inlet 26 to the flow outlet 27, the propane bubbles can therefore be detected directly, without them 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.

[0047] Although the propane bubble sensor 1 and its operation 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 propane bubble sensor 1 shown can also be considered independently of the heat pump.

[0048] Basically, the propane bubble sensor 1 has a sound transmitter 11 and a sound receiver 12, which - as shown - can be arranged on a fluid channel 10 of the propane bubble sensor 1 through which the fluid flows.

[0049] In addition to the sound transmitter 11 and the sound transducer 12, the propane bubble 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.

[0050] To detect propane bubbles in the fluid, a predetermined broadband 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, thereby generating a backsound.

[0051] The backsound is detected by the sound sensor 12 and evaluated by the evaluation unit 13 for acoustic frequency responses typical for propane bubbles, so that an indicative value can be determined by the evaluation, which indicates the number and / or the size and / or the probability of propane bubbles in the fluid.

[0052] The feedback sound is preferably transformed into the frequency domain by the evaluation unit, and individual frequency responses of gas bubbles are isolated.

[0053] 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.

[0054] 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.

[0055] Therefore, the evaluation unit is designed to first decompose the frequency response into individual curves, each attributable to a gas bubble P, L, to determine the associated curve properties, and to identify gas bubbles P, L as propane bubbles P using the curve properties of the associated curves, and preferably to categorize them into propane bubbles P and air bubbles L, as exemplified in Fig. 3 is shown.

[0056] Based on the curve width B in Hz determined from the curves, as indicated by the ordinate in Fig. 3 corresponds to the curves and thus the bubbles can be categorized into propane bubbles P and air bubbles C, whereby the size of the bubbles can also be determined by the resonant frequency rf in kHz, which can also be determined and plotted as an abscissa.

[0057] An example decision limit C is also shown, so that curves and thus bubbles with a bandwidth in Hz above the decision limit C can be categorized as propane bubbles P and below the decision limit C as air bubbles.

Claims

[1] Propane bubble sensor (1) for a heat pump (2) for detecting propane bubbles (P) in a fluid circuit (3), wherein the propane bubble 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 includes an evaluation unit (13), wherein the evaluation unit (13) is designed, to evaluate the backsound for the detection of propane bubbles (P) on acoustic frequency responses typical for propane bubbles (P) and to determine an indicative value of the number and / or size and / or probability of propane bubbles (P) in the fluid through evaluation. [2] Propane bubble sensor according to claim 1, wherein the sound transmitter (11) is configured to generate a predetermined broadband signal as a sound signal. [3] Propane bubble 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 response of the gas bubbles (P, L) to the sound signal. [4] Propane bubble sensor according to claim 3, wherein the evaluation unit (13) is formed, to determine the indicative value from an evaluation of the frequency response to typical acoustic frequency responses of propane bubbles (P). [5] Propane bubble sensor according to claim 3 or 4, wherein the evaluation unit (13) is designed, to decompose the frequency response into individual curves, each attributable to a gas bubble (P, L), to determine the associated curve properties and to identify gas bubbles (P, L) as propane bubbles (P) using the curve properties of the associated curves. [6] Propane bubble sensor according to claim 5, wherein the evaluation unit (13) is designed, To categorize gas bubbles (P, L) into propane bubbles (P) and other gas bubbles (L), in particular air bubbles (L), using the curve properties of associated curves. [7] Propane bubble sensor according to any one of the preceding claims, wherein the evaluation unit (13) is formed, to perform the evaluation of the backsound for the detection of propane bubbles (P) by nonlinear analysis and / or machine learning. [8] Propane bubble sensor according to any one of the preceding claims, wherein the evaluation unit (13) is designed, to compare the indicative value with a corresponding limit value and to generate a notification signal based on the comparison. [9] Propane bubble sensor according to one of the preceding claims, wherein the evaluation unit (13) is configured to determine the course of the indicative value over time, to compare the course with a corresponding border course and to generate a notification signal based on the comparison. [10] Propane bubble 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 transit 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. [11] Heat pump (2) with a propane bubble sensor (1) according to any 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 propane bubble 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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