Heat pump and method for detecting a loss of refrigerant in a heat pump

Abstract

The invention relates to a method for detecting a loss of refrigerant in a heat pump which, in a refrigerant circuit (6), has a collector container (3) for the refrigerant (7), wherein: the collector container (3) is excited so as to vibrate; at least one vibration sensor (8) is used to detect vibration data representing the vibrations of the collector container (3); the vibration data are detected in an operating state of the heat pump in which, with a closed expansion valve (4), all of the refrigerant (7) has been conveyed into the collector container (3) by means of the compressor (1); the vibration data themselves form evaluation data or the vibration data are converted into evaluation data; the evaluation data are compared with stored reference data; and a fault signal is generated depending on the result of the comparison. The invention also relates to a heat pump configured to carry out the method.

Description

[0001] July 23, 2025

[0002] RWTH Aachen

[0003] Heat pump and method for detecting refrigerant loss in a heat pump

[0004] The invention relates to a method for detecting a refrigerant loss in a heat pump which has a collector container for the refrigerant in the refrigerant circuit.

[0005] The invention also relates to a heat pump with a refrigerant circuit in which at least one compressor, one condenser, one expansion valve, one evaporator, and one receiver for the refrigerant are arranged. Depending on the application, further components may also be present in the heat pump, in particular valves, temperature sensors, pressure sensors, etc.

[0006] Heat pumps and their function are well known in the art. They serve to absorb energy from an ambient medium using a refrigerant, raise the refrigerant to a higher pressure and temperature level by means of a flow-driven compressor, and transfer the heat to another medium. The media used on both sides of the heat pump are typically air, waste heat, brine, or water. Heat pumps can be used for both cooling and heating. The invention thus uses the term "heat pump" regardless of whether the application aims at heating or cooling a medium, because in both cases "heat is pumped"—only the direction differs.As part of the ongoing energy transition, more and more heat pumps are being used, but according to current projections, there is not enough trained personnel available for installation and maintenance to ensure the smooth start-up of heat pumps.

[0007] A common malfunction in heat pump operation is refrigerant leakage, which over time leads to a reduction in the refrigerant charge and consequently to a decrease in the heat pump's performance and efficiency. Many conventional refrigerants are also environmentally harmful, so refrigerant leaks must be prevented or detected and rectified as early as possible.

[0008] In recent years, heat pumps equipped with variable-speed compressors have become established in the market. Different mass flow rates are required in the heat pump circuit at different speeds. To adjust these flow rates across the operating range, a collector tank is used as a reservoir.

[0009] Heat pumps with a refrigerant receiver in their refrigerant circuit present a particular problem: even with a leak (refrigerant loss), the heat pump can continue operating for extended periods until the refrigerant level in the receiver drops sufficiently to detect the leak. Early detection of refrigerant leaks in receiver-based refrigerant circuits is not possible due to the phase separation of the refrigerant using pressure and temperature sensors. Currently, leak detection using conventional sensors (e.g., pressure and temperature sensors) is only possible after a significant loss of refrigerant. This typically delayed detection results in emissions and a reduction in performance and efficiency.It is therefore an object of the invention to be able to detect a loss of refrigerant as early as possible in heat pumps with a collector container in the refrigerant circuit.

[0010] According to the invention, this problem is solved by a method in which the collector container is excited to vibrate, and vibration data representing the vibrations of the collector container are recorded by means of at least one vibration sensor, in particular by an evaluation unit, and the vibration data themselves constitute evaluation data, or the vibration data are converted into evaluation data, in particular by the evaluation unit, and the evaluation data are compared with stored reference data, in particular with reference data stored in the evaluation unit, and depending on the comparison result, in particular by the evaluation unit, an error signal is generated, in particular signaled.

[0011] Preferably, the at least one vibration sensor is arranged on the collector tank, preferably on the outside of the collector tank or on a component of the heat pump that vibrates together with the collector tank. Such a component can preferably be the refrigerant line connected to the collector tank. Preferably, the vibration sensor is then arranged on the refrigerant line adjacent to the collector tank.

[0012] In particular, if the evaluation data deviates from the reference data, preferably beyond a predetermined extent, preferably depending further on an exclusion condition, an error signal is generated, and in particular signaled.

[0013] The vibration data is preferably acquired using an evaluation unit located in or on the heat pump, preferably integrated within it. For example, the evaluation unit can be integrated into the heat pump's electronics required for its operation, or into separate electronics. The latter also allows for the retrofitting of existing heat pumps using the method according to the invention.

[0014] The aforementioned preferred conversion of the vibration data into evaluation data preferably also takes place in the aforementioned evaluation unit, but can in principle take place in any data processing unit, in particular which may also be external to the aforementioned evaluation unit.

[0015] The comparison with reference data is preferably carried out using the aforementioned evaluation unit, but can also be carried out in any data processing unit, in particular one that may be external to the aforementioned evaluation unit.

[0016] The generation of an error signal, and in particular its signaling, preferably takes place in the aforementioned evaluation unit, but can in principle take place in any data processing unit, in particular one that may also be external to the aforementioned evaluation unit.

[0017] The invention thus enables, for example, the entire process from the acquisition of vibration data to the possible generation / signaling of an error signal in the event of a fault in the heat pump, preferably to be carried out within one and the same evaluation unit, which is preferably arranged in / on the heat pump. In this way, the process can preferably be carried out independently with a heat pump.

[0018] The invention also makes it possible, for example, to record only the vibration data in the heat pump, particularly with an evaluation unit that participates in the evaluation and the process steps according to the invention through the recording, but does not carry them out completely itself. For example, it can also be provided that the recorded vibration data or evaluation data converted therefrom are transmitted by remote data transmission to an evaluation service / server external to the heat pump, which is, for example, cloud-based. For this purpose, the aforementioned evaluation unit can preferably include a communication connection, in particular for connection to a wide area network, especially the internet. For example,The subsequent process steps are carried out there, in particular the conversion of the vibration data into evaluation data, especially the comparison with reference data, which are then also stored there, and in particular the generation and / or signaling of an error signal. In this case, some of the process steps take place internally within the heat pump and some externally. The aforementioned evaluation service / server then includes the previously mentioned external data processing device.

[0019] Furthermore, the problem is solved by a heat pump of the type mentioned above, which has at least one vibration sensor and an evaluation unit with which vibration data can be recorded from the at least one vibration sensor, representing the vibrations of the collector container, and the evaluation unit is set up to compare evaluation data formed from the vibration data or which can be calculated from the vibration data with the evaluation unit with reference data and to generate an error signal depending on the comparison result, in particular to signal it.

[0020] Here too, it is preferably provided that the at least one vibration sensor is arranged on the collector tank or on an element of the heat pump that can be set into vibration together with the collector tank, e.g. on the refrigerant line in front of or behind the collector tank, in particular adjacent to the collector tank.

[0021] The invention's mode of operation is based on the consideration that the receiver, with its fill-level-dependent mass, can be viewed as a damped oscillating spring-mass system. A loss of refrigerant mass in the receiver causes a reduction in mass and / or damping, resulting in changes to the oscillation amplitude and frequency, particularly the natural frequency. These changes are detected and evaluated by the invention, specifically by comparing the oscillations of the receiver in its current state with those of the receiver in a target state, particularly when the receiver has a target fill level.In order to be able to compare the vibrations metrologically, they are recorded in both states by vibration data which represent the respective vibrations, whereby the vibration data to the target fill level form reference data with which the comparison takes place.

[0022] In particular, reference data are understood to be data that correspond to the evaluation data at the same operating point, especially at the same compressor rotational speed (Z-frequency), and at a predefined target fill level of the collector tank. The reference data were thus generated and stored in the same way as the evaluation data during the process. A comparison can therefore be made, for example, by calculating the difference between the evaluation data and the reference data. The term "reference data" does not necessarily imply multiple data points. A single value can also be understood as reference data.

[0023] The operating point is characterized, for example in air / water heat pumps, by the specification AxWy, where x denotes the temperature of the air from which the heat is extracted and y the temperature of the water to which the water is raised.

[0024] Preferably, a vibration sensor mentioned above is designed by an acceleration sensor which, in addition to the vibration data according to the invention, then provides acceleration data, in particular which also represent the vibrations of the collector container, in this case based on the accelerations occurring during the vibrations.

[0025] The vibration data provided by the vibration sensor can preferably represent the evolution of an electrical signal over time, in particular, it can represent the evolution of acceleration as an electrical signal over time. The term "data" does not necessarily imply that the data must be digital. Analog data, e.g., as an electrical signal, is also included in this term.

[0026] Acquisition preferably means receiving the vibration data from the sensor, and in particular also storing the vibration data, especially in the evaluation unit, for which a storage space may be provided in the evaluation unit.

[0027] Preferably, the aforementioned signaling can be achieved by displaying the error signal on the heat pump or, for example, by communicating the error signal to a receiving device, e.g., via cable or wireless connection, e.g., via a mobile network connection, WLAN, Bluetooth, etc.

[0028] A previously mentioned exclusion condition can, for example, define that the detected deviation does not lead to the generation of the error signal upon its first detection, but that the generation only occurs if the detection occurs multiple times, preferably more often than a predetermined limit per defined period, e.g., per day or week.

[0029] The invention requires that the collector container vibrates for the process to be carried out.

[0030] Preferably, in a first embodiment of the invention, the receiver tank can be excited to vibrate by the compressor during operation of the heat pump, in particular by its vibrations being transmitted to the receiver tank via the pipe connections of the refrigerant circuit. This eliminates the need for any further measures to induce vibration in the receiver tank, as this occurs automatically during operation. In this case, the receiver tank is preferably excited to vibrate by the rotational frequency of the compressor and its harmonics and / or by the mains frequency of the current used to drive the compressor and its harmonics.

[0031] Preferably, in a second embodiment of the invention, the collector tank can be excited to vibrate by a vibration generator arranged on the collector tank. This generator can, for example, be designed as a motor with an imbalance, preferably with a fixed predetermined or adjustable frequency. In this case, the collector tank is preferably excited to vibrate by the rotational frequency of the vibration generator and its harmonics. This second embodiment has the advantage that the refrigerant loss test can also be carried out when the heat pump is at standstill or switched off, particularly when it is ensured that all the refrigerant from the heat pump is collected in the collector tank.

[0032] Regardless of the type of excitation, it is preferably provided that the excitation takes place in a frequency range of 10 Hz to 3000 Hz, preferably in a frequency range of 10 Hz to 2000 Hz, more preferably in a frequency range of 10 Hz to 1500 Hz, and even more preferably in a frequency range of 500 Hz to 1500 Hz.

[0033] Preferably, in all possible embodiments of the invention, the vibration data are recorded during operation of the heat pump at a reproducibly existing and / or a steady-state operating point of the heat pump, in particular exclusively at a steady-state operating point, or (exclusively) at an at least substantially steady-state operating point of the heat pump, preferably in conjunction with a predetermined rotational speed / frequency of the compressor. This ensures that the recorded vibration data are comparable with correspondingly recorded and available reference data. In particular, it is alternatively or cumulatively provided that the vibration data, and especially that the reference data, are recorded when all the refrigerant has been collected in the receiver tank.

[0034] Preferably, the reference data is generated from evaluation data that is recorded and stored by the evaluation unit at a target refrigerant level, and especially also at lower levels, in the receiver tank at at least one predetermined operating point of the heat pump, particularly in conjunction with at least one predetermined compressor rotation speed. This can be done, for example, during installation or maintenance of the heat pump at its intended location or during a test run of the heat pump at the manufacturer's premises.

[0035] It can therefore be provided that reference data can be regenerated at any time and stored, preferably in the evaluation unit, in particular by overwriting previous reference data or at least rendering it invalid. Such an overwrite can also be carried out externally by the manufacturer, for example by an OTA update (over-the-air update), preferably for which the heat pump, in particular its evaluation unit, has a communication interface, e.g. a radio interface.

[0036] The invention can also provide that the reference data are formed by evaluation data which are transferred from a database to the evaluation unit by the manufacturer of the heat pump before its installation at the destination, or that these are pre-programmed into the evaluation unit during its manufacture depending on the technical data of the heat pump.

[0037] A particularly preferred embodiment is one in which the vibration data, especially when the receiver is excited by the compressor, are recorded during an operating state of the heat pump in which, with the expansion valve closed, the refrigerant has been completely pumped into the receiver by the compressor, and in particular, the suction-side sections of the refrigerant circuit between the compressor and the expansion valve are empty, and the compressor has not yet been switched off. For example, such an operating state could be a shutdown phase of the heat pump or the charging of a storage tank.

[0038] Such conditions are reproducible and therefore particularly suitable for comparison with reference data, especially data that were generated in the same state at a target fill level.

[0039] It is further preferred that the vibration sensor records vibration data representing the vertical vibration of the receiver tank, i.e., in which the mass of the receiver tank oscillates in and against the direction of gravity. Investigations of vibrations in different directions have shown that vertical vibration exhibits the greatest changes in refrigerant loss compared to other directions.

[0040] Particularly in this design, but also when detecting other vibration directions, it is preferably intended to arrange the vibration sensor on top of the lid area of ​​the collection container.

[0041] In a preferred embodiment, which can be implemented in all possible versions of the invention, the invention provides that the vibration data are acquired, preferably repeatedly, over a predetermined period, in particular over a period of less than 30 seconds, preferably less than 20 seconds, and preferably less than 10 seconds. "Repeatedly" preferably means that the vibration data are acquired multiple times at a given static operating point and / or that the vibration data are acquired whenever the same operating point or one of several predetermined operating points is reached. Thus, the periods between repeated acquisitions can also include the switching-off times of the thermal points.

[0042] As mentioned at the beginning, the recorded vibration data can directly form the basis of the evaluation data. This can be the case, for example, if the vibration data does not require any conversion or other processing in order to be compared with reference data. If, for example, a discrete value is recorded during a measurement with a vibration sensor, this discrete value can form the basis of the evaluation data, which is then compared with reference data.

[0043] Here too, the plural of "data" does not necessarily imply multiple values / data to be compared. It can also refer to a single value.

[0044] In the preferred case, the invention will provide that the vibration data are converted into evaluation data before the comparison with reference data according to the invention.

[0045] For example, one implementation may provide for the conversion of vibration data into evaluation data by integrating the vibration data over a predetermined time period, specifically the period during which the vibration data were recorded. It may also be possible to calculate an RMS (Root Mean Square) value from the vibration data in conjunction with this integration, particularly by dividing the value obtained from the integration by the time period and then taking the square root.

[0046] For example, such a procedure can be implemented if a vibration sensor is already configured to detect vibrations only within a specific frequency interval of interest, or if the vibration data is restricted to such a frequency interval by means of a bandpass filter, particularly where changes due to refrigerant loss lead to measurably detectable vibration changes. A particularly preferred embodiment involves converting the vibration data into evaluation data by transforming the vibration data from the time domain to the frequency domain, especially by Fourier transformation or by generating periodic diagrams. The invention can thus provide for the generation of the power spectral density (PSD) of the vibration data.This spectral power density represents the power of the vibrations at the respective frequencies for which the vibration data from the previous recording is available.

[0047] In a preferred embodiment, the invention provides that a frequency interval is selected from the vibration data in the frequency domain, in particular from the spectral power density of the vibration data, in particular a frequency interval which includes the resonance frequency or a resonant frequency range of the collector container, in particular which includes the resonance frequency of the collector container excited by a harmonic of the mains voltage frequency.

[0048] The selected frequency interval is preferably chosen to be smaller than the total interval of all frequencies occurring in the vibration data. Suitable frequencies for comparison, or the power levels present at those frequencies, can thus be specifically selected, and in particular, other frequency components can be discarded.

[0049] Even more preferably, the invention provides that the integral is formed from the vibration data in the frequency domain, in particular from the spectral power density of the vibration data, or from data calculated therefrom over all frequencies of the selected frequency interval, preferably wherein an RMS value is calculated from the powers of the frequencies of the selected interval.

[0050] For example, to preferably calculate an RMS value, i.e., a squared mean, the integral is formed of the square of the vibration data in the frequency domain, in particular of the spectral power density of the vibration data, which already includes a squaring, over all frequencies of the selected frequency interval, this integral is multiplied by the reciprocal of the frequency width of the selected frequency interval, and the square root of this is formed.

[0051] The evaluation data thus includes a single RMS value and is compared with a reference value formed in the same way under the same operating conditions (in particular given by the operating point of the heat pump and the rotation frequency of the compressor) at a target fill level of the collection tank.

[0052] The conversion steps mentioned above can, as mentioned, preferably be carried out in the evaluation unit mentioned, but can also be carried out externally.

[0053] An embodiment of the invention is explained with reference to the following figures.

[0054] Figure 1 shows a schematic block diagram of a heat pump according to the invention. This comprises a compressor 1, a condenser 2, a receiver 3, an expansion valve 4, an evaporator 5 and a refrigerant circuit 6 formed by pipe sections, which connects the aforementioned components, and in which the refrigerant 7 stored in the receiver 3 can be circulated through these components.

[0055] The function of a heat pump, which is known in itself, is essentially as follows:

[0056] When compressor 1 is operating, liquid refrigerant 7 is drawn in from the receiver 3. As it passes through the expansion valve, the refrigerant expands, cooling down as it enters the evaporator. In the evaporator, it absorbs energy from an environmental medium, such as air or water, thereby becoming gaseous. In compressor 1, the gaseous refrigerant 7 is compressed, increasing its pressure and temperature. In condenser 2, the energy carried by the refrigerant 7 is transferred to another medium, such as water in heating applications, or to air. This causes the refrigerant 7 to condense back into liquid and return to receiver 3, whereupon the cycle repeats.

[0057] The receiver 3 can store the refrigerant 7 at various fill levels. Figure 2 shows that the coefficient of performance (COP) of a receiver-based heat pump remains virtually unaffected over a wider range of fill levels. In this example, the COP is almost constant between approximately 1200 grams and 2500 grams of refrigerant. Only above or below this range does the COP decrease significantly.

[0058] Standard internal temperature or pressure sensors in heat pumps cannot detect a decrease in the refrigerant level (7) due to a leak in the range of 2500 to 1200 grams of refrigerant. A leak could only be detected after approximately 1300 grams of refrigerant had escaped into the environment.

[0059] However, the invention also enables the detection of the loss in the aforementioned area when the heat pump still exhibits normal operating behavior.

[0060] According to Figure 1, the heat pump has a vibration sensor 8 and an evaluation unit 9 on the collector tank 3, with which vibration data from the vibration sensor 8 are recorded when the collector tank 3 is set into vibration, e.g. by the operation of the compressor 1 or alternatively with a vibration generator 10 attached to the collector tank 3, in particular to its bottom.

[0061] The vibration generator 10 is optional and is therefore shown with a dashed line. Figure 1 also shows, as an alternative, the arrangement of a vibration sensor 8 (hatched) on a section of the refrigerant circuit, which is set into vibration together with the collection tank.

[0062] Preferably, the evaluation unit 9 calculates the required evaluation data from the acquired vibration data and compares it with reference data. Depending on the comparison, an error signal is generated and signaled externally, for example, via the signaling device 11. However, these steps can also be performed externally by the evaluation unit 9, which acquires the vibration data. This is optionally illustrated in Figure 1 by the dashed cloud, which represents, for example, an internet-based service.

[0063] In the preferred embodiment presented here, vibration data is recorded over a predetermined time interval, e.g., 10 seconds. This data is then converted into evaluation data, e.g., by calculating the spectral power density, particularly using Fourier transformation. From the calculated spectral power density, a frequency interval is selected, and an RMS value is calculated for this interval. The selected frequency interval preferably includes a natural frequency of the vibrations of the collector container, which is excited.

[0064] Figure 3 shows, by way of example, the power densities of a resonant oscillation in a selected frequency interval in the range of 880 Hz to 1080 Hz for three fill levels of 700 grams, 1000 grams and 1500 grams of refrigerant in the collector vessel 3. The invention is not limited to the aforementioned frequency interval. Any sub-interval of the frequencies of the calculated spectral power density is possible.

[0065] Here it can be seen that as the fill level decreases, the frequency of the resonant oscillation shifts significantly to higher frequencies, and the power density increases. In this example, the shift is from approximately 960 Hz to 980 Hz. If, for instance, the power spectrum at a fill level of 1500 grams were to serve as the reference data, and the power spectrum at a fill level of 700 grams as the evaluation data, then the frequency shift and the change in amplitude would indicate that refrigerant has escaped.

[0066] To facilitate a comparison of the power spectra at a target fill level and a currently measured fill level, the invention preferably provides to generate an RMS value for the selected frequency interval.

[0067] Figure 4 shows RMS values ​​in several curves representing different operating points of the heat pump, plotted against various fill levels. Looking again at Figure 2, a target fill level that ensures reliable operation of the heat pump lies between 2000 and 2500 grams, for example, 2200 grams.

[0068] Looking at Figure 4, it can be seen for all measured operating points of the heat pump that the RMS values ​​increase with decreasing refrigerant level, starting from the RMS value at 2200 grams, which forms the reference data.

[0069] By comparing the RMS values ​​of the vibration data from a currently operating heat pump with the reference data generated in the same way, it can be determined that refrigerant is escaping. This finding, according to the procedure, leads to an error message that can be signaled externally.

[0070] Figure 5 shows a possible procedure implementation using a flowchart.

[0071] Starting (top left) with the recording of acceleration data as vibration data of the invention by means of an acceleration sensor as a preferred embodiment of a vibration sensor, preferably in an operating state of the heat pump in which, with the expansion valve closed, the refrigerant has been completely pumped into the collector tank by the compressor, the spectral power density is subsequently calculated as described above, and from this the vibration power is calculated as an RMS value for a predetermined frequency band or interval, as described above.

[0072] The following decision diamond checks whether the measurement is an initial measurement. If so, the calculated RMS value is used as reference data, stored, and then made available for comparison. If it is not an initial measurement, the decision diamond branches directly to the comparison and uses the reference data from a previously performed initial measurement.

[0073] In the following comparison diamond, the current RMS value (RMSaktueii) is compared with the reference RMS value (RMSRef), i.e., the reference data, specifically taking into account a multiplication of the RMS value forming the reference data by at least one further factor. Instead of at least one factor, the RMS value forming the reference data can also be added with an offset. In both cases, this results in a minimum difference between the RMS values ​​being compared that must be exceeded before an error is considered detected.

[0074] If the comparison diamond leads to a fault detection, it can be preferentially checked whether this fault has already been detected multiple times, namely more than a predefined limit of detections per day or week. Taking this exclusion criterion into account, the leakage is considered detected downwards in the flowchart and not detected upwards.

[0075] If the comparison diamond does not lead to any fault detection, the evaluation unit waits for a detection mode and checks in the decision diamond shown above whether this is the case because the heat pump is at least essentially in a steady-state operating point at a constant compressor frequency.

[0076] If this is the case, acceleration data is (again) recorded as vibration data. If this is not the case, the evaluation unit is in a waiting loop.

[0077] The process flow shown here in the flowchart preferably takes place entirely in an evaluation unit that is located in or on the heat pump, but can also be carried out at least partially externally to an evaluation unit which records at least the vibration data in / on the heat pump.

Claims

July 23, 2025 Patent claims 1. Method for detecting refrigerant loss in a heat pump which has a receiver tank (3) for the refrigerant (7) in the refrigerant circuit (6), wherein a. the receiver tank (3) is excited to vibrate, and b. vibration data representing the vibrations of the receiver tank (3) are recorded by means of at least one vibration sensor (8), in particular by means of an evaluation unit (9), in particular wherein the at least one vibration sensor (8) is arranged on the receiver tank (3), preferably on the outside of the receiver tank (3) or on a component that vibrates together with the receiver tank (3), and c. the vibration data are recorded in an operating state of the heat pump in which, with the expansion valve (4) closed, the refrigerant (7) has been completely pumped into the receiver tank (3) by the compressor (1), and d.the vibration data themselves form evaluation data, or the vibration data are converted into evaluation data, in particular by the evaluation unit (9), and e. the evaluation data are compared with stored reference data, in particular with reference data stored in the evaluation unit (9), and f. depending on the comparison result, in particular by the evaluation unit (9), an error signal is generated, in particular signaled. g. in particular wherein, in the event of deviations of the evaluation data from the reference data, preferably beyond a predetermined extent, preferably depending further on an exclusion condition, an error signal is generated, in particular signaled.

2. Method according to claim 1, characterized in that the collector tank (3) is excited to vibrations a. by the compressor (1) during operation of the heat pump, in particular its vibrations are transmitted to the collector tank (3) via the pipe connections of the refrigerant circuit (6), or b. by a vibration generator (10) arranged on the collector tank (3), in particular a motor having an imbalance, preferably with a fixed predetermined frequency.

3. Method according to one of the preceding claims, characterized in that the vibration data are recorded during operation of the heat pump at an operating point of the heat pump that is at least substantially reproducible and / or steady-state, in particular exclusively at a steady-state operating point, preferably in conjunction with a predetermined rotational speed of the compressor (1).

4. Method according to one of the preceding claims, characterized in that a. the reference data are formed by evaluation data which, at a target fill level of the refrigerant (7), and in particular also at lower fill levels, in the receiver tank (3), correspond to at least one predetermined operating point of the heat pump, in particular in conjunction with at least one predetermined rotational speed of the compressor (1), in particular with the Evaluation unit (9), are recorded and stored, in particular during installation or maintenance of the heat pump at the destination or during a test run of the heat pump at the manufacturer, or b. the reference data are formed by evaluation data which are transferred from a database to the evaluation unit (9) by the manufacturer of the heat pump before its installation at the destination, or c. are pre-programmed into the evaluation unit (9) during its manufacture depending on the technical data of the heat pump.

5. Method according to one of the preceding claims, characterized in that the vibration data, in particular when the collector tank (3) is excited by the compressor (1), are recorded in an operating state of the heat pump in which the suction-side line sections of the refrigerant circuit (6) between compressor (1) and expansion valve (4) are emptied, and the compressor (1) is not yet switched off.

6. Method according to one of the preceding claims, characterized in that vibration data representing the vertical vibration of the collector container (3) are recorded with the vibration sensor (8), preferably which is mounted on top of the lid area of ​​the collector container (3).

7. Method according to one of the preceding claims, characterized in that the vibration data are recorded, preferably repeatedly, over a predetermined period of time, in particular over a period of less than 30 seconds, preferably less than 20 seconds, preferably less than 10 seconds.

8. Method according to claim 7, characterized in that the vibration data is converted into evaluation data by integrating the vibration data over the predetermined time period.

9. Method according to claim 7, characterized in that the conversion of the vibration data into evaluation data is carried out by transforming the vibration data from the time domain into the frequency domain, in particular by Fourier transformation or by forming periodigrams, preferably for forming the spectral power density of the vibration data.

10. Method according to claim 9, characterized in that a frequency interval is selected from the vibration data in the frequency domain, in particular from the spectral power density of the vibration data, in particular a frequency interval which comprises a resonance frequency or a resonant frequency range of the collector container (3), in particular which comprises the resonance frequency of the collector container (3) excited by a harmonic of the mains voltage frequency.

11. Method according to claim 10, characterized in that the integral of the vibration data in the frequency domain, in particular of the spectral power density of the vibration data, or of data calculated therefrom, is formed over all frequencies of the selected frequency interval, preferably to form an RMS value.

12. Heat pump with a refrigerant circuit (6) in which at least one compressor (1), a condenser (2), an expansion valve (4), an evaporator (5) and a receiver (3) for the refrigerant (7) are arranged, characterized in that it has at least one vibration sensor (8), in particular on the receiver (3) or on an element that can be set into vibration together with the receiver (3), and a The evaluation unit (9) has a vibration sensor (8) with which vibration data representing the vibrations of the collector tank (3) can be acquired from the at least one vibration sensor (8), wherein the heat pump, in particular the evaluation unit (9), is configured to acquire the vibration data in an operating state of the heat pump in which, with the expansion valve (4) closed, the refrigerant (7) has been completely conveyed into the collector tank (3) by the compressor (1), and the evaluation unit (9) is configured to compare evaluation data formed from the vibration data or which can be calculated from the vibration data with the evaluation unit (9) with reference data and to generate, in particular signal, an error signal depending on the comparison result.

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