Acoustic-thermal method and device for determining leakiness in a building envelope
Patent Information
- Application Number
- EP2024700195
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-01-13
- Filing Date
- 2024-01-03
- Publication Date
- 2025-11-19
AI Technical Summary
Current methods for detecting leaks in building envelopes, such as the blower door test and infrared thermography, are complex, time-consuming, and require additional pressure or temperature differences to accurately distinguish leaks from thermal bridges.
A method and device that combine acoustic and thermographic imaging by generating a sound signal and capturing both images to overlay and locate leaks in the building envelope, using beamforming to enhance the accuracy of leak detection without influencing each other's errors.
This approach allows for quick and precise localization of leaks by integrating acoustic and thermographic data, increasing the accuracy of leak detection in building envelopes without the need for additional pressure or temperature differences, reducing the complexity and time required for assessments.
Smart Images
Figure 1.1
Abstract
Description
[0001] Acoustic-thermal method and device for determining leaks in a building envelope
[0002] The present invention relates to a method for determining leaks in a building envelope. Furthermore, the present invention relates to a device for carrying out the method.
[0003] The most commonly used measurement technique for assessing a building's airtightness is the pressure difference measurement method (known as the "blower door test"). This measurement method is used to measure the airtightness of buildings to meet energy standards, compare the airtightness of different buildings, or determine the reduction in air permeability after renovation measures. However, this method only determines the integral air exchange rate of a room or building. Since identifying leak locations and prioritizing sealing of larger leaks increases the airtightness of buildings, quick and easy localization is highly relevant. Leaks can currently be identified using smoke sticks or anemometers in conjunction with a blower door test or trace gases. However, these methods are very complex and time-consuming.
[0004] Infrared thermography (IR thermography) is a non-contact, non-destructive, and standardized (DIN EN 13187: 1998) measurement method for displaying the temperatures of building surfaces and thus enabling the visualization of leaks and thermal bridges in the building envelope. Surface temperatures near leaks are significantly influenced by the air flow through these openings, thus allowing for easy identification of these leaks. However, to date, a significant pressure difference, in addition to a temperature difference (at least 10°C), is usually required to clearly distinguish leaks from thermal bridges. This so-called differential thermography also takes approximately half an hour per measurement.
[0005] The object of the present invention is to provide a method and a device for improved detection of leaks in a building envelope.
[0006] The object is achieved by a method according to claim 1 and a device according to claim 10.
[0007] Methods according to the invention for determining leaks in a building envelope of a building comprise the following steps:
[0008] Generating a sound signal,
[0009] Capturing a thermographic image of at least part of the building envelope;
[0010] Acquiring an acoustic image of the same part of the building envelope by spatially resolved detection of the sound signal; and
[0011] Overlaying the thermographic image and the acoustic image to locate the leak in the building envelope.
[0012] The building envelope includes, for example, the exterior walls, glazing, roof, or any other structural elements that separate the interior of the building from its surroundings. A sound signal is then generated within the building. A thermographic image is taken from the outside of at least part of the building envelope. An acoustic image is also taken of the same part of the building envelope. In this case, the part of the building envelope for which the thermographic image was taken and the part of the building envelope for which the acoustic image was captured overlap at least partially.
[0013] The method is based on locating noises or the generated sound signals that propagate through leaks in the building envelope. One way to locate sound sources is through beamforming. In general, beamforming is a signal processing technique that enables an array of microphones to distinguish between sound sources from different directions. The measurement principle is based on the microphone array targeting different measurement points on a measurement object. During evaluation, the time signals from the individual microphones in the array are superimposed with a time delay that corresponds to the time it takes for the sound wave to travel from the measured focal point to the microphone. These time-corrected signals from all microphones are summed, resulting in a time signal assigned to the respective focal point.If the origin of a noise component is located at this point, positive interference results for all microphone signals after the corresponding time shift, thus achieving a maximum signal value. However, if the viewing angle does not match the angle of incidence of the sound waves, partial cancellation of the signals occurs. Therefore, noise sources outside the focus direction of the acoustic camera are reduced.
[0014] The method is also called an "acoustic camera" because the result of a scanning process across a range of viewing angles produces an image of the most intense constructive interference of the acoustic waves. The advantage for a variety of applications is the visual result, which can be overlaid with a visible image of the same scene. Such an acoustic camera is known, for example, from WO2013 / 024926 A1.
[0015] The thermographic image and the acoustic image are then superimposed to determine the leakiness of the building envelope. The information from the thermographic image and the acoustic image is combined by overlaying the thermographic image and the acoustic image, thus increasing the accuracy of determining the leakiness of the building envelope. Sources of error in the creation of the thermographic image do not affect the creation of the acoustic image. Likewise, errors in the creation of the acoustic image do not affect the acquisition of the thermographic image. For example, an external sound source, which would lead to errors in the creation of the acoustic image, has no influence on the acquisition of the thermographic image. Thus, by overlaying the acquired information, leaks in the building envelope can be determined with high accuracy. The thermographic image can, for example, show temperature differences.Furthermore, the acoustic image can contain spatially resolved acoustic amplitudes. The overlay of the thermographic image and the acoustic image can preferably be achieved, for example, by selecting the maximum / minimum values of the amplitudes of the acoustic image or the temperature differences of the thermographic image.
[0016] Although the method described above assumes that the sound signal is generated inside the building and the thermographic image and acoustic image are captured from outside, this can of course also be reversed, so that the sound signal is generated outside the building and both the thermographic image and acoustic image are captured and recorded from inside the building. However, it has proven advantageous to capture the thermographic image from outside, as this allows a larger area to be captured simultaneously.
[0017] Preferably, the thermographic image is acquired before the acoustic image. Alternatively, the thermographic image is acquired after the acoustic image. Alternatively, the thermographic image and the acoustic image are acquired simultaneously.
[0018] Preferably, the entire building envelope is captured using a thermographic image and / or an acoustic image. Alternatively, only sides or parts of a side of a building can be captured using a thermographic image and an acoustic image, with a separate thermographic image and acoustic image being captured for each side of the building, for example.
[0019] Preferably, the acoustic image and / or the thermographic image are overlaid with a visible image of the same scene or the same part of the building envelope. Alternatively or additionally, the result of the overlay of the thermographic image and the acoustic image is overlaid with a visible image of the same scene or, for example, the overlap between the thermographic image and the acoustic image. This allows for a simple visual location of leaks in the building envelope.
[0020] Preferably, the thermographic image and the acoustic image are captured from the same location. This ensures that the alignment of the thermographic image and the acoustic image match and, in particular, that no distortion needs to be considered when overlaying the thermographic image and the acoustic image.
[0021] Preferably, the acoustic image is captured at different frequencies. This allows for different propagation characteristics of the generated sound signal to be taken into account. Noise at certain frequencies can also be suppressed or absent at other frequencies, thus no longer affecting the creation of an acoustic image.
[0022] Preferably, the acoustic images are superimposed at different frequencies, for example, by averaging or maximum / minimum value selection. Alternatively, one or more acoustic images can be selected, provided they are not affected by background noise and / or allow clear localization of the sound signal. The acoustic images are preferably acquired in a frequency range between 20 Hz and 100 kHz. Particularly preferred are the acoustic images in a range between 400 Hz and 40 kHz.
[0023] Preferably, the sound signal is generated once, periodically or continuously.
[0024] Preferably, the sound signal is noise, in particular white noise, in the specified frequency range.
[0025] Preferably, one or more loudspeakers are positioned inside or outside the building to generate the sound signal. The loudspeaker can be a dodecahedral loudspeaker, for example, or an omnidirectional loudspeaker, so that the sound signal is generated as evenly as possible in all directions within the building.
[0026] Preferably, a positive or negative pressure is created in the building to generate the sound signal. This positive or negative pressure causes air to flow through the leaks in the building envelope. The sound signal generated by the flowing air can be used to detect the leaks. At the same time, the temperature difference is increased, for example, by warm air flowing out of the building into the cooler surroundings or vice versa, thus further increasing the signal of the thermographic image and, in particular, the temperature difference detected by the thermographic image.
[0027] Furthermore, the method is carried out using a device as described below.
[0028] The present invention further relates to a device for capturing a thermographic image and an acoustic image for determining leaks in a building envelope. The device comprises a thermographic camera and a microphone array with a plurality of microphones. The microphones are arranged at a fixed distance from one another and preferably at a fixed distance relative to the thermographic camera. The acoustic image is captured by the microphone array. Thus, the device offers a combined option for capturing the thermographic image and the acoustic image. Due to the fixed relative position between the microphone array and the thermographic camera, the thermographic image and the acoustic image can be superimposed particularly easily.Unwanted offset and / or distortion of the thermographic image and the acoustic image due to overlap, which would otherwise lead to inaccuracies in leak detection, can be minimized or corrected. Only calibration is required before the device is used for the first time.
[0029] Preferably, the thermographic camera is positioned centrally or substantially centrally of the microphone array. Thus, the microphone array surrounds the thermographic camera, ensuring a substantially identical image section of the building envelope through the thermographic camera and the microphone array when creating the acoustic image.
[0030] The microphones are preferably arranged in a circle. This circular arrangement ensures a particularly efficient arrangement of the microphones. To optimally calculate the mapping of the sound source on the building envelope, it is necessary to measure or estimate the distance between the measuring system and the wall. The specific advantage of a circular arrangement is its good insensitivity to errors in determining the distance between the measuring system and the wall or to unevenness in the wall. The microphone array preferably has more than ten, and especially more than twenty, microphones.
[0031] The microphone array preferably has an extension of between 40 cm and 200 cm, preferably between 50 cm and 120 cm, and particularly preferably between 50 cm and 100 cm. The extension defines the maximum distance between two microphones. If the microphones are arranged in a circle, the extension defines the diameter of the selected circle. The extension is an indicator of the lowest measurable frequency. The greater the extension, the lower the frequencies that can be used to locate a noise source.
[0032] Preferably, the microphones are connected to an evaluation device, wherein the evaluation device is designed to generate an acoustic image from the signals received by the microphones. To this end, the evaluation device can delay the received acoustic signals from the individual microphones using appropriate delay elements and then superimpose them to determine the noise amplitude with spatial resolution.
[0033] Preferably, each pixel of the thermographic image is assigned a noise amplitude from the acoustic image. This allows for a simple overlay of the thermographic image with the acoustic image. Alternatively, the thermographic image and the acoustic image can have different resolutions, allowing the values to be mathematically assigned to locations on the building envelope, for example, by extrapolation or averaging.
[0034] The thermographic camera is preferably an infrared thermographic camera that captures the thermographic image using infrared radiation. The invention is explained in more detail below using a preferred embodiment with reference to the accompanying drawings.
[0035] They show:
[0036] Fig. 1 is a schematic flow chart of the method according to the present invention,
[0037] Fig. 2 shows a first embodiment of the device according to the present invention,
[0038] Fig. 3A and 3B show a detailed representation of the acoustic image capture,
[0039] Fig. 4A-4C an illustration of the method according to the present invention and
[0040] Fig. 5 Measurement results according to the method of the present invention.
[0041] Figure 1 shows a process diagram according to the present invention. In step SOI, a sound signal is generated. This sound signal can be generated, for example, inside the building.
[0042] In step S02, a thermographic image of at least part of the building envelope is captured.
[0043] In step S03, an acoustic image of the same part of the building envelope or at least in an overlap with the part of the building envelope captured by the thermographic image is captured.
[0044] In step S04, the thermographic image and the acoustic image are superimposed to locate leaks in the building envelope.
[0045] Even though Figure 1 shows the acquisition of the thermographic image in step S02 before the acquisition of the acoustic image in step S03, the timing is not limited to this and the acquisition of the thermographic image can take place after, before or simultaneously with the acquisition of the acoustic image.
[0046] Figure 2 shows the device according to the present invention. Device 10 has a thermographic camera 12. Furthermore, device 10 has a plurality of microphones 14 arranged in an array. The microphones 14 are arranged at a fixed and unchangeable distance from each other and from the thermographic camera 12. In the example in Figure 2, the microphones 14 are arranged in a circle in the array, with the thermographic camera 12 being arranged centrally in the microphone array. Other array geometries are also possible. By determining the distance between the microphones, the acoustic image can be generated. By determining the distance between the microphone array and the thermographic camera 12, the acoustic image and the thermographic image can be easily superimposed, and in particular, distortion or other image errors or inaccuracies in alignment can be avoided.In the example of Figure 2, the circle has a diameter between 40 cm and 200 cm, and preferably between 50 cm and 120 cm. Furthermore, in the example of Figure 2, sixteen microphones 14 are shown as an example. Of course, the device 10 can have more or fewer microphones and, in particular, has more than twenty and preferably more than forty microphones 14.
[0047] Reference is made to Figures 3A and 3B, which schematically depict the general process for creating the acoustic image. Figure 3A shows the device 10 with eight microphones 14, which record noise amplitudes / sound amplitudes in a rasterized manner across a building envelope. This is illustrated schematically in Figure 3B. A noise from a noise source 16 reaches the respective microphones 14 via propagation paths 18. The length of the respective propagation paths 18 differs, whereby the same noise from the noise source 16 arrives at the respective microphones 14 at different times. This is illustrated in the bottom of Figure 3B. An evaluation device, which is connected to the microphones, then has delay elements 20, by which the signals from the microphones 14 are appropriately delayed. The respective delay is varied by the delay elements 20, whereby the area of the building envelope can be scanned.If the signals from microphones 14 overlap due to the set delay by delay elements 20, the location of the noise source 16 is determined from the set delays, and the combined signal from each microphone 14 is converted into a pixel of the acoustic image. Subsequently, the delays of delay elements 20 are adjusted such that the respective delays correspond to the propagation times of the corresponding transmission paths 18 of the new pixel, and the signals from microphones 14 are again superimposed. This creates an acoustic image. This process is also known as beamforming.
[0048] Reference is made below to Figures 4A-4C. Figures 4A-4C show different excitation options for detecting possible leaks in the building envelope of the building 26. For this purpose, the device 10 is arranged outside the building. In the example of Figure 4A, a loudspeaker 28 is installed, through which the sound signal is generated. The sound signal is then received by the device 10, making it possible to identify leaks through which the sound waves can pass.
[0049] Figure 4B shows an example in which a blower 29 is used to generate positive pressure in the building. Escaping air 30, which flows out through leaks in the building envelope, generates a flow noise, which is used by the device 10 to locate leaks in the building envelope. At the same time, the escaping air 30 can increase the temperature difference at the location of the leak if warm or cold air (depending on the weather conditions or regionally in air-conditioned rooms) flows out from the interior of the building through the leaks.
[0050] The example of Figure 4C combines the generation of the sound signal by means of a loudspeaker 28 and the generation of an overpressure in the building by means of a fan 29.
[0051] The following refers to Figure 5. Figure 5a shows a thermographic image of a building's window façade. This shows an increased temperature difference in the area of the window frame. Figure 5b shows an example of an acoustic image, which also implies a leak in the area of the window frame. The thermographic image in Figure 5a and the acoustic image in Figure 5b are combined so that a leak can be identified, as shown in Figure 5c.
Claims
Patent claims 1. A method for determining the locations of leaks in a building envelope of a building, comprising the steps: Generating a sound signal, Capturing a thermographic image of at least part of the building envelope; Acquiring an acoustic image of the same part of the building envelope by spatially resolved detection of the sound signal; and Overlaying the thermographic image and the acoustic image to locate the leak in the building envelope.
2. The method according to claim 1, wherein the thermographic image and the acoustic image are acquired from the same location or from different locations.
3. Method according to claim 1 or 2, wherein the acoustic image is captured at different frequencies.
4. The method according to claim 3, wherein the acoustic images are superimposed at different frequencies or one or more of the acoustic images are selected.
5. Method according to one of claims 1 to 4, wherein the sound signal is single, periodic or continuous.
6. Method according to one of claims 1 to 5, in which a loudspeaker is positioned inside or outside the building to generate the sound signal.
7. Method according to one of claims 1 to 6, in which an overpressure or negative pressure is created in the building to generate the sound signal.
8. Method according to one of claims 1 to 7, in which the sound signal is generated inside or outside the building and the thermographic image and the acoustic image are correspondingly recorded from outside or inside the building.
9. Method according to one of claims 1 to 8, wherein the acoustic image and the thermographic image are captured with a device according to one of claims 10 to 16.
10. Device for capturing a thermographic image and an acoustic image for determining the locations of leaks in a building envelope, comprising a thermographic camera for capturing the thermographic image and a microphone array having a plurality of microphones, wherein the microphones are arranged at a fixed distance from one another and preferably at a fixed distance relative to the thermographic camera, wherein the acoustic image is captured by means of the microphone array.
11. Device according to claim 10, characterized in that the thermographic camera is arranged centrally or substantially centrally in the microphone array.
12. Device according to claim 10 or 11, characterized in that the microphones are arranged in a circle.
13. Device according to one of claims 10 to 12, characterized in that the microphone array has more than 10 and in particular more than 20 microphones.
14. Device according to one of claims 10 to 13, characterized in that the microphone array has an extension of between 40cm and 200cm, preferably between 50cm and 120cm and particularly preferably between 50cm and 100cm.
15. Device according to one of claims 10 to 14, characterized in that the microphones are connected to an evaluation device, wherein the evaluation device is designed to generate an acoustic image from the received signals of the individual microphones.
16. Device according to one of claims 1 to 15, characterized in that each pixel of the thermographic image is assigned a noise amplitude of the acoustic image.