Method for determining leakages in building envelopes

Abstract

A method for determining leakages (11) in a building envelope (3) of a building (1) comprising the following steps: a) generating a positive or negative pressure in the building (1) for a prescribed time period within a prescribed time frame, wherein the prescribed time period is shorter than the prescribed time frame, b) recording multiple image data of the building envelope (3) by means of infrared thermography during the prescribed time frame, c) repeating steps a) and b), and d) evaluating the image data, wherein the changes in temperature occurring at leakages (11) in the building envelope (3) as a result of step a) being repeated are detected by air flowing out or flowing in.

Description

[0001] Method for determining leaks in building envelopes

[0002] The present invention relates to a method for determining leaks, in particular air leaks, in building envelopes.

[0003] Leaks in building envelopes lead to leaks in the building itself. The applicant is aware of various measurement methods for determining the airtightness of a building, although the measurement methods described do not necessarily represent the current state of the art.

[0004] In the so-called blower door test, a differential pressure is established between the building's interior and its surroundings, and the resulting airflow is used as a measure of airtightness. The entrance door or another opening in the building is equipped with a fan. The fan can create a static positive or negative pressure within the building. The airflow through the fan is measured. This allows the quantification of the building's integral airtightness. Smoke detectors or air velocity meters can also be used to detect local airflows, allowing a qualitative determination of the location and size of a leak.

[0005] Another method is the so-called tracer gas method. In this method, an easily detectable tracer gas, often SF6, is introduced and distributed into the building under investigation. The decay curve of the tracer gas concentration in the room is determined by measuring the concentration over a certain period of time. This method quantifies the air exchange rate, which occurs due to ventilation systems, open windows, or uncontrolled leaks in the building, for example, at material transitions and corners.

[0006] This method sometimes requires the tracer gas to be injected for several hours. Depending on the gas used, this gas can displace breathable air and / or be harmful to the climate. Therefore, other uses of the building are impaired during the measurement. Furthermore, wind and other environmental conditions influence the measurement results.

[0007] Leaks in building components can also be detected using infrared thermography. This visualizes local changes or deviations in surface temperatures resulting from airflow through building components. However, the temperature difference between the building interior and the surrounding area should be at least 5-10 °C in order to be able to resolve temperature differences. In this case, it is difficult to determine the difference between a thermal bridge and an air leak. To improve the quality of the measurement, difference images can be used. In this so-called differential thermography, an infrared image is first taken in the original state of the building and a second image is taken after a fan has been switched on, which creates positive or negative pressure in the building and thus airflow through the leaks. The time interval between switching on the fan and the image capture is usually several minutes to half an hour.This time is required to generate a sufficiently measurable local temperature difference. Both images are subtracted, and the resulting thermographic image shows the temperature differences at the leaks, which can facilitate localization. In addition to differential measurement, the temperature trend of pixels or objects after the fan is switched on is sometimes analyzed. In such measurements, changes over the measurement period in wind, the radiant temperature of the sky, or the temperature of surrounding objects, which become visible as reflections in the image, can significantly distort the results, so differential infrared thermography is generally only suitable for indoor use, i.e., for measuring individual rooms.

[0008] It is therefore the object of the present invention to provide a method and a system for determining leaks in building envelopes, in which a short measuring time is realized and which is advantageously also suitable for outdoor areas and entire facades.

[0009] The method according to the invention is defined by claim 1.

[0010] The method according to the invention for determining leaks in a building envelope of a building comprises the following steps: a) generating an overpressure or underpressure in the building for a predetermined period of time within a predetermined time period, wherein the predetermined period of time is shorter than the predetermined time period, b) recording several image data of the building envelope by means of infrared thermography during the predetermined time period, c) repeating steps a) and b), d) evaluating the image data, wherein the temperature changes caused by the repetition of step a) at leaks in the building envelope due to outflowing or inflowing air are detected or determined.

[0011] Since the time period and duration are specified in step a), image data can be advantageously analyzed, as it is known when a temperature change caused by overpressure or underpressure in the building can occur on the building envelope. The image data can be assigned to a specific time period using appropriate time stamps. This allows temperature changes induced by external influences, such as shadows or wind, to be easily detected or eliminated.

[0012] The image data is preferably recorded during the specified period, both during the period in which the over- or under-suppression is generated and outside of this period. Preferably, the image data is recorded from the outside, i.e., the exterior of the building envelope is recorded.

[0013] Preferably, the predetermined time periods are of equal length when repeating step a). It can also be provided that when repeating step a), the predetermined time periods in which an overpressure or underpressure is generated in the building are of equal length, whereby the point in time within the predetermined time periods at which the generation of an overpressure or underpressure in the building begins is the same. In other words: the temporal sequence of the generation of the overpressure or underpressure in step a) is the same for each repetition of step a). Thus, an overpressure or underpressure is periodically generated in the building, so that the evaluation of the image data can be carried out in a particularly advantageous manner, since the temperature change that also occurs periodically at the leaks due to the periodic generation of the overpressure or underpressure can be detected in a particularly advantageous manner.

[0014] The positive or negative pressure in the building can be generated using a blower door system (i.e., a fan installed in a doorway). Such systems have been tried and tested many times and are therefore particularly advantageous for reproducibly generating positive or negative pressure in a building.

[0015] The method according to the invention has the particular advantage that, compared to conventional methods, it can be carried out relatively quickly and is relatively insensitive to environmental influences. The method can provide that, in step b), a temporal series of image data from the same location on the building envelope is recorded. In other words: while the method is being carried out, the camera used to record the image data is not moved, and the images are recorded at the same time intervals. Of course, it is also possible for image data to be recorded using a moving camera, with image data from the same location on the building envelope being assigned to one another for later analysis using image recognition.

[0016] When evaluating the image data in step d), the temporal temperature profile for each pixel of the image data can be broken down into frequency components and analyzed. This allows for a particularly advantageous analysis of the image data.

[0017] During evaluation, the analysis can be performed using an excitation frequency that generates overpressure or underpressure in the building. The excitation frequency can advantageously be used to infer signals caused by the overpressure or underpressure.

[0018] To decompose the temporal course of the temperature into frequency components, a Fourier transformation, preferably a fast Fourier transformation, can be carried out over each pixel of the image data.

[0019] In step a), an overpressure can be generated with a target pressure of at least 50 Pa. This value has proven particularly advantageous.

[0020] Furthermore, it can be provided that in step a), the predetermined time period has a duration of x seconds and the predetermined time duration has a duration of x / 2 seconds. In this way, a periodic generation of the overpressure or underpressure can advantageously occur. For example, the time period can be 20 seconds long, and the duration during which the underpressure or overpressure is generated can be 10 seconds.

[0021] The image data can be captured using an infrared camera. The infrared camera can, for example, be one sensitive in the spectral range of 7-14 pm.

[0022] The method according to the invention can, in principle, also be used to detect leaks in walls within a building. In this case, in addition to creating a negative or positive pressure in a room within the building, a temperature difference must be created between the room and an adjacent room from which image data is being acquired. The temperature difference can be created, for example, by heating or cooling one of the two rooms.

[0023] The invention is explained in more detail below with reference to the following figures.

[0024] Fig. 1 is a schematic representation of a system for carrying out the method according to the invention,

[0025] Fig. 2 is a schematic representation of the time sequence of the periodic generation of an overpressure and

[0026] Fig. 3 the evaluation using Fast Fourier Transformation on an exemplary pixel at a leak.

[0027] Figure 1 schematically shows a system for determining leaks 11 in a building envelope 3 of a building 1. A blower door system 7 is installed in an opening 5 in the building envelope 3, for example in a door, by means of which overpressure can be generated in the building 1. An infrared camera 9 is installed outside the building 1 and records image data of the building envelope 3. Due to the overpressure in the building 1, air escapes through leaks 11 in the building envelope 3, resulting in temperature changes that are recorded by the infrared camera 9.

[0028] In the method according to the invention for determining leaks 11 in the building envelope 3 of the building 1, the following steps are carried out: a) First, an overpressure or underpressure is measured in the building 1 for a predetermined period of time X n within a given period Z n generated, where the specified time period X nshorter than the specified period Z n During the specified period Z n In step b), several image data of the building envelope 3 are recorded using the infrared camera 9. Steps a) and b) are repeated in step c).

[0029] In a step d), the image data are evaluated, whereby the temperature changes caused by the repetition of step a) at the leaks 11 in the building envelope 3 due to the incoming or outgoing air can be detected.

[0030] In the method according to the invention, it can thus be provided that a positive or negative pressure is periodically generated in the building 1. The predetermined period Z n or specified periods Z n and the specified time period X n or the specified time periods X n are shown as a diagram in Figure 2. For example, a given time period X n, in which an overpressure or underpressure is generated in the building 1, be half as long as a given period Z n As shown in Figure 2, in one run the specified period Z n from a time tn-i to t n . At about half of the specified period Z n the blower door system 7 is switched on, so that an overpressure or underpressure is generated in the building 1 (beginning of X n ). The time period X n , in which the blower door system 7 is switched on, ends with the end of the specified period Z n By repeating the periods Z n This results in a periodic increase and decrease in pressure in building 1 and thus also a periodic temperature change at the leaks 11 in the building envelope 3. These can be advantageously detected during the evaluation of the image data. As can be seen from Figure 2, the specified time periods Z nin step a) always the same length, just like the time periods X n at which the overpressure or underpressure is generated in building 1.

[0031] For the evaluation, a Fourier transform, specifically a Fourier transform (FFT), is calculated for each pixel of the image (equation (1)). This decomposes the temporal temperature profile into frequency components and analyzes it. The result of the FFT is a complex pair of values ​​from which the amplitude (equation (2)) and phase (equation (3)) can be determined at discrete frequencies in the signal.

[0032] Figure 3 shows an example of the amplitude spectrum for a pixel near one of the two leaks 9. Since the period and thus also the frequency (in this example, 0.025 Hz) with which the blower door system 7 excited the temperature oscillations in building 1 are known, the amplitude and phase spectrum at this frequency and, if applicable, at the harmonics can be evaluated for each pixel. In this way, it can be evaluated for each pixel whether a temperature change with the known frequency or its harmonics is present, so that it can be concluded whether the pixel represents a location of a leak 11 in the building envelope 3.

[0033] Thus, the method according to the invention enables the rapid and reliable detection of leaks 11 in the building envelope 3, allowing measurements to be easily performed from the outside. External interference factors are advantageously eliminated, thus providing a reliable result. Furthermore, the results of the method according to the invention can be easily interpreted by laypersons and are thus more objective than conventional methods for leak detection in buildings.

[0034] Reference symbols Building Building envelope Opening Blower- Door system Infra red camera era Leaks

Claims

PATENT CLAIMS Method for determining leaks (11) in a building envelope (3) of a building (1) comprising the following steps: a) generating an overpressure or underpressure in the building (1) for a predetermined duration within a predetermined period, wherein the predetermined duration is shorter than the predetermined period, b) acquiring multiple image data sets of the building envelope (3) using infrared thermography during the predetermined period, c) repeating steps a) and b), d) evaluating the image data, wherein the temperature changes resulting from the repetition of step a) at leaks (11) in the building envelope (3) due to escaping or inflowing air are detected. Method according to claim 1, characterized in that during the Repetition of step a) the specified time periods are of equal length. Method according to claim 2, characterized in that during the Repetition of step a) the predetermined time periods in which an overpressure or underpressure is generated in the building (1) are of equal length, wherein the time within the predetermined time periods at which the generation of an overpressure or underpressure in the building (1) begins is the same. Method according to one of claims 1 to 3, characterized in that the overpressure or underpressure in the building (1) is generated by means of a blower door system (7). A method according to any one of the preceding claims, characterized in that in step b) a time series of image data of the same location on the building envelope (3) is recorded. A method according to any one of the preceding claims, characterized in that, during the evaluation, the temporal profile of the temperature is decomposed into frequency components and analyzed for each pixel of the image data. A method according to claim 6, characterized in that, during the evaluation, the analysis is performed using an excitation frequency to generate overpressure or underpressure in the building (1). A method according to claim 6 or 7, characterized in that, to decompose the temporal profile of the temperature into frequency components, a Fourier transform, preferably a Fast Fourier transform, is performed on each pixel of the image data.A method according to any of the preceding claims, characterized in that in step a) an overpressure with a target pressure of at least 50 Pa is generated. A method according to any of the preceding claims, characterized in that in step a) the predetermined time period has a duration of x seconds and the predetermined time duration has a duration of x / 2 seconds.

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