DETERMINATION OF THERMAL TRANSIT THROUGH BUILDINGS

Description

[0001] The invention relates to a method for determining a measure of heat transfer of a building component, a radar system with a computing unit for carrying out such a method, and an aircraft with such a radar system.

[0002] In the publication by Haas, Alexander, Peichl, Markus, and Dill, Stephan (2017) "Theoretical and experimental investigations of microwave signatures for characterization of building structures" in: 2012: 13th International Radar Symposium (IRS), 2017.07.28 - 2017.07.30, Prague, Czech Republic, the theoretical foundations of microwave propagation in layered media are presented. Furthermore, simulations of radar signatures and measurements for them are presented. Various layer materials are analyzed.

[0003] Furthermore, the publication by Haas, Alexander, Peichl, Markus, and Dill, Stephan (2019) "Layer determination of building structures with SAR in near field environment" of the European Radar Conference, 2019-10-02 - 2019-10-05, Paris, France, proposes the use of a synthetic aperture radar to generate high-precision images of building exterior walls using microwave radiation. Initially, measurements are proposed that focus on a single layer of the building exterior wall, but eventually, multi-layer measurements will also be considered.

[0004] The publication by Estevam Schmiedt, Jacob and Cerra, Daniele and Dahlke, Dennis and Dill, Stephan and Ge, Nan and Göttsche, Joachim and Haas, Alexander and Heiden, Uta and Israel, Martin and Kurz, Franz and Linkiewicz, Magdalena and Patel, Dhruvkumar and Peichl, Markus and Plattner, Stefan and Pless, Sebastian and Schiricke, Björn and Schorn, Christian and Tiddens, Arne and Zhu, Xiao Xiang (2017) "Remote sensing techniques for building models and energy performance studies of buildings" from EBC Annex 71: Building energy performance assessment based on in-situ measurements, April 26-28, 2017, Loughborough, UK, provides an overview of state-of-the-art methods and their application to building façades. New developments and an outlook are also presented.

[0005] In addition, the publication by Chernyshov, Vladimir N. et al., "Microwave method of nondestructive control of thermal characteristics of building materials," INDUSTRIAL LABORATORY. DIAGNOSTICS OF MATERIALS, Vol. 84, No. 10, October 26, 2018, provides a method for analyzing building components by heating samples with microwaves.

[0006] Finally, CN 208 171 449 U relates to a heat leak identification system for buildings, which comprises an infrared thermal imaging camera and a microwave moisture meter. An infrared image containing infrared image data for a heat leak is generated using infrared radiation. The microwave moisture meter performs a microwave scan at the heat leak, from which microwave scan data is generated. The system further comprises a transmission subsystem comprising a short-range transmission device, a processor, and a long-range transmission device.The short-range transmission device is connected to the infrared thermal imaging camera and the microwave moisture meter to receive the infrared image data from the infrared thermal imaging camera of the microwave moisture meter and transmit it to the processor; the server is connected to the long-range transmission device, and the processor sends the infrared image data and the microwave scan data to the server via the long-range transmission device.

[0007] The object of the invention is to provide an improved measure of heat transfer of a building element for a building or on a building.

[0008] The invention is based on the features of the independent claims. Advantageous developments and refinements are the subject of the dependent claims.

[0009] A first aspect of the invention relates to a method for determining a measure of heat transfer of a building component, comprising the steps: Emitting microwave signals at a plurality of frequencies onto a respective component, detecting microwave signals reflected at the respective component and at layer transitions in the respective component, determining a number of layers in the respective component from the reflected microwave signals, in particular by determining the propagation time of the reflected microwave signals, electromagnetically modeling the respective component in a computer model, wherein the computer model has a layer structure of the respective component with the determined number of layers and includes, as variable parameters, respective layer thicknesses and respective complex permittivities of the layers, specifying starting values ​​for the variable parameters of the computer model,iteratively adapting the computer model by repeatedly varying the values ​​of the variable parameters and by selecting a set of values ​​of the variable parameters based on a match between i) a reflection characteristic of the computer model determined analytically or by simulation and ii) an actual reflection characteristic determined from a ratio between the emitted and the detected reflected microwave signals, for each of the layers modeled in the computer model with the selected set of variable parameters: determining a respective thermal conductivity of the respective layer on the basis of a first predetermined data set, wherein the first predetermined data set specifies a relationship between complex permittivities and thermal conductivities, and determining the measure of the heat transfer of the respective component from the determined layer thicknesses and thermal conductivities of the respective layers.

[0010] In particular, previously defined frequency values ​​of interest are used in the computer model.

[0011] The measure of heat transfer is expressed in particular as the thermal transmittance coefficient, which in the case of a flat wall indicates the heat flow relative to an area and relative to a temperature difference when both sides of the wall are surrounded by air at different temperatures. The thermal transmittance therefore indicates the energy efficiency of a building element and allows statements to be made as to whether relatively higher or lower heating costs for a building will be incurred. The thermal transmittance coefficient is typically also referred to in the construction industry as the U-value and is preferably given in the unit [W / (m 2 < K)] (watts per square meter and Kelvin). Instead of the thermal transmittance coefficient, a value of the thermal resistance can also be given as a measure of heat transfer, which is in particular the inverse analogue of the thermal transmittance coefficient.In other words, the measure of the heat transfer of the building component indicates how well the building component protects a heated interior of the building from cooling down, for example in winter when outside temperatures are cold.

[0012] In contrast, the term thermal conductivity refers to a material property that indicates the material's ability to conduct heat via a heat flow. In other words, thermal conductivity essentially indicates whether a material is suitable for thermal insulation of buildings and is typically expressed in the unit [W / (mK)] (watts per meter and Kelvin). Thermal conductivity is preferably expressed as a specific quantity, namely the thermal conductivity coefficient. Equivalently, thermal conductivity can be expressed as thermal resistance, also typically a specific quantity, which is, in particular, the inverse of thermal conductivity. Which measure of thermal conductivity is used, as a nominal value or inverse value, and in which unit, is irrelevant for the implementation of the method as such.

[0013] The term "building component" refers to a component for a building or, alternatively, to a component on a building. Thus, the method according to the first aspect of the invention can be applied both to individual exposed components in the sense of samples or specimens and to finished buildings. The term "building component" therefore refers to a component for a building or, alternatively, to a component on a building, for example, a wall, a floor, a ceiling, a roof, or the like.

[0014] The microwave signals are defined and thus completely known microwaves emitted by an antenna. Microwaves are a form of electromagnetic radiation in the range, in particular, between 300 MHz and 300 GHz, i.e., in the range with wavelengths between 1 mm and 1 m. The microwave signals are radiated at a variety of frequencies in the direction of a respective component. Microwave signals are preferably emitted in a frequency range between 0.1 and 50 GHz, particularly preferably between 0.5 and 20 GHz, and even more preferably between 0.8 and 18 GHz. While lower frequencies, for example in the 0.1 GHz range, enable a greater penetration depth than high frequencies, the lower frequencies typically also require larger antennas. Therefore, a compromise must be found between the size of the antenna and the penetration depth into the component material, especially when choosing the lowest frequency.Very high frequencies, for example in the range above 18 or 20 GHz, typically penetrate less deeply into matter because the high frequencies are more likely to be attenuated than lower frequencies due to the typically present low-pass damping characteristics.

[0015] The microwave signals are emitted at a variety of frequencies. This is preferably done by a frequency sweep, in particular by a chirp or frequency-step method. This generates a microwave signal with a sinusoidal waveform, with frequencies increasing (or decreasing) over time. The emitted microwave signal is used for a predetermined period of time. For example, at the beginning of the microwave signal's transmission, very low frequencies are emitted, starting with a starting frequency (e.g., 0.8 GHz). The microwave signal exhibits increasingly higher frequencies towards the end of the predetermined period, until the final frequency (e.g., 18 GHz) is finally reached. Such a waveform therefore exhibits a correspondingly broad spectrum. A frequency sweep is particularly suitable for analyzing the emitted and reflected microwaves in the frequency domain.In contrast, a pulse of finite width in the microwave signals, especially one with an ideally needle-shaped profile, is particularly suitable for time-domain analysis. Other shapes such as a triangular or Gaussian-like profile are possible. Such a pulse with finite width also has a large number of frequencies; however, in contrast to the frequency sweep mentioned above, the large number of frequencies appear (ideally) at the same time, whereas in the frequency sweep the large number of frequencies appear one after the other. In theory, both methods are equivalent and interconvertible. Technological reasons may be used for the selection. What both examples have in common, however, is that the microwave signals have a large number of frequencies, thus covering a broad spectrum of frequencies with theoretically the same information content.

[0016] Alternatively, it is possible to impose a noise signal or another signal form with identical bandwidth on the microwave signals, whereby, regardless of the signal form, the emitted microwave signal must also be recorded so that it is defined and thus completely known.

[0017] The microwave signals emitted toward the respective component are reflected at the component's surface and at layer transitions within the component. The speed of light typically changes at these transitions between layers of the component, resulting in a change in the characteristic impedance and, consequently, in a partial reflection of the microwave signals. Since the microwave signals are reflected at different times along their path through the respective component due to the finite speed of light, depending on the distance between the layer transitions, these echoes of the microwave signals are received at different times. Preferably, a time-of-flight determination method is used (particularly using a time or distance profile after conversion to the speed of light) to detect the time- or location-shifted reception of the echoes of the microwave signals.The detection of the reflected microwave signals is particularly coherent, meaning that the amplitude and phase of the reflected microwave signals are detected.

[0018] The reflection characteristic, particularly the temporal and spatial variation of the reflection strength, is determined primarily by the number of layers, the layer thicknesses, and the complex permittivities of the respective layers. A complex permittivities correlate directly with the speed of light of a microwave signal passing through the respective layer. A component's reflection factor is typically specified as a complex value in the frequency domain, including magnitude and phase, while the reflection characteristic is specified as a real value in the time domain (particularly with a time or distance profile).

[0019] A priori, however, the absolute value of the speed of light for each layer of the component is generally unknown because its (complex) permittivity is unknown. This means that not only the layer thickness but also the complex permittivity must be adjusted through subsequent process steps. If, in a special case, the material of a layer of the component is known, an estimate of the permittivity and thus the speed of light for microwaves in the material of the layer would also be known. This known estimate could therefore be determined. However, if the exact layer structure is not exactly known, as is to be expected in existing buildings, both the layer thickness and the permittivity of a layer must be determined using a particularly iterative process according to the following steps.In individual cases, iterative adjustment of the computer model by repeatedly varying the values ​​of the variable parameters can be replaced by an analytical solution, particularly linear optimization. However, the solution executed in one step can generally be traced back to iterative adjustment and repeated variation of the values, so both solutions can be considered equivalent.

[0020] The term "layer" does not necessarily refer to a continuous and homogeneous layer of material extending completely across the respective component; rather, the term "layer" should be understood as a uniform material along a normal to the component, which is particularly planar in shape, with the microwaves passing through the component, particularly along this normal. For example, pipes, electrical cables, pores, plaster, screws, drill holes, dowels, fasteners, or other "disturbances" in the respective component lead to a transition between layers. The layers are determined in particular by material changes along an imaginary straight line through the respective component.In practice, due to the antenna directional characteristics, it is typically a volume area essentially shaped like a cone segment along the imaginary straight line from which the measurable interaction of the microwaves with the matter or layers takes place.

[0021] The next step involves the electromagnetic modeling of the respective component in a computer model. This computer model has the number of layers determined above from the reflection characteristics. The layer thicknesses and the respective complex permittivities of the layers are used as variable parameters of the computer model. The layer thicknesses describe the extent of an essentially homogeneous and coherent material along a perpendicular to the respective component, which is particularly planar in shape, with the microwave signals propagating essentially along this perpendicular. In contrast to the propagation of microwaves in a vacuum, the reflection characteristics of microwaves in matter are typically dependent on the frequency of the microwave signals. The complex permittivity therefore represents an amplitude and a phase for a specific respective frequency based on the concept of complex numbers.In particular, the complex permittivity has a real part and an imaginary part, which are indirectly responsible for the reflection behavior at a layer transition and attenuation due to absorption in a layer.

[0022] The variable parameters of the computer model, i.e., the respective layer thicknesses and the respective complex permittivities, are preferably varied using an iterative process, whereby initial values ​​for these variable parameters of the computer model are initially specified. The specification of the initial values ​​of the variable parameters is advantageously determined based on prior knowledge, particularly if, for example, it is known that most of the (thicker) layers consist of typical building materials such as concrete or brick, and presumably thinner layers of the building element, for example, consist of plaster, an insulating layer, or an air gap. Typically, initial values ​​for complex permittivities of common building materials are selected, in particular, a real part between 1 and 10 and an imaginary part between 0.01 and 1.Subsequently, these variable parameters are modeled as parameter combinations of the computer model and the particularly iterative procedure ends with a selection of a set of variable parameters.

[0023] The selection of the (most probable) values ​​of the variable parameters is based on a particularly best match between i) a reflection characteristic of the computer model determined analytically or by simulation and ii) an actual reflection characteristic determined from a ratio between the emitted and the detected reflected microwave signals.

[0024] While the above point i) concerns the reflection characteristic determined on the basis of a calculation, point ii) refers to the reflection characteristic determined on the basis of a measurement.

[0025] In i), a reflection characteristic of the computer model is determined for each of the varied values ​​of the variable parameters by simulation or analysis, whereby exactly one reflection characteristic is then determined for each tuple of varied values ​​of the variable parameters. Using these varied values ​​of the variable parameters, a multitude of reflection characteristics of the computer model is thus generated. This multitude of reflection characteristics is compared with a determined actual reflection characteristic of the respective component. Preferably, the set, i.e., the tuple, of variable parameters is used whose assigned reflection characteristic determined by simulation or analysis best matches the determined actual reflection characteristic.

[0026] The selection of these values ​​for the variable parameters is based on the best match, as explained above. Preferably, a grid is defined over a predefined range of values ​​with a specified spacing of the variable parameters in order to calculate the respective reflection characteristics using the respective variable parameters. After calculating all reflection characteristics for all variable parameters of the grid, the best match with the actually determined reflection characteristics is preferably transmitted. Alternatively, a nonlinear optimization method is preferably used to achieve targeted convergence of the variable parameters towards a best match, whereby the match is converted into a cost function to be minimized by the nonlinear optimization.

[0027] The ratio between the emitted and the detected reflected microwave signals makes it possible to determine the actual reflection characteristics. The data obtained in this way is preferably normalized, which can be achieved, for example, by calibration with known measurement standards. This is particularly important to ensure that the measured and theoretical results have the same scale for comparison. The analysis is preferably carried out by correlation analysis with a number of data points, preferably from the range of 512 to 4096 data points, particularly preferably from the range of 1024 to 2048 data points. The number of data points is advantageously adapted to the radar system used. A number of data points in powers of two is preferably used, as this allows the efficient application of the fast Fourier transform (FFT) in order to switch between display in the time domain and the frequency domain.

[0028] While a reflection factor as a measure of the reflection characteristics can be analytically calculated from the computer model, a preferred alternative is to simulate the computer model by providing the computer model with virtual microwave signals as signal input, which correspond to the actually emitted microwave signals. One output of the computer model used in a simulation is simulated reflected microwave signals, which can be compared in the time domain or frequency domain with the actually recorded reflected microwave signals of the respective component.In contrast, when using a reflection factor that is analytically determined from the computer model, the reflection factor calculated from the computer model is compared with an actually determined reflection factor. The actually determined reflection factor is preferably determined by an appropriately calibrated radar system for transmitting the microwave signals and detecting the reflected microwave signals. In other words, the parameter combinations are preferably calculated with each other using the computer model and its layers to obtain a calculated reflection factor in the frequency domain or, equivalently, a reflection characteristic in the time domain, and compared with the reflection factor determined based on a measurement.

[0029] By comparing the reflection factor determined from the computer model with the reflection factor of the respective component empirically determined from the actual test, the agreement can be verified and the most suitable set of values ​​for the variable parameters of the computer model can be selected. This provides a computer model that, using the selected values ​​of the variable parameters, includes a layer structure corresponding to the respective real component.

[0030] The first predefined data set, which was preferably determined empirically, in particular using a corresponding (different) measurement method, conveys a general relationship, i.e., a regularity, between complex permittivities and thermal conductivities, preferably in the form of a table with a finite number of discrete support points whose values ​​can be interpolated, or in the form of a graph, a linear function, a polynomial function, or similar. Using this first predefined data set, it is possible to assign a respective thermal conductivity of the respective layer in the computer model to the respective modeled complex permittivity of the computer model with the selected set of variable parameters.This empirical relationship includes, in particular, the relationship between a respective complex permittivity and a density of a substance, and in turn a relationship between the density and the thermal conductivity of the respective substance, which results in, in particular, an overall relationship between a respective complex permittivity of the substance and the thermal conductivity of the substance.

[0031] Finally, the measure of heat transfer is determined from the determined layer thicknesses of the component, which correspond to the selected layer thicknesses from the variable parameters of the computer model, and from the determined complex permittivities of the layers, which correspond to the selected complex permittivities of the variable parameters. This is possible in particular because the thermal conductivities of layers with known layer thicknesses are known, especially over a surface of the respective component.

[0032] It is therefore an advantageous effect of the invention that by transmitting microwave signals to a component and receiving the reflected microwave signals, a measure of the component's heat transfer can be determined very quickly, without contact and without damage. This enables a rapid analysis of the thermal insulation properties of building components or building elements.

[0033] According to an advantageous embodiment, the method further serves to determine a measure of a heat capacity of the building component, further comprising the steps: for each of the layers modeled in the computer model with the selected set of variable parameters: determining a respective specific heat capacity of the respective layer on the basis of a second predetermined data set, wherein the second predetermined data set specifies a relationship between complex permittivities and specific heat capacities, and determining a total heat capacity of the respective component from the determined respective layer thicknesses and the determined specific heat capacities of the respective layers.

[0034] The second predefined data set specifies a regularity between complex permittivities and specific heat capacities in general. The relationship is preferably specified by a finite number of discrete support points, which can then be interpolated; alternatively, preferably by a graphical relationship or a linear function such as a straight line or a polynomial function. In particular, the second predefined data set comprises a relationship, i.e., a regularity, between real parts of the complex permittivities and specific heat capacities in general. While the specific heat capacity is a generalized value dependent on a mass, the total heat capacity specifies an absolute heat capacity of the component, whereby the mass of the component is already taken into account in the total heat capacity.

[0035] According to a further advantageous embodiment, the microwave signals are emitted and the reflected microwave signals are detected by a radar device, wherein the radar device is moved along a building and wherein the method described above and below is repeated in a plurality of positions of the radar device relative to the building.

[0036] By moving the radar device along a building, in particular along an outer or inner wall of the building, the method according to the invention can in principle be carried out for structural elements of any size and entire building sections. If an essentially one-dimensional beam of microwave signals is emitted and the radar device is moved in a straight line, a two-dimensional image of the structural element or building section can be determined. If, in addition, the radar device is also moved in a direction different from the first straight line, so that the radar device is moved over a surface of the structural element or building section, a three-dimensional image can be generated in the computer model. The radar device is preferably moved manually, i.e., guided by a user. In particular, it is moved on guide rails.Alternatively, the radar device is preferably arranged on a mobile robot or an unmanned aerial vehicle, the latter advantageously flying over an outer wall of a building in particular by means of a corresponding autopilot control in order to generate the above-mentioned three-dimensional computer model of the building's structural elements.

[0037] According to a further advantageous embodiment, the reflected microwave signals detected at the plurality of positions are combined to form an overall image using a synthetic aperture method or by simply arranging them one after the other. In particular, the arranging is performed in a positionally correct manner, i.e., consecutively and consistently, so that the successively detected reflected microwave signals across various positions of the building can be combined to form an overall image. Using the synthetic aperture method, the movement of the radar device over a certain path length is utilized to achieve significantly higher spatial resolution in this direction, with the assembling of the individual images extending this high resolution to a fundamentally unlimited area of ​​the building.

[0038] According to a further advantageous embodiment, a respective complex permittivity comprises a respective real part and a respective imaginary part, wherein the first predetermined data set and / or the second predetermined data set indicate a relationship between respective real parts of the complex permittivities and thermal conductivities. Especially during the empirical acquisition of information for generating the first predetermined data set, a linear relationship between a respective real part of the complex permittivity and the respective thermal conductivity of the respective material can be revealed. Likewise, during the empirical acquisition of information for generating the second predetermined data set, a linear relationship between a respective real part of the complex permittivity and the specific heat capacity of the respective material can be revealed.In these cases, the respective imaginary part of the complex permittivity can advantageously be neglected.

[0039] According to a further advantageous embodiment, for areas of the building with overlapping detected reflected microwave signals, the detected reflected microwave signals are averaged at least in sections. Averaging the detected reflected microwave signals in areas of a building element or part of a building that are repeatedly illuminated by microwave signals advantageously reduces distortions that would otherwise result in a lower-quality detected reflected microwave signal due to interference or other effects. Errors, noise, and very small-scale fluctuations in the actual material distribution are therefore advantageously also averaged, thus improving the quality of the information content of the detected reflected microwave signals for the overall result of the building characterization.

[0040] According to a further advantageous embodiment, the microwave signals are emitted and / or the reflected microwave signals are detected fully polarimetrically. In particular, linearly or circularly polarized microwave signals are emitted, and co- or cross-polarized microwave signals are received. Furthermore, a bi-static arrangement of a transmitting and receiving antenna with a corresponding angle of the main beam direction to the wall normal is preferably used.

[0041] According to a further advantageous embodiment, the reflection characteristic, in particular of the computer model, is determined analytically by using a computer model that includes a model of line theory in which imaginary high-frequency lines of different lengths and different complex permittivity are connected in series and have a terminating resistor at the output in order to determine a frequency-dependent reflection factor of the computer model.

[0042] A further aspect of the invention relates to a radar system with a computing unit, wherein the radar system is specially configured and designed to carry out the method.

[0043] According to an advantageous embodiment, the radar system is used bi-statically, i.e., with separate transmitting and receiving antennas. This advantageously allows for the use of an angle-of-incidence dependency.

[0044] Advantages and preferred developments of the proposed radar system result from an analogous and analogous transfer of the statements made above in connection with the proposed method.

[0045] A further aspect of the invention relates to an aircraft with such a radar system. The aircraft is in particular an unmanned aircraft, preferably a multicopter such as a quadrocopter or hexacopter, on which such a radar system is mounted. The unmanned aircraft is preferably manually controlled; alternatively, a predetermined path is preferably flown using an autopilot system, in each case to capture large-scale building walls and generate a 3D model of the building's structural elements.

[0046] Further advantages, features, and details will become apparent from the following description, which – where appropriate with reference to the drawings – describes at least one embodiment in detail. Identical, similar, and / or functionally equivalent parts are provided with the same reference numerals.

[0047] They show: Fig. 1 a method for determining a measure of heat transfer of a building component according to an embodiment of the invention, Fig. 2 a radar system which according to the embodiment according to Fig. 1 is used, Fig. 3 shows an exemplary empirically determined relationship between complex permittivities and specific heat capacities, and Fig. 4 shows an exemplary empirically determined relationship between complex permittivities and thermal conductivities.

[0048] The representations in the figures are schematic and not to scale.

[0049] Fig. 1 shows a method for determining a measure of heat transfer of a building component 1 and for determining a measure of heat capacity of the building component 1. Such a building component 1 is shown in Fig. 2 shown in a sectional view. Also shown in Fig. 2 a corresponding radar system 10 is shown, with the aid of which the method described below can be carried out. For a better understanding of the following description of the method, the Fig. 2 can be used. In a first step of the method, microwave signals are emitted S1 at a variety of frequencies onto the component 1 in question. A sinusoidal microwave signal is emitted, the frequency of which increases continuously from a start frequency to an end frequency over time. In the next step, microwave signals reflected from the respective component 1 and from layer transitions 3 in the respective component 1 are detected S2. Since several material changes are passed through along an imaginary straight line through the component 1, reflections from several layer transitions are detected. The emission of the microwave signals and the detection of the reflected microwave signals are carried out fully polarimetrically with the polarization combination HH-HV-VV, where 'H' stands for horizontal and 'V' for vertical and the first designation marks the transmitter and the second the receiver.The combination VH is theoretically identical to HV for non-gyrotropic media, which is true for the majority of materials. This is followed by determining S3 the number of layers 3 in the respective component 1 from the reflected microwave signals by determining the propagation time of the reflected microwave signals and counting the individual reflections. The component currently under consideration is then electromagnetically modeled S4 in a computer model. For this purpose, the computer model shows a layer structure of the component 1 with the determined number of layers 3. Variable parameters, however, are the respective layer thicknesses and the respective complex permittivities of the layers 3. For these variable parameters of the computer model, initial values ​​are initially specified S5. The initial values ​​are specified according to the complex permittivity of concrete and an estimated thickness of the component.This is followed by iterative adjustment S6 of the computer model by repeatedly varying the values ​​of the variable parameters and selecting the set of variable parameter values ​​with the best match between i) an analytically determined reflection factor of the computer model and ii) an actual reflection factor determined from a ratio between the emitted and the detected reflected microwave signals. For this purpose, an appropriately calibrated radar device is used, which determines an actual reflection factor by comparing the spectra of the emitted sinusoidal microwave signal with the reflected microwave signal.For each of the layers 3 modeled in the computer model with the selected set of variable parameters, a respective thermal conductivity of the respective layer is now determined S7 based on a first predefined data set, wherein the first predefined data set specifies a relationship between complex permittivities and thermal conductivities. Each complex permittivity has a respective real part and a respective imaginary part, wherein the first predefined data set specifies a relationship between respective real parts of the complex permittivities and thermal conductivities. Such an exemplary first predefined data set is shown in FIG. Fig. 4 shown. Likewise, for each of the layers 3 modeled in the computer model with the selected set of variable parameters, a respective specific heat capacity of the respective layer is determined S9 based on a second predefined data set, wherein the second predefined data set indicates a relationship between the real parts of the complex permittivities and specific heat capacities. Such an exemplary second predefined data set is shown in the Fig. 3 shown. The measure of the heat transfer of the respective component 1 is then determined from the determined layer thicknesses and thermal conductivities of the respective layers 3 S8. Analogously, the total heat capacity of the respective component 1 is determined from the determined respective layer thicknesses and the determined specific heat capacities of the respective layers 3 S10.

[0050] Fig. 2 symbolically shows an unmanned aircraft 100 with a radar system 10, which in turn has a computing unit 12 to carry out the method according to Fig. 1 This shows a horizontal section through building element 1, namely a reinforced concrete wall. This wall has a concrete slab with steel reinforcements as its core. The steel reinforcements are drawn as elliptical "disturbances." Plaster is applied to both the inside and outside of building element 1. Furthermore, there are two small cracks in the concrete due to age. The radar system 10 emits a beam of microwave signals toward the surface of building element 1. The beam of microwave signals essentially travels in a defined radiation direction, but exhibits a certain lateral extension in a slightly fan-shaped pattern.A first transition between the layers 3 is located on the one hand on the outside surface of the building component 1, another layer transition between plaster and concrete, another layer transition at the crack in the concrete, another layer transition from concrete to steel reinforcement, another layer transition from the steel reinforcement back to concrete, and analogously from concrete to plaster and from plaster to the inside of the wall. All of these layer transitions generate a respective radar echo for the radar system 10, i.e. they appear as a reflection of the emitted microwave signals, since the speed of light changes at the layer transitions, resulting in a change in wave impedance. Each layer transition is shown in the . Fig. 2 with a small end circle of a respective reference symbol line for the reference symbol of the layers 3. For the operation of the wire system 10 with its computing unit 12, please refer to the explanations of the method according to Fig. 1 In particular, the radar device of the Fig. 1 , which the radar system 10 of the Fig. 2 and is used to emit the microwave signals and to detect the reflected microwave signals, is moved along the wall of the building in order to carry out the method according to Fig. 1 to repeat so that the computer model includes all steel reinforcements, cracks and other elements in the wall, as in Fig. 2 outlined. For this purpose, the reflected microwave signals recorded at the numerous positions are combined into an overall image using a synthetic aperture method, with received reflected microwave signals for areas of the building with overlapping illumination being averaged.

[0051] Fig. 3 shows an empirically determined relationship between complex permittivities and specific heat capacities, which represents the second data set. The horizontal axis describes a linear range of values ​​between 0.2 and 0.65, whereby these values ​​on the horizontal axis represent the result of the following expression: (ε' r -1) / (ε' r +2), where ε' r indicates the respective real part of the complex permittivity. The vertical axis describes a linear range of values ​​between 0.4 and 1.8, whereby these values ​​on the vertical axis indicate the specific heat capacity in the unit [MJ / m 3 < K] ("megajoules per cubic meter and Kelvin"). The different symbols, which lie approximately on a straight line, describe different building materials.For example, open diamonds represent aerated concrete, filled diamonds represent sand-lime brick, filled squares represent yellow bricks, open squares represent red bricks, filled circles represent closed lightweight concrete, and open circles represent open lightweight concrete. Once a specific complex permittivity has been determined for a layer of building element 1, its real part can be inserted into the above formula, and the corresponding specific heat capacity can be determined by graphical solution or linear interpolation.

[0052] Fig. 4shows an empirically determined relationship between complex permittivities and thermal conductivities, which represents the first data set. The horizontal axis describes a linear range of values ​​between 0.2 and 0.65, whereby these values ​​on the horizontal axis correspond to the result of the following relationship: (ε' r -1) / (ε' r +2), where ε' r indicates the respective real part of the complex permittivity. The vertical axis describes a linear range of values ​​between 0 and 1.8, whereby these values ​​on the vertical axis indicate the thermal conductivity in the unit [W / mK] ("watts per meter and Kelvin"). The different symbols, which lie approximately on a straight line, describe different building materials.For example, open diamonds represent aerated concrete, filled diamonds represent sand-lime brick, filled squares represent yellow bricks, open squares represent red bricks, filled circles represent closed lightweight concrete, and open circles represent open lightweight concrete. Once a respective complex permittivity has been determined for a layer of building element 1, its real part can be inserted into the above formula, and the corresponding thermal conductivity can be determined by graphical solution or linear interpolation.

[0053] Although the invention has been illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned by way of example are truly only examples and should not be construed as limiting the scope, possible applications, or configuration of the invention in any way.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description. List of reference symbols

[0054] 1Component 3Layers 10Radar system 12Computing unit 100Aircraft S1Emit S2Detect S3Determine S4Model S5Specify S6Adapt S7Determine S8Determine S9Determine S10Determine

Claims

1. Method for the determination of a metric for a thermal transmittance of a building element (1), comprising the steps: - Emission (S1) of microwave signals in a multiplicity of frequencies onto a particular building element (1), - Detection (S2) of microwave signals that are reflected at the particular building element (1), and at transitions between layers (3) in the particular building element (1), - Determination (S3) of a number of layers (3) in the particular building element (1) from the reflected microwave signals, in particular by determination of the propagation time of the reflected microwave signals, - Electromagnetic modelling (S4) of the particular building element (1) in a computer model, wherein the computer model has a layered structure of the particular building element (1), with the determined number of layers (3), and comprises particular layer thicknesses and particular complex permittivities of the layers (3) as variable parameters, - Specification (S5) of initial values for the variable parameters of the computer model, - Iterative customisation (S6) of the computer model by repeated variation of the values of the variable parameters, and by selection of a set of values of the variable parameters on the basis of a match between i) a reflection characteristic of the computer model, determined analytically or by simulation, and ii) an actual reflection characteristic, determined from a ratio between the emitted and the detected reflected microwave signals, - For each of the layers (3) modelled in the computer model with the selected set of variable parameters: determination (S7) of a particular thermal conductivity of the particular layer on the basis of a first predetermined data set, wherein the first predetermined data set indicates a relationship between complex permittivities and thermal conductivities, and - Determination (S8) of the metric for the heat transfer of the particular building element (1) from the determined layer thicknesses and thermal conductivities of the particular layers (3).

2. Method in accordance with Claim 1, wherein the method is furthermore used for the determination of a metric for a heat capacity of the building element (1), furthermore comprising the steps: - For each of the layers (3) modelled in the computer model with the selected set of variable parameters: determination (S9) of a particular specific heat capacity of the particular layer on the basis of a second predetermined data set, wherein the second predetermined data set indicates a relationship between complex permittivities and specific heat capacities, and - Determination (S10) of a total heat capacity of the particular building element (1) from the determined particular layer thicknesses and the determined specific heat capacities of the particular layers (3).

3. Method in accordance with one of the preceding claims, wherein the emission of the microwave signals, and the detection of the reflected microwave signals, are achieved by means of a radar device, wherein the radar device is moved along a building, and wherein the method in accordance with Claim 1 or Claim 2 is repeated in a multiplicity of positions of the radar device with respect to the building.

4. Method in accordance with Claim 3, wherein the reflected microwave signals detected at the multiplicity of positions are combined into an overall image using a synthetic aperture method, or by apposition.

5. Method in accordance with one of the preceding claims, wherein a particular complex permittivity comprises a particular real part and a particular imaginary part, wherein the first prescribed data set specifies a relationship between particular real parts of the complex permittivities and thermal conductivities.

6. Method in accordance with one of the Claims 3 to 5, wherein for areas of the building with overlapping detected reflected microwave signals, the detected reflected microwave signals are averaged, at least section by section.

7. Method in accordance with one of the preceding claims, wherein the emission of the microwave signals, and / or the detection of the reflected microwave signals, is fully polarimetric.

8. Method in accordance with one of the preceding claims, wherein the reflection characteristic is analytically determined, in that a computer model is used, which comprises a line theory model in which imaginary highfrequency lines of different lengths and different complex permittivities are connected in series, and have a termination resistor at the output, so as to determine a frequency-dependent total reflection factor of the computer model.

9. Radar system (10) with a computing unit (12), wherein the radar system (10) is specifically designed and equipped for the execution of the method in accordance with one of the preceding claims.

10. Aircraft (100) with a radar system (10) in accordance with Claim 9.