Building external envelope structure heat transfer coefficient estimation method based on infrared thermal imaging

Abstract

The invention discloses a building external envelope structure heat transfer coefficient estimation method based on infrared thermal imaging, and relates to the technical field of energy-saving buildings, and the method comprises the steps: employing a heat flow meter method to select a plurality of measurement points on to-be-measured external walls in different orientations, so as to obtain the heat transfer coefficients of the plurality of measurement points, the inner surface temperature and the outer surface temperature of the to-be-measured outer wall corresponding to the multiple measuring points are collected at the same time; obtaining a temperature distribution diagram of the outer surface of the to-be-measured outer wall through an infrared thermal imager; the temperature distribution diagram is divided into a plurality of uniform temperature areas, so that the plurality of measuring points are distributed in different uniform areas, and the temperature difference value of each point of the uniform temperature areas is smaller than a preset temperature difference; constructing a heat consumption conservation model to calculate and obtain heat transfer coefficients of all the uniform temperature regions; and according to the area of the uniform-temperature region, carrying out weighted calculation to obtain the average heat transfer coefficient of the to-be-measured outer wall. The method solves the problem that the exact numerical value of the heat transfer coefficient cannot be directly given by adopting an infrared thermal imaging method for the heat transfer coefficient of the external envelope structure of the building in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy-saving building, and particularly relates to a building envelope heat transfer coefficient estimation method based on infrared thermal imaging. BACKGROUND

[0002] Currently, the methods for obtaining the average heat transfer coefficient of building envelope (mainly external walls and roofs) mainly include the following: heat box method, heat flow meter method and infrared thermal imaging method.

[0003] The heat box method has high precision, but it is mainly suitable for testing building materials or components in the laboratory and cannot be used for existing buildings on site.

[0004] The heat flow meter method is a standard method for testing heat transfer coefficients on site, but it has the following shortcomings: 1. Point limitation: only a limited number of points on the building can be measured, and the test results only represent the local situation. It involves danger and access limitations, and many points cannot be measured.

[0005] 2. Lack of representation: there are complex situations such as thermal bridges, cracks, uneven materials, and uneven sunlight on building external walls, and the measurement values of a few points cannot truly reflect the average thermal performance of the entire wall or building.

[0006] 3. Time-consuming and labor-intensive: sensors need to be installed at each measurement point and monitored for a long time (usually several days), making it difficult to achieve large-area rapid assessment.

[0007] The infrared thermal imaging method can quickly and intuitively display the temperature distribution of the surface of the building external wall and find thermal defects, but it cannot directly give the accurate value of the heat transfer coefficient. SUMMARY

[0008] In order to overcome the defects of the prior art, the present application provides a building envelope heat transfer coefficient estimation method based on infrared thermal imaging, to solve the problem that the existing building envelope heat transfer coefficient cannot directly give the accurate value of the heat transfer coefficient using the infrared thermal imaging method.

[0009] In order to achieve the above purpose, a building envelope heat transfer coefficient estimation method based on infrared thermal imaging is provided, comprising the following steps: Using the heat flow meter method, select multiple measurement points on the external wall to be measured in different directions to obtain the heat transfer coefficients of the multiple measurement points, and simultaneously collect the internal surface temperature and external surface temperature of the external wall to be measured corresponding to the multiple measurement points; Obtain the temperature distribution map of the external surface of the external wall to be measured by an infrared thermal imager; The temperature distribution map is divided into multiple uniform temperature regions, so that multiple measuring points are distributed in different uniform temperature regions, and the temperature difference of each point in the uniform temperature region is less than a preset temperature difference; A heat consumption conservation model is constructed to calculate the heat transfer coefficient of all uniform temperature regions, and the heat consumption conservation model is: , wherein, is the heat transfer coefficient of the uniform temperature region whose heat transfer coefficient is unknown, is the average value of the heat transfer coefficient of the uniform temperature region j and other uniform temperature regions on the same side whose heat transfer coefficients are known, , is the temperature difference between the inner surface temperature and the outer surface temperature of the measured outer wall at the uniform temperature regions i and j; According to the area size of the uniform temperature region, the average heat transfer coefficient of the measured outer wall is calculated by weighting.

[0010] Further, the measured outer wall where the measuring point is located is a non-damaged region.

[0011] Further, the outer surface temperature of the measured outer wall at the measuring point is collected by an infrared thermal imager.

[0012] Further, the number of measuring points is less than the number of uniform temperature regions.

[0013] Further, the preset temperature difference is 1℃.

[0014] Further, the average heat transfer coefficient of the measured outer wall is calculated by a weighting formula, and the weighting formula is: , wherein, is the average heat transfer coefficient; is the area of the uniform temperature region.

[0015] The beneficial effects of this invention are that the method for estimating the heat transfer coefficient of building envelopes based on infrared thermal imaging is an average heat transfer coefficient estimation method that can balance measurement accuracy, evaluation efficiency, and reflection of overall performance, while also identifying local differences. This method combines precise measurement at a limited number of points with the advantages of large-area scanning in infrared thermal imaging, enabling rapid and accurate assessment of the overall thermal performance of a building. Furthermore, this method establishes a simple relationship for converting heat transfer coefficient ratios through temperature difference ratios. By utilizing the heat transfer coefficients and temperature differences at a few measured points, combined with the overall temperature difference obtained from infrared images, the heat transfer coefficient of any other area on the wall can be calculated. This greatly expands the value of limited measurement data, cleverly avoiding the complex problem of directly measuring total heat loss, making the method simple and practical. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating the method for estimating the heat transfer coefficient of a building envelope based on infrared thermal imaging, according to an embodiment of the present invention. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Reference Figure 1 As shown, this invention provides a method for estimating the heat transfer coefficient of a building envelope based on infrared thermal imaging, comprising the following steps: S1. Using the heat flow meter method, select multiple measuring points on the exterior wall to be tested in different orientations to obtain the heat transfer coefficient of multiple measuring points, and at the same time collect the inner surface temperature and outer surface temperature of the exterior wall to be tested corresponding to multiple measuring points.

[0020] Specifically, using the heat flow meter method, n (n≥2) representative measurement points (i.e., undamaged areas on the first-floor outer envelope) are selected on each of the exterior walls of the building under test on different orientation sides. The heat transfer coefficients K1, K2, ..., K at these points (n measurement points) are accurately measured. n .

[0021] At the same time, record the indoor environment temperature T in1 ,T in2 ,...,T inn of the corresponding positions of these measuring points (n measuring points) during the test out1 ,T out2 ,...,T outn of the outer surface of the outer wall to be tested at these measuring points using an infrared thermal imager.

[0022] S2, acquire the temperature distribution map of the outer surface of the outer wall to be tested by the infrared thermal imager.

[0023] Scan the entire outer wall to be tested using the infrared thermal imager in strict accordance with the detection process requirements, and acquire the complete temperature distribution map of the outer surface of the outer wall to be tested.

[0024] S3, divide the temperature distribution map into multiple uniform temperature regions, so that multiple measuring points are distributed in different uniform temperature regions, and the temperature difference of each point in the uniform temperature region is less than a preset temperature difference.

[0025] According to the difference in temperature distribution, divide the outer wall to be tested into m uniform temperature regions (m≥n, and the n measuring points are distributed in different uniform temperature regions) on the infrared image. The outer surface temperature of the outer wall to be tested in each uniform temperature region is relatively uniform.

[0026] The temperature difference of each point in the uniform temperature region is less than a preset temperature difference. As a preferred embodiment, the test temperature of each point in each uniform temperature region in the infrared image differs by ±1℃.

[0027] S4, construct a heat consumption conservation model to calculate the heat transfer coefficient of all uniform temperature regions.

[0028] The heat consumption conservation model is: , wherein, is the heat transfer coefficient of the uniform temperature region whose heat transfer coefficient is unknown, is the average value of the heat transfer coefficients of the uniform temperature region j and other uniform temperature regions on the same side whose heat transfer coefficients are known, 、 is the temperature difference between the inner surface temperature and the outer surface temperature of the outer wall to be tested at the uniform temperature regions i and j.

[0029] Specifically, during the test, the indoor-outdoor temperature difference of the outer wall to be tested is relatively stable, and it can be considered that the total heat consumption Q total of the entire building (or the face of the outer wall to be tested) is constant.

[0030] According to the basic heat consumption calculation formula of the envelope structure For each region, its heat consumption: .

[0031] The total heat consumption can be expressed as the sum of the heat consumptions of each region: .

[0032] For any two regions i and j (where j can be a measured point), the ratio of their heat transfer coefficients can be approximately expressed as (when the indoor temperature is similar): , Where, This formula is derived based on the assumption that the heat consumption of each region is equal to the ratio of its calculated heat consumption.

[0033] Calculate the unknown region heat transfer coefficient: Based on the average value of the n measured points of the same side j region of the unknown region, use the above ratio formula to calculate the heat transfer coefficients K of the other m-1 regions according to the ΔT of the region and other regions read from the infrared image i : .

[0034] S5, according to the area size of the uniform temperature region, the average heat transfer coefficient of the measured outer wall is obtained by weighted calculation.

[0035] In this embodiment, the average heat transfer coefficient of the measured outer wall is obtained by weighted calculation through the weighted formula, and the weighted formula is: , Where, is the average heat transfer coefficient; is the area of the uniform temperature region.

[0036] Specifically, after obtaining the heat transfer coefficients K1, K2,..., K m of all m regions, the average heat transfer coefficient K i of the whole outer wall is calculated by weighted average according to the area A avg : .

[0037] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application is an average heat transfer coefficient estimation method that can consider measurement accuracy, evaluation efficiency, and overall performance, and can also identify local differences.

[0038] The application provides an infrared thermal imaging-based building envelope heat transfer coefficient estimation method, aiming at overcoming the shortcomings of the prior art, and providing an infrared thermal imaging-based building envelope heat transfer coefficient estimation method which is simple in operation, low in cost, high in efficiency and reliable in result. The infrared thermal imaging-based building envelope heat transfer coefficient estimation method provided by the application combines the accurate measurement of limited points with the large-area scanning advantage of infrared thermal imaging, and realizes rapid and accurate evaluation of the overall thermal performance of a building.

[0039] The substantial improvement of the infrared thermal imaging-based building envelope heat transfer coefficient estimation method of the application does not lie in the invention of a new sensor or hardware, but in the creative proposal and implementation of a brand-new systematic method combining existing measurement tools with mathematical modeling, which can be summarized as the following three progressive innovation levels: The first level of innovation: the innovation of method architecture - the mixed model of "point and surface combination". This is the uppermost strategic innovation.

[0040] The infrared thermal imaging-based building envelope heat transfer coefficient estimation method of the application systematically integrates local accurate measurement (heat flow meter) and full-field temperature scanning (infrared thermal imager), and constructs an evaluation model of "point to surface and surface to whole".

[0041] The infrared thermal imaging-based building envelope heat transfer coefficient estimation method of the application breaks through the limitation of heat flow meter method "only seeing trees but not forest"; and breaks through the bottleneck of infrared thermal imaging method "only seeing a general situation but not quantitative calculation". It is not a simple superposition of two technologies, but a deep integration and complementation in function: the heat flow meter provides a quantitative scale for the infrared image, and the infrared image provides spatial expansion for the heat flow meter data.

[0042] The second level of innovation: the innovation of core algorithm - the heat transfer coefficient ratio calculation model based on heat consumption conservation. This is the soul of the technical contribution of the application, and is a key step with creativity.

[0043] The infrared thermal imaging-based building envelope heat transfer coefficient estimation method of the application proposes a core hypothesis (the heat consumption of the whole building or envelope is constant within a certain time), and deduces a key mathematical relationship based on this hypothesis: .

[0044] This formula can use the easily obtained temperature difference ratio to calculate the difficult-to-directly-measure heat transfer coefficient ratio.

[0045] In the prior art, there is no direct and calculable mathematical model between infrared temperature data and heat transfer coefficient. The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application first (or creatively) establishes a simple relationship for converting the heat transfer coefficient ratio through the temperature difference ratio.

[0046] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application realizes the extrapolation of data. This is a key step from "known" to "unknown". The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application uses the K j and ΔT j of a few measured points to "calibrate" the entire infrared temperature field, so that the final result is more representative than simply averaging a few measured points, and realizes the balance between detection accuracy and detection efficiency. j and ΔT j , combined with the full-field ΔT i obtained from the infrared image, the K i of any other area on the wall can be calculated. This greatly expands the value of limited measurement data.

[0047] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application simplifies the calculation. The heat consumption conservation model of the building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application cleverly avoids the complex problem of directly measuring the total heat consumption Q total , making the method simple and practical.

[0048] Third level of innovation: innovation of implementation process - "zoning weighted average" precision solution. This is a specific tactical innovation to put the above model into practice.

[0049] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application performs intelligent regional division based on the infrared temperature field, and finally adopts the area-weighted average calculation method, realizing the transition from "blind average" to "intelligent zoning". The traditional simple arithmetic average after multi-point measurement is "blind", which assumes that each point has the same weight. However, the present application divides the regions according to the actual thermal performance differences revealed by the infrared image, and acknowledges that the heat transfer capacities of different regions are different, which is more consistent with the physical facts and the results are more representative. The final average heat transfer coefficient not only considers the heat transfer coefficients of each region, but also considers the area weight. This makes the final result more truly reflect the overall thermal performance of the entire wall, especially can more reasonably take into account the influence of local defects such as thermal bridges and cracks on the overall energy consumption.

[0050] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application not only utilizes the measurement accuracy of the heat flow meter method, but also takes advantage of the full-field measurement of infrared thermal imaging. A small amount of accurate measurement "calibrates" the entire infrared temperature field, making the final result more representative than simply averaging a few measured points, and realizing the balance between detection accuracy and detection efficiency.

[0051] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application does not need to densely distribute points on the entire wall surface, greatly reduces the number of expensive sensors such as heat flow meters and the monitoring time, and reduces the detection cost.

[0052] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application adopts infrared thermal imaging to directly display defect areas such as cold bridges and missing insulation layers, and considers the areas when dividing and weightedly averaging, so that the evaluation result is closer to the real situation and thermal defects are identified.

[0053] The building envelope heat transfer coefficient estimation method based on infrared thermal imaging of the present application is particularly suitable for diagnosis before energy-saving reconstruction of existing buildings and effect evaluation after reconstruction, and has strong practicability.

[0054] The above description is only the preferred embodiment of the present application and the explanation of the applied technical principles. It should be understood by those skilled in the art that the scope of the present application is not limited to the technical solutions formed by the specific combination of the above technical features, and also covers other technical solutions formed by any combination of the above technical features or equivalent features without departing from the inventive concept. For example, the technical solutions formed by replacing the above features with the technical features disclosed in the present application (but not limited to) having similar functions.

Claims

1. A method for estimating the heat transfer coefficient of a building envelope based on infrared thermography, characterized in that, The method comprises the following steps: A heat flow meter method is used to select multiple measuring points on the to-be-tested outer wall in different orientations to obtain the heat transfer coefficients of the multiple measuring points, and meanwhile, the inner surface temperature and the outer surface temperature of the to-be-tested outer wall corresponding to the multiple measuring points are collected; An infrared thermal imager is used to obtain a temperature distribution diagram of the outer surface of the to-be-tested outer wall; The temperature distribution diagram is divided into multiple uniform temperature regions, so that the multiple measuring points are distributed in different uniform temperature regions, and the temperature difference of each point in the uniform temperature region is less than a preset temperature difference; A heat consumption conservation model is constructed to calculate the heat transfer coefficients of all the uniform temperature regions, and the heat consumption conservation model is: ， wherein, is the heat transfer coefficient of the uniform temperature region whose heat transfer coefficient is unknown, is the average of the heat transfer coefficients of the uniform temperature region j whose heat transfer coefficient is known and other uniform temperature regions whose heat transfer coefficients are known on the same side as the uniform temperature region j, , is the temperature difference between the inner surface temperature and the outer surface temperature of the exterior wall to be measured at the uniform temperature regions i and j. According to the area size of the uniform temperature regions, a weighted calculation is performed to obtain the average heat transfer coefficient of the to-be-tested outer wall.

2. The method for estimating the heat transfer coefficient of a building envelope from infrared thermography according to claim 1, characterized in that, The to-be-tested outer wall where the measuring points are located has no damaged area.

3. The method for estimating the heat transfer coefficient of a building envelope from infrared thermography according to claim 1, characterized in that, An infrared thermal imager is used to collect the outer surface temperature of the to-be-tested outer wall at the measuring points.

4. The method for estimating the heat transfer coefficient of a building envelope from infrared thermography according to claim 1, characterized in that, The number of the measuring points is less than the number of the uniform temperature regions.

5. The method for estimating the heat transfer coefficient of a building envelope from infrared thermography according to claim 1, characterized in that, The preset temperature difference is 1℃.

6. The infrared thermography-based building envelope heat transfer coefficient estimation method according to claim 1, characterized in that, A weighted calculation is performed by using a weighted formula to obtain the average heat transfer coefficient of the to-be-tested outer wall, and the weighted formula is: ， wherein is the average heat transfer coefficient; A is the area of the uniform temperature zone.

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