CN113533418A - Novel method for quantitatively analyzing heat loss of thermal bridge of building based on thermal infrared imager - Google Patents
Novel method for quantitatively analyzing heat loss of thermal bridge of building based on thermal infrared imager Download PDFInfo
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Abstract
The invention relates to a novel method for quantitatively analyzing heat loss of a thermal bridge of a building based on a thermal infrared imager, which takes the thermal infrared imager as a tool, provides a noninvasive and easy-to-use quantitative evaluation method for heat loss, can explain the correlation between surface temperature and convection and radiation heat exchange coefficients under the condition that the internal structure of a building enclosure is unknown, and evaluates the heat loss of the thermal bridge part of the building enclosure by calculating the heat flow rate of unit height and linear heat transmittance obtained by thermal image data, thereby realizing the optimization of the thermal performance of the building enclosure and further achieving the purpose of building energy conservation.
Description
Technical Field
The invention relates to the technical field of building energy conservation and thermal imaging, in particular to a novel method for quantitatively analyzing heat loss of a thermal bridge of a building based on a thermal infrared imager.
Background
The building energy consumption accounts for about one third of the global primary energy consumption, and the improvement of the thermal performance of the building can make a great contribution to the global reduction of the energy consumption. In the evaluation of the thermal standard of a building envelope, a heat flow meter method and a heat box method are mainly used at present, the two methods have certain limitations and large errors, the thermal infrared imager is mainly used as a qualitative analysis means to provide reliable data support for energy-saving reconstruction, and the research on quantitative analysis is less, but the infrared thermal imaging technology is a new technology and has remarkable advantages compared with the traditional thermal standard evaluation method. Therefore, the development of infrared thermal imaging technology as a means of quantitative analysis has become a major research point.
Disclosure of Invention
In order to solve the problems, the invention provides a non-invasive and easy-to-use heat loss evaluation method by taking a thermal infrared imager as a tool, which can explain the correlation between the surface temperature and the convection and radiation coefficients under the condition that the internal structure of a building envelope is unknown, and evaluate the heat loss of a thermal bridge part of the building envelope by calculating the heat flow rate and the linear heat transmission rate of unit height obtained by thermal image data so as to realize the optimization of the thermal performance of the building envelope and further achieve the aim of saving energy of the building.
The invention specifically adopts the following scheme:
a new method for quantitatively analyzing heat loss of a thermal bridge of a building based on a thermal infrared imager comprises the following steps:
s1: setting a thermal bridge specimen of the enclosure structure;
s2: setting the temperature difference, the wind speed flow direction and the size of the environment where the thermal bridge specimen is located;
s3: setting the resolution and the placement distance of the thermal infrared imager;
s4: acquiring the surface temperature of each pixel point in the thermal bridge specimen and the physical property parameters of the ambient air;
s5: determining the convective heat transfer coefficient and the radiative heat transfer coefficient of the pixel points;
s6: thermal bridge specimen determination of heat flow rate per unit height of a thermal bridge part and linear heat transmission rate.
The further scheme is that the length of the thermal bridge specimen in S1 is 1.5m, the height is 1.5m, all the specimens are composed of structural insulation plates, the total thickness is 130mm, the structural insulation plates are composed of low-conductivity polystyrene insulation plates with the thickness of 100mm, two sides of the structural insulation plates are provided with Europe pine plates with the thickness of 15mm, and a steel hollow pipe with the thickness of 100mm multiplied by 5mm is arranged in the center of the thermal bridge specimen to simulate a linear thermal bridge.
The further scheme is that the thermal bridge specimen in S2 is embedded into a heat insulation partition wall of a cold and hot chamber, the temperature difference of the environment is maintained at about 30 degrees, the surface of the specimen is set to be 0.1m/S, and the direction of the uniform air flow is parallel to the surface and from top to bottom.
Further, the thermal infrared imager described in S3 has a resolution of 320 × 240 and is placed at a middle-high position at a suitable distance from the sample.
Further, the surface temperature of each pixel point of the thermal bridge specimen described in S4 is obtained by establishing an average IR line at a middle-high position of the thermography and by curve fitting, and the physical property parameters of the air around the pixel points are obtained by table lookup at the surface air film temperature.
Further, the convective heat transfer coefficient in S5 is determined by an equation relating to the knossel number.
Further, the heat flow rate in S6 is obtained by summing the heat flow rates of each pixel point.
The invention has the beneficial effects that: the invention provides a noninvasive and easy-to-use heat loss evaluation method by taking a thermal infrared imager as a tool; the method can explain the correlation between the surface temperature and the convection and radiation coefficients under the condition that the internal structure of the building envelope is unknown, and estimate the heat loss of a thermal bridge part of the building envelope by calculating the heat flow rate per unit height and the linear heat transmission rate obtained by the thermal image data so as to realize the optimization of the thermal performance of the building envelope and further achieve the aim of building energy conservation. The thermal infrared imager is small in size, easy to carry and short in detection time, and detection efficiency is improved.
Drawings
FIG. 1 is a flow chart of a new method for quantitatively analyzing heat loss of a thermal bridge by using a thermal infrared imager in an embodiment of the invention;
FIG. 2 is a graph of a curve fit of the surface temperature of a thermal bridge specimen in an embodiment of the invention;
FIG. 3 is a graph of a curve fit of convective heat transfer coefficients of a thermal bridge specimen in an embodiment of the invention;
FIG. 4 is a graph of a curve fit of emissivity of a thermal bridge specimen in an embodiment of the invention;
FIG. 5 is a graph of a curve fit of heat flow rate per unit height for a thermal bridge specimen in an embodiment of the invention;
FIG. 6 is a graph fitting the heat flow rate per unit height of the heat bridge portion of the heat bridge specimen in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.
The new method for quantitatively analyzing the heat loss of the thermal bridge by using the thermal infrared imager comprises the following steps:
s1: setting a thermal bridge specimen of the enclosure structure;
s2: setting the temperature difference, the wind speed flow direction and the size of the environment where the thermal bridge specimen is located;
s3: setting the resolution and the placement distance of the thermal infrared imager;
s4: acquiring the surface temperature of each pixel point in the thermal bridge specimen and the physical property parameters of the ambient air;
s5: the method for determining the convective heat transfer coefficient and the radiative heat transfer coefficient of the pixel point is characterized in that:
nux is the Nussel number of each pixel point on the thermal imaging graph, and is dimensionless; k is a radical ofxThe thermal conductivity coefficient W/(mK) of the surface air film of each pixel point on the thermal imaging graph at the temperature is shown; lchIs the characteristic length of the thermal bridge specimen, m; the method comprises the following steps of: hc isx＝εσ(Tsx+Ti)(Tsx 2+Ti 2) In the formula, epsilon is the surface emissivity of the thermal bridge specimen and is dimensionless; σ is Boltzmann constant, W/(m)2K4)；TsxFor the surface temperature of each pixel on the thermal imaging map,K；Tithe air temperature at the hot side of the thermal bridge specimen, K;
in the formula RaxIs Rayleigh number and has no dimension; pr (Pr) ofxIs a prandtl number, dimensionless;
wherein g is gravity acceleration, m/s2(ii) a Beta is the volume expansion coefficient, 1/K; t isiThe air temperature at the hot side of the thermal bridge specimen, K; t issxThe surface temperature, K, of each pixel point on the thermal imaging graph; lchIs the characteristic length of the thermal bridge specimen; v is kinematic viscosity m at the temperature of the air film on the surface of each pixel point on the thermal imaging diagram2S; and alpha is the thermal conductivity of the surface air film of each pixel point on the thermal imaging graph at the temperature, W/mK.
S6: the method for determining the heat flow rate and the linear heat transmission rate of the heat bridge part of the heat bridge specimen is based on the calculation method of the heat flow rate: q. q.sx＝lx[(hcx+hrx)(Ti-Tsx)]In the formula IxThe actual length, m, corresponding to each pixel point; hc isxIs the convective heat transfer coefficient of each pixel point, W/(m)2K)；hrxIs the radiant heat transfer coefficient of each pixel point, W/(m)2K)；TiThe air temperature at the hot side of the thermal bridge specimen, K; t issxThe surface temperature, K, of each pixel point on the thermal imaging graph;
qxTB＝qx-qxu；qxthe heat flow rate per unit height, W/m, of each pixel point on the thermal imaging graph; q. q.sxuThe heat flow rate of each pixel point of the thermal imaging graph without the thermal bridge part is the unit height; according to the calculation method of the linear heat transmission rate:
in the formula qTBIs the heat flow rate per unit height of the heat bridge section; t isiThe air temperature of the hot side of the thermal bridge specimen; t iseThe air temperature of the hot bridge specimen for cold measurement.
In this embodiment, the heat transfer process of the heat passing through the thermal bridge specimen is regarded as one-dimensional heat transfer, when the temperatures on the two sides of the cold and hot chambers are stable, the infrared thermal imager is used for thermal imaging, the thermal imaging data is processed, and finally the heat flow rate q per unit height of the thermal bridge specimen is obtainedTB6.776W/m, and a linear thermal transmittance psi of 0.229W/(mK); q obtained by a hot box method under the same conditionsTB7.32W/m, a linear heat transmission rate psi of 0.247W/(mK),
the error of the heat flow rate per unit height of the invention is 7.43 percent, and the error of the linear heat transmission rate psi is 7.29 percent.
In this embodiment, the thermal bridge specimen described in S2 is embedded in the heat insulation partition wall of the hot and cold chamber, the temperature difference of the environment is maintained at about 30 degrees, the surface of the specimen is set to be 0.1m/S, and the direction of the air flow is parallel to the surface and uniform from top to bottom.
In the present embodiment, the thermal infrared imager described in S3 has a resolution of 320 × 240 and is placed at a middle-high position at a suitable distance from the sample.
In this embodiment, the surface temperature of each pixel of the thermal bridge specimen described in S4 is obtained by establishing an average IR line at a middle-high position in the thermal image and by curve fitting, and the physical parameters of the air around the pixel are obtained by table lookup at the surface air film temperature.
In the present embodiment, the convective heat transfer coefficient in S5 is determined by an equation relating to the knossel number.
In the present embodiment, the heat flow rate per unit height in S6 is obtained by summing the heat flow rates per unit height for each pixel point.
Finally, the foregoing is illustrative only of specific embodiments of the invention. The invention is not limited to the specific embodiments described above. Equivalent modifications and substitutions by those skilled in the art are also within the scope of the present invention. Accordingly, equivalent alterations and modifications are intended to be included within the scope of the invention, without departing from the spirit and scope of the invention.
Claims (7)
1. A new method for quantitatively analyzing heat loss of a thermal bridge of a building based on a thermal infrared imager is characterized in that: the method comprises the following steps:
s1, setting a thermal bridge specimen of the enclosure structure;
s2, setting the temperature difference of the environment where the thermal bridge specimen is located, the surface wind speed flow direction and the size;
s3, setting the resolution and the placement distance of the thermal infrared imager;
s4, acquiring the surface temperature of each pixel point in the thermal bridge specimen and the physical property parameters of the ambient air;
s5, determining the convective heat transfer coefficient and the radiative heat transfer coefficient of the pixel point;
and S6, determining the heat flow rate and the linear heat transmission rate of the heat bridge part of the heat bridge specimen per unit height.
2. The new method for the thermal infrared imager to quantitatively analyze the heat loss of the thermal bridge of the building as claimed in claim 1, characterized in that:
the length of the thermal bridge specimen described in S1 is 1.5m, the height is 1.5m, the specimen is composed of a structural insulating plate, the total thickness is 130mm, the structural insulating plate is composed of a low conductivity polystyrene insulating plate with a thickness of 100mm, two sides are provided with europa plates with a thickness of 15mm, and a steel hollow tube with a thickness of 100mm × 100mm × 5mm is arranged in the center of the thermal bridge specimen to simulate a linear thermal bridge.
3. The new method for thermal infrared imager to quantitatively analyze heat loss of thermal bridge as claimed in claim 1, characterized in that:
the thermal bridge specimen in S2 is embedded in the heat insulation partition wall of the cold and hot chamber, the temperature difference of the environment is maintained at about 30 ℃, the surface of the specimen is set to be 0.1m/S, and the direction of the specimen is parallel to the surface and the air flow is uniform from top to bottom.
4. The new method for thermal infrared imager to quantitatively analyze heat loss of thermal bridge as claimed in claim 1, characterized in that:
the thermal infrared imager described in S3, having a resolution of 320 × 240, was placed at a medium and high position at a suitable distance from the sample.
5. The new method for thermal infrared imager to quantitatively analyze heat loss of thermal bridge as claimed in claim 1, characterized in that:
the surface temperature of each pixel point of the thermal bridge specimen in the S4 is obtained by establishing an average IR line at the middle-high position of the thermal image and by means of curve fitting, and the physical property parameters of the air around the pixel points are obtained by table lookup at the surface air film temperature.
6. The new method for thermal infrared imager to quantitatively analyze heat loss of thermal bridge as claimed in claim 1, characterized in that:
the convective heat transfer coefficient in S5 is determined by an equation relating to the knossel number.
7. The new method for thermal infrared imager to quantitatively analyze heat loss of thermal bridge as claimed in claim 1, characterized in that:
the heat flow rate per unit height in S6 is obtained by summing the heat flow rates per unit height for each pixel point.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US20230204424A1 (en) * | 2021-12-28 | 2023-06-29 | University Of North Dakota | Surface temperature estimation for building energy audits |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101246137A (en) * | 2008-01-29 | 2008-08-20 | 西北民族大学 | Method for detecting heat transfer resistance/heat transfer factor of building enclosure structure by infrared thermal imaging system |
| CN111189541A (en) * | 2018-11-14 | 2020-05-22 | 中国石油化工股份有限公司 | Online heat loss measurement method based on infrared thermal image scanning |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101246137A (en) * | 2008-01-29 | 2008-08-20 | 西北民族大学 | Method for detecting heat transfer resistance/heat transfer factor of building enclosure structure by infrared thermal imaging system |
| CN111189541A (en) * | 2018-11-14 | 2020-05-22 | 中国石油化工股份有限公司 | Online heat loss measurement method based on infrared thermal image scanning |
Non-Patent Citations (2)
| Title |
|---|
| MALGORZATA O"GRADY等: "《Infrared thermography technique as an in-situ method of assessing heat loss through thermal bridging》", 《ENERGY AND BUILDINGS》 * |
| MALGORZATA O"GRADY等: "《Quantification of heat losses through building envelope thermal bridges influenced by wind velocity using the outdoor infrared thermography technique》", 《APPLIED ENERGY》 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20230204424A1 (en) * | 2021-12-28 | 2023-06-29 | University Of North Dakota | Surface temperature estimation for building energy audits |
| US11828657B2 (en) * | 2021-12-28 | 2023-11-28 | University Of North Dakota | Surface temperature estimation for building energy audits |
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Application publication date: 20211022 |