A field testing device and method for thermal resistance of building walls

Abstract

The present invention proposes a device and method for testing the thermal resistance of a building wall on site. The testing device includes a heating plate, a temperature controller, and two temperature sensors, two heat flux sensors, and two insulation plates. The first temperature sensor, the first heat flux sensor, the heating plate, and the first insulation plate are all attached to the hot side of the wall to be tested, and the second temperature sensor, the second heat flux sensor, and the second insulation plate are all attached to the cold side of the wall to be tested. A through hole serving as a one-dimensional channel for heat flux is provided in the middle of the second insulation plate, and the second temperature sensor and the second heat flux sensor are both located in the through hole. The testing method is to quantitatively determine the size of the one-dimensional heat transfer area on both sides of the wall, and to calculate the equivalent thermal resistance of the wall by measuring and recording the surface temperature of the one-dimensional heat transfer area on both sides of the wall and the heat flux density passing through the one-dimensional heat transfer area. The present invention can quickly establish steady-state heat transfer and effectively shorten the test time by setting a one-dimensional channel that is conducive to the concentrated passage of heat flux and adopting a two-stage heating method.

Description

Technical Field

[0001] The invention belongs to the field of building wall thermal resistance testing, and in particular relates to an on-site testing device and method for on-site testing of building wall thermal resistance. Background Art

[0002] Building energy consumption in my country accounts for more than 20% of the country's total energy consumption, and the total building area is huge. Building energy conservation has become an inevitable trend in the construction industry. Heating, ventilation and air conditioning energy consumption account for a large part of building energy consumption, of which 20%-50% of cooling and heating energy consumption is caused by heat transfer in building envelope structures. As the main envelope structure component, the thermal resistance of the building wall is an important indicator to measure the thermal insulation performance of the wall, and it is also the main basis for calculating the heat dissipation of the wall.

[0003] The actual performance of the wall may not be consistent with the design value, especially after the building has been in use for a long time, due to moisture, material damage and other reasons, the actual thermal performance may be far from the design value. Therefore, the determination of the thermal resistance of the building wall cannot rely solely on design drawings, construction materials, etc., but requires on-site testing. Accurate on-site determination of the thermal resistance of the enclosure structure will be widely used in many aspects such as post-evaluation of green buildings, energy-saving renovation of existing buildings, and simulation software applications.

[0004] At present, the commonly used methods for on-site detection of thermal resistance of building walls include heat flux meter method, hot box method, cold and hot box method, etc.

[0005] The heat flow meter method requires simple test instruments, including thermocouples, heat flow meters, data acquisition instruments, etc., to test the temperature of the inner and outer surfaces of the wall and the heat flux density passing through the wall, and calculate the thermal resistance of the wall. The test results are more accurate when there is a certain temperature difference on both sides of the wall and the heat transfer is one-dimensional. The test can only be carried out when there is a large temperature difference between the inside and outside of the heated room in winter, or the closed room needs to be heated for a long time to achieve steady-state heat transfer. Therefore, high requirements are placed on the test season and test duration (usually 3-7 days).

[0006] The hot box method is an improvement on the heat flux meter method. The temperature inside the box can be controlled at a constant value by using a constant temperature box, artificially creating a temperature difference between the two sides of the wall, testing the temperature of the inner and outer surfaces of the wall and the heat flux density passing through the wall, and calculating the thermal resistance of the wall. The hot and cold box method is to install a hot box on one side of the wall and a cold box on the other side. The conditions are relatively harsh.

[0007] The hot box method and the cold and hot box method tests are not restricted by seasons, but due to the local heating of the wall, the actual wall heat conduction process has a three-dimensional effect of lateral heat loss, which is not conducive to the rapid establishment of one-dimensional heat transfer and will inevitably cause errors in the test results under the one-dimensional assumption. In order to weaken the influence of three-dimensional heat transfer, the box equipment is very large (at least 1m×1m in area), and there may not be enough suitable space for large-area heating on the wall site due to the formation of thermal bridges by doors, windows, beams and columns, resulting in inconvenience in installation and operation. In addition, the large volume of the cold / hot box also causes a large amount of cooling / heating energy consumption during the test process.

[0008] Therefore, it is necessary to innovate the existing technology to address the above problems. Summary of the invention

[0009] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a device and method for on-site testing of thermal resistance of building walls, which has the characteristics of simple structure, convenient installation and use, and short measurement time.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0011] The present invention provides a field test device for thermal resistance of building walls, characterized in that it includes a heating plate, a temperature controller, and two temperature sensors, two heat flux sensors, and two insulation plates; wherein the first temperature sensor, the first heat flux sensor, the heating plate, and the first insulation plate are all attached to the hot side of the wall to be tested, the first temperature sensor and the first heat flux sensor are close to the hot side wall of the wall to be tested and are completely covered by the heating plate, the heating plate is completely covered by the first insulation plate, and the temperature controller is electrically connected to the heating plate; the second temperature sensor, the second heat flux sensor, and the second insulation plate are all attached to the cold side of the wall to be tested, a through hole serving as a one-dimensional heat flux channel is provided in the middle of the second insulation plate, the second temperature sensor and the second heat flux sensor are both located in the through hole and are respectively arranged opposite to the first temperature sensor and the first heat flux sensor. The present invention also proposes a testing method using the above-mentioned field test device for thermal resistance of building walls, characterized in that it includes the following steps:

[0012] 1) Install the building wall thermal resistance field test device on the tested wall that meets the requirements; turn on the building wall thermal resistance field test device, and heat the tested wall using a two-stage heating method, with the first stage set at a constant temperature T 1 To quickly increase the internal temperature of the wall, this stage lasts for 0.5 to 8 hours; the second stage is set to the required heating temperature T 2 ; The two-stage set temperature satisfies the following formula:

[0013] 10℃≤T 2 -T c ≤27℃

[0014] T 1 -T 2 ≥10℃

[0015] Where: T c is the surface temperature of the cold side of the measured wall;

[0016] During the above heating process, all test data are collected and recorded at the set frequency, and the recording interval is no longer than 1 minute;

[0017] 2) Determine whether the approximate steady-state heat transfer is achieved based on the test data collected in step 1). If the approximate steady-state heat transfer is achieved, that is, the following conditions must be met at the same time: (a) within 0.5 hours, the absolute value of the cold side temperature change does not exceed 0.5°C; (b) within 0.5 hours, the heat flux density changes on the cold side and the hot side do not exceed 20%, then execute step 3); if the approximate steady-state heat transfer is not achieved, wait until the approximate steady-state heat transfer is achieved, and execute step 3); wherein, the temperature T(x, τ) of any point in the test area of ​​the tested wall at any time is calculated by the following formula:

[0018]

[0019] Where x is the distance from any point in the test area of ​​the tested wall to the center of the hot side test area; τ is the current heating time; a is the thermal conductivity of the tested wall; T h is the surface temperature of the hot side of the measured wall; T 0 is the surface temperature of the hot side of the measured wall at the initial moment of heating; T′ c is the rate of change of the surface temperature on the cold side of the measured wall; n is a continuous positive integer starting from 1; t is the time integral variable, t∈[0,τ];

[0020] 3) Take the collected data of any 10 minutes after entering the approximate steady state, and calculate the thermal resistance of the measured wall according to the following formula:

[0021]

[0022] Where R is the thermal resistance of the wall being measured; is the temperature measurement value of the hot side surface of the measured wall at time τ; is the temperature measurement value of the cold side surface of the measured wall at time τ; is the measured value of heat flux density on the hot side of the measured wall at time τ; is the measured value of heat flux density on the cold side of the measured wall at time τ.

[0023] Features and beneficial effects of the present invention:

[0024] 1. The one-dimensional heat transfer zone in the present invention achieves approximately steady-state heat transfer, which can improve the accuracy of the results calculated using Fourier's heat conduction law, simplify the calculation, and reduce the test error caused by the three-dimensional effect of wall heat transfer.

[0025] 2. Compared with the existing measuring devices, since a one-dimensional heat flow channel is installed on the unheated side wall of the wall, it is beneficial for the heat flow to pass through the one-dimensional channel, reducing the loss from the area around the heat flow meter, thereby quickly establishing a steady-state heat transfer process and effectively shortening the test time.

[0026] 3. The present invention adopts a two-stage heating method, and the heating temperature set in the first stage is higher than that in the second stage, which is conducive to quickly reaching an approximately steady-state heat transfer state and shortening the test time.

[0027] 4. The present invention adopts a heating plate as a heat source. The minimum size of the required heating plate is significantly reduced compared with the traditional hot box method, which greatly reduces the requirement for the installation area of ​​the wall to be tested. The device is lighter in size and weight than the traditional hot box, and the installation process is simple to operate, which saves labor costs for detection, reduces energy consumption during the detection process, and is easy to promote and utilize. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the on-site test of the wall thermal resistance of the present invention.

[0029] Figure 2 Schematic diagram of test data curve according to an embodiment of the present invention.

[0030] Figure 3 Schematic diagram of the wall heat transfer side profile and the determination of the one-dimensional heat transfer zone size during the wall thermal resistance test.

[0031] Figure 4 It is a schematic diagram of the side cross-section of the heat flow inside the wall with and without the one-dimensional heat flow channel device during the wall thermal resistance test. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0033] In order to better understand the present invention, an application example of a building wall thermal resistance on-site testing device and method proposed by the present invention is described in detail below.

[0034] A building wall thermal resistance on-site testing device according to an embodiment of the present invention has an overall structure as shown in Figure 1, including a heating plate 3, two temperature sensors (1 and 7), two heat flux sensors (2 and 8) and two insulation plates (4 and 9). Among them, the first temperature sensor 1 and the second temperature sensor 7, as well as the first heat flux sensor 2 and the second heat flux sensor 8 are respectively close to the walls of the hot side and the cold side of the measured wall 10 and are arranged opposite to each other; the heating plate 3 is attached to the hot side of the measured wall 10 and completely covers the first temperature sensor 1 and the first heat flux sensor 2; the first insulation plate 4 is attached to the hot side of the measured wall 10 and completely covers the heating plate 3; the heating plate 3 is connected to the temperature controller 6 through the wire 5, and the temperature controller 6 controls the temperature of the heating plate 3; the heating plate 3, the first temperature sensor 1, the first heat flux sensor 2 and the first insulation plate 4 constitute a heating device, and a uniform high-temperature isothermal surface can be created on the hot side surface of the measured wall. Further, the first temperature sensor 1 and the first heat flux sensor 2 should be in contact with the heating plate 3, and the heating plate 3 and the first insulation plate 4 should be in contact with each other. The second insulation board 9 is attached to the cold side of the measured wall 10, and the second temperature sensor 7 and the second heat flux sensor 8 are located in the through hole 91 set in the middle of the second insulation board 9 and do not contact the side wall of the through hole 91. The through hole 91 is used as a one-dimensional heat flow channel to create a one-dimensional heat transfer area. This test device can ensure that the temperature field and heat flux field inside the measured wall do not change with time.

[0035] The specific implementation methods of each component in this embodiment are described as follows:

[0036] like Figure 1 As shown, in order to address the shortcomings of existing on-site test hot boxes that are large in size and inconvenient to install, the present invention adopts a heating plate 3 as a heat source. The heating plate 3 is a flat metal plate made of a metal material with good thermal conductivity and light weight (such as aluminum, copper, silver and related alloy materials). The shape of the heating plate 3 has symmetrical characteristics (such as square, circle), and the boundary of the heating plate 3 can completely cover the boundary of a circular area. The size of the circular area satisfies: L≥0.5δ+0.15, L is the diameter of the circular area (m); δ is the thickness of the wall 10 to be tested (m).

[0037] The first temperature sensor 1 and the first heat flux sensor 2 are integrated at the center of the surface of the heating plate 3. Under the premise of not affecting the uniformity of the temperature field inside the heating device and the uniform heating of the surface of the measured wall 10, the temperature and heat flux density at the center point of the heating plate 3 can be accurately measured by the first temperature sensor 1 and the first heat flux sensor 2. The heating plate 3 is connected to the temperature controller 6 through the wire 5, which can automatically maintain the surface temperature of the heating plate 3 constant. The control accuracy of the temperature controller 6 is ±0.1°C. A sufficient amount of thermal insulation material is covered on the back of the heating plate 3 to form a first thermal insulation plate 4, which is used to reduce the heat loss of the heating plate 3 from the back thereof, thereby reducing the heating energy consumption. Preferably, the heating plate 3 is attached to the inner side of the first thermal insulation plate 4. The size of the first thermal insulation plate 4 meets:

[0038] L 1 ≥L+0.05,δ 1 ≥0.30

[0039] Where: L 1 is the side length of the first insulation board 4 (m); δ 1 is the thickness of the first insulation board 4 (m).

[0040] In view of the disadvantage of large errors caused by existing on-site three-dimensional thermal conductivity testing, the present invention adopts a second thermal insulation board 9 to reduce the lateral heat loss of the measured wall 10. The size of the second thermal insulation board 9 meets the following requirements:

[0041] L 2 ≥L

[0042]

[0043] Where: L 2 is the side length of the second insulation board 9 (m); δ 2 is the thickness of the second insulation board 9 (m).

[0044] The size of the through hole 91 in the second heat insulation plate 9 is not less than the size of the second temperature sensor 7 and the second heat flow sensor 8 .

[0045] During the test, the second insulation board 9 is pasted and fixed to the cold side surface of the wall 10 to be tested, and the through hole 91 of the second insulation board 9 is aligned with the positions of the second temperature sensor 7 and the second heat flux sensor 8, so that the second insulation board 9 covers the area around the second temperature sensor 7 and the second heat flux sensor 8 and corresponds to the area of ​​the heating plate 3. The heat flux is concentrated through the one-dimensional channel, which is conducive to the rapid establishment of the one-dimensional heat transfer zone.

[0046] The temperature measurement accuracy of each temperature and heat flow sensor is ±0.2°C, and the heat flow measurement accuracy is ±5%. The length of each temperature and heat flow sensor is not more than 100mm to ensure that each temperature and heat flow sensor is in the one-dimensional heat transfer area, thereby ensuring the accuracy of the temperature and heat flow measurement values.

[0047] A method for on-site testing of the thermal resistance of a building wall using the above-mentioned device in an embodiment of the present invention is to quantitatively determine the size of the one-dimensional heat transfer area on the hot and cold sides of the measured wall, and to calculate the equivalent thermal resistance of the measured wall by measuring and recording the surface temperature of the one-dimensional heat transfer area on the hot and cold sides of the measured wall and the heat flux passing through the one-dimensional heat transfer area.

[0048] Before testing, you can do the following preparations:

[0049] Test time selection: It is best to conduct the test on a cloudy or overcast day, avoid weather with drastic temperature changes, and avoid rainy or snowy days.

[0050] Heating area selection: Try to select areas that are not exposed to direct sunlight throughout the day. To avoid thermal bridges, do not select heating areas near doors, windows, metal structures, beams and columns, or near structural defects with cracks and air infiltration. Do not be directly affected by airflow from heating and cooling devices such as radiators, air conditioners, and fans. Use a thermal imager to scan the wall to be tested before testing to exclude areas that are not suitable for testing.

[0051] Wall polishing: If the wall surface of the selected heating area is too rough, directly installing this test device will form an overly thick air layer between the wall surface and the heating plate surface, causing non-negligible test errors. The wall surface needs to be simply polished. The common method is to use sandpaper for polishing and cleaning, but it should not cause significant changes to the wall surface material or thickness. And apply an appropriate amount of thermal conductive silicone grease or vaseline.

[0052] After the above preparations are completed, follow the steps below to conduct on-site testing of the thermal resistance of the building wall:

[0053] 1) After completing the test preparation, refer to Figure 1 , install the heating device in the selected heating area on the surface of one side of the wall (hot side), specifically: install the heating plate 3 with the first temperature sensor 1 and the second heat flux sensor 2 on one side of the wall 10 to be tested, close to the wall surface, and install the second temperature sensor 7 and the second heat flux sensor 8 on the other side of the wall 10 to be tested (cold side) in close contact with the wall surface facing the center of the heat source. Fix the second insulation board 9 close to the cold side wall surface, align the through hole 91 in the second insulation board 9 with the second temperature sensor 7 and the second heat flux sensor 8, so that the insulation material covers the area of ​​the heating board 3 around the measuring point. After the test device is correctly installed, turn on the power supply, turn on the heating device, and use a two-stage heating method. The first stage is set to a constant high temperature to increase the internal temperature of the wall 10 to be tested, and the duration is generally not less than 0.5h and not more than 8h; the second stage is set to the required heating temperature. And the two-stage set temperatures satisfy the following formula:

[0054] 10℃≤T 2 -T c ≤27℃

[0055] T 1 -T 2 ≥10℃

[0056] Where: T c is the surface temperature of the cold side of the measured wall 10 (°C); T 1 and T 2are the heating temperatures (°C) of the first and second stages, respectively, i.e., the temperatures of the heating plate 3 at the end of the corresponding stages controlled by the temperature controller 6. In the formula, 10°C and 27°C are derived through theoretical formulas. When the temperature is less than 10°C, the error of the calculation result increases significantly. When the temperature is greater than 27°C, the contribution to the reduction of the error of the calculation result is very small.

[0057] During the above heating process, all test data are collected and recorded at a set frequency, and the recording interval is no longer than 1 minute.

[0058] 2) Determine whether the approximate steady-state heat transfer is achieved based on the test data collected in step 1). If the approximate steady-state heat transfer is achieved, it must simultaneously meet the following conditions: (a) the absolute value of the cold side temperature change does not exceed 0.5°C within 0.5h; (b) the heat flux density changes on the cold side and the hot side do not exceed 20% within 0.5h, see formulas (1) to (3), then execute step 3); if the approximate steady-state heat transfer is not achieved, wait until the approximate steady-state heat transfer is achieved, and execute step 3). The temperature T(x, τ) of any point in the test area of ​​the tested wall 10 at any time is calculated by the following formula:

[0059]

[0060] Where x is the distance from any point in the test area of ​​the tested wall 10 to the center of the hot side test area (m); τ is the current heating time (s); a is the thermal conductivity of the tested wall 10 (m 2 / s); T h is the surface temperature of the hot side of the measured wall 10 (°C); T 0 is the surface temperature of the hot side of the measured wall 10 at the initial moment of heating (°C); T c is the surface temperature of the cold side of the measured wall 10 (°C); T′ c is the rate of change of the surface temperature of the cold side of the measured wall 10 (°C / s); n is a continuous positive integer starting from 1; t is the time integral variable, t∈[0,τ].

[0061] Formulas (1) to (3) are:

[0062]

[0063]

[0064]

[0065] In the formula, is the surface temperature of the cold side of the measured wall at time τ (℃); is the surface temperature of the cold side of the measured wall at the time τ-Δτ (℃); is the heat flux density on the hot side of the measured wall at time τ (W / m2 ); is the heat flux density on the hot side of the measured wall at the time τ-Δτ (W / m 2 ); is the heat flux density on the cold side of the measured wall at time τ (W / m 2 ); is the heat flux density of the cold side of the measured wall at the time τ-Δτ (W / m 2 ).

[0066] The data diagram of the entire test process is as follows: Figure 2 As shown, (a) is the temperature and (b) is the heat flux. h is the surface temperature of the hot side of the measured wall (℃); T c — is the surface temperature of the cold side of the measured wall (℃); q h is the heat flux density on the hot side of the measured wall (W / m 2 );q c is the heat flux density on the cold side of the measured wall (W / m 2 ); τ 1 —Time of the first stage (s); τ 2 —Approximate steady-state time (s); τ 3 —Total test duration (s).

[0067] 3) After the heat transfer process enters the approximate steady state, continue to measure for a period of time (0.5h in this embodiment) to complete the entire test process. The thermal resistance can be calculated according to Fourier's law. The temperature difference between the cold and hot sides of the measured wall is the difference between the cold and hot side temperatures at the same time. The arithmetic mean of the heat flux density on both sides of the cold and hot sides at the same time is taken as the average heat flux density passing through the measured wall, which can meet the requirements of on-site detection. In order to reduce the random error caused by different data value time periods, take the data of any 10 minutes after entering the approximate steady state for calculation. That is:

[0068]

[0069] Where: R is the thermal resistance of the wall being tested (m 2 K / W); is the temperature measurement value of the hot side surface of the measured wall at time τ (℃); is the temperature measurement value of the cold side surface of the measured wall at time τ (℃); is the measured heat flux density of the hot side of the wall at time τ (W / m 2 ); is the measured heat flux density of the cold side of the measured wall at time τ (W / m 2 ).

[0070] Considering the three-dimensional heat conduction, the cold side of the wall to be tested can be divided into the following types: Figure 3The three regions shown are the one-dimensional heat transfer region I, the non-one-dimensional heat transfer region II, and the unaffected region III. Figure 3 The heated area refers to the area inside the measured wall that is affected by the heat transfer of the heating device. The dotted lines inside are isothermal flow lines, and the heat flow direction at any point is the normal direction of the isothermal flow line passing through the point. The solid line segment perpendicular to the horizontal axis represents the one-dimensional heat transfer area at the thickness.

[0071] In the one-dimensional heat transfer zone I, the lateral heat loss ratio of the measured wall is low, and the internal isotherms are basically parallel to the wall surface. It is considered that the one-dimensional heat transfer assumption is met. This area is the best location for arranging temperature sensors and heat flux sensor measurement points. The maximum values ​​of the cold side temperature and heat flux density appear at the center point, and 95% of the heat flux density value at the center point is used as the judgment condition for the boundary of the one-dimensional heat transfer zone. 0 For example, the maximum heat flux density q xm Appears at the center point y = 0, that is, the center of the test area on the hot side of the tested wall, then 0.95q xm The isothermal flow lines and the straight line x = x 0 The two intersection points are the endpoints of the one-dimensional heat transfer zone. As the heat transfer process proceeds, the size of the one-dimensional heat transfer zone d(x) gradually decreases as the x coordinate increases, and is reduced to d on the cold side wall. Temperature is not used as the boundary judgment condition of the one-dimensional heat transfer zone because the absolute value of the temperature deviation as a boundary judgment criterion will not be universal for different working conditions.

[0072] In the non-one-dimensional heat transfer zone II, there is a large proportion of lateral heat dissipation ( Figure 3 The y-axis component of the heat flux vector in the middle), the temperature and heat flux density values ​​of the cold side surface of the measured wall in this area are lower than those in the one-dimensional heat transfer zone, which does not meet the one-dimensional heat transfer assumption. In actual tests, if temperature sensors and heat flux sensors are installed in this area, it will cause large errors in the results.

[0073] In the unaffected zone III, the measured wall is not affected by the heating device, and the temperature and heat flux density are in the natural state without heating.

[0074] When testing and calculating the thermal resistance of the test piece, the heat flux density value on the cold side of the tested wall should be selected from the one-dimensional heat transfer zone, that is, the heat flux density value passing through the one-dimensional channel of the heat flow.

[0075] like Figure 4As shown in the figure, when the thermal resistance of the wall under test is tested, whether there is a one-dimensional heat flow channel device on the cold side will cause different heat flow distribution inside the wall (the dotted line in the figure shows the heat flow distribution inside the wall when the one-dimensional heat flow channel device is not set, and the actual line in the figure shows the heat flow distribution inside the wall when the one-dimensional heat flow channel device is set). When there is no one-dimensional heat flow channel on the cold side, a large proportion of the heat flow is lost laterally, resulting in the one-dimensional heat transfer zone required for the test not being easy to form, and a larger heating area is required to ensure the accuracy of the results; when a one-dimensional heat flow channel device is installed on the cold side, the thermal resistance of the heat transfer path outside the one-dimensional channel is significantly greater than that within the middle one-dimensional channel, so a large proportion of the heat flow is concentrated through the one-dimensional channel, which is conducive to the rapid formation of a one-dimensional heat transfer zone where Fourier's law is established, the test results are more accurate, the required heating area is reduced, and the device is simple.

[0076] In summary, the present invention adopts a two-stage heating heating plate-heat flow meter method, which overcomes the shortcomings of the heat flow meter method, such as long measurement time and being greatly affected by environmental conditions, as well as the shortcomings of the hot and cold box method, such as large equipment size and inconvenient installation. It has the characteristics of fast on-site testing, accurate test data, and simple device. This test device constructs a heat transfer temperature difference on both sides of the wall, and the heating device creates a uniform isothermal surface on the surface of one side of the wall to be tested, and the heat flow one-dimensional channel device on the other side surface creates a one-dimensional heat transfer zone. After a period of time, in the one-dimensional heat transfer zone, the surface temperatures on both sides of the wall remain unchanged, and the internal temperature field and heat flow field do not change with time, so it can be considered that Fourier's law of heat conduction is valid in this area. The test instrument calculates the equivalent thermal resistance of the wall by measuring the surface temperatures on both sides of the hot and cold sides of the one-dimensional heat transfer zone of the wall and the heat flux density passing through the one-dimensional heat transfer zone.

[0077] It can be understood that the technical solution of the present invention can be modified or some of the technical features can be replaced by equivalents without departing from the essential features of the present invention; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the present invention.

Claims

1. A method for on-site testing of thermal resistance of building walls, characterized in that: The test method utilizes a building wall thermal resistance on-site test device, the test device includes a heating plate, a temperature controller, and two temperature sensors, two heat flux sensors and two insulation plates; wherein the first temperature sensor, the first heat flux sensor, the heating plate and the first insulation plate are all attached to the hot side of the wall to be tested, the first temperature sensor and the first heat flux sensor are close to the hot side wall of the wall to be tested and are completely covered by the heating plate, the heating plate is completely covered by the first insulation plate, and the temperature controller is electrically connected to the heating plate; the second temperature sensor, the second heat flux sensor and the second insulation plate are all attached to the cold side of the wall to be tested, a through hole as a one-dimensional heat flux channel is provided in the middle of the second insulation plate, the second temperature sensor and the second heat flux sensor are both located in the through hole and are respectively arranged opposite to the first temperature sensor and the first heat flux sensor; The test method comprises the following steps: 1) Install the building wall thermal resistance field test device on the tested wall that meets the requirements; turn on the building wall thermal resistance field test device, and heat the tested wall using a two-stage heating method. The first stage is set to a constant temperature T1 to quickly increase the internal temperature of the wall, and the duration of this stage is 0.5 to 8 hours; the second stage is set to the required heating temperature T2; the two-stage setting temperatures satisfy the following formula: 10℃≤T2-T c ≤27℃ T1-T2≥10℃ Where: T c is the surface temperature of the cold side of the measured wall; During the above heating process, all test data are collected and recorded at the set frequency, and the recording interval is no longer than 1 minute; 2) Determine whether the approximate steady-state heat transfer is achieved based on the test data collected in step 1). If the approximate steady-state heat transfer is achieved, that is, the following conditions must be met at the same time: (a) the absolute value of the cold side temperature change does not exceed 0.5°C within 0.5h; (b) the heat flux density changes on the cold side and the hot side do not exceed 20% within 0.5h, then execute step 3); if the approximate steady-state heat transfer is not achieved, wait until the approximate steady-state heat transfer is achieved, and then execute step 3); wherein, the temperature T(x,τ) of any point in the test area of ​​the tested wall at any time is calculated by the following formula: Where x is the distance from any point in the test area of ​​the tested wall to the center of the hot side test area; τ is the current heating time; a is the thermal conductivity of the tested wall; T h is the surface temperature of the hot side of the measured wall; T0 is the surface temperature of the hot side of the measured wall at the initial moment of heating; T′ c is the rate of change of the surface temperature on the cold side of the measured wall; n is a continuous positive integer starting from 1; t is the time integral variable, t∈[0,τ]; δ is the thickness of the measured wall; 3) Take the collected data of any 10 minutes after entering the approximate steady state, and calculate the thermal resistance of the measured wall according to the following formula: Where R is the thermal resistance of the wall being measured; is the temperature measurement value of the hot side surface of the measured wall at time τ; is the temperature measurement value of the cold side surface of the measured wall at time τ; is the measured value of heat flux density on the hot side of the measured wall at time τ; is the measured value of heat flux density on the cold side of the measured wall at time τ.

2. The on-site testing method for thermal resistance of building walls according to claim 1, characterized in that: The shape of the heating plate is symmetrical, and the boundary of the heating plate can completely cover the boundary of a circular area, the diameter L of the circular area satisfies: L≥0.5δ+0.15, δ is the thickness of the measured wall; the side length L1 and thickness δ1 of the first insulation board satisfy: L1≥L+0.05, δ1≥0.30; the side length L2 and thickness δ2 of the second insulation board satisfy: L2≥L 3. The on-site testing method for thermal resistance of building walls according to claim 1, characterized in that: The first temperature sensor and the first heat flux sensor are integrated at the surface center of the heating plate and contact each other, and the heating plate and the first insulation plate contact each other; the second temperature sensor and the second heat flux sensor do not contact the side wall of the through hole in the second insulation plate.

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