A device and method for determining the thermal conductivity of a green roof

Abstract

The application relates to a device and a method for measuring the thermal conductivity coefficient of roof greening, which comprises a closed test chamber, a heater (1) arranged at the top of the closed test chamber, a water sample contrast module (6) arranged at the bottom of the closed test chamber, and temperature sensors arranged on the upper and lower surfaces of the water sample contrast module (6) and a roof greening or wall greening module (3) to be tested. The closed space is heated by a non-contact heater in a hot air diffusion mode, the roof greening module to be tested and the water sample contrast module with the same specification are placed on the bottom ground of the closed space, the heat is conducted downward, and when the temperature difference between the upper and lower surfaces of the roof greening reaches stability, the thermal conductivity coefficient of the roof greening can be calculated by referring to the known water sample contrast. Compared with the prior art, the application avoids the damage of a heat source to plants, only needs to record the temperature difference between the upper and lower surfaces of the test sample in a steady state during the test, and can be applied to the measurement of the thermal conductivity coefficient of various non-homogeneous and complex structure materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of determining the thermal conductivity of building energy-saving insulation materials, and particularly relates to a method and device for determining the thermal conductivity of roof greening and wall greening. BACKGROUND

[0002] Buildings consume about 40% of the world's energy and contribute more than 30% of carbon emissions, so building energy saving and emission reduction is an important obstacle that must be overcome. Roof greening and wall greening not only have good ecological improvement and living environment improvement effects, but also have good building insulation effects. In summer, roof greening and wall greening can block the conduction of solar radiation from the building roof or wall to the indoor, reduce the indoor temperature, and thus reduce the use of air conditioning and energy consumption in summer; in winter, they can effectively reduce the loss of indoor temperature and heat, and improve the insulation effect of buildings in winter, thereby reducing the heating energy consumption in winter.

[0003] The thermal conductivity of building insulation materials is the most basic thermal data indispensable for energy-saving building design and construction, and is the most important technical index for evaluating the insulation performance of various building materials. Architects need to calculate the thermal conductivity of different materials to design and achieve the energy-saving goal of buildings. For energy-saving buildings, roof greening and wall greening are also effective building insulation materials. In the design of energy-saving buildings, the thermal conductivity and other basic thermal data need to be understood in order to design according to the corresponding energy-saving effect, so as to achieve the predetermined design goal of building energy saving.

[0004] The thermal conductivity of building insulation materials can be measured by existing thermal conductivity measuring instruments. The international and domestic standards for measuring the thermal conductivity of building materials basically use the steady heat flow method, such as ASTM C177-2013 (Standard test method for steady-state heat flux measurements and thermal transmission properties by means of the guarded-hot-plate) in the United States and GB / T 10294-2008 (Determination of steady-state thermal resistance and related properties of thermal insulations - guarded hot plate method) in China. The principle of these methods is to place the sample to be tested between the hot plate and the cold plate, and when the temperature of the case and the temperature of the hot and cold plates are stable, the heat flow in the sample reaches a steady state. The thermal conductivity of the thermal insulation material can be calculated by the Fourier heat formula through the energy applied to the hot plate, the temperature gradient of the sample and the hot plate and the cold plate, and the thickness of the sample, i.e. Q = λ x S x ΔT / h. Where Q is the heat transferred by the test material, with the unit of W; λ is the thermal conductivity, with the unit of W / m°K; S is the contact area of the test material and the hot plate and the cold plate, with the unit of m 2 ; ΔT is the temperature difference between the sample and the hot plate and the cold plate, with the unit of °C or °K; h is the thickness of the test sample. The steady heat flow method for measuring thermal conductivity has the advantages of accuracy and stability, but the time-consuming for measurement is too long, and the test time for each sample is up to 24 hours (ASTM C177-2013). Some studies even propose to extend to 48 hours in order to obtain more stable and accurate data (Alengaram et al., 2013). In order to seek rapid and efficient measurement, some measurements use dynamic heat flow method, such as heat pulse method and hot wire method. The principle is to introduce a heat source into the sample, and the temperature of each point in the sample will change with the heat conduction time. By detecting the change of temperature, the thermal conductivity of the sample can be calculated.

[0005] No matter steady-state heat flow method or dynamic heat flow method, the test sample needs to be in direct contact with the heat source. The steady-state heat flow method is that the sample is in direct contact with the hot plate, and the dynamic heat flow method is that the sample is in direct contact with the heater or the hot wire is directly inserted into the sample. These methods for determining the thermal conductivity cannot be applied to roof greening and wall greening because: ① the main body of roof greening and wall greening is green plants, and direct contact (or hot wire insertion) with the hot plate and the heater will directly burn the plants and even kill the plants; ② the plant layer of roof greening or wall greening is very loose, and it cannot be clamped and fixed between the hot plate and the cold plate of the measuring instrument for measurement; ③ roof greening or wall greening is composed of two parts of cultivation matrix and green plants, and is a completely inhomogeneous texture structure, and the current steady-state heat flow method and dynamic heat flow method can only measure the building materials with uniform texture, and cannot be used for determining the thermal conductivity of inhomogeneous roof greening or wall greening. SUMMARY

[0006] The purpose of the present application is to provide a method and device for determining the thermal conductivity of roof greening and wall greening.

[0007] The purpose of the present application can be achieved by the following technical scheme: a device for determining the thermal conductivity of roof greening, comprising: a closed test chamber, the top of which is provided with a heater, and the bottom of which is provided with a water sample control module, the upper surface of which is provided with a temperature sensor a, and the lower surface of which is provided with a temperature sensor b, and the roof greening or wall greening module to be tested is arranged at the bottom of the closed test chamber, and the upper surface thereof is provided with a temperature sensor c, and the lower surface thereof is provided with a temperature sensor d.

[0008] Further, the size, area and thickness of the water sample control module and the roof greening or wall greening module to be tested are the same.

[0009] Further, the water sample control module and the roof greening or wall greening module to be tested are in complete contact with the ground at the bottom of the closed test chamber without leaving space, preventing hot air from penetrating into the bottom for conduction and affecting the accuracy of the measurement.

[0010] The application also provides a method for determining the heat conductivity of the roof greening by using the device, which is a non-contact steady heat flow method, that is, the heat source is not in contact with the roof greening or wall greening to be determined, the heater heats the closed test chamber by air diffusion, the roof greening or wall greening module to be determined is placed on the ground in the closed space, the heat flow is conducted downward through the plant layer and the cultivation substrate layer of the roof greening or wall greening from top to bottom, and the heat flow is also conducted downward through the water sample control module from top to bottom, the upper surface temperature and the lower surface temperature of the water sample control module and the roof greening or wall greening module to be determined are recorded, and when the temperature difference between the upper surface and the lower surface reaches a stable state, the heat conductivity of the roof greening or wall greening module to be determined can be calculated.

[0011] In the determination of the heat conductivity of the roof greening or wall greening, a water sample control module with the same size, area and thickness as the roof greening or wall greening module is arranged, the water sample control with a known heat conductivity is used as a reference to calculate the heat conductivity of the roof greening or wall greening, so as to avoid the determination system error caused by the lateral flow of heat flow and water evaporation.

[0012] Further, the method specifically comprises the following steps:

[0013] S1, turning on the heater switch to heat the closed test chamber, and conducting the heat downward with air diffusion;

[0014] S2, recording the temperature change of the temperature sensor c, the temperature sensor d, the temperature sensor a and the temperature sensor b every minute;

[0015] S3, when the temperature difference between the upper surface and the lower surface of the roof greening or wall greening module to be determined reaches a stable state, the heat conductivity of the roof greening or wall greening module to be determined is calculated.

[0016] Further, the calculation method of step S3 is as follows:

[0017] λ 屋顶绿化 = λ 水 ×△T 水 / △T 屋顶绿化 ,

[0018] wherein λ 屋顶绿化 is the heat conductivity of the roof greening or wall greening module to be determined,

[0019] λ 水 is the heat conductivity of the water sample control module,

[0020] △T 水 is the temperature difference between the upper surface and the lower surface of the water sample control module.

[0021] △T 屋顶绿化The temperature difference between the upper surface and the lower surface of the roof greening or wall greening module to be tested.

[0022] Further, the temperature difference between the upper surface and the lower surface of the roof greening or wall greening module to be tested reaches a steady state, and the temperature difference measured by the temperature sensor c and the temperature sensor d is constant.

[0023] Further, the time for the temperature difference between the upper surface and the lower surface of the roof greening or wall greening module to be tested to reach a steady state is 10-20 minutes, and is generally 15 minutes.

[0024] Further, the heat received by the water sample control module and the roof greening or wall greening module to be tested in the closed test chamber is the same, that is, Q 屋顶绿化 = Q 水 .

[0025] According to the Fourier heat formula: Q = λ × S × △T / h (1)

[0026] Therefore,

[0027] λ 屋顶绿化 × S 屋顶绿化 × △T 屋顶绿化 / h 屋顶绿化 = λ 水 × S 水 × △T 水 / h 水

[0028] The area and thickness of the water sample control module and the roof greening or wall greening module to be tested are the same, that is, S 屋顶绿化 = S 水 , h 屋顶绿化 = h 水 .

[0029] Therefore, λ 屋顶绿化 × △T 屋顶绿化 = λ 水 × △T 水

[0030] λ 屋顶绿化 = λ 水 × △T 水 / △T 屋顶绿化 (2)

[0031] Since λ 水 is known at a certain temperature, the heat conductivity coefficient of the roof greening can be calculated only by measuring the temperature difference between the upper surface and the lower surface of the water sample control module and the roof greening or wall greening module to be tested.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] 1) The heater does not contact the test sample, and the heat diffused and conducted by the hot air has no obvious effect on the plants of the roof greening or wall greening.

[0034] 2) The temperature difference between the upper and lower surfaces of the roof greening or wall greening module can reach a steady state in about 15 minutes, which significantly improves the determination efficiency of the thermal conductivity compared with the traditional 24-hour steady heat flow method.

[0035] 3) The previous thermal conductivity determination method can only determine samples with uniform material, and the present application can be applied to the determination of thermal conductivity of various complex structure samples similar to roof greening, and the thermal conductivity of various complex structure materials can be calculated by only recording the temperature difference between the upper and lower surfaces of the sample to be tested. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The present application is a schematic diagram of a method and device for determining the thermal conductivity of roof greening.

[0037] In the figure: 1 heater, 2 heat flow downwardly conducted by air, 3 roof greening or wall greening module to be tested, 4 temperature sensor c, 5 temperature sensor d, 6 water sample control module, 7 temperature sensor a, 8 temperature sensor b.

[0038] Figure 2 Temperature dynamic change of the thermal conductivity determination device;

[0039] Figure 3 Relationship between matrix moisture and thermal conductivity of tall fescue roof greening. DETAILED DESCRIPTION

[0040] The embodiments of the present application will be described in detail below, which are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0041] As Figure 1 described, the present application provides a device for determining the thermal conductivity of roof greening, comprising: a closed test chamber, the top of which is provided with a heater 1, and the bottom of which is provided with a water sample control module 6, the upper surface of which is provided with a temperature sensor a 7, and the lower surface of which is provided with a temperature sensor b 8, and the roof greening or wall greening module to be tested 3 is arranged at the bottom of the closed test chamber, the upper surface of which is provided with a temperature sensor c 4, and the lower surface of which is provided with a temperature sensor d 5.

[0042] Among them, the size, area and thickness of the water sample control module 6 and the roof greening or wall greening module to be tested 3 are the same.

[0043] The water sample control module 6 is in full contact with the bottom ground of the closed test chamber and does not leave any space for the hot air to penetrate and conduct to the bottom, thereby preventing the influence on the accuracy of the determination.

[0044] The method for determining the heat conductivity coefficient of the roof greening by using the above device is as follows:

[0045] S1, turn on the switch of the heater 1 to heat the closed test chamber, and the heat is diffused downward 2 with the air;

[0046] S2, record the temperature change of the temperature sensor c4, the temperature sensor d5, the temperature sensor a7, and the temperature sensor b8 every minute;

[0047] S3, when the temperature difference between the upper and lower surfaces of the roof greening or wall greening module to be tested reaches a steady state, the heat conductivity coefficient of the roof greening or wall greening module to be tested is calculated by the following formula.

[0048] The calculation formula is as follows:

[0049] λ 屋顶绿化 =λ 水 ×△T 水 / △T 屋顶绿化 ,

[0050] Wherein λ 屋顶绿化 is the heat conductivity coefficient of the roof greening or wall greening module to be tested,

[0051] λ 水 is the heat conductivity coefficient of the water sample control module,

[0052] △T 水 is the temperature difference between the upper and lower surfaces of the water sample control module;

[0053] △T 屋顶绿化 is the temperature difference between the upper and lower surfaces of the roof greening or wall greening module to be tested.

[0054] The following is further illustrated by specific examples:

[0055] Example 1

[0056] Determination of the heat conductivity coefficient of the Sedum lineare roof greening:

[0057] The Sedum lineare is planted in a planting tray with a length of 530 mm, a width of 330 mm, and a height of 74 mm, and the planting substrate is grass charcoal with a thickness of 5 cm. The determination is started after the Sedum lineare roof greening module is completely formed. The vegetation coverage of the Sedum lineare roof greening is 100% during the determination, the thickness of the roof greening planting substrate is 5 cm, the height of the plant is 8 cm, the thickness of the entire roof greening module is 13 cm, and the water content of the grass charcoal planting substrate during the determination is 80%.

[0058] At the start of the test, the roof greening module and the water sample control module of the same size and 13cm thickness were rotated together on the ground at the bottom of the measuring device to check that the bottom was in complete contact with the ground without any gaps.

[0059] Turn on the heater at the top of the device to allow heat to diffuse downwards within the enclosed space. Record the temperatures of the upper surface (T1) and lower surface (T2) of the roof greening module and the upper surface (T1') and lower surface (T2') of the water sample module every minute. After 15 minutes of heating, the temperature difference between the upper and lower surfaces of the roof greening module and the water sample control module reached a stable state (see...). Figure 2 ).

[0060] Through formula (2)λ 屋顶绿化 =λ 水 ×△T 水 / △T 屋顶绿化 The thermal conductivity of the rooftop greening was calculated to be λ. 屋顶绿化 = 0.4812 W / m°K.

[0061] Example 2

[0062] Determination of thermal conductivity of seaside paspalum rooftop greening:

[0063] Seashore paspalum was planted in planting trays measuring 530mm × 330mm × 74mm (length × width × height), with peat moss as the planting substrate, 6cm thick. Measurements were taken after the seashore paspalum rooftop greening module was fully established. At the time of measurement, the vegetation cover of the rooftop greening was 100%, the planting substrate thickness was 6cm, the plant height was 6cm, the total thickness of the rooftop greening module was 12cm, and the moisture content of the peat moss planting substrate at the time of measurement was 76.6%, 77.7%, 78.8%, 79.8%, 80.3%, 81.3%, 82%, and 82.6%, respectively.

[0064] At the start of the test, the roof greening module and the water sample control module of the same size and 12cm thickness were rotated together on the ground at the bottom of the measuring device to check that the bottom was in complete contact with the ground without any gaps.

[0065] Turn on the heater at the top of the device to allow heat to diffuse downwards through the enclosed space of the device. Record the temperatures of the upper surface (T1) and lower surface (T2) of the *Paspalum notatum* rooftop greening module and the upper surface (T1') and lower surface (T2') of the water sample module every minute. After the temperature difference between the upper and lower surfaces of the rooftop greening module and the water sample control module reaches a stable state, use formula (2)λ 屋顶绿化 =λ 水 ×△T 水 / △T屋顶绿化 The thermal conductivity of the roof greening is calculated as follows:

[0066] Table 1 Thermal conductivity of different substrate moisture content of beach paspalum roof greening

[0067]

[0068]

[0069] Example 3

[0070] Relationship between substrate moisture and thermal conductivity of tall fescue roof greening:

[0071] The tall fescue is planted in a planting tray with length x width x height of 530 mm x 330 mm x 74 mm, and the planting substrate is grass charcoal with a thickness of 6 cm. After the tall fescue roof greening module is completely established, the determination is started. When determining, the vegetation coverage of the roof greening is 100%, the thickness of the planting substrate of the roof greening is 6 cm, the height of the plant is 8 cm, the thickness of the entire roof greening module is 14 cm, sufficient water is poured at one time, and the maximum water holding capacity is reached, and then the water is consumed by the roof greening through normal evapotranspiration. The determination of the thermal conductivity is carried out every day, and the influence of the substrate moisture on the thermal conductivity of the roof greening is discussed. The moisture content of the substrate is 83.8%, 82.7%, 81.8%, 80.6%, 79.6%, 77.6%, 75.5%, 73.3%, 71.6%, 67.6%, 63.2%, 56.7%, and 50.2% respectively every day. When the substrate moisture decreases to 50.2%, the tall fescue leaves begin to curl and reach the wilting point.

[0072] At the beginning of the test, the roof greening module and the water sample control module with the same specification and thickness of 14 cm are rotated together on the bottom ground of the determination device, and it is checked that the bottom is in complete contact with the ground without any gap.

[0073] The heater at the top of the device is turned on, and the heat is diffused in the closed space of the device with air downward conduction. The temperature (T1) on the upper surface of the tall fescue roof greening module, the temperature (T2) on the lower surface, and the temperature (T1') on the upper surface of the water sample module and the temperature (T2') on the lower surface are recorded every 1 minute. After the temperature difference between the upper and lower surfaces of the roof greening module and the water sample control module reaches a stable state, the thermal conductivity of the roof greening is calculated by formula (2). The thermal conductivity of the tall fescue roof greening increases with the increase of the moisture content of the substrate (see Figure 3 ).

[0074] The above only describes the preferred embodiments of the present application and is not used to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A device for determining the thermal conductivity of green roofs, characterized in that, include: A sealed test chamber is provided with a heater (1) at the top and a water sample control module (6) at the bottom. The water sample control module (6) is provided with a temperature sensor a (7) on the upper surface and a temperature sensor b (8) on the lower surface. The roof greening or wall greening module (3) to be tested is located at the bottom of the sealed test chamber, and is provided with a temperature sensor c (4) on the upper surface and a temperature sensor d (5) on the lower surface. The method for determining the thermal conductivity of roof greening using the above-mentioned device is a non-contact steady-state heat flow method. The heat flow of the heater (1) heats the sealed test chamber through air diffusion. The heat flow is conducted downwards from top to bottom through the water sample control module (6) and the roof greening or wall greening module (3) to be tested. By recording the upper and lower surface temperatures of the water sample control module (6) and the roof greening or wall greening module (3) to be tested, the thermal conductivity of the roof greening or wall greening module (3) to be tested can be calculated after the temperature difference between the upper and lower surfaces reaches a stable state. The specific steps include: S1. Turn on the heater (1) switch to heat the sealed test chamber. The heat diffuses downward with the air. S2. Record the temperature changes of temperature sensor c (4), temperature sensor d (5), temperature sensor a (7), and temperature sensor b (8) every minute; S3. After the temperature difference between the upper and lower surfaces of the roof greening or wall greening module (3) to be tested reaches a steady state, the thermal conductivity of the roof greening or wall greening module (3) to be tested is calculated. The calculation method of step S3 is as follows: l 屋顶绿化 =λ 水 ×△T 水 / △T 屋顶绿化 , Where λ 屋顶绿化 The thermal conductivity of the rooftop greening or wall greening module (3) to be tested is given. λ 水 The thermal conductivity of the water sample control module (6) is given. △T 水 The temperature difference between the upper and lower surfaces of the water sample control module (6); △T 屋顶绿化 The temperature difference between the upper and lower surfaces of the roof greening or wall greening module (3) to be tested.

2. The device for determining the thermal conductivity of rooftop greening according to claim 1, characterized in that, The water sample control module (6) is the same in size, area and thickness as the roof greening or wall greening module (3) to be tested.

3. The device for determining the thermal conductivity of rooftop greening according to claim 1, characterized in that, The water sample control module (6) and the roof greening or wall greening module (3) to be tested are in complete contact with the bottom floor of the sealed test chamber, leaving no space.

4. The apparatus for determining the thermal conductivity of rooftop greening according to claim 1, characterized in that, In step S3, the temperature difference between the upper and lower surfaces of the roof greening or wall greening module (3) to be tested reaches a steady state when the temperature difference measured by temperature sensor c (4) and temperature sensor d (5) is constant.

5. The apparatus for determining the thermal conductivity of rooftop greening according to claim 1, characterized in that, The time for the temperature difference between the upper and lower surfaces of the roof greening or wall greening module (3) to be tested in step S3 to reach a steady state is 10 to 20 minutes.

6. The apparatus for determining the thermal conductivity of rooftop greening according to claim 1, characterized in that, The water sample control module (6) and the rooftop greening or wall greening module (3) to be tested receive the same amount of heat in the sealed test chamber, i.e., Q 屋顶绿化 = Q 水 .

7. The apparatus for determining the thermal conductivity of green roofs according to claim 1, characterized in that, The water sample control module (6) has the same area and thickness as the rooftop greening or wall greening module (3) to be tested, that is: S 屋顶绿化 = S 水 h 屋顶绿化 = h 水 .

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