CN115231834A - A design method of radiation cooling glass with two-way regulation of inner and outer radiation characteristics - Google Patents

Abstract

The invention discloses a design method for radiation refrigeration glass with two-way regulation of inner and outer radiation characteristics. TiO ₂ /Ag/TiO ₂ is used as a reflective layer, which is recorded as NIR; PDMS is used as an emission layer; for buildings without or closed indoor refrigeration systems, The structure of radiation cooling glass is PDMS/NIR/Glass from outside to inside; for buildings with indoor cooling systems, the structure of radiation cooling glass is PDMS/Glass/NIR from outside to inside. According to the relative changes of the indoor and outdoor environments, the invention designs radiation cooling glass with different structures, and realizes the purpose of building energy saving and consumption reduction to the maximum extent through the bidirectional regulation of the radiation characteristics of the inner and outer sides.

Description

A design method for radiative cooling glass with two-way control of inner and outer radiation characteristics

technical field

The invention belongs to the technical field of radiation cooling, and in particular relates to a radiation cooling glass design method with bidirectional control of inner and outer radiation characteristics.

Background technique

Refrigeration is an essential requirement in production and life. The traditional cooling system used in most buildings consumes electricity and produces a large amount of greenhouse gases. Radiant cooling technology does not consume external energy and is widely used in building energy saving, clothing cooling, water cooling and air cooling , battery cooling and other fields. Window glass is the part with the lowest energy efficiency in closed spaces such as buildings or car windows. For these special applications, both transparency and cooling needs to be taken into account, but the sunlight projected into the interior will bring heat and affect the radiative cooling performance. Therefore, the radiative cooling coating is required to meet: (1) high transmittance in the visible light range (0.4-0.8 μm) to meet the indoor lighting requirements to the greatest extent; (2) high reflection in the sunlight band (0.3-2.5 μm) Efficiency to reduce the accumulation of solar radiation heat as much as possible; (3) High emissivity in the atmospheric window (8-13μm), effectively radiating heat to outer space.

Some scholars have conducted research on transparent radiative cooling coatings, and used them to prepare radiative cooling glass for building energy saving, but they only considered the impact of changes in the outdoor environment (such as geographical location, weather conditions, etc.) The impact of indoor environment changes is not involved, so that the obtained radiant cooling glass cannot maximize energy saving and consumption reduction.

Contents of the invention

In order to solve the defects existing in the existing radiation cooling glass, the purpose of the present invention is to provide a radiation cooling glass design method with two-way control of the radiation characteristics of the inside and outside, according to the relative changes in the indoor and outdoor environments, design radiation cooling glass with different structures, through the inner and outer The two-way regulation of the outer radiation characteristics maximizes the energy saving and consumption reduction of the building.

In order to realize above-mentioned technical purpose, the present invention adopts following technical scheme:

A radiation cooling glass design method with two-way control of the radiation characteristics inside and outside, using TiO ₂ /Ag/TiO ₂ as the reflective layer, denoted as NIR; PDMS as the emitting layer;

For buildings without or with closed cooling systems indoors, the structure of radiative cooling glass is PDMS/NIR/Glass from outside to inside;

For buildings with indoor refrigeration systems, the structure of radiant cooling glass is PDMS/Glass/NIR from outside to inside.

The inventors found that the cooling energy consumption of a building is not only affected by geographical location and weather conditions, but also the opening and closing of the indoor air-conditioning system will also have an impact on the cooling energy consumption. In hot summer weather, for buildings with air-conditioning systems turned on, the temperature of the external structure (including the roof, walls, and windows, etc.) is high, while the indoor temperature is low, and the inner layer has low emissivity. Reduce the heat transfer from the outside to the interior of the building to a certain extent, maintain a lower internal temperature, thereby reducing cooling energy consumption; and for buildings without or with air-conditioning systems turned off, the indoor temperature is higher due to the heating of the interior by sunlight through the glass , The inner layer has a high emissivity, that is, energy-saving windows with a high absorption rate can improve the heat dissipation from the interior of the building to the outside, so as to reduce the indoor temperature and save cooling energy consumption. Therefore, according to the relative changes of the indoor and outdoor environments, the present invention designs radiation cooling glass with different structures, and achieves the purpose of building energy saving and consumption reduction to the greatest extent through bidirectional regulation of the radiation characteristics of the inside and outside.

Among the above design methods, the design method of PDMS thickness is as follows:

Atmospheric window average emissivity

Among them, I _BB (T, λ) represents the emission intensity of the blackbody spectrum at temperature T, and ε(λ) represents the emissivity of the coating;

进而选定PDMS厚度。As shown in Figure 1, in the mid-infrared part, the reflectivity of the single-layer Ag film and the TiO ₂ /Ag/TiO ₂ three-layer film are basically the same. The TiO ₂ /Ag/TiO ₂ is simplified as a single-layer Ag film, and the selected The thickness of the Ag film, and the PDMS thickness is set. The thickness of the _PDMS and the Ag film varies within the same order of magnitude, and the average emissivity of the atmospheric window is calculated.

The PDMS thickness is then selected.

如图2所示，当PDMS厚度H_PDMS为50μm时，

当PDMS厚度H_PDMS继续增长时，大气窗口平均发射率

增长趋于平坦，故选定PDMS厚度范围为50μm～100μm；最优选的PDMS厚度H_PDMS＝50μm。Further preferably, the thickness of the selected Ag film is 10 μm, and the PDMS thickness H _PDMS varies in the range of 10 μm to 100 μm, and the average emissivity of the atmospheric window is calculated

As shown in Figure 2, when the PDMS thickness H _PDMS is 50 μm,

Atmospheric window average emissivity when PDMS thickness H _PDMS continues to grow

The growth tends to be flat, so the selected PDMS thickness ranges from 50 μm to 100 μm; the most preferred PDMS thickness H _PDMS =50 μm.

Among the above design methods, the design method of the thickness of TiO ₂ /Ag/TiO ₂ is as follows:

Average Visible Light Transmittance

Average solar reflectance

Wherein, I _AM1.5 (λ) represents AM1.5 standard solar intensity, and T (λ), R (λ) represent spectral transmittance, reflectivity of coating respectively;

和平均可见光透过率

In the sunlight band, within the same order of magnitude, the thickness of the Ag film H _Ag and the thicknesses H ₁ and H ₂ of the upper and lower layers of TiO ₂ are selected to calculate the average solar reflectance under different thickness combinations

and average visible light transmittance

不低于0.7，基于此，取最大

出现的H_Ag、H₁、H₂，分别设定为Ag膜的厚度、上层TiO₂的厚度、下层TiO₂的厚度。In order to meet the minimum daily lighting requirements, take the average visible light transmittance

Not less than 0.7, based on this, take the maximum

H _Ag , H ₁ , and H ₂ appearing are respectively set as the thickness of the Ag film, the thickness of the upper layer TiO ₂ , and the thickness of the lower layer TiO ₂ .

和平均可见光透过率

Further preferably, in the solar light band, considering the error of vapor-depositing nanoscale films, the thickness H _Ag of the Ag film is selected at intervals of 5 nm within the range of 5 to 30 nm, and at intervals of 10 nm within the range of thickness of 0 to 60 nm. The thickness H ₁ and H ₂ of the upper and lower layers of TiO ₂ is used to calculate the average solar reflectance under different thickness combinations

and average visible light transmittance

不低于0.7，基于此，如图3所示，最大

出现在H_Ag＝25nm，H₁＝H₂＝40nm处，此时该辐射制冷玻璃在满足采光需求下，具有最优的辐射制冷性能。Take the average visible light transmittance

not less than 0.7, based on this, as shown in Figure 3, the maximum

Appearing at H _Ag =25nm, H ₁ =H ₂ =40nm, at this time, the radiation cooling glass has the best radiation cooling performance under the condition of meeting the lighting requirements.

The advantages of the present invention are:

外层大气窗口平均发射率

PDMS/NIR/Glass则将玻璃作为最内层，其内层平均发射率

外层大气窗口平均发射率

本发明证实了辐射制冷玻璃内层发射率对开启和关闭空调系统建筑内部温度的影响，对于室内无或关闭空调系统的建筑应选用具有高内层发射率的辐射制冷玻璃，对于开启空调系统的建筑应选用具有低内层发射率的辐射制冷玻璃，通过内外侧辐射特性双向调控，从而实现建筑内部降温和节约制冷能耗的目的。According to the relative changes of indoor and outdoor environments, the present invention designs radiation cooling glasses with two different structures, PDMS/NIR/Glass and PDMS/Glass/NIR, both of which use PDMS as the emission coating, and TiO ₂ /Ag/TiO ₂ as the The reflective coating and the spectral characteristic curve of the outer structure are consistent, and all have high solar reflectance, high visible light transmittance and high atmospheric window emissivity. PDMS/Glass/NIR places the reflective coating on the innermost layer of the glass, and the average emissivity of the inner layer

Average emissivity of the outer atmosphere window

PDMS/NIR/Glass uses glass as the innermost layer, and the average emissivity of the inner layer

Average emissivity of the outer atmosphere window

The present invention proves the influence of the emissivity of the inner layer of the radiation cooling glass on the internal temperature of the building with the air-conditioning system turned on and off. For buildings without or with the air-conditioning system closed indoors, radiation cooling glass with a high inner layer emissivity should be selected. For buildings with the air-conditioning system turned on Buildings should use radiation-cooled glass with low inner layer emissivity, and through two-way regulation of the inner and outer radiation characteristics, so as to achieve the purpose of cooling the building and saving cooling energy consumption.

Description of drawings

Figure 1 is a reflectance diagram of a single-layer Ag film and a TiO ₂ /Ag/TiO ₂ three-layer film in the mid-infrared part;

的关系变化图；Figure 2 shows the PDMS thickness H _PDMS and the average emissivity of the atmospheric window

The relationship change diagram;

和平均太阳光反射率

的关系变化图。Figure 3 shows the Ag thickness H _Ag and the average visible light transmittance in TiO ₂ /Ag/TiO ₂

and mean solar reflectance

relationship change graph.

Fig. 4 is the spectral characteristic curve of PDMS(50μm)/TiO ₂ (40nm)/Ag(25nm)/TiO ₂ (40nm)/Glass radiation cooling glass;

Figure 5 shows the application of radiation cooling glass with different inner layer emissivity, in which: (a) model with air conditioning system turned on; (b) model without or with air conditioning system turned off; (c) experimental spectral characteristics of the inside and outside of radiation cooling glass with low inner layer emissivity; (d) Experimental spectral characteristics of the inner and outer sides of radiation-cooled glass with high inner emissivity; (e) The internal temperature of the air-conditioning system changes with the emissivity of the inner layer; (f) The internal temperature of the air-conditioning system with no or closed changes with the emissivity of the inner layer.

Detailed ways

The technical solutions of the present invention will now be further described in conjunction with examples, but the present invention is not limited to the following implementation situations.

In the present invention, a 75mm×75mm glass substrate is selected as a substrate, and a reflective coating is prepared by thermal evaporation coating to obtain NIR/Glass and Glass/NIR transparent reflective glass. The PDMS emissive coating was prepared using a film applicator to obtain PDMS/NIR/Glass and PDMS/Glass/NIR transparent radiation cooling glass.

1. The thickness design method of PDMS layer is:

Atmospheric window average emissivity

Among them, I _BB (T, λ) represents the emission intensity of the blackbody spectrum at temperature T, and ε(λ) represents the emissivity of the coating;

可以发现大气窗口平均发射率随着PDMS层厚度的增加而逐渐增大，当H_PDMS＝50μm时，

此后H_PDMS对

影响较小，增长趋于平坦，故选定PDMS层的最佳厚度为50μm。As shown in Figure 1, in the mid-infrared part, the reflectance of the single-layer Ag film and the TiO ₂ /Ag/TiO ₂ three-layer film are basically the same, and the TiO ₂ /Ag/TiO ₂ is simplified as a single-layer Ag film, and the selected The thickness of the Ag film is 10 μm, and PDMS with different thicknesses in the range of 10 μm to 100 μm is coated, and the average emissivity of the atmospheric window is calculated

It can be found that the average emissivity of the atmospheric window increases gradually with the increase of the thickness of the PDMS layer. When H _PDMS =50 μm,

Thereafter H _PDMS pair

The influence is small, and the growth tends to be flat, so the optimal thickness of the selected PDMS layer is 50 μm.

2. The thickness design method of TiO ₂ /Ag/TiO ₂ layer is:

Average Visible Light Transmittance

Average solar reflectance

Wherein, I _AM1.5 (λ) represents AM1.5 standard solar intensity, and T (λ), R (λ) represent spectral transmittance, reflectivity of coating respectively;

和平均可见光透过率

In the solar light band, considering the thickness error of the evaporated film, within the range of 5-30nm, select the thickness H _Ag of the Ag film at an interval of 5nm, and within the thickness range of 0-60nm, select the upper and lower layers of _TiO2 Thickness H ₁ , H ₂ , calculate the average solar reflectance under different thickness combinations

and average visible light transmittance

不低于0.7。当要求

不低于0.7时，最大

出现在H_Ag＝25nm处，优化得到的对应结构的PDMS(50μm)/TiO₂(40nm)/Ag(25nm)/TiO₂(40nm)/Glass辐射制冷玻璃的光谱特性曲线见图4。For building energy-saving design, in order to meet the minimum daily lighting requirements, it is usually necessary to meet the average visible light transmittance

Not less than 0.7. when requested

Not less than 0.7 when the maximum

Appearing at H _Ag = 25nm, the optimized spectral characteristic curve of PDMS(50μm)/TiO ₂ (40nm)/Ag(25nm)/TiO ₂ (40nm)/Glass radiation cooling glass with corresponding structure is shown in Fig. 4 .

3. Application of radiation cooling glass with different inner layer emissivity

The cooling energy consumption of a building is not only affected by the geographical location and weather conditions, but also the opening and closing of the indoor air conditioning system will also have an impact on the cooling energy consumption. In hot summer weather, for buildings with air-conditioning systems turned on, the temperature of the external structure (including the roof, walls and windows, etc.) is high, while the indoor temperature is low, the inner layer has low emissivity, and the radiant cooling glass with high reflectivity can Minimize the heat transfer to the interior of the building to maintain a low internal temperature, thereby reducing cooling energy consumption, as shown in Figure 5a; for buildings without or with air-conditioning systems turned off, the temperature of the external structure is low, while the indoor air The temperature is high, and the inner layer has a high emissivity, that is, the radiation cooling glass with a high absorption rate can improve the heat dissipation from the interior of the building to the outside, so as to reduce the indoor temperature and save cooling energy consumption, as shown in Figure 5b. Choosing radiant cooling glass with different structures for different buildings is an effective strategy to reduce cooling energy consumption.

外层大气窗口平均发射率

PDMS/NIR/Glass将玻璃基底作为辐射制冷玻璃的最内层，其内层平均发射率

外层大气窗口平均发射率

The present invention designs radiation cooling glasses with two different structures, PDMS/NIR/Glass and PDMS/Glass/NIR, both of which use PDMS as the emission coating, TiO ₂ /Ag/TiO ₂ as the reflection coating, and the outer layer structure The spectral characteristic curves are consistent, and they all have high solar reflectance, high visible light transmittance and high atmospheric window emissivity, and their spectral characteristic curves are shown in Figure 5c and 5d. PDMS/Glass/NIR puts the reflective coating on the innermost layer of radiation cooling glass, and the average emissivity of the inner layer

Average emissivity of the outer atmosphere window

PDMS/NIR/Glass uses the glass substrate as the innermost layer of radiation cooling glass, and the average emissivity of the inner layer

Average emissivity of the outer atmosphere window

In order to compare the cooling performance of radiation cooling glasses with different inner emissivity, the indoor temperature under the glass with different inner emissivity was calculated based on the energy conservation equation. The calculation results when the building’s air-conditioning system is turned on are shown in Figure 5e. As the emissivity of the inner layer of the radiative cooling glass decreases, the radiation heat exchange between the high-temperature radiative cooling glass and the inner wall of the low-temperature building weakens, reducing the loss of internal cooling capacity of the system. The average internal temperature decreases and the maximum temperature gradually increases as the maximum system temperature is the radiatively cooled glass temperature. The calculation results when the building’s air-conditioning system is turned off are shown in Figure 5f. It can be seen that with the increase of the emissivity of the inner layer of the radiative cooling glass, the radiation heat exchange between the low-temperature radiative cooling glass and the inner wall of the high-temperature building is enhanced, and the heat dissipation of the system to the external environment is enhanced, and the system is balanced. The maximum internal temperature and the average temperature gradually decrease. The calculation results confirm the influence of the emissivity of the inner layer of radiative cooling glass on the internal temperature of the building with the air-conditioning system turned on and off. For buildings without or with the air-conditioning system turned off, radiation-cooled glass with high inner layer emissivity should be selected. For buildings with the air-conditioning system turned on Radiation cooling glass with low inner layer emissivity should be selected to achieve cooling inside the building and save cooling energy consumption.

Claims (5)

1. A radiation cooling glass design method with two-way regulation of the radiation characteristics inside and outside, characterized in that TiO ₂ /Ag/TiO ₂ is used as the reflection layer, denoted as NIR; PDMS is used as the emission layer; For buildings with no or closed indoor cooling system, the structure of radiation cooling glass is PDMS/NIR/Glass from outside to inside; For buildings with indoor refrigeration systems, the structure of radiant cooling glass is PDMS/Glass/NIR from outside to inside. 2. the design method according to claim 1, is characterized in that, the design method of PDMS thickness is specifically: Atmospheric window average emissivity

Among them, I _BB (T,λ) represents the black body spectral emission intensity at temperature T, and ε(λ) represents the emissivity of the coating; Simplify TiO ₂ /Ag/TiO ₂ into a single-layer Ag film, select the thickness of the Ag film, and set the PDMS thickness H. The thickness of _PDMS and the Ag film change within the same order of magnitude, and calculate the average emissivity of the atmospheric window

Then select the thickness of PDMS. 3. design method according to claim 2, it is characterized in that, the thickness of selected Ag film is 10 μ m, PDMS thickness H _PDMS changes in the scope of 10 μ m～100 μ m, calculates atmospheric window average emissivity

Atmospheric window average emissivity when PDMS thickness H _PDMS is not less than 50 μm

The growth tends to be flat, and the PDMS thickness range is selected to be 50 μm to 100 μm. 4. The design method according to claim 1, characterized in that the design method for the thickness of TiO ₂ /Ag/TiO ₂ is specifically: Average Visible Light Transmittance

Average solar reflectance

Among them, I _AM1.5 (λ) represents the AM1.5 standard solar intensity, and T(λ) and R(λ) represent the spectral transmittance and reflectance of the coating, respectively; In the sunlight band, within the same order of magnitude, the thickness of the Ag film H _Ag and the thicknesses H ₁ and H ₂ of the upper and lower layers of TiO ₂ are selected to calculate the average solar reflectance under different thickness combinations

and average visible light transmittance

Take the average visible light transmittance

Not less than 0.7, based on this, take the maximum

H _Ag , H ₁ , and H ₂ appearing are respectively set as the thickness of the Ag film, the thickness of the upper layer TiO ₂ , and the thickness of the lower layer TiO ₂ . 5. The design method according to claim 4, characterized in that, in the solar light band, within the range of 5-30nm, the thickness H _Ag of the Ag film is selected at an interval of 5nm, and within the thickness range of 0-60nm, the thickness H Ag of the Ag film is selected at an interval of 10nm Select the thickness H ₁ and H ₂ of the upper and lower layers of TiO ₂ as the interval, and calculate the average solar reflectance under different thickness combinations

and average visible light transmittance

Take the average visible light transmittance

not less than 0.7, based on which the maximum

Appears at H _Ag = 25 nm, H ₁ = H ₂ = 40 nm.

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