Analysis of influencing factors on the energy savi

Analysis of influencing factors of insulating glass energy-saving characteristics

[Abstract] through a large number of simulation calculations of heat transfer coefficient and solar heat gain coefficient of various types of insulating glass, this paper analyzes the influence trend and degree of relevant factors on insulating glass energy-saving indicators, such as original sheet combination, spacing type, service environment and so on. On this basis, this paper discusses the combination mode and service conditions of insulating glass that should be correctly selected and can achieve the best energy-saving effect in architectural and production design

[Key words] heat transfer coefficient of insulating glass solar heat gain coefficient building energy conservation

I. requirements of building energy conservation on glass performance

with the improvement of social and economic development, building energy consumption accounts for an increasing proportion of total social energy consumption. At present, the proportion of building energy consumption in western developed countries is about 30% - 45%. Although China's economic development level and living standard are not high, this proportion has reached 20% - 25%, and is gradually rising to 30%. In some big cities, air conditioning has become the main component of peak load in summer. Whether in western developed countries or in China, building energy consumption is a major problem affecting the overall social and economic development. According to the three-step plan for building energy conservation formulated in 1986, energy conservation management departments at all levels of the government are actively starting the preparation of standards to achieve the goal of 65% energy conservation in the third step. Among the four envelope components of doors and windows, walls, roofs and floors that affect building energy consumption, the thermal insulation performance of doors and windows is the worst, which is one of the main factors affecting indoor thermal environment quality and building energy conservation. As for the typical building envelope components in China, the energy consumption of doors and windows accounts for about 40% - 50% of the total energy consumption of building envelope components. According to statistics, under the conditions of heating or air conditioning, the heat loss of single glass windows accounts for about 30% - 50% of the heating load in winter, and the cooling capacity consumed in summer due to solar radiant heat entering the room through single glass windows accounts for about 20% - 30% of the air conditioning load. Therefore, enhancing the thermal insulation performance of doors and windows and reducing the energy consumption of doors and windows are important links to improve the environmental quality of various materials such as indoor hot double column tensile testing machine, which are widely used in all kinds of gold, metal, rubber and plastic, footwear, leather, clothing, textiles, insulators, wires and cables, terminals and other materials, and improve the level of building energy conservation

insulating glass has outstanding thermal insulation performance. It is an important material to improve the energy-saving level of doors and windows. In recent years, it has been widely used in buildings. However, with the continuous improvement of energy-saving standards, ordinary insulating glass can not fully meet the technical requirements of energy-saving design. For example, in the energy-saving design standard in hot summer and cold winter areas, the heat transfer coefficient limit index of the outer window with large window wall ratio is 2.5 w/m2k, and in hot summer and warm winter areas, this index is 2.0 w/m2k under some conditions. Therefore, on the one hand, we should vigorously promote Low-E insulating glass, a new product with excellent energy-saving characteristics, and on the other hand, we should deeply analyze and master the various factors affecting the energy-saving performance of insulating glass, so as to ensure that insulating glass can give full play to its best energy-saving performance from the aspects of glass original sheet, spacing composition and use environment

II. Basic indicators of energy-saving characteristics of insulating glass

among many performance indicators of insulating glass for construction, the main ones that can be used by the news universal experimental machine to distinguish its energy-saving characteristics are the heat transfer coefficient K and the solar heat gain coefficient SHGC. The heat transfer coefficient K of insulating glass refers to the heat transfer through 1 square meter of insulating glass in a unit time when the air temperature difference on both sides of the glass is 1 ℃ under stable heat transfer conditions, expressed in w/m2k. The lower the K value is, the better the insulating performance of insulating glass is, and the more significant the energy-saving effect is in use. The solar heat gain coefficient SHGC refers to the ratio of the amount of solar radiation energy entering the room through the window glass to the solar heat entering the room through the opening of the same size but without glass under the same conditions of solar radiation. When the SHGC value of glass increases, it means that more direct solar heat can enter the room, and when it decreases, more direct solar heat will be blocked outside. The influence of SHGC value on energy-saving effect is related to the different climatic conditions in which the building is located. Under hot climatic conditions, the influence of solar radiation heat on indoor temperature should be reduced. At this time, glass needs to have a relatively low SHGC value; In cold climate, we should make full use of the heat of solar radiation to improve the indoor temperature. At this time, we need glass with high SHGC value. Between K value and SHGC value, the former mainly measures the heat transfer process caused by temperature difference, and the latter mainly measures the heat transfer caused by solar radiation. In the actual living environment, the two effects exist at the same time. Therefore, in each building energy-saving design standard, the combination conditions of K and SHGC are limited to make the windows achieve the specified energy-saving effect

at present, the K value of insulating glass is actually measured in the laboratory, and the SHGC value is calculated from the spectral data. Because the actual measurement of K value is limited by the cost, it is difficult to collect a large number of data of various types, so the analysis process of this paper will use window5.2 software developed by Lawrence Berkeley Laboratory in the United States for simulation calculation. The software can calculate the K value, SHGC value and other related parameters of various types of glass, and its calculation results can approximately replace the actual measured values. In order to ensure the consistency of the calculation results, unless otherwise specified, this paper adopts the environmental condition setting data of NFRC series standards in the calculation and analysis

III. analysis of influencing factors of energy-saving indicators

III. analysis of influencing factors of energy-saving indicators

1. Thickness of glass:

the heat transfer coefficient of insulating glass is directly related to the product of the thermal resistance of glass (the thermal resistance of glass is 1mk/w) and the thickness of glass. When the thickness of the glass is increased, the blocking ability of the glass to heat transfer will inevitably be increased, so as to reduce the heat transfer coefficient of the whole insulating glass system. For ordinary insulating glass with 12 mm air partition, when both pieces of glass are 3mm white glass, k=2.745w/m2k, and both are 10mm white glass, k=2.64 w/m2k, which is reduced by about 3.8%, and the change of K value is basically a linear relationship with the change of glass thickness. It can also be seen from the calculation results that increasing the glass thickness does not have a great effect on reducing the K value of insulating glass. The K value of 8+12+8 combination is only 0.03 w/m2k lower than the commonly used 6+12+6 combination, which has little impact on building energy consumption. The change of the hollow system composed of endothermic glass or coated glass is similar to that of white glass, so the commonly used 6mm glass will be mainly used in the following analysis of other factors

when the glass thickness increases, the energy of sunlight penetrating the glass into the room will be reduced, resulting in the reduction of solar heat gain coefficient of insulating glass. As shown in Figure 2, when the hollow is composed of two pieces of white glass, the thickness of single glass increases from 3mm to 10mm, and the SHGC value decreases by 16%; When the hollow glass is composed of green glass (select typical parameters) + white glass, it is reduced by about 37%. Different manufacturers and different colors of endothermic glass will have different degrees of influence, but in the same type, the glass thickness will have a greater impact on the SHGC value, as well as the visible light transmittance. Therefore, when selecting insulating glass composed of heat absorbing glass in buildings, the influence of glass thickness on indoor solar energy intensity should be considered according to the design parameters of building energy consumption and on the premise of meeting the structural requirements. When the coated glass forms a hollow, the thickness will have varying degrees of influence depending on the type of substrate, but the main factor will be the type of film

2. Types of glass:

the types of glass that make up the hollow include white glass, heat absorbing glass, sunlight control coating, Low-E glass, etc., as well as the deep-processing products produced by these glasses. The optical and thermal properties of the glass after hot bending and tempering will have slight changes, but will not have significant changes to the hollow system. Therefore, only the raw glass without deep processing is analyzed here. The energy-saving characteristics of different types of glass when used in a single piece are very different. When synthesizing hollow, various forms of combinations will also show different changing characteristics

heat absorbing glass reduces the transmittance of sunlight and heat and increases the absorption rate through body coloring. Since the air flow speed on the surface of outdoor glass will be greater than that in the room, it can take away more heat from the glass itself, thereby reducing the degree of solar radiation entering the room. Different color types and different shades of endothermic glass will greatly change the SHGC value and visible light transmittance of the glass. However, the emissivity of heat absorbing glass of various color series is the same as that of ordinary white glass, which is about 0.84. Therefore, in the case of the same thickness, the value of heat transfer coefficient K when composing insulating glass is the same. Several representative 6mm thick heat absorbing glasses from different manufacturers are selected. The hollow combination method is heat absorbing glass + 12mm air + 6mm white glass. Table 1 lists various energy-saving characteristic parameters. The calculation results show that the heat absorbing glass can only control the heat transfer of solar radiation, and cannot change the heat transfer caused by temperature difference

Table 1 Effect of different types of heat absorbing glass on hollow energy-saving characteristics

0.673

sunlight control coated glass is coated with a layer of metal or metal compound film on the surface of the glass. The film not only makes the glass show rich colors, but also plays a more important role in reducing the SHGC value of the solar heat gain coefficient of the glass and limiting the direct entry of solar heat radiation into the room. Different types of coatings will greatly change the SHGC value and visible light transmittance of the glass, but there is no obvious reflection effect on far-infrared thermal radiation. Therefore, when the sun controlled coated glass is used single or hollow, the K value is close to that of white glass

low-e glass is a kind of coated glass with high reflectance to far-infrared rays in the wavelength range of 4.5~25 microns. In our surrounding environment, the heat transfer caused by temperature difference is mainly concentrated in the far-infrared band. White glass, heat absorbing glass and sun controlled coated glass have very low reflectivity and high absorptivity to far-infrared thermal radiation. The absorbed heat will increase the temperature of the glass itself, which will cause the heat to transfer to the side with low temperature again. On the contrary, Low-E glass can reflect more than 80% of the far-infrared thermal radiation transmitted from the side with high temperature back, thus avoiding the secondary heat transfer caused by its own temperature increase. Therefore, Low-E glass has a very low heat transfer coefficient. Taking the Low-E glass produced by Yaohua as an example, the comparison with other types of glass is shown in Table 2. When Yaohua Low-E is combined into a hollow, the heat transfer coefficient can reach 1.9 w/m2k, which is 30% lower than the hollow K value of ordinary white glass. In addition, the SHGC value and visible light transmittance of Low-E insulating glass can be adjusted during production according to the needs of energy saving. Yaohua Low-E insulating glass with high visible light transmittance can be used in severe cold areas, and Yaohua sun-e insulating glass with sunshade effect can be used in hot areas

Table 2 Comparison of energy-saving characteristics of different types of glass

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3. Emissivity of Low-E glass:

the heat transfer coefficient of Low-E glass is directly related to the emissivity of its film surface. The lower the emissivity, the higher the reflectivity to far infrared ray, and the lower the heat transfer coefficient of glass. For example, when the film emissivity of 6mm single Low-E glass is 0.2, the heat transfer coefficient is 3.80 w/m2k; When the emissivity is 0.1, the heat transfer coefficient is 3.45 w/m2k. The change of K value of single glass will inevitably cause the change of K value of insulating glass, so the Low-E insulating glass