Analysis of Factors Affecting Energy Saving Characteristics of Insulating Glass

Abstract: Through a large number of simulation calculations on the heat transfer coefficient and solar heat gain coefficient of various types of insulating glass, this paper analyzes the influence of relevant factors such as the combination of original film, interval type and use environment on the energy-saving index of insulating glass. degree. On this basis, the combination of insulating glass and the conditions of use that should be correctly selected in the construction and production design to achieve the best energy-saving effect are discussed. Keywords: insulating coefficient of insulating glass, solar heating coefficient, building energy conservation, building energy saving, glass performance requirements With the improvement of social economy, building energy consumption is increasing in the total energy consumption of society. At present, the developed countries in the West are about 30% to 45%. Although China's economic development level and living standards are still not high, this proportion has reached 20% to 25%, and is gradually rising to 30%. In some large cities, summer air conditioning has become a major component of peak power loads. Regardless of the developed countries in the West or China, the energy consumption of buildings is a big problem that affects the overall situation of social and economic development. According to the three-step plan for building energy conservation in China, which was formulated in 1986, the current energy-saving management departments at all levels of the government are actively launching the standard preparation for achieving the 65% energy-saving goal of the third step. Among the four major enclosures, such as doors, windows, walls, roofs and floors, which affect the energy consumption of buildings, the insulation performance of doors and windows is the worst, which is one of the main factors affecting the quality of indoor thermal environment and building energy. As far as the typical surrounding components in China are concerned, the energy consumption of doors and windows accounts for about 40% to 50% of the total energy consumption of building envelopes. According to statistics, under the condition of heating or air conditioning, the heat lost by the single glass window in winter accounts for 30%~50% of the heating load, and the amount of cold consumed by solar radiant heat into the room through the single glass window in summer. It accounts for 20%~30% of air conditioning load. Therefore, enhancing the thermal insulation performance of doors and windows and reducing the energy consumption of doors and windows is an important part of improving the quality of indoor thermal environment and improving the energy-saving level of buildings. Insulating glass has outstanding thermal insulation properties and is an important material for improving the energy-saving level of doors and windows. It has been widely used in construction in recent years. 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 of hot summer and cold winter zone, the heat transfer coefficient limit of the outer window of the large window-to-wall ratio is 2.5 W/m2K, and the index of hot summer and warm winter zone is 2.0 W/m2K under some conditions. Therefore, we should vigorously promote Low-E insulating glass, which is a new product with excellent energy-saving characteristics. On the other hand, we must deeply analyze and master the various influencing factors of energy-saving performance of insulating glass, from the original glass, the composition of the space and the use environment. The aspect guarantees that the insulating glass can exert its best energy-saving performance. Second, the basic indicators of energy-saving characteristics of insulating glass In the performance indicators of architectural insulating glass, the main energy-saving characteristics can be used to distinguish the heat transfer coefficient K and the solar heat gain coefficient SHGC. The heat transfer coefficient K of the insulating glass refers to the heat transfer amount per square meter of insulating glass per unit time when the temperature difference between the air on both sides of the glass is 1 ° C under stable heat transfer conditions, expressed as W/m 2K. The lower the K value, the better the thermal insulation performance of the insulating glass, and the more significant the energy saving effect 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 under the same conditions of solar radiation and the amount of solar heat entering the room through the same size but no glass opening. When the SHGC value of the glass increases, it means that more direct sunlight can enter the room, and when it is reduced, more direct sunlight is blocked outdoors. The effect of SHGC on energy saving effect is related to the different climatic conditions of the building. In hot climate, the effect of solar radiation heat on indoor temperature should be reduced. At this time, the glass needs to have a relatively low SHGC value; In cold weather conditions, the solar radiation heat should be fully utilized to increase the indoor temperature. At this time, a glass with a high SHGC value is required. Between the K value and the SHGC value, the former mainly measures the heat transfer process due to the temperature difference, and the latter mainly measures the heat transfer caused by the solar radiation. In the actual living environment, both effects exist simultaneously, so In the building energy-saving design standards, the window is adjusted to achieve the specified energy-saving effect by limiting the combination of K and SHGC. At present, the K value of the insulating glass is obtained by actual measurement in the laboratory, and the SHGC value is calculated from the spectral data. Because the actual measurement of the K value is difficult to collect a large amount of data of various types due to cost constraints, the analysis process of this paper will be simulated by Window5.2 software developed by Lawrence Berkeley Laboratory. The software can calculate related parameters such as K value and SHGC value of various types of glass, and the calculation result can be approximated instead of the actual measured value. In order to ensure the consistency of the calculation results, in addition to the special instructions, this paper uses the environmental conditions of the NFRC series to set the data in the calculation analysis. Third, the analysis of the influencing factors of energy-saving indicators 1, the thickness of the glass: 2 The heat transfer coefficient of the insulating glass is directly related to the product of the thermal resistance of the glass (the thermal resistance of the glass is 1 mK/W) and the thickness of the glass. When the thickness of the glass is increased, the blocking ability of the sheet glass to heat transfer is inevitably increased, thereby reducing the heat transfer coefficient of the entire insulating glass system. For ordinary insulating glass with 12 mm air gap layer, when both glasses are 3mm white glass, K=2.745W/m2K, when both are 10mm white glass, K=2.64 W/m2K, which is 3.8% lower. Left and right, and the change in the value of K is substantially linear with the change in the thickness of the glass. It can also be seen from the calculation results that increasing the thickness of the glass is not very effective in reducing the K value of the insulating glass. The combination of 8+12+8 is only 0.03 W/m2K lower than the commonly used 6+12+6 combined K value. The impact of building energy consumption is minimal. The hollow system consisting of endothermic glass or coated glass has a similar change to white glass, so it will be based on the commonly used 6mm glass in the analysis of other factors below. As the thickness of the glass increases, the amount of sunlight entering the room through the glass will decrease, resulting in a decrease in the heat gain coefficient of the hollow glass. As shown in Fig. 2, when the hollow glass consists of two pieces of white glass, the thickness of the single piece of glass is increased from 3 mm to 10 mm, and the SHGC value is reduced by 16%. When the green glass (selecting typical parameters) + white glass is hollow, it is reduced. 37% or so. The influence degree of different manufacturers and different colors of heat absorbing glass will be different, but in the same type, the influence of glass thickness on SHGC value will be relatively large, and the influence on visible light transmittance is also great. Therefore, when hollow glass composed of heat-absorbing glass is used in the building, the influence of the glass thickness on the solar energy intensity in the room should be considered according to the design parameters of the building energy consumption and the structural requirements. When the coated glass is hollow, the thickness will vary to different extents depending on the type of substrate, but the main factor will be the type of film.


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