The main functions of building doors and windows are lighting and warmth preservation. With the improvement of people's living standards, residential users are more inclined to use large-area glass doors and windows, allowing for sufficient natural lighting and a wide outdoor view during the day. However, compared to the four major enclosure structures of walls, roofs, and floors, doors and windows have the worst insulation performance. The energy consumption of doors and windows accounts for about 40% to 50% of the total energy consumption of building enclosure structures. In order to maintain a comfortable indoor temperature, a large amount of energy can only be consumed, such as using air conditioning in summer and heating in winter.
In order to solve the problem of energy loss in glass, the industry has developed Low Emission Glass, which has become one of the main products developed in the glass industry today. If double silver Low-E glass with a radiation rate of e=0.04 is selected in the insulating glass, its heat transfer coefficient can reach 1.3~1.1 after being filled with inert gas, which is equivalent to the insulation performance of a 370mm thick brick wall. This can not only increase the lighting area but also reduce energy consumption. We call this type of glass, which has excellent thermal insulation, thermal insulation, and lighting properties, and effectively reduces energy consumption, energy-saving glass. So, which indicators are the key energy-saving indicators of energy-saving glass?
(1) Visible light transmittance tv
For the most basic function of glass windows, which is "day lighting", it is the ability of glass to transmit visible light, measured by the visible light transmission ratio tv. The industry standard JGJ151-2008 defines visible light transmittance as the ratio of the visible light flux of a standard light source passing through glass, doors and windows, or glass curtain walls to the visible light flux projected onto the glass, doors and windows, or glass curtain walls, weighted using the human visual function. The higher the visible light transmittance, the better the indoor lighting effect.
(2)Heat transfer coefficient K value (or U value)
For the second major function of glass windows, which is insulation, it is the ability to block temperature difference and heat transfer, measured by the heat transfer coefficient K. The industry standard JGJ151-2008 defines the heat transfer coefficient as the amount of heat that passes through a unit area of doors, windows, or glass curtain walls per unit time when the temperature difference between the two sides is 1K (℃). The smaller the heat transfer coefficient, the better the insulation performance.
(3) Total transmittance of solar infrared thermal energy gIR
The third major function of glass windows is "insulation", which is the ability of glass to block solar radiation heat, measured by the total transmittance of solar infrared thermal energy gIR. In the latest monogram HB002-2014, gIR is defined as the total solar transmittance in the wavelength range of 780nm to 2500nm. The smaller the gIR value, the stronger the glass's ability to block solar radiation heat.