Last time, we introduced the key performance indicators of energy-efficient glass in detail, and deep into these defining concepts, in this part we will give you an example to analyze the impact of the structure of Low-E glazing on energy efficiency.
To meet the demand for energy efficiency as well as comfort in buildings, energy-efficient glazing has become an essential component of environment-friendly buildings. There are many products and ways to save energy and shading in buildings. This article looks at how energy is transferred through glass and how the glass can be energy efficient from the perspective of Low-E technology in windows and doors.
How heat is transferred through glazing
There are many sources of energy consumption in buildings, among which the heat transfer through the transparent part of glass occupies a large proportion. There are two ways of heat transfer to the interior through the glass, namely solar radiation heat transfer and temperature difference heat transfer, among which solar radiation heat transfer includes the direct transmission of sunlight and secondary interior heat transfer.
According to the current building energy-saving design code and evaluation system, the total solar transmittance ratio and heat transfer coefficient U-Value of transparent windows, doors and curtain walls are limited to two important parameters for different regions and different building types, where the total solar transmittance ratio is used to evaluate solar radiation heat transfer and the heat transfer coefficient U-Value is used to evaluate temperature difference heat transfer.
In winter and summer, the heat transfer through the glass is higher in both seasons. In summer, solar radiation heat transfer is the main factor, and in winter, especially in harsh and cold regions, temperature difference heat transfer is the main factor. Regardless of any region and season, the lower the heat transfer coefficient U-Value is, the better, and the U-Value of high-performance energy-efficient glass can reach 0.8 or less, and the total solar energy transmission ratio should be chosen between a reasonable value according to the area and orientation.
High performance of Low-E coated glazing
Low-E coat, which represents low emission, is a film system consisting of multiple layers of metal or other compounds coated on the glass surface. The coating layer has the characteristics of high transmission of visible light and high reflection of middle and far infrared rays, which makes it have an excellent heat insulation effect and good light transmission compared with ordinary glass and traditional architectural coated glass.
The use of triple silver Low-E has been very common in developed countries such as Europe and the United States, both public office buildings and private homes, have given priority to the use of triple silver glass, and even supermarkets equipped with standardized whole Low-E windows.
With the Low-E glazing, the interior space’s sunburn can be improved. Low-E glazing’s infrared transmission can be less than 0.06, which means that most of the heat is reflected, and the sunburn sensation is significantly reduced as the comfort level is increasing.
What about super cold areas? If the infrared heat transmittance ratio of glazing is so low, how can I sunbathe in winter? Indeed, after the installation of Low-E glazing one really can not tan in the interior space, so we need to do is according to the different regions and climate characteristics, such as to take a comprehensive consideration on U-Value and visible light transmission factors, to choose reasonable glazing. I must say, every architecture is a complex, we can not rely on one single product to solve all the problems.
With the progress of technology, although a variety of glass and new technologies continue to appear, but from the technical maturity and the current state of industrialization, Low-E glass can not be replaced by any other product, Low-E coat can be combined with vacuum insulation into high-performance energy-efficient windows and doors, which can achieve different needs in various areas, such as passive houses.
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