Improving Building Energy Efficiency: Retrofitting Existing Glass Curtain Walls
The energy shortage issue has become a significant concern today. At the 1979 United Nations Vienna Conference on Science for Development, energy was listed as one of the four major challenges facing humanity, along with food, population, and the environment. Currently, my country's economy is experiencing rapid development, and energy demand is also growing rapidly. The contradiction between urban and rural construction and energy supply and demand is particularly prominent, especially in the construction and residential sectors, which are major energy consumers. How can we address the energy shortage issue? Currently, energy conservation is the top priority in addressing the current global energy crisis, and energy conservation in buildings has become a key component of the national energy conservation strategy. Building energy conservation encompasses both new construction and energy-saving retrofitting of existing buildings. Existing buildings are the true major energy consumers. This is due to their vast number and the fact that most existing buildings lack energy-saving measures. Their poor insulation and inefficient equipment systems result in significant heating and cooling energy waste. However, thanks to national efforts in recent years, most new buildings have achieved energy-saving targets, and some regions have begun implementing energy-saving programs. Therefore, energy-saving retrofitting of existing buildings is crucial for building energy conservation in my country. If we only consider energy conservation in newly built buildings in this regard and do not consider energy conservation renovation of existing buildings, the actual effect of building energy conservation can only be limited to a very small range. Therefore, it is urgent to strengthen the research on energy conservation renovation of existing buildings.
Energy-Saving Principles of Glass Curtain Walls
The use of glass curtain walls in building construction has become a growing trend in the modern construction industry, primarily due to their energy-saving properties. Glass is a transparent material that allows heat to transfer, primarily through convection, radiation, and conduction. Besides these three methods, heat transfer through glass also occurs through direct sunlight. To better evaluate the energy transfer process of glass, the number of joules transferred per unit area, per unit temperature difference, and per unit time can be used. A higher joule number indicates greater energy loss, which is particularly detrimental to energy conservation. To further measure the energy-saving performance of glass curtain walls, the concealment coefficient can be used. Under identical conditions, a glass assembly and a transparent glass are placed in sunlight. The ratio of the solar radiation energy to the radiant energy is used to determine the concealment coefficient. A lower concealment coefficient indicates greater energy conservation. When sunlight shines through the glass into the room, part of the solar energy passes directly through, and the other part is absorbed by the glass curtain wall and converted into heat energy, which enters the room directly. This will increase the heat energy of the house and can increase the temperature in the room.
Problems and Causes of Glass Curtain Wall Construction
1. Glass curtain walls possess a certain modern and contemporary appeal. Their shape, structure, and color can be freely adapted, making them a popular choice for architects to enhance the beauty of their buildings. However, the energy costs of glass curtain wall construction have also become a problem for my country. My country is a major energy consumer, and rapid energy consumption has hindered its economic development. Currently, in Chinese cities, energy consumption in construction accounts for a quarter of total energy consumption, with public buildings accounting for the majority. Glass curtain walls are typically constructed in public buildings in my country, and they do not effectively utilize sunlight. In summer, glass curtain walls absorb more heat due to high solar radiation. In winter, due to lower outdoor temperatures, glass curtain walls dissipate heat more rapidly. This results in increased air conditioning use in both winter and summer, resulting in significant energy consumption in my country. 2. Glass curtain walls are ubiquitous in cities today. While they enhance the city's image to a certain extent, they also contribute to light pollution. Glass curtain walls inherently reflect light, hindering safe vehicle movement on roads. Furthermore, the prolonged reflection of light by glass curtain walls can negatively impact vision, cause certain illnesses, and affect mood. In some prosperous metropolitan areas, city managers frequently receive complaints from citizens regarding light pollution.
3. Glass curtain walls, exposed to prolonged exposure to rain, wind, and sunlight, are deteriorating in their safety, quality, and functionality. Consequently, in some areas, such as Shanghai, there have been numerous incidents of glass curtain walls cracking or falling. The beauty of glass curtain walls no longer attracts citizens; instead, they avoid them when approaching them. Glass curtain walls are like ticking time bombs, poised to explode overhead at any moment. Even if the designed service life of a glass curtain wall does not exceed 25 years, its energy consumption and safety hazards are still embarrassing.
4. These problems with glass curtain walls are almost always due to material problems. Glass is the primary material used in the construction of a glass curtain wall. As the primary external protective component, the performance of glass directly affects its quality. After my country formulated new energy-saving standards, some glass curtain wall technologies no longer meet these standards.
5. During the construction of a glass curtain wall, the sealing material connecting the glass is crucial. The weather resistance of the sealing material will have a certain impact on the service life of the glass curtain wall. Researchers investigating glass curtain walls in some cities found that some of the sealing materials connecting the glass had developed a series of problems, such as cracking and tempered glass damage. These problems have a certain impact on the building's interior environment and also result in significant energy consumption.
Materials
Use heat-reflective Low-E glass and insulating glass. These glass types have long been produced in China, but their high price has led to their limited use in glass curtain wall projects. For example, insulating glass composed of heat-reflective and transparent glass can provide better insulation than a brick wall one brick thick. Use aluminum-plastic composite materials and insulating profiles for curtain wall beams and columns. When choosing insulating aluminum profiles, if produced using the strip-through process, use PUR as the insulating material. Applying film to existing curtain wall glass can also effectively reduce energy consumption. Currently available insulating safety films can save over 15% in energy.
Structural Features
Using shading features such as blinds, grilles, and sunshades can minimize direct sunlight, prevent overheating, and achieve better insulation and energy savings. Shading blinds include horizontal and vertical louvers, with individually controlled, motorized, and adjustable systems. Different shading systems with different control methods can be selected based on the architectural style and needs.
A ventilated curtain wall, also known as a double-skin curtain wall, a breathing curtain wall, or a heat channel curtain wall, consists of two layers of glass. A ventilation layer is formed between the two layers. The air circulation within this ventilation layer brings the temperature of the inner curtain wall closer to the indoor temperature, minimizing temperature differences. Compared to traditional curtain walls, this system saves 42%-52% of energy for heating and 38%-60% for cooling.
Smart curtain walls are an extension of ventilated curtain walls. They leverage intelligent architecture to manage building technologies (heating, cooling, lighting, and electricity). Using computers, they effectively regulate indoor air, temperature, and light, while consuming only 30% of the energy of traditional curtain walls.
The fundamental unit of a photovoltaic curtain wall is the photovoltaic panel, an array of photovoltaic cells connected in series and parallel. This array is enclosed between two layers of glass (the top layer is transparent, the bottom layer can be any color), and is heat-cured with cast resin. Junction boxes and wiring are connected to the back of the panels, converting solar energy into electricity for human consumption. Typically, the columns and beams of this type of curtain wall are made of insulated aluminum profiles.
