Composite insulation materials improve the insulation value of windows
Windows, whether in homes or commercial buildings, are notorious sources of energy inefficiency, with too much indoor heat in summer and too much outdoor heat in winter. For centuries, this inefficiency has been tolerated, because windows have brought benefits to mankind: access to sunlight, a view of the outside world, and a strong sense of design beauty. In short, the window is here.
In view of the permanent nature of windows in buildings, the past few decades have emphasized making them more insulating and efficient. This is done through various materials and designs. For example, double glazing was first developed in the early 1900s, but it was not widely used until the 1980s. It added an insulating air layer (between the glass panels) to the window system. The application of aluminum and vinyl materials on window frames, the emergence of anti-ultraviolet films, and the addition of a third pane of glass have also improved efficiency.
In the window manufacturing industry, one of the greatest efforts to improve window efficiency revolves around the use of advanced materials to thermally isolate the external window frame structure from the internal window frame structure, thereby minimizing the energy transfer through the window system.
In the past few decades, what has been pursuing this challenge silently and tenaciously is a series of increasingly complex extruded or pultruded profiles designed to integrate fiber-reinforced composite gaskets into the space directly below the glass. And between the structure including the external and internal frames. These "thermal fractures" brought window systems into a new era of energy efficiency.
Windows provide countless opportunities for heat loss or increase in buildings or homes. Bill Blazek, marketing team manager at insulation manufacturer Technoform (Twinsburg, Ohio, USA), says that heat energy outside or inside windows can be easily transferred through the window system in one of three ways. Convection, the air circulation in the cavity, accounts for about 35% of the energy flow. Conduction, the flow of energy through solid materials, accounts for about 50% of the transmission. Finally, radiation occurs from the warmer surface to the cooler surface, accounting for about 15% of the energy flow. Therefore, the quality of window design and building materials have a significant impact on the overall energy efficiency of windows.
Over the past 20 years or so, as concerns about global climate change and energy efficiency have increased, government regulators have increasingly used improving window energy efficiency as a tool to help reduce homes, office buildings, and other Energy consumption of the structure. Therefore, every new building or renovation project provides an opportunity to gradually increase the energy efficiency of the windows and thus the expansion of the building.
Each country responds to this challenge in a different way. In the United States, the ability of windows to resist heat transfer is characterized by the U factor, in Btu/hr-ft2°F. In Europe, the characteristic of efficiency is a similar term, the U value, which is measured in W/m2K. In these two areas, the smaller the U factor/value, the better. The characteristic that measures the performance of windows under direct sunlight is the solar heat gain coefficient (SHGC), which has a value range of 0.0-1.0; again, the lower the better.
There is a complex network of building codes around the world to manage and regulate window energy efficiency. Leading the way are the International Building Code (IBC) and International Residential Code (IRC) managed by the International Code Council (ICC). However, each country and each state in the United States has also developed its own codes, which may differ from the ICC specifications. In addition, although laws and regulations vary from country to country, European energy efficiency standards guided by aggressive energy-saving and greenhouse gas emission reduction targets are stricter than those in the United States. For example, in Finland, one of the EU countries, the U-value requirement is 1.0, which translates to a U-factor of 0.18 in the United States.
In contrast, in the United States, energy efficiency standards are defined by region. There are four regions, each of which covers a belt from west to east in the country: the north, the north-central, the south-central, and the south. In the northern region, the U-factor standard is 0.27-0.30. It is 0.30 in the north-central and south-central regions, and 0.40 in the southern region. These standards use European U values in the range of 1.5-2.3.
The cutaway view of a Schüco aluminum window frame shows a series of polyamide/fiberglass (black) and foam (white) insulation materials that separate the outside of the frame (left) from the inside of the frame (right) to minimize energy Pass and maximize efficiency. Please also note that this is a three-pane window. Image source: Schüco
David DeSutter, vice president of engineering and project services at window and curtain wall manufacturer EFCO (Joplin, Missouri, USA) said that aluminum frame windows are preferred globally, especially in commercial buildings. Aluminum is relatively inexpensive to obtain and extrude, and because it is easy to paint, it can meet various color requirements. In addition, DeSutter said, the thickness of the aluminum frame can be easily adjusted to meet various architectural needs—for example, emphasizing or not emphasizing the frame, thereby emphasizing or not emphasizing the glass of the window itself. One thing aluminum is also particularly good at is conducting energy. "Aluminum is one of the best heat conductors on the planet," he said. "It has many great features, but thermal efficiency is not one of them."
As mentioned earlier, multi-pane glass and other technologies can effectively reduce the energy loss in the aluminum frame window, but there are still challenges in reducing the energy loss around the aluminum frame. DeSutter said that one method is to completely isolate the outer and inner parts of the aluminum frame by inserting a highly insulating polymer material to minimize the surrounding energy transfer.
DeSutter said that such insulation gaps or thermal breaks are usually made of polyamide, or extruded with multi-directional glass fiber reinforced materials, or (less commonly) pultruded with continuous glass fiber reinforced materials. forming. Blazek extruded thermal fracture for EFCO at Technoform. He said that polyamide is usually the material of choice for thermal fracture because its CTE is similar to aluminum, it has good thermal and structural characteristics, reliable quality, and can manufacture precision parts with strict tolerances. , And easy to recycle. He added that, depending on the structural requirements, the glass fiber load in thermal fracture is usually between 25-40%.
In the most basic design, the thermal fault consists of a tubular profile with a hollow center. EFCO’s first thermal fracture was developed ten years ago, about 12 mm wide and 5 mm thick, but today, DeSutter says, EFCO’s thermal fracture width can span more than 25 mm; Blazek says Technoform can produce wider The thermal fracture. Much of the evolution of EFCO's thermal insulation design has been driven by increasingly stringent U.S. building codes. DeSutter pointed out that for many years, the U-factor standard in the United States was 0.45, but as it gradually reduced to the range of 0.27-0.40 that is in effect today, EFCO was forced to adopt a more complex thermal insulation design. "I know that the window efficiency from 0.33 to 0.31 doesn't seem to have changed much, but I can tell you this is a very big change," DeSutter said.
Tylenol provides various thermal insulation designs for window manufacturers. Shown here is a slice of one of the company's extruded polyamide/glass fiber thermal fracture (black) between two aluminum frame structures. Image source: Tylenol
The use of extrusion and pultrusion to create thermal fracture boils down to the value and advantages of the fiber-reinforced type-discontinuous (multi-directional) extrusion and continuous pultrusion. DeSutter said that EFCO's thermal fracture is extruded and uses discontinuous fiber-reinforced polyamide 66 to meet the strength and thermal performance requirements the company seeks.
In Technoform, which extrudes EFCO’s polyamide 66/glass insulation material, Blazek stated that the design of the insulation material is affected by many factors: “The size and complexity of the insulation The performance level is selected, the thermal transmittance-also known as the U value-structural requirements, other system design features, such as window type, hardware, glass composition, functions of the components in the system, and overall system cost targets."
Naturally, as the complexity of the insulation design increases, the cost will also increase, Blazek said: “The associated cost is usually determined by the value it brings to the system, the long-term energy saving, and the health benefits that it brings to the building and its occupants. Offset. Through our global network and extensive resources, we continue to innovate and develop the right solutions to meet any challenges, overcome design and tool challenges.” Blazek added that for many projects in North America, value engineering (although Emphasis on "value") usually leads to acceptance of lower cost/lower performance systems. "The biggest obstacle to the adoption of advanced insulation materials is that the North American market focuses on short-term costs, rather than long-term values related to building energy efficiency and healthy structures," Blazek said.
What would a more advanced insulation layer look like? In Europe, stricter thermal efficiency requirements have facilitated the development of highly complex multi-chamber thermal fractures. For example, window manufacturers Schüco (Bielefeld, Germany) (Technoform also provides insulation materials) and Thermeco (Victoria, Australia) demonstrated fixed and open window systems with multiple insulation materials, each The materials are all designed to fit a specific space frame. In addition, such interruptions usually have multiple chambers with reinforced insulation.
One question is whether and how pultrusion is an option for thermal fracture manufacturing. Composite material manufacturer Exel Composites (Vantaa, Finland) specializes in manufacturing composite parts and structures for various end markets, including residential and commercial buildings and infrastructure applications. Gert De Roover, the owner of the Exel Group's construction and infrastructure department, said that the extrusion of polyamide/glass fiber profiles, and sometimes the addition of polyurethane foam to increase insulation, is a standard material and process combination for window insulation manufacturing. However, he acknowledged that as window systems become more complex and frames become wider, the demand for insulation materials that also provide structural properties may increase.
European building codes set strict standards for the energy efficiency of windows, which has promoted the development and use of more complex thermal insulation designs, including pultruded structures. American standards lag behind EU standards, but they may become more stringent in the next few years. Shown here are windows from Thermeco, Australia, with thermal breaks shown in green. Image source: Thermeco
For example, De Roover said, Exel has developed a series of pultruded fiberglass/polyester door leaves and lintels to provide insulation and structural features. These attributes may become very attractive in window systems-especially considering the widespread use of aluminum frames. "In [Blades and Lintels], you can see the benefits of thermal insulation, as well as the structural integrity of the material," he said. "Blades and door lintels have a certain span and a certain important stiffness. Pultrusion allows us to meet these requirements."
Some manufacturers of custom window systems, especially residential applications, have begun to turn to pultrusion thermal fracture. For example, Arcadia Custom, a US window manufacturer, specifically called for the use of pultrusion in its thermal insulation system. Polyurethane (PU) resin supplier Covestro (Pittsburgh, Pennsylvania, USA) aims to use its Baydur PU for pultrusion of window insulation materials specifically for the Chinese market.
Regardless of the process, Technoform's Blazek said that the US construction industry should see an increase in the complexity of thermal fracture design in the next few years. "Building codes are evolving at a slow and steady rate, allowing incremental system development," he said. "In the United States, several regions of the country are in leading positions, such as California and New York. In California, Article 24 has become a catalyst to encourage innovation and improve the thermal performance of the system. In New York, NYC Local Law 97 and WA State HB1257 will Vigorously promote the renovation of existing buildings to avoid fines for exceeding carbon and energy emission limits. This starts with the worst buildings in 2024 and will expand to cover more by 2030."
In addition, he said that the 2020 National Energy Building Regulations (NECB) in Canada will be issued soon and will include very radical U-factor changes. Similarly, the U.S. government is taking more active actions to encourage the adoption of more energy-efficient systems through the 2020 Energy Act, which is included as part of the COVID-19 relief and funding plan passed by the U.S. Congress in December 2020. Blazek said that the 2024 International Building Code (IBC), the 2024 International Energy Conservation Code (IECC), and ASHRAE 90.1 and 189.1/International Green Building Code all have strong initiatives to promote more energy-efficient systems. Blazek concluded: "I expect that with the slight shift in the market towards long-term energy efficiency and healthy building practices, and the increase in the adoption and enforcement of regulations that require improved energy efficiency and performance, I expect this evolution in the United States to continue. "
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