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By Eduardo Souza

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With the amount of information and technology we currently have, whether from academic research or from the manufacturers of construction products themselves, there is very little room for empiricism and experimentation when we design on the most diverse scales. Even worse is when design specification misconceptions can pose huge costs and headaches. However, long before construction and occupancy of the building, it is possible to clearly understand how the construction will function thermally, its photovoltaic power generation capacity, and even how much power will be required to cool and/or heat it. There are software, tools and applications that allow you to quantify all these design decisions to avoid errors, extra costs, unnecessary waste generation, and ensure the efficiency of all materials applied.

With the increasingly widespread adoption of BIM (Building Information Modeling), the virtual models of new projects or even of renovations and retrofits are becoming more and more accurate, allowing greater cost control and efficiency in the work. There is the possibility to simulate the completed building, understanding its behavior before the start of construction, and supporting the project throughout its phases, including after it is built, or even disassembled and demolished. With better control of the design stage, it is possible to size and order the most accurate quantities and dimensions of the products that make up the construction.

When we approach thermal efficiency of a building, there is no getting around the “Facade” issue. The building envelope is the first barrier between the exterior and interior climate, where heat exchanges occur. Thermal transmittance, also called U-value, allows us to know the level of thermal insulation in relation to the percentage of energy that goes through the envelope; if the resulting number is low, we have a well-insulated surface. On the contrary, a high number will alert us to a thermally deficient surface. This analysis is made for all materials such as tiles, masonry, plaster, etc. For glass there are some special parameters.

Though often considered the villain, there are already several glass options on the market for various uses, which vary in thermal characteristics, colors, and their relationship between interior and exterior. Saint-Gobain has a huge range of project solutions that work for a variety of situations. When specifying glass for a project, it is essential to take some factors into account:

  • Its use and location. Is it a residential or a commercial project? Is it facing south or east? In São Paulo or Stockholm?
  • The type of planned facade. Curtain wall? Double skin? Indented frames?
  • What is the desired aesthetic, not only of the glass, but of the amount and the frames. Grayed out? Bluish? Reflective, not reflective?

On top of safety, acoustic or aesthetic considerations, and the location and orientation of the building, when specifying a glass, it is also important to take into account some of its properties:

  • Light transmission: Percentage of visible light transmitted directly through the glass.
  • Radiation reflection: Percentage of visible light reflected directly from the outer surface of the glass.
  • U-value: The U-value is a measure of the heat loss from penetrating the glass. The lower the U value, the better the insulating properties. Expressed in W / m2K.
  • Color rendering index: Capacity of the glass to keep colors equal, as if they were observed without glazing. Measured on a scale of 1 to 100. A low CRI provides blurry colors and a high CRI provides natural, bright colors.
  • Solar factor: Percentage of solar energy transmitted through glass. Therefore, it measures the ability of a window to reduce the heating of the room. The lower the solar factor, the better it helps improve comfort within the building.
  • Selectivity: The selectivity of the glass is expressed as the ratio between its transmission of light and the solar factor. When the selectivity of the glass is greater than 2, it provides twice as much light as heat.

With these parameters in mind, glass performance tables are extremely important information in the product specification stage for projects, as they allow you to easily compare the performance of the products to understand the most appropriate use for each case, compiling all the data collected previously.

There are also digital simulation programs that can contribute to a more correct and appropriate decision for each situation. Calumen Live, for example, calculates the lighting, energy and thermal performance of any individual glass or combination of glass types and thicknesses for double and triple insulating glass units. It generates calculation reports to compare the performance of alternative configurations and arrive at a well founded solution, with good long-term efficiency.

Another concern when using special and technological glasses concerns the aesthetics and colors they bring to the project. GlassPro is an interactive software that simulates a realistic image of different glass products on building facades and allows the user to view the rendering under a variety of lighting conditions (cloudy or sunny) and to substitute other parameters as well. It can be employed as a guide for the user to demonstrate the type of glazing product at different stages of building construction.

Sometimes using solar shading elements can be a design decision that combines aesthetics with good efficiency and cost-effectiveness, protecting the glass from much of the solar radiation. Understanding the shading behavior of sunscreens in relation to variations in the intensity and incidence of solar radiation throughout the year is a key step for the designer to determine their ultimate consequences for energy consumption, comfort and thermal performance of the building. is a tool for evaluating the efficiency of shading devices and helping to design them. By including data such as latitude, facade orientation, and shading element type, you can receive the incident solar radiation values.

An appropriate decision about the façade materials, and especially the glass, will directly influence the building’s thermal comfort levels, their costs during construction, and especially the maintenance costs and energy consumption many years after inauguration. It is therefore vital that the specification is accurate and that, in addition to aesthetics, all technical parameters are considered.

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