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How to design high-performance façades to optimize building efficiency and occupant comfort?

Why do we need high-performance façade?

Thermal efficiency and occupant comfort are two of the most important elements of modern building design. Not only are there significant financial benefits attached to operating an efficient building, but modern regulations and market demand for buildings with LEED certifications and other environmental accreditations compel designers to put a major focus on efficiency. There is also an increasing awareness about the need for modern interiors that lend towards the comfort, health, and productivity of occupants. While these two requirements may seem unrelated, both efficiency and occupant comfort depend heavily on the building’s façade. Considering this influence, façade performance must be a major focus early in the architectural design process to insure a balance between aesthetics, thermal and energy efficiency, and occupant comfort.

Modern architects and designers understand this need for balance. But finding equilibrium between aesthetics and performance can be challenging if there is a lack of awareness or understanding of the parameters that affect these outcomes. Proper understanding and utilization of building information modelling allows designers to consider façade performance from the onset of the project and quickly find the balance between performance and aesthetics to reduce the potential for costly late stage redesigns.

The Schneider Electric building in South Africa is LEED Gold certified and features prominent shading elements around a glazed façade to control interior lighting and solar heat gain.

Effect of Facades on Occupant Comfort

Since buildings are made specifically for people to work and live in, it should be no surprise that they must be designed according to the needs of their occupants. The façade is one of the most important influences on occupant health, comfort, and productivity because it directly controls the amount of natural lighting and passive heat gains that that enter a building’s interior. Therefore, the desired use of the interior space must be understood before design begins so that appropriate heating and lighting targets can be established. Considerations include factors such as privacy or scenery requirements and when rooms will be occupied. The façade must provide enough natural light to the interior without over-lighting the space or creating painful glares. By adjusting the distribution of glazing across the façade and the properties of the glazes used, architects can account for the varied lighting conditions occupants experience over the course of a day and throughout the year.

In addition to lighting comfort, designers must also account for the thermal comfort of occupants. As glazing is added to a building’s façade, occupants experience increased levels of solar thermal heating, which can cause discomfort if improperly controlled. These effects are particularly noticeable around the perimeter of the interior where occupants are often exposed to direct sunlight. To control solar heat gains, the amount of glazing on the building can be adjusted and fritting can be added to the glass to reduce its solar transmittance. A third solution is to modify the shading elements surrounding the building. Natural greenery can be particularly effective in this department. Not only does it beautify the exterior, but plants that shed their leaves can provide shading in the summer and allow the sun to heat the building in the winter for better thermal efficiency across all conditions. Proper control over heating fluctuations maximizes occupant comfort and minimizes the need to add air conditioning and shading devices later, further increasing the designer’s control over aesthetics.

The LEED Platinum certified Yale School of Forestry building allows natural sunlight to act as the main light source for occupants, saving energy costs by limiting the use of artificial lighting.

Effect of Facades on Efficiency

Because the façade makes up the majority of the building’s envelope separating the interior and exterior environments, it is the single most important factor in the energy efficiency of the structure. The façade’s efficiency is significantly dependent on the building’s location and orientation to the sun, as well as the materials and construction methods used in the façade. The design of high-performance buildings begins with determining the optimal shape and placement of the building according to its intended use and other limitations. Next, the use of glazing on the façade must be optimized for thermal efficiency, lighting, and solar heating.

The University of Arizona’s ENR2 is a LEED Platinum certified building with a façade specially designed to cope with Arizona’s harsh sun and scorching climate.

Because glazing defines the amount of sunlight that reaches occupants, the amount and type of glaze required on each face depends on heating and lighting needs, the path of the sun, and the position of nearby shading elements. Insufficient natural lighting creates a need for artificial lighting fixtures and increases energy costs. In cold environments, insufficient solar heating can also increase the air conditioning loads. Too much sunlight creates comparable effects, making additional shading devices necessary to manually limit sunlight exposure and increasing cooling loads due to excessive solar heating.

Although glazing allows sunlight to enter a building for lighting and heating purposes, it also tends to decrease the thermal performance of the façade because glass provides less insulation than walls. By positioning glazing to optimize solar lighting and heating, the percent area of the façade covered by glazing can be reduced to mitigate heat loss. Double and triple glaze constructions and glazing frames that are thermally broken should also be used to reduce heat conduction across the envelope and minimize thermal losses. Because glazing has such a strong impact on energy efficiency, it is imperative that glazing and shading devices be positioned to ensure that heat fluctuations are minimized, reducing air conditioning and lighting energy usage.

Conceptual Design Stage

To optimize a façade for all these factors, conceptual mass models should be used early in the design process. These simple BIM models include basic building properties such as its general shape, glazing locations, and material properties to allow for the basic idea of the building to be sorted out before detailed design begins. Building orientation and glazing placement can be adjusted in accordance with the path of the sun throughout the year and the effects of surrounding structures shading the building. By adjusting the glazing percentages on different surfaces, the building can be tuned for how each area is affected by the environment. In this step, the overall design and performance of the building façade can be reasonably estimated and optimized so that major changes can be avoided late in the design process when they would be costly and time consuming. With the main parameters sorted out, architects can direct their focus to aesthetic decisions and worry less about whether they will have detrimental effects on building performance.

Detailed Design Stage

After the orientation of the building is determined and general glazing and shading requirements of the building are understood, more detailed models can be created. As the design develops into a better representation of the final product, it should continue to be analyzed in BIM to ensure the thermal envelope and occupant comfort goals are being met. More specific design elements such as glaze constructions, colors, and fritting can be chosen to further optimize envelope efficiency and lighting performance. Detailed shading elements can be added to optimize the solar heating and daylight factors. Since the conceptual mass and detailed models can be utilized very early in the process, designers can stay aware of how aesthetic decisions affect the façade’s performance as design decisions are made.

High-performance facade – final words

The importance of high-performance façade design continues to grow along with need for high-performance buildings that maximize efficiency and occupant comfort. Despite the complex challenges presented by efficiency and occupant comfort optimization, façade designers have access to more knowledge, tools, and materials than ever to create aesthetically pleasing buildings that satisfy performance goals. As requirements become more rigorous and complex, the use of simulation models to assist in the understanding of a building’s  interaction with its environment is key to maximizing overall building performance without sacrificing aesthetics. And technologies like FenestraPro and Revit allow for this holistic approach of achieving performance and aesthetic goals and help prevent late redesigns and provides better results than are possible if aesthetics and performance are considered independently.

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