Facades: The Key to Achieving Nearly Zero Energy Buildings

Abstract

The increasing demand for energy-efficient buildings has led to the development of nearly Zero Energy Buildings (nZEBs). Facades play a crucial role in the energy performance of a building, as they can significantly influence the amount of heat gain and loss. This article reviews the importance of facades in achieving nZEBs and the different facade strategies that can be employed to improve energy efficiency. The article also highlights the importance of considering the local climate and building orientation in designing the facade of a nZEB.

Introduction

Nearly Zero Energy Buildings (nZEBs) are buildings that have a very low energy consumption, with the remaining energy required being produced by renewable sources. Achieving nZEB status requires a combination of energy-efficient design, efficient building systems, and the integration of renewable energy sources. Facades are an essential element of a building’s energy performance, as they determine the amount of solar radiation that enters the building, the level of insulation, and the amount of air infiltration. Therefore, the design of the facade plays a crucial role in achieving nZEB status.

Importance of Facades in Achieving nZEBs

The facade is the interface between the indoor and outdoor environment and is, therefore, the first line of defense against energy loss or gain. The performance of the facade determines the energy demand of the building, as the majority of energy consumption in buildings is due to heating, cooling, and ventilation. A well-designed facade can reduce the energy demand of the building by minimizing the heat transfer through the envelope. This can be achieved through the use of high-performance insulation materials, materials with high thermal inertia inside the building, efficient glazing, shading devices, and air tightness.

Facade Strategies for Achieving nZEBs

There are several façade strategies that can be implemented to achieve nZEB status, including passive solar design and high-performance facades. Passive solar design involves the use of building orientation, shading devices, and glazing to maximize solar gain in winter and minimize it in summer. This strategy can reduce the building’s heating demand by up to 80 % depending on the climate zone. High-performance facades employ advanced insulation materials, the use of materials with high thermal inertia in the interior of the building, efficient glazing, and air tightness to minimize energy loss and gain.

Consideration of Climate and Orientation

The design of the facade should take into account the local climate and building orientation to maximize energy performance. In cold climates, the facade should be designed to maximize solar gain, while in warm climates, glazed surfaces should be reduced  and shading devices should be used to minimize solar gain. The orientation of the building should also be considered: facades facing south (northern hemisphere) and north (southern hemisphere) offer the greatest potential for solar gain. The use of shading devices, such as shutters or awnings, can help reduce solar gain on east- and west-facing facades. during the warmer months.

How to maximize solar gain in winter on a facade

Maximizing solar gain in winter on a facade involves using passive solar design strategies that allow sunlight to enter the building and heat up the interior space. Here are some ways to maximize solar gain on a facade in winter:

• Building orientation: The orientation of the building plays a critical role in maximizing solar gain. In the Northern hemisphere, the south-facing facade receives the most sunlight during the winter months. Therefore, the building should be oriented to face south to maximize solar gain.
• Window placement and size: Windows should be placed on the south-facing facade to allow sunlight to enter the building. The size of the windows should be optimized to capture the maximum amount of sunlight while minimizing heat loss.
• Glazing: High-performance glazing can be used to allow sunlight to enter the building while minimizing heat loss. Low-e coatings on the glass can reduce heat loss by reflecting the heat back into the interior space.
• Thermal mass: Thermal mass materials, such as concrete or masonry, can be used to store the heat gained from sunlight during the day and release it into the interior space at night.

Through the combination of these strategies, solar gain in winter can be maximised, reducing the need for heating and decreasing the building’s energy consumption.

How to make sure that during summer the facade does not overheat and let heat in

To ensure that the facade does not overheat and let heat in during the summer, it is important to employ shading strategies to block direct sunlight. Here are some ways to prevent overheating on a facade in summer:

• Building orientation: The orientation of the building can be optimized to reduce solar heat gain during the summer. One should always try to maintain a south-north axis and try to place the longest facades to the north and south. East and west facades should be reduced because they receive a lot of solar energy in summer and little solar energy in winter.
• Shading devices: Shading devices, such as louvers, fins, or awnings, can be used to block direct sunlight from entering the building. These devices can be fixed or adjustable to allow for flexibility in shading. For example, shading devices can be used to block the sun from the east and west-facing facades, which receive the most sun during the summer. In countries where it is hot all ‘year round, it is important to create sunscreens even in the south or north ( depending on the hemisphere).
• Glazing: Reducing the glazed area to the minimum necessary and using high-performance glazing can reduce solar heat gain. Tinted or reflective glass can reduce the amount of sunlight entering the building and reduce the heat gain.
• Ventilation: Proper ventilation can help reduce the temperature inside the building during summer. Natural ventilation can be achieved at the entry by using operable vents and at the exit by opening the top of windows or creating ventilation chimneys.
• Roofs: The roof of the building can also contribute to solar heat gain. It is therefore important not to use skylights on roofs in very hot countries and to use strategies to reduce heating such as Cool roofs, ventilated roofs, or green roofs.
• Light-Coloured Facades and Roofs: Opting for white or other light colours can significantly reduce heat absorption by reflecting more sunlight. However, it’s important to carefully consider the positioning to avoid unwanted light reflection into the building, which could affect interior comfort or cause glare.

Through the combination of these strategies, overheating on a facade during the summer can be prevented, reducing the need for air conditioning and decreasing the energy consumption of the building.

Conclusion

Achieving nZEB status requires a holistic approach to building design, with the facade playing a crucial role in energy performance. The design of the facade should consider the local climate, building orientation, and the use of high-performance materials to minimize energy loss and gain. Facades should also be designed to maximize solar gain in winter and minimize it in summer through the use of shading devices and glazing. By adopting these strategies, nZEBs can be achieved, providing a sustainable and energy-efficient solution for future buildings.