Facades: Saving face

Using the building’s energy model as an essential tool in sustainability

Cladding facade stone from the Chamesson quarry in Burgundy, France. A hard French limestone with excellent resistance to salt damage.
Cladding facade stone from the Chamesson quarry in Burgundy, France. A hard French limestone with excellent resistance to salt damage.

For the Middle East climate, the building façade is a necessary barrier which separates the comfortable internal spaces from unsuitable temperatures and humidity outside. However, the façade is far more than a purely technical solution since it is fundamental to how a building is viewed and how the world is viewed from within.

With efficient mechanical cooling, facades are no longer limited to select passive design measures to meet climatic needs and thus a whole spectrum of façade designs have emerged. Likewise, green building tools and technologies are ever refining façade choice with a re-prioritising and quantification of performance and occupant well-being.

Green building concepts are based on the impacts across the whole building timeline and focused on all building users. Green building provides a useful contrast to the traditional segmentation of project phase or the classic owner-occupant divide. The building façade is of key concern as it affects two critical elements of a green design – energy and occupant well-being.

The energy implications of building façade relate to the requirement of cooling and the avoidance of the over reliance on artificial lighting during the day. Since the façade conducts heat from the outside into the space is a significant cooling demand management element. Good insulation is required to minimise this heat transfer. While glazing is more conductive than walls, its key energy impact comes from its ability to trap in solar energy from direct sunlight entering the space via windows and warming it up. Indirect sunlight, however, offsets the need for artificial lighting.

One of KEO’s approaches to tackling these different requirements and parameters during design, which has been applied in various projects in the region, is based on the use of the building energy model as an essential tool. Energy models effectively allow the performance simulation of hundreds of design element variations for every hour of every day across the annual climatic cycle.

Optimisation can explore the sweet spot of design all before construction starts on site. Questions can be raised and answered – such as at what length will horizontal shading stop saving energy from cooling and start increasing energy from interior lights. Likewise, capital cost and performance can be balanced with structural shading elements offsetting glazing requirements or by quantifying the chiller size uplift cost with the absence of these features.

The materials used within the façade are also necessary for their environment impact from within the extraction, manufacturing and construction processes. Growing recognition of the benefits of the use of off-site prefabricated elements, such as precast walls, has centralised a construction activity previously locked to the site. The centralisation also allows for reduced waste and the reuse or recycling of waste materials. This trend towards module construction also bodes well for the theme of disassembly where facades are designed for ease of disassembly to allow dismantling and reuse at the end of the building lifespan.

Therefore, the choice of façade green building ideas, solutions and priorities provide real design consideration as well as useful tools. The use of energy modelling and green building rating systems, allow these diverse and competing factors to be quantified and communicated permitting the choice of façade and its implications to extend well beyond the surface of the building.

Holley Chant is executive director, Corporate Sustainability and Commissioning Sustainability Unit Services for KEO International Consultants.

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Construction Week - Issue 767
Sep 01, 2020