Structures, not aircon, should be the first stop for cooling buildings

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The construction industry has, for a long time, talked about the benefits of collaboration, about joined-up design and how that improves coordination and buildability. But it is far from the only benefit. Integrated design has the potential to deliver truly sustainable, energy-efficient projects, low in embodied and in-use carbon.  

This thinking implies a passive approach to environmental control. Of course, at one time all buildings were naturally ventilated and we understood how to make them comfortable, pleasant places to inhabit. We started falling out of love with naturally ventilated buildings with the invention of cooling systems; we no longer needed to rely on outdoor air to provide comfort and remove odours. Buildings could be designed with great glass facades that could never have been made comfortable with natural ventilation. 

As the climate warms, it is difficult to see a future without active cooling systems, but that doesn’t mean that buildings shouldn’t be designed to work passively for large parts of the year, or that we shouldn’t aim to drive down peak cooling loads through passive means.

Lower peak loads result not just in less energy use, but they also reduce the embodied carbon that comes from the manufacture of active cooling equipment. Even as the electricity grid becomes greener with more and more energy generated from renewable sources and we move towards zero carbon in use, the embodied carbon and material used to make energy-generating and storage equipment, photovoltaic panels, wind turbines and batteries will remain an issue. There will always be a case for using less energy. 

Comfortable in summer

The greatest challenge for a passively designed building will increasingly be about ensuring comfort during the hottest weeks or months of the year. The key to achieving a level of comfort is to keep the sun out and let the cold in. Letting the cold in, typically overnight, only works if the building has enough thermal mass to absorb it before slowly releasing it, maintaining comfortable temperatures throughout the following day.

Mass is provided by exposed structure and internal finishes; concrete, brick and stone all provide thermal mass that can do this. They also create heavy buildings that require substantial foundations and, in the case of concrete buildings, have significant embodied carbon.  

Structural stone buildings can provide the same thermal mass but with much lower embodied carbon than concrete buildings. The foundations will still be substantial. Timber buildings are lighter in weight for the same volume and have lower embodied carbon, but do not provide any useful thermal mass. 

Whatever the structural solution, sustainable design demands that resources are used intelligently, that materials are used in a way that suits their inherent structural properties. Using modern design tools and testing allows the creation of new systems that couldn’t have been designed or built in the past. 

Composite structural solutions that employ timber and concrete or timber and stone working together, utilising the strengths of each material, can create lighter-weight solutions that still provide thermal mass. Each element, each different material, is doing at least one job very efficiently, making the building stand up and, in the case of the stone or concrete, exposed as part of the architecture, a second, equally important job of keeping the building cool, as well as providing an attractive finish. 

Hybrid systems

Truly integrated structure and services design optimises the use of each of these elements, using the minimum amount of material to deliver on both fronts.  

As we strive towards lower-carbon buildings, we look towards hybrid structural systems where the use of concrete is reduced or even completely replaced with laminate timber products and prestressed, achieving similar thermal mass but with very low embodied carbon. 

This allows a building to be designed with the passive systems that achieve very low in-use carbon emissions. Examples such as the Kantor Centre of Excellence have achieved embodied carbon of approximately 50 per cent of a typical concrete-frame construction (using M4i benchmarks), comfortably meeting RIBA 2030 Climate Challenge targets, and net-zero carbon in use. 

Understanding the relationship between structures and services is therefore an important step in reducing the carbon footprint of any building. And if we really are to tackle the climate emergency, it’s imperative that the construction industry works together: architect, engineer, builder, and everyone in between.

This article was originally published in Construction News.