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Designing buildings for a warmer future

Andrew Minson FIStructE discusses how we can design new buildings to better cope with extremes of heat.

The three ways designers of new buildings can reduce the risk of overheating are through consideration of solar shading, ventilation and by utilising thermal mass.

Shading

More solidity in building facades is a sensible strategy to minimise solar heat gains. This solidity is effectively permanent solar shading. A more solid facade offers different opportunities for perimeter vertical structure, and so design decisions benefit from an integrated design team approach. It is likely, for example, that slender blade columns that maximise views through full height/width glazing will become less common.

Shading is best provided outside the building as opposed to by internal blinds, as this avoids heat build-up within the building. At residential scale vernacular architecture often provides the right answers - external shutters in Mediterranean countries keep the heat beyond the building envelope.

Ventilation

Ventilation is most effective if it is across the building maximising the benefits of any external breeze, or includes roof vents that also use the natural buoyancy of hotter air. Of course, ventilation design must recognise the need for security and adverse impacts like external noise, especially in built-up locations. 

Thermal mass

Thermal mass is helpful in avoiding overheating both by absorbing energy from the hot air thereby cooling it, and by providing cool surfaces that themselves provide comfort through radiance. 

Purging heat from thermally massive structures which have removed energy from the air, is important. In passive systems, ventilation is a key to this. In built up areas designers need to provide ventilation options that account for security and external noise intrusion.

In locations that are likely to experience prolonged hot periods, designers can consider active methods to make the thermal mass more effective. Possible active solutions include passing cooled air or water through the floor slabs or beams (e.g chilled beams). This then “prepares” the thermally massive structure for the next day, by creating within it a large energy sink that can absorb energy from the air throughout the following day.

Another option for using thermal mass is well known from Roman times and provides cool fresh air even when the outside air temperature is high. In summer, the warm outside air is brought through a labyrinth of thermally massive walls in a basement structure, naturally cooling it.  The ground becomes the ultimate “sink” for the heat.  The same can be achieved by bringing air in through tunnels or buried pipes.

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