Cities are hot. It’s well known that the concentration of vehicles and industry, the absence of greenery and the swathes of concrete and tarmac can make urban areas warmer than the countryside – the urban heat island effect.
Since the city is hot, residents install air conditioning. But AC works by extracting heat from the buildings and pumping it to the outside, so it makes the problem worse. As incomes rise, and as global warming increases, the world is headed for an air conditioning crisis. According to the IEA, current trends in AC alone will make climate targets impossible to meet. So how do we reduce the heat island effect, and thereby reduce demand for AC?
Green space is an important factor, including green roofs and walls. I like the ‘vertical forests‘ that architects have been experimenting with. Another strategy is to paint roofs white to increase the amount of heat they reflect. The problem can also be reduced by controlling traffic numbers and raising efficiency standards.
These I had heard of before. One thing I hadn’t considered was a proposal in Bill Dunster’s book ZEDlife. He suggests that rainwater should be captured and stored in concrete tanks underneath the pavement. There are several advantages – it addresses water shortages, providing water for flushing toilets, or for water features or irrigation of parks and gardens. Rainwater can also be used for car washing or in construction. It could help to ease pressure on drains during storms, perhaps working as part of a water plaza. And it could be used in cooling.
The tanks would fill through porous concrete above, which would top them up without letting in any dust or debris. Adding a solar canopy over the top of the sidewalk would allow people to walk in the shade, while the water tanks beneath their feet cooled the pavement.
The book has the technical details of how this could be done. There are also notes on adding bead insulation, integrating it with heating and cooling within buildings, and their own ice slurry cooling system. Does anyone know of anywhere that this has been done?