Storing summer heat for winter
In a reverse implementation of the Tokyo pavement-watering experiments, the UK’s Transport Research Authority has buried a network of pipes which will store summer’s heat underground in insulated water pipes.
In a trial of the idea, a network of polyethylene water pipes 25 millimetres in diameter has been buried below a section of private road in the UK. The pipes are laid in rows about 15 centimetres apart and at a depth of 12 centimetres, where the ground temperature is normally about 12 °C on average. In the summer this can rise to 25 °C.
The sun warms the asphalt at the surface, which absorbs heat and in turn warms the water in the pipes. This is then pumped for storage to a second array of pipes at the side of the road, which are insulated by a 1-metre-thick layer of polystyrene.
Then in winter, when sensors detect that the temperature of the road surface has fallen to 2 °C, the warm water is pumped back to the pipes under the road where it warms the ground and prevents ice from forming on the road surface.
There is some speculation that similar methods of heating the ground might be employed to heat office blocks. Similar road systems have been built in the Netherlands and Austria, but the UK plan differs in the depth that the water is stored at. The systems in Austria and the Netherlands are buried 20 meters under the ground, which make them far more expensive to implement and maintain.
I wonder how long the water will stay warm enough to thaw the roads? The systems in the Netherlands and Austria seem like they might be more robust during an especially cold winter — being pumped back way down into their holding tanks, the Earth’s heat could warm the water again for the next time it is needed. But water stored so close to the surface has no such re-heating mechanism, and the insulation that once kept the water warm will now keep it cold.
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