In theory, the difference in temperature between the water at the surface of the ocean (+25°C in tropical regions) and that at a depth of 1000 m (5°C) constitutes an enormous reservoir of energy. The idea has been floated of installing mega heat pumps using this temperature difference to recover a part of the energy.
But this idea has not as yet given birth to any recent project. The problem is that with only 20°C of difference between the warm water and the
cold water, we are at the limit of current technology. The energy yield would be very low
(2%), for an enormous investment.
On a smaller scale, there are experiments with the recovery of heat from warm seas such as the Mediterranean, using heat pumps. Following the 30-year-old example of Monaco, the town of La Seyne-sur-Mer, in the Var department, decided in 2007 to begin using sea water to heat several public buildings (a 500-seat theatre centre, the Town Hall…) and, as a first stage, 500 new accommodation units planned for construction, all by means of a heat pump system. For the project to be economically viable, the buildings to be heated must, however, be located not more than 600m from the coast.
Even water from colder seas can be used to provide heating in winter and air conditioning in summer. For example, the Almedalen “ecological” library, at Visby in Sweden, on the island of Gotland in the Baltic sea, uses sea water to feed an electric heat pump, which permanently maintains a stable temperature favourable to the conservation of the books. The heat pump is driven by solar energy and uses propane as the heat-exchange fluid. |