Climate control in the Gibraltar tunnel project
A project for a tunnel linking Punta Paloma in Spain and Malabata Point in Morocco and currently in preparatory phase raises some interesting and crucial climate control issues. Governments of both nations appointed the Swiss engineer Giovanni Lombardi to draw up plans for the EurAfrican tunnel, between two railway stations, situated 40 km apart. Parameters such as geothermics of the Earth's crust, the local environment at 36° latitude and the heat loads of the trains and their piston effect (heating due to their high speed) will have to be taken into consideration. Construction is planned to start in 2010 and last until 2025. As in the Channel tunnel (which would otherwise heat up to 50°C in summer), two cooling networks consisting in smooth tubes would run through the walls, using water as a secondary refrigerant. Both networks would be operated by two separate cooling stations on both sides equipped with electric pumps. Cooling the water from 13 to 1°C in the Channel tunnel requires 80 MW on each side and brings the air inside the tunnel down to about 30°C. Due to the shorter tunnel, and the use of fewer and lower trains allowing for a weaker "piston effect", the EurAfrican tunnel should only require two 40 MW cooling stations. However, outside temperatures preclude the use of air cooling for the cooling medium (water) and cooling towers or (better) heat exchangers in a water closed loop system would have to be used instead. The cooling systems could comprise large refrigeration sets, which are generally energy consuming and require reliable local energy grids. An alternative is to use medium-voltage stand-alone thermo-refrigeration cogeneration systems that could send their surplus energy to the national power grids. These cogeneration systems could be based on a gas turbine or a reciprocating engine. Renewable energy sources such as solar energy could be used to guarantee the power supply to the system's control and safety circuits, with batteries as back up.