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ABB says its variable speed drives have reduced the energy consumption of three luxury cruise ships by up to 1,600 tonnes of fuel a year per vessel, a huge saving in both operating costs and CO2 emissions, all with a payback time of less than one year.

The ABB low voltage AC drives control the speed of the large fans and extractors in the engine rooms of three cruise ships operated by Costa Cruises, Europe's largest cruise line. Costa Cruises runs a fleet of 14 luxury vessels on routes all over the world.

The fans and extractors were originally designed to run at a fixed speed as if the outside air temperature were a constant 35°C. This works if vessels are sailing in the tropics, like the Caribbean or South China Sea, but is an inefficient waste of energy in much colder places like the Norwegian Fjords, or Canada's North Atlantic coast.

To rectify the design inefficiency, Costa Cruises and ABB developed an alternative high-efficiency concept, in which each fan and extractor is equipped with an ABB low-voltage AC (alternating current) drive.

These drives automatically adjust the speed of the fans and extractors according to actual process requirements and real air temperatures, instead of operating at fixed speeds calibrated for a constant outside temperature of 35°C.

This has enabled the ships to reduce power consumption by between 600 kilowatts (kW) and 840 kW a year, depending on the size of the vessel. Because the ship's electric power is produced by diesel generators, this reduced power consumption translates into substantially reduced amounts of fossil fuel burned, and greenhouse gases emitted.

Costa Cruises calculates that the 30 ABB drives on the first ship to be equipped with the solution, the Costa Fortuna, have cut the ship's diesel fuel consumption by about 1,150 metric tonnes a year, and subsequently reduced its annual CO2 emissions by 3,622 metric tonnes, and its nitrogen oxide (NOx) emissions by 66 metric tonnes.

According to ABB, similar savings have also been achieved by the 30 drives on the Costa Magica. The 37 drives on the larger Costa Serena have reduced the ship's fuel consumption by 1,618 metric tonnes a year, and lowered annual CO2 and NOx emissions by 5,100 and 92 metric tonnes respectively.

An ABB low-voltage drive can reduce the energy consumption of a pump, fan or extractor by as much as 50 percent. Quantification of the savings is based on constant monitoring of the ships' electrical load and on the amount of fuel consumed during each cruise. For all three ships the payback time for the drives solution is said to be less than one year.

Maintenance costs have also been minimized by the reduction in the number of hours the fan and extractor motors are in operation, which helps save wear and tear, and prolongs maintenance intervals.

Not surprisingly, Costa Cruises is retrofitting the ABB drives solution in its flagship cruise liners, the Costa Concordia and Costa Pacifica, and has installed it during construction in the two latest additions to its fleet: the Costa Luminosa and the Costa Deliziosa.

The Costa Cruises drives solution was a recipient of the 2009 ABB Energy Efficiency Award, an annual award made by ABB Italy to companies who have made the most progress in reducing their energy consumption in motor and drive systems.