There are always cooling systems on board vessels, such as sea water cooling system and engine room ventilation. These processes are always dimensioned according to the design point so that they can deliver the cooling demand for all the extreme conditions that the vessel may operate in. However, how often do these vessels operate in these extreme conditions? Some of them operate very much in these conditions, but most of the vessels do not approach these conditions in everyday operation.
The easiest and most efficient way to reduce the power consumption is to install a VFD to control the cooling capacity when operating at less than extreme conditions. ABB provides specialized solutions and services to improve the energy efficiency in these processes. Average annual savings are 40-60%. Pumps and fans on board vessels are mainly of a centrifugal type, which means that a speed reduction of 10%, will give 27% power savings. This is called the cube law or affinity law, where the relationship between speed, power and flow are as follows:
- Soft starting – no high starting currents causing disturbance on the network.
- No process disturbance due to voltage drops; no trips of other electrical devices connected to same bus.
- No excessive thermo-mechanical stress on the motor; longer lifetime of the motor.
- Immediate start-up without warming-up delays (e.g. steam turbines).
- Controlled and smooth start-up.
- Accurate process control – flow based on production need.
- Mechanical wear of piping is minimized.
- Risk of cavitation in the pump is minimized.
- Passenger comfort (in air conditioning applications).
- Reliability/technical improvement.
- Environmental compliance.
- Lower energy bills.