In passenger vessels, the heating, ventilation, and air conditioning (HVAC) system is the second largest consumer of energy after propulsion. It is estimated that up to 30% of the total energy consumption of a passenger ship comes from HVAC systems for cabins, public areas and galley ventilation. When the ship is berthed in the port, the HVAC system even becomes the main energy consumer. Needless to say the HVAC system is not a negligible value and the gains regarding energy efficiency are more than clear. With increasing fuel costs and fast approaching regulations for emission reductions, innovative developments from land-based systems are making their way into the marine markets to help meet these challenges.
By adding variable frequency drives to the HVAC system will become more energy efficient with a low capital cost. Below explains how.
Onboard ships, the most used chiller systems are vapor compressed refrigeration cycle chillers, comprising compressor, condenser, expansion or flow control devices, as well as evaporators.
The most used compressors are screw or centrifugal types, with an indirect central cooling system design. This means that secondary circuits are also installed, where the condenser is cooled via a seawater cooling circuit and the chilled water circuit (evaporator side) uses cold water to cool the air handling units.
Main benefits are the following:
- Installing VFDs on chilled water pumps and on the evaporator cooling side provides accurate control and energy consumption based on process demand. In most cases, the typical payback time is less than one year. On average, savings are between 30 – 40% of total power consumption.
- Using VFDs for supply and exhaust fans, rather than relying on inlet vanes and two-speed motors, generates energy savings in every case. The payback time is less than one year.
- In theory, installing a VFD on a centrifugal compressor can reduce power consumption by as much as 25%. This depends heavily on the chiller plant’s control strategy. The investment cost of a chiller upgrade is relatively high, generating a payback time of between 2 – 2.5 years.