Sergio Divano
Senior HVAC Engineer
ABB Marine & Ports
ABB’s chiller optimization targets the substantial hotel load required for a heating ventilation and air conditioning (HVAC) system on board passenger ships – and the solution gives consistent energy savings.
In passenger vessels, HVAC system is the second largest consumer of energy after propulsion. It is estimated that up to 30 percent of the total energy consumption of a passenger ship comes from HVAC systems used for cabins, public areas and galley ventilation. When the ship is berthed in the port, the HVAC system 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.
Where the energy savings come from
HVAC is the technology of indoor environmental comfort; its goal is to provide thermal comfort and acceptable indoor air quality. In passenger vessels, such as cruise ship or ferries, the HVAC system is essential for the passenger comfort.
The total energy consumption of a HVAC system can be divided by the following areas:
- chillers
- air handling units and fans
- pumps
Chiller operation
HVAC systems use chillers to cool water, which flows through coils, thus cooling the air in a room. Chillers and rooms have separate thermostats. The room thermostat stops cooling the room down by regulating or closing the water flow through a coil, without affecting the chiller’s operation. On the other hand, the chiller’s thermostat does not directly affect the temperature in the rooms.
Chillers are designed to handle demanding weather conditions, such as high temperatures and humidity. As a rule, the water temperature is chosen by the installation company. For example, for an outdoor temperature of +30°C, the chiller may supply water at +6°C to provide the desired conditions inside the chilled spaces. But for a lower outdoor temperature, for instance +16°C, these conditions may be achieved with water at the temperature of +10°C or higher.
The higher the required water temperature, the lower the energy required to produce it. This happens when the increase of a chiller’s efficiency – the COP (Coefficient of Performance) – is higher for higher set points. In a chiller, the electrical power absorbed by the compressor motor depends on the pressure difference that the compressor has to produce. Increasing the chilled water temperature set point causes a decrease in the pressure difference, which leads to a subsequent decrease in the absorbed power. Increasing the chilled water temperature set point by +1°C takes down the electric power consumption by 3-4%.
ABB ARKM20 – optimizing the full energy saving potential of onboard HVAC systems
By continuously optimizing the water temperature set point, ABB’s solution helps significantly decrease the amount of energy consumed by a chiller.
The optimum chilled water supply temperature is not a fixed point, and it changes during the vessel’s voyage time constantly, depending on the thermal load, weather conditions and other factors affecting the performance of the HVAC system.
Typically, the water temperature set point on board a vessel is manually changed by the refrigeration engineer no more than a few times a year, depending on the season or a climate zone. ABB’s solution ARKM20 defines and sets the optimized chilled water set point every five minutes. It monitors comfort requirements determined by the users, as well as environmental conditions (temperature, humidity, CO2 levels), and processes this information to get the most efficient chiller set points.
The solution optimizes chiller plant performance based on advanced algorithms, managing chiller plants using real-time data, weather forecasts and active learning. Chiller energy consumption can be reduced up to 15 percent without affecting cooling capacity or indoor climate through the optimization of chilled water temperature set-point. A local onboard controller is interfaced to HVAC control system and chiller control panel.
Client interface allows for active monitoring and control both onboard and ashore via remote connection: energy savings can be monitored through a real-time online dashboard.
The ARKM20 system can fit with HVAC retrofit campaigns, getting the right data about plant performance and areas of improvement.
