Besides of being necessary in delivering a pleasant indoor environment onboard, the HVAC system is one of the largest consumers of energy onboard. Depending on factors such as the operating environment, size of the vessel, operating profile as well as the operating principle of the HVAC system, it can consume between 20-40% of the total energy consumption of a cruise vessel. As a large consumer, it is naturally also at the forefront of energy savings efforts together with other major consumers such as the propulsion system. The instability in fuel prices as well the need to decarbonize the industry in the medium to long term has further increased interest in reducing the consumption of cabin ventilation solutions while maintaining a clean and comfortable indoor environment quality.
Each ventilation system has its own advantages and disadvantages but it is important to note that the energy efficiency can be improved
Cabin ventilation technology has gone through a significant evolution process over the past 20 years, with the industry switching from cabin units to fan coil units to achieve energy savings. Today we are on the verge of chilled beams, a technology that has been used for several decades already in land based applications, making a breakthrough also in the marine industry, promising us further energy savings while reducing maintenance costs while also enabling a comfortable onboard experience. Each ventilation system has its own advantages and disadvantages, however it is important to note that the energy efficiency of each system can be improved for both newbuilds as well as for existing vessels.
As a rough summary it can be stated that while delivering excellent indoor air quality with 100% fresh air delivery to the cabins, cabin units are the least efficient of the three technologies. This is due to air being the medium for heat transfer instead of chilled water and that cabin units use 100% fresh air, which in typical cruise ship operating environments such as the Caribbean or Mediterranean means that hot, humid outside air needs to be cooled down to a desired temperature and dehumidified. In case the temperature set point on the cabin thermostat is higher than the incoming air, the air flow needs to be reduced via a modulating damper or heated using an electrical heating coil, further increasing energy consumption. However, having 100% fresh air reduces the amount of any contaminants in the cabin air such as viruses or bacteria and a properly set up cabin unit system also has a relatively low sound level. Since a typical cabin unit has no fans or chilled water coils, the units themselves are also extremely durable and tend to last for the lifetime of the vessel, with the exception of electrical parts such as the damper actuator or controller.
With a significant amount of the current existing fleet utilizing cabin unit technology, optimizing the energy consumption of these vessels can be a quicker and more effective way of optimizing fleet energy consumption than focusing on newer vessels. While new buildings are more energy efficient than older vessels, ships with cabin unit technology still make up about 30% of the current cruise fleet, making efficiency upgrades for these vessels a relatively low cost investment with a major impact on consumption. Most cabin unit systems operate as constant pressure systems, meaning that the one air handling unit (AHU) usually serves a certain area, typically around 50 cabins, and keeps the pressure in the duct at a certain measuring point on a constant level as well as the air temperature at a constant level. Each cabin unit is only controlled by its own controller, connected to the room thermostat, so no direct information about the room set point and actual temperature is communicated to the AHU.
Creating a network for all the cabin unit controllers connected to a PLC communicating with the AHU, it is possible to optimize both the air temperature and the AHU fan speed, provided that the AHU is equipped with a variable frequency drive controller enabling optimal fan speeds. Actual data from ships in operation have shown energy savings of 15-25% for the cabins fitted with a network when measured from the AHU’s. These are impressive figures even when the full savings potential such as the lower use of the cabin units heating coils and potential cabin occupancy detection is not taken into account. For a typical cruise vessel cabin for a vessel operating in tropical conditions, this translates to a yearly saving of 500-700 kWh per cabin, so that a vessel with 1.500 cabins can save over one million kWh on an annual basis, with the potential for even higher savings when using balcony door switches and occupancy detection. Halton has a suite of solutions for retrofitting existing vessels with cabin units. These solutions can be applied to both Halton cabin units as well as cabin units from other manufacturers.
While fan coil units offer a significant efficiency gain over cabin units by recirculating air that is already cooled and by using chilled water as the transfer medium instead of air, there are ways to increase their efficiency as well. In a typical cabin fan coil unit systems are set up to deliver 7 liter per second of fresh air per occupant, resulting in a typical fresh air volume of approximately 75 m3 per hour. However, this flow can be reduced if the cabin air quality or occupancy can be controlled in a reliable way, such as through a CO2 sensor or cabin occupancy sensor and by installing variable air volume (VAV) dampers on the fan coil units. While the savings potential per cabin is lower than for cabin unit vessels, for larger vessels the total savings can be significant. Due to the lower saving per cabin the VAV solution also has to be cost effective in order to for the return on investment to be reasonable.
Chilled beams offer even higher energy efficiency than fan coil units as well as reduced maintenance and higher comfort for passengers, yet they are mostly suited for new buildings as the HVAC system setup significantly differs from existing designs optimized for fan coil units. The active chilled beam system circulates air from the room throughout its heat exchanger where the supply air is either cooled or heated before being diffused back to the room through the system’s nozzles. Fresh ventilation air is delivered to the beam by a central air-handling system via ductwork. Since the beam requires no fan and uses higher temperature chilled water than fan coil units, it is significantly more efficient while having the lowest sound level of any system. Beams also do not require separate filters and since there is no fan, maintenance costs are lower and operational reliability is increased.
With over 150.000 cabin ventilation systems delivered, Halton is a global leader in the cabin ventilation market. Halton also delivers a substantial amount of projects per year for major landside HVAC projects for applications such as hotels, casinos, office buildings and demanding healthcare projects, including operating rooms where the highest hygiene and operational standards are required. This unique experience coupled with state of the art inhouse R&D facilities (called Halton Innovation Hubs) enables Halton to test its products and solutions in the most demanding operating environments, enabling customized solutions that meet the needs of each specific indoor environment.
Want to learn more about energy efficiency options for your cabins?
Contact
Erik Schobesberger
Director, Ships Segment
erik.schobesberger@halton.com
