Due to the risk of corrosion, seagoing ships must be equipped with high-quality air handling units. For cruise ships sailing in the Caribbean Sea, the quality requirements are even higher. Interruptions must be avoided; an order for such a cruise ship, therefore, requires extra attention.
The Systemair plant in Waalwijk has produced and delivered 88 air handling units this year for a new ship in the Norwegian Cruise Line (NCL) shipping company, which will be built on a German yard.
The ship is 325 meters long, 41 meters wide, has 2,100 cabins and is designed for 4,200 passengers. Systemair has been servicing cruise ships for a long time and is now a specialist in this area. "The first order was fulfilled fifteen years ago. Over the years we have supplied air handling units to fifteen cruise ships”, says Wim Kampen, sales director of Systemair. "That's one ship a year, which is also roughly the effective construction time for a cruise ship. From the start of construction to the launch, the whole process takes about two years."
The ship that Systemair worked for this year is the fourth in a row at the shipyard for which the company has received orders for air handling units. Kampen: "This ship is practically the same as the first three. Only the interior, the decoration and the length have been adjusted. There are also some differences in the basic design and technology."
However, the production of such units for cruise ships is quite complex. This year's order of 88 air handling units had more than five different variations in both design and technical terms. The quality requirements are also high, which has to do with the silted air that can be quite aggressive to the materials. This applies especially to the ship for which Systemair has been working this year.
It sails mainly in the Caribbean Sea, where the ship has to handle the tropical heat. The shipping company absolutely wants to avoid any interruptions. Passengers want to stay in the ship in pleasant cool air. Since they pay a lot for their vacation, it is not acceptable that there are disturbances.
To ensure the quality, the client needs extensive documentation about the products delivered. Included are drawings, the actual values, and all corresponding test certificates. "All air handling units are being tested on-site by specialists. Once found to be good, we have to pass the corresponding test reports," says Martijn van Falier, project engineer at Systemair. Another important part of the order is prompt and reliable delivery. The air handling units have to be delivered on fixed dates within a period of six months. "These ships are built-in parts that are welded together on a tight schedule. The plan has to be followed since the shipyard can’t afford a delay”, says Kampen.
The fact that the air handling units have so many different shapes comes from the limited space onboard. The units have to be as small as possible to save space. Many units, therefore, are non-rectangular as well as irregular to make space for other installations. While the units are placed in small spaces, it still must be possible to access large parts of the cabinets for maintenance or repairs. This requires extra attention to the design. "The spaces are so tight that you just can get a shoehorn in the unit. Engineers who have worked on a ship will not be complaining about tight technical spaces when they are back working on the land," says Van Falier.
The ship is built using pre-made blocks 3 floors high and 30 meters long. These blocks are made upside down because it's easier for welding. In the blocks, many components are assembled beforehand, such as equipment, pipelines and cabling that are later linked together. Due to the construction method, there are air handling units in two blocks at the same time. These units are delivered in two parts and then welded together on the site.
The units are also different at the technical level, with regard to supplying, return, fans, valves and heat recovery heat sink. They also vary in air capacity. The largest unit can deliver 28,500 m3 air per hour; the smallest 6,000 m3. The construction of the air handling units for cruise ships does not differ much from normal units. They are usually flat cabinets with two fans next to each other. "The only difference in construction is that the cooler is placed after the fan. That's what we do to cool the heat that comes from the engine", says Falier. The heat exchanger wheel is used to cool and dehumidify the outside air. The units are designed for an outside air temperature of 35ᵒC and an RV of 80 per cent. In order to dehumidify, the temperature is first reduced to 12ᵒC. The return air is heated using the units reheaters, which results in a temperature of around 22°C. The 88 air handling units are spread over the ship and have a combined maximum capacity of 1.5 million m3 fresh air per hour. The air moves at a speed of three meters per second through the air handling units, which is a lot faster than in the normal buildings. Centrifugal fans are used to handle the pressure. The motors are located directly on the shaft; no V-strings are used because they cause more maintenance and also cause capacity loss. The engines are 'ordinary' AC type. Sound level is not a big issue here because the noise is damped by the steel. The air handling units are made of stainless steel, with extra coatings. The coolers drainage is important, therefore the drawer gets extra attention. It is extra deep and contains three sloping bottom surfaces for good drainage.
The air handling units are cooled using cold water supplied by a chiller. Therein the water is cooled through a heat exchanger using seawater. If the seawater is too warm, there is a chance that the maximum cooling capacity will be reached. In order to maintain sufficient cooling capacity, the ship might have to divert more power for cooling. Maintenance is an important point to keep in mind in the design. "Everything must be reasonably easy to exchange. In addition, certain parts must be easily accessible for maintenance such as the heaters that must be lubricated regularly," says Van Falier. Special maintenance teams are on board too – for example - lubricating bearings or changing filters. "These teams work in a tight schedule, ensuring that all maintenance is done on time. They are busy with this all year round." This year's series of air handling units from Systemair has all been delivered on time. If everything goes according to plan, the ship in which they are installed will be launched in a few months' time. After that, the construction of a fifth cruise ship begins which will be a copy of number four. Systemair will provide the air handling units for that ship as well.