A chill in the air

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To understand just how smart a smartship is, it’s important to know that as soon as a person walks into a room and takes a breath, the air there changes – oxygen level drops, CO2 level rises.

That simple fact is the basis for one of the most innovative energy efficiencies built into Royal Caribbean’s smartships, those of the Quantum-class; and to some degree on the world’s largest class of cruise vessels, RCL’s Oasis-class.

HVAC – heating, ventilation and air conditioning – is no longer all or nothing.

Before smartships, public rooms on RCL ships were air-conditioned according to their maximum capacity – say, 200 people.

“By doing that, you first spend huge energy on reducing the temperature for 200 people,” says Eddie Wehus, RCL’s HVAC and refrigeration manager. “But because you only have 50 people inside the room, your temperature drops. Now we need heating, so we expend additional energy on heating this area up.”

Today, using a computer-operated demand-based system, the new ships measure the CO2 in the room, use that to calculate the actual number of people, condition only the air needed for their comfort and continue to adjust as needed when more people enter or leave the space.

Chilling onboard air was another ripe area for savings – especially dehumidification, which accounts for 75 percent of AC power consumption on board.

Dealing with this in smart ways resulted in energy efficiencies and less impact on the environment. And there’s another major benefit.

“More energy is more fuel, and more fuel is a higher cost for the company,” Wehus says. “The investors want their return on investment. So we’re trying to minimize energy cost in any way we can without jeopardizing the comfort of our passengers.”

One way is recirculating the air inside the ship instead of venting it outside, as had been the practice. Now warm air is pulled out of a room and sent to a recovery wheel – also called a rotary heat exchanger – where heat is caught and the now cooler air is returned to the fresh air intake.

“By doing so we’ve reduced our cooling by a quarter,” Wehus said.

The bulk of the air is brought on board and sent into chillers that use a closed loop of pipe filled with water instead of a chemical refrigerant. That loop passes through a cooling coil below decks that does all the chilling before the air is returned to staterooms, common areas, galleys – anywhere on board.

Supplementing air-handling units that bring fresh outside air to all areas of the ships are “fan coils” that recirculate the internal air once it has been cooled. Because excess humidity has already been removed from that air, it’s dryer and uses less energy to cool again.

Galleys that might otherwise run on full all day or night now are switched to standby when demand isn’t high. Staterooms link temperature control to the guest’s keycard, saving energy when no one is inside.

Compared to older ships, Wehus says, it all cuts HVAC costs in half.