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Aquarium lifts heat from ocean's stored energy

Posted: December 17, 2012 - 12:03am
Kelsey Dunlap and her 1-year-old son, Cyrus, enjoy the seabird exhibit at the Alaska SeaLife Center on Tuesday, Dec. 11, 2012, Seward, Alaska. The center is using a heat pump system to extract energy from seawater to partially heat its facilities. (AP Photo/Dan Joling)  Dan Joling
Dan Joling
Kelsey Dunlap and her 1-year-old son, Cyrus, enjoy the seabird exhibit at the Alaska SeaLife Center on Tuesday, Dec. 11, 2012, Seward, Alaska. The center is using a heat pump system to extract energy from seawater to partially heat its facilities. (AP Photo/Dan Joling)

SEWARD — Alaska’s Resurrection Bay teems with salmon, herring and humpback whales, but when Alaska SeaLife Center chief executive officer Tara Riemer Jones looks at the fiord outside her window, she sees a way to cut her building’s heating bill.

The center this month turned off boilers that burn expensive fuel oil in favor of America’s farthest north seawater heat pump system, which taps a summer’s worth of solar energy stored in the deep bay.

The system sucks in seawater, extracts a few degrees of its warmth and returns it to the ocean. The upfront costs of the system were significant — about $830,000. But the SeaLife Center expects the system to pay for itself in less than nine years, saving at least $15,000 and possibly double that each winter month, with the added benefit of keeping 1.3 million pounds of carbon emissions out of the atmosphere each year.

“It working just as it was designed and we’re getting huge savings out of it,” Jones said.

About 160,000 visitors pass through the SeaLife Center each year to see underwater views of sea lions and harbor seals plus rare seabirds and fish from all depths. The center employs 90 people year-round and hosts volunteers and interns who help with its other missions, research and ocean wildlife rescue.

The SeaLife Center is in Seward, a city of 2,700 about three hours south of Anchorage by car. The city buys electricity from a utility that produces power mostly by natural gas, but the gas lines don’t stretch to Seward. Homes and businesses burn fuel oil that in 2008 was selling for $5 per gallon.

At that price, the 120,000-square-foot building’s annual heating cost reached $463,000, said operations manager Darryl Schaefermeyer.

A maintenance worker suggested heat pumps and Schaefermeyer called in Anchorage clean energy consultant Andy Baker to see if an answer to the center’s heating problems could be found in its front yard.

Baker, who’s also an engineer, studied systems pioneered in Scandinavian countries, visited four seawater heat exchange systems in Canada and reviewed the latest technology offered by U.S. companies. He found Resurrection Bay to be ideal.

The bay is elongated on a north-south axis and includes a 5-mile long area that’s more than 900 feet deep. It collects solar energy all summer. Glacier melt adds a bit of cold water but it’s largely not flushed by ocean currents, allowing it to retain heat.

“The only place it loses heat is at the surface,” Baker said.

The coldest water, 37, degrees, is found at the end of winter in April. A summer of sun raises that to 52 degrees by late October. Heating that volume of water 15 degrees would take 50 days of the entire daily throughput of the trans-Alaska pipeline — 600,000 barrels — burned at 85 percent efficiency, Baker said.

“It’s staggering. The sun does all that for free. We’re just tapping a tiny, tiny portion of that,” he said.

Federal and state agencies reviewed Baker’s findings and offered $713,000 in demonstration project grants.

In principal, the heat pump technology is no more complicated than a refrigerator, he said. However, instead of discarding heat like the kitchen appliance does, the system discards the cold and uses the heat.

It’s hard to think of 42-degree seawater as a hot medium but steam rising from the surface on a cold day is a clue to the warmth below the surface of Resurrection Bay. From Baker’s perspective, any seawater that stays above 35 degrees is a potential heating source.

The system works like this: seawater from the bay is piped to a titanium heat exchanger, where it warms a mixture of glycol and water.

The cooled seawater returns to the ocean. The glycol mixture moves by pipe to a heat pump, where it comes into contact with refrigerant. The warmed glycol mixture causes the liquid refrigerant to boil, turning it into gas. The gas is run into an electric-powered compressor. Compressing the gas raises the temperature.

The compressed gas raises the temperature of another loop of water from 100 to 120 degrees. That water is pumped throughout the building to warm ventilation air, preheat the hot water system and warm concrete slabs to keep ice from forming on pavement around animal enclosures and walkways.

The project only pays off if heat energy produced by the seawater system exceeds the electrical power used by the heat pumps. The system has been consistently producing three units of heat for every one unit of electricity.

Schaefermeyer sees possibilities for heating commercial buildings and homes in Seward. Alaska’s Panhandle and communities such as Cordova and Homer are also candidates, Baker said.

The water off Alaska’s largest city, Anchorage, may not be suitable. Cook Inlet is silty, Baker said, and the water temperatures drop to 30 degrees and stay there.

“It’s really a bit too cold,” he said.

Low-cost electricity, preferably clean hydro, is needed to power the heat exchange system, Baker said. The SeaLife Center has a favorable industrial rate and also had the advantage of a seawater intake system for its aquariums.

There’s a fairly large capital cost and technical experience is required to design and run systems, Baker said. That may not be appropriate for small communities currently struggling to operate less complicated equipment.

“You’re probably not doing them a service by giving them one of these systems,” he said.

Jones is happy with the results so far at her four-story aquarium.

“It’s winter and we’ve turned off our fuel boilers,” she said.

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