Heat Pumps Tap Ocean’s Thermal Energy
Using seawater to heat large buildings in Alaska is no longer a pipe dream.
Andy Baker, an engineer with YourCleanEnergy LLC, helped design an ocean-sourced heat pump system for the Alaska Sealife Center in Seward which will pay back the community’s investment in less than nine years — just in fuel savings.
Baker spoke to the Sitka Chamber of Commerce about practical applications for a technology that has quickly moved from theory into reality.
There’s a big difference between talking about an innovative heating system that’s on the drawing board, and talking about one that’s now used in places like Seward, NOAA’s research lab in Auke Bay, and the Whistler Village and Convention Center in Vancouver.
Baker described how the thermal energy carried in the current along Alaska’s coastline originated on the equator. Resurrection Bay, which supplies the Seward SeaLife Center, has a staggering amount of energy available.
Baker tried to describe it in terms Alaskans might understand:
“Here’s the real ah-ha picture. This was taken by the CEO of the SeaLife Center in 2009. In November, the seawater temperature is 50 degrees, the outdoor air temperature is 22. You see the latent heat of that body of water. It’s just a big hot tub steaming off. This bay is two miles wide and 11 miles long. So we’ve calculated the volume of the bay, and we know it raises 15 degrees in temperature over each summer season. We calculated how much heat that was, and if you tried to heat that bay using the Trans-Alaska Pipeline, you would have to burn it for 50 days, 600,000 barrels a day, at 85-percent efficiency. So it’s 20 percent of TAPS, in just one bay.”
The disparity between ocean and air temperatures in the fall in Seward is because of the warm current. The difference isn’t quite as extreme in Sitka, but the result is the same: A basically limitless supply of seawater at a stable temperature that never freezes.
Baker says the taxpayer-owned SeaLife Center turned off its two oil-fired boilers in 2012 and began to realize savings of $10,000 a month in fuel, or $120,000 a year. This will pay back the original investment in a little under nine years.
Air-source heat pumps have been gaining ground in Sitka. Blatchley Middle School has heat pumps, the remodeled Harrigan Centennial Hall is slated to get them, and dozens of homeowners have installed residential versions.
Only the Sitka Sound Science Center has been actively pursuing seawater heat pumps, and has installed an upgraded seawater intake for its aquarium that can be adapted to heat pumps.
Baker says there’s a common misconception that heat pumps circulate corrosive seawater. Not true. The seawater raises the temperature of a coolant loop through a heat exchanger, and then is returned to the ocean.
And for corrosion-resistance, the heat exchanger — like the one in Seward — is made from titanium.
“And so this is really the star of the system,” Baker said “There’s no moving parts. That’s a $28,000 unit. It’s about 7-feet tall. There are 126 plates in it. In advance of it is an in-line filter that traps particles, so we don’t have clogging in the plate exchanger. And the Science Center here is looking at having a similar system — similar hardware, but on a smaller scale. And this is one of the most important investments. If you do this right and size it right, you’ll have plenty of heat coming into your system.”
Baker also discussed expanding a seawater system beyond a single building — into a neighborhood district. The concept is already in use in Scandanavia. It functions like any utility, electricity or drinking water, but it this case it would be a coolant loop. Residents could connect heat pumps to it, or not. And cities understand pipes.
“For the city it just means that they’re not in the heat business, they’re just pumping a loop of cold water around. That’s something you already do with your water system.”
Baker touched on some other advantages of seawater-sourced heat pumps: Unlike air-source, they don’t become inefficient as the air cools down. Just the opposite. The greater the difference between the air temperature and the water source, the better they perform. There’s also no pollution — especially when the electricity is coming from hydropower.
Baker said that liability — which can be mitigated in other forms of alternative energy like biomass — is off the table for seawater heat pumps. He cited other tangible benefits like more jobs for people to run and maintain neighborhood districts, and lower costs for residents and businesses in the winter. But he said not all benefits would be tangible.
“If you do a project like this, people will start to identify your town with that innovation. People respect that. They look for that leadership.”
Baker says that the Seward project benefited from two grants from the Alaska Energy Authority’s emerging technology fund. He described the Alaska Renewable Energy grant fund as “more problematic,” since it assigns communities like Sitka and Juneau lower fuel costs than elsewhere. Baker felt that if the AEA accurately reflected the cost of oil in its grant formula, Sitka would have had seawater heat pumps last year.