DUINDORP, THE NETHERLANDS — When most people think of harnessing renewable energy from the ocean, the gigantic spinning blades of offshore wind farms are probably the first thing that come to mind. Or maybe it’s gracefully bobbing buoys capturing wave energy or dams that skim power off rushing tides. Very few people, however, think of the oceans as a vast source of renewable heat that can be used to keep homes warm and showers steaming. But that’s exactly what a growing number of seaside towns in northern Europe are doing, despite having some particularly chilly ocean water.
Technologies like solar panels were just too expensive and wouldn’t produce enough energy in this region.
It should perhaps come as no surprise that the ocean can be used to climate control our homes. After all, the Earth’s oceans essentially climate control the entire planet. The more than 70 percent of the Earth that is covered by water serves as a kind of global thermostat. Oceans take in carbon dioxide from the atmosphere, which helps to moderate temperatures, and they also emit heat from the sunlight they absorb. Clouds, too, which perform a variety of cooling and insulating functions to help regulate temperature on Earth, form from water evaporating off the ocean.
Harnessing just a tiny fraction of the heat stored in the world’s oceans has theoretically been possible for many years, but has only recently been put into practice. One of the first places in the world to draw on the ocean for residents’ heating needs is Duindorp, a small harbor town near the Hague in the Netherlands.
Being dependent on the ocean is nothing new for Duindorp — for decades, the small fishing village relied almost entirely on the water for its economic lifeblood. Fishing in the harbor has since declined, but now a new era of reliance on the ocean for energy has begun.
The project began nearly a decade ago, as 1,200 cramped fishermen houses dating back to 1915 were taken down in town to make room for 800 new homes that met modern standards for affordable housing in the Netherlands.
“Residents wanted their homes to be heated using renewable energy,” said Paul Stoelinga, senior consultant at Dutch environmental engineering firm Deerns International, which designed Duindorp’s current heating system. “But how to offer that for low-income residents was a problem. Technologies like solar panels were just too expensive and wouldn’t produce enough energy in this region.”
District heating using seawater turned out to be the most affordable solution, insuring no resident would have to pay more than the national average of €70 (about $94) a month for heat and hot water.
While deeply connected to the sea, Duindorp seems like an unlikely place to take advantage of heat in the oceans. The birds skimming over the choppy harbor are mostly cormorants, familiar cold-weather birds that proclaim the fact that the water here is hardly warm. For most of the winter, the temperature in the harbor is right around 35 to 40° Fahrenheit, although in summer it can climb to near 70° Fahrenheit.
The system is based on a district heating plan, which is quite common in Europe, but only recently starting to catch on in the U.S. District heating systems warm water at a central location and then distribute it through a system of underground pipes. None of the water in the pipes is used directly in homes, but the heat from the water is skimmed off and used to warm showers and floors.
The process is similar to the circulatory system in a person’s body. Blood gets oxygen from the heart and then delivers it through the body, returning de-oxygenated blood to the heart to start the process all over again. Likewise, the water in the pipes that services the neighborhood is heated at the central facility and then runs through town distributing heat and eventually loops back to the power plant to be heated up once again.
In the summer, creating warm water to flow through the district heating network of pipes is relatively straightforward. Intake pipes at the harbor draw in about 25,000 to 50,000 gallons of warm seawater every hour. An extensive series of filters throughout the intake system ensures that no sea life is sucked into the plant. That seawater is then used in a heat exchanger to heat freshwater for the pipes to around 54° Fahrenheit. The warmed freshwater is then sent out along a five mile network of insulated pipes that services the 800 homes in the new affordable housing neighborhood. At every house connected to the system, a 5 kWh-capacity heat pump raises the temperature of the water to between 110–150° Fahrenheit, to then be used for heating and warm water.
In the winter, the system is more complex.
“Just at the moment when you really want a hot shower and need heating in your home, that’s when the ocean is at its coldest,” said Stoelinga. “Sometimes just 2° Celsius. It’s a tricky contradiction, when you need the heat, its not there.”
During these chilly months, a heat pump is used to transfer heat from the seawater to the district heating system. Every home in the U.S. uses similar technology in refrigerators and air conditioners. Heat pumps don’t create heat, they merely transfer it from one medium to another. Heat pumps require a source of energy as they push heat against its natural gradient — heat naturally wants to flow from hot to cold until an equilibrium is reached. In a refrigerator, they push heat from a cold area, the inside of the fridge, to a warmer area, the kitchen. Unlike a typical fridge, the heat pump in Duindorp uses ammonia as the refrigerant. It’s extremely efficient, but also quite toxic, and not something any homeowner would want in their kitchen.
Much more water is needed in the winter, compared to the summer, to keep the system running. About 190,000 gallons of water is taken in every hour when the ocean is at its coldest and only a few degrees of heat can be transferred.
“You can’t get much heat out of water which is just a few degrees above freezing” explained Stoelinga, “so you need much more flow.”
Originally, Deerns planned to make the system 100 percent renewable by building two 1.5 MW wind turbines in the harbor to supply all of the energy needed to run the heat pump during the winter. Unfortunately, local zoning codes didn’t allow wind turbines to be built in the area, so the electricity needed to run the heat pumps, about 3 MW, is taken off the grid. The system is still extremely efficient, however, generating 15 kilowatt-hours of heat for every 1 kWh of electricity pumped into the system. This reduces carbon emissions by 50 percent when compared to conventional heating using natural gas.
Stoelinga explained that while district heating systems and heat pumps certainly aren’t new ideas, making the system run smoothly with an affordable price tag was a massive undertaking.
This design would work especially well and cost even less if the community was near a large body of freshwater.
“I would say that about 80 percent of the engineering work we did at this site was dedicated entirely to battling the problem of corrosive seawater,” said Stoelinga. “We are dealing with huge volumes of very salty water in our mechanical systems every day and finding ways to cut down on how often we had to replace corroded components was by far the biggest challenge. “
Now that solutions to that problem have been designed, Stoelinga says that seawater district heating is a promising alternative for any community near the shore. The system will be most cost effective in areas where new development is taking place. Since district heating depends on an underground network of pipes, retrofitting a community to run on a district heating system would add considerably to the price tag.
“This design would work especially well and cost even less if the community was near a large body of freshwater,” said Stoelinga. “If you don’t have to worry about saltwater ruining equipment, it’s much simpler.”
In the U.S., any town or city on the coasts, along the Great Lakes, or even near large rivers like the Mississippi could benefit from a similar system.
For Stoelinga, the next project is a seawater cooling system based on the similar principles for resorts in Aruba. In order to cool the resort, intake pipes will be built to collect the cold water deep in the ocean. That cold water can then be used in a heat exchanger to provide cold water in taps and air conditioning throughout the hotel.