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This 18th Century Mansion Is Heated with Seawater

The UK's largest marine heat pump has replaced a system that used up to 1,500 litres of oil a day.
Image: Flickr/Snapshooter46

This 18th century mansion used to use up to 1,500 litres of oil a day, and now its heating is powered by the sea, with the UK’s largest marine heat source pump.

It’s not one of the more well-known or popular renewable solutions, presumably because installing that kind of system is necessarily very site-specific; it needs to be on the coast, for one. At the Plas Newydd property in Wales, which is run by British conservation charity the National Trust, the pump uses seawater from the nearby Menai Strait (part of the Irish Sea). “You’ve got to have the right property in the right place to take full advantage of the heat in the sea,” Paul Southall, the National Trust’s environmental practices adviser for Wales, told me.

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The UK isn’t exactly renowned for its warm coastal waters, but he explained that researchers they’d been working with at Bangor University had been measuring the temperatures of the Menai Strait and found it to range from seven to 14 degrees Celcius—perhaps not ideal for swimming, but still harbouring a bit of latent heat.

To harvest it, they use two pipes that stretch around 50 metres into the strait. One pipe takes water from the strait to a heat exchanger in a pump house building on the shore, and the other takes the seawater, now a few degrees cooler, back into the sea.

From there, the system works much like a ground source heat pump—the sea’s involvement stops at the heat exchanger. Then the heat is carried 30 metres up the cliff face to an old boiler house, and into four 75kW heat pumps, totalling 300kW. On their way up, the system gathers a couple more degrees from latent heat in the soil around the pipes and the heat pumps compress it to gain more. “It’s a fridge working backwards, basically,” said Southall. He said when he monitored it yesterday, the temperature coming out of the sea was at 13 degrees, and it ended up at 58.

The heat exchanger does use a little bit of electricity, but that comes from solar panels on the estate. Southall said Plas Newydd has 50kW of PV solar, and that rather than selling the energy produced back to the grid, it’s all taken down to the heat pump building. Some of it is also used for hot water and lighting, for instance in the tea rooms when they’re open.

Laura Shack, an energy and sustainability spokesperson for the National Trust, confirmed that the heat pump system now provides 100 percent of the heating needed for the house, which was formerly the National Trust’s biggest oil user.

It’s now a pilot for other projects that hope to switch some of Britain’s old estates over to renewables. In addition to saving them around £40,000 annually in operating costs, Shack said the new heat source is in fact ideal for helping preserve the building’s collections. “The marine source heat pump itself is actually perfect for conservation because it has a really steady heat, which means that collections like our military uniform at Plas Newydd is kept at a really good temperature and actually helps to conserve it, so it’s a win-win for us,” she said.