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HotTwist water-based thermal system cuts heating bills by 75%
Michael Irving

Water can hold a huge amount of thermal energy, and a new system to tap into this resource is being trialed in Scotland. A startup called SeaWarm uses heat stored in bodies of water for buildings, pulling four times more heat out than electricity used.

Simply put, heat pumps are designed to take thermal energy (heat) from one medium and give it to another. Your fridge, for instance, takes heat from the air inside and pumps it outside, cooling the interior. An air conditioner works in a similar way, cooling the inside of your house (or heating it in winter).

That, however, requires a lot of energy, because air isn’t a great medium for storing heat. But water, according to SeaWarm, can hold up to 3,400 times more thermal energy than the same volume of air. That represents a pretty enticing energy source, so SeaWarm, a spin-off company from the University of Edinburgh, is working to tap it.

The company’s Water Source Heat Pumps (WSHPs) can harvest heat from bodies of water like oceans, rivers and lakes, or water from underground or mines. The SeaWarm unit can be placed up to 500 m (1,640 ft) from the source, with the water pumped or gravity-fed to the heat exchanger.

A diagram illustrating how the SeaWarm system works

That’s where SeaWarm’s “HotTwist” tech comes in. Inside the water tank is a spiral-shaped set of pipes through which glycol is pumped. This liquid absorbs heat from the water, before it’s compressed in the heat pump to raise its temperature even further. This hotter glycol can then be used to warm up buildings through radiators or underfloor heating systems. After it cools off, the glycol is then cycled back into the heat exchanger to start over.

SeaWarm has demonstrated the effectiveness of the new system in a few real-world trials in Scotland, including a museum, a greenhouse and a housing estate built into an old naval barracks. The lattermost, for example, was able to use a 13-kW heat pump and 12 radiators to warm a 140-m2 (1,500-sq ft) uninsulated building to a cozy 25 °C (77 °F). Importantly, it can produce four times more heat energy than the energy expended as electricity to compress the glycol.

The SeaWarm system can apparently maintain a more consistent efficiency year-round through different weather conditions than systems relying on air or ground heat. It’s also more sustainable, the team says, helping to transition away from fossil fuel sources for heating – the museum case study, for instance, is expected to save up to 75% of the organization’s heating bills.

While it wouldn’t work everywhere, the SeaWarm system is at least an intriguing idea that could be one solution in a patchwork of many in the transition away from fossil fuels. Further test runs are planned to check its viability in the real world.



Michael has always been fascinated by space, technology, dinosaurs, and the weirder mysteries of the universe. With a Bachelor of Arts in Professional Writing and several years experience under his belt, he joined New Atlas as a staff writer in 2016.

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