UK could heat coastal homes with capillary heat exchangers

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The UK could become a leader in technology that heats its coastal towns by drawing warmth from the seabed, researchers claim.

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An international study involving Nottingham Trent University (NTU) has shown the potential for using capillary heat exchangers for heat pumps in the shallows of the seabed, with the potential to provide homes with an infinite supply of heating.

The study shows that during winter - with a seawater temperature of only 3.7°C - it can produce up to 60W/m2 of heat energy to nearby coastal properties. The amount required to heat an average UK home is 100W/m2.

The research - with Beijing University of Technology, Zhengzhou University of Light Industry and Beijing Municipal Institute of Labour Protection - builds on the development of ground-source and air-source heat pumps as alternatives to gas boilers.


The warmth would be delivered to homes through air-conditioning units, and the same technology could be used to cool properties in hot countries by utilising the cooler seabed temperatures to supply cold air.

Data from the Office for National Statistics (ONS) show that more than 5.3 million people reside in coastal towns in England and Wales.

In a statement, senior lecturer Hua Zhong, a specialist in applied energy and environmental engineering at NTU, said: “This technology has the potential to become a new and significant addition to the way in which homes around the world can reduce their carbon footprint.

“Due to their proportionately large coastlines, and rich sources of shallow geothermal energy in coastal areas, the UK, US and China have the potential to pioneer this under-researched renewable energy source.”

According to NTU, the technology works by a capillary heat exchanger – featuring capillary tubes of 4.3mm in external diameter - extracting heat or cooling energy from the shallows of the seabed.

Heat or cooling energy is then transferred to an indoor heat exchanger by pump. The indoor heat exchanger then heats or cools the indoor air of the property through a system similar to an air-conditioning unit.

As part of the study, a hotel in Qingdao, China, was used to pilot test the technology. A 250m2 capillary was laid 5m deep in the shallows, 50m offshore. The total distance from the hotel to the capillary was 300m.

Tests showed that the water exiting the seabed in the capillary was heated to 40.6oC, before it was pumped to the hotel and used to warm the air in the building.

Zhenpeng Bai, a researcher in energy saving technology from Beijing University of Technology and Zhengzhou University of Light Industry, said: “The heat capacity of the seabed is infinite – making this an extremely impressive potential source of renewable energy.

“Unlike ground-source heat pumps which can require extensive excavation work, a capillary seabed heat pump requires very little set up and causes minimal damage to the seabed.

“It can have a large heat exchanger area, is less susceptible to corrosion from seawater, is more affordable than other technologies, and does not need auxiliary equipment such as filtration and water treatment.

“The UK, China and US are geographically ideal to develop this technology and help drive down global carbon emissions in a sustainable way.”

The findings are set to be presented at an NTU research conference during the summer of 2022.