UK could heat coastal homes with capillary heat exchangers

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

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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 shallow seabed waters, with the potential to provide homes with an infinite supply in heating.

The study shows that in winter – with a seawater temperature of just 3.7°C – it can produce up to 60 W/m2 of thermal energy for nearby coastal properties. The amount needed to heat an average UK home is 100W/m2.

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


Heat would be supplied to homes by air conditioning units, and the same technology could be used to cool properties in hot countries by using the cooler seabed temperatures to supply cold air.

Data from the Office for National Statistics (ONS) shows that more than 5.3 million people live 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 an important new addition to the way homes around the world can reduce their carbon footprint.

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

According to NTU, the technology works by a capillary heat exchanger – featuring capillary tubes 4.3mm outside diameter – extracting heat or cooling energy from the shallow waters of the sea floor.

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

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

The tests showed that the water coming out of the seabed into the capillary was heated to 40.6ohC, before being pumped to the hotel and used to heat the air in the building.

Zhenpeng Bai, an energy-saving technology researcher at Beijing University of Technology and Zhengzhou University of Light Industry, said, “The heat capacity of the seabed is infinite, making it an extremely impressive potential source of renewable energy.

“Unlike geothermal heat pumps which can require extensive excavation work, a seabed capillary heat pump requires very little installation and causes minimal damage to the seabed.

“It can have a large heat exchange surface, is less susceptible to seawater corrosion, is more affordable than other technologies, and does not require ancillary equipment such as filtration and treatment of the water.

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

The results are expected to be presented at an NTU research conference in the summer of 2022.

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