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Water source heat pumps on trial in Scotland

Words:
Stephen Cousins

Live trials use technology that extracts warmth from sea or rivers – performing at levels comparable to the most efficient air source heat pumps

SeaWarm’s HotTwist heat exchanger at the Museum of Lead Mining Museum demonstrator site
SeaWarm’s HotTwist heat exchanger at the Museum of Lead Mining Museum demonstrator site Credit: Andrew Fraser-Harris/ SeaWarm

Researchers from the University of Edinburgh have developed a low carbon home heating system that draws energy from seawater, rivers or ponds to provide domestic heating and hot water.

Developed with funding from the Scottish Enterprise High-Growth Spinout Programme, the SeaWarm system can deliver 350-400% more heat than electricity required for operation, compared to the most efficient air source heat pumps.

Three trials are under way at an affordable housing project close to the Firth of Forth, at a lead-mining museum in southwest Scotland and in a commercial greenhouse in Fife. Another system is due to be installed at the Scottish Seabird Centre in North Berwick over the Summer.

SeaWarm’s innovative HotTwist heat exchanger is engineered to maximise heat extraction from water, handing over thermal energy to a glycol/water refrigerant circulating through a coiled tube, which is sent to a heat pump inside the property.

Sea water intake at the LAR Housing Trust development demonstrator
Sea water intake at the LAR Housing Trust development demonstrator Credit: Andrew Fraser-Harris/ SeaWarm

The system is designed to exploit the fact that sea and river water is typically a more predictable source of energy than air because it remains at a consistent temperature.

While similar technology is already used in large district heating networks, such as at the Queen’s Quay housing development at Clydebank near Glasgow, SeaWarm is compact and suitable for homes or small buildings. On larger developments with greater heat demand, a modular design allows multiple units to be connected.

The heat exchanger is housed inside a 2m-wide by 1.5m-high drum-shaped tank that holds 3.7m3 of water, roughly the same volume as 12 bathtubs. This can either be placed outside or buried underground, while the interior heat pump is roughly the size of a domestic fridge.  

The technology makes several advancements over existing heat collectors for water, says Gus Fraser-Harris, a postdoctoral research associate at the University of Edinburgh: 'We developed an all-plastic heat exchanger, using a specific type of high-density polyethylene pipe, which is more efficient at heat transfer than standard heat collectors used in water. In addition, the heat exchanger doesn't need to be placed directly in water.'

SeaWarm’s HotTwist heat exchanger at the Museum of Lead Mining Museum demonstrator site with (left to right) Professor Chris McDermott (Project lead), Cameron Muir (installation lead) and Sean Muir. Credit: Andrew Fraser-Harris/ SeaWarm
The SeaWarm heat exchanger tank at the Museum of Lead Mining demonstrator site in Wanlockhead with Professor Chris McDermott. This installation is gravity fed by the nearby burn support by minewater discharge Credit: Andrew Fraser-Harris/ SeaWarm

The system has been tested up to a distance of 275m away from a property, with 'little difference in overall efficiency' and the aim is to increase that to 500m.

According to Fraser-Harris, R&D is partly focused on reaching different markets and end users, including a 'whole host of waterside properties and businesses, like marinas, with very close available access to the sea.' The plan is to spin out SeaWarm from the university as a company at the end of the summer and a commercial product could be available by the end of the year.

 

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