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Could the Free Heat in Water Bodies Help Heat our Towns and Cities?

Could a renewable source of energy be sitting right under our noses waiting for us to exploit it?

Last week, a large-scale type of heat pump development on the River Thames in London achieved the 'best new technology' award at the 2014 Climate Week Awards.

Kingston Heights is a large-scale development in Surrey of 137 residential apartments and a hotel and conference centre. When complete it will receive all its heating, hot water and cooling using the solar energy stored naturally within the River Thames, with a pioneering Open Water Heat Pump System that went live in Autumn 2013, saving about 500 tonnes of CO2 a year.

Ed Davey switching on the Kingston heat pump systemGiven that most cities are situated on rivers, Ed Davey, The UK's Secretary of State for Energy and Climate Change, who switched on the system (see picture, right), believes there is huge potential for other locations to emulate this practice.

Installed by developers United House and NHP Leisure Developments, the £70 million mixed-use development has, perhaps ironically, been created on the site of a former power station right in the heart of Kingston-upon-Thames, and 200 metres from the river.

The development includes 56 'affordable' homes plus 81 luxury private apartments known as River Walk. All 137 apartments will benefit from the cutting-edge heat pump system that harvests solar energy that has been soaked up by the water in the River Thames. The community heating scheme concentrates this heat to the temperature required for the underfloor heating and hot water needed by residents.

"At two metres below the surface the water never falls below 7°C, even in winter, so we can be certain that it can provide enough energy to heat the apartments," explains Mike Spenser-Morris, managing director of NHP Leisure Developments and the visionary behind the scheme. "If we had fitted gas boilers, then the site would be dumping around 500 additional tonnes of carbon into the atmosphere each year.

"In addition, because of this system's exceptional energy efficiency, the equivalent heating cost for a couple living in a one bedroom apartment would be 18% more. For an average home, this would mean hundreds of pounds extra."

How the system works

The system can draw up to 13 million litres of water each day – the equivalent of five Olympic-sized swimming pools. The water is filtered into stages to ensure that no aquatic life can enter the system. Inside a specially-built plant room adjacent to the river, the water passes through high-efficiency heat exchangers and, once the low grade heat has been harvested, the water is immediately fed back into the river, untreated in any way.

The trench for the district heating system being dugThe heat exchangers transfer this low grade heat into an internal closed loop water system which is piped to a plant room in the apartment building. There, 41 Mitsubishi Electric Ecodan water source heat pumps increase the temperature of the low grade heat up to 45°C, before sending it to mini plant rooms right across the development. The inverter-driven Ecodan units offer a completely scalable solution for almost any ground or water-based community heating need and offer low maintenance, a small footprint and easy installation.

The heat pump boilers are completely modular and connect to the ground or water source units. This allows the system to be specified on many different types of application according to the individual design requirements and efficiency needs on each project.

At the end of this year a new 142-bedroom hotel with conference facilities will also be completed at the site and will use the same system. The system will supply not only heating and hot water but cooling as well. Heat recovered from cooling the hotel rooms will be returned to the system to support the heating and hot water demands for the whole site.

Mike Spenser-Morris believes the scheme can be replicated widely. Any development taking place near an open body of water could benefit from such a highly efficient system, doing away with traditional combustion boilers, the need to purchase fuel, and carbon emissions.

Kingston Heights is a large-scale development in Surrey"This open water heat pump system will be capable of producing over 2 MW of thermal energy for this development and will provide it 24/7, 365 days a year regardless of the weather or air temperature, even in the depths of winter," he explained. "Almost every major city in this country is close to a river, lake, reservoir, canal or the sea. Every litre of water naturally stores, with the greatest efficiency, the valuable energy Sun delivers to the Earth each day.

"There will be thousands of businesses and homes that can benefit from this."

This has attracted the attention of Ed Davey and his Department for Energy and Climate Change (DECC). He said: "This is at a really early stage, but it is showing what is possible. You never have to buy any gas – there are upfront costs but relatively low running costs. My department is exploring the potential for this sort of water-source heat pump across the UK, so we're going to map the whole of the UK for the potential."

Water is not the only source of heat of course. Ground source heat pumps are being widely used; the difference is that the installation and carbon costs might be lower in a body of water since trenches and boreholes do not have to be dug.

As with much renewable energy technology, the initial capital costs are perhaps higher than for other types of plant, but over a levelised, lifetime approach, the fact that the fuel costs are close to zero, yields huge benefits.

Waste industrial heat is also reclaimable and DECC published last week a report - The potential for recovering and using surplus heat from industry - which identifies "a technical potential of 11 TWh/yr (2.2 MtCO2/yr) from around 250 potential individual combinations of heat sources, heat sinks and heat recovery technologies including heat exchangers, heat pumps and heat-to-power technologies."

It also found that, of this 11TWh/yr, 7 TWh/yr might be realistically achievable, and this would account for about 4% of heat energy use within the leading eight heat intensive sectors.

District heating is eligible for the Renewable Heat Incentive the UK, a form of net metering, and heat pumps also received targeted support.