The potential for extracting heat from natural sources is enormous, and a substantial development in Scotland should be an impressive demonstration. The £250m Queen’s Quay regeneration project in Clydebank will incorporate a large-scale water source heat pump scheme, using heat extracted from the River Clyde to supply hot water and heating to a district heating network that covers 1,200 homes, as well as businesses and public buildings.
The project, the largest of its kind in Scotland, will cost around £15m. It has been developed by West Dunbartonshire Council and is being delivered in partnership with renewable energy company Vital Energi. West Dunbartonshire Council is covering 60% of the cost, while the Scottish government will contribute £6m through the European Regional Development Fund, via the Low Carbon Infrastructure Transition Programme. “The project will build out over the next 10 years,” explains Vital Energi operations manager Scott Lutton. “Initially, we’ll pick up existing buildings that the council owns, and then, through the lifetime of the project, we will pick up the new developments.”
The two 2.5MW heat pumps are being supplied by Star Renewable Energy (pictured) and will be installed, he says, “at the initial stage – as soon as we produce heat, the heat pumps will be producing that heat,” but they have the capacity to support future expansion. They are supplemented by two gas boilers supplying up to 7MW each – the ‘energy centre’ has an overall capacity put at 20MW.
The gas boilers, says Lutton, are not for routine use but “for resilience – there’s spare capacity and there’s always redundancy. The heat pumps are the lead heat source for the site – the gas boilers will just run to top it up as and when”. Both the heat pumps and the boilers can operate in parallel, through a fully-automated control system. The heat pumps themselves are electrically driven: the motors “are big electrical consumers,” says Lutton, “driven through large-scale variable speed drives and they ebb and flow with the requirements of the heat pumps”.
If the heat pumps are off-line for maintenance, there is also a 130,000-litre thermal store (“basically a big hot water tank”) that can be topped up by the heat pumps or the gas boilers. The thermal store is integral to the system design and is utilised to maximise the system efficiency. “We’ve got capacity for another 130,000-litre thermal store besides”, adds Lutton. There is also the future provision to add further heat pumps and another gas boiler, for a total output of around 30MW.
The heat pumps do not directly take the water from the river. “We have an extraction system,” says Lutton. “We put filter heads into the water, the water is pumped through two stages of filtration and then feeds the heat pumps in the energy centre.
“Filtration is a massive consideration – making sure that water is taken out at an appropriate rate and put back in an appropriate condition – and also to give the heat pumps the level of filtered and safe water that they require. Taking the water out can be done a number of ways, but making sure it’s in a condition to be used is probably more challenging.”
But of course, ensuring that the site is appropriate is vital: “There’s the survey, detailed analysis and there’s also looking at historical data. We’ve applied for and received Scottish Environment Protection Agency licences, we’ve gained permission from Scottish Water, we’ve liaised with environmental agencies. We had environmental impact assessments done. Positively, everyone’s been in favour of these works, from the outset we have made consideration to ensure that there’s no detrimental effect on flora and fauna, and everything’s been done working with the statutory bodies.
“In the long term there’s an enormous amount of heat that can be extracted from such sources – there’s loads of conversations over time, and statutory bodies that will assess the impact of this.”
Vital Energi and its partners have done a good deal of research on implementation: “We have been to see various different scenarios and different projects,” says Lutton. “We went out to see how it had been done in Drammen in Norway.” This scheme uses heat pumps (also from Star Renewable Energy) to harvest district heat from the waters of the North Sea.
The temperature of the water from the Clyde can be between 4°C and 15°C, while the heat pumps provide an output at between 75°C and 80°C – the system is rated at a supply temperature of 75°C, with the return at 45°C.
The availability of heat from the heat pumps does not vary with the seasons as one might expect: “The difference between summer and winter is really just an efficiency calculation against the heat pump inlet temperature,” says Lutton. “The lower the temperature of water going in, the lower the efficiency of the system. The higher the temperature of water going in, the higher the efficiency. The system will produce less in the summer because there’s less demand. The energy centre is there and available to take all demand all year.”
The hot water is distributed using 2.5 km of pre-insulated pipe made by Danish firm Logstor. The fully welded stainless steel pipe is insulated with polyurethane foam, with an outer casing of high-density polyethylene and a pair of internal copper wires for leak detection: “It’s connected to the site-wide control system and monitored to ensure integrity of the distribution network”. The pipes have a design life of 50 years.
The heat network does not just supply new-build systems: a number of existing buildings are included in the scheme, which typically operate at 82°C/72°C flow/return temperatures. “New buildings will be built with 75°C/45°C in mind, but existing buildings need modification. It’s basically about the adjustment and the amendment of control of existing systems,” says Lutton. By modifying pumps – fitting VSDs to give speed control – changing from 3-port to 2-port valves, and adding some control logic, Vital Energi can lower the flow and return temperatures in the buildings. “It’s detailed work,” he adds, “of critical importance to this type of project – heat networks need the appropriate building temperatures”.
Residents need to be brought on board too: “With anything new there is change, but a residential customer will be met with a heat interface unit – it’s very similar to a combi boiler,” says Lutton. “It’s not typically a hurdle, but we do prepare information packs, have briefing days, and have customer liaison.”
The overall heat network has been designed to be resilient over the long term: “Everything is interchangeable. If a heat pump was to go down in 10 years’ time it’s just a component changethe system doesn’t stop operating. It can operate forever with appropriate maintenance.”
Box: 10:10 ups the heat
London-based charity 10:10 is researching and campaigning to harness renewable energy, including stored heat from water and ground sources, as part of its broader aim to cut carbon emissions. The charity focuses on projects involving commercial and public sector organisations rather than individuals, but the key is community involvement, as 10:10’s director of campaigns Max Wakefield explains: “Our guiding philosophy is that we can’t move where we want to be and as fast as we need to get there unless everybody is involved. You end up with something where everybody feels they are contributing.”
The ‘Solar Schools’ project ran from 2010-15 and involved 80-90 schools. Wakefield says that a school works well both in terms of local involvement and also technical feasibility. The charity’s ‘Lost Rivers’ project, meanwhile, explored the possibility of extracting heat from the underground rivers flowing beneath London – including a suggestion of installing heat pumps in the Tyburn to supply nearby Buckingham Palace. One of 10:10’s current projects is ‘Powering Parks’, a partnership with Scene Consulting and Hackney Council that will demonstrate the benefits of ground-source heat pumps in green spaces to heat on-site or nearby buildings.