16 April 2025
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A recent educational visit brought together students from Glasgow Kelvin College and members of the Institute of Refrigeration (IOR) for a behind the scenes tour of the energy centre which includes the UK's largest water source district heat pump scheme.
Located at West Dunbartonshire Council’s Queens Quay Energy Centre in Clydebank, the award-winning project was designed and delivered by Vital Energi, with the two water source heat pumps engineered and supplied by Star Refrigeration. The zero carbon industrial heat pumps harness the ambient thermal energy of the River Clyde to deliver low-carbon, more affordable heating to local homes, local government buildings and other organisations. The informative session gave attendees the opportunity to witness firsthand how theoretical concepts translate into a realworld application that addresses today's energy challenges. The visit was made possible through collaboration between Star Refrigeration, Vital Energi, and West Dunbartonshire Council, with special thanks to Nicky Cowan of Star Refrigeration, Shannon O'Neil of Vital Energi, and Adam Strachan of The Institute of Refrigeration for their expert guidance throughout the tour.
Sustainable heating at scale
The Queens Quay energy centre houses two 2.6 megawatt ammonia heat pumps, delivering a combined 5.2 megawatts of heating capacity. This system is at the heart of a 5 kilometre district heat network that currently serves local residential, council-owned buildings and other organisations, but has been future proofed to expand throughout the development and bring low-carbon heating to more organisations and residents.
Natural heating from the local river to the radiator
The heat pump operation is simple in concept. Water is taken from the River Clyde and then passed through a specialised filtration systems designed to remove debris and prevent mussel colonisation. The river water passes through the heat pump system where thermal energy is extracted, cooling the water by approximately 3 degrees Celsius before returning it to the river.
The ammonia heat pumps then boost this thermal energy to produce water at 75°C- 80°C, which circulates through the district heating network to provide heating and hot water to connected buildings. The system was originally designed to produce water at 85°C to accommodate older buildings with smaller radiators, but through upgrades to heat exchangers and radiator sizes in connected buildings, the network temperature has been optimised to operate between 75°C-80°C, therefore improving efficiency.
Efficiency
The system has a high level of seasonal efficiency, which contributes to lower energy costs and higher carbon savings.
The system maximises efficiency through a series of heat exchange stages, including desuperheaters, condensers, and subcoolers, to extract the maximum amount of useful heat from the ammonia refrigerant. Even the heat from the oil used to lubricate the compressors is incorporated into the heat recovery system, as it exits at the same discharge temperature as the refrigerant (110°C) and can be used to heat district water from 55°C to 80°C.
Climate change at work
One of the interesting facts the hosts revealed during the visit was that the facility has already observed the effects of climate change on the river's temperature profile. Historical data going back 50 years suggested the Clyde would reach maximum temperatures of 18°C to 19°C, but recent measurements have recorded temperatures as high as 21°C.
The real face of climate change is showing, and its impact can be felt in the Clyde’s water.
Future expansion
The project was delivered to support a long-term masterplan and the plans remain in place to expand the network's reach. The energy centre was built with this expansion in mind and the building has space for two additional heat pumps and another thermal storage tank to increase capacity.
One of the truly exciting things about this project is that, as it expands and more heat loads are connected, it will continue to become more efficient, which will lead to lower energy costs and higher carbon savings.
Technical innovations
The system incorporates several technical innovations to maximise efficiency and overcome challenges associated with using river water. These include:
- Self-cleaning filtration systems that prevent debris and mussel seeds from entering the system. One of the most significant technical challenges in the operation of the Queens Quay heat pumps is this filtration system. The system employs a sophisticated three-stage filtration process to ensure smooth operation. The first stage consists of mesh baskets submerged in the river that prevent large debris from entering the system. These are self-cleaning, with water jets that spin and eject pressurised water to keep the mesh screen clear of plastic bags and other debris. The second stage targets smaller particulates, particularly mussel seeds, which can pose a serious threat to the system. Mussel seeds can grow into a full-size mussels and cause damage to heat exchangers, pipes and other components. The filtration system filters water down to 20 microns and includes a backflush system that returns filtered material to the river. The third level of protection is the heat exchanger evaporator itself, which includes automated cleaning systems to prevent the buildup of silt, algae, and other residue inside the tubes.
- Specialised Pumps and titanium heat exchangers. The water abstraction system employs self-priming suction lift pumps situated above the water level. Since pumps excel at pushing water but struggle with initial suction, a vacuum pump is used for priming to bring the water up to the pump. It then just acts like a syphon. The heat exchangers use titanium tubes due to the brackish nature of the Clyde water. Each heat exchanger contains approximately 750 tubes that are both internally and externally enhanced to maximise surface area for heat transfer. A unique ‘spray chiller’ evaporator design pumps liquid ammonia to the top of the evaporator vessel and sprays it over the tubes containing river water. To maintain efficiency, each tube is equipped with a brush that can be pushed through to clean internal surfaces when flow is reversed, removing accumulated silt and algae that would otherwise reduce heat transfer efficiency.
- The two 900 kilowatt electric motors driving the twin screw compressors are air-cooled and equipped with variable speed drives (VSDs) that serve a dual purpose. They allow for capacity modulation based on demand and they provide a gradual startup that prevents electrical surges.
- A 130,000 litre thermal storage tank that allows the system to operate at optimal efficiency and take advantage of lower nighttime electricity rates. During periods of low heat demand, rather than reducing the output of the heat pumps, they continue to run at full capacity and charge the water tank.
When the network requires heat, it is delivered from the tank via a pump, avoiding the need to frequently switch the heat pumps on and off. Often, a jockey pump is used to pump water through the district network instead of the full size pumps in order to reduce energy consumption. Since electricity is typically cheaper at night, the heat pumps can operate during off-peak hours to generate and store heat. During peak pricing periods, the heat stored overnight can be used to meet demand, allowing the heat pump to remain off. In this type of system, a larger thermal store provides greater flexibility and cost savings.
Queens Quay represents just one of the f irst water source heat pump projects carried out in the UK, with similar installations in Bristol, Jarrow and Liverpool. These projects demonstrate the viability of water source heat pumps as a key technology in the transition to heat decarbonisation.
With the UK's ambitious targets for carbon reduction, district heating networks powered by renewable sources like the River Clyde are likely to become increasingly common in cities with a river nearby. As developers at Queens Quay continue to build out the planned 23-hectare development, which is expected to create 1,000 private homes, 200 rented homes and the associated infrastructure to support them, more residents and businesses will benefit from this sustainable city heating network that could serve as a model for communities across the country.
