January 2022

30 n VARIABLE-SPEED DRIVES January 2022 www.drivesncontrols.com How the Clyde is heating 1,200 homes I n a pioneering project, two large water source heat pumps (WSHPs) are extracting heat from the River Clyde and feeding it to more than 1,240 homes and businesses in the area. This district heating network is the first and largest high- temperature (80°C) WSHP system in the UK. It received £6m of government backing via the Low Carbon Infrastructure Transition Project. The Clydebank project is located on the site of the former John Brown Shipyard, now known as Queens Quay. It is being developed byWest Dunbartonshire Council, with Vital Energi as the main contractor. In its first year, the scheme is expected to cut CO 2 emissions by 409 tonnes, rising 1,903 tonnes when the project is completed, and an expected 5,705 tonnes a year by 2040 as a result of the grid being decarbonised. The scheme will cut CO 2 emissions by more than 90% compared to burning gas, as well as eliminating NOx emissions. The hot water is pumped through a network of insulated underground pipes to heat 1,000 private homes, 200 rental properties and businesses spread over a 23 hectare area. “Harnessing heat from a river is quite easy,” says Dave Pearson, group sustainable development director at Glasgow-based Star Refrigeration, which designed, manufactured and installed the two 2.65MWWSHPs at the heart of the project.“We simply utilise the thermodynamic principles used in fridges but with a focus on the heat produced. Where the hard work comes is doing this with the minimal amount of energy input from the electric motors.” The two heat pumps will deliver most of the area’s annual heat demand. It is estimated that for around 25 hours in a typical year, a peak demand of 20MWwill occur, and this will be met using a combination of a thermal store – which captures excess heat from theWSHPs and releases it when needed – and backup gas boilers that can deliver 15MW of heat. During the summer, when demand is low, one heat pump can be taken offline for scheduled maintenance, while the other continues to operate. The scheme extracts heat from the river water – which normally has a temperature in the range 6-12°C – by compressing an ammonia refrigerant in a high-efficiency screw compressor. The compression process raises the water temperature before releasing the heat, via a heat exchanger, to the district heating loop at up to 80°C. Each property connected to the network will have an hydraulic interface that looks like the traditional boiler which it replaces. Occupants and landlords will be able to turn on heating and hot water when they need it, and can monitor the amount of energy they consume. They won’t need to worry about servicing or repairs. Older buildings need input temperatures of around 82°C and return the water at 71°C. They are being retrofitted with updated controls and, in some cases, larger radiators. New buildings will be designed from the outset for 75°C inputs and 45°C returns. The compressors are driven by IE4- efficiency motors rated at 836kW, controlled by VSDs which can boost the compressor capacity by over-speeding up to 60Hz. ABB supplied both the motors and the low- harmonic VSDs, which were chosen to minimise interference on the mains supply. The VSDs exceed the requirements of EN 61000-3-12 and IEEE519 and offer unity power factor with no compensation needed, thus avoiding reactive power penalties. The standalone design of the VSDs results in small footprints, minimising space requirements in the control panel. “ABB supported our extensive analysis of dozens of data points to ensure we had the maximum flexibility, control and efficiency,” says Pearson.“This will be even more important when we modulate demand for electricity to help balance the grid; offloading in times of under-generation, and increasing demand to reduce the amount of wasted generation, known as curtailment.” The VSDs are a key element in this grid- balancing scheme.“The really great thing about this heat pump is that we can deliver around six times as much heat as if the electricity was converted into hydrogen for combustion,”Pearson reports.“No one should squander scarce resources.” n In the UK’s first large-scale water-source heat pump scheme, energy is being extracted from the River Clyde to heat more than 1,200 homes and businesses. The scheme is based on two 2.65MW ammonia heat pumps controlled by high-efficiency motors and VSDs. The Clydebank water-source heat pump scheme is using low-harmonic VSDs to drive the compressors without causing interference in the mains supply.