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Driving ammonia compressors for an innovative heating solution
TWO LOW VOLTAGE MOTORS and low harmonic variable speed drives (VSDs) from ABB have been specified to drive the compressors for a new heating system which is set to transform the way homes, businesses and public buildings in Clydebank, Scotland are heated.
The District Heating Network is the first high temperature (80°C) water source heat pump (WSHP) system in the UK. The system works by extracting water from the River Clyde to generate heat for buildings on the Queens Quay.
The two 2.65 MW WSHPs have been designed, manufactured and installed by Star Refrigeration in Glasgow and are part of the company's Neatpump range. The renewable energy heat pump extracts heat from the river's water by compressing the ammonia refrigerant in a high-efficiency screw compressor. ABB's motors and drives are used to power the ammonia compressors, each rated at 836 kW. Applying variable speed control makes it possible to increase screw compressor capacity by overspeeding up to 60 Hz. The compression process raises the water's temperature before releasing the heat via a heat exchanger to a district heating loop at up to 80°C. Pumping water through a network of underground pipes provides heating for several hundred homes and businesses in the area.
Dave Pearson, Group Sustainable Development Director for Star Refrigeration, said: "Harnessing heat from a river is easy. We simply utilise the thermodynamic principles used in fridges but with a focus on the heat produced. The hard work comes from doing this with the minimal amount of energy input from the electric motors.
"ABB supported our analysis of dozens of data points to ensure we had the maximum flexibility, control and efficiency. This will be even more important when we modulate electricity demand to help balance the grid; offloading in times of under generation and increasing demand to reduce the amount of wasted generation known as curtailment."
Most usefully, the VSDs reduce the starting current. Low harmonic VSDs were chosen to minimise harmonic interference on the mains supply. The VSDs exceed the requirements of EN 61000-3-12 and IEEE519 and offer genuine unity power factor with no compensation needed, thereby avoiding reactive power penalties. In addition, the standalone design of the VSD gives it a small footprint, minimising space requirements in the control panel.
