The district heating system extracts energy from seawater to deliver more than 13MW of heat to Drammen, a community of around 60,000 people living on the Drammen Fjord, near Oslo. Hot water is pumped to several thousand homes and businesses in the city through a network of underground pipes.
The heat pump system, supplied by Star Refrigeration of Glasgow, uses heat from the seawater to raise the temperature of an ammonia refrigerant via a heat exchanger. The now-gaseous ammonia is then compressed by the motor-driven compressors, raising its temperature to around 90°C. This heat is transferred to the hot water supply via another heat exchanger.
The ammonia compressors are powered by six ABB 11kV motors – three rated at 1.25MW, and three at 660kW. The motors, which are usually air-cooled, have been fitted with air-to-water single-tube coolers. To optimise the cooling of the motor while delivering the best heat output, the cooling water contains 30% glycol.
Three of the ammonia compressors and their 11kV motors
Water enters the coolers at 30°C. Every hour, about 3.1m3 of water is fed into the 1.25MW motors, and leaves them at 46°C. The 660kW motors have an inflow of 2.8m3 per hour and they raise its temperature from 30°C to 42.2°C.
The motors have to handle frequent starts and stops to accommodate the varying heating demands during the day and year.
