The world´s largest district-wide natural heat pump system, providing 13MW for Drammen, near Oslo, Norway, has been built using a heat pump package developed by Star Refrigeration of Glasgow.
The system passed its efficiency trials last December 2012, and will now supply hot water through underground pipes, for heating several thousand homes and businesses.
Its heat pump extracts energy from sea water, raising the temperature of ammonia refrigerant via a heat exchanger, explains Dave Pearson, director of innovation for Star.
Gaseous ammonia is then compressed by a motor-driven compressor, raising the temperature of the ammonia to around 90C. That heat is then transferred via another heat exchanger to the hot water supply side.
Six ABB 11kV motors were selected to drive the ammonia compressors – three rated at 660kW and the rest 1,250kW.
“This was a very challenging project and we chose ABB because we needed a partner that could step up to the plate and help us develop some of the technical aspects,” states Pearson.
On recovering waste heat from the compressor motors, he says: “We had never bought water-cooled motors before and we needed someone who could understand our requirements,” comments Pearson.
“ABB had the right attitude and were prepared to use first principals engineering not just standard conditions from a brochure,” he adds.
Usually supplied as air-cooled units, ABB fitted the motors with air-to-water single tube coolers. Also, to optimise cooling and the heat output, ABB specified cooling water with 30% glycol.
As well as the cooling requirements, the motors also had to cope with frequent starts and stops, matching demand as it varies through the day and year.
The 660kW motors have a water inflow of 2.8 m3 per hour and raise the temperature to 42.2C, while the 1,250kW motors have an inflow of 3.1 m3 per hour and raise the outlet water temperature to 46 0C.
Source: Plantengineer Org. UK