A pump which heats freezing water to 90˚C to warm buildings in Norway has saved a total of €8 million (£5.7m).
The technology, which was manufactured in Glasgow, has been installed in the city of Drammen.
Professor Paul Younger from the University of Glasgow worked with Star Renewable Energy to install the system.
He said: “This impressive zero carbon district heating system provides an inspirational example which has ignited enthusiasm for the potential of water-source heat pumps worldwide.”
It supplies more than 75% of the annual heat demand of the city of Drammen which is home to 63,000 people.
Jon Ivar, CEO of Drammen Fjernvarme AS, said: “With total savings of €8 million (£5.7m) and overall carbon savings equivalent to driving 8,320 times around the globe, the Drammen Fjernvarme water heat pump represents a new era of sustainable heating for our cities.
“Aside from seeking lowest cost, we believe the new heat pump is the cleanest possible solution and we are delighted in just four years to have delivered 200GWh of clean heat.”