Heat pumps extract warmth from cold water

The residents of Drammen have rather an unusual way of keeping warm.

The county capital, 40 miles west of Oslo in Norway, extracts most of the heat needed to insulate its houses, offices and factories against the biting Nordic cold from the local fjord, or more precisely from the water held within it.

Averaging 8C throughout the year – it’s literally cold enough to take your breath away. So cold, in fact, that open water swimmers classify it as freezing.

But somehow, an open-minded district heating company, backed by an environmentally-conscious city council, together with a large measure of Glaswegian nous, have built a system to meet the heating needs not just of Drammen’s 65,000 residents, but its businesses as well.

How the Drammen heat pumps works

  • Water from the fjord at 8C is used to heat liquid ammonia at four times atmospheric pressure (4 bar), till it boils at 2C and evaporates
  • By increasing the pressure to 50 bar, the evaporated gas is heated to 120C
  • The gas is then used to heat the water in the heating system from 60C to 90C (the water goes out of the plant at 90C and comes back in at 60C)
  • Once the heat has transferred to the water, the ammonia gas changes back into a liquid state
  • The process begins again

Source: BBC