The town of Drammen in Norway heats most of its buildings with water that is at a temperature of just 8oC. The secret? Heat pumps. If they can do it, why don't many more towns copy them?

Heat pumps work by concentrating the heat from a large volume of water into a smaller volume, thereby (if you can recall Boyle's Law from your school physics lessons) increasing its temperature.

Dramman (pop. 65,000) sits alongside a fjord that is too cold to swim in. But the water-source heat pump technology still works very economically, feeding the heat into a heat main that connects to many of the town's buildings' central heating systems.

The company which installed some of the system, Star Renewable Energy, based in Glasgow, says that its success speaks for itself. It is pushing to build similar installations in other towns and cities throughout Europe.

Most heat pumos sold in the world are ground or air source. But water source is at least as reliable as ground source, if a nearby watercurse or body of water is available, because water holds heat well and is commonly at a higher temperature than the land and air when the heat is most needed.

Sustainable Cities Collective has previously reported on two other schemes: a 2MW installation at Kingston Heights on the River Thames in London and a 300kW one at Plas Newydd on the Menai Straits in north Wales.

District heating

The UK's Department of Energy and Climate Change has published a map of the water source heat pump resource potential in the UK and has recently offered grants from £16,000 to £263,000 to 74 municipalities to build low carbon district heating mains.

The successful local authorities will be offered to help set up their projects. The government's Heat Networks Delivery Unit has been providing grant funding and expert guidance to local authorities since 2013.

Government estimates show that around 15 per cent of UK heat demand could be cost effectively met by heat networks by 2030 and over 40 per cent by 2050.

The 74 new heat networks will bring the total number of heat network projects benefitting from government grants to 180.

District heating systems are inherently more efficient, once installed, than each building having its own heat generation boiler.

How the Dramman system works

A 45MW district heating system serves over 200 large buildings in the city. The heat was originally from a mixture of fossil fuel and biomass but a new system was designed to make a large heat pump the primary source.

This draws 75% of the network heat from ammonia heat pumps with 15% from biomass and 10% from gas/oil.

The fjord water is used to heat ammonia, at four times atmospheric pressure, till it evaporates (at 2oC). The pressure is then increased to 50 tmes atmospheric pressure (50 bar), bringing the gas to 120oC.

The heat is transferred via a heat exchanger to the water in the heating system, which (returning from the district heat main at 60oC) is heated back up to 90oC and sent round again.

The ammonia returns to a liquid state and begins its own cycle over again.

The pumps are driven by electricity, but the whole system produces three times more energy than is put in. If the elecricity comes from a renewable source then the system is zero carbon.

The Dramman system has paid for itself very quickly and now saves the town around €2m and 1.5m tonnes of carbon emissions a year.

Star is now working with housing associations in Glasgow and projects in Zurich and the South of France, and bidding for a system in Belgrade. It is in negotiations with around twelve English local authorities including Newcastle, Durham, Manchester and Stoke.

Prof Paul Younger at Glasgow University, who was behind the Thames heat pump system, can't understand why the technology has not caught on more widely. It's not new, it just doesn't get the press that wind or solar get.