Researchers have devised a technique that extracts heat from water leaking into the Glasgow Subway tunnels

New heat pumps will be installed by the end of March at two stations on Glasgow's Subway network after researchers spent nearly 18 months looking for ways to turn the waste water which leaks into the Victorian tunnels into an energy-efficient power source.

Humid air which collects in the tunnels will also be captured as used a heat source as part of the same pilot scheme, to test which method is more effective.

St George's Cross and Bridge Street stations will be the first to trial the technology, which will pump heat into the stations' ticket offices.

If successful, the devices could eventually be rolled out across all 15 stations on the six and a half mile loop.

The pumps have been developed by geotechnical specialists at Glasgow Caledonian university who were tasked with finding methods to extract heat from the waste water, which averages temperatures of 10-14ºC.

The technique, which is already a fairly common method for providing ground-source heating for homes, has the potential to cut both heating and maintenance costs and reduce disruption for passengers.

The 119-year-old underground is the world's third oldest after London and Budapest, which have also attempted to develop similar technology.

The Glasgow Subway is vulnerable to water ingress because it intersects the city's two rivers.

The River Clyde cuts diagonally across the subway, between Patrick and Govan stations to the west and St Enoch and Bridge Street to the east, while water also leaks in from the River Kelvin which bisects the subway at Kelvinbridge station.

The tunnels vary in depth between seven and 115ft below the Clyde's high water level.

As the soil surrounding the subway is made up of silt, sand and gravel it is impossible to prevent rain and river water soaking through, forcing the operator to continually pump water back out to prevent the tunnels from flooding.

Konstantinos Ninikas, a renewable energy engineer, is part of the team developing the heat pumps.

He has worked alongside Professor Rohinton Emmanuel and Bjorn Aaen, under the supervision of Dr Nicholas Hytiris, to analyse all 21 sumps in the tunnels and monitor the water flow and water temperature.

Since June last year, the researchers have also been taking measurements for the air temperature, air humidity and air flow along the network.

He said: "We're trying to get the air at a relatively stable temperature and we pass it through the heat exchanger - this is the pump - to try to exploit this relatively high temperature and produce heating.

"We're planning to do one installation with water as the source, and another installation using the air that there is inside the Subway tunnels which is a relatively stable temperature throughout the year.

"Part of this heat exchanger will be inside the Subway tunnels, in a place where it will absorb the water or the air, and the mains unit will be installed in an area inside the ticket office which is where the heat will be pumped out.

"The hope is it will improve the overall efficiency, and reduce the maintenance costs."

The £130,000 study, which has been partly funded by Subway operator Strathclyde Partnership for Transport (SPT), is expected to deliver its first results by the end of May.

Gordon Maclennan, SPT Chief Executive, said: "We are delighted to be working with GCU on this important trial. The potential of exploiting waste water in Subway tunnels to turn it in to power is very exciting. Until now, work has focused on analysis and study. However, in the longer term we hope to improve overall energy efficiency, reduce maintenance costs alongside a sustainable source of energy in the Subway system so this is just the beginning."

Yen Pham