The UK's first geothermal energy and combined heat and power (CHP) district heating and chilling scheme in Southampton City Centre is ensuring it maintains its environmental credentials by using state-of-the-art electronic descaling instead of chemicals to remove scale build-up from its chillers and cooling towers.

Launched in 1986, Southampton Geothermal Heating Company's £4 million multi-source heating and chilling scheme generates 7MW of electricity per hour to supply 20 major consumers in the city centre as well as the newly opened West Quay shopping centre, the largest of its kind in Europe.

Following the dramatic rise of oil prices in the late 1970s, the Department of Energy set up a research programme looking into the potential for alternative energy sources in the UK, particularly wind, wave and geothermal energy. At one such site, located at Marchwood power station on Southampton Water, the Department of Energy began drilling a well, hoping to test geothermal resources held in the Wessex basin.

Following these initial successful trials, the Department of Energy, working with Southampton City Council and the Energy Technology Support Unit, drilled a further well in the centre of Southampton. Within this well, water was found at a depth of nearly 1,800 metres and at a temperature of 76°C. The size of the resource was deemed too small to develop by the Department of Energy, but the City Council refused to let the project fail and eventually found Utilicom, a French-owned energy management company, as a partner with whom to develop the scheme.

The original well, which currently provides about a fifth of the system's heat input, now operates alongside combined heat and power generators. These use conventional fuels to make electricity, with the waste heat from this process being recovered for distribution through the 11km mains network.

The domestic heating scheme in Southampton, which helps reduce its customers’ energy bills by 25% and the City's CO2 emissions by 10,000 tonnes a year, closely resembles a huge domestic central heating system.

Hot, treated water circulates underground from the heat station to a growing number of customers in the city centre and is then returned for reheating. Power for the downhole circulation pumps and plant is generated at the heat station by CHP. The heat from the CHP generators is fed into the district-heating scheme with surplus power being sold to the National Grid.

Since the pioneering launch of the initial geothermal project in 1986, Southampton's district heating scheme has grown dramatically, primarily due to the use of up-to-the-minute technology, which has included the use of a Wartsila 5.7MW multi-fuelled CHP generator.

In 1994 the company decided to use waste heat from the CHP generators to provide chilled water for air conditioning. Initially connected to the five-star De Vere Grand Harbour Hotel, the scheme was expanded in 2001 to include the city's leisure centre, West Quay development and the BBC studios.

A water softener was used to control scale in the first chilling system installed. However, with a tonne of salt a week being used at a cost of £250, when the chilling scheme was extended four-fold, the company decided to source an alternative means of preventing scale. This was done for cost-saving as well as operational reasons, as the softener could not keep up with peak demand of 100 Tons of water per day, resulting in the system scaling.

ScalewatcherTM ENiGMA units were fitted onto five linked cooling towers, used in the condensers of six 500 Ton Chillers. After a few weeks one of the chillers was opened for the first time in 12 months and found to be completely scale free.

" We would have expected to see some residual scale on the chillers and inlet pipe, but both were completely clean," said Mike Zorab, Engineering Manager. “ Since then the chillers and cooling towers have remained scale free, resulting in reduced maintenance and downtime and less power being used. The units will provide us with a payback within 18 months based on savings in salt alone."

"This was an exciting and fascinating project," said John Thompson, Managing Director, Environmental Treatment Concepts. "We have worked very closely with Southampton Geothermal Heating Company to ensure the Scalewatcher ENiGMA worked successfully, visiting the site on a weekly basis to check and monitor unit performance.”

Plans have now been drawn up to increase the district heating and chilling scheme to encompass the redevelopment of Southampton Football Club's old ground at The Dell and a new Barrett Housing development at the former site of the Polygon Hotel. The Barrett Homes project consisting of 108 private residential flats will be the first private housing in the UK to use district heating.

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