The district heating scheme in Southampton 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 re-heating.
Hot brine from the geothermal well today provides only 18% of the total district heating mix. Fuel oil (10%) and natural gas (70%) account for the remainder.
Southampton's well is more than a mile deep. The temperature of the water is 76°C at its source and two degrees less by the time it reaches the surface.
The water rises naturally in the well to within 100 metres of the surface. It is then pumped to the heat station. The hot brine is passed through a heat exchanger, working in conjunction with an absorption heat pump. The heat exchanger transfers the heat to clean water. The cooled brine, at about 28°C, runs out to the sea.
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. Surplus power is sold to the National Grid.
The schematics show how we provide heating and chilling from a variety of energy sources.
At the heat station, heat transfers from the brine to the hot waterheat distribution system.
The station houses the heat exchanger, brine and water filters, heat distribution pumps, a CHP generator to meet the systems electricity demand, plus control and data monitoring equipment.
During periods of exceptionally high demand, extra heat can be provided by back-up boilers.