Monday, April 30, 2018

United Kingdom: More Details on Bath Geothermal District Heating Project

Bath Abbey’s geothermal floor (Designing Buildings)

The Roman Baths with Bath
Abbey in the background.
Photo by Ian Crawford (2017)
The Roman Great Drain is a key to the Footprint project. It carries waste water from the hot springs servicing the Roman Baths complex to the River Avon nearby, passing right through the Abbey’s south courtyard. This provides an opportunity for the Abbey to use a natural energy source that will reduce its energy cost and carbon footprint.

The drain has a flow rate of 14–15 litres/second of natural hot water at a constant temperature of 45°C. This is well within the 35–55°C for a typical modern underfloor heating system of the low-temperature hotwater type, producing an output temperature of around 23°C on the floor, and an inside air temperature of 20°C. Unfortunately, the thermal spring water is far too caustic to use directly in the underfloor heating system, as it contains over 42 different minerals and particularly high levels of sulphates and chlorides.

The plan is to raise the water level in a section of the drain using an internal weir. Corrosion-resistant heat exchangers in the flow of the drain will extract the heat, using water-source heat pumps to warm the closed flow loop of the underfloor heating system. Although the output is not sufficient to run the whole system, it will enable a significant reduction in the current gas bill. Tests were carried out in February 2016 to ensure that the new weir would not have any adverse effects on the hot water supply to the Roman Baths complex.

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