Context 152 - November 2017

24 C O N T E X T 1 5 2 : N O V E M B E R 2 0 1 7 of the floor, and illustrate the ineffectiveness of the heating system. The Abbey authorities have a plan: the Bath Abbey Footprint. Its aim is to modernise the welfare and leisure facilities; expand the service and interpretation space; update the rehearsal space for the choir; house the archives; highlight the archaeology; and upgrade the floor and the heating system. Resolving the structural weakness of the floor will require disturbing the underfloor archaeology and human remains, but it also provides justification for introducing a geothermally sourced underfloor heating system.This would bring huge benefits to the Abbey by improving its viability as a performance venue, and reducing its heating costs and carbon footprint. The current Abbey was started in 1499 by Bishop Oliver King, he who supposedly dreamt of angels ascending to and descending from heaven, inspiring the wonderful facade of the west front. It replaced an earlier, much larger, Norman cathedral, begun in 1099 by Bishop John ofTours. Bishop King’s monastic abbey was still unfinished by the Dissolution of the Monasteries in 1539. The city authorities refused to buy it from the crown, so it was stripped and left for ruin, until Queen Elizabeth I supported a project to raise money to repair and rebuild it as the city’s parish church in the 1570s. The Norman foundations remain under the sur- rounding courtyards, where to the south also lies the Roman Great Drain and archaeology associated with the Roman temple and baths complex of the 1st century AD. A separate project from the city heritage services, the Archway Centre,will provide underground interpretation space for the Roman archaeology. 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 hot- water 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. Planning permission and listed building consent for the project were obtained in 2013 from Bath and North East Somerset Council, and work began on the floor of the north aisle as a test phase.The findings and methodolo- gies developed there informed the consolidation and underfloor heating installation for the rest of the floor. The pews were removed from the north aisle, exposing the ledger stones for the first time in 140 years.The stones were cleaned, recorded and photographed by volunteers from the Abbey and from the National Association of Volunteers recording Bath Abbey’s historic ledger stones (Photo: Bath Abbey Footprint)