CASE STUDY | BATH ABBEY Bath Abbey heat recovery strategy Map showing the course of the Great Drain and the position of the energy blades where energy will be recovered from the hot spring water The drain is 7m below street level and difficult to access, so engineers must have had confined-space training A similar heat recovery system at the Roman Baths must not reduce the visible steam during the design stage involved the study of water flows and temperature; the installation of a mock-up pair of heat exchangers; and the installation of a mock-up weir to raise the water level in the drain sufficiently to submerge the heat exchangers while not flooding the upstream Roman Baths. Testing was done in the winter, when river levels were high. The river backed up the drain, and there was some dilution of the hot spring water in the drain, but without impact on the energy blades. Great Drain and heat exchanger Heat exchanger pipework to rise up into Abbey vaults Entrance to dry section York Street access manhole Great Drain main flowing channel Heat exchanger pipework on side wall of drain Energy-blade heat exchangers submerged indrain Ten pairs of energy blades will recover heat from the drain in closed loop Weir plate to raise water level Not to scale Because of the amount of silt in the spring water, the weir had to be designed to avoid the build-up of mud, and the final design allows for both overflow and underflow. The site chosen for the energy blades was in a straight section of drain, around 1.8m high, that offers access via York Street. The drain at this point has a raised walkway ledge running above the flow of the water (see image on page 47), but because the drain is 7m below street level and difficult to access, maintenance engineers must have confined-space training and be lowered by tripod into the drain. At this point, the temperature of the water is 35-37C and the extraction of the heat will cause it to drop by 5C. The water is calculated to enter the Avon at 30C (see map, above). The pipework and fixings installed in the drain connecting up the energy blades will be in reverse return arrangement and will be made from stainless steel to prevent corrosion. Fixings must be kept to a minimum to avoid damaging the Georgian walls in the drain, and the pipework while following the contours of the drain must not protrude so far that it stops engineers from accessing the ledge running alongside the water. The project design started in earnest in 2010, and on site in summer 2018, and should be completed in 2020. Heat-recovery works in the drain should begin early this year, with heat recovery starting later in 2019 to allow for commissioning and fine-tuning. Calculations for heat recovery from the Great Drain took into account the fact that a similar system also being worked on by BuroHappold is being designed for the Roman Baths. The challenges are similar to the Abbey project, but with the added requirement that the steaming effect in the hot bath is not lost when heat is recovered from the spring. It is calculated that taking out 80kW of heat will supply buildings at the Roman Baths with background heating at night and some mid-season heating, while having a negligible visible effect on Baths world-famous steaming baths. CJ 48 February 2019 www.cibsejournal.com CIBSE Feb19 pp46-48 Bath Abbey.indd 48 25/01/2019 16:17