LOW CARBON CASE STUDY THERMAL ENERGY
The approach has been to design and build the energy centres in a modular format to enable plant to be added in the future
HWS cylinder,’ he explains. Making use of the ground to store heating and cooling energy helps to drive up the system’s operational efficiencies. ‘The reversible energy store drives up the coefficient of performance of the heat pump because it helps drive up the temperature difference between the heat pump’s on- and off- temperatures,’ explains Shennan. Further efficiencies were obtained by
designing the heating system to run at lower flow and return temperatures of 45C to 35C, and the chilled water circuits run at a higher flow and return temperatures of 6C to 12C. The majority of spaces in the new
building are mechanically ventilated, so deeper heating and cooling coils have been used in the building’s air handling units to compensate for the reduced flow and return temperatures. Shennan expects other schemes to
utilise ATES technology in the future. ‘The system is at the smaller end of where the technology works,’ says Shennan. He is currently working on a study for a giant 20 MW scheme for South Kensington in London, which includes all the area’s museums, the Royal Festival Hall and Imperial College. The system is not confined to the London basin. ‘The system could also be suitable for Birmingham, which sits on a sandstone aquifer,’ he says. The National Maritime Museum’s system
Top: Plant room showing the prefabricated, skid- mounted unit containing the plate heat exchangers and control valves Bottom: Ground-level chamber for one of the boreholes
‘What happens in our system to enable
those buffers to maintain temperature is a controls strategy set up to deliver hot and cold to the buffers in the best way,’ he says. ‘This means signals to and from the building are minimal’. The ATES system provides all of the
278kW heating and 330kW cooling loads for the new wing. ‘There is a slight imbalance in terms of annual energy with a higher annual cooling demand,’ says Boid. This could have resulted in excess heat being stored in the ground. ‘To overcome this possibility there is a circuit that can reject heat from the ATES system to the
26 CIBSE Journal October 2011
will have to run for a year before the aquifer can achieve its full energy storage capacity. If all goes to plan, it is predicted the ATES will reduce the new wing’s C02 emissions by 21% below 2006 Part L of the Building Regulations. In terms of lifespan for the system, Shennan says it is difficult to be precise. ‘There are very few schemes to compare
this with,’ he says. However, he adds, the boreholes ‘should have a life of a minimum of 30 years but probably longer because the system is reversible, so it self-purges every year’. Which means the public will be able to enjoy Captain Cook’s journals in low-carbon comfort for the foreseeable future.
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