The Appliance of science

It seems appropriate that a museum should turn its building into an exhibit, but putting the nuts and bolts of its inner workings on show might seem more surprising. However, when the museum is one that aims to demystify technology, it is an opportunity not to be missed. This is precisely what London’s Science Museum has done with a new combined heat and power unit in its £45m Wellcome Wing, which opens this summer. The plant has been put behind glass, bright colours added and, hey presto, it has become a children’s exhibit.

Yet providing a draw for young visitors was not the museum’s main motivation. The economic benefits and eco-friendly nature of the new generation of CHP units was what really hooked the museum’s estates team. These units are a cost-effective means of generating electricity from gas because they use heat that is wasted in other forms of generation. By doing this they can cut carbon dioxide emissions by up to 50% and reduce power bills.

Previously, the museum bought power from the National Grid and was heated by the boilerhouse of the nearby Natural History Museum. With the construction of the new wing, however, it decided to review its options. Ove Arup & Partners was brought on board as M&E engineer and the museum plumped for a 600 kW natural gas-fired CHP unit that could generate electricity and provide heating in winter and cool the building in summer. The system will not be confined to the Wellcome Wing: by 2002, it is expected to be serving the whole museum.

The system was supplied by Nedalo, a West Sussex-based firm, which installed a £700 000 CHP unit and chiller but arranged a 10-year deal under which the museum pays only for the electricity generated. Nedalo claims its rates are significantly lower than the National Grid’s.

With the museum spending about £100 000 a year on running its existing 30-year-old heating system, and an estimated £30 000 more if the new wing had used the same system, payback for the CHP unit has been calculated at seven or eight years. And that does not take into account the cheap electricity generated. Running costs will be further reduced because Mobil – a benefactor of the museum – has agreed to supply natural gas at a preferential rate through an agreement with gas supplier Transco.

The natural gas-fired CHP unit is powered by a water-cooled gas engine that drives a generator. Heat is recovered from the engine water, exhaust gases and lubricating oil. The engine will use about 75% of gas input to provide 600 kW of electricity output and 873 kW of heat output in the form of 90°C low-pressure hot water. This will be piped to radiators located in toilets and staircases, as well as to two giant air-handling units that will provide warm air heating.

What makes the system particularly cost- effective is that in summer, the heat generated by the CHP unit will be piped as hot water to a 500 kW absorption chiller that provides chilled water to cool the museum, thereby saving on energy that would otherwise be required for air-conditioning.

To keep noise levels down, the engine is housed in an acoustic enclosure, which means that the noise 1 m away from the enclosure is reduced from 100 dBA to 65 dBA.

Operating 17 hours a day, the CHP unit will generally be self-sufficient, apart from between midnight and 7am, when it will be turned off in favour of cheap-rate electricity sourced from the National Grid. Top-ups may also be needed at peak times. To supplement peak heating demand in winter or in the event of a breakdown, any one of five 800 kW gas-fired Viessman boilers will be activated by the building management system. The conventional heating systems, however, will not be on show.