The retrofit, which will include 6,500 better insulated windows, as well as high-tech lighting, furnaces and air conditioners, is expected to reduce the building's energy use by almost 40 per cent.

“You have one of the marquee buildings in the United States demonstrating an old building can increase its energy efficiency,” says Branko Terzic, energy and resources regulatory policy leader for Deloitte, the consultancy.

Such high-profile efforts are helping to make energy efficiency “cutting edge”, according to Mr Terzic.

The global potential for energy efficiency is vast.

This year, McKinsey calculated that in the US alone an investment of $520bn would cut non-transportation energy in the country by 23 per cent of projected energy demand – which would save the US economy more than $1,200bn.

Japan and western Europe are more efficient, but still have hundreds of billions of potential savings, while fast-emerging economies such as China and India have typically grown without much regard for efficiency until now.

Energy efficiency is benefiting strongly from the government stimulus packages globally, many of which single out efficiency as a key target for spending. Of a total of $350bn so far allocated to green endeavours under the stimulus packages, the energy efficiency sector is due to receive more than half.

Little wonder, then, that energy efficiency stocks have been outperforming not just the market, but other clean technology stocks, according to recent research from HSBC.

Energy efficiency and energy management specialists enjoyed the strongest sectorial return in clean tech, up 16 per cent on the first half of the year, according to HSBC.

The sector is exceptionally broad, encompassing software start-ups, engineers, management consultancies and a host of multinational manufacturers.

Ian Simm, of Impax, a green investment company, points to companies such as Ricardo, which offers energy efficiency services to the automotive industry, and Kingspan, a maker of insulation materials, as being particularly high profile within the sector.

A look at another refit of a landmark building reveals some of the range of products that come under the energy efficiency banner.

Evolve Energy has been recruited to cut energy use at the Savoy hotel in London, replacing old boilers and heat transfer equipment.

It will introduce ultra high-efficiency hot water and heat recovery systems, low-energy air conditioning, intelligent building controls, insulation, glazing, more efficient appliances, smart metering and 24-hour monitoring and targeting of energy use.

A single supplier of energy efficiency products can also span dozens of client industries. Alfa Laval of Sweden has long made improving customers' energy efficiency a focus. Recent customer projects include a new brewery in Hyderabad for Asia Pacific Breweries, the first in India to incorporate an energy-saving high-gravity brewing line technology.

Relatively few of the companies involved in energy efficiency are “pure plays”. Companies such as General Electric, Honeywell, Siemens, Philips, Johnson Controls and ABB have strong interests in the sector through activities as diverse as lighting products, building controls and more efficient appliances.

Many companies involved in energy efficiency implementation are likely to be winners from the renewed focus on energy efficiency in the stimulus packages.

In the US, for instance, President Barack Obama has pledged to spend stimulus funds on making government-owned and other public buildings more efficient.

Chevron is the only oil major to offer an energy-efficiency service and has carved out a niche serving the US public sector, improving efficiencies at places including public schools, military bases and federal government offices.

Furthermore, new government regulations in some parts of the world are also expanding the market.

For example, the European Union has decided to phase out incandescent bulbs in favour of energy- efficient models, transforming the market at a stroke.

Michael Weinhold, chief technology officer for Siemens Energy, points out that lighting accounts for 17 per cent of worldwide energy consumption, making it a big source of greenhouse gas emissions.

Philips sees a large new market in LEDs, which are much more efficient than conventional lighting.

By the end of this year, the worldwide market for inorganic LEDs in business and residential applications is expected to be worth $4.5bn, more than triple its value in 2005.

In the UK, the introduction of a new regulation – the Carbon Reduction Commitment – from next year is likely to encourage the owners of commercial premises to make buildings much more efficient.

Shops, public buildings, leisure facilities and some offices will be among the more than 5,000 companies to be covered by the new rule, which will reward companies for cutting their energy use and penalise them if they fall below their industry benchmark.

As travel budgets have shrunk, another set of winners from the increased focus on energy efficiency include companies with video conferencing technology, such as Cisco, HP, Intel and Polycom. These companies are now marketing their wares as a “green” alternative to air and road miles.