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Special report: energy

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We are coming to terms, belatedly,with the need for energy efficiency, but too many buildings pay only lip service to the idea

And so farewell to the twentieth century - man's most consumptive hundred years ever. Buildings now consume 50 per cent of all energy used globally. The last 20 years have seen 12 of the hottest years on record. Global warming is now a fact.

Buildings consume 50 per cent of the energy used globally. We cannot avoid the realisation that our methods and outlook will have to change soon if resource use and the associated poisoning of the atmosphere are not to prove our nemesis.

There is an important argument that the main priority for improvements in the developed world to should be to existing property stock but, despite the small scale of new build's contribution to the existing housing stock, it must be designed with CO2 reductions in mind.

It was not until the late 1920s that the opportunities afforded by the invention of mechanical refrigeration liberated architects from the responsibility for producing well-tempered environments. But it was not until the 1970s that energy began to rise up the design agenda.

The conservation era came and went as fast as the oil-price squeeze and now the issues are toxicity and co2 emissions. Now we are at a new watershed as building technology adapts to the electronic age.

Are there inventions that will revolutionise energy use in building in the twenty-first century in the way that happened in the 1920s? Will carbon taxes, the development of Global Emissions Trading or some far-sighted government initiative generate ways to fund the technical innovation that is within our grasp but beyond the cost plan of most projects?

In Germany and Scandinavia the Building Regulations framework enforces efficient use of energy by setting high standards for new building and renovation. The cost of implementation is borne by the private sector but this approach at least eliminates complications of the split incentives that are the issue with house-builders and speculative office developers when considering energy-efficiency measures (they do not pay the running costs so there is no demonstrable cost benefit). The uk regulations, though greatly improved in the 1990s, still lag behind much of Europe.

There are a growing number of low-energy and high-efficiency buildings designed in the uk. But high-efficiency buildings are by no means a universal objective in any sector, and the continued development of the type still requires inspired patronage.

There is also a trend to label buildings as green when they are manifestly not - for example, buildings with glass facades. A big part of high-efficiency design is the balance and optimisation of glazed areas in facades, to optimise daylighting, glare, heat loss and heat gain - this process would never yield a building where the walls are made completely of glass, no matter how many layers or how well shaded. Adding a heating system that runs on a biomass fuel and cooling through heat pumps and boreholes does not make the building green, it is merely presenting an alibi for the poor performance of the building.

Two distinct approaches can be identified in the movement for more energy- efficient buildings. The advocates of natural ventilation believe that all fans are bad and must be avoided, no matter the architectural gymnastics. Reyner Banham would have categorised this approach as 'selective', but it does preclude the use of heat recovery, eliminating the benefits of recycling internal gains.

An alternative approach is to apply 'Factor 4' type reductionist methods using low-power occupancy-responsive systems with either room coupled or de-coupled thermal storage, evaporative cooling and heat recovery in an optimised building envelope to provide better performance and lower energy use than the natural option.

Next, get rid of common practices in sizing networks, and use energy requirements rather than noise or pressure drop to determine pipe and duct sizes. The power required to drive water around buildings varies as the inverse third power of the diameter. A 10 per cent increase in diameter reduces friction by 25 per cent; a 50 per cent increase reduces it by 70 per cent. This is for the whole life of the building and at a very small increase in capital cost. The effect is the same with air ducts.

If a duct sized at 450mm deep and an aspect ratio of 4:1 has its depth increased to 600mm, with a commensurate reduction in velocity, the pressure drop required to drive the air through the duct is reduced to just 18 per cent of the original. If this is carried through the network, a six- fold saving in fan power will be achieved. Add variable speed drives so that fans only run at full power when absolutely necessary and even greater savings can be achieved.

Evolution of design tends to be slow because much of the market replicates systems that work. It does not test them for efficiency and there is an unwillingness to take a commercial risk to develop new products. But the simple changes described above can be applied as easily to a speculative four-pipe fan-coil office building as to a state of the art low-energy building for only a small additional cost. Thus the previously 'exclusive' buildings can be nudged towards the 'selective'.

The trend in high-efficiency building design is generally towards better insulated and thermally massive buildings with balanced daylighting and flexible solar protection. A new generation of responsive cladding materials must emerge, integrating some photovoltaic or generating capability, which will herald a new breed of intelligent building that absorbs less and produces more, while achieving its prime objective - comfort and facilities for the humans within.

Patrick Bellew is an environmental engineer and founding director of Atelier Ten

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