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Every lining has a cloud

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In our monthly round-up of technical issues we look at ways of harnessing the elements and keeping them at bay

In one of the most remote parts of the world - the mountainous desert village of Chungungo in Chile - the local peasants are developing new ways of obtaining water.

For years, locals have had to truck in water from distant wells, often containing hazardous pollutants. Today, a simple technology supplies villagers with two or three times more water than they once used, in a purer condition and at a lower cost.

The solution lies in the persistent, extensive cloud cover (camanchacas) along the coast of Chile.This creates continual fog cover over Chungungo as the prevailing winds move inland across the mountains.

It is not really the peasants who have developed the technology, but rather Chilean and Canadian scientists, backed by International Development Research Centre (IDRC) funding.

It comprises stretched polypropylene mesh between two posts - like an oversized volleyball net. As the fog passes through it, water droplets form on the mesh, which run down into gutters that feed a reservoir and network of pipes in Chungungo.

More than 80 mesh collectors supply Chungungo, providing an average total of 10,000 litres of water per day.This figure is set to increase year on year as advances are made in the fogcatching technology.

This technology is best suited to areas which are consistently foggy and where the fog can be intercepted on land. Fog should occur during the season when water is most needed. Five other conditions are important:

a mountain range with an average altitude of 500m or higher;

the principal axis of the range should be perpendicular to the prevailing wind (this increases the amount of water collected);

the water collection site should be as close as possible to the user community;

a broad basin on the other side of the mountains, where high daytime temperatures help to draw the ocean air through the mountains is desirable; and there should be prevailing winds of constant direction throughout the year.

Back in Chungungo, water once brought in by truck has been replaced entirely by fog water. Since the mesh collectors began operating in 1992, water availability has exceeded local expectations. The technology has enabled them to increase their consumption from about 15 litres per person per day to 33 litres (by comparison, in the Northern Hemisphere we each use an average of 340 litres of water a day).What's more, there is now enough water to grow vegetables for local use and sale, increasing the health and income levels of the residents.

For more information contact Professor Pilar Cereceda at the Instituto de Geografia, Pontificia Universidad Catolica de Chile, Santiago, Chile tel 00 56-2-552 2375 (extension 4721) or email dcereced@ws13.crisol.puc.cl

For those of you who have not bothered to specify roof-mounted solar panels because you do not think they will get past the planners, Solar Century has developed a product which might help, writes Austin Williams. These are slate-sized solar photovoltaic modules that can be integrated into the traditional roof pattern.

'Looking at these slates side by side with traditional roofing materials you will be hard pressed not to prefer solar slates on aesthetic grounds alone, ' says the company.

It is hard to see a hardened planning officer falling for that one, however.

It might be worth trying it on, though - the slates are a great advance on the monstrous carbuncular solar panels that commonly bespoil the architecture of the eco-friendly.

The slates are installed and connected in the standard manner and can be wired for grid-connected or off-grid applications.

Approximately 10m 2of sunslates will provide 1kW of peak power (800kWhr/yr).

Although the costs are dependent on the particularities of the scheme, this area of sunslates will cost around £500/m (supply only).

Compared with the average supply-only cost of Burlington Westmorland Green slates, for example, at circa £ 93 for 155/m , the photovoltaic cells are not unreasonable, especially when energy savings for the lifetime of their use is considered. However, the appearance of the sunslates compared with the slates at the quality end of the market is totally different. The more complicated installation costs and comparative maintenance costs of the system also need to be factored in.

For more information contact Clare Hawtin at Solar Century on 0870 735 8100.

Air leakages are responsible for up to 40 per cent (typically) of total heat loss through the building fabric and also cause condensation opportunities, so the drive to improve air tightness through the building regulations is a sensible measure. It has always been very hard to determine the how airtight a building is once it has been built. New, handy-sized portable test equipment is now available to provide straightforward test measurements of the airtightnesss of the structure.

Retrotec's infiltrometer exaggerates air leaks through walls, floors and ceilings by pressurizing or depressurizing the building, allowing air leaks to be detected and sealed.The beauty of this system is that it is a small piece of kit, designed to be packed into a suitcase though it opens up into a full-sized unit which is fitted into the frame of a standard external door.

To carry out the test, all combustion appliances are switched off, all other exterior doors and windows are closed and openings such as exhaust fans and flues are sealed. The infiltrometer fan is then switched on. As the fan speed is changed, a series of readings are taken, recording the amount of air passing through the fan and the corresponding pressure created by the fan across the building envelope.

These measurements, along with the volume and surface area of the building and other relevant data, are entered into the computer, which then calculates the relative airtightness of the building in several different ways.With this method the actual air movement criteria inputted into design stage SAP calculations etc, can be tested to determine the SAP rating in use.

To contact Retrotec e-mail Paul Jennings at Retrotec@aecb.net

Legal precedent confirms that contractors and subcontractors have a duty to warn if they consider that there are, what they perceive to be, design flaws within a given package of information (Victoria University of Manchester v Hugh Wilson 1984). However, it has been determined by a recent case that a subcontractor breached his duty by not protesting vigorously enough.

In the case of Plant Construction v Clive Adams Associates, the dispute concerned the issue of the excavation subcontractor's company, JMH, having prepared - in accordance with its contractual obligations - a design for an over-roof. It was ruled that even though the client's own engineer overruled the design in favour of a design subsequently shown to be defective, JMH had an implied obligation to protest more strongly than it did.

The court considered that where JMHwas aware that there was a risk of serious injury by the client's engineer's faulty design, it should have 'protested more vigorously'. Indeed, the court stressed that JMH should have made progressively more formal approaches to comment on the faulty design and to register its concern.

JMH's original design was theoretically safe (though untested).

The fact that it had been overruled in favour of a lesser product was not sufficient defence to discharge JMH's duty. The court held that if JMH had acted properly, it would have insisted upon a safe design and/or refused to carry out works with the revised design.

Hardly a recipe for good working relations!

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