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Towers of comfort

technical & practice: Wind towers are emerging as part of the architectural roofscape. Battle McCarthy has produced a guide BY BARRIE EVANS

Wind Towers* is a state-of-the-art guide to using towers for cooling buildings. Though published in Academy Editions' Detail in Building series, the guide offers a large measure of practicality as well as the normal visual inspiration. Though a few illustrations appear to have suffered in the printing, the guide is well illustrated and written in an architect- friendly way.

Wind towers are presented as a means of reducing reliance on mechanical ventilation and air conditioning. Wind scoops also get a look in; stack- effect ventilation appears only as part of hybrid systems with wind towers. This focus on one technological solution rather than a functional design topic - such as overall passive cooling or ventilation - arises because the guide is a by-product of research exploring the

use of wind energy for ventilation. The research project by Battle McCarthy and Imperial College Aeronautical Department was partly funded by detr.

Designers are reminded of the wider picture, of ways to use building form and shading to limit heat build-up. These are usually crucial since wind towers are rarely likely to provide a surfeit of cooling. In some cases hybrid systems will be needed, with mechanical ventilation or cooling provided for the most demanding times of the year or parts of the building.

In general, a wind tower is an air-extract flue, open at the top though with some rain protection. Thus it functions for all wind directions. The air inlets to the building may be windows, grilles, concrete pipes or labyrinths in the ground (to pre-cool the air) or wind scoops. Scoops are flues with cowls that point into and catch the wind. Traditional ones were often fixed in direction; but rotating ones aligned by wind vanes make better use of variable uk wind directions. Scoops funnel the wind, so introduce it at relatively high velocities. Thus they work best for high-ceilinged, large-volume spaces. This air movement can give some sense of contact with outside conditions. The malls of Bluewater Shopping Centre at Dartford are a recent example.

Towers in context

Having described the basics of wind in climatic design and illustrated traditional precedents for differing climates, the guide goes on to discuss design issues, such as:

climate and microclimate, how the wind blows, using stack ventilation when its doesn't, noise and air pollution

form, fabric and layout to limit heat gains and allow easy air movement

smoke extract and compartmentation

security, notably leaving inlets open for night-time ventilation

simple controls, which may include dynamic regulation of inlet areas

weatherproofing tower tops - a problem not fully resolved

flexibility, for example, the effects on air movement of future cellularisation, or the system's capacity to deal with increased it heat loads

cost implications such as reduced plant and plant space, simple technology, simple controls (except for hybrid systems), reduced operating and maintenance costs.

One issue not touched on is any extra cost of design time for these novel systems.

The guide finishes with 16 brief case studies, mostly projects in progress. Disappointingly, no performance data are given. There are no cases yet of attempts at retrofitting towers to buildings.

Wind towers are not yet mainstream technology, but this guide should help them on their way.

* Wind Towers: Battle McCarthy Consulting Engineers. Academy Editons: Detail in Building series. From John Wiley & Sons. 95pp. £19.99.

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