Passive downdraught evaporative cooling (PDEC) is a traditional means of environmental control that has been used for centuries in parts of the Middle East, notably Iran and Turkey. It operates on the premise of windcatchers guiding external air over porous pots filled with water, inducing evaporation and lowering air temperature before it enters the interior. Recent applications include the 30m high towers at the Seville Expo (AR June 1992) which employed high pressure water misting nozzles to induce downdraught cooling. Compared with air conditioning, the benefits of cooling buildings in this way include lower capital, maintenance and energy costs and the elimination of refrigerant. But the use of PDEC also has architectural implications, especially in the provision of transitional space to circulate the cooled air around the building.
Italian architect Mario Cucinella is a partner in a multi-disciplinary research group exploring the application of PDEC in non-domestic buildings. Funded by European Commission's joule programme, the research aims to investigate how this historic, passive cooling technique could be applied to modern institutional and commercial buildings in the hot, dry regions of southern Europe. Cucinella's work has been consistently informed by a concern for energy use and passive environmental control -- for instance the headquarters for iGuzzini lighting in Recanati (AR February 1999) sought to maximize daylighting and natural ventilation.
The current research programme has studied three main issues: experimentation and monitoring, architectural design studies and building performance assessment. To evaluate environmental performance, Cucinella designed a full-scale experimental rig of a downdraught tower and linked office space. Wind tunnel tests were carried out on different forms of windcatchers to find the most efficient conduit for air flow. The research conclusions were then applied to design studies involving refurbishment and new build projects. These include the hypothetical refurbishment of the Pavilion of the Americas at the Seville Expo site, and two new office buildings for sites in Seville and Catania, Sicily. The latter also exploit another advantage of PDEC for urban locations; since air is taken in at high level, the external skin can be sealed against noise and pollution.
The design for the Catania office block evolved from an initial proposal for a building with a large atrium at its core, to a design with a more evenly distributed approach to PDEC. The energy required to cool a large volume of air in a single atrium and then circulate it around each floor is too high to be considered a fully passive strategy, so Cucinella reduced the size of the atrium and reconfigured it as a series of fluted towers that run vertically through the building. The tapering, conical form of each tower responds to the way in which cooled air flows when generated by an evaporative system. Each tower cools the immediate surrounding area. Towers are also used for night ventilation and to bring daylight into the deep plan through glazed walls, which break up and animate the office floors. Micronizers are located at the top of each cone.
Cucinella's research suggests that under this system, peak cooling loads could be reduced by a third compared with the original single atrium design (58 W/sq m compared with 82 W/sq m). Further investigations into daylighting aim to reduce the loads generated by artificial lighting, enhancing the economic and environmental potential of this intriguing prototype.