An ancient approach to ventilating buildings in the notoriously hot countries of the Middle East and North Africa – so-called windcatchers – could become a viable zero-energy alternative to electric air-conditioning units, according to research published in the International Journal of Energy Technology and Policy. The relatively simple wind- and solar-powered devices could significantly reduce the carbon emissions of many buildings across the globe that currently rely on energy-intensive air conditioning.
Mohamadjavad Mahdavinejad and Kavan Javanroodi of the Architecture Department at Tarbiat Modares University, in Tehran, Iran, explain how windcatchers, or “Baud-Geer” in the Persian language, comprise a tower housing a shaft capped by a cabinet with ducts to funnel the prevailing wind down the shaft. Such towers are commonplace in Iran and other parts of the region and simply channel air from above the buildings into the living space to cause evaporative cooling. There have been countless designs used through the centuries to greater or lesser effect, many with elaborate systems of vents within the main cabinet.
The team has now investigated the cooling efficiency of the three main types of windcatcher used in Iran, the Ardakani, with a single vent, the Kermani with its two openings, and the Yazdi which has four openings. The basic findings suggest that the Ardakani is not at all efficient mainly because during the summer months there is a negative flow with air being drawn up the windcatcher shaft rather than dry, cooling air being drawn down into the living space. The second and third types, the Kermani and the Yazdi, both generate a good airflow downward during the hot summer months but they also generate a significant and uncomfortable cooling draft during the winter.
The team has now modeled the different windcatcher designs in order to determine what design features can be optimized to improve overall cooling efficiency during the summer and to reduce unwanted winter cooling. Vent size, number, orientation of the vents and their fins, height and internal diameter of the shaft can all affect efficiency. Of course, one factor that can never be controlled is the wind speed entering the windcatcher vents. Nevertheless, the design of optimal windcatchers for passive cooling of buildings in the summer could be a tenable way to reduce air-conditioning energy bills and shrink the building’s carbon footprint especially if solar heating is also exploited to create a thermal gradient and increase the cooling down draft, the team reports.
Mahdavinejad, M. and Javanroodi, K. (2014) ‘Natural ventilation performance of ancient wind catchers, an experimental and analytical study – case studies: one-sided, two-sided and four-sided wind catchers’, Int. J. Energy Technology and Policy, Vol. 10, No. 1, pp.36–60.