Thermal Comfort Performance of Wind Towers in the Australian Residential Context

Abstract

This study investigates the performance of a wind tower in contemporary medium-density residential structures in subtropical Sydney, Australia. Wind towers have been a traditional residential and commercial natural ventilation system for more than three thousand years in Persia and neighbouring countries. Wind-induced ventilation offsets solar gain by cooling the building structure and improving occupant comfort in warm to hot weather by increasing indoor air movement. As Australian metropolitan cities increasingly tend towards medium-density apartment-style housing, urban canyons are created where pollution and noise result in a heavy dependence on air conditioning behind sealed windows. Concerns about climate change and global warming also support the introduction of a natural ventilation system to provide occupant comfort and reduce cooling load. This four-phase study evaluates wind tower natural ventilation using wind-driven indoor air movement for occupant comfort. First, a sealed scale model of a typical residential apartment incorporating a wind tower was tested within a boundary layer wind tunnel under three urban context scenarios, assessing the effects of windward obstructions on the external pressure distribution over the building model and the associated wind tower. A large number of internal and external geometrical configurations of wind tower were analysed leading to an optimised wind tower design. In the second phase, this design was exposed to Sydney’s contemporary meteorological data to assess its applicability in the Sydney climate. The third phase of study quantified comfort performance of a wind tower for the six warmest months of the year. In the fourth phase, the cumulative total improvement in indoor comfort temperatures was applied in an energy calculation procedure to predict the potential of wind tower ventilation to reduce electricity demand and carbon emission. The results indicated that, in ambient temperatures of 23°C and above, the optimised wind tower in the most conservative scenario increased indoor air speeds at average 0.4 m/s and improved indoor comfort by 4935 degree hours (ΣΔSET*) compared to the default design relying on through-window ventilation. The wind tower produced an average cooling potential (ΔSET*) of 3°C and decreased cooling loads by 25 kWh/m2/y.