Design and optimisation of a novel passive cooling wind tower

Buildings are responsible for almost 40% of the world energy usage. Heating Ventilation and Air-Conditioning (HVAC) systems consume more than 60% of the total energy use of buildings. In hot climates, the percentage of energy consumption by air conditioning is significantly larger due to the more extreme conditions of the local climate. Clearly any technology which reduces the HVAC consumption will have a dramatic effect on the energy performance of the building. Natural ventilation offers the opportunity to eliminate the mechanical requirements of HVAC systems by using the natural driving forces of external wind and buoyancy effect. A technology which incorporates both wind and buoyancy driven forces is the wind tower. Wind towers are natural ventilation systems based on the design of traditional architecture. Though the movement of air caused by the wind tower will lead to a cooling sensation for occupants, the high air temperature in hot climates will result in little cooling. In order to maximise the properties of cooling by wind towers, heat transfer devices were incorporated into the design to reduce the supply air temperature. The aim of this work was to design and optimise a wind tower integrated with heat transfer devices using CFD modelling, validated with wind tunnel and field experiments. Care was taken to generate a high-quality CFD grid and specify boundary conditions. An experimental model was created using 3D printing. Qualitative and quantitative wind tunnel measurements were compared with the CFD data and good correlation was observed. Field testing of the wind tower was carried out to evaluate its performance under real operating conditions. A prototype of the device was produced and installed on top of a test facility in Ras Al Khaimah, UAE. The study highlighted the potential of the wind tower in reducing the temperature by up to 12°C and supplying the required fresh air rates. The technology presented here is subject to a patent application (PCT/GB2014/052263).