Determining the optimum spacing and arrangement for commercial wind towers for ventilation performance

CFD analysis of multiple wind towers located on the same building was performed following validation of a benchmark model against wind tunnel data. The positioning of the wind towers was varied in six different cases, two different arrangements with three different spacing lengths between wind towers. All analysis was compared against the benchmark (isolated) wind tower. The ability of the wind towers, particularly the leeward wind tower, to ventilate the space below was determined for a set occupancy against current guidelines for air supply rates. Furthermore, the effect of the spacing and arrangement on CO2 concentration within rooms ventilated by the leeward wind tower was investigated (re-entry of exhaust air pollutants into fresh supply). It was found that a parallel arrangement of wind towers was not effective for ventilating an occupied volume, regardless of the spacing between the two wind towers when incident wind direction was parallel to the arrangement. The maximum supply rate for the leeward wind tower in parallel arrangement at a spacing of 5 m was just over 50% of the regulation rate (10 L/s/occupant) and 40% of the supply rate of an isolated wind tower. Decreasing the spacing between the parallel wind towers to 3 m further reduces the supply rate to 2.4 L/s/occupant and the device was observed to be operating in reverse (airflow entering from leeward opening). As the angle of wind increased, an improvement of air supply rates was seen. For a staggered arrangement of wind towers, the leeward wind tower was capable of supplying the recommended ventilation rates at all tested spacing lengths. The average indoor CO2 concentration of the space with the leeward wind tower was higher in the parallel arrangement than the staggered arrangement at 0° wind angle. For the parallel arrangement, the average CO2 concentration was 28–50 ppm higher than the outdoor air. The staggered arrangement effectively minimised the re-entry of pollutants, with the indoor CO2 concentration 1–3 ppm higher than the outdoor.