Effect of Fence Design on Natural Ventilation in Residential Spaces: An Experimental Study
Fences are often designed as territorial markers to assert defensibility of spaces, and enhance the potentials for â€˜prospect-refugeâ€™ in private residential developments. In the tropics where natural ventilation is a critical functional requirement, fences may be antithetical to air movement around and within enclosed residential spaces. This simulated experimental study sought to ascertain the effect of fences on natural ventilation in residential spaces. An architectural model of a 2-bedroom house on (with cross ventilated living room and bedrooms) a rectangular plot enclosed by 2.1m high fence was the object of the study. Six fences of different porosities (0.0% to 29.4%) and porosity-height (0.2m to 1.6m above ground) on the approach side of the plot, and 6m from the house were exposed to simulated wind (generated by a solar-powered standing fan) at 30o, 60o and 90o; the other three side-fences were kept solid. These were in addition to a case of the approach side without fence. Three hot-wire anemometers were deployed to simultaneously measure wind speeds outside the plot, in the living room (6.0m x 4.2m; 21.4% window area)and a bedroom(3.6m x 3.6m; 27.8% window area) of the house. About thirty readings at ten seconds intervals were taken in each space and wind direction. Ventilation coefficients for the spaces were computed from mean values of observed wind speeds. Mean ventilation coefficient values of the seven fencing cases were compared for each space using Analysis of variance (ANOVA) to establish any significant difference (at 0.05 level of significance).Ventilation coefficients ranged from 0.02 to 0.46 in the living room, and 0.04 to 0.21 in the bedroom across wind directions. The highest values were obtained from approach side without fence; and contrary to expectation, fence of the highest porosity produced ventilation coefficients lower than the solid (non-porous) fence.In the three wind directions, significant differences were found in the ventilation coefficients of the living room; while in the bedroom, two of the wind directions resulted in significant differences in ventilation coefficients from the fence designs.