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Wind Tunnel Study for Estimating Outdoor Ventilation in a Dense
Low-Rise Building Area

Bin Su

School of Architecture and Landscape Architecture, UNITEC Institute of Technology,
Auckland, New Zealand  

Abstract

To accurately estimate the natural ventilation of outdoor spaces surrounded by low-rise buildings using a wind tunnel requires correct representation of the natural wind regime combined with appropriately scaled building models and testing method.  Existing outdoor ventilation studies are largely based on wind speed and estimated air change rates.  Wind speeds mainly influence: peoples’ comfort, safety in pedestrian areas, the heat transfer between outdoor surfaces and airflow, and evaporation from wet surfaces.  Studies of air change rates in outdoor spaces (for regions below surrounding roof height) are mainly related to the dispersion and/or removal of pollutants, moisture and hot air. This paper considers the application of wind tunnel studies to estimate the ventilation of outdoor spaces.  It also considers the role of CO₂ as a tracer gas for such studies. It concludes that to accurately estimate the ventilation of outdoor areas by means of a wind tunnel analysis, the natural wind properties in the wind tunnel model must be correctly related to the local terrain category.  Buildings themselves can be represented by low cost small scale models constructed from expanded polystyrene.  The CO₂ tracer gas method is a safe, low cost and efficient quantitative test method for estimating the ventilation of outdoor spaces using a wind tunnel.

Key words:  natural outdoor ventilation, wind tunnel study, CO₂ tracer gas, air change rate, pollutant dispersion, low-rise building.

References

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Aynsley RM, and Su B: (2002) “Estimating wind frequency for natural ventilation at remote site”, The International Journal of Ventilation, 1, (2), pp157-163 

Hunter LJ, Johnson GT and Watson ID: (1993) “An investigation of three-dimensional characteristics of flow regimes within the urban canyon”, Atmospheric Environmental, Part A, General Topics, 26B, (4), pp425-432, c1990-1993.

Lee BE, Hussain M and Soliman B: (1980) “Predicting natural ventilation forces upon low-rise buildings”, ASHRAE Journal, February, 1980, pp35-39.

Su B: (1999) “A study of residential development with particular reference to indoor and outdoor natural ventilation of medium density houses in hot-humid tropical climate”, PhD Thesis, The University of Auckland, New Zealand.

Su B: (2001a), “Estimation of natural ventilation around medium density housing in the humid tropics”, Architectural Science Review, 43, (3), pp341-249.

Su B: (2001b), “Estimation of natural cross-ventilation potentials of medium-density housing in the humid tropics”, Architectural Science Review, 44, (4), pp405-418.

Su B: (2003), “Developments in wind tunnel studies for estimating the cross ventilation potential for a low-rise building in a built-up area”, International Journal of Ventilation, 2 (1), pp77-85.