Direct wind tunnel modelling of natural ventilation for design purposes

Abstract

The paper describes an investigation into the feasibility of natural ventilation design by means of direct wind tunnel modelling of ventilation rates. The investigation covers the three cases encountered in practice, i.e. wind alone, buoyancy alone and wind and buoyancy combined. The direct determination of ventilation rates from a wind tunnel model is potentially a very powerful tool for natural ventilation design of nondomestic buildings, where the design aim is to specify the size and position of purpose-provided openings. It offers more accuracy in the determination of wind effects than either the indirect use of wind tunnels (where pressure coefficients are measured for use in a mathematical model) or the salt-bath technique. From an analysis of experimental and theoretical results it is concluded that the direct technique is feasible for a wide range of building sizes. Some desirable improvements to the technique have also been identified. Further work is also required to clarify why the observed values of discharge coefficients are larger than might be expected.