Low and High Pressure Experimental Analysis of Ventilators for Natural Ventilation in Buildings

The wind and buoyancy pressure driving forces for natural ventilation of buildings are very low, typically less than 10 Pa. Depending upon the prevailing climatic and thermal conditions, or even the location of a building on a site in relation to other surrounding buildings and landscape, the predominant pressure force incident on a purpose-provided natural ventilation opening can either be closer to the lower range of pressure differentials (< 2 Pa) or vary over a wider range of higher pressures (2 - 10 Pa). This study investigated, via a series of experiments, variations in power law characteristic equations of ventilators derived from low pressure measurements, relatively higher (typical) pressures and those derived by considering the whole pressure range. The results obtained indicate that the characteristic equation is not only influenced by the constituent components of the ventilator but also by the pressure range from which it was generated. As such, design and operation of natural ventilation needs to incorporate some methods to adapt resulting air flow rates to account for variations in pressure differentials, thus ensuring that a given ventilator maintains a consistent air flow pattern over the whole range of pressure differentials encountered.