Mechanisms of natural ventilation in livestock buildings: Perspectives on past achievements and future challenges

Studies on the mechanisms of natural ventilation in livestock buildings are reviewed and influences on discharge and pressure coefficients are discussed. Compared to studies conducted on buildings for human occupation and industrial buildings which focus on thermal comfort, ventilation systems, indoor air quality, building physics and energy etc., our understanding of the mechanisms involved in natural ventilation of livestock buildings are still limited to the application of the orifice equation. It has been observed that the assumptions made for application of the orifice equation are not valid for wind-induced cross ventilation through large openings. This review identifies that the power balance model, the concept of stream tube and the local dynamic similarity model has helped in the fundamental understanding of wind-induced natural ventilation in buildings for human occupation and industrial buildings. These concepts have distinguished the flow through large openings from that of 'cracks' (i.e. small openings), which is where the orifice equation is normally used for prediction of airflow rate. More field measurements on the effect of wind turbulence on ventilation rate need to be encouraged, particularly under conditions where the mean pressure differences through building openings are much lower than the fluctuations of pressure differences. Research on bidirectional flow that occurs at openings is also limited.