CIGR Handbook of Agricultural Engineering, Volume II Animal Production & Aquacultural Engineering, Part I Livestock Housing and Environment, Chapter 2 Environment for Animals, Part 2.3.1 Environmental Control of Livestock Housing

Abstract

First paragraph: All ventilation systems once were natural but, with the availability of electricity on farms and a blossoming control technology, mechanical or fan-powered ventilation took over. This shift from natural to mechanical ventilation took place mainly because building designers felt that the performance of mechanical systems was predictable, Environmental Control of Livestock Housing 55 controllable, dependable, and effective and that natural ventilation was none of these. In recent decades, studies of the theory and practice of natural ventilation have shown that natural ventilation can be all of these thingsand very much cheaper. We have progressed to the point, in many applications, at which natural ventilation has been accepted as preferable to mechanical ventilation. For example, most new pig buildings in the United Kingdom have automatically controlled natural ventilation (ACNV). In the past, the reputation of natural ventilation suffered due to ignorance of theory and consequent inconsiderate design. Far too often, natural ventilation has been blamed for the failures of designers. Natural ventilation of buildings is generated by two distinct sources. Buoyancy or gravity effects are present, and in large part these are due to temperature differences between the outside and the inside air. The second source is wind blowing over a building, generating pressures and suctions at different points, which can force air in and out of the building.