In this final article of a three-part series on the basic principles of chicken housing, independent poultry consultant Jan Grobbelaar discusses natural and environmentally controlled ventilation.
Two ventilation systems are used in egg and boiler production: natural ventilation (opensided houses), and mechanical ventilation (environmentally controlled houses).
The main difference is the way in which the environment is controlled. In a naturally ventilated house, the inside environment is controlled using natural wind and airflow; in a mechanically ventilated house, electric fans are employed.
NATURAL VENTILATION
In a naturally ventilated poultry house, the key is to maximise the wind; the building should therefore be constructed so that it uses the natural wind to create airflow. This means it should be oriented so that the open sides face the direction of the prevailing wind. The precise angle is not that critical, as effective ventilation occurs up to 30° either side of the wind direction.
(The house should also be as close as possible to an east-west direction lengthwise to minimise direct sunlight into the house.)
Natural ventilation in a building can be created by means of two actions: the stack effect and the wind force (pressure) effect. The ventilation requirements for a naturally ventilated building are expressed in terms of the fresh air exchange rate, which indicates the number of times the volume of air in the building is replaced (volume = wall height x building width x building length). The ventilation system must replace this interior air with fresh air over a specified period. Irrespective of the outside temperature and age of the chickens, ventilation must be sufficient to ensure there is no build-up of stale air in the house.
THE STACK EFFECT
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