STABILITY-CRITERIA FOR AIR-FLOW PATTERNS IN LIVESTOCK BUILDINGS

The environment experienced by stock housed in intensive livestock buildings depends on the ability of the ventilation system to control not only the air temperature but also the pattern of air movement. Although traditional ventilation systems aim to keep a constant temperature at the detector by varying the ventilation rate, as the external temperature changes both the internal air movement and consequently the distribution of internal air temperatures vary. This is because the small quantities of air required in cold weather and large quantities required in hot weather enter through the same inadequately adjusted vents with the result that both the buoyancy and dynamic pressures in the inlet air jet are continuously varying. Consequently to provide the most desirable environment for livestock at all times it is necessary to maintain a stable airflow pattern by exercising control over these two factors. It is shown that the airflow pattern depends on the buoyancy and dynamic pressures the ratio of which is defined as the Archimedes number. It is concluded that the jet remains horizontal for an Archimedes number less than 30 and falls when it is greater than 75, thus causing stable air flows with opposite directions of rotation. Intermediate values should be avoided to prevent unstable patterns and unstable environmental conditions near to the stock. © 1979.