The forced ventilation system in livestock farms

The forced ventilation system in livestock farms

Modern livestock farming, for several decades, has been oriented towards an intensification of production by creating increasingly larger farming units. This fact has highlighted the importance of being able to control the internal climate of these facilities, due to its influence on the growth and health of the animals. The main parameters that must be controlled to obtain an adequate environment in a livestock farm are:

1. The temperature
2. The humidity
3. The air quality
4. The speed
5. The lighting

In the spaces where animals are housed, a set of gases is emitted, such as carbon dioxide, ammonia, and sulfuric acid. The maximum content of these gases in the air should be:

1. Carbon dioxide ≤ 3.5 ‰
2. Ammonia ≤ 0.1 ‰
3. Sulfuric acid ≤ ≤ 0.02 ‰

It is essential to extract these gases, along with excess humidity, to ensure that the indicated values are not exceeded and do not negatively affect the health of the animals and the conservation of the facilities and the building. To do this, it is necessary to replace the contaminated air with new and clean air from the outside. This supply of new air will also serve in summer to mitigate the excess heat that can be harmful to the various species in the facility.

The air speed is a consequence of the necessary flow to ventilate the inside of the barn. It is also related to the temperature. Thus, in winter it should not exceed 0.5 m/s. The air speed is different in winter than in summer and is also conditioned by the type of animal species: poultry, rabbits, pigs, cattle, and sheep. In general, minimum values can be established between 0.10-0.15 m/s and a maximum of 0.25 m/s for rabbit species.

Mechanical ventilation and duct ventilation

Due to the fact that with natural ventilation, the airflow cannot be accurately determined, and therefore it is not possible to regulate the interior environment, its use is dismissed in favor of mechanical ventilation systems. Depending on how the airflow is introduced, it can be: depression ventilation or overpressure ventilation. In both cases, the design must be based on the following principles:

• Clean air should be introduced from the upper part of the barn, so that before reaching the animals it has some warming.
• The extraction of contaminated air must take place from the lower part of the building to compensate for the overpressure created in the upper part.

When the installation contains poultry species, the use of this type of ventilation is especially recommended, especially in warm climates to avoid thermal stress during the early phases of bird growth. This ventilation decreases their thermal sensation by increasing the air speed along the barn. In these situations, the air speed will be around 2.5 m/s. Duct ventilation should be interrupted at night, when the outside temperature decreases and the relative humidity inside the enclosure increases.