As South Africa’s climate is more moderate than that of some countries overseas, natural ventilation has been used in piggeries here for decades. This produces excellent results, provided that proper design considerations are taken into account.
Ventilation involves replacing the air inside a building with fresh air from outside. The aim of ventilation is to control
the ambient temperature and humidity, provide fresh air, and remove harmful gases. Inadequate ventilation can lead to poor health, unnecessary mortality, reduced production performance, unsatisfactory working conditions, and increased maintenance costs for buildings and equipment.
Also known as the ‘micro-climate’, this is the temperature inside the piggery. Pigs herded together create heat. This can be used to good effect during cold conditions, but during warm weather it must be removed by means of effective ventilation.
Controlled ventilation regulates the rate at which the air is replaced in the building, depending on temperature and wind speed outside. In this way, the ambient temperature is neither too hot nor too cold. Controlled ventilation also removes harmful gases, which is good for the pigs’ health.
Humidity plays an important part in the micro-climate inside a piggery. The ideal is to keep pigs in a relative humidity range of between 45% and 75%. Relative humidity values of more than 80% and less than 40% should be avoided.
This requires particular care. Draughts, as opposed to the controlled movement of air, should be avoided, as they can either increase or decrease the temperature. During summer, however, air movement should be used to cool the environment by means of ventilation control.
Two factors have to be taken into account in the natural ventilation of a building: thermal forces (the stack effect) and wind forces (the wind pressure effect). The stack effect occurs when warm air inside the building rises and is replaced with cold air lower down. Its intensity depends on the following:
- The temperature difference between the air inside and the air outside the building;
- The height difference between the ventilation inlet and outlet points;
- The size (area) of the inlet and outlet vents.
The wind effect develops due to pressure differences generated when the wind blows over the building. The pressure forces affect air movement or natural ventilation through the building.
The following basic principles should be followed when designing a piggery:
- Fresh air must be drawn from a lower level;
- Stale air must be extracted from a higher level;
- A roof with little or no pitch is subject to suction during windy conditions and this aids the extraction of stale air;
- Air flow is directly linked to the size of the vents and is limited by the area of the smallest vent;
- The further apart the vents, the poorer the air flow will be.
Apply damp-proofing to the floors and insulate with no-fines (porous) concrete, especially in wet areas. Insulate the roof where a high temperature can be expected. Space buildings at least 18m apart to ensure effective air movement between the buildings and combat the spread of disease.
Make sure that there are no obstructions in the way of warm wind; if you can, install obstructions to reduce the effect of cold wind.
Source: South African Pork Producers’ Organisation (www.sapork.com).