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Ventilation control in pig housing

In this first article in a series on pig housing by the ARC’s Institute for Agricultural Engineering, ventilation control is discussed, as this is one of the most important aspects in the planning and designing of a piggery. Intensive pig production facilities require ventilation systems to regulate the moisture and heat produced by the pigs as well as air pollution produced by dung, feed and the pigs themselves.As South Africa’s climate is more moderate than that of some overseas countries, natural ventilation has been used here for decades with excellent results, provided that proper design considerations have been taken into account. Mechanical ventilation (air and temperature conditioning) is indeed used, especially for piglets that are weaned early at 21 days.
Objectives of ventilation
The objective of ventilation is the control of the ambient temperature and humidity, the provision of fresh air, the removal of harmful gases and the movement of air.

  • Controlling ambient temperatures

The micro ambient temperature that surround each pig, can be controlled effectively by means of ventilation. Pigs that are herded together in a building create heat. The heat may be applied to good effect during cold conditions, but during warm conditions it must be removed by means of effective ventilation.
Ventilation means replacing the air inside a building with fresh air from outside. Controlled ventilation is to control the rate at which the air is replaced, depending on the environmental conditions outside the building, such as temperature and wind speed. Figure one indicates the expected increase in solar heat inside an uninsulated piggery with a maximum height of 3,0 m in South Africa.

  • Controlling humidity

Humidity plays an important part in the micro climate conditions inside piggeries. 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.

  • Supplying fresh air

Fresh air is best for pigs. Ventilation supplies fresh air rich in oxygen.

  • Removing harmful gases

This should be removed for the sake of the pig’s health. The building should be managed in such a way that it requires the minimum amount of air changes to regulate the temperature.

  • Air movement

Draughts cause temperature to all due to evaporative cooling, that is to say increases in both the lower critical and upper critical temperatures occur. Draughts should be avoided. During summer, however, air movement should be used to cool the environment by means of judicious ventilation control.

  • Light

Artificial lighting is not usually required in piggeries. Translucent flaps or shutters usually allow enough daylight to enter the building.
Ventilation control
This is a most important facet. Inadequate ventilation could have the following results: more deaths; poor health; lowered production performance; unsatisfactory working conditions; and increased maintenance costs for buildings and equipment.

  • The mechanism of natural ventilation

There are two mechanisms involved in the natural ventilation of a building
They are:

  • Thermal forces or the stack effect.
  • Wind forces or the wind pressure effect.

The stack effect occurs when warm air inside the building rises and gets replaced with cold air lower down. It depends on the following:

  • The temperature difference between the air inside and the air outside the building;
  • The height difference between the inlet and outlet points; and
  • The areas of the inlet and the outlet vents.

Buildings in this figure are designed in such a way that, when the flaps are fully opened, the stack effect will ensure sufficient air replacement to provide oxygen and remove gases.
The wind effect develops due to pressure differences generated when the wind blows over the building. The pressure forces effect air movement or natural ventilation through the building.

  • Requirements for effective natural ventilation

The design, layout and construction of buildings have to be accurate from the start in order to facilitate ventilation. The following basic principles include:

  • Fresh air has to come from a lower level;
  • Stale air has to be extracted from a higher level;
  • Roofs with flat gradients are completely subject to suction during windy conditions. This aids the extraction of stale air.
  • Air-flow is directly linked to the size of the vents and is determined by the area of the smallest vent.
  • The further apart the vents, the less the air-flow will be.
  • Design, layout and management of buildings

The design of buildings should adhere to the basic dimensions as showed in the figure. This is to ensure optimum ventilation regulation. The following should also be kept in mind:

  • Use economical materials;
  • Use good quality concrete;
  • Apply damp-proofing to the floors and insulate the floors with no-fines concrete, especially in wet areas.
  • Insulate the roof where high temperatures can be expected.

The following are important points to consider when planning the layout of buildings:

  • Buildings must be spaced at least 18m apart to ensure effective air movement between the buildings and also to combat the spread of disease;
  • There should be no obstructions in the way of warm winds;
  • If the land falls in the direction of prevailing warm winds, smaller spaces between the buildings may be considered;
  • Obstruction to cold wind, however, are advisable.
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