When a large number of pigs occupy a building, there is a significant risk of overheating and disease because the pigs produce body heat, dung, moisture and harmful gases. Their feed can also contaminate the air. For this reason, piggeries need to have the contaminant-laden air in the building replaced with fresh outside air.

Why Mechanical Ventilation?

Ventilation systems fulfil several functions that facilitate the raising of healthy and productive pigs:

• Ambient temperature control: In hot conditions, air movement lowers the temperature by evaporative cooling and removing air heated by the pigs.
• Humidity control: The ideal RH (relative humidity) for the health of your pigs is 45%-75%. Ventilation removes moisture produced by the pigs. A humidity level of about 60% also reduces the risk of infection, as pathogen activity and viability is reduced.
• Supplying fresh, oxygen-rich air.
• Removing noxious gases, odours, dust and pathogens. Ammonia, hydrogen sulphide, and methane are produced in piggeries. Where heaters are used, carbon monoxide can be emitted as well.

Inadequate ventilation can result in health problems for the pigs (especially respiratory infections), reduced production, poor working conditions, as well as higher maintenance, building and equipment costs. Pig growth is especially sensitive to variations in environmental conditions, so production losses are a distinct possibility.

While piggeries can be naturally ventilated, this method is sometimes inadequate, either because the orientation, layout and construction of planned or existing buildings make it impractical, or because outside conditions do not permit the indoor climate to be adequately controlled. In particular, buildings for piglets that are weaned early are often mechanically ventilated. Even naturally ventilated piggery housing may benefit from cooling fans.

Influences on Ventilation Requirements

To ensure that the mechanical ventilation system will function properly, attention must be given to

• Ventilation vent control;
• Temperature and humidity monitoring, and ideally static pressure monitoring and gas as well;
• Ensuring that piglets are provided with enough heat; and
• Preventing the exposure of pigs to draughts.

The way pigs are housed depends on their growth stage, since different growth stages have different requirements. Heating and ventilation needs to be adjusted according to the age of the pig. Over time, as pigs grow, they need more ventilation. Pigs need to be protected from draughts and excessive heat and they need a dry bed, fresh air, a minimum amount of space and adequate sanitation. With stable and appropriate ambient conditions, their feed use and growth can be optimised. Their sensitivity to temperature, their social nature and the fact that many are kept in a confined space mean that their behaviour will also be affected by ambient conditions.

Cooling

One problem that sometimes occurs even in well-designed housing is that inexperienced workers think of the space as too cold or draughty. In general, however, high temperatures are more of a problem.

Excessive heat can reduce feed intake and cause lower animal production and can have higher costs than excessive cold. Fluctuations and uneven temperatures in the building can also be a concern. Pigs will prefer poor surroundings to areas with poor temperature control. The air temperature, air velocity, wall and ceiling temperature and floor material all influence the temperature actually experienced by the animal.

Heat stress problems can result from inadequate air exchange caused by too much recirculation with too little makeup air, poorly placed thermostats, a lack of fan capacity, poor fan maintenance, not enough inlet area, air not reaching the pigs despite sufficient air displacement, short circuiting (where air moves from one opening to another without mixing properly), fan or heater control system problems or variable-speed fans blowing in the wind.

Preventing Draughts

Draughts can be caused by incorrect adjustment of inlet vents when exhaust ventilation is used. Closing inlets while maintaining adequate air flow volumes will create more draughts. Instead, the inlet area should be increased. Obstructions in the air stream can also deflect draughts onto the pigs. If possible, they should be removed. Excessive air recirculation is another problem to be avoided. Apart from causing draughts, it can stir up dust. The same is true of excessive exhaust flow volumes, which can also dry out air. Any overuse of fans will, of course, also waste power.

While timer-controlled and variable-speed fans save energy, a continuously operating cold-weather fan and properly adjusted inlets may be better to ensure that are draughts eliminated.

Inlets need to be adjusted do that fresh air mixes with the air in the room, in order to keep down air velocity and hence draughts near the pigs. Ensuring a static pressure of 9.95-24.9 Pa is generally adequate to maintain low air velocities. Young pigs are especially susceptible to draughts and may need a covered area.

Air Exchange

“Dead air” zones and poor indoor air quality (IAQ) can arise from poor air distribution. To prevent this, there should be few or no opening (such as open doors) apart from designated inlets, as they will reduce the static pressure and therefore air velocities. Static pressure should be at 24.9 Pa and 4.06 m/s air velocities to maintain sufficient mixing. (Opinions on static pressure differ).

The locations of fans, vents and heaters significantly affect the airflow in the area. Correctly placing the ventilation components is made more difficult by many kinds of wall and floor arrangements. Temperature control, for example, depends on how much heat is retained by the floor. Uneven spacing of fans can lead to skewed airflow distributions. Inlet problems may include: improper closing due to poor maintenance, uneven placement resulting in dead air zones, or a lack of options to direct the air to pigs in hot conditions.

A happy medium between installation costs, operational costs and reliability must be found in choosing ventilation equipment. It is also true that every swine housing facility is different, and not every ventilation problem has a solution that is both simple and cost-effective. A system performance analysis should ideally be performed. In many cases, the specific needs and challenges of a particular facility are best considered with the aid of experienced agricultural engineers or environmental control professionals.