Ventilation systems in piggery sheds

Commercial ventilation and cooling systems use automate adjustment of items such as fans, sprays, heaters and shutters to achieve the pigs' comfort zone.

Ventilating air must be directed so it creates air circulation within your shed without draughts flowing directly on to your pigs, especially young pigs and in cooler weather.

Under the pig welfare, you must have failsafe backups in sheds with automated ventilation in case of power failure. Naturally ventilated sheds that rely on automated equipment must be inspected at least twice a day or have failsafe backups or an alarm to warn of a breakdown.

Observation of the pigs' behaviour is important when adjusting ventilation and cooling, not just relying on a set temperature.

Fans

Fans can improve ventilation, but they only affect a small area and you have little control over air direction or speed. Also, air won't circulate to partitioned areas. Fan systems can be properly designed by engineers.

Air quality

Fresh air must be introduced into your piggery to remove:

• water vapour
• carbon dioxide
• ammonia
• airborne dust
• bacteria
• odours.

The pig welfare code lists the maximum levels for pollutants in air.

Shed design

Ventilation in a shed depends on the shed design and type:

• closed sheds have automatically controlled temperature and ventilation (and fail-safe systems if there is a power outage)
• naturally ventilated sheds are narrow to allow good ventilation (and may also have automatically controlled temperature systems).

You can improve shed ventilation by opening up areas of the walls and roof:

• increase the area of your sidewall openings. Ideally, the sidewall opening should be able to be fully opened to get the best air circulation for your sows and growers
• install a 2 shutter system, 1 above the other, for flexible adjustment. Shutters can be linked to a thermostat to automatically adjust opening.
• build ridge vents into the roof to allow warm air to leave a wide shed (wider than 10m and usually a steeper roof pitch). Contact an agricultural engineer to design the correct size of the opening – a rule of thumb is 10% of the floor area for grower and adult pig sheds.

Make sure there are no nearby trees and foliage to block natural breezes. Trees and other sheds should be distant by at least 5 times the shed's height for good ventilation.

Poly-ducted ventilation

Ducted airflows let you control ambient temperature and spreads fresh air to virtually any area. Poly-ducted ventilation is cheaper and is easier to install and use than steel-ducted systems that can corrode in piggeries. It is often added to wide, naturally ventilated sheds to improve ventilation.

Talk to a ducted ventilation supplier for advice about the best system for your shed.

Design and size

Polythene ducts direct air from a fan through a polythene tunnel that has holes so the air escapes and spreads over your pigs. The size of the duct depends on how fast you need the air to go through. There has to be enough air pressure for the flow to reach the pigs, but if it is too fast and the duct is too small it will flap and eventually wear out.

Polythene ducted ventilation systems need to be tailored to each of your buildings. The holes are made in the duct using a hole-punch, scalpel and a template. The holes are spaced evenly to make sure air spreads evenly and reaches the far end of your system. If the holes are too large the duct will collapse because the fan can't keep the duct inflated.

Duct material

There are 2 types of polythene for piggery ducts that provide efficient airflow and longevity:

• woven polyethylene fabric – sewn or heat-welded into the duct shape
• extruded polythene tubing – a ready-formed duct and the cheapest alternative.

Choose your ducting based on the ease of use, and how long the material lasts.

Extruded polythene can be black or clear. Piggeries often prefer clear polythene as it shows rodents in the duct before they do damage. Clear polythene ducting lasts about 5 years. Make sure clear polythene ducts are between 150–250 micrometres thick.

Normally cooling designs call for tubing that is 557mm in diameter. You can use smaller diameters to duct heated air from central oil or gas-fired heaters in farrowing and weaning buildings.

The duct is suspended – usually by a thin wire that runs inside the duct's top edge – so that either a piece of tie wire or a fence netting fastener can attach the duct (at approximately 1800mm spacings) to either the roof structure or a length of wire strung above the line of the duct. The duct's far end is closed off by folding and fixing it neatly back on itself. The duct must not have any bends in it and is usually lightly tensioned. When deflated, the duct will hang down from its top edge. Ensure it has sufficient clearance available so that it does not hang into pig pens or obstruct access.

Ventilation fans

Ducted air ventilation systems commonly use axial flow propeller fans or package evaporative coolers. The fan's capacity is needed for the design and it should be the capacity at a head of 6mm water gauge. It is preferable to mount the fan on the end wall of your piggery to draw in fresh outside air.

Transition pieces

The transition piece is a section of sheet metal ducting that connects the larger fan diameter to the smaller duct. It is a truncated cone in shape and the length is twice the fan's diameter. Having 4, or preferably 8, radial fins inside the transition piece will straighten the airflow.

Control systems

Automatic fans and shutters need a fail-safe system to open shutters in case there is a power failure and the temperature rises above safe levels.

Insulation

Ventilation systems may reduce the temperature in your shed, so it's important that you insulate the roof and walls to reduce heat loss by conduction.

Insulation protected by a vapour barrier reduces condensation inside pig sheds (some insulation forms its own vapour barrier). This protects interior linings and reduces the amount of ventilation you need to prevent condensation in your building. Insulation also reduces the shed heat load in hot weather.