Background 828 views


Condensation is the process of passing from a gaseous to a liquid (most common) or solid phase. It causes considerable problems which some farmers find difficult or expensive to counteract. Drips from ceilings pipes and stanchions are not only annoying to workers but damaging to the pigs which need a relatively dry environment to resist infection.

Searching my shelves of textbooks, only one covers the subject adequately (and that very technically) so I continue this journey through a simplified guide to piggery ventilation with some observations from the many call-outs I have been asked to make on condensation.

Pigs are very wet animals. Quite apart from urine and dung, a pen of 12 midweights will exhale 5 litres of moisture a day. As this is in fine droplet form and warm, it rises to condense on the nearest cool surface. So what does 'condense' mean? Water vapour tries to move from an area of high humidity to one of lower humidity.

If the surface it meets is cool or cold, as it does so it cools down to its 'dewpoint', the temperature at which a change from a fine mist into a liquid (condensation) occurs. Drips from this surface are bad enough, but if the droplets condense inside a structure such as an insulation layer this reduces its heat-retention properties to almost nothing. Subsequently a damp patch occurs which eventually rots the structure by bacterial and fungal decay. We tend to put a damp proof course under our concrete floors, but a damp course is equally important inside the building superstructure, especially if the building is pressure ventilated either by positive or negative pressure – pushing air in or pulling it out).

How can internal rot be prevented?
Line the gap between the outer facing board and the insulation layer with 1,000-guage polythene sheeting. This provides an effective vapour seal. Facing board joins should also be sealed with heavy duty adhesive tape. If the surfaces are old or greasy, thin timber battens should be nailed to seal them using a dab of insulation paint on the nailheads.

Condensation also strikes in other ways:

Inside ventilation ducts
Always divide the warm, moist exit air from the cold outer surface of the duct with 25 mm insulation board or wrap. Trunk ventilators condense towards the upper or outside lengths and must always be insulated all the way up to stop dripback.

Drop-out (fail-safe) panels
These often condense on the upper surface so make them from insulation board.

Internal surface condensation
Nearly always caused by warm moisture-laden air hitting a 
cooler surface. This is the most common reason for all my condensation callouts, and I tackle them like this.

A condensation route map

  1. Look for dead spots where the humid air has time to deposit its load of moisture droplets on a cold surface. Use smoke phials to see where the air is first meeting the cold surfaces, how fast it is moving and from which direction it is coming.
  2. Most ventilationists say that scouring the cold surface with a gentle airflow of 0.1 m/ sec (10 seconds to cross a metre) will remove condensation. It will sometimes help, and the use of a plywood baffle board suspended on strings which, with the use of smoke can be adjusted to direct more of the airflow to the required place. Look out for obstructions such as pipes, purlins, ceiling lights etc., which can deflect it.
  3. But these are palliative measures, and more effective action may be needed. Increasing the fan power reducing the inlet area to 'throw' the airflow further, or inserting an extra inlet nearer to the problem. Wise to call in a ventilation engineer to do this as the 'thermal envelope' around the pigs must be kept to a satisfactory level to keep them in their comfort zone – which is also your profit zone.
  4. A further extension of this idea is to install a polythene duct to blow air across a trouble spot, but be careful about creating cold down draughts at pig level. This system originated from the recirculation principle (an excellent, lower-cost, but undervalued ventilation system) and in this case a simpler and cheaper 'straight-through' version is all that is needed. You can easily make your own trunking and supports for this – I will show you how to do this in my next article.
  5. I have left the correct solution until last, which is to insulate/ re-insulate the trouble spots. This is usually difficult or very expensive to do. It should have been done earlier, but hasn't. Sometimes however, surface insulation is the only answer. Some insulation board tacked on to a surface; spraying the troublespot with polyurethane foam; using insulation paint for nailheads and small areas - are all solutions where stripping, re-insulation panelling and mineral wool replacement to secure a target U-value* of 0.5 are ruled out.

* U-value: The amount of heat which passes through 1 m2 of the material(s) when the temperature difference from one side to the other is 1 degree centigrade.

[Source: Pig Progress magazine Vol 29 nr 10, 2013 - 'What the textbooks don't tell you about...' series]

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