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
* 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]