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Science behind mould in Air Conditioned hotels, hospitals, and commerical buildings
6 June 2016
In the tropics, as incomes rise air conditioning is rapidily changing from a luxury into an every day white applicance. It has been estimated that 700 million air conditioning units will be installed globally over the next 15 years, and consider the future electricity demand!
Mould is already an issue in the tropics, but will this demand for air conditioning be matched by an equal number of damp, mould and IAQ problems? Probably.
A common cause of mould is lining the walls of air conditioned buildings with a vapour retarder, this prevents the natural moisture flow through the structure and thereby creating damp and mould. I don't need to do a calculation, it is basic science. A result of Air Conditioning, besides space cooling, is lowering the vapour pressure inside the building, whilst on the other hand, the exterior vapour pressure is significantly higher, this mismatch of pressures forces moisture flow from outside to inside during the summer months.
Normally (without vapour retarder) this is no a problem, the ventilation system (air conditioning) will remove that moisture, and condense it on the cooling coil, provided the wall surface is not covered with an obstacle preventing air flow (and thus preventing moisture removal).
But, problems occur (refer diagram) when the interior face of the external wall is lined with a vapour retarder, for example vinyl wall covering.
The pressure difference is driving moisture inward in summer, but interupted by the internal vapour retarder the area behind the vapour retarder is isolated from the ventilation system, so the air conditioning cannot remove the hidden moisture, an accumlation of moisture, causes damp, quickly followed by the growth of mould (mold).
And that vapour retarder doesn't need to be 'vinyl' wall paper. Many materials and coatings are also vapour retarders, for example polymer paints and coatings, PVC coverings, mirror, persex, foil faced materials, plastics, whiteboards and the like will halt the moisture flow, causing damp, mould, and building damage.
The solution is simple (1) In air conditioned buildings avoid internal vapour retarder (2) Dont block the air flow that will allow moisture in the space to be removed by the air conditioning system. So simple, but it still happens today.
About the Author
John A. Herbert is a constuction veteran with more than 30 years construction
experience, educated in the United Kingdom he has been working across Asia for
the last two decades. He is a Registered Energy Assessor (REA), and BEAM