Wood and wood products are known to help regulate the humidity in buildings because they are hygroscopic; when there is high humidity in a room, wood products will absorb water and swell. Conversely, they desorb when humidity is low.
The relative humidity (RH)
of air depends on temperature and pressure. In this article I only want to cover RH at atmospheric pressure.
Air at 20°C and 100% RH will contain 14.6g of water vapour per kg. So if the air in a room has an RH of 50%, and it is at 20°C, the air will have 7.3g of water vapour per kg of air.
Everyone has seen the effects of wood shrinking and swelling. Many assume wood products swell in winter and shrink in summer. This is generally true of exterior timbers, but the opposite is true indoors, because people keep room temperature around 20°C, so rooms are cool in summer and warm in winter, relative to the outside.
As I write this article, it is 6°C and 90% RH outside. Thus the amount of water in the outside air is 5.5g/kg. As the air from outside enters, it is warmed to 20°C and its RH falls to about 38%. This is a dry atmosphere so the wood products in my room are probably drying out, slowly.
My furniture and floors drying out means the water lost
raises the RH in the room. RH affects our perception of comfort. Wood products provide a useful regulation of RH.
In my current research on reducing formaldehyde emission from panels I have been investigating emission from glue-free plywood-type products to try to differentiate between formaldehyde from the glue and the wood.
I am beginning to conclude that the formaldehyde found in wood does not necessarily originate from the wood but from the water in the wood. Formald-
ehyde is very soluble in water and in ambient conditions prefers to be dissolved in water rather than to be a gas.
If formaldehyde is dissolved in the bound water of wood, when we measure its release the formaldehyde observed may not originate from chemical reactions within the wood but simply be driven out of solution.
If true, then wood products are sinks for formaldehyde and not necessarily sources.
I am confident that wood products cannot only regulate RH but also the concentration of other water-soluble compounds, like formaldehyde, in
the air.