What is condensation?

Condensation is moisture droplets from the air that form on a surface when the temperature of that surface drops below the dew point (or saturation level) of the surrounding air.

When you take a bottle of wine out of the fridge you will shortly see droplets of water forming on the outside of the bottle. This is condensation. As air passes over the surface of the bottle its temperature is reduced and it can no longer hold on to all the gaseous water vapour and it deposits it on the cold surface.

A more important occurrence that we unfortunately see in buildings is condensation on window frames (particularly aluminum), glass and other internal surfaces. This has two primary causes:

• Inadequate removal of internally generated moisture from activities such as a showering, cooking, & drying clothing.
• Poor insulation of building fabric whereby “thermal bridges” (poorly insulated areas) allowing internal building surfaces to fall to low temperatures that are below the dew point (or saturation level) of the air inside the building. In a typical building, when internal surface temperatures fall below 12 degrees the likely result in condensation formation (with this occurring much sooner in high humidity regions).

The use natural ventilation (from operable windows or similar) to prevent and remove condensation is often unreliable for a number reasons including uncontrollable occupant behaviour, and external wind speeds.

For this reason good ventilation systems (such as a HRV) are essential to remove internally generated moisture , and also provide some removal of condensation that may occur from thermal bridging by the continuous circulation of lower humidity fresh air.

Heat recovery system

Heat recovery unit

Heat recovery system

Energy recovery unit