Condensation is caused when warm humid air comes into contact with a cold surface. A perfect example of this is when steam from a shower comes in contact with a cold bathroom window. Droplets of water form on the cold window surface. The point at which condensation occurs is called the dew point. The dew point is dependent on the water content of the air, not on the humidity, as the relative humidity (RH) is only a measure of the ability of air to hold water. Warm air can hold more moisture than cool air, when warm air carrying moisture is cooled below dew point it can no longer hold the moisture in the air and condensation occurs. Dew point is always at 100% RH. In conditions of high water content, condensation will occur on any surface which is cold relative to the surrounding air. These surfaces such as external walls and windows, are usually ones where heat is being conducted through them which makes them cold. Condensation or dew point can be avoided if there are no cold surfaces available for it to happen on. This can be achieved in two ways:
- Extra heating in the space.
- Very well insulated surfaces.
Sources of Moisture Water is continuously produced by the activities of the occupants of the space (breathing, washing, and cooking). According to the British Standard BS5250 Code of practice for control of condensation in buildings (Sept 2005) typical moisture generation rates are:
- Sleeping: 0.04 litres/hr per person,
- Active: 0.055 litres/hr/person,
- Cooking: 2 – 3 litres/day/household,
- Dishwashing: 0.4 Litres/day/household,
- Bathing/washing: 0.2 litres/day/person,
- Washing clothes: 0.5 litres/day/household,
- Drying clothes indoors (e.g. using an unvented tumble drier): 1.5 litres/day/person.
- A reduction of cold surfaces by means of good insulation.
- Space heating.
- Energy efficient ventilation.
How can ProAir help? The ProAir HRV units remove the moist air at the source, above the shower for example, and replaces the moist air with filtered fresh air that is at a comfortable and healthy humidity level. This will ensure that condensation and mould growth does not occur in your home.