Center for Education and Raising Awareness of Energy Efficiency â€“ Energis in collaboration with one of the most significant windows and doors manufacturers in the country and the region FTM doo Novi Travnik presents the Guidline to windows, with goal to educate visitors of portal Energis.ba and help them make educated decisions when installing and
Center for Education and Raising Awareness of Energy Efficiency â€“ Energis in collaboration with one of the most significant windows and doors manufacturers in the country and the region FTM doo Novi Travnik presents the Guidline to windows, with goal to educate visitors of portal Energis.ba and help them make educated decisions when installing and retrofitting the windows.
Condensation and Windows
What IsÂ Condensation?
TheÂ occupants of a house rightly feel that condensation on the inside surfaces ofÂ windows is not good. They immediately think of obstructed visibility, reductionÂ of the intensity of natural lighting and, above all, deterioration of interiorÂ finishes (rings, stains, peeling paint) and mould.
SuperficialÂ condensation occurs when the surface temperature of a solid (glass, sash,Â frame) is lower than the dew point of the humid air in its immediate vicinity.Â The moisture, naturally present in the air in the form of vapour, changes intoÂ liquid water on contact with these cold surfaces. The resulting droplets form aÂ film of water and run down the glass when the condensation is heavy or does notÂ evaporate fast enough. In the case of windows, condensation will often occur atÂ the edge of the glazing because of conduction through the spacer and airÂ convection within the glazing cavity. Such condensation can be decreased or eliminated by raising the inside surface Â temperature and/or decreasing theÂ relative humidity of the indoor air.
ReducingÂ or eliminating condensation often means using several complementary techniques.Â These techniques concern the window itself, the method of installation, theÂ interior window accessories (curtains, blinds, valances), the arrangement ofÂ heat sources (hot air registers, baseboard heating, convection heaters) and theÂ relative humidity of the indoor air. The overall condensation resistance of aÂ window depends on each of these factors.
CondensationÂ Resistance of Windows
SeveralÂ techniques are used by manufacturers to increase the condensation resistance ofÂ windows. These include windows filled with a convection-limiting inert gas,Â low-emissivity coatings that increase the temperature of the glass, insulatingÂ spacers that reduce heat conduction, and non-conducting sashes and frames (Fig.Â 1).
Energy-efficientÂ windows are least likely to have condensation. Their resistance toÂ condensation, however, depends on the indoor humidity level. A humidity levelÂ of more than 40 percent, when the outside temperature is -20Â°C or colder, mayÂ cause condensation even on a well-performing window.
ToÂ minimize condensation on windows, follow these guidelines during installation:
- position theÂ window as close as possible to the interior finish;
- insulate theÂ space between the window frame and the rough opening around the perimeterÂ of the window; and
- seal the jointÂ between the frame and the rough opening on the interior side.
InteriorÂ Window Accessories
ToÂ maintain the condensation resistance of the window, interior window accessoriesÂ such as curtains, blinds and valances must not inhibit or impede the movementÂ of air at the surface of the window. Any restriction of air movement willÂ reduce the condensation resistance and thus increase “sweating” onÂ the window.Â Fig. 2Â illustrates installation techniques thatÂ are recommended, acceptable or not recommended.
ArrangementÂ of Heat Sources
AlthoughÂ energy-efficient windows are now available, the heat loss through them is stillÂ greater than through the adjacent walls. This is why windows with heat sourcesÂ located below them are less prone to condensation. When the heating system isÂ in operation, the air temperature will be higher in the vicinity of the windowÂ than in the centre of the room, resulting in increased condensation resistance.Â Care must nevertheless be taken to ensure that the hot air from the registersÂ does not flow directly onto the interior surface of the glass, as this couldÂ give rise to thermal stress problems in the glazed unit that could cause theÂ glass to break.
ControllingÂ the Relative Humidity of Indoor Air
ReplacingÂ old windows with new, more efficient ones generally results in a significantÂ improvement in the airtightness of the building enclosure, and thus substantialÂ energy savings and improved comfort for the occupants.
However,Â when living habits and the production of humidity in the house (showers, baths,Â cooking activities, plants, etc.) remain unchanged, and there is a significantÂ reduction in the rate of air exchange, the resulting relative humidity atÂ certain times during the winter may become excessive and cause condensation onÂ the inside surface of new windows.
ReducingÂ the amount of humidity in the house may enable you to limit or eliminate theÂ problems caused by humidity. Some simple but effective measures can be applied.
- If your heatingÂ system is fitted with a humidifier, or if you use portable humidifiers,Â disconnect them.
- Avoid hangingÂ laundry inside to dry, and make sure that the exhaust from the clothesÂ dryer is vented outside.
- If you have aÂ crawl space under your house, cover the beaten earth with 0.15 mm (6 mil)Â polyethylene. The crawl space may have to be ventilated during the summer.
- Make sure thatÂ your basement is well drained and protected against excess moisture. Also,Â make sure that gutters and the slope of the land around the house drainÂ water away from the house.
- Try not toÂ produce too much humidity. Plants, laundry, showers and cooking withoutÂ lids are major sources of water vapour.
- Avoid dryingÂ firewood in the house. A cord of wood can release more than 270 litres (60Â gallons) of water.
IfÂ the signs of excessive humidity persist, you should increase the ventilation ofÂ your house. When the frequency of condensation is low (once or twice duringÂ winter), you can reduce or eliminate the problem by briefly opening two windowsÂ located on opposite walls or by turning on the kitchen or bathroom exhaust fan.Â If the frequency of condensation is unacceptable, you should install aÂ controlled mechanical ventilation system (fig 3). Systems incorporatingÂ a heat recovery unit and a relative humidity control are preferred.