Improved Windows for Cold Climates

A large part of the energy consumption in countries in Nordic and Arctic climates is used for space heating in buildings. In typical buildings the windows are responsible for a con-siderable part of the heat losses. Therefore there is a large potential for energy savings by developing and using windows with improved energy performance. Traditionally evaluation of the energy performance of windows has focused on the thermal transmittance, but as windows differ from the rest of the building envelope by allowing solar energy to enter the building, the total solar energy transmittance is equally important. In the heating season in cold climates the solar gain through windows can be utilized for space heating which results in a corresponding reduction in the energy production that is often based on fossil fuels. A suitable quantity for evaluating the energy performance of windows in a simple and direct way is therefore the net energy gain, which is the solar gain minus the heat loss during the heating season. Especially in arctic climates where the heat-ing season covers the whole year there is a large potential for exploiting the solar gain dur-ing the summer season. Furthermore the presence of snow increases the solar radiation be-cause of the reflection. In this paper the energy saving potentials for different window types have been examined by determining the net energy gains in Danish and Greenlandic climates. Furthermore the windows have been evaluated by performing building simulations of the heating demand in typical single-family houses in Denmark and Greenland. The examined windows are typical new windows from Nordic countries and new proposals of improved windows with low thermal transmittance and high total solar energy transmittance. The results show that net energy gain can be increased considerably by reducing the frame width, which results in a larger transparent area causing a larger solar gain but still main-taining a low thermal transmittance. Using three layers of glass with large gaps, using very slim frame profiles, and omitting the edge constructions that normally causes thermal bridges achieve this. Applying shutters or low emissivity coated roller blinds incorporated in the glazing that are activated during night time can improve the energy performance of windows. The results from this work show that it is possible to develop windows with a positive net energy in a fairly simple way, which means that it contributes to the space heating of the building.