Windows and other glass facades are another major source of heat loss in the winter and heat gain in the summer. However, when properly selected and installed, windows can help minimise a building’s heating, cooling, and lighting costs. The following factors affect the heat flow through a window.

• The type of glazing material (e.g., glass, plastic, treated glass)
  Some glass has a special surface coating to reduce heat transfer back through the window. These coatings reflect from 40% to 70% of the heat that is normally transmitted through clear glass, while allowing the full amount of light to pass through. In solar intensive regions glass has been coated with a reflective film and is useful in controlling solar heat gain during the summer. It also reduces the passage of light all year long, and, like heat-absorbing glass, it reduces solar transmittance.
   
• The number of layers of glass
  Double- or triple-pane windows have insulating air- or gas-filled spaces between each pane. Each layer of glass and the air spaces resist heat flow. The width of the air spaces between the panes is important, because air spaces that are too wide (more than 1.6 cm) or too narrow (less than 1.3 cm) allows too much heat transfer. Advanced, multi-pane windows are now manufactured with inert gases (argon or krypton) in the spaces between the panes because these gases transfer less heat than does air.
   
• Thermal resistance of the frame and "tightness" of the installation
  Window frames are available in a variety of materials including aluminium, wood, vinyl, and fibreglass. Frames, as well as the air leaks from the installation of the frame, have substantial influence on the heat transfer coefficient.

Demonstration Projects:
Tenants’ influence and CO₂ reduction, Copenhagen, Denmark
Low-income housing with reduced energy costs, Houtvenne, Belgium
New identity for urban area, Austria - Radstadt
Improving efficiency of urban energy supply systems, France - Grenoble
Leamington House – Highly efficient heating system for improving thermal performance in Portsmouth, UK
A new "tune up" of innovative technologies, Italy - Brescia
Energy efficient technology to control costs of modern architecture, Finland - Kuopio
High-tech preservation of architectural heritage, Greece - Volos
Renewable energy supply to a "Green Region", Italy - Abruzzo

Technology Producers
www.pilkington.dk
www.velux.com
www.dasolas.dk
www.glaverbel.com