Building Layout & Design: Passive Solar Design: Windows.

Windows are essential for natural lighting light, heat from the sun, ventilation and views. Windows can be the strength or weakness in a building envelope. Design, selection, orientation, and shading of any window are critical elements in the design of a 'sustainable house'.

Conventional windows can permit heat to move from inside to outside in cold weather and vice versa in hot weather. Energy can transmitted through a window via radiation, conduction, convection and poor seals. Conventional windows may have excessive heat loss and gains, which leads to reduced comfort levels.

Advanced Windows

'Advanced windows' admits and retain more energy than is lost in winter. The initial cost of these windows must be compared against the lifelong cost of heating and cooling without these windows. Their selection must be based on local climate and building orientation.

Advanced window technology includes multiple glazing levels, inert gas fills between glazing layers and low-emissivity coatings. These technologies come with high embodied energy cost.

The Australian Greenhouse Office has introduced a 5 star rating for windows, Window Energy Rating Scheme. Rating based on their cooling efficiency in summer and heating in winter.

Covering Windows

Heavy drapes fitted over windows will affect air flows around a window. In winter, air close to a window becomes cold and will fall towards the floor. In doing so it draws more warm air down the face of the cold glass. Pelmet boxes can interrupt this airflow over the curtains. Curtains should also extend to the floor and past the windows on either side to prevent air movement around the curtains. Deciduous trees on the north and evergreen trees on the south will provide seasonal window shading.

Applying Window Principles to the Newton House

The Newton House has been built using single pane, timber framed, recycled windows. The following factors influenced this decision:

1. High embodied energy in advanced windows compared to recycled windows.

2. The passive solar design principles used in the Newton House will provide seasonal control of heat movement through window.

3. Timber frames have a low thermal conduction compared to aluminium windows.

4. The ability to control air movement through the window by occupier involvement in opening and closing of drapes to personal comfort needs.

5. The occupier making informed decisions about the type of drapes to be used.

6. High financial cost of advanced windows.

Link:

http://www.greenhouse.gov.au/yourhome/technical/fs18a.htm
http://windows.lbl.gov/software