Shading Windows

Windows are the bane of the air conditioning designer for a number of reasons.

• The heat load from the window increases the size of the air conditioner required.
• During winter the cold air adjacent the window sinks to the floor, causing a pool of cold air just above floor level, which may be cold enough to give patrons cold feet
• In summer, the sunlight shining through the window heats patrons when they are sitting in the sun, making them uncomfortably hot.
• The presence of the window can create a hot or cold spot. (Sometimes the hot or cold spot caused by the window is not actually at the window, depending on the air conditioning system design)
• Opening of the window can cause additional problems.

• If you are designing a new building, then the best way to minimise these problems is by correct orientation of the windows. The best orientation of windows for commercial buildings is not the same as for residences. The best direction is generally south followed by north (with extensive shading) and east (with extensive vertical shading). The worst is west facing windows. As there are a number of factors that influence this, it is best if your architect and air conditioning consultant discuss this at an early stage in the project.
• Use external shade. Correctly designed pergolas, verandahs and similar architectural features can dramatically reduce the heat load and associated problems.
• Use reflective glass or add a reflective film to the glass. This has a similar effect to external shade, although it can cause problems of unwanted reflections, particularly if the window is visible from a road.
• Use thermal glass or add a heat absorbing film to the glass. This is not as effective as the above options, but it does give a worthwhile improvement.
• Use internal blinds or curtains. These generally perform similarly to thermal glass, although they can also be designed to reduce the pooling of cold winter air at floor level.