Introduction

Solar shading can have a major impact on building energy use and occupant comfort (see BRE Report BR364 and Information Paper IP11/02). Moveable shading is especially appropriate for many buildings. During times of peak solar gain such shading can reduce cooling loads[1] and overheating. Under cloudy conditions, or in winter, it can be withdrawn to allow daylight and useful solar gains to enter the building, reducing its dependence on electric lighting and its heating requirement.

This strategy requires that the shading be appropriately controlled. Otherwise, unwanted solar gain may enter the building in heat-wave conditions, causing overheating. Occupants may experience glare from the sun and be unable to operate the shading to alleviate it. Conversely, and more commonly, the shading may be in place at times when it is performing no useful function; this can lead to excessive use of electric lighting and occupant complaints about loss of view out.

Mechanical operation of shading by the occupants is still common^[2]. Such systems typically include pull cords or crank handles. This type of control is principally used for internal blinds although many external and mid-pane systems can also be controlled in this way.

However, a wide range of motorised systems is now available for all types of shading devices. Motorised operation is generally more expensive, but has several advantages.

• Control by the occupants is often easier; a wall switch (Figure 1) or hand-held infra-red or radio-frequency control is usually easier to operate than a pull cord or crank handle. The same controller could be used to switch electric lighting, and maybe heating and ventilation.

• For large shading systems or where access is limited, mechanical control may be difficult or impossible.

• Various forms of automatic control (see Automatic control later) are possible. For example, the system can be automatically lowered on hot days.

• External systems can be automatically withdrawn on windy days to prevent damage to the shading.

Sometimes a combination of mechanical and motorised control is possible. For example, some venetian blinds can have motorised tilt of the slats, but withdrawal of the blind is carried out mechanically using a pull cord.