The Design of Seasonal Awnings for Low Cooling and Heating Loads in Offices

In cold climates, exterior shading devices can provide larger annual energy savings than tinted and reflective glass since they can be used seasonally thus allowing for a passive utilisation of solar gains during the winter (Dubois 1998). Awnings and similar types of shading devices are of particular interest because they have a low shading coefficient since 1) they reject solar energy before it reaches the building and 2) most of the heat absorbed in the shade is convected to the outdoor air. Awnings also leave some part of the window view unobstructed, which is positive both in terms of occupant satisfaction and daylighting availability. However, awnings are particularly susceptible to mechanical failure and wind damage. Another problem is that little is known about the relationships between energy use and an awning’s geometry and attributes such as colour (absorptance, reflectance) and transmittance. In an attempt to elucidate these complex relationships, a parametric study of energy use for heating and cooling an office room located in Stockholm was initiated as part of a large project on solar shading devices at Lund Institute of Technology (Wall & Wallenten 1999).