Developing a Clearly Better Building Envelope: Daylighting pitfalls

Navigating daylighting design in commercial buildings is no easy task. Well-balanced design takes into account how climate, location, and building orientation affect a glazed opening’s potential for glare, quality of light transfer, and thermal performance. When analyzing daylighting strategies to ensure optimal performance, it is important to understand and avoid common mistakes. The Whole Building Design Guide (WBDG) and Daylighting Guide for Canadian Commercial Buildings outline many considerations including the following.

Overglazing to improve light transfer and views
More glazing does not always equate to better daylighting design. Increasing the window-to-wall (WWR) ratio without incorporating high-performance coatings, silk-screening, or triple-glazing can lead to excess sunlight increasing cooling costs and occupant complaints. Building occupants might also pull down shades to help control these side effects, limiting interior access to daylight.

Relying solely on exterior shading devices
Exterior overhangs, vertical louvres, fins, and other exterior shading devices can help protect interiors from excessive lighting and unbalanced heat loads. However, for large curtain walls it might prove beneficial to use interior shading devices to protect against the adverse effects of excess sunlight. Incorporating blinds that automatically raise and lower with sunlight levels, roller shades allowing light transmittance, and other interior devices can help filter light during hours when the sun is most direct to prevent glare and unnecessary heat gain.

Transferring excess light through toplighting
Skylights, clerestories, and other toplighting assemblies allow for daylight penetration high in a space. Although effective at drawing daylight deep into a building’s core, they are not immune to the adverse effects of excessive sunlight. Best toplighting practices include using glazing materials that can diffuse sunlight in areas with a significant number of sunny days, incorporating dimming controls for areas with low daylight levels, and carefully spacing toplighting to ensure uniform lighting.

Small, closely spaced skylights are suitable for large, open spaces like lobbies and waiting rooms, as they reduce the amount of shadows and allow for more balanced illumination of floor plates. Large areas of vertical glazing are ideal for applications where spotty illumination is less of a concern, including elevators and corridors.

Developing non-integrated lighting systems
According to the Daylighting Guide for Canadian Commercial Building, artificial lighting accounts for 30 to 40 per cent of electricity consumption in commercial buildings. As such, it is essential to pair daylighting applications with lighting controls to reduce energy use. With appropriate specification, they can supplement natural light and ultimately help converse energy.

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