Design Strategies

Shading & Redirecting Sunlight
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Shading & Redirecting Sunlight

Shading is an important set of strategies for visual comfort and thermal comfort.  As such, successful shading is measured by the overall success of visual and thermal comfort.

Shading strategies include overhangs, louvers, and vertical fins.  Light redirection strategies include light shelves and baffles.  All of these strategies can be external to the building or internal, and can be fixed-position or adjustable.  Some elements both shade and redirect light at the same time.  Both thermal comfort and visual comfort should be considered simultaneously when designing these elements, as they affect both.

Shades can keep the heat and glare of direct sun from coming through windows, while still allowing diffuse light and views to enter. They can also keep direct sunlight off of walls or roofs, to reduce cooling loads.  Interior shades do not block solar heat gain, but can block glare and even-out light distribution.

Shading for Solar Heat Gain

Shades can keep the heat and glare of direct sun from coming through windows. They can also keep direct sunlight off of walls or roofs, to reduce cooling loads.

 

Interior shades can improve visual comfort, but do not block out solar heat gain

The most common form of shade is an exterior fixed horizontal overhang.  These are used on the side of the building facing the sun’s path, sometimes including east and west faces.  However, east and west faces often have more need of vertical fins to avoid low-angled sun.

The side of the building facing away from the equator needs no shading, except near the equator where the sun may be on the north or south side depending on the season.

There are many variations on fixed external shades, to reduce the profile and/or let more diffuse light in.

Common shading strategies
Lawrence Berkeley Lab’s “Tips for Daylighting With Windows”

In hot climates, it can be especially useful to shade the building’s roof to avoid solar heat gain.  Rooftop solar panels, if placed right, can act as shades and thus perform double duty as energy generators and energy load reducers.

 Adaptive Shades

Shading can be designed to allow the sun’s light and heat into the building at some times of day or year, while rejecting it at other times.  The simplest method for this is to use a fixed horizontal overhang whose width is calculated to shade during summer months when the sun is high, and allow the sunlight in during winter months when the sun is at a lower angle.

An overhang shades in summer but lets heat in during winter

You can visualize the sizes for such overhangs for your location with this shading angle tool.

Shading can also be adapted by making it movable–either manually operated by occupants or automatically controlled.  Such systems can be much more responsive and finely tuned, but they are also more expensive, and require more maintenance and repair over the years.  User-operated systems may require occupant training, and are often not properly used.

 

Redirecting Light

Redirecting light is the use of building elements to bounce sunlight into more desirable locations in the building. Light shelves and baffles are two strategies that can distribute light more evenly.

Light Shelves

To evenly distribute light, it is often desirable to bounce sunlight off of surfaces. Direct sunlight on work surfaces often causes glare.  Light shelves are devices that both shade view windows from glare and bounce light upward to improve light penetration and distribution.

A light shelf is generally a horizontal element positioned above eye level that divides a window into a view area on the bottom and a daylighting area on the top. It can be external, internal, or combined and can either be integral to the building, or mounted upon the building.

A light shelf avoiding glare and pulling daylight deeper into the room

Light shelves are most effective on walls facing the sun’s path; on pole-facing walls they simply act as shades. Light shelves on east and west orientations may not bounce light that much further into the spaces, but are an effective means of reducing direct heat gain and glare.

Exterior light shelves reduce daylight near the window but improves the light uniformity. The recommended depth of an external light shelf is roughly equal to its height above the work plane.

To reduce cooling loads and solar gain, an exterior light shelf is the best compromise between requirements for shading and distribution of daylight.  Because they are only shades, they do not change the ratio of incoming light to heat, but better distribution of light can reduce the amount needed in a space, which helps with cooling.

Light shelves may be constructed of many materials, such as wood, metal panels, glass, plastic, fabric, or acoustic ceiling materials. Considerations that affect the choice of material include structural strength, ease of maintenance, cost, and aesthetics.

Light shelves and vertical fins do not need to be opaque; when they are transparent but diffusive, they can help evenly distribute light without reducing the total amount of light significantly.

Diffusing glass fins on a west-facing wall help distribute light evenly without reducing incident light. 

Sizing Light Shelves

The orientation, height, position (internal, external, or both), and depth of the light shelf are critical.  A rule of thumb is that the depth of the internal light shelf be approximately equal to the height of the clerestory window head above the shelf.  The optimal width and placement of light shelves depends on the site’s location and climate.

Baffles

When light shelves are oriented vertically, they are known as baffles.  They are used with skylights or roof monitors to better distribute daylight and avoid glare.  Designing the optimal height and placement of baffles is done the same way as designing light shelves.

 

Baffles in a roof monitor avoid direct glare while bringing in the sun’s full brightness

Source: http://sustainabilityworkshop.autodesk.com/buildings/shading-redirecting-sunlight

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