Window Covering Design
Window covering is another important aspect when designing for daylight spaces. Spaces must be designed to block glare, allow the view, and achieve energy savings at the same time. Exterior shading devices are the best option to keep the space cool because they block the heat gain before it enters the space.
To block glare, select a window covering that is opaque enough to block the sun, such as fabric window covering that has 3% or less openness. Horizontal blinds could also be used but tend to block more of the view than fabric shades.
Manually operated systems can be effective if properly used. Since they rely on constant user attention to maintain glare control, these systems are usually installed in private offices or in “worst-case” scenarios. This typically results in poor daylight performance and elimination of views throughout much of the year.
Automated glare control has the advantage of being deployed only when needed and retracting without the user intervening. This creates greater energy savings when coupled with daylight controls while also allowing for longer periods of unobstructed views to the exterior.
TIP for Shading and Exposure
Northern Exposure – Shading typically isn’t needed with the exception of buildings angled to the east or west which may require shading on the north side in the early morning or late afternoon.
Southern Exposure – Less variable sun angles, making it easier to design shading systems. Good access to strong illumination.
Eastern/Western Exposure – Shading design is difficult but critical for occupant comfort.
Influence of Furniture
Workstations must be kept low (42” or less) and directed parallel to the daylight source to ensure the views to the exterior. Where higher panels (48” or greater) are needed or desired for privacy, they should be oriented perpendicular to the perimeter glazing. Creating this workstation orientation allows for the most efficient use of natural daylight.
Workstations should be designed so that the occupant’s task view is parallel to the perimeter glazing, meaning that the daylight is coming from either side of the occupants view instead of straight ahead or behind. This helps lessen the contrast between the task view plane (dark) and the daylight penetrating the glazing (bright). This also helps prevent the shadow of the view from falling on the task view plane.
Interior Surface Finishes
When choosing interior finishes, the walls are another important surface to remember. The “back wall” (wall opposite of the glazing) of a space is crucial to the perception of the space, since it is the furthest from the glazing and attains the smallest amount of daylight. If this wall is brighter in appearance (higher reflectance value,) it will help balance out the bright glazing wall. Having a lower contrast between the glazing wall and the back wall will give the perception of a larger space. With this perception, occupants will be less likely to turn on the electric lighting.
This effect can be done with the remaining walls and ceiling to make the space appear brighter. However, the larger the space, the more difficult this effect becomes due to the inherent initial contrast.
Electric Lighting and Control Integration
Different Types of Controls
Photocell Controls: Automatically adjusts the light output based on detected illuminance. This can be configured as step lighting (on/off) or be configured with a dimming capability.
Occupancy Sensors: Turn lights on and off by detecting motion within the space.
Vacancy Sensor: Requires user to manually turn on lights, but will automatically turn lights off after a pre-set duration.
A good rule of thumb for control systems is to place occupancy sensors in spaces with low occupancy numbers, such as private offices and bathrooms. Spaces with low occupancy numbers (private offices being the best example) also utilize vacancy sensors. Daylight sensors, or photocell controls, work best in spaces with large occupancy numbers. This is due to the way the control works by automatically adjusting the electric lighting to coincide with the daylight addition. This creates an environment that is self-efficient and is not dependent on the occupants of the space.
Guidelines for specific spaces are as follows:
Open Office Areas: Where daylight is present, utilize daylighting controls.
Workstations: Utilize occupancy sensor controlled plug strips to control plug loads.
Restroom/Copy/Storage: Install occupancy sensor controlled lighting.
Private Offices/Conference Room/Break Rooms: Install vacancy sensor controlled lighting.
Organizing Lighting Controls
A daylight “control zone” is a group of fixtures in locations of similar daylight availability that are controlled together via a photocell to reduce light output when daylight is present, thus reducing the energy consumption.
Automated lighting controls should be prioritized to areas where daylight contribution is expected to be high over time and where individual occupant control of lighting is not realistic, such as open office areas or lobby areas.
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