Desires of Daylight Harvesting
Design analysis often shows daylighting control to be one of the most promising energy conservation strategies for commercial buildings. Because energy codes are moving towards a mandate in the use of daylighting controls, it seems prudent to look for object lessons for success and failure from the set of early adopters.
An intense program reviewed dozens of completed projects, most of which were sidelit using windows, and separated the success stories—some of them operating for 25 years—from projects they considered to be failures. They focused on eight that represented different components of the success/failure spectrum. In some cases, the project was largely successful except for a single element which caused it to fail—a case of daylight harvesting systems being only as strong as their weakest component.
The analysis concluded:
- Savings from automatic daylighting control systems are often not realized fully when a building is turned over to users.
- Daylighting performance needs attention and evaluation from multiple design disciplines during the design development and construction process.
- Users are not educated about the installed control systems; when something doesn’t work, users often disable the system instead of getting it fixed.
What aspects lead to failure?
Conclusions of the survey led to a few key component points:
- Lack of coordination or understanding between the design disciplines concerning the daylighting control system.
- Improper location of daylighting controls.
- Inadequate specification of the controls systems, component parameters and sequence of operations.
- Shop drawings made by contractors that detail the system are not checked, or the lighting designer does not know what to check.
- Field changes to tune a system are not documented and taken back to the designer to complete the feedback loop.
The Office Building Example
The 300,000-sq.ft. office building featured a deep perimeter open office arrangement and ribbon glazing to a 10-ft. ceiling height. A series of dimmable T5HO direct/indirect light fixtures were installed in rows parallel to the windows, each row controlled as a separate zone with its own photosensor.
At first, everything seemed to be done perfectly. The controls were calibrated and responded well to changes in daylight levels. However, furnishings colors were not selected to support the daylighting conditions; dark furnishings were installed, resulting in a light level of 25-40 footcandles on work surfaces when the daylight harvesting system was active. The occupants, accustomed to a brighter work environment that lacked daylight, generated so many complaints that the system was deactivated. In addition, the sensors were calibrated too aggressively considering occupant preferences. Most significantly, the users were not told about the control system and its benefits, so there was no buy-in. Because there was no problem-reporting process for the controls, the operations staff lost confidence in the system.
Daylight harvesting need not be complicated—it just needs attention. What led to success in many of the projects was a commitment to daylighting and proper coordination between disciplines. The only way to have successful daylight harvesting is to make the whole team responsible for the outcome and have a project team focused on understanding the ROI for a system based on the power of the sun.