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written by Sarah Moore , May 25, 2011

"Learning From Performance” by Cathy Higgins and Karl Brown in the Spring 2011 issue appears to draw the conclusion that daylighting controls are “major contributors to low energy use,” but provides no causal
evidence that would lead to this conclusion.

While daylighting controls are certainly a widely adopted technology in energy-efficient buildings, I believe it is misleading to say that they deliver significant energy savings as a blanket
statement across all buildings.

Energy savings associated with daylighting controls will reduce the lighting and cooling energy in a building, and increase heating energy in cold climates. Savings are additionally limited to perimeter zones with good daylight access. In my experience, I’ve observed that daylighting controls contribute to no more than 10% to 12% overall energy savings, but 2% to 3% is typical in most buildings I’ve worked on. When you are trying to get to 50%, 60%, or 70% savings, I’ve found that the daylighting controls start to make a difference
only after a number of other measures have been taken to reduce total building energy consumption.

I do not argue that good daylighting design and controls have other benefits.However, I’d like to point out that the energy savings benefits of good daylighting controls is highly dependent on the building type, shape, glazing, and climate zone. As always, the answer is “it depends.”

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written by Cathy Higgins , May 25, 2011

Ms. Moore makes excellent points that I believe are universally agreed upon.Specifically, that the “building type,shape, glazing, and climate zone” are critical for effective daylighting, and that the answer on energy savings from daylighting is “it depends.”

The article represents the frequency of measures in high performance buildings,not specific savings numbers. Proving a causal relationship between energy use and the measure deserving the savings “credit”— particularly for interdependent measures such as controlled electric light, daylight and envelope — is challenging at best, with a debatable result regardless of the depth of the research pockets.The objective was to identify the most common practices in low-energy buildings
as probable performance factors.

We clearly agree that daylighting controls are a widely adopted technology in energy-efficient buildings. NBI’s review of measured energy data from hundreds of buildings rarely finds one without this strategy, and most practitioners consider them a key part of a high performance design.

The 10% to 12% overall energy savings Ms. Moore references “under the best conditions” is significant, and the lower numbers she states are countered by studies showing greater potential. With as much of 80% of commercial space in the U.S. within 20 feet of a perimeter wall, or directly under a roof,the potential exists for significant savings toward our deep savings targets. While I maintain that daylighting controls are a “major contributor to low energy
use,” the focus should rightly be on integrating systems to create those best conditions Ms. Moore mentions that maximize savings. The list in the article is a good first step for consideration by any project, but the options per building are always “it depends.”