High Performing Buildings - Summer 2011 - (Page 66)

L e T T e R s Daylighting Controls and Energy Savings “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 are highly dependent on the building type, shape, glazing, and climate zone. As always, the answer is “it depends.” sarah moore, P leed AP .e., , Associate member AsHrAe, seattle TechnoLogies in high P e R f o R m A n c e D ATA s e T daylighting Controls High r-value glazing increased insulation High-efficiency HVAC natural Ventilation Heat recovery Applied renewable energy Variable frequency drives underfloor Air distribution/displacement ground source Heat Pump demonstration renewable energy The Author Responds Ms. Moore makes excellent points that I believe are universally agreed upon. 66 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. National Building Institute’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 as 80% of commercial space in the U.S. within 20 feet of a perimeter wall, or directly under a roof, the potential summer 2011 The 12 technologies most commonly identified as part of the design or efficiency upgrades. 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.” Cathy Higgins, White salmon, Wash. Comments on “Learning from Performance” may be posted at http://tinyurl.com/3bhwhdh. To post and read comments on all of the articles in this issue, visit http://hpbmagazine.org. HigH Performing Buildings http://www.tinyurl.com/3bhwhdh http://www.hpbmagazine.org

Table of Contents for the Digital Edition of High Performing Buildings - Summer 2011

Commentary
Contents
Stanford University's Y2E2
The Christman Building
The Gettysburg National Military Park Museum and Visitor Center
Cannon Design Regional Offices, Power House
Great River Energy Headquarters
Letters
Products
Advertisers Index

High Performing Buildings - Summer 2011