Commissioning for Optimal Savings from Daylight Controls

Overview

This 84-page final report was prepared by the Energy Center of Wisconsin for the Minnesota Department of Commerce under a Conservation Applied Research and Development grant and released in February 2013. It sets out to answer a practical question: when automatic daylighting controls are installed in real buildings, how much of their designed energy savings is actually captured, and how much does a basic commissioning pass add? Rather than model the answer, the authors measured it in 20 office and public-assembly spaces across Minnesota and Wisconsin, first with the controls exactly as they found them and then again after recommissioning.

Key Findings

• As found, the median system was trimming about 23% of controlled lighting energy once heating and cooling effects were included (roughly 915 kWh per year for each kW of lighting under control). Four of the 20 spaces were saving nothing at all.
• The team's "controls effectiveness" metric, which compares actual savings to what ideal controls would deliver, averaged just 51%. In other words, about half of the available savings was being lost to controls that were miscalibrated, mis-zoned, or disconnected.
• Recommissioning took only one to two hours per space and consisted of ordinary startup tasks: recalibrating photosensors, shielding or re-aiming them, reconnecting relays, and adjusting timing. Afterward the median savings rose to 63%, or about 1,976 kWh per kW controlled.
• The median gain from that effort was 88% more savings (690 kWh per kW), and the worst-performing space picked up as much as 2,420 kWh per kW.
• Problems, in order of frequency, were calibration, zoning, heavy interior shading added to fight glare, wrong relay connections, and furniture. Cubicle walls worked with daylighting only when they sat at least five feet below the window head.
• At the measured performance levels, owners break even at a control cost of $1,000 to $2,200 per kW of controlled lighting, which the authors judged to be in line with market prices. They estimated Minnesota's annual achievable potential at 1,100 to 5,600 MWh from new installations plus 400 to 1,500 MWh from recommissioning existing systems.
• After commissioning, average controls effectiveness climbed to 75% (median 86%), a figure the authors suggest utilities could use to derate deemed savings that assume perfect operation.

Why It Matters for Daylighting

Prismatic skylights and other toplighting deliver free light, but the electric lighting bill only drops when the controls actually dim or switch fixtures in response. This study is the clearest field evidence that the control layer, not the glazing, is where daylighting projects most often underperform. For warehouse, manufacturing, and retail buildings with large skylight arrays, that means specifying commissioning scope early, setting explicit illuminance targets, functionally testing every zone, and training the facility team. The 2012 IECC began requiring functional testing of daylighting controls, and this report shows why: a couple of hours of tuning nearly tripled median savings.

The findings also argue for periodic recommissioning. Space plans change, furniture moves, and sensors drift, so a system that performed on day one can quietly slide back toward the 23% median. Logistics Lighting recommends pairing any skylight installation with a documented controls startup and a recheck after the first year of occupancy.

About the Source

The report was written by senior energy engineers Scott Hackel and Scott Schuetter of the Energy Center of Wisconsin (ECW Report 264-1, grant project 34558) and published February 19, 2013. It runs 84 pages including appendices with the survey instruments and site checklists. The Energy Center of Wisconsin was a Madison-based nonprofit research organization that later became Seventhwave and is now part of Slipstream, which continues to host the report. The full PDF, including the methodology, per-space results, and lessons-learned sections, is available from Slipstream's research page.