Study Reveals Significant Additional Savings From Proper Commissioning of Daylighting Controls
Automatic (versus manual) control of electric lighting levels in response to the amount of natural daylight available in the space is a strategy that is growing in popularity for commercial buildings in the Midwest. Some new energy codes are even beginning to require it. In October 2013, the Minnesota Department of Labor and Industry is expected to adopt the 2012 International Energy Conservation Code for commercial buildings, which includes a daylighting control requirement. However, research and field experience has shown that successful automatic daylighting controls require significant calibration and commissioning efforts during and after construction in order to function properly and reach their energy savings potential (Rubinstein, et al., 1997). Research has also suggested that typical field calibration and start-up procedures are falling short of achieving all possible savings.
This CARD grant, titled “Automatic Daylighting Control Commissioning in the Midwest” and awarded to the Energy Center of Wisconsin in 2011, measured, analyzed and demonstrated the importance of commissioning daylighting systems by first determining the baseline conditions in a group of 20 spaces included in the study, and then determining the amount of savings that could be achieved if commissioning practices are optimized in the same 20 spaces. Figure 1 below shows results from before and after recommissioning in these 20 spaces.
Figure 1. Energy savings before and after recommissioning
Before recommissioning, the median energy savings was 23% of lighting energy, or 915 kWh saved for every kW of lighting controlled (including impacts on cooling). However, the average effectiveness of the controls as found was only 51%. (Effectiveness is a measure of the energy saved in current operation versus the energy that could be saved in ideal operation.) In fact, as figure 1 indicates, four of the spaces actually had negligible savings when initially measured. After recommissioning, the median savings was 63%, or 1,976 kWh for each kW of lighting controlled (including cooling impacts). Figures 2 and 3 below are photos of one of the buildings and one of the spaces which were investigated in the study.
Figure 2. One of the buildings that participated in the daylighting control study was the Minneapolis Central Library (photo courtesy of Energy Center of Wisconsin).
Figure 3. A typical space in the Minneapolis Central Library which has daylighting controls that were monitored and analyzed as part of the project (photo courtesy of Energy Center of Wisconsin).
The final report details the project methodology, analysis, and results. It also identifies specific problems that can contribute to sub-optimal performance of the lighting controls, discusses how these problems can be solved or mitigated through commissioning, outlines other lessons learned, and suggests specific opportunities for utility CIP managers.