Code challenges: specify daylighting for IECC 2015 compliance

There is some confusion in the design and specification community surrounding how to achieve the latest daylighting requirements mandated by the International Energy Conservation Code (IECC) 2015. The confusion lies not in the complexity of the new code requirements, but in the practical application that enables specifiers to best satisfy those requirements with the daylighting solutions that are currently available.

Following are details about the new requirements as well as strategies for meeting them and ensuring a quality installation.

IECC 2015 daylighting requirements

IECC 2015 includes revamped and redefined daylighting requirements.

• Although previous versions of IECC allowed daylighting controls to be manual, they must now be automatic, and they must be incorporated into sidelighted and toplighted areas that contain at least 150W of connected lighting. While sidelighted and toplighted areas must still be controlled separately, the code further diversifies the control of sidelighted zones, requiring that sidelighted areas facing different cardinal directions (N, E, S, W) be controlled independently.
• IECC 2015 also specifies that daylight-responsive light reduction in offices, classrooms, laboratories and reading rooms must occur through continuous dimming. Controls in these areas must be able to dim continuously from full light output to less than 15 percent. Stepped-dimming and bi-level switching are no longer considered acceptable methods of daylight-responsive light reduction in these spaces.

Code confusion and types of daylighting systems

One of the greatest causes of daylighting confusion is the industry nomenclature used to describe the two different types of daylighting systems. Daylighting systems are described as either open loop or closed loop, although the differences between the systems and the implication on lighting system design is widely considered unclear.

• Open loop systems refer to daylighting sensors that consider only the amount of daylight in a space and adjust the electric light levels accordingly. These systems employ a linear relationship between the daylight that the sensor sees and the appropriate dimming response that should occur in each zone of lighting. One open loop sensor can control up to three daylighting zones; this offers the benefit of a smaller number of components that must be installed and reduced disturbance on the ceiling.
• Sensors in closed loop systems look straight down at the target surface in the space, such as a desk or conference table, and consider the total amount of daylight and electric light illuminating that specific area. Closed loop sensors are zone-specific, requiring a minimum of one sensor per zone. However, these sensors provide a more exact fit between the actual conditions of the space and its target illumination goals, which can generate greater energy efficiency.

Another cause of confusion is a misunderstanding of a common daylighting design goal. Uniform light levels constitute a basic tenet of good design in any space. In daylighting, the confusion arises from whether or not that uniform light level should be across the ceiling or across the work surface. Daylight-responsive controls are designed to eke out as much energy savings as possible. If conditions of the space allow for daylight levels to be slightly different, which they often do, then the areas that receive more daylight will have lower overhead light levels, and the areas where daylight is less intense will have slightly higher electric light levels. The target level of illumination will be maintained and uniform at the work surface, but the light output from the fixtures in each daylight zone may be slightly different, within a certain acceptable range.

Fewer opportunities for shortcuts

Another reason why the new daylighting requirements may elicit collective groans from much of the industry is that they remove inherent opportunities for shortcuts made possible by traditional daylighting solutions. Traditional systems required the specification of a separate daylight sensor, open loop or closed loop, and then relied on contractors to build an effective daylight-responsive system in the field. Previously, daylighting systems required that the right number of sensors be placed in the right locations, depending upon whether they were open or closed loop, and then the sensors, fixtures and power supplies had to be wired together. This left plenty of chances for less-than-perfect execution to deliver poorly operating daylighting systems that were not compliant with the necessary code requirements. IECC 2015 daylighting requirements mandate a more stringent approach.

The integrated fixture solution

Today, specifiers can meet all IECC 2015 daylighting requirements and ensure a quality installation by specifying lighting fixtures that have integrated daylighting sensors. These fixtures arrive on-site with the sensors already installed. Contractors only install the fixtures, and the daylighting system begins working as soon as the lights are powered on. These closed loop systems improve the efficiency of the lighting system by responding more precisely to the dynamic presence of daylight throughout a space, throughout the day.

To specify an IECC 2015-compliant daylighting system, look for lighting fixtures that have:

• Integrated daylighting and occupancy sensors
• Out-of-the-box functionality
• Continuous dimming, depending upon the type of space being designed

Then, sit back and let the sun shine.