In a recent blog post, we discussed the 2012 International Energy Conservation Code (IECC) and how it has impacted lighting designs and controls. Now we’ll discuss what your options are to ensure your lighting control design meets code requirements.
Occupancy and vacancy sensors are useful for small spaces; however, in larger spaces, they can become a nuisance if the lights automatically shut off unnecessarily when others are present in the general vicinity. Proper coverage design is critical. The A/E team is wise to require the sensor manufacturer to provide coverage map shop drawings to ensure proper design.
Interestingly, occupancy and vacancy sensors are the same physical piece of equipment, but they differ in how they are programmed. With an occupancy sensor, the lights turn on and off automatically. Per the code, these are required in classrooms, conference rooms, lunch and break rooms, private offices, restrooms, storage rooms and janitor closets no matter what. A vacancy sensor, on the other hand, requires that the lights be turned on manually, but shuts them off automatically.
If you opt for occupancy sensors, the lights can be turned on automatically to only 50%. The other 50% must be turned on manually by the occupant. This requires dual switching either through step-dimming ballasts, two ballasts per fixture, or a checkboard switching pattern. With vacancy sensors someone needs to turn on the lights manually, but they can be turned on to 100 percent. The question is really how you want your controls to behave based on your operations and users. Vacancy sensors, for example, have the advantage of not turning on unnecessarily if someone pokes their head into a room for a brief moment.
Installing a timer panel allows the lights to turn on and off automatically on a timed schedule. Though the upfront cost may be a little higher, it’s ultimately cost effective because you get more energy savings from it through greater control over the lighting. It’s also important to note that automatic switches and controls need an override switch that turns the lights back on for a maximum of two hours, per the code. This is a good ‘catch-all’ solution for larger buildings and institutions where occupancy sensors may not be cost-effective or appropriate in every area of the building.
Daylighting helps lower energy usage by using natural ambient light to reduce the amount of artificial light required in a space. As part of the 2012 energy code, daylighting must be used in any space that has a window and the ‘daylighting zone’ extends two feet passed the window edges and 15 feet into the space. However, it is not required in spaces with two or less lighting fixtures, such as a private office. There are two options when it comes to daylighting: automatic and manual.
With automatic daylighting, a sensor is installed in the ceiling that senses how much natural light is coming in, and dims the lights accordingly. This is the most effective control method because it does not rely on people to remember to turn off the lights. Additionally, there is a less noticeable change when the artificial lighting is dimmed. It’s important to keep in mind that standard fluorescent lights are not dimmable, so if you’re working on a retrofitting project with fluorescent lights, a dimming ballast will need to be installed along with the daylight sensor and controller. Another option is to install LED lights that are dimmable in a standard model. LEDs offer additional energy savings because they consume less power and may be eligible for utility rebates.
The other option is to simply employ a manual method, which involves using a tradition toggle switch to shut off the artificial lights when there is enough sunlight. This is by far the more cost effective option, especially in retrofit projects. It requires no controller, sensor, and most importantly, can be used with standard fluorescent ballasts. However, it requires a person to be conscientious enough to remember to shut off the lights for that area. In practice, this method results in far less actual energy savings.
Regardless of the daylight harvesting method chosen, occupants must be educated about the system, how it works, and why it is used. This will prevent complaints and unnecessary maintenance calls for ‘dim’ or ‘burnt out’ lights. It may take some time to adjust, but education and positive reinforcement will surely help expedite this process.