Lighting continues to be a huge chunk of a building’s annual energy costs—between 20 and 40 percent. While the need for light will never go away, analyzing its costs through energy modeling can help secure the installation of more efficient technologies.
Industry experts say any energy simulation program or model that reflects total building energy use will include a lighting and lighting controls component. Electrical contractors (ECs) are in a unique position to team up with energy modelers to provide this information for the goal of constructing or upgrading to smarter buildings.
“Contractors can play a much stronger role in helping owners to minimize their annual operating expenses, get the highest utility rebates, and achieve more LEED points by being lighting advocates in the energy modeling process,” said Elizabeth Gillmor, building energy analysis manager and lighting energy engineer, Group14 Engineering Inc.
By working directly with the energy modeler to analyze the energy-saving effects of different lighting strategies and providing first-cost estimates for those options, the contractor can build an optimized lighting and controls package that helps the team get the most bang for its buck.
Calculating energy consumption
With its ability to simulate the functional characteristics of a system’s energy use, sophisticated modeling software can estimate the demand and consumption of energy resources and their costs. A computer model simulation also can calculate heat loss or gain and predict the amount of energy needed to operate building systems. Additionally, energy models can help evaluate different options for lighting systems in new construction or upgrades.
The American Institute of Architects’ AIA 2030 Commitment report shows that 57 percent of commercial building projects completed in 2011 used energy modeling. However, the design performance levels of the corresponding buildings suggest that modeling was used more for LEED certification or for heating, ventilating and air conditioning (HVAC) system selection and sizing rather than during initial architectural design.
According to the U.S. Department of Energy’s (DOE) building technologies program manager, Roland Risser, the DOE is planning to collect more detailed information about the use of modeling in 2012. The focus of new studies will be increasing cost-effective use of modeling to improve customer satisfaction of completed buildings, for function, energy use and associated costs.
“Since lighting also generates heat, in order to properly account for a whole building’s expected total electricity consumption, you must include both lighting energy use, as well as the heat generated by the lights, which subsequently effects zone heating or cooling requirements,” Risser said.
By virtue of using energy modeling with many different lighting options, including the effect on the heating and cooling system, contractors can improve equipment selection to ensure chosen solutions meet customer needs while reducing long-term energy use.
Being a team player
Gillmor and other industry experts said that modeling is typically performed by professionals whose foundation is in mechanical engineering and by those who are formally trained to integrate the method into whole-building analysis.
Most lighting systems currently don’t require the use of modeling; however, lighting and lighting controls have potential to be an essential part of the energy model. Gillmor said, as a result, the lighting team may need to work a little harder to ensure that the model accurately captures the lighting energy. Communication of accurate loads, actual fixture wattage—not just lamp wattage—control strategies and zoning is critical, yet it is often insufficient. The plans and submittals should have enough detail that a layperson can easily understand the design’s energy use.
“Contractors should encourage the design team to generate a control intent narrative. This is an invaluable tool that translates electrical plans and submittals into simple, regular-person language that anyone, including the energy modeler, should be able to understand,” Gillmor said. (For more on control narratives, read Craig DiLouie’s December 2011 feature.)
Controlling lighting costs
As more reliance is being placed on the results of energy models, those who create them are starting their work earlier. With energy codes becoming more stringent and projects targeting lower energy use, the integrated design process relies heavily on the whole-building analysis that an energy model can provide.
“It’s critical for the integrated design team to understand the synergistic effects of how different building systems work together, and the energy model can quantify these effects into annual energy costs,” Gillmor said.
While energy models can provide a fairly accurate idea of how a building compares to other similar buildings because they are built using a fixed set of rules, some engineers contend they aren’t meant to predict actual energy use. Rather, they’re considered more of a benchmark. They can, however, be calibrated to actual energy usage by refining the operating characteristics, such as schedules, actual plug loads, weather and equipment-operating characteristics.
“An energy model that,predicts costs that are dramatically different from a building’s current utility bills may not necessarily mean that there is something wrong with the model. It may be a strong indication that there is something wrong with how the building is operating,” Gillmor said.
She recommends that, before trying to determine lighting energy savings for different lighting efficiency options, it’s important to define a baseline for comparison. Comparing different lighting and controls options to a baseline ensures that ECs are comparing apples to apples with results that are meaningful and relevant to a project. The details can vary by project type and may include a local energy code, LEED-established parameter, utility metric or perhaps even the existing building systems.
Gillmor said it’s very possible that projects will have multiple baselines. Regardless of the baseline that is chosen, it is typically derived from a fixed set of rules, such as those found in ASHRAE 90.1 Appendix G.
What specific information can be gleaned from energy modeling and applied to the selection of lighting fixtures and controls?
“When you model different lighting and controls options relative to the established baseline, you can get quantified energy cost savings for your specific project and utility rate structure, not just what a manufacturer puts on their sales brochure. This allows you to calculate true payback time, return on investment, life-cycle cost, or any other economic analysis that will help to justify a system that might have a higher first cost,” she said.
Applying smart tools
The DOE’s Risser recommends that energy modelers and interested ECs integrate energy models and detailed lighting analyses into a dedicated tool to gain a true picture of their needs, but he recognizes some shortcomings. He said that energy models can be used to evaluate the energy consumption of lighting technologies, but they are not as effective at calculating visual comfort.
This factor was taken into account when the DOE released current versions of its free energy analysis and thermal load simulation program, EnergyPlus 7.1.0. Based on a user’s description of a building from the perspective of the building’s physical makeup and associated mechanical and other systems, EnergyPlus calculates heating and cooling loads necessary to maintain thermal control set points, conditions throughout a secondary HVAC system and coil loads, and the energy consumption of primary plant equipment.
EnergyPlus performs interior work-surface illuminance calculations, glare simulation and control, luminaire controls, and evaluates the effect of reduced artificial lighting on heating and cooling. The tool can integrate inputs to simulate both electrical light dimming and operable shading devices for daylighting control. The shading devices, in particular, can be programmed according to a specified schedule or operate to respond to a number of external and internal conditions, two of which are illuminance and glare.
“There is considerable flexibility in this tool, but at the same time, the calculations themselves are not nearly as sophisticated as those used in tools built for this specific purpose,” Risser said.
Risser admitted that the DOE’s programs are not currently considered sufficient to support lighting design or lighting control design. Typically, EnergyPlus is used to evaluate the energy consumption of a lighting system after that system has been designed using another modeling tool like AGi32 or Radiance.
“The limitations of lighting calculations in energy analysis tools have spurred a recent push to provide robust energy and visual comfort analyses from a single shared model, to perform the lighting calculations in the lighting tool, and to pass the results to the energy tool,” Risser said, adding that OpenStudio Application Suite and DesignBuilder link Radiance with EnergyPlus.
OpenStudio is a cross-platform (Windows, Mac and Linux) collection of software tools to support whole-building energy modeling using EnergyPlus and advanced daylight analysis using Radiance. Additionally, compatible weather data, which is critical to the accuracy of a building model, can be downloaded and interfaced with EnergyPlus.
Another tool available to perform energy modeling calculations is NECAWORKS. This online screening application provides National Electrical Contractor’s Association contractors with the fundamental tools and information links to develop all types of energy solutions projects—solar PV and energy-storage solutions to energy efficiency and distributed generation—and allows for the analysis of combined solutions. Using readily available data supplied by ECs, the screening tool generates a benefit/cost ratio and a simple payback period.
Gillmor encourages EC design teams to evaluate upgraded lighting and controls options through an energy model and be prepared to provide simple cost estimates for those options.
“Team up with an energy modeling firm that really knows lighting and daylighting and can support your efforts,” she said. “The end result will be a better building and happier client and a leg up for your company on the next job.”
MCCLUNG, owner of Woodland Communications, is a construction writer from Iowa. She can be reached at firstname.lastname@example.org.