Audits lead to efficient, safe lighting designs

Energy audits require detailed documentation and calculations, and they can offer owners more energy-efficient lighting solutions.

By Jeff Donaldson, PE, CDM Smith, Boston; Michael Stevens, CDM Smith, Bellevue, WA August 16, 2018

Consultants often are tasked with providing energy audits for owners, and these audits can eventually become design projects. As part of these audits, taking inventory of light fixtures requires the auditors to be diligent with detailed note-taking. Proper preparation to document orientation and layout, fixture types, the condition of the conduit system, controls, and existing footcandle measurements are essential items to provide the owner an accurate assessment of their entire lighting system. These audits items can also provide the proper recommendations for upgrades. Audits not only help provide the owner with a clear picture of their lighting system, theyalso can turn into full-scale design projects that will benefit the owner with cost savings and improved safety. 

Over the past several years, CDM Smith has provided both audit services and new lighting systems designs with LEDs for various types of owners. Often the scope of work from the owner, or recommendation from a previous audit report, is to provide a one-for-one replacement of existing fixtures with LEDs. The one-for-one replacement method is typically completed by comparing the lumen output of the existing fixture and then matching it with a new fixture with a similar lumen output. While this method does reduce the energy used, it does not consider existing conditions and several other factors that could lead to increased energy savings and improved lighting conditions. 

Unfortunately, upgrades to LEDs as part of either a retrofit program or energy-conservation measure are completed with little consideration to the existing footcandle levels and infrastructure condition. Paying attention to both items is key to ensuring that what is installed will maintain proper operation for the life of the fixture. Examining the infrastructure condition also can help reveal conditions that were not expected. 

For instance, a room with light fixtures rated for a dry environment may be connected to a conduit system showing signs of corrosion. The designer should then consider the possible reasons for the corrosion, if it is an anomaly, and whether to install a corrosion-resistant fixture instead. The evaluation of existing footcandle measurements allows the designer to use more recent guidelines or updated owner standards. This evaluation may also help further reduce energy usage if the space is overlit or, if the space is underlit, provide proper illumination for that space. 

The final item to examine is the existing layout. Because LEDs can be arranged in countless array patterns, the distribution of light is much more precise. There may be more lumen-output options in a single-fixture footprint, which means a one-to-one replacement of a 2×4-ft fluorescent fixture to a 2×4-ft LED based on lumen output may not provide the owner with the best value or most energy savings. 

LED fixtures often provide several options for lumen output on a fixture type, similar to how a 2×4-ft fluorescent fixture can be found to have two, three, four, or even six lamps. The difference that has been revealed through completing various scenarios of lighting calculations is, that with the right LED fixture, a similar footcandle average can be achieved with fewer light fixtures installed in the existing fixture locations. Where this has been the case, reductions of up to 50% of the fixtures in a space has been typically realized. 

The same success has been seen in high-bay applications where an existing configuration of 50 metal-halide fixtures were replaced with an installation of 30 LED fixtures, all while providing the owners with better lighting conditions after the installation. In all these scenarios, the new LEDs were installed using existing conduit and wiring. Because existing fixture layouts were used where fixtures were no longer needed, the boxes were covered and became junction boxes. 

This technique maximizes payback for the new lighting system. Figure 5 is an example of a new LED calculation using an existing high-intensity discharge (HID) fixture layout. The sample lighting calculation used Visual Lighting 2017 and shows the reduction of light fixtures when replacing HID fixtures with LEDs-all while reducing the power density, increasing the footcandle average, and producing a more uniform lighting design. 

For these reasons, it is recommended that owners include complete lighting calculations in the assessment of their existing lighting system. The rapid change in lighting technology means that engineers need to be confident in using the new fixtures, and calculations are one way to provide this assurance. While the upfront engineering cost is increased, the evaluation of a whole lighting system has multiple benefits. These calculations may lead to the reduction of hundreds, or even thousands, of fixtures on large projects. It is important to provide adequate footcandle levels when lighting conditions are being evaluated. The ultimate goal of the improvements are to address any conditions that are hazardous to staff while maximizing energy savings through the improvements.

Jeff Donaldson is a senior electrical engineer at CDM Smith. He has more than 10 years of experience working in the power electrical engineering field providing design engineering and construction observation of electrical systems for municipal, industrial, and private clients. 

Michael Stevens is a technical writer and editor with CDM Smith and has been supporting technical submittals and deliverables across multiple engineering disciplines for more than 20 years.