Wiring Methods: Paths to Compliance

As jurisdictions continue to adopt building codes centered on driving energy efficiency, it is important to understand the new technologies and approaches that can be used to meet these stringent requirements, in addition to the associated costs. Working alongside Casey Construction and WSP, we investigated the requirements set forth by Washington DC’s Energy Conservation Code with regard to lighting and plug loads by assessing four possible paths to compliance. This local regulation requires that occupancy sensors control all interior lighting and a minimum of 50 percent of receptacles.

Three systems tested were traditional 120/277 voltage systems: Acuity nLight, Wattstopper, and Lutron Vive. Low-voltage systems are relatively common in other parts of the world, so the team identified a fourth low-voltage option made by Platformatics, which was installed by NTI. Our goal was to assess the relative cost for each of the systems, since a detailed ROI was difficult because of the estimates required given the project size and scope. A baseline of 52 kWh was held constant for all four systems based on the calculated energy savings between manually controlled offices and occupancy-controlled systems. We then tallied the approximate installation and material costs of each system, which is variable and dependent on project specifications. To demonstrate initial input costs and scalability of the systems, we priced an individual office as well as a 25,000 sf office space with 30 individual offices and 50 percent open space.

By using occupancy-controlled systems instead of manually controlled systems, an assumption was made that the end-user could reduce energy consumption by 50 percent (equivalent to 54 kWh or $6.48, depending on the variable rate) per year in one office. When those same estimates were applied across the 25,000 sf space, a savings of 2,970 kWh ($356.40) per year resulted. Although the utility savings are minimal with this assumed energy conservation by leveraging occupancy controls, this is a strong assumption and will vary based on building use and individual plug loads.

The team calculated the approximate installation and material costs for the four selected systems tested. Using the single office scale, the order from most cost-effective to least cost-effective was:

When applying cost estimates using the scale of a 25,000 sf office space, the economics flipped and Platformatics became the most cost-effective method because the upfront costs were scaled across a larger space.

While all four occupancy-based systems are viable paths for compliance with the DC Energy Conservation Code, they come with different features that may be desired in different applications and by different end users. We priced the four systems in a controlled study environment, but understand relative costs fluctuate based on manufacturer and subcontractor workload, project size, and competition. As local municipalities continue to adopt net zero energy requirements, occupancy-based and low voltage systems will become more mainstream to leverage automation, to comply with local code, to meet corporate sustainability targets, and to give facility managers better insight into building operations by capturing granular electricity usage data.