DC power distribution’s role in the race to net zero
The built environment accounts for 40% of annual global emissions, making it a critical target for tackling climate change. The United Nations says emissions must drop by 45% by 2030 and reach net zero by 2050 to hit the Paris Agreement target of limiting global temperature increases to below 1.5°C. The Biden administration’s Executive Order 14057 seeks to make all federal facilities net zero by 2045, and the 2022 Inflation Reduction Act offers significant funding and incentives to owners to transition to a clean energy economy.
While achieving net zero is a significant challenge, more smart buildings are hitting the milestone. In 2020, the New Building Institute verified 700 net-zero facilities in North America, and it expects the number to increase by as much as 50% every two years. One approach to net zero is with a direct current (DC) power distribution system that incorporates a renewable microgrid with energy storage to generate and deliver enough DC power to support building loads while eliminating the inefficiencies of traditional AC grid power. Incentives and technological advancements can facilitate the adoption of DC power distribution.
A more efficient, incentivized way to power
Since the early 20th century, the electric power grid has used alternating current (AC) to distribute power to buildings. However, nearly all electronic equipment and devices internally operate with DC power via components such as printed circuit boards, diodes, resistors, transistors, and microchips. LED lighting, electrical vehicle chargers, variable speed HVAC systems, and other energy-efficient motors, such as variable speed fans, blowers, pumps, and compressors, within smart building system appliances and equipment also use DC power.
More than 70% of the world’s generated AC power gets converted into DC power. The traditional method of delivering DC power uses power supplies with transformers and rectifiers that step down AC voltage and convert it to DC power; the power supplies can be internal to equipment and devices or within external adapters that plug into AC outlets. However, each AC-to-DC conversion can introduce power losses of up to 30% and distortions into power distribution systems that decrease efficiency. Additional losses occur when the battery energy storage systems (BESS) storing energy generated from renewable sources, like wind, solar, and hydro, deliver DC power that gets converted to AC for distribution throughout a building.
Each AC-to-DC conversion can introduce power losses of up to 30% and distortions into power distribution systems that decrease efficiency.
Smart buildings with an all-DC power distribution system can achieve an estimated 10% to 20% energy savings by eliminating the bulk of AC-to-DC conversion and parasitic loads of the AC-to-DC transformers of building equipment power supplies. A DC power distribution system consists of an on-site renewable energy source, a BESS configured as a microgrid, and a DC power infrastructure to deliver power throughout a building. Building resiliency is improved by enabling operation when utility power is down due to power outage events. It also provides independence from the utility grid by storing energy gathered during peak renewable energy generation for use during nonpeak hours.
While a building with a DC power distribution system may never use grid power, remaining connected to the grid with net metering enables it to feed excess energy back into the grid for revenue, tax incentives, and overall improved grid efficiency.
Under the 2022 Inflation Reduction Act, a DC power distribution system qualifies for tax credits, including a 30% credit for the renewable energy source, a 30% credit for energy storage, and additional credits for kilowatt-hours of electricity produced. Collectively, these incentives can lower the cost of a DC power distribution system to be competitive with traditional AC power. Not only can it help a building achieve net-zero, a DC power distribution system can satisfy requirements for LEED certification credits and other smart building certification programs.
Technology advancements pave the way
DC power distribution has received much attention over the past few years and is a primary focus area for the U.S. Department of Energy (DOE). While the ubiquity of AC power and a lack of technology and standards have previously limited adoption, advancements in DC power distribution technologies are now paving the way.
Fault-managed power (FMP), pioneered as Digital Electricity (DE) by VoltServer (a technology partner of Sinclair Digital, which employs the author), safely transmits bulk DC power throughout a building. Adopted as Class 4 power in Article 726 of the 2023 National Electrical Code (NEC) with a voltage limit of 450V, an FMP system uses centrally managed transmitters and remote receivers to detect faults and immediately stop transmission, providing the same level of protection from electric shock and fire initiation as safe extra low-voltage (SELV) Class 2 power systems. The power and distance capabilities of FMP vary based on the vendor’s technology and the number and size of conductors. For example, VoltServer’s DE system operates at 336VDC, delivering 300W and 600W to about 1,200 feet over one and two conductor pairs, respectively. It can reach levels up to 2000W using multiple pairs of larger conductors.
While the ubiquity of AC power and a lack of technology and standards have previously limited adoption, advancements in DC power distribution technologies are now paving the way.
FMP systems can connect directly to DC power sources to distribute hundreds or thousands of watts of DC power throughout a building, eliminating the need for AC power. FMP supports monitoring and controlling energy usage via centralized management for additional energy savings. FMP uses small, lightweight cables deployed via typical low-voltage installation practices that can reside in chases with other communications cables, with no conduit required in most environments. FMP can also combine fiber optics into a single cable to converge power and data for connected electronic equipment and devices.
Power over Ethernet (PoE) technology is another DC power option for smart buildings. PoE delivers up to 90W of DC power to 100 meters (328 feet) via network cabling with Ethernet data. PoE powers connected devices such as Wi-Fi access points, security cameras, access control readers, LED lights, smart shades, speakers, sensors, and more.
Universal Serial Bus (USB) technology is another option gaining ground. Traditionally used for computer peripherals, the latest USB standard can deliver data and up to 240W of DC power to distances of about 1 meter (3.3 feet) via small connectors. USB power, which can charge personal devices such as smartphones, tablets, and laptops, is delivered through computers, power and data rendering devices, or USB receptacles powered by FMP or PoE.
Combining a DC microgrid with FMP, PoE, and USB infrastructure can collectively provide significant energy savings.
Overcoming barriers
One primary adoption barriers to DC power adoption has been the lack of equipment and devices that directly accept DC power without AC-to-DC conversion. The September 2020 report DC Lighting and Building Microgrids: Opportunities and Recommendations, published by Pacific Northwest National Laboratory (PNNL) with the DOE, identifies “a lack of available equipment that accepts DC input” as one of the most common barriers. The report recommends that PoE switch, lighting, HVAC, and EV charger manufacturers offer options for DC input.
Grassroot efforts and strategic partnerships are influencing vendor technology roadmaps. The market is now seeing the development of electronic equipment and devices that directly accept DC power without conversion, including network switches, LED lighting drivers, HVAC controllers. Multiple network switches can now be powered directly via FMP. These switches then deliver PoE, USB, or other forms of DC power to a wide range of connected end devices throughout a building. Additional DC power advancements such as Single Pair Ethernet and the development of voltage standards will drive vendors to bring more electronic equipment and devices with DC power to market.
Showing big promise and opportunity
While the DC power distribution system market is growing at only 8%, energy regulations and initiatives, new enabling technologies, and the growing adoption of DC microgrids, EVs, and PoE lighting will likely increase the growth rate over the next five years. Several DC microgrid projects are underway across the country, including a Maryland smart energy bus depot, a major food production facility in California, and a university and several military bases in Washington, D.C.
In 2022, Hotel Marcel in New Haven, Conn., became the country’s first net-zero energy and net-zero carbon hotel by successfully deploying a DC power distribution system, using recycled materials, and emitting no operational carbon. The hotel generates electricity via an on-site solar microgrid with BESS, purchasing renewable energy for additional needs. FMP delivers DC power to various loads throughout the hotel, including network switches that deliver PoE power for LED lighting, automatic window shades, door access readers, temperature controls, interactive touchscreens, digital displays, and USB connectors. The project earned LEED Platinum certification from the USGBC.
DC power distribution throughout the hotel is virtually invisible to the guests.
Since its opening, the hotel has also consistently measured and analyzed its energy consumption over the past year. It continues investing in technology and tweaking its DC power distribution system for greater efficiency. “We have discovered that drying the linens uses more energy than expected, so we are now negotiating to add more solar panels in adjacent properties and adding two additional battery racks to increase our storage from 1 MWH to 1.5,” says architect Bruce Redman Becker, president of Westport, Conn.–based design and development firm Becker + Becker.
Becker says it’s important for guests to see the building more as a comfortable refuge rather than a technical marvel. To that end, the DC power distribution throughout the hotel is virtually invisible to the guests. “We receive a lot of reviews on how comfortable and quiet the hotel is, and many guests like being able to control the shades and lights,” he says. “There is a myth that net zero means less comfortable, and we’ve busted that.”
The hotel has been a teaching resource for other hotel developers interested in DC power distribution, Becker says. “You can get to net zero without distributing DC power throughout the building, but you’ll need to generate more renewable energy,” he says. “A DC power infrastructure certainly simplifies the process, gives you more control, and offers significant savings.”
Luis Suau is chief business officer at Sinclair Digital Services.
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