Wiring - Cabling - Devices
DC presents a strong case for more sustainable and energy-efficient buildings
The proportion of electrical loads that require DC electricity is even greater in smart homes and buildings.
December 6, 2022 By Erin Kelly
December 6, 2022 – Most power grids have distributed alternating current (AC) power in the United States since Westinghouse—with the help of Nikola Tesla—won the War of the Currents in the late 1800s.
AC power was largely chosen to power the modern world because its infrastructure was more cost-effective than Thomas Edison’s direct current (DC) power. AC voltages could be easily stepped up and down because AC electricity is compatible with transformers, while DC electricity is not. Additionally, at the time, many devices used AC electricity anyway (including incandescent bulbs).
Now it’s been over 100 years, and we are still primarily transmitting AC power, despite the fact that technology, devices, and infrastructure have changed dramatically since then.
According to Physics World [tinyurl.com/8y7p9er7], a growing fraction of the electricity consumed in modern buildings is now either “consumed as DC or passes through a transient DC state on its way to being consumed”. Which begs the question: Should AC electricity remain our standard?
DC electricity travels in a straight line (direct) on a graph of voltage versus time. It does not have a frequency, and its voltage remains constant. AC electricity, on the other hand, alternates polarity 50-60 times per second (depending where you are in the world). This gives it a frequency, and also means that its voltage is not constant over time.
Let’s take a closer look at the differences between AC and DC, and the benefits that DC power distribution can bring to building managers and designers who are considering powering their building systems (e.g. lighting and HVAC) with direct current.
A strong case can be made for adopting DC power into commercial and residential power systems because it supports the development of sustainable, energy-efficient infrastructure and building systems.
In this article, I’ll cover four of the main benefits to building owners when distributing DC electricity throughout their buildings:
• Eliminate inefficient power conversions
• DC power helps smart buildings work more efficiently
• Many DC-powered devices are intrinsically efficient
• Distributing DC aids in obtaining a LEED certification for your building
Eliminate inefficient power conversions
An increasing number of modern devices use DC electricity, including LED lights, HVAC systems, laptops, microwave ovens, and more [tinyurl.com/ydwbjmth]. In fact, DC consumption currently makes up about 74% of total energy loads in buildings that support electric vehicles and HVAC equipment with DC motors [tinyurl.com/3ksdab5k].
Power grids currently distribute AC power to homes and buildings, meaning our devices must convert the AC power they get into the DC power they need.
To do that, these devices are equipped with drivers and converters. When cost is not an object, this conversion can be up to 96% efficient. However, Argentum Electronics performed in-lab comparison testing on various LED light bulbs, and found that most drivers are only about 80% efficient (on average)—meaning about 20% of the initial energy is lost during conversion.
By providing our DC devices with DC power, the need for these inefficient conversions is outright eliminated, as is the energy waste that they would have caused.
DC power helps smart buildings work more efficiently
The proportion of electrical loads that require DC electricity is even greater in smart homes and buildings. Sensors, cameras, LED lights, and other smart devices are all powered by DC electricity.
An important feature in smart buildings is the ability to manage and optimize energy consumption with an energy management hub. With a smart hub and sensors implemented, the energy consumption of smart devices can be tracked, and could be based on occupancy, indoor air quality, and more. But when high-consumption devices (e.g. HVAC) still have to convert AC electricity, the potential energy savings remain unrealized.
Brad Koerner said it best at the Smart Building Conference (2020): “[We] need a revolution in just basic electricity before a lot of our smart building technologies will actually be implemented” [youtu.be/4_TcpH5VhO0].
Many DC-powered devices are intrinsically efficient
LED lights are a great example of an efficient DC-powered device; they use 75% less energy than AC-powered incandescents. Additionally, HVAC motors running on DC operate at least 50% more efficiently than AC motors [tinyurl.com/2tbbtbxd].
Were a building powered by DC electricity, a building manager would have more of an incentive to incorporate energy-efficient DC-powered devices like those above.
Available for virtually all building types, the U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) Green Building Rating System provides a framework for healthy, efficient, and cost-saving buildings [tinyurl.com/4n8an337].
There are four possible levels of LEED certification, ranging from Certified to Platinum. The more “points” a building earns, the higher the certification, and implementing DC power distribution will earn owners up to 19 LEED points.
“Owners and project teams choose LEED certification to inform, benchmark, and celebrate their sustainability goals and achievements,” says USGBC. But what does this mean in practical terms? What are the benefits to being LEED-certified?
Gain a competitive edge
USGBC says 61% of corporate leaders believe that sustainability leads to market differentiation and improved financial performance. Additionally, green workplaces attract job-seekers who care about sustainability, so energy optimization actually plays a role in employee attraction and retention [tinyurl.com/y63t5fc8].
Become a net-zero energy building (NZEB)
The Intergovernmental Panel on Climate Change says we need to reduce our energy consumption; in response, businesses have begun prioritizing their carbon reduction efforts to become net zero-emission organizations. If building owners don’t know where to start, LEED provides a good framework that weighs different possible solutions proportionately with their point system.
Attract higher-quality tenants
According to USGBC, LEED-certified buildings command the highest rent, and vacancy rates are estimated to be 4% lower in green buildings than non-green properties [tinyurl.com/3zpaemrf].
Boosted ability to manage building performance
The LEED program defines a framework for optimizing a building’s energy consumption. When you can control and/or automate building systems, you not only optimize energy consumption, but also comfort and air quality. This can additionally support the productivity—and even happiness—of building occupants.
Green buildings are cost-effective
While optimizing a building for energy efficiency can be an expensive investment at the outset, it is just that: an investment. Often, the cost of retrofitting a building to be sustainable—or designing one with sustainability in mind—is covered through the energy savings in the first few years of operation.
According to USGBC, LEED-certified buildings account for $1.2 billion in energy savings, $149.5 million in water savings, $715.3 million in maintenance savings, and $54.2 million in waste savings (estimates from 2015-2018) [tinyurl.com/y3e5kbwb]. The LEED program provides points for DC-powered buildings as a way of influencing the market to improve the energy efficiency, resilience and reliability of electrical systems in buildings.
The program’s DC Power credit also complements LEED’s Renewable Energy and Grid Harmonization credits, because solar photovoltaic systems produce DC power. In this way, the DC power credit also encourages people to invest in renewable energy sources.
Tomorrow is nearly here, so get ready
As it becomes ever-more beneficial for buildings to reduce their energy consumption, it is time to reconsider whether AC electricity should remain the standard (in our buildings, at least).
But it’s not as simple as it sounds. There’s a reason AC beat out DC electricity all those years ago.
At the time, Tesla’s advancements in AC power distribution were chosen as the standard way to transmit electricity over long distances because the infrastructure for it was cheaper (AC is compatible with transformers, DC is not). As technology advanced, the first high-voltage DC transmission system was actually implemented in the 1950s via rectifier stations or mercury arc values.
Despite DC transmission having fewer power losses along lines (thus more efficient), those rectifier stations are relatively inefficient and very expensive. DC power transmission only starts becoming justifiable over 600 kilometres (its accepted “break-even” distance) [tinyurl.com/u4dc7jez].
As technology advances, however, these inefficiencies will be addressed, or new solutions will be devised, and the infrastructure costs for DC power transmission will come down. When they do, we’ll see systems pumping DC directly into our buildings, saving our DC-powered devices a significant amount of energy at the load level.
If your client shows an interest in implementing a DC power distribution system, there are a few different methods by which to achieve this. Power-over-Ethernet, for example, is safe and easy to install, but very expensive and not very powerful (max. 90W).
However, a new development in the world of power electronics improves upon PoE. In the U.S., the National Electrical Code has proposed a new electrical class for power systems that distribute up to about 450 VDC electricity that is safe to the touch. In Class 4 systems, a computer often monitors a circuit to detect any faults, including contact with human skin. Should the computer detect any, the power shuts off immediately [tinyurl.com/2x72v959].
Thankfully, some Class 4 DC power distribution systems are entering the market. With them at your disposal, you’ll be well on your way to delivering the rewards of a more sustainable, more energy-efficient building.
Erin Kelly is the creative director at Argentum Electronics, and loves technology—especially when it makes the world a better place. A longer version of this article was originally published March 2022 on Argentum Electronics’ blog.
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