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DC Current


  • 12.1 IT Networks
  • 12.2 DataCenters
  • 12.3 Renewables, Electric Vehicles, Storage
  • 12.4 Lighting
  • 12.5 Appliances
  • 12.6 DC Power Infrastructure
  • 12.7 Standards

While AC current is the worldwide electrical distribution system for buildings, we are surrounded by electronic devices and equipment that operate internally on Direct Current (DC). These devices are plugged into a typical Alternating Current (AC) outlet, but the AC is then converted to DC, typically using a rectifier or convertor to operate the internal electrical components and equipment. A rectifier converts AC, which periodically reverses direction to DC, which flows in only one direction. This process is known as rectification. Now, many newly constructed buildings are deploying renewable energy sources such as solar or wind which can generate AC or DC power. One of the growing uses of DC is digital devices with transistors relying on direct current;smart- phones, personal computers, flat screen TVs, and tablets. One example almost everyone can relate to is that there are 6.8 billion cell telephone subscriptions that require and consume DC power.

According to the director of the Power & Energy Initiative at the University of Pittsburgh, digital consumer devices and devices such as LEDs and solar panels account for up to 20% of total power consumption.

The history of AC and DC power started in the late 1880's and 1890's. Thomas Edison (who once held the world record of 1093 patents for inventions) developed the first commercial electric power transmission system which used direct current (DC). After he deployed about 200 power stations, a war of currents started. Opposing the use of DC was the inventor of transformers and alternating current, Nikola Tesla, and George Westing- house, a proponent of AC power. Their basic argument was that DC power couldn't be transmitted very far, only around a mile and half, whereas AC current could be carried over hundreds of miles and was better suited for central power stations. The war of currents got nasty at times but eventually AC power won out for power generation, transmission, and distribution.

DC is described as the unidirectional flow of current; current only flows in one direction. Voltage and current can vary over time so long as the direction of flow does not change. Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, and office buildings.

Converting AC to DC or DC to AC generally results in small conversion losses. While the efficiencies of power conversion are dependent on current and voltage, conversion equipment is typically rated from 90 to 95% but can be much lower. So at best we're wasting 5-10% of energy in the conversion and more with multiple conversions using less efficient conversion equipment. To minimize conversion losses, the conversion of AC power should be upstream of individual devices.

For buildings to deploy DC systems would be a monumental change, but, the benefits of a DC infrastructure can be very persuasive. The following sections include observations and examples of existing or potential use of DC in buildings.

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