Waste cases: What data centers and office lighting systems have in common

What do data center power and cooling and building lighting systems have in common? In both cases, engineers have tried to address issues by throwing power at the problem. In both situations the attempt not only failed to solve the problem, but made it worse. This analogy came to mind after I spoke recently with energy efficiency experts.

In the data center the problem is cooling. High density racks create hot spots. The response has been to turn down the thermostat, in effect raising the temperature of the entire room to address a point problem. Energy loads soar, the room is colder than it should be - but that cold air still doesn't get to the problem equipment. Better air flow management or task-specific cooling are required.

In the typical office, everything is over lit. Arrays of 32-Watt tube lights blanket the ceiling, creating an excessive amount of ambient light - a Wal Mart effect. To ensure that workers can read on the desktop they add another 32-Watt fluorescent tube, which is mounted under the cabinet and directly over the reading surface. The result is drastic over lighting of the workspace. The harsh fluorescent lighting creates glare and cuts productivity rather than improving it. In many offices lighting consumes as much as 3 Watts per square foot. In California the code currently calls for 1 Watt per square foot. With better designs, .5 Watt per square foot is attainable.

Better designed lighting can both save energy and makes the user more comfortable. New LED lighting systems can replace under-desk lighting with fixtures that consume 6-9 Watts of power yet provide a softer light that's easier on the eyes. Once proper task lighting is in place, it's possible to also reduce the amount of ambient (overhead) lighting, either by moving to lower wattage bulbs or by spreading out the fixtures.

More efficient designs not only save the energy used to power the lighting itself, but reduce room cooling requirements. "There’s an air conditioning multiplier for all of this. Big buildings are dominated by cooling load. If you make a significant reduction in lighting load you’re knocking down air conditioning in the order of 5% per increment of lighting," says Peter Turnbull, senior program manager with the office sector at PG&E.

"The basic principle of good lighting design is that you should light surfaces, not volume; not over light; and use little accents and layers if needed to add drama and depth, rather than blasting light indiscriminately all over," says Amory Lovins, chairman and chief scientist at Rocky Mountain Insitute. Here are his tips for more effective lighting:

  • Make effective use of daylight as an ambient lighting source in the office. The trick is to use natural light without creating glare. It can be done, says Lovins, but "it's an art requiring skill." A professional lighting system designer can help with that.
  • To avoid screen glare on computers, arrange the room so that bright lighting is not behind the user.
  • Use indirect lighting systems that bounce light off the ceiling. "That lets you see better with about 7 times fewer lumens," says Lovins.
  • Put ambient lighting on occupancy control systems that turn off power when no one is present. And use daylight dimming systems that adjust for natural light levels to further cut power. "That ambient lighting system, using the best modern equipment, will typically have a connected load of 0.6-0.7 Watts per square foot and will actually use 0.1-0.3 Watts per square foot net of control savings, depending on how good your daylighting is," Lovins says.

Copyright © 2007 IDG Communications, Inc.

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