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Light Inspires Energy Efficient Building Design

March 1, 2010

Photo of a man and a woman in a lab holding a window with tinted glass. Enlarge image

NREL Researchers Dane Gillespie and Erin Whitney will get to see the windows they normally test in the lab used in a real world environment at the RSF.
Credit: Pat Corkery

Artists find inspiration in many ways. But for the artists (architects and researchers) working collaboratively to create the most energy efficient office space in the U.S., the inspiration was simply light. In fact, light and the access to light turned out to be a top factor when designing the U.S. Department of Energy's (DOE) Research Support Facility (RSF) located on NREL's South Table Mountain Campus near Golden, Colo.

"One of the most powerful drivers in the project is daylight," Philip Macey, RSF project manager for Haselden, said. "It's the reason why the building is fairly slim from front to back and long. Daylight and solar energy are at the core of the building and the windows are the vehicle that gets the daylight into the building."

Scheduled to open this summer, the 222,000 square-foot RSF will house more than 800 staff and an energy efficient information technology data center. Because 19 percent of the country's energy is used by commercial buildings, DOE plans to make this facility a showcase for energy efficiency. DOE hopes the design of the RSF will be replicated by the building industry and help reduce the nation's energy consumption by changing the way commercial buildings are designed and built.

Size Matters

In order to draw as much light into the building as possible, designers looked at a variety of window sizes and glass combinations that would maximize the amount of light, reduce glare and prevent heat from entering and escaping the building.

"There's this push and pull between the size and the construction of the window and getting all of the benefits of daylight into the building," Macey said.

According to Macey, the team spent a good deal of time deciphering which windows would be just the right size. "The south side RSF windows are a little smaller than the north side windows," Macey said. "That was so we could get the light to come into the building in just the right way. On the north side, the glass goes up considerably higher and that's because north light is really gentle. It's soft and diffuse and there really isn't much direct sun. The south side requires a lot more attention because you can get direct sunlight — and it's typically not helpful when it comes to conserving energy.

"The windows are literally the balance point in how the building manages energy. Get the windows too big and you'll get too much heat gain and heat loss. Too small and you won't get enough daylight to light the interior of the building to the middle of the floor plan. You want to have nice even, balanced light across the floor plan."

To help boost the light to the middle of the office space, some of the windows have "light louvers" inside the widow. The light louvers look like a mini venetian blinds hung upside down in the window. The curve of the louver is shaped precisely to catch the light and bounce it deep into the building. By literally helping to toss the light across the room, designers were able to maximize the sunlight increasing its distance from 20 feet to 30 feet inside the office.

The windows in the RSF will also serve double duty as a working part of the buildings' ventilation system. To help cool things down in the summer, employees will get notification to open windows to let cool air in or to shut windows to keep warm air out (see Building Panels Protect, Provide Comfort and Labyrinth to Store Energy in Basement for Later Use). While windows that open and light bouncing louvers are elegant solutions for letting light and air into the building, the windows on the west and eastern exposures will employ a different strategy — keeping heat out — to help the building conserve energy.

Windows to Energy Efficiency

Photo of a man and a woman in a lab holding a window with tinted glass. Enlarge image

NREL Senior Construction Manager Carl Cox demonstrates how the windows will actually open at the RSF as part of the buildings' ventilation system.
Credit: Pat Corkery

"One of the challenges is that although windows let in the daylight, on the other hand, windows are also how you lose most of the energy out of the building," Macey said. "You have to find this really careful balance if you care anything about energy."

Special challenges like this mean looking for new technology. At the extreme ends of the office wings, there will be two kinds of special "dynamic" windows — electrochromic and thermochromic — to ensure energy savings.

"The essence of energy efficiency isn't simply about being 'green' — it's about cost savings and smart resource use," Erin Whitney, NREL's dynamic window testing coordinator, said. "Intelligent solar-managed windows are a simple yet effective way to reduce energy consumption while retaining our Rocky Mountain views and the architectural integrity of the building."

Although it is tempting to take maximum advantage of mountain views west of the RSF, western windows get overloaded with direct sun, even in the winter. When the days are longer in the summer, the windows also could let in a ton of heat thanks to the direct exposure to the sun.

To keep out the heat, western windows will employ electrochromic technology. Electrochromic windows tint once a small electric current is applied. "When these windows tint, you control the solar radiation that gets in the room by shutting out more of the solar spectrum," NREL Research Scientist Dane Gillaspie said. "These types of windows help to reduce the heating loads — especially the peak heat — which is the most expensive in terms of electricity."

The other advantage to electrochromic windows is the ability to control when the windows tint. "Because the electrochromic windows tint when you apply voltage across the window, they are user controlled, which means they can be integrated into a building control system allowing you to decide when to darken the window," Whitney said.

Another type of dynamic window will be used on the eastern balconies. Thermochromic windows also provide resistance to the transfer of heat by reacting to temperature changes. "During winter days the sun comes up late, isn't high, and doesn't warm up the eastern exposure," Macey said. "These windows have glass resistant to heat transfer that will help us dramatically reduce the heat we would normally lose."

"Thermochromic windows react to changes in the environment so you don't have to wire them to the building, you just put them in," Gillaspie said. "You don't get the fine control of the electrochromic windows but, the thermochromic windows are cheaper and it's a killer technology. "

Windows Part of a Living Laboratory

Photo of an office space under construction with large windows. Enlarge image

The RSF design team looked at a variety of glass combinations to ensure the maximum conservation of energy at NREL's RSF. Researchers are looking forward to seeing how the windows perform in a "living laboratory."
Credit: Pat Corkery

While DOE is looking to the RSF to be a showcase building for energy efficiency, researchers at NREL see the RSF as a living laboratory to study building energy use, which includes the windows. "Part of the test is to see how normal office workers react to the technology," Gillaspie said. "As researchers we'll love seeing it, and other tests have shown people really like the technology — but we'd like to see that for ourselves."

Through the years, NREL has worked with a lot of companies to test window technologies, but seeing products in a real world environment is something that Whitney is looking forward to. "We have no way of simulating how those lab results will transfer to use in the real world so this is a great real-life test of these windows that have not been tested in a building situation.

"It will be an interesting comparison of the two technologies and how well they each respond to different situations." Whitney said.

Haselden Construction and RNL are building the 222,000 square-foot Research Support Facilities building, which is designed to be a model for sustainable, high-performance building design, and will provide DOE-owned work space for administrative staff who currently occupy leased space in the nearby Denver West Office Park. The RSF was designed by RNL. Stantec Consulting served as the project's engineering, energy modeling and sustainability consultant.

Learn more about electrochromic windows, Sustainable NREL, the RSF and see a video on NREL Buildings Research.

—Heather Lammers