Harvesting Light to Save Energy

The New York Times building is using a shading system to dictate lighting and heat levels in areas.

You may have heard of daylighting that uses window positioning and even motorized window treatments to let light in at appropriate times of a day and save in energy costs. But have you heard of daylight harvesting? It’s being done at the new New York Times Building in Manhattan, also via motorized window treatments.

In the Times building, MechoShade’s SolarTrac shading system helps dictate lighting and heat levels in areas. First, radiometers on the roof measure the amount of light to indicate whether it’s a sunny or cloudy day. That’s fed into a computer program that also takes into account the position of the sun every day on every window, as well as the effects of shadows from all the buildings in a five-block radius, to determine the height of the shades on each window.

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In addition, the Times opted to add interior photo sensors that help determine how far the shades come down. The Times building uses a low-iron Starphire floor-to-ceiling glass that lets in more light that ordinary glass. “Even with shades, a bright overcast day can have a high amount of glare,” says MechoShade president and chief operating office Jan Berman. “Interior sensors every 30 feet tell us if brightness on window exceeds a certain threshold, and a shade will come down further if it’s above midpoint.”

The shades can be set in six different positions, says Berman. And although the shading and lighting systems are not connected, a dimmable fluorescent lighting system from Lutron reacts to the light allowed in by the shades. Considering that lighting is the number one use of energy in an office environment, the savings can be tremendous. The shading system also works to keep the building cooler in warmer months, cutting down on air conditioning demands.

According to Berkeley Lab, “Research suggests that proper daylighting can reduce perimeter-zone lighting energy by as much as 60 to 70 percent of the annual electric lighting energy, with additional reductions in electric demand. Overall building energy use can be reduced by 10 to 30 percent compared to a similar nondaylit building. Additional savings come from reducing building air conditioning and heating loads through the selection of efficient glazings and automatic shading.”

Occupants in the floors that the Times occupies have manual override options, via touchscreens placed in columns around the work area. In addition to manually controlling the shades, the touchscreens will ask a user the reason for the change, and that data will be used to improve the software.

Berman says although the Times is still moving in, some adjustments have already been made. “Some shades that go all the way to the floor we stopped to about three-quarters, because there was no sense in them go all the way down, [as doing so was just shading the floor], and this adds more light to the area.”

Although this is a very high-tech commercial system, Berman infers that we could see scaled-down systems such as this for residential use, without having to rely on timers and solar sensors. “We have some ability to do that, and I could see that in the next six to 12 months. We can’t do everything in the New York Times system, but we can have a system provide incremental movement [of shades up and down] throughout the year.”

As a side note, another unique feature of the Times building is a curtain wall consisting of horizontal ceramic tubes placed on a steel framework one and a half feet in front of the glass. This screens the glass, thus reducing the building’s cooling loads. (The glass is low-emissivity glass, an energy-efficient material that helps reduce heating and cooling use.) The ceramic tubes provide an aesthetic bonus, taking on the changing color of the sky during the course of the day as light diffuses through them from different angles. Curtain walls are a more common feature in Europe.

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