A 110,000-square-foot building with glass covering 80 percent of the exterior walls will make for a distinct, architecturally iconic anchor for the Gateway Park when it opens April 8, but the building’s unusual properties offered some distinct challenges to engineers, said engineer Scott Bowman, a principal owner of KJWW Engineering Consultants.

When the Public Library of Des Moines’ new $48 million Central Branch opens April 8, it will be more energy efficient than that expanse of copper-colored glass might suggest. That’s due largely to the work of KJWW, a Quad Cities-based company that won the mechanical engineering contract for the new library. KJWW has offices in Des Moines, as well as Moline and Rock Island in the Quad Cities, Madison, Wis., and St. Louis; employs 250; and has received a bevy of rankings and awards that list it among the top mechanical engineering firms in the world.

The stretched copper between panes of glass contributes to the retention of solar energy, but the amount of energy captured varies depending on the angle of the sun. “Usually, glass doesn’t have that effect,” Bowman said. “It’s the copper.”

Retaining the solar energy was one challenge. Another was minimizing the amount of ultraviolet rays coming into the library, which was as important a consideration as energy efficiency, because UV rays contribute to faster deterioration of books and other printed materials. By calculating the angle of the sun at specific times of the day and times of the year, engineers were able to make modifications that will reduce the ultraviolet radiation coming into the building by 83 percent

The new library is outfitted with all the bells and whistles expected in buildings designed for use in the 21st century, including energy-saving features like motion sensors that turn lights on and off when people enter and leave rooms. Some are visible, but others, like an under-floor heat-distribution system, are hidden – except in the children’s section, where a series of 2-foot-by-2-foot durable acrylic tiles expose the wiring and duct work. Library director Kay Runge wanted that feature included to enhance not only children’s understanding of how such systems work, but also their awareness of environmental and energy conservation issues in general.

The raised tiles allow for easy access to data ports and other wiring without having to tear out walls. They have been used for years in buildings where space needs change frequently, but also are also more energy efficient than the more standard convection air flow systems that push the heated or cooled air down. Air diffusers mounted in the 2-foot-by-2-foot, 18-inch-deep tiles that make up the raised flooring can be adjusted to individual comfort level.

KJWW first designed an under-floor air -distribution system supported by a geothermal pond for a Des Moines Area Community College’s West campus technology center, a 2003 winner of an international award from the American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. But working with Arup, an international engineering firm based in London that’s closely associated with British architect David Chipperfield, creator of the amoeba-like design of the library, gave the Iowa-based engineering company access to greater expertise on the installation of such systems.

Energy efficiency is also enhanced by the use of energy-recovery ventilators, which recover 80 percent of the energy that would be lost in conditioning air. “It’s a very simple thing with a complex tentacle,” Bowman said, explaining the rotating wheel filled with material that absorbs energy on one side and releases it on the other. It retains the moisture in the air, which contributes to energy efficiency. As a side benefit, the energy recovery system reduces the need to humidify the air, a special need in libraries.

Other energy efficiencies may not be immediately apparent, Bowman said.

The new library’s organic roof builds on the “library as part of the park” concept, but may also contribute to energy efficiency. Bowman and his peers at Arup are convinced that the roof will reduce energy usage because evaporation has a cooling effect, “but we don’t have a way to model it,” he said. “We are a few years a way from being able to quantify it.”