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Recycled Water Improves Energy Efficiency

Exterior rendering of the new addition to the Denver Museum of Nature & Science
The new $56.5-million addition to the Denver Museum of Nature & Science comprises an educational and exhibition space above grade and an underground science collection center to house the museum’s collection of 1.4 million artifacts. © Rick Wicker, Denver Museum of Nature & Science

A new addition to Denver’s nature and science museum deploys a novel heating system.

March 25, 2014—Founded in 1900, the Denver Museum of Nature & Science opened its landmark neoclassical home on the edge of City Park—Denver’s largest green space—in 1908. During the next hundred years, the museum grew to become the largest natural history museum between Chicago and the West Coast.

But as the museum grew physically over the years, its collection grew as well— to more than 1.4 million artifacts. To this point, the museum had artifacts stored in nearly 50 spaces around the museum, including underneath the venue’s IMAX theater and behind historic dioramas.

The museum’s new $56.5-million, 126,000 sq ft addition, which opened earlier this year, comprises two main elements. One is a 63,000 sq ft storage facility, called the Rocky Mountain Science Collections Center, which occupies two levels below grade. The other, the Morgridge Family Exploration Center, is an aboveground education center, with classroom spaces, a discovery zone for small children, and an upper-story space for temporary exhibitions.

The below-ground storage center consists of high-density filing storage, housing everything from meteorites to Mastodon bones. The museum “works earnestly as stewards of the collection in the Rocky Mountain region,” says Maria Cole, AIA, a principal of klipp, a division of gkkworks, the Irvine, California-based designers of the addition. “They know they have the public trust in preserving the collection and take that obligation very seriously.” 

One of the challenges of engineering the basement was figuring out the loads for the artifacts, says Brian Tinkey, P.E., LEED-AP, an associate of Martin/Martin, Inc., of Lakewood, Colorado, the project’s structural engineering firm. He says the scientists at the museum had to weigh a variety of artifacts to calculate the storage facility’s floor loading capacity, which came to 300 to 400 psf. The floor also had to provide 45 ft wide column-free spaces and strict deflection limits of L/700 for the heavy filing system. The space was constructed out of reinforced concrete—the museum didn’t want anything to be posttensioned, Tinkey says, to make it easier to adapt to future needs. Above grade, the building was constructed with a composite reinforced concrete and steel.

Louvers on the building’s south face automatically adjust to changing light conditions

Louvers on the building’s south face automatically adjust to
changing light conditions. © Rick Wicker, Denver Museum of
Nature & Science

“We had some pretty heavily reinforced-concrete structure,” Tinkey says. “It would have been a little smaller structure and easier to build if we’d had additional columns in there, but that would not have accommodated their needed filing system.”

He says Martin/Martin also had to add reinforcing along the entire circulation path around a single artifact, a 10,000 lb stone monument known as a Maya stela—the heaviest artifact at the museum.

Developing the new wing’s heating and cooling system also required thinking outside the box. The city’s parks department was not excited about the museum digging up City Park, so the museum developed a novel solution. The plan, believed by museum officials to be the only one of its type in the country, uses recycled water from the Denver’s existing recycled water system to source and sink heat from the building’s existing heat pumps. Using recycled water in this way will reduce heating expenditures by 60 percent and help the museum to meet its sustainability and energy efficiency goals.

According to Dave Noel, the vice president of facilities, capital projects, and sustainability at the museum, the final engineering design resulted in a system with seven 30-ton heat pumps which provide 100 percent of the heating and cooling for the entire facility, as well as the dehumidification necessary in the summer. The recycled water is sourced from a 3,300 ft service line that connects to a nearby main operated by the city’s water utility, Denver Water. A second line returns all of the water to the Denver Water main after the system “uses” the water’s thermal properties. The maximum flow of the recycled water required for summer cooling is estimated to be 650 gpm; for heating in the winter, is roughly 270 gpm. The system design includes back-up capabilities that will provide the heat pumps with auxiliary hot and/or cold water should the recycled source water become temporarily unavailable. 

It’s robust enough for the unique requirements of a large institutional building. For instance, during the winter, a big exhibit may have 400 people, and the heat gain in that room is high enough to require air conditioning. Yet other spaces in the building will have to be heated because the outdoor temperature may be 30 degrees Fahrenheit. “So the system has to be able to manage heating or cooling at any time,” Noel says.

The building also requires climate control for the exhibits themselves. Building below grade, where temperature and humidity is more consistent, is part of the solution. But designers also created a “purge cavity,” which Cole describes as essentially a building inside a building. The innermost space is humidified, while the envelope that wraps it is not. Both the innermost space and the building envelop have vapor retarders to provide, she says, a “belt and suspenders” approach to protect the building envelope from humidified air.

The building is clad in variegated buff- and gray-colored Indiana limestone

The building is clad in variegated buff- and gray-colored Indiana
limestone. Small punctured windows allow a glimpse into the
space where new artifacts are prepped for storage. © Rick Wicker,
Denver Museum of Nature & Science

If that vapor barrier is penetrated, the humidity can enter and condense in the space against the outside wall. If the outside temperature drops too low, water drops out of the humid air and moisture can develop behind the walls, leading to mold or other environmental toxins. So the cavity space is pumped with dry air whenever the temperature gets too low. “If humidity gets through there, they’ll purge it out,” Noel says.

Additionally, no wet piping extends through the storage space—the pipes run along the interstitial space between the existing building and the basement. Since the two-level basement rests about 50 ft below grade, just above the water table, engineers built a drainage system underneath he slab and waterproofed the whole basement.

To achieve certification in the U.S Green Building Council’s Leadership in Energy and Environmental Design (LEED) program, paints, sealants, and carpets all had to have low levels of volatile organic compounds (VOCs). This not only helps earn LEED credits but benefits the sensitive artifacts as well; Cole notes that off-gassing from more harmful materials could damage, for example, the animal skins pulled across an ancient drum.

Rooms, rest rooms, and even stairwells are fitted with occupancy sensors, and the lighting throughout is high-efficiency compact fluorescent lamps or light-emitting diode bulbs.

Most of the water for the museum is provided by solar thermal panels on the roof. Additionally, a 200,000-watt photovoltaic array, also on the roof, produces about 25 percent of the energy used by the new additions. Meanwhile, the two floors of south-facing science education spaces have glass facades with automatic louvers to track the movement of the afternoon sun. The west facade features electrochromic glass, which can be tinted electronically.

The museum is also installing submeters throughout the entire museum complex to more effectively monitor energy performance. Previously the museum had but one energy meter, so gauging the specific impact of different efficiency moves was a challenge.

The museum master plan called for an addition on the south side of the building, reflecting a desire to not sprawl west into the heart of City Park. (The museum is situated on the eastern edge of the green space.) Additionally, the Denver Parks and Recreation Department wanted to preserve historic trees, which served to limit the footprint of the basement spaces, so the plan further integrates the rolling landscape around a small pinetum on the south side of the museum. An access road for school buses was redesigned to allow students to pass through a bit of the park before entering the new addition.

There’s also a collection preparation space where new objects can be inspected and cleaned before going into the basement for storage. On the plaza, gkkworks designed small punctured windows that provide little glimpses for visitors, especially children, into this preparation work.

The educational studios utilized patterned glass, which Cole calls, “our abstraction of organic patterning of animal species,” to provide privacy for groups of students. The main atrium space is large enough to host activities like shooting rockets or egg drops. And it connects back to the primary spine of the building. Because the museum wanted a visual connection to the park, there’s a series of glass demising walls that bring in light from the south.

The new building is clad in variegated, buff- and gray-colored Indiana limestone that relates to the buff masonry color of the museum’s historic main building. Variegated limestone can be found along the water table in this region. The museum’s thinking was that the material would be educational for students. “Geology can lightly be expressed when kids come in,” says Cole.



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