San Francisco, California
Anticipated LEED® Rating:
Uponor Radiant Heating and Cooling
Approximately 175,000 square feet
Outside Dew Point:
High 50s to low 60s (Fahrenheit)
EHDD (San Francisco)
Integral Group (Oakland, Calif.)
Nibbi Brothers (San Francisco)
Radiant System Installer:
ACCO Engineered Systems (San Leandro)
Uponor Radiant Heating and Cooling
Late 2012. Opens Spring 2013
EXPLORATORIUM MUSEUM PROJECT
Exploratorium’s New Waterfront Home Features Innovative Radiant System Using S.F. Bay Water
BY DEVIN A. ABELLON, P.E.
SAN FRANCISCO — When it comes to celebrating the new Exploratorium museum project, located at Pier 15 along San Francisco’s Embarcadero, the engineering and systems design professionals at the Integral Group tend to take it a bit… well, personally.
“From the outset, our client was determined that its new home be as sustainable as possible, so we knew the Exploratorium would be a perfect match with our own corporate commitment to green values,” says project manager Joseph Wenisch, who then adds that other factors have also spurred Integral’s enthusiasm for the project.
“While it is exciting and gratifying to work on a project that will leave a huge and lasting mark on the entire Bay area, the Exploratorium is also a very cool institution that occupies a prominent place in the cultural and educational life of San Francisco,” he continues, noting that the museum draws 500,000 visitors annually and another 26 million to its web site. Attendance at the new site is estimated to exceed one million.
“Many Integral employees, including [founder and managing director] Peter Rumsey, grew up in this area and visited the Exploratorium as kids,” he continues. “Now these professionals will get to enjoy it with their own families at the new, more easily accessible facility they helped design and whose commitment to sustainability they helped bring to life.”
Compelling contrast: The Exploratorium’s current home at the Palace of Fine Arts in San Francisco’s Marina District was erected nearly a century ago for the 1915 Panama-Pacific International Exposition. “No heating, no air conditioning, no ventilation, poor lighting,” Wenisch marvels. “Yet they still have managed to build a very successful space that has revolutionized museums around the world. Their signature participatory exhibits can be found in 80 percent of the world’s science centers.
“But they’ve outgrown it, and are now in a position to address the building issues they have struggled with for decades.”
At the heart of San Francisco’s waterfront, the newly renovated facility at Pier 15 promises to offer a compelling contrast in terms of breathtaking vistas, visitor amenities and an impressive assortment of architectural and engineering innovations. Built 1931 and vacant for a number of years, the more than 800-foot-long pier has undergone a gut renovation, including major structural repairs to its pilings to make it earthquake-safe for the next century.
Completed at the end of 2012, the massive construction project will yield approximately 330,000 square feet (sf) of indoor and outdoor space. A new mezzanine level will house classrooms, conference areas and offices. The finishing touch is an all-glass Observatory that anchors the back of the new complex at the end of the pier’s 800-foot projection into the bay.
All these upgrades and alterations were done within strict historical-preservation guidelines, with the idea of returning the building to its original look. As a consequence, certain architectural aspects, such as the façade and many of the windows, could be repaired and cleaned, but otherwise left unchanged. Some alterations, such as the addition of solar panels to the roof, won approval. Others, such as insulating the walls to prevent heat loss or gain, were disallowed. “Historical preservation was a factor in virtually every design decision we made,” says Wenisch.
Net-zero goal: When the Exploratorium becomes fully operational in the spring of 2013, its goal is to become the largest net-zero energy museum in the United States, if not the world. True to the spirit of the Exploratorium — and the nature of net zero — achieving such an ambitious degree of energy efficiency will require monitoring and tinkering over time. The entire undertaking will be a real-time education exhibit, with live energy use and photovoltaic (PV) production on public display.
“This project combines an effort to both innovate and think critically about the impact science can have on the world,” says Exploratorium executive director Dennis Bartels, Ph.D. “Our net-zero goal is, in part, a way to reduce our global footprint and help improve the community we’ve been a part of for more than 40 years. Net zero is a process — and an opportunity for the public to learn with us.”
Targeting LEED® Gold certification, the new Exploratorium will have many notable green features, including:
The job of raising or lowering the temperature of that bay water to meet comfort demand will be handled by eight, 50-ton, water-to-water heat pumps, made by Multistack. These electric chilled heaters feed a four-pipe system that carries either hot or chilled water to a 200,000-foot network of crosslinked polyethylene (PEX) tubing. Made by Uponor Inc., the tubing is embedded in concrete slabs on two levels and spanning 82 different heating-cooling zones. Each zone has a control valve and a thermostat to switch between heating and cooling, whatever the need.
No other type of water-heating equipment is used in the building, nor is there any use of fossil fuels except for highly limited cooking purposes in a small restaurant—thus, the net-zero carbon designation.
“We did not wish to sacrifice comfort for energy savings on this project, and radiant is a premium comfort system,” says Wenisch, explaining why the technology was deemed an excellent fit for an institution dedicated to innovative thinking. In addition, almost half of the Exploratorium is open exhibit space with 30- to 40-foot-high ceilings. “Radiant allows us to heat and cool at the floor level where the people are, rather than attempting to condition such a large volume of air in those high-ceiling rooms,” he says.
A third major contributor to water savings is a rainwater recapture system covering roughly a third of the roof area, despite all the real estate occupied by the PV system. The rainwater is routed from the roof to underneath the pier and into a large “storage tank” that is actually part of the building’s structure. “A pile cap beneath the pier, constructed to resist earthquakes, contains a large cavity where the rainwater is stored until it is needed to flush toilets,” says Wenisch, who estimates that the recapture system will save roughly 300,000 gallons of water annually.
Is radiant right? Integral began its mechanical, electrical and plumbing engineering work on the Exploratorium project in 2007, following EHDD Architecture, whose own involvement began a number of years prior. The two firms had successfully worked on several projects with a strong green orientation, most notably the Carnegie Institution for Science (Department of Global Ecology) at Stanford University in 2004. At 11,000 sf, this earlier development was smaller than the new Exploratorium, but uses a similarly innovative radiant system that distributes heating and cooling via PEX tubing. Instead of bay water, water is sprayed on the Carnegie Institution’s roof at night and then recaptured to cool the interior during the day.
As Exhibit I shows, the Exploratorium aims to achieve substantial energy savings over the ASHRAE 90.1 baseline in several areas. But heating and cooling, along with lighting and pumps, are expected to make the biggest contributions: a 55 percent savings in yearly electrical consumption for heating; and 94 percent for cooling. All of which is why the use of radiant slab heating and cooling was an integral part of the Exploratorium plan from the outset, according to Wenisch. But it was far from a slam-dunk.
“Building ownership opted for an integrated design approach, involving all the disciplines in the early programming and schematic phases of the project,” he says. “With the support of EHDD, Integral did a lot of energy modeling to demonstrate the benefits of radiant versus a more conventional VAV reheat system and to prove the operational cost savings to the owner.”
But the engineers at Integral also needed to fully convince themselves that radiant was the right choice. “Because most of the structure is situated over the water, there is a substantial amount of heat loss through the pier floor and into the air between the building and the bay below,” Wenisch continues. “Until we did the energy modeling, we were not 100 percent certain we could make the radiant work.”
One of the more critical modeling exercises involved tracking the temperature of the water beneath Pier 15 for a full year. The purpose: to verify that a demand for either heating or cooling—sometimes both simultaneously in different parts of the building—could be readily met, whatever the season. Integral documented a high-to-low range of 50°F to 65°F, which turned out to be “perfect for a radiant system,” says Wenisch.
“To cool the building, we need 58°F to 60°F water for the slab. On the heating mode during the winter, the low-range temperatures actually boost the efficiency of the water-source heat pumps. Overall, the San Francisco Bay is a fairly stable heat source or heat sink throughout the year.”
How the system works: Let’s take a closer look at how the radiant heating and cooling system is designed to function at different points throughout the year.
Bay water will be continuously pumped in and out of the building. First, it moves through low-pressure microscreen drum filters to sift particles larger than 30 microns. Then it circulates through an ultraviolet-ray sterilizer that keeps the system free from plant growth.
The filtered water is then transferred to a 4,000-gallon concrete tank beneath the pier before moving to a pair of titanium heat exchangers. Each exchanger is designed to handle half the load during normal operations and two thirds during maintenance periods. Depending on the need for heating or chilled water, the bay water exchanges heat with the “condenser water” circulating on the opposite side of the titanium units. Variable-speed pumps then move the condenser water to the eight Multistack chiller heaters and to the 82-zone, Uponor PEX tubing network embedded in the floors throughout the building.
The bay water never moves beyond the heat exchangers. That’s because salt water would corrode the heat pumps and other mechanical components in just a few months. Once the heat exchange process is complete, the bay water returns to its source—completely unchanged and with no chemical treatment, as stipulated by the local permitting authorities. All of the above is accomplished in a single space inside Pier 15, called the Bay Water Mechanical Room, whose operations will be available for viewing by museum visitors.
The system operates differently at various times of the year, based on the comfort needs of the building and the temperature of the bay water.
Integral expects that the waterside economizer mode will yield the bulk of the cooling system energy savings by keeping the heat pump chillers idle. “In San Francisco, we are very fortunate in that we have very few days over 80 degrees,” Wenisch notes. But even when the heat pumps are operational, “the chiller plant runs more efficiently because we designed the building to use a higher water temperature.”
Radiant also reduces the amount of energy normally expended to blow air. “Radiant has a lot of secondary benefits, and in this project we’re trying to take full advantage of all of them to minimize energy consumption,” Wenisch remarks.
The dryness of the San Francisco climate also obviated the need for dehumidification in all but the most heavily trafficked areas, such as the theater and the retail store inside the old pier and, most especially, the Observatory, which houses a cafeteria-style restaurant on the lower level and an exhibition and event space above. These areas are also equipped with radiant slab cooling, but when occupancy rises to several hundred people on a warm day, water-to-air heat pumps will activate to dehumidify the spaces.
“The radiant system is designed to operate on 55-degree chilled water, which is not likely cold enough to handle peak loads, especially when 500 people are gathered in the restaurant or the event room,” says Wenisch. “Rather than lower the system temperature, we opted for the water-source heat pumps. But radiant allowed us to use heat pumps one or two sizes smaller than they would have been if they were handling the spaces themselves.”
Success the second time around: The new Exploratorium is distinctive and even unique in many ways. But it is not the only renovated pier on The Embarcadero to employ radiant slab heating and cooling. Nor is it the first to attempt to save water and energy by using bay water with such a system.
Completed in 2001, the renovation of Pier 1 also employed these cutting-edge technologies. Unfortunately, while the building’s heating and cooling systems have continued to function properly, there were problems with the use of bay water at the outset.
“They ended up replacing the bay water system with a cooling tower,” says Wenisch, who also acknowledges that the Pier 1 situation “had an impact on the planning of the Pier 15 renovation a decade later. We had to fight through the negatives associated with that earlier project.”
But Integral believes that the bay water-driven radiant slab system at Pier 15 will avoid the problems of its counterpart a half-mile away down The Embarcadero, on its way to becoming “a great and long-lasting example of how to do green design.”
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Devin A. Abellon, P.E., has 18 years of experience in the HVAC industry with a focus on engineering and consulting. His passion is promoting and raising awareness of radiant cooling via training and education for engineers on energy-efficient strategies, concepts and designs. Devin can be reached at email@example.com.
Uponor, Inc. is a leading supplier of plumbing, fire safety, and radiant heating and cooling systems for the residential and commercial building markets in the United States. Uponor, Inc. employs 380 people at its North American headquarters in Apple Valley, Minn. For more information, visit www.uponor-usa.com or call (800) 321-4739.
For more information about Uponor, visit the Uponor media room at http://uponor.greenhousedigitalpr.com/archive/
© 2012 Uponor, Inc.
The design information in this case study is provided for illustrative purposes only. The actual requirements of similar projects will depend on regional climatic conditions, project-specific heat loss, owner expectations, applicable building codes, etc. Please contact your Uponor representative for assistance in designing your specific projects.
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For more information about the benefits of cross-linked polyethylene (PEX) tubing, contact a reputable manufacturer, such as Uponor North America (www.uponor-usa.com).
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Exploratorium: Projected Energy Use Breakdown
Measure: Annual Electricity Usage (kWh)
How to Make a PEX-Rebar Sandwich
“There were a number of peculiar field conditions we did not—and could not—anticipate until we got into the project,” says project manager Joseph Wenisch of Integral Group. “The radiant tubing layout in the mezzanine was easier, because that level did not previously exist, so we built the slab new. But the first floor of Pier 15, which extends right over the shoreline and the bay itself, was far more difficult.”
Upstairs, downstairs: The second level consists of a 5.5-inch structural slab poured onto a metal deck. The 5/8-inch PEX tubing loops for the radiant system are positioned at approximately one and a half to two inches beneath the finished slab surface. The slab contains a single layer of rebar to which the PEX is tied. All in all, the mezzanine proved to be a fairly straightforward design and installation.
Because of the need for earthquake protection, the specification on the first level was necessarily more complex, consisting of two layers of rebar with the PEX loops positioned in between and fastened to the lower stratum. The tubing was specified to sit three to three and a half inches beneath the surface to avoid being punctured by anchors securing the museum’s floor-mounted exhibits.
This “rebar-PEX-rebar sandwich” was then to be encased in a new, eight-inch concrete slab built atop the pier’s existing slab, which itself was to be tied into the existing pier pilings. Installers drilled holes and inserted vertical steel dowels to connect the two slabs at the existing-beam locations throughout the lower level. As Wenisch notes:
“We couldn’t insulate the first floor in the dowel areas, so we ended up with this checkerboard of two-inch, rigid insulation covering roughly half to 60% of the area. This checkerboard wasn’t particularly easy for the installers to walk on—let alone work on—and that added to the installation time.” It also helped necessitate a larger diameter of PEX, as we shall see shortly.
Fortunately, the use of the Uponor Radiant Rollout™ Mats on approximately 80 percent of the floor surface helped shorten installation time substantially. Custom-designed and prefabricated to project specifications at Uponor’s Apple Valley, Minn. factory, the Radiant Rollout Mats are pre-pressurized rolls of PEX-a tubing loops fitted with Uponor ProPEX® engineered polymer fittings. Once on the job site, the mats roll out like carpeting over the floor space, while requiring fewer ties to secure their position. As a result, Radiant Rollout Mats can install approximately 85 percent faster than conventional radiant tubing methods.
Double work: The first level of Pier 15 presented one additional complication, and it was a doozy. Early on, Integral and mechanical contractor ACCO Engineered Systems (San Leandro, Calif.) learned that the end of the structure sloped into the water at a far steeper angle than they had anticipated. To keep the first floor perfectly flat, the eight-inch top slab had be 12 inches or more in depth in certain spots.
“ACCO’s people had to first tie the PEX to the lower rebar, so it remained firmly in place when the ironworkers returned to install the top layer of the sandwich. Once the upper rebar was in place, the mechanical contractor had to return to the site, untie the PEX from the bottom rebar, pull it up to the top rebar layer, and finally re-tie it into place.”
Bigger PEX to compensate: Integral specified larger-diameter tubing on the first floor than it had on the mezzanine—3/4-inch versus 5/8-inch—for a couple of reasons: First, the imperatives of historical preservation precluded the use of insulation on the pier’s concrete walls, although Integral was able use R30 insulation on the roof.
The second factor once again derives from the building’s water’s-edge location. Much of the first-floor slab sits over air and water, and the “checkerboard” insulation covers only 60 percent of its surface. “We had to allow for a fifty-percent heat loss to the air from the bottom of the slab,” says Wenisch, adding: “Even at high tide, you have eight feet of air. Fortunately, that air is at the water temperature, which never gets below 50 degrees [Fahrenheit].”
In short, the radiant system must work harder to compensate for the heat loss or gain, depending on the time of year. The larger PEX tubing provides more heating and cooling capacity (surface), while also permitting Integral to keep the pressure drop below 10 feet for each of the 82 zones, thus minimizing the pumping energy.
“We are doing nine-inch spacing on center for the PEX loops throughout the building to meet the peak cooling loads, giving us a more uniform slab temperature,” Wenisch explains. “Fortunately, we shouldn’t have to do that much heating because really cold days in San Francisco are a rarity.”