Tilt-Up Skeleton
Washington County School District officials, together with contractors and architects, have actualized a functional prototype intermediate school that complements the colorful sandstone hills and red soil of southwestern Utah. The tilt-up concrete prototype is economical, low- to no-maintenance, and its geothermal heat pump system uses no fossil fuels to heat or chill the building.
Surprisingly, the heat pump system actually cost the district less to install than a conventional chiller/boiler system.
The Geothermal Loop
The system is called a ground-coupled geothermal heat pump system and it has approximately 200, three hundred feet deep bore holes that provide the interface for discharge of heat or discharge of cool into the ground.
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PROJECT DATA Owner: Washington County School District |
“This technology has been around for quite a while but really has not been embraced too well,” says Ken Naylor, AIA, NCARB, principal at Naylor Wentworth Lund Architects. “When we first got into it, we found that it was much more expensive to do this kind of system, initially. What we have found after doing it for six or seven years is that if the building is about 70,000 square feet or more, we can actually make it initially less expensive than a conventional boiler/chiller plant. For that reason it becomes the ideal mechanical choice for schools.”
Fossil Ridge Intermediate School’s 134,000-square-foot footprint made the facility an ideal candidate for a geothermal heat pump system, and officials had good reason to move in that direction. In St. George, known as Utah’s Palm Springs, summer temperatures can reach 115 degrees during the daytime.
Tilt-up concrete also plays a role in maintaining comfortable temperatures because, as a heavier mass structure, it retains heat and cool for a longer period.
“Our experience with ground source is that we are using about 39,000 to 45,000 Btus per square foot per year; our chiller/boiler applications run somewhere between 50,000 and 60,000 Btus per square foot per year,” says Phil Williams, director of physical facilities at the Washington County School District. “There is a definite savings in operating cost. Also, our initial installation is usually about $4 per square foot cheaper using ground source than the typical chiller/boiler systems that they’ve used in the past in schools.”
Williams adds that although he does not have much experience with maintenance, he knows from trade journals that his maintenance costs will also be significantly less. “We are pretty excited about the ground source thing and it is definitely working for us in our area.”
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| Aptly named Fossil Ridge Intermediate School is sited in an area of southwestern Utah where some of the world’s most significant dinosaur fossils have been found. Designers cast a 30-foot-long dinosaur skeleton into the interior concrete panels in the commons area using a polycarbonate template. These templates gave an almost glass-like finish, setting the impressions off both in color and texture. All photos by Frank Carter |
Tilt-up construction lasted 480 days. The prototype for Fossil Ridge, the 125,000-square-foot Lava Ridge Intermediate School, had been designed by Naylor Wentworth Lund Architects. The facility is the second repeat of this prototype intermediate school, following Lava Ridge by a couple of years.
The use of tilt-up construction at the two schools also incorporated an innovative coloring strategy. In fact, both school exteriors are unpainted.
Integrally Colored Concrete
Naylor Wentworth Lund Architects has now completed 15 tilt-up schools for Washington County School District. The firm initially did painted tilt-up concrete buildings for district, but it was district officials who suggested creating a building that they would not have to paint. Lava Ridge was the first district school to employ this next generation tilt-up philosophy that adds integral colorants to the concrete. (Lava Ridge was planned in association with the mechanical engineering firm of Van Boerum & Frank Associates.)
“So the nice rosy color is colorant all the way through the thickness of the concrete wall panels,” says Naylor. The colorant is mixed right in with the ready-mix concrete when it is poured at the site. To avoid the heat, concrete pours began at 2 a.m. so the site could be cleared by 10 a.m.
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| The two-color look is achieved by sandblasting. The lighter colored panels were more heavily sandblasted than the darker ones. Washington County School District officials opted not to paint the exterior, and avoid the associated maintenance. |
Naylor Wentworth Lund Architects is one of a small number of architects that has been exploring and developing the integrally colored tilt-up concrete structure. It is a single liquid colorant.
Is tilt-up a material of choice in the desert area of St. George? According to Naylor, “It is becoming that because it matches the environment so well.” Most of St. George has the red cliff look; most of the surroundings are pink to red to vermilion kinds of cliffs. The rock has a lot of bright red color to it, so these buildings, in the words of the city, “look as though they have grown out of the ground.”
At Fossil Ridge, Hughes General Contractors implemented the use of a new liquid coloring system. “With this new high-tech system, they no longer add colored powder to the concrete,” says Dan Pratt, Hughes project executive. “They now dye the water and then they mix the water with the concrete, and that is how they get the color in the concrete. By going to this new system we are getting a much more consistent color. It is still fairly uncommon. Many batch plants do not have that capability yet.”
The tilt-ups were integrally colored using a Solomon liquid color dubbed “Light Plum.” To decide on the tilt-up concrete color, sample pours were viewed before construction began so that the district was able to pick from a wide range of colors and decide which color they ultimately wanted for the new school.
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“A construction cost of $80.60 per square foot is incredibly inexpensive,” explains Project Manager Rick Ellertson, of Hughes General Contractors, the firm that served as the GC and the concrete/tilt-up subcontractor. “Most school construction costs run about $100 per square foot.” |
“I believe it was eight different samples, using several different liquid colors,” explains Pratt. “Once we stood up those sample panels, we sandblasted part of each one so that it would simulate the two different textures that would ultimately be on the project.”
To ensure further consistency, the ready-mixed producer stockpiled enough cement powder from the same source for all panels and also kept the same aggregate source throughout the project. Entire wall elevations were poured, corner-to-corner, on the same day and onsite, and all panels were pumped to avoid the inconsistencies in finish that can occur when concrete is placed directly from the chute.
The integrally colored concrete will not fade over time; in fact, it is expected to require zero maintenance over the first 20 years. “One of the beautiful things about integrally colored concrete is that the color goes all the way through the wall, so it virtually is there forever,” says Pratt. “The sun doesn’t lighten it and the rain doesn’t lighten it or darken it, whereas any kind of a paint surface will eventually fade and go chalky.”
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PRODUCT DATA Construction Materials Composite Materials Acoustic Products Carpet and Flooring Washroom Equipment/Supplies Physical Education Equipment Miscellaneous |
With just one color of concrete panel, it is very easy to get two or even three different appearances by the degree of sandblasting performed – light to medium to heavy. But at Fossil Ridge only two degrees of sandblasting were implemented – light and medium. To make it a maintenance-free panel, it does not require painting. Architects put a sealer on the panel, which is both a concrete sealer and a graffiti coat. It is one product, called Evercrete, which is not a sacrificial coating. If you want to learn more about concrete sealers, check out Seal With Ease.
“It is a good enough sealer that you can peel off graffiti from it,” says Naylor.
In addition to the cost savings, durability and quick construction period, the tilt-up has been called the “highest quality.” In fact, Pratt feels the school achieves a level of quality that is more comparable to a precast product, which is typically about twice the cost of tilt-up.
Then of course, there are the energy savings, both monetary and environmentally. In reference to the ground-coupled geothermal heat pump, Naylor stressed: “Now that we have learned how to design this system and we have people trained to install it, it not only is more economical in terms of continuing operational cost and energy cost, but it is now less expensive to install.
“So initially it is less and the on-going maintenance cost is less. We get the energy savings every day that this building is in operation as compared to a typical system. It is not burning any fossil fuels. In our opinion there is no reason for schools not to be embracing this technology.”