Shopping In Utah's Great (Semi-) Out-doors
In-slab radiant heating and cooling, cooling towers, and a serious array of pumps and tubing create just the right retail environment in this 20-acre downtown complex.
There’s a new and shimmering upscale tourism and retail destination in the heart of Salt Lake City that has won the attention of city planners worldwide. Some call it urban renewal on steroids. Others regard it as just one more extension of the buoyant and optimistic resource that Utah is.
When Salt Lake City planners looked at many options for a revitalization of their downtown area, they wanted ambitious ideas. Today, the mixed-use City Creek Center is the realization of that dream.
The $1.5 to $1.7 billion development is an upscale, open-air shopping center that includes office and residential buildings and a variety of water features developed by Property Reserve, Inc., the commercial real estate division of the Church of Jesus Christ of Latter Day Saints. City Creek is managed by the Taubman Company and City Creek Reserve, Inc. (The design teams included architects ZGF, Hobbs+Black, and Callison; structural and civil engineers Magnusson Klemencic Associates; consulting MEP engineers, Glumac. )
City Creek Center spans nearly 800,000 sq ft (20 acres) of downtown Salt Lake City and is part of an estimated $5 billion sustainable design project to revitalize the downtown area.
Smart by design
At City Creek Center, mechanical systems were integrated smartly, by design. The mechanical plan was developed by a team of consulting engineers at Glumac’s Irvine, CA, office and put into action by the 250-person firm, CCI Mechanical, Inc., based in Salt Lake City. The firm (with revenues of about $60 million annually) is involved in the design, installation, and maintenance of mechanical systems for commercial and industrial facilities throughout the Western United States.
To give you a sense of the enormity of the project, all exterior walkways, stairs, and common areas in both of the project’s city blocks are snow-melted. These areas cozy up to the large open or enclosed space of both malls which are fully served with in-floor heating and cooling.
Planners set out to provide environmental control and comfort for two 160,000 sq ft retail mall spaces, each connected by an enclosed, environmentally-controlled sky bridge. Each of the malls can be opened to the elements and fresh air, or closed to provide optimal comfort inside, thanks to the automatically retractable roof and wall systems.
‘Streets of Florence’ … with a roof
Steve Straus, president and CEO of Glumac, said that the presiding Bishopric’s “Streets of Florence” vision served as the aesthetic driver for the city’s sweeping renovations.
According to Straus, many design options were looked at over many months, but the one key concept that united people on both sides of a debate and supercharged the project were recommendations by MKA (Seattle-based Magnusson Klemencic Associates, a structural and civil engineering firm) that enabled mall spaces to be both an open-air pedestrian streetscape — what the church most wanted — and also a suburban-style covered mall to encourage all-weather shopping.
“They came up with the concept of a retractable roof and end walls, offering the best of both worlds,” said Straus.
Shelley Clark, structural engineer and a principal with MKA knew that a clamshell roof design would stick out conspicuously and also wasn’t practical because the site is near the Wasatch Fault, where seismic design loads are 25% higher than in San Francisco.
Clark sought counsel with Jon Magnusson, MKA’s chairman and CEO. Apparently, it took him only 15 minutes to devise a solution that called for a bi-parting vaulted skylight on rails. Not only would it retract; it would swing out of sight from the concourse below.
The essential structural element was affectionately dubbed the “whalebone.” The clever design, quickly blessed by Taubman managers, proved to be the crucible moment for several other facets of the immense construction project; they fell into place like so many aligned dominoes.
“The retractable design also proved ideal for environmental control, with huge advantages to reduce energy consumption,” added Straus.
The retractable roof and end wall capability permitted Glumac’s engineers to design mechanical systems around the expectation — now realized — that retail mall areas remain open most of the year, with no call for heating or cooling most of the time.
“We now see that energy consumption is reduced by 25 to 50% when compared to conventional, closed structures,” said Straus. “Other success indicators are revenues generated by the stores within the malls, and business is very good.”
The retail areas were awarded LEED Gold status by the USGBC as part of the LEED for Neighborhood Development rating system and also were a “gold” level recipient of the 2013 ICSC (International Council of Shopping Centers) Design & Developments Award in both the “new development” and “sustainable design” categories.
“We wanted to provide optimal comfort while using a minimal amount of energy. A scale model of downtown Salt Lake City was built in a wind tunnel and computational fluid dynamic studies were performed to help determine the effectiveness of natural ventilation,” explained Brian Berg, Glumac’s project manager for City Creek Center whose team focused on the retail areas.
“Even with the roof closed, the side walls remain open, natural ventilation was the answer,” he added. “With no air handlers needed for the main galleria areas in each mall 84% of the year, it’s easy to see why the energy savings are so substantial.”
Another key concern for Glumac’s mechanical system designers was their desire to conceal most of the equipment — including the 30-ft cooling towers.
“We concealed all of the chillers, boilers, air handlers, outside air fans, most of the kitchen equipment and exhaust fans below the roof level,” explained Berg. “The large cooling towers were recessed into the roof so that they were flush with the roofline. The outside air fans that serve the retail areas were rather difficult to fit, but we found ways to do it.”
“Today, aerial photos show roofs with mostly-hidden mechanical systems,” he continued. “All told, it’s 5,000 tons of mechanical gear ‘buried’ for two reasons: One, to be good neighbors so that the adjacent high-rise tenants don’t look down into a mish-mash of mechanical equipment — the owner’s directive from the beginning — and two, we had to be sure that our systems wouldn’t obstruct movement of the roof panels.”
Yet, as substantial as the mechanical infrastructure is, a key attribute of the plan was the effort to simplify all facets of the design so that the overall system’s many mechanical parts and pieces wouldn’t be strewn across the two city-block-sized space. Fluid systems integrate immense heating and cooling functions, connected through the efficient exchange of Btus at many levels.
Though there are thousands of interconnected components, and many key mechanical stations, there are arguably two main elements of the vast mechanical systems at City Creek Center. First, there are the evaporative cooling towers and the water-sourced heat pumps connected to them. And there’s the interior, in-slab radiant heating and cooling systems, and much larger exterior areas with snow-melting capability.
“The cooling tower arrangement is unique,” said CCI’s Seth Roth who, for 36 months, supervised and coordinated the work of up to 60 CCI craftsmen at City Creek Center. “There are three large Evapco closed-circuit fluid coolers and two smaller open-circuit cooling towers, all raised on 8-ft pedestals on a rooftop — with raised work platforms for access to the cooling towers (also supplied by Evapco) — a smart arrangement that provides space for mechanical systems below them, including a bank of large pumps.”
“The low-noise cooling towers were chosen for their suitability for an urban environment,” said Roger Johnson, sales engineer for Salt Lake City-based manufacturer’s rep firm, TMS, Inc.
The closed-circuit “ESWA” induced-draft hybrid cooling towers — connected to large water-to-water heat pump systems — have stainless steel heat exchangers to reject heat.
“The cold water basins are also made of stainless for durability,” added Johnson. “Two of the closed-circuit towers are rated at 4,052 gmp (w/40% glycol, 90°F in/80°F out with 65°F entering wet bulb), and one is a 2,038 gpm system.”
According CCI’s Nathan Gover, HVAC technician who supervises all ongoing mechanical system service and maintenance needs at City Creek, the open-circuit “UT” Evapco cooling towers are of an induced-draft, counter-flow design. One is rated at 1,400 gpm; the other at 2,800 gpm; both with 90°F in/80°F out and 65°F wet bulb. They serve the heat rejection needs for five, 280-ton Daikin Magnitude magnetic bearing centrifugal chillers.
The key challenge in connecting these large systems was how to orchestrate the movement of fluids between the cooling towers, water-sourced heat pumps, and the fluid cooler heat exchangers.
Five Taco “TA” horizontal split-case, 60 HP pumps rated at 2,026 gpm at 75 head/FT serve the fluid coolers and water source heat pump system. Five more TA’s — sized at 25 hp and 840 gpm at 75 head/FT — and four “FI” base-mounted, end-suction pumps, each rated at 125 hp and 2,375 gpm at 130 head/FT — serve the condenser water loop.
“The TA pumps can be mounted horizontally, so this was especially useful for installation in the space that was created under the cooling towers,” continued Johnson. “The FI pumps were installed inside the building.”
All of the large, multi-horsepower pumps connected to the heating and chilled water systems are powered by variable frequency drives.
For the radiant and snowmelt systems, the VFDs modulate flow to track heating or snowmelting demand precisely as ambient temperatures change. On the cooling side, the VFDs adjust flow based on the need to transport and reject heat. As the load diminishes, flow and energy usage are reduced.
Protecting the domestic water supplies in the main mechanical areas at City Creek Center are five Watts backflow assemblies. There are three, 3-in 909 reduced pressure principle assemblies (“RPZ”s), one each to serve makeup water for the cooling towers, the glycol side of the water-source heat pump condenser loop, and another connected to the makeup water for the water-source heat pumps.
Also, there are two, 2-in 909 RPZs. One serves the makeup water for the boilers; the other is connected to makeup water for the chillers.
A glycol/water mix circulates between the water-source heat pumps and the radiant tubing below all mall common areas and walkways to provide year-round comfort. Even more impressive is the snowmelt system that removes snow and ice from a combined 30 acres of outside walkway and stair areas, mostly stone paver surfaces.
Make no mistake: this is a high-volume system, the gamechanger, the one worth writing home about.
All things radiant
CCI craftsmen installed 18.5 miles of .75-in Watts Radiant PEX+ tubing for the 84,365 sq ft snow melt systems alone. According to Gover, there’s another 102,600 lineal ft of Watts Radiant PEX+ (5/8-in in size) to circulate fluids within the 25 indoor radiant heating and cooling zones (for a total of 47,656 sq ft).
“We chose Watts Radiant tubing for the project for a couple of reasons,” said Roth. “The design reports or tubing layouts provided by Lundquist Sales are very detailed and accurate. Their service is excellent. We also appreciate the 1,200-ft rolls of tubing; only a few suppliers offer that. At City Creek, we had the giant rolls on wheeled uncoilers and simply cut off four 300-ft rolls from each. We could cover a lot of ground quickly.”
In “Block 75,” CCI technicians installed 15 snowmelt zones, and 12 radiant heating or cooling zones. In “Block 76,” 13 snowmelt zones and 13 radiant zones were installed.
Each zone is served by tekmar 090 snow and ice sensors, each is nestled into an 091 socket. The 090 is an in-ground sensor which automatically detects snow or ice on solid exterior surfaces. The sensors are set up to activate the vast snowmelt systems when snow or ice is present, while also providing slab temperature feedback to the control.
CCI installers also used 2,400 lineal ft of 5/8-in Onix EPDM synthetic rubber tubing to provide snowmelting capability for several exterior stairways. “CCI requested that they be allowed to buy the tubing specifically for the stairways because of its superb flexibility — a valuable attribute when doing stairs and risers,” said Mike Lundquist, president of Lundquist Sales, Inc.
Source of warmth
Of course, for all this warmth there’s got to be a source for it, and a way to move heat from one place to another.
For the snowmelt system, CCI pros installed thirty 3-million Btu boilers, which stand ready to wage war with the area’s expected 60-plus inches of snowfall each year.
There are 34 Taco “KV” vertical in-line, direct-coupled pumps rated at 130 gpm and six “TC” 40 hp, 480 gpm vertical split case pumps to move Btus about the entire developed space, serving 38 zones of snowmelt, and the indoor radiant systems. Each of the boilers is partnered with a 1.5 hp KV pump so that warmth is provided for all space heating and snow melt needs. Thermal energy is also shared with a large, indoor fish habitat that includes a created stream and pond, home to several schools of cutthroat trout.
The heat plant avails more than 90 million Btus to remove snow and ice outside, or to provide indoor radiant heat, whenever there’s demand. The boilers provide 190°F fluid into a large main, which is then injected and tempered-down to feed circuits for the radiant heat and snowmelt zones.
The mechanical recipe includes a broad list of Taco hydronic components, including large suction diffusers, multi-purpose valves, two 1,056-gallon expansion tanks, six 6-in 4900 Series air separators, four 12-in air separators, and one 14-in unit on the chilled water system.
“Naturally, we’re very proud of the work our crews did at City Creek Center,” said CCI’s Dave Katsanevas, vice president and senior partner. “Considering the overall scope and magnitude of the job, the duration of the project, and the involvement of many people at CCI, it’s been very rewarding for us to see it come to fruition this way.
“When we walk those snow-melted pavers while shopping in the winter, we have a unique understanding of what’s involved,” he added. “In the cold months, it’s easy to imagine all of the interconnected parts, and the mechanical systems serving tubing below.”
And, in the summer, when the roof is closed, the same network of tubing — while engaged in the business of radiant cooling — wicks away heat almost unnoticeably.
“Radiant cooling is amazing,” concluded Katsanevas. “The source of comfort — just as it is with the heat for winter snowmelting — comes from equipment that was installed with care by a fine group of professionals who I’m proud to work with. The mechanical systems perform just as designed, according to a system design that works amazingly well, a masterpiece.”