San Francisco's Moscone Center Adds an Underground Cooling Tower, 21 New AHUs, and More
San Francisco’s Moscone Center is a main driver for local economic growth, generating more than 20 percent of the city’s tourism economy, according to the San Francisco Travel Association. As part of the city’s efforts to build for the future, the Moscone Center is undergoing a major expansion project to ensure that it continues to serve locals and visitors alike.
Once completed, the improved Moscone Center is anticipated to generate fewer carbon emissions per visitor than any major convention center in North America. Southland Industries was selected as the partner to perform design-assist services and installation of the mechanical and plumbing systems, including both wet and dry HVAC, controls, and plumbing with significant integration into existing infrastructure.
The mechanical, controls, and plumbing systems provide significant energy savings and controllability, and the facility is projected to save more than 5 million gallons of water annually via an on-site water treatment plant. The project also includes one of the largest rooftop solar installations in San Francisco. The San Francisco Green Building Ordinance requires that the project achieve LEED Gold, though, with a strong focus on sustainability, the center is going above and beyond and seeking LEED Platinum certification.
An Environment For Many Environments
Since shows hosted at the Moscone Center range from indoor forests with real trees to high-end mobile phone shows, full floor plan auto shows, food-based conventions with on-site cooking, and more, the space needs to be capable, flexible, and adaptable to large and rapid changes in heat and moisture load. Since the expansion creates a new facility of greater than 500,000 square feet of show space and significantly more glazing exposure from the new architecture, the conditioning and control systems needed significant augmentation. The expansion project includes 21 new AHUs with 511,000-plus cfm capability, a new chilled water plant adding more than 1,600-plus tons of cooling, and approximately 5,000 hardware control points — triple that number to include software points.
When a large convention moves into the Moscone Center, the facility goes through a rapid transformation. Typically, within three days, the quiet, empty concrete show floors can be completely transformed into a prime show and industry gathering space. Indoor curved LED screen installations two stories tall are the norm. Automated lighting systems are hung from the structure on rigging, and decorations are fitted to every visible surface while forklifts and scissor lifts negotiate foot traffic all in preparation of opening day.
During these move-in periods, the building systems come alive to support new loads. Arrival of the visitors brings significant cooling needs. To be most efficient, all AHUs in the expansion project are equipped for economizing and can utilize the crisp, cool San Francisco Bay air as a first stage of cooling instead of enabling the chilled water loops. Using air-side economizers on this scale allows the convention floor to bring in cool, refreshing outside air at a minimal energy impact. Some of our largest ducts are 144 by 70 inches, so any savings is significant. The control system monitors conditions continuously and locks out economizers if outside air keeps warming up.
All air handlers are VAV-capable, and almost all are downstream VAV systems. At Moscone, both temperature and pressure of the supply air are reset using a trim-and-respond control sequence. This aggressive approach forces the system performance to most accurately fit the loads generated in the space compared to basic thermostatic set points.
The way this sequence works is by constantly reducing, or “trimming,” the supply pressure down and the supply temperature up. Both variables have outer bounds and adjustable trimming increments and periods. Since the system is constantly trimming these for energy use, once it hits the real needs of the space, the zones will no longer be satisfied. Once the minimum number of zones is not able to make set point, the system “responds” by incrementing the set points back. The rate of change for response is larger than the trim rate to provide conditioning when needed.
Having just one zone call for cooling or heating would most assuredly lead to a “rogue zone” driving the chilled water plant and air handler operation. By looking at the built space carefully, we can identify certain zones that may act as rogue zones and increase our minimum zone count required as such. At Moscone, an example of one of these potential “rogue zones” is an elevator lobby on the second floor that has full-height, south-facing glass that can heat up well before most of the building. Setting the minimum number of zones, and calibrating this sequence, is an art and is specific to each project.
Two Blocks, Two Plants
Moscone is a large site spanning two full city blocks and requires two chilled water plants — both an existing north plant near Howard Street and new south plant near Folsom Street. When enough zones in the facility can no longer be satisfied and chilled water is called for, one of the new 800-plus-ton south twin chillers responds first. This plant was installed as the new modern primary plant to supply the new building and supplement the existing north plant. The intent of the new control configuration is to have the south plant (new) staging up to the first stages of cooling at part loading, and then enabling the north plant (existing) to assist, if needed, as a final stage. This keeps the part-load efficiencies higher on the new variable-speed south plant and saves energy on unnecessary capacity.
The south plant is at the most southern end of the property adjacent to Folsom Street and sits just below grade. The chiller room equipment placement was extremely tight. Southland laser-scanned the existing space to make a point cloud data file for use as a background for three-dimensional modeling as preparation. Through thoughtful modeling of the space’s piping and electrical needs, all equipment safety and access clearance requirements are met with only inches to spare. To place the two new chillers into position, they needed to be lifted by crane indoors from the show floor through a temporary wall opening.
The cooling tower location is nearby and also just below grade (underground cooling towers!). Because of this challenging location, the towers were delivered in six modular segments, which required them to be rigged from the structure into position in a logical order of the top most segment of the far tower, then the bottom segment, and so on until all were in place like puzzle pieces. The fitment of the cooling tower segments was so tight to the structure opening that on the day of delivery, there were hammers and chisels ready for any rogue aggregate looking to delay progress. Since the mechanical space is mostly enclosed and below grade, the towers are drafted up through the architecture to the atmosphere.
A loop of this scale, with both new and existing equipment, has its own set of challenges. The plant installation included piping interfacing with existing distribution, use of existing spaces, and other associated hurdles. Even connections to the new chillers from the towers posed a challenge. As expected, emergency exits from an expansive subgrade show floor are many and line the perimeter of the property. Because the show floor is sub-grade, there are rated stairwells up to the street level, which challenged our paths of travel for our system’s piping in the massive concrete structure. Through the significant use of penetrating radar scanning, we were able to map rebar locations in existing walls and make careful custom cores around these existing MEP no-fly zones.
Control of the two chilled water loops is a unique feature of this site. The loops can operate independently of each other, each serving half of the property, or can be combined via interconnect valving and operate as one. When the loops are connected, both sets of pumps continue to run, requiring careful control of pump VFDs and loop pressure set points. The chiller control sequence can stage up and down intelligently as needed in this combined capacity. Two smaller adjacent properties also utilize these chilled water loops through existing piping, so our Envise control team is working with those facilities teams to engineer devices and a sequence of operation for remote enablement. The water side control also utilizes the aforementioned trim-and-respond control schemes for pressure and temperature set points, and the same strategy for thoughtful avoidance of rogue zones is utilized.
Controls Without Surprises
Operator interfacing for this project required additional strategy, since the Moscone Center has minimal scheduled operation. There either is an active show or there isn’t, so typical schedule optimization techniques, such as optimal start, have limited usefulness. In addition to typical controls pages, such as overviews and equipment detail views, Southland and Envise worked to create a special operator page, where all systems have, in essence, a simple software switch for enablement. This page enables us to have careful control logic over system start and stop sequences, allows us to enable or disable status reading, and grants us access to time delay safeties while still giving the operators the simple on/off operation they expect.
An often-overlooked feature of control systems is how it can be engineered and graphically designed to match the existing facility staff’s behavior. Major behavioral changes should not be assumed with large facility remodels, so the greatest chances for operator success can hinge on a few simple questions: How do you typically enable systems for move-in? When the show is over, how do you shut down? When there is a comfort complaint in a conference room, what do you tend to do? The combined nature of the significant amount of equipment and the multiple shifts of facilities staff requiring training poses a challenge that works best as a soft handover. During this period, it is highly useful to trend user activity logs.
At the Moscone expansion project, every space has a story. A massive concrete facility with many notches in its belt from prior remodels and smaller improvement projects has a natural design-build nature that requires certain types of project partners and a certain type of project team. Among these challenging conditions, our Southland team just celebrated our three-year no-injuries safety milestone. While partially open to the public now, by the end of 2018, the final phase of construction will conclude with the public fully experiencing the magnitude of the new floor plan. The new building will blend seamlessly with the existing structure, both visibly and invisibly. Through the teamwork of the general contractor Webcor, the understanding of challenging existing conditions by the city, and the creative and flexible approaches from our world-class field team, no challenge is insurmountable.