Overcoming Hurdles Produces Power Reliability
Prentice Women’s Hospital in Chicago
Ensuring power reliability for Northwestern Memorial Hospital’s new Prentice Women’s Hospital in Chicago was as demanding a project as Randy Ehret, senior vice president of Environmental Systems Design, had ever faced. Configuring electrical infrastructure, such as emergency power, is never easy in the heart of a major metropolitan center. Getting the job done was at the same time a 100-yard dash and a 26-mile marathon.
The hospital provides comprehensive women’s healthcare throughout all stages of life. At 937,230- sq.-ft., the facility contains 32 labor and delivery rooms, 134 labor obstetric beds, 144 normal newborn bassinets and 86 special care nursery beds. There is a surgical unit with 10 operating rooms, and a large comprehensive breast center. Supporting the healthcare units are retail stores, a chapel, dining services and an education center. The hospital cost $450 million to build.
The need for high power reliability for the hospital’s life-safety, critical and other loads was obvious, but there was a finite budget. As the engineering firm of record for designing the hospital’s mechanical, electrical, plumbing, fire protection and emergency power systems, ESD faced a daunting range of obstacles.
One was connecting three, 2000 kW engine-generators and engine paralleling switchgear to power transfer switches in the hospital. The job would require literally miles of wire because the gensets and switchgear couldn’t be located in the hospital.
“Forming a strong project management team from the very beginning helped make this project successful,” Ehret said.
Northwestern University’s Prentice Women’s Hospital in downtown Chicago has high power reliability as a result of normal power and emergency power redundancy throughout the building.
Hospital and university officials, code authorities, the construction manager, the architect, engineering, commissioning agent, power utility representatives, power transfer switch manufacturer and others comprised the team. The group worked together from conceptualization to design, construction and commissioning. They balanced their different perspectives on budget, constructability, maintenance, reliability and other issues.
Connectivity is the garage across the street
The engine generators and switchgear couldn’t be located in the hospital due to space limitations. The equipment originally was scheduled to be installed in a garage that was to be built adjacent to the hospital, but the space was dedicated for another use. Instead, the gensets and paralleling switchgear found a home in an existing parking garage across the street from the hospital. Dealing with rights of way concerning the street added layers of complexity.
Connecting the gensets and paralleling switchgear with the transfer switches would require spanning a 500 to 700-ft. stretch underneath the street through a pedestrian tunnel that connects the new hospital, the garage and Northwestern Memorial Hospital, and then up to the new hospital’s seventh and seventeenth floors.
The emergency power system includes 62 transfer switches, including bypass-isolation transfer. That added up to a lot of wiring since two wires for engine intelligence and two wires for load shedding would be required for each transfer switch. Redundant wiring for higher reliability added to the total.
Close to 3,000 wires as long as 700 feet would need to be threaded. That’s conservatively nine miles of wiring.
ASCO Power Technologies, which supplied the low voltage transfer switches, medium voltage engine paralleling control switchgear and design expertise, laid out a fiber optic communications control circuitry for the project. It’s a self-sustaining, isolated network that includes an Ethernet “self-healing” dual fiber optic ring. The design helped eliminate the massive quantity of wires that otherwise would have been needed.
Joe LaMartina, ASCO manager for the Chicago area, said, “This is the most complex hospital project in the Midwest, if not the country.”
Two pairs of traditional hard wires carry the start signals from the transfer switches to the gensets. This provides recognized reliability and helped get the variance required from the city of Chicago for remotely locating the gensets in another building.
For communication between the transfer switches and switchgear, two cables, one redundant, run from the switchgear to three, remote terminal units (RTUs). The terminals serve as interconnection points to the power transfer switches.
Substations house connections for a dual fiber optic local area network for load shedding, Ethernet switches for power transfer communications and hard-wired engine-start parallel circuitry. The emergency power system design incorporates layers of communications and control redundancy by providing redundant system controls and multiple communications and control paths for the systems most critical circuits, engine start and load shed. In the event of a failure of a PLC, communications LAN or hard-wired engine start circuitry, the system will continue to operate as designed. The substations also contain Liebert UPS’s and 24 volt DC power supply for backup communications power to power transfer control panels and substations.
Fiber optics produced a number of benefits. For starters, it eliminated signal loss that otherwise would have occurred with hard wire due to the long distances. Ehret also recognized a monetary benefit. “Running two cables gave us a robust system, and we didn’t have to buy all that copper twice,” he said, “and that saved a lot of dollars.”
To be honest, there were initial concerns about fiber optic since emergency power was a fairly new application for it at the time.
“But in the end, I think we produced a faster and more reliable system, he said. “Information travels back and forth on that bus at a higher speed than it could on copper.”
Ehret added another benefit: “One of the challenges is that every manufacturer’s control wiring is a little different. Fiber optics eliminated ambiguity in the bidding process.”
Three feeds for powerful configuration
Connectivity wasn’t the only issue created by the long distance between the generators and loads across the street. Running 4160 volt feeders from the generators to the transfer switches also proved problematic as room height for the generators was extremely tight.
“We practically had to shoe horn in the engine paralleling switchgear,” Ehret said. “The original concept was to cut the garage’s floor slab and take two 5 kV feeders, one redundant, underground and up adjacent to the pedestrian tunnel,” he explained. The structural engineer determined, however, that the slab contributed to the building’s structural support so it could not be cut.
The design allowed the feeder conduit to run outside and along the garage, under the sidewalk and beside the tunnel to get across the street and into the new hospital.
The overall power configuration for the hospital includes three utility feeds. At least two power any given floor. A fourth emergency utility line on an automatic throw over switch also is part of the system. It’s guaranteed to switch within nine seconds and tests show that it switches in fewer than two seconds. The four feeders connect to double-ended service gear with an automatic tie in between.
Redundancy also was built into the emergency power distribution system. It’s an N+1 configuration with load shed capabilities that ensure power to life-safety and critical loads if not enough generators are available. The two 5 kV feeds run to five unit substations within the building. Transformers rated at 2600 kVA step down power to 480 volts from 4160. Each substation serves a different area of the hospital.
A 3000 amp emergency power distribution board and a 480 volt distribution board from each of the substations also are part of the overall design.
On the 480 volt side, there are two levels of transfer switches for life safety and critical loads configured such that the first level is between two separate and independent normal sources of power that feed into the second level transfer switches along with the emergency feeder and out to the switches’ loads.
“Starting at the garage’s lower level and going to the seventeenth floor, we believe we have taken those redundant feeds throughout the hospital,” Ehret said.
Medium voltage engine paralleling control switchgear handles load optimization and management for the Prentice Women’s Hospital emergency power system.
Another step the team took to enhance redundancy and reliability was to keep the ampere ratings of the transfer switches small—800 amps or less. The four electrical closets on each floor are fed from various transfer switches to further enhance redundancy and reliability.
Monitoring for accurate data
Besides reliable power, hospital officials wanted reliable information. Getting accurate and timely data on power system status is essential in today’s operational environment so the team paid close attention to the emergency power’s monitoring and control system.
Northwestern Memorial Hospital personnel liked the local monitoring and control capabilities they had at another facility.
Ehret said, “They wanted the LED Christmas tree lights on the equipment itself that show system status at a glance. That’s the way they like to operate. It’s very visual. They don’t want to flip through screens or touch anything during an emergency situation.”
But they also wanted to communicate and share information more efficiently. A 40-in. LCD screen that’s part of the engine paralleling switchgear is in the engineering office on the 18th floor. It displays a one-line diagram of the onsite power system and shows a wide range of operational and other parameters.
A second, 40- in. screen was installed at another facility so personnel there can track system status as well. The remote capability is strictly for monitoring, not control.
A SCADA system monitors and controls the automatic transfer switches, medium voltage paralleling switchgear, engine-generator sets and graphically displays the status of more than 250 breakers.
A strategy for load management
The approach to ensuring redundancy and reliability is carried over to powering air handling units that ventilate each floor. Two supply and return fans in each unit have a separate emergency feeder and transfer switch.
Other loads, such as kitchen equipment and primary imaging, are not fed by the emergency power system since those capabilities are largely provided by the general hospital across the street. One of two MRIs and CTs that support outpatient services in the new hospital are included in emergency power, however.
Not surprisingly, two IT closets per floor are classified critical loads because the hospital considers electronic medical records essential to patient care. The closets manage primarily patient treatment data and are cross-connected for enhanced reliability. If power is interrupted to one of them, the other could manage data handling and storage for both. A 400 kW UPS maintains power to the closets until gensets can provide power when utility power fails.
A 10,000-sq.-ft. data center located in another building on campus supports the primary IT requirements of the hospital. A tier 3 onsite power system and UPS help provide business-critical continuity during loss of utility power.
Testing, testing, testing
The resulting power infrastructure for the new hospital promised to be highly reliable. But would it be? Hospital officials were determined to know. They demanded that commissioning be ratcheted up a notch to build their confidence in the power distribution system.
The team devised a two-night “blackout” test that would include not only the electrical systems, but also the integration and interactions of all the building systems on normal and emergency power. The test included the Illinois Department of Public Health, state officials who had to sign off on the project, local city inspectors, contractors, owners and design teams.
Ehret said, “We tested every potential failure condition that we could think of over the course of two nights.” Questions the test needed to answer included, what would happen if feeds were lost? Would all the transfer switches transfer? Would all the mechanical systems that were supposed to come back on, actually come back on? Was the building automation system properly integrated with the emergency power system? Were the elevators properly integrated with the emergency power systems? How would the life-safety and critical loads function? What would happen with the UPS system and the IDF closets?
“We found very few problems and in the end, the owner had a very high degree of confidence that this system was going to perform in the event of a true, actual emergency,” Ehret said. “Under any failure condition, they knew what to expect. Their facilities personnel were there observing. They know how to respond to any kind of a failure. It was fantastic training.”
It all adds up to a “powerful” new medical facility serving women’s health.
Randy Ehret, senior vice president of Environmental Systems Design, helped design solutions for communications wiring and fiber optic cables, and 4160 volt feeders for the emergency power system at Prentice Women’s Hospital in downtown Chicago. The challenge was to reach from engine generators and engine paralleling switchgear in a parking garage to power transfer switches across the street and up to the seventh and 17th floors of the hospital, while respecting rights of way.