Figure 1. Terminal cooling equipment on the right distributes supply air to rows of switching racks on the left.
Chicago's famed Prudential Building is home to numerous businesses, but not many require cooling during the city's harsh Midwestern winter.

MCI WorldCom's telecommunications switch facility on the second floor of the 40-story Prudential Building, however, needs year-round environmental control. Housing millions of dollars of computers and telecommunications equipment, the facility generates an extensive amount of heat and requires a steady level of humidity, and must be free of airborne contaminants.

The 18,200-sq-ft facility provides local and national long-distance telephone and data service to thousands of businesses inside 40 square blocks of downtown Chicago, including the famed Chicago Board of Trade (CBOT). In fact, the computers at the company's facility handle more than 1 million transactions daily from the CBOT. The CBOT's early hours and frenzied trading creates a large and fluctuating demand for information processing.

The demand for telecommunications capabilities has increased so drastically during the past several years that MCI WorldCom chose to install more equipment in its Prudential Building facility to expand its capacity. The additional capacity was expected to generate even more heat, requiring a larger cooling system. And with so many people and businesses relying on this facility, downtime is never an option.

Industrial and commercial hvac firm Team Mechanical Inc. (TMI), based in nearby Wheeling, IL was entrusted to install the vital concentrated cooling system the telecommunications switch facility.

"MCI WorldCom's facility in the bottom of the Rock was going to exceed its current cooling capacity," said Tony Cribari, project foreman for TMI. "The facility needed a dependable system that would be flexible enough to accommodate future demands."

TMI found a completely reliable cooling source located just one block away: the Chicago River.

Environmental Control Requirements

Cooling is critical to the viability of high-end data transmission. If the cooling system were to fail, the facility would shut down within 15 min, knocking out telephone and data service to hundreds of thousands of businesses, including the CBOT.

"The heat generated is comparable to a baker's oven," added Cribari. "With so much data being processed and so much money at stake, downtime is not an option, and we needed a cooling source that never fails."

Computers and electronics are extremely susceptible to heat, humidity, and airborne dust and contaminants. With the explosion of computers into every facet of commerce and business, sensitive computer-based electronics are no longer confined to areas originally designed to house advanced electronics. Traditional office spaces are now being adapted to house complex telecommunications networks, and this requires installing industrial-strength environmental control systems in spaces that were previously served by smaller systems.

Modern computer systems, such as MCI WorldCom's switch facility, require controlled environments that prevent downtime from:

  • High-temperature conditions, which force equipment to fail or shutdown.
  • Drastic temperature changes, which causes random computer errors.
  • Low-humidity conditions, which produce static electricity that can damage electronic components as well as alter saved data.

"Precision environmental control is an absolute necessity in these adapted spaces," said Cribari. "Not only is cooling a major concern, but the humidity has to stay in an exact range and the air has to be kept free from contaminants."

Numerous Challenges

Started in early spring of 2000 and completed in late fall of 2000, the process of installing the cooling system for the switch facility provided many challenges. To meet an accelerated installation schedule, TMI employees worked double shifts, six days a week during the installation.

The first challenge TMI faced was cooling the facility during the switchover to the new cooling system.

"MCI WorldCom did not have the option of shutting down the facility while we installed the system," said Cribari. "We needed to install reliable, large temporary cooling units that would allow us to take the primary system off-line."

The humidity level inside the facility is required to stay between 40% and 50%, which prohibited the use of some traditional temporary cooling methods. TMI opted to install temporary spot coolers, and allocated them to "hot spots" as data loads increased and fluctuated throughout the day. These temporary systems were installed on two days' notice.

Following the installation of a reliable and suitable temporary cooling source, TMI began installing the permanent cooling and environmental control system throughout the switch facility.

Environmental Control System

After carefully considering the benefits of several cooling methods, the decision was made by the engineer to use the Chicago River as the cooling source to create an efficient, environmentally friendly way to maintain a constant temperature in MCI WorldCom's switching facility.

There are several branches of the Chicago River, all of which flow to and from Lake Michigan, and many buildings in Chicago once used river water for their cooling needs, including the Prudential Building, which was completed in 1955.

With the popularity of modern air conditioning systems, however, river water cooling systems in many buildings were allowed to deteriorate and, consequently, not many take advantage of this option anymore.

Although more recently constructed buildings do not have access to this natural cooling source, buildings such as the Prudential fortunately have "grandfather" rights allowing them to make use of the river water as a cooling source, which is more energy efficient than air and offers energy savings.

The river water enters the cooling system through a 30-in. intake valve located beneath the building. While the natural river current does provide some flow to two plate exchangers that are located in the mechanical room in the third subbasement of the Prudential Building, two 6-in., inline mounted, close-coupled centrifugal pumps power the flow to the exchangers. These pumps produce 1,200 gpm at 105 ft of head to provide the necessary water to two plate exchangers.

The mechanical room in the third subbasement is an old coal chute. In addition to being located near the Chicago River, the Prudential Building was constructed next to a rail line, allowing coal to be fed directly into the building. The coal was used to heat the building during the middle part of the 1900s, before cleaner heating sources were used. Since the building is no longer heated with coal, this area was transformed into the mechanical room for this project.

After being brought in from the river, the water flows to two plate heat exchangers, that are also connected to a closed-loop, variable-speed pumping system that serves the environmental control units. The river water absorbs thermal energy from the system return water, lowering the water's temperature before two inline pumps send the cooled water to one of the cooling units in the switching facility on the second floor. The warmed water is then returned to the river. While thermal pollution was an initial concern, the water released to the river is well within current EPA temperature standards.

The system provides several key benefits to the environment and the building's owners. The building no longer needs to build, maintain, and operate onsite chilling plants. And building and plant engineers can also avoid regulations affecting the availability of CFC refrigerants used in almost every centrifugal chiller and are also linked to the thinning of the ozone layer.

Specifying the system's equipment required careful consideration of equipment costs, durability, and maintenance issues, as well as operational requirements. The equipment chosen was the most cost-effective and durable, further eliminating downtime risks.

Figure 2. Due to space constraints, TMI installed in-line mounted pumps to drive the river water.

Environmental Control Units

This system is capable of meeting the varied cooling demands and fluctuating temperatures of the switching facility. Demands are so great in some areas that a single 30- by 30-ft area in the switching facility generates enough heat to require 60 tons of air conditioning. Chicago's weather fluctuates from below zero in the winter to above 100 degrees F in the summer, affecting the river water temperature as well as creating varied cooling demands.

There are nine environmental control units incorporated into this system. Seven 20-ton units, one 10-ton unit, and one 5-ton unit regulate temperatures, humidity, and filtered air. Designed to cool facilities with high heat-load densities, the units are flexible enough to target extreme hot spots in facilities such as the switching facility that are loaded with heat-generating computer equipment. The units also keep the air free from contaminants and regulate the humidity of the room. Space for the cooling units was limited, and even the smallest unit provides complete humidity control and air filtering as well as cooling.

The cooling capabilities were also engineered for extra capacity. If one unit is taken off-line for maintenance or repair, the others can handle the extra load for a short period of time.

The cooling units are served by a closed-loop, variable-speed system that is in operation 365 days a year. Two base-mounted, end-suction pumps providing 700 gpm with 130 ft of head are also located in the third subbasement and send the cooled water to the condensers.

A variable-frequency drive installed in the mechanical room responds to the switching facility's cooling needs and instructs the pumps to drive cooled water to the condensing units on the second floor, keeping the facility cool and the telecommunications equipment operating properly.

"While the cooling system is not complex, it has to be reliable, and few things are as reliable as the Chicago River," said Cribari. "MCI WorldCom now has an environmentally friendly system that meets its needs and is flexible enough to be expanded in the future."

Installing Control Units and Piping

Since the switching facility was operating, TMI grounded the coolers during the installation of the cooling system to avoid creating static electricity, which is potentially damaging to the operation of the switch facility.

TMI faced several challenges when installing the new system's piping. The new piping was installed using special vacuum equipment that kept the air free of sparks that could have interrupted data transmission. In addition, existing equipment on the second floor prevented piping the system directly to the condensing units. The pipes extend to the third floor and then return to the second, adding an equipment expense but saving the building costly renovations.

TMI installed the cooling units on the second floor first, then installed the piping on the second floor. The piping from the subbasements and the third floor was installed last, reducing the demand on the temporary cooling units used during installation.

None of the installation work compromised the integrity of the architecturally significant Prudential Building.

Upgrading the Electrical System

To match the needs of the expanded switching facility, the electrical system was also upgraded at the same time the environmental control units were installed. As the power demand increased, TMI adjusted the coolers' energy supply to keep the electrical system from overloading and the computer equipment running in proper form.

A generator installed in the second subbasement powers the pumps and plate exchangers. In addition to the generator, TMI installed a 25,000-gal fuel tank in the second subbasement to supply energy to the generator. The generator also required TMI to install 300 ft of exhaust piping, that leads from the generator, out of the back of the subbasement along the length the building to an exhaust port that faces away from the building. The generator is also kept cool by the river water cooling system.

Future Projects

Despite the demand of the dot-coms, the demand for new telecommunications capabilities is not expected to ease any time soon. MCI WorldCom is already expanding its facilities at the Prudential Building to match projected demands, and relying on TMI to provide the environmental control systems. TMI is currently installing new environmental control systems in the ever-expanding facilities, and the new projects are expected to be complete this year. ES