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Pru1 and Pru2 - Before and After

Prudential Plaza aka
"The Rock"

Today, when we think of tall Chicago buildings, we think of the Sears Tower. Before that was the Hancock Tower and the Standard Oil Building. But for over a decade, the Prudential Building, rising a mere 601 feet and 41 stories was the one at the top. Dedicated on December 8, 1955, The Prudential Building was the first major skyscraper built after World War Two. Building Magazine called it the "$40 million secret" and related:

"To make sure Chicago's biggest real estate secret didn't leak out, the men involved used code names, met at secret hideaways, carefully guarded every scrap of wastepaper. It was so secret, in fact, that the identity of the buyer wasn't revealed to the seller for over a year."

At the time it was state-of-the-art with 30 automatic elevators that didn't need operators and traveled at 1,400 feet per minute, making them the world's fastest. It also featured 2,617 double-glazed windows (more glass than any of its Chicago neighbors), the largest air conditioning capacity in America and the biggest built-in parking garage for a single office building in the world. For many years, the Top of the Rock restaurant and observation deck on the 41st floor were major tourist attractions. After only two years, over 1 million visitors had come through. Although the Top of the Rock has been closed for over a decade, people still ask about it.

On March 27, 1985, Prudential announced plans to redevelop the 3.3 acre lot that makes up the Plaza today. The result of that redevelopment was the renovation of the Prudential Building, renamed One Prudential Plaza and the construction of Two Prudential Plaza. For brevity, throughout this story we will refer to the two buildings as Prudential 1 and Prudential 2. Prudential 1 is coated in Indiana limestone and aluminum, which was cleaned in 1985. It was then completely updated with state-of-the-art computerized controls in 1990. Prudential 2 construction began in 1987 and was completed in September, 1990. That same year the nearly one acre outdoor plaza was also completed. The complete Prudential Plaza is located 1 block east of Michigan Avenue, and is bounded by East Randolph Street to the south, North Beaubien Court to the west, East Lake Street to the north and North Stetson Avenue to the east.

From the start, Prudential 1 was a huge undertaking. To build it involved constructing above 21 tracks of the Illinois Central lakefront railroad, something that had never been done because of the complicated legal ramifications over air rights. To make matters worse, once approved, construction had to take place without interrupting railroad operations. And to support the building, huge caissons had to be dug - by hand - more than 100 feet down to bedrock. This entire process took almost three years.

Once completed, the new Prudential Plaza became a first-class office complex. The two buildings are architecturally distinct from a distance, but at ground level up close one can see that they are actually one unified office complex joined by two 5-story atriums and surrounded by an extensively landscaped one-acre outdoor plaza.

As mentioned above, the exterior of Prudential 1 consists of aluminum and Indiana limestone, which is arranged in alternate vertical ribbons. Prudential 1's renovation included new heating, ventilation and cooling systems, a new life safety system, new lighting, carpeting and wallcoverings and redecorated elevators. A new boiler system, heat exchanger and other energy saving devices were also employed to maximize Prudential 1's efficiency.

The lobby of Prudential 1 was remodeled and linked by a pedestrian walkway to the lobby of Prudential 2. Underground walkways also provide easy access to the AON Center as well as the Illinois Central train. The elevators of Prudential 1, in addition to being redecorated were renovated with new cabs and controls to make them completely modern and efficient.

And who do you think appreciates these renovations and amenity improvements more than anyone else? The tenants. Major tenants include Deloitte & Toucle; Peoples Energy Services; Baker & McKenzie; Leydig, Voit & Mayer and Grant Thornton. Ground was broken for Prudential 2 on March 11, 1987. The completed structure stands 900 feet from ground level to the base of the building's 50-foot spire. Designed by tenant architectural firm Loebl, Schlossman & Hackl, this new tower is covered in granite & glass to match the look of Prudential 1 and totals 930,000 square feet of rentable space. Of that square footage, 30% was leased prior to the completion of construction! Major tenants of Prudential 2 include Deloitte & Touche; McGraw-Hill and Leydig, Voit & Meyer.

Prudential Plaza is owned by the Shorenstein Company. As mentioned above, architecture services were provided by tenant Loebl, Schlossman & Hackl. Consulting engineers for the project were CBM engineers. Mechanical, Electrical & Plumbing was handled by Environmental Systems Designs, Inc. Civil engineering services were provided by McDonough Associates. General Contractor for One Prudential Plaza (Prudential 1) was Pepper Construction Company. And, General Contractor for Two Prudential Plaza (Prudential 2) and the outdoor plaza was Turner Construction Company.

The modernization of Prudential 1 was an exciting process. The first step in the mechanical work was the conversion from a high-pressure boiler operation to a low pressure system. New boilers were brought in through the railroad siding and laid in place.

One of two 750 Bhp Kewanee boilers after the new Boiler Room renovation. there also is one 500 Bhp and 200 Bhp. All four boilers run on gas or oil.

The air conditioning system uses Chicago River water for its condensers. Package units were controlled by domestic water. When the city regulations changed, in the process of modernizing the Prudential 1, this system was updated to plate heat exchangers. The condenser water system was converted to a closed-loop system using river water which had to be pulled 1500 feet. However, this led to other problems. >

Plate heat exchanger was an example of energy saving technology incorporated into the renovation process.

The original boilers at Prudential 1 were one 120psi 250-HP gas-fired, self-contained Cleaver Brooks boiler and three Erie City water-tube boilers that were originally coal and oil burners, converted to gas and oil. In 1986 these boilers were replaced with four Kewanee boilers: two 750 HP, one 500 HP and one 200 HP. All four boilers run on gas and oil, and 50,000 gallons of #2 fuel is stored in reserve tanks.

The air-conditioning system consists of three 900-ton Carrier 17M centrifugal chillers and one Carrier 19C 1000 ton. Steam at 125 psi was used for fans and steam at 8 psi was used for heating air handling units. Perimeter offices are heated and cooled Carrier Weathermaster units mounted under the window sills, and interior spaces were heated and cooled by an air circulation system. After renovation perimeters were heated and cooled by 10 high pressure perimeter fans and four secondary water loops. The interior space's constant volume fans were replaced with variable frequency drives (VAVs). This provides the opportunity to send cooling where it's needed as opposed to discharge air controlling.

One of Three 900 Ton Carrier centrifugal chillers. There also is another Carrier 1000 ton chiller .

Older buildings often have creative solutions in place in their mechanical systems. One example is Prudential 1's interesting domestic water system. It is based on gravity with large storage tanks in high and low zones at the 40th floor mezzanine and the 18th floor.

Another upgrade to Prudential 1 was its windows. The windows are Adlake Reversible windows. These windows had an interesting feature: they reversed so they could be cleaned from the inside. They no longer open however. Also worth noting is the 73-foot antenna that sits atop Prudential 1. In its day it was one of the biggest. Its tubular steel tower is 10-feet wide at its base, 3-feet wide at its peak, stands 311 feet and is designed to withstand 134 mph winds.

Prudential 1 controls were, in their day, the latest and greatest. Building Magazine referred to this "scientific" air control: "... heating-cooling plant is constantly monitored by 1,100 electronic pneumatic and electric thermostats integrated into a single system featuring a unique master control center." This revolutionary control system consisted of 800 space and individual unit thermostats, with a master control center. The control center featured master switches enabling engineers to switch between heating and cooling, and between daytime and nighttime operation. Needless to say, Prudential 1's building controls were updated. An Andover Infinity building automation system and Teletrol Automation System is used to constantly monitor and control all the equipment in both Prudential 1 and Prudential 2. All lighting, life safety, heating, ventilation and cooling is controllable from this single system. Two 1500 Kw emergency generators supply emergency power to both Prudential 1 and Prudential 2, keeping life safety, emergency lights, the 64 elevators in the complex and fire equipment operational. >

Two Caterpillar 1500 kW emergency generators supply emergency power to both Pru1 and Pru2. Emergency lights, 64 elevators and fire equipment are kept operational at all times.

Prudential 2 is a much simpler building, designed with late 1980s technology. Systems are more streamlined. For example, Prudential 2 uses three 1000-ton Carrier 19DR chillers. The main structure is served by three Woods fans with variable pitch blades. Four Evapco Cooling towers are in place: Three for the Carrier chillers and one for the tenant condenser water. And for heat, Prudential 2 uses electric resistance heat. Vertical turbine water keeps water temperature at constant pressure, rather than the old method of using steam tanks.

But in spite of all its modern utility, Prudential 2 has its own share of quirks. Take window cleaning - Prudential 2 has 83 roofs. It's beautiful, but the angular design of the exterior makes conventional window cleaning impossible. To clean the windows, a custom window washer was designed to go up and down the building. This specialized rig is run by the engineers - but they let window washers ride in it!

All Management of Prudential Plaza is handled by Shorenstein Realty Services. General Building Manager Steve Smith and Building Manager Dennis Lambert handle the properties and employ a fairly large engineering staff of 25 men, all members of Local 399. Chief Jack O'Rourke oversees the entire operation with the help of Assistant Chief Monty Schwandt and Assistant Chief Mike Woulfe. Assistant Chief/Day Supervisor Anthony Tuzzolino, Assistant Chief/Afternoon Supervisor Wayne Strama and Assistant Chief/Midnight Supervisor Gary Risser manage the plaza's 13 shift engineers and 6 apprentices. Why such a large staff? Remember, we are talking about 2 structures totaling 105 stories and 2,050,000 square feet of office space. That's a lot of building to maintain. Consider also the fact that Prudential 1 is of 1955 vintage - it has 38 mechanical rooms! And when you finally consider that the Prudential Plaza engineers do virtually everything but winter maintenance on the chillers, it is clear that there is plenty of work to keep 25 engineers extremely busy.

Jack O'Rourke, Chief Engineer, oversees the entire Pru1 and Pru2 complex.

On a daily basis, as referred to above, the engineering staff uses the Andover building automation and Teletrol to control all systems. In addition the engineers use MP2, a preventative maintenance program. Besides operating and maintaining the plaza complex, the engineering staff is often called on to work on special projects. For example, to prevent winter freeze ups, the engineers engineered and winterized Prudential 1's secondary water system in the heat exchangers. This was a long-term problem in the 1950s vintage building. The engineering staff analyzed the problem, and implemented the necessary upgrades.

Chief O'Rourke began in the business at 300 South Riverside where he served for 12 years working his way up to Assistant Chief. From there he went on to accept a position at 400 West Superior as Chief Engineer where he worked for 1 year before being offered the Chief's slot at Prudentialdential Plaza, which he accepted in April of 1999. In addition to his extensive experience, Chief O'Rourke has taken numerous Triton courses and continues to expand on his education. Jack lives with his wife Laura and their two children John Ryan and Abby in Park Ridge. In his spare time he enjoys golf and cross country skiing.

In our interview we also got a chance to talk with Assistant Chief Mike Woulfe. Mike has grown up in the business with Prudential. He started with the plaza in 1983 as an apprentice as Prudential 2 was going up and has worked his way up through the ranks over the past 16 years. Mike attended Moraine Valley College and has also taken numerous Union Hall classes, Triton Classes and manufacturer's seminars. Mike lives in Worth and enjoys golf and skiing.

Hopefully this overview has provided a look into one of Chicago's historic buildings and shown how old and new technologies can be used to create modern office complexes. While the Top of the Rock is no longer at the top of Chicago's skyline, its new sister building reaches up to reclaim Prudential's distinctive spot among the tall ones. And the new face of Prudential Plazqa is certainly among Chicago's brightest.

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