The client said, "We've got this building located underground with 2-ft concrete walls; it was originally designed as an emergency telephone switching facility built to withstand a nuclear blast. That was 30 years ago. Now we're adding new telephone equipment and the existing infrastructure won't be able to handle the additional load. The mechanical equipment is all original, and most of it needs to be replaced. Our temperature control system isn't doing much for us, just monitoring and alarming - the entire system should be replaced with contemporary technology. We don't have city water service, and our fire protection system won't be big enough to handle anything more, so it'll need to be addressed. Fire detection is antiquated and needs to be upgraded. Electrical service from the utility is pretty much maxed out. Our main transformer may need to be replaced.

By the way, we need to do all of this without shutting anything down. Ever."

That was the challenge facing Grumman/Butkus Associates (G/BA) when approached by AT&T for ideas for expansion of its central office in Plano, IL. Several months later, contractors broke ground on the project.

Nature of the Business

Rapidly changing technology, fierce competition, evolving regulation, and staggering economic stakes have made telecommunications one of the most dynamic industries of the modern global economy. AT&T's Plano facility is a typical example of a facility built at a time when no one in their wildest dreams could imagine what the industry would look like today.

Compressed into a shortened design and bid period were numerous tasks, including conceptual design and design basis document (DBD); funding approval; design of a new hvac system, temperature control, power, lighting, fire detection, plumbing, fire protection, architectural, and structural systems; design of temporary measures to maintain service continuity; competitive bidding and evaluation; contractor selection; and mobilization.

While no building owner likes to see interruptions to heating, cooling, or electrical utilities, the telecommunications industry has zero tolerance for downtime. Sensitive switching equipment can easily be affected by rapid changes in temperature or momentary losses of power. Operational communications equipment serves as the lifeline for countless businesses and emergency services. Thanks to extreme measures to ensure reliability, consumers have been able to take phone service for granted.

Requirements for the Plano project were simple, if not easy to achieve: cooling and electrical systems were not to be interrupted at all.

The Facility

The existing building consisted of four underground levels for telephone equipment and support areas totaling approximately 70,000 sq ft, plus a 2,000-sq-ft aboveground shelter housing the main entryway and storage areas. Most mechanical equipment, including chillers, pumps, and air handlers, was located on the first underground level. Emergency generators, main electrical switchgear, and the sprinkler water storage tank were located on the lower level underground. The building breathed through three airshafts, one to bring in outside air and two to remove exhaust air. Numerous "blast valves," each 4 ft in diameter, were originally used to close off the airshafts and isolate the building in response to a blast as detected by "blast sensors" on the surface.

The primary objective of the building addition project was to replace and upgrade aged mechanical, electrical, plumbing, control, fire detection, and fire protection systems. Difficult access and the prohibition of service interruptions were the largest hurdles that needed to be overcome to accomplish this objective. Laurence Steiner, project manager for G/BA, noted, "The nature of the underground building added a special challenge to this project. Designed to withstand a nuclear blast, the existing systems were complex and massively built. Space constraints and limited access often required innovative solutions."

The Design Basis Document

The first phase of the design process was development of the DBD. The DBD listed design criteria for indoor and outdoor conditions, codes and standards to govern the design, general specifications for new systems (hvac, control, plumbing, fire protection, and electrical), anticipated building loads, schematic design sketches, ballpark construction cost estimates, and a preliminary project schedule. The DBD serves as a common reference that will be updated at the conclusion of the commissioning process to document the entire evolution of the project.

Perhaps the most critical component of the DBD is the cooling load analysis. Various pieces of information and scenarios were used to determine the capacity of equipment to be installed as well as to determine appropriate allowances for future additional capacity. Inputs used included actual measured loads, loads based on published product data, future planned loads, and future "unplanned" loads (equipment to occupy space that was not yet specifically identified).

Ultimately, the central mechanical equipment installed was designed to satisfy the existing load plus the future load from planned equipment. The building design included space for additional central equipment to serve the potential maximum load with all vacant space filled with telephone equipment. Distribution components (ductwork and piping) were designed to handle the ultimate maximum load.

Careful planning was also essential to ensure a smooth transition from the old to the new systems. "This project had a significant risk attached to it," said Jeff Conner, G/BA's principal supervising the project. "To minimize this risk, it was mandatory that G/BA thoroughly plan the construction phasing during the design process and incorporate the vast number of details necessary to make the transition from the old systems to the new building systems transparent to existing telephone equipment operation. We are very proud of this significant project accomplishment," he added.

G/BA worked closely with AT&T and the architect (MFH Associates) to develop and refine all of the inputs that were used to generate the DBD and ultimately determine the course of the entire project.

The Addition Takes Shape

In addition to providing easier access for mechanical equipment, locating the new equipment above ground freed up close to 5,500 sq ft in the underground building for use for telephone equipment expansion or other purposes.

A 9,500-sq-ft aboveground building addition was designed to house mechanical equipment (including allowances for future equipment) and administrative offices. Half of the existing above- ground shelter was salvaged and remodeled. A new passenger elevator was added for access to the underground floors. Access for supply air and return air to and from the underground building was accomplished by installing new duct risers inside the old outside air and exhaust air shafts. These new duct risers were installed while the fan systems below continued to operate.

Painstaking measures were taken to protect the sensitive telephone equipment below from dirt and dust during construction. The existing air filter banks needed to be removed to accommodate the new systems. Temporary filter banks were installed and checked regularly to allow adequate ventilation air to be supplied throughout construction.

Three 140-ton air cooled chillers were installed to provide chilled water for the entire facility. Since cooling is critical to the operation of the telephone equipment, systems were designed to avoid a single point of failure that could jeopardize the entire hvac system. Air cooled equipment was selected to avoid reliance on the site's aging wells and treatment plant. Chillers were sized for full redundancy, ensuring building cooling in the event of a single chiller failure. Provisions were made for a future fourth chiller to accommodate installation of more heat-producing telephone equipment in the future.

Three 40,000-cfm air-handling units (AHUs) were also installed in the aboveground addition, with provisions for installation of a future fourth unit. AHUs were designed to provide precise control of temperature, temperature rate of change, humidity, as well as high-efficiency filtration. Economizers and evaporative humidifiers provided tremendous energy savings in a building that has very large sensible cooling loads year round. Design features on the humidifiers and careful optimization of the control loops allowed precise humidity control.

Variable-frequency drives (vfd's) were fitted to supply and return fans. This accommodates cooling load changes due to telephone equipment addition or removal, as well as relatively minor changes due to outside conditions. Normally all fans run at a reduced speed, providing energy savings. In the event of a failure of one of the fan systems, the remaining systems will automatically ramp up to meet the cooling load.

Simplicity and ease of maintenance are crucial for high reliability. Access to major equipment was improved by incorporating access sections, and grating walkways for roof-mounted chillers and piping. Removable wall panels were provided for installation of future equipment. Redundant fan systems, chillers, and pumps allow scheduled maintenance shutdowns without jeopardizing the telephone equipment.

A new, 30,000-gal water storage tank was installed below the parking lot, with a new fire pump to provide water for sprinklers in the building's administrative areas. Accidental operation of sprinklers is a serious risk to telephone switching equipment. A dry preaction system was selected to provide an extra level of safety for sprinklers and piping in the underground building. A smoke evacuation system was also required to meet Illinois Commerce Commission rules for telecommunication facilities. Keyed switches activate the building's smoke purge system. This operates AHUs in a ventilation mode to flush smoke from the building after a fire. Motorized fire dampers installed in the ductwork allow reopening of closed fire dampers and ventilation of the building.

Early warning fire detection is installed in telephone equipment areas. Using air sampling tubing connected to central sensors, this can detect very low levels of combustion products to provide an early warning in the event of a fire.

The unique configuration of the building required other innovative design features. "The mere feat of getting air to move through the shafts by passing through specially designed bell-mouth fittings in 2-ft-thick concrete walls full of rebar" is one example, said Roger Turczak, AT&T's building engineer responsible for the Plano facility. These fittings were designed to reduce the resistance through the old blast valve openings to avoid having to cut through the heavily reinforced concrete walls.

As with any retrofit project, the construction process was full of challenges. The project was kept on track by the common focus of everyone involved - contractors, engineers, architects, and the owner - on getting the job done. Keith McIntosh, a member of AT&T's on-site workforce, adopted a sincere interest in the project, stating that "everyone has come up with really good ideas" during construction.

Temporary Measures

With the underground building's outside air intake being used to house the new main supply duct, the existing air handlers were prevented from operating in economizer mode during construction. Restrictions on outside airflow to the underground building during construction also meant that the underground, air cooled chillers and generator plant could not be used. In order to keep the building operating normally during construction, a temporary, 360-ton cooling plant and 1,750-kW power plant were designed and installed at grade. The temporary plants were used to provide chilled water and emergency power for the existing building during demolition and construction.

The temporary air-cooled chillers were sized to provide redundant capacity for the cooling loads present during construction. Each chiller was equipped with two refrigerant circuits, and since outside air was not available for cooling during construction, each was field modified by York for winter operation to -25 degrees F.

Chilled water piping and electrical feeds were routed through the underground building's exhaust shaft and through the old blast valves to interface with the existing building systems without interruption. Once the temporary plants were in place, the existing chiller plant was no longer needed and the building operations could continue throughout the year-long construction as if nothing had changed.

The Switch

Once construction was substantially completed, the building was ready to crossover from the existing to the new systems. Ductwork from the new addition was connected to the underground building. At this point, the building could be served by either the new equipment in the aboveground addition or the existing equipment in the underground building.

Proper operation of the temperature controls is critically important in the telecommunications facility. A nuisance failure that causes a fan to shut down or a damper to close could quickly cause a telecommunications service outage. The new systems were installed and thoroughly tested by Sys-Tek, the controls contractor, then verified by G/BA and Sys-Tek, individually checking all control sequences, safety interlocks, and backup controls. Equipment failures were simulated, verifying that the backup equipment started as planned.

Once testing was completed, thanks to careful planning and detailed temporary procedures, the crossover was virtually as simple as opening a few volume dampers. At no time was service to the building interrupted.

After a two-week "safety" period, where both the new and old systems were available in case of emergency, removal work began on the existing and temporary systems.

Turczak, reflecting upon the project, said that, "Every possible aspect of the underground building - fire protection, hvac, domestic water - was replaced without a service outage. This major undertaking was done successfully." ES

Project Roll Call

Throughout the project, AT&T building engineering and on-site staff, the contractors, and consultants were able to work closely to complete the project and resolve problems. By carefully preplanning much of the temporary work during the design phase, accurate bidding and cost estimating was possible. While controlling costs, the customer benefited from a very high level of workmanship and installation quality from the project contractors.

G/BA worked directly with AT&T and provided complete engineering design and construction administrative services for hvac, lighting, power, grounding, fire detection, emergency power, plumbing, fire protection, security, public address, and control/alarming systems. G/BA was also intimately involved in the commissioning process.

Architectural and structural design services were provided by MFH Associates under a separate contract with AT&T. Civil/site engineering was by Webster, McGrath & Ahlberg. C.E. Crowley & Associates provided roofing design consultation.

The general contractor was F.J. Lawdensky Construction. Edwards Engineering provided mechanical services, electrical was by Geary Electric, Sys-Tek was the temperature control contractor. Great Lakes Fire Protection was responsible for fire protection, and Fettes, Love & Sieben was the plumbing contractor.

AT&T's building engineer for the Plano facility is Roger Turczak. On-site AT&T personnel include Clark Gomes, Keith McIntosh, Jack Goetz, Roger Steensen, and Geno Biffany.