Raising the Bar, with Raised Floors

The best moments in consulting are when clients need to solve seemingly intractable problems, and the consultant can offer creative ideas and approaches that—more than simply overcoming the challenge—create a project of superior value and performance. Such an opportunity arose at the new Student Services Building at San José State University (SJSU), San José, Calif.

By STEVEN GUTTMANN, P.E., Principal, Guttman Blaevoet Consulting Engineers, San Francisco, Calif. October 1, 2000

The best moments in consulting are when clients need to solve seemingly intractable problems, and the consultant can offer creative ideas and approaches that-more than simply overcoming the challenge-create a project of superior value and performance. Such an opportunity arose at the new Student Services Building at San Jose State University (SJSU), San Jose, Calif. The team created a facility that met the owner’s aggressive schedule while exceeding functional, first-cost and energy-efficiency goals.

Part of the solution was a raised-floor system. The use of raised floors in commercial office environments has led to the development of new systems for delivering conditioned air as well as power, data and telecommunications infrastructure. The use of these systems at the Student Services Center addressed all the implementation challenges.

A part of the California State University system, the university needed to relocate several student-services departments to allow for demolition of an existing building to make way for a new library for SJSU and the city of San Jose. As the project took shape, school officials were elected to consolidate all of the student-services functions into a one-stop facility. To meet the university’s schedule for demolition of the existing building, however, the new student-services center had to be occupied within 10 months of the start of programming and conceptual design.

Student center from a garage

The architect, while examining an aerial map of the campus for a site to develop the project, focused on the large expanse of open space on the top floor of an existing parking garage. Upon further examination, it was found that the top floor was not structurally suitable; the ground floor, however, held some promise. After a feasibility study and financial analysis, the 97,000-square-foot ground floor-with its generous 15-foot floor-to-floor height-was selected for development of the student center.

Converting the ground floor of the existing parking garage would save a significant amount of time and construction funds. Its selection was the first of numerous creative solutions that helped the team exceed the owner’s objectives. Still, converting the ground floor of the garage implied numerous challenges: For example:

each attachment point.

An implementation strategy

To meet these challenges effectively and at a reasonable cost, the design team considered the use of a raised-floor system, typical of those employed in commercial office environments. Raised floors have allowed for the creation of new systems for delivering conditioned air, as well as a way to handle the power, data and telecommunications infrastructure. Best of all, its use for the proposed Student Services Center would address all of the implementation challenges (see “A Report Card for Raised Floors,” this page).

First, the raised-floor approach would eliminate attachments to the post-tensioned slab, except those required for return and exhaust ductwork, some minimal supply ductwork and for plumbing vents and fire-sprinkler piping. Second, underfloor air delivery would maximize ventilation effectiveness, thereby ensuring the best indoor-air quality possible.

Third, the raised-floor system would enhance the energy efficiency of the HVAC system by allowing for increased supply-air temperatures, which in turn would significantly increase the number of hours of free cooling-where outside-air temperatures are at or below the supply-air temperature. The raised-floor HVAC scheme would also reduce the power consumption of the air-cooled systems.

In addition, the raised floor would create a level surface for office use without modifying the garage floor slab. This way, the garage could also be easily restored when the new facility became available, and the raised floor could be reused in another location. Lastly, the raised floor would offer students and staff all of the basic amenities required for a cutting-edge institutional facility: an inexpensive means of distributing data and telecommunications infrastructure without the use of power poles or false columns.

HVAC system configuration

To condition the space, seven air-cooled split systems are used. Air-cooled condensers are mounted on the top floor of the garage, and double suction risers are used to address lift and oil-return issues. Air from each air-conditioning unit is delivered directly into the floor, resulting in an average of one air input per 14,000 square feet of plenum.

To maximize redundancy, 80 percent of the facility is built on one large floor plenum served by six of the seven units. This eliminates almost all interior plenum dividers; dividers were used only at perimeter zones and conference rooms. Numerous relief openings are included in the design to allow passive relief of outside air; one system has a return fan with a variable-frequency drive, with speed controlled based on measured building pressure.

One air-conditioning unit serves a segregated 14,000-square-foot area. This area, including the floor plenum, is isolated by the main lobby on the north and by the only rated partitions in the building on the east. This unit also has a return fan controlled by space pressure.

Perimeter zones are provided with pressure-dependent modulating dampers located in the plenum dividers; the low plenum pressures and inherent performance of the underfloor system make the use of pressure-independent devices an unnecessary expense. Recessed convectors are located under a continuous perimeter grille.

Prior to the design, detailed analysis of ventilation-air quantities suggested that in order to ensure adequate delivery of fresh air under all load conditions, a very high minimum outside-air setting was required. This was due to the density of occupancy of the center’s conference rooms. Rather than penalize the entire system performance by this minimum outside-air setting, a more reasonable setting is used by making the conference rooms constant-volume zones with reheat coils (see Figure, page 50).

IAQ and daylighting concerns

To further address occupant concerns about indoor-air quality, environmental monitoring for carbon monoxide and hydrocarbons was performed at the existing student-services facility as well as at various locations and elevations around the parking garage. Outside-air intake ducts were extended on the outside of the building to the fifth level, resulting in intake-air quality that was shown to be better than the occupants’ existing facility. In addition, extensive cleaning of the original garage floor was performed, and a special epoxy sealer-suitable for use in an environmental air plenum-was laid down to seal in potential contaminants and reduce moisture infiltration in the occupied space.

Two pulse-combustion boilers were specified to provide heating hot water for the facility. These boilers are located in a remote mechanical room, separated from the center by the garage exit ramp. This isolates the noise of the boilers from the occupied space, and eliminates the need for combustion-air louvers in the design.

Private offices are located in the building’s interior to allow maximum daylighting. In spite of the amount of glazing, the facility has a highly efficient envelope. This is achieved by:

These features, together with the efficiency of the underfloor system, helped achieve an energy performance that exceeds California Energy Code requirements by 20 percent.

On-schedule occupancy

The university occupied the building on schedule, and the total construction cost of the facility was half of what a new building on a new site would have cost. Due to the projected energy efficiency of the project, the University expects to receive a rebate from the local utility company.

Still, the HVAC system costs were higher than other typical underfloor systems, because of the following project-specific conditions and costs:

Overall, the system uses relatively few air inputs for such a large floor plenum, an issue that caused some concern during the design phase. Four sensors were installed under the floor to provide a means of individual fan control that could compensate for variations in plenum pressures. However, the variation in static pressure under the floor is virtually immeasurable.

The project surpasses all of the needs and expectations of the clients, while providing superior energy efficiency and enhanced indoor-air quality. It is projects like these that make a consulting career more fulfilling.

Statistics of a Garage Conversion

Conditioned Area (square feet) 97,000

Installed Cooling Capacity (tons)

Installed Cooling Capacity (sq. ft. per ton)

Installed cfm per square foot

Installed Heating Capacity (MBtuH)

Total kW per Ton of Refrigeration

Mechanical System Cost*

Total Construction Cost

*HVAC, plumbing and fire protection