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CSAA Livermore

Figure 1: California State Automobile Association Inter-Insurance Bureau (CSAA-IIB) Member Service Center (CSAA is an affiliate of AAA)

Building Design Features

Underfloor Air Distribution System Characteristics

UFAD System Performance

Building Use:  
Serves as the Northern California call center for CSAA.
Currently houses 300 of the 400 total possible occupants.

Location: Livermore, California

Design Team:
Owner/developer: CSAA-IIB
Architect: Levoski/Donaldson
Mechanical Design: ACCO Mechanical
Contractors: Harbison Mahoney Higgins, Inc.

Two-story (equal floor area per floor)
7,407 m2 (80,000 ft2)

Construction Status:
Completed in 1997

Building Design Features
The construction of this building is typical for the rapidly growing area of Livermore. A combination of tilt-up concrete walls with generous windows is used. Some areas of the exterior wall are windowless, as shown in Figure 1, but about 60% of the exterior wall area is glazed. For windowed areas the glazing accounts for about 75% of the wall surface. These windows are double-glazed, slightly gray tinted with an estimated shading coefficient of 0.6. Manually operated perforated metal interior blinds (blinds blades are non-perforated on West exposure) are provided for all windows. An overhang shades the lower story windows.

Figure 2: Interior Layout

Inside, virtually the entire building is open plan with only a few private offices on the perimeter. Conference rooms and services are concentrated in the central area of each floor, as are the mechanical services and roof-mounted equipment.

Modular furniture by Steelcase is used throughout. Some interior areas are provided with 1.5 m (5 ft) high partitions; other areas have minimal partitions as shown in Figure 2. Raised floors cover virtually the entire building except in the entry lobby. Glued down non-coincident carpet tiles, 0.46 m x 0.46 (18 x 18 in), are used for the surface treatment. Swirl diffusers are used throughout the building for both perimeter and interior areas. They are generously supplied and located close to workstations in many instances, as shown in Figure 2. A suspended acoustical ceiling includes ceiling mounted fluorescent lighting fixtures.

Electrical distribution is accomplished as follows: Hard conduit is used from the central core to various distribution junction boxes (J-box); flexible conduit is used between the junction box and a similar one screwed to the floor panels in a workstation. Another flexible conduit is used to connect the workstation J-box to a furniture based electrical distribution system. Telecom cables are free run in the plenum and then pass through small holes drilled through the floor panels


Underfloor Air Distribution (UFAD) System Characteristics

Design Intent
CSAA desired a state-of-the-art solution and a high efficiency building. The high concentration of computers used to support the call center work also motivated an access floor for power and communications cabling flexibility.  CSAA had experience with at least two other projects before this one, and based on the positive results from those, decided to use a UFAD system for this project.


Plenum Height: 0.61 m (24 in)
Diffuser Types: Swirl diffusers, supplied by Titus are used throughout the building.
Raised Floor: 0.61 m (24 x 24 in) concrete-core panels using a post and stringer mounting system supplied by Tate.

Supply Air Temperature:

Nominal 17°C (63°F), varies with load.
UFAD System Types: Titus single duct VAV boxes supply variable volume, constant temperature (VAV-CT) air to perimeter and interior. Hot water reheat is used in the perimeter for heating.

This system, as depicted in Figure 3, exemplifies one system type commonly used in early UFAD installations. It is essentially a VAV overhead system installed in the underfloor plenum space. Underfloor ducting supplies VAV boxes that deliver air into partitioned underfloor perimeter and core zones. Perimeter partitions are 9.14 m (30 ft) from the exterior walls. Zone sizes vary from about 83 m2 (900 ft2) in perimeter corner offices to about 417 m2 (4500 ft2) in the interior. One or two VAV boxes typically serve a zone. Service areas in the central core are treated in a similar manner. Each zone contains swirl diffusers that are uniformly laid out; a row of diffusers is located along the exterior walls as shown in Figure 4.

Figure 4: 
Perimeter Diffuser Layout

The operation of this system is relatively simple. Pneumatic thermostats control the VAV boxes. Cooling is controlled by varying the volume of ~17°C (65°F) air to each partitioned plenum zone via one or two VAV boxes; air is in turn supplied to the space though the floor diffusers. In the larger zones where two VAV boxes are used, a single thermostat controls both. Heating is provided to perimeter zones by activating a hot water reheat coil when the zone is calling for heating (and airflow is minimum). Additional sensors that connect to the Johnson (JCI) Metasys building management system have been installed at various interior locations. These are used primarily for monitoring purposes and to indicate when the supply air temperature should be reset in response to the occupied space being too hot or cool. Otherwise the JCI system controls only the central equipment and system scheduling. Scheduling is generally not required since this building is a 24/7 operation. Air is returned to the AHUs through ceiling light fixtures and return grilles via a ceiling plenum. Some areas such as the lobby and restrooms use a conventional overhead system.

UFAD System Performance

The complaint rate has dramatically dropped after an initial shake out period (see CBE Findings). In general the system meets the objectives of CSAA and provides good overall comfort. The easy and quick relocation of the diffusers to accommodate individual needs and easy access to services infrastructures in the plenum were noted as a significant benefit.

CBE Findings
(These comments reflect the views of CBE researchers based on a limited study of the building and do not necessarily represent those of the designers and/or owners)

Overcooling - The system was initially operated with 12.7°C (55°F) supply air, which resulted in numerous “too cool” complaints. Once the supply setpoint was adjusted to its current range of 17°C (65°F), the complaints ceased.

Too cool complaints were exacerbated by the fact that a number of diffusers were located too close to the occupants. The occupants also had difficulty with adjusting the diffuser dampers. Some of these dampers became stuck, frustrating the occupant’s attempts to lower the airflow. In addition, occupants sometimes replaced the diffuser plate upside down, causing further problems. Before these problems were addressed by relocating diffusers occupants would turn the offending diffusers off by placing paper inside or a phone book on top.

During a recent carpet renovation project (see below) it was discovered that as many as 50% of the diffusers were closed off. For this type of system closing a large number of diffusers exacerbates overcooling at the remaining open ones; although the supply fan speed is controlled to maintain duct pressure, plenum pressure is not controlled thus resulting in increased plenum pressure as diffusers are closed down. This has resulted from many diffusers being inappropriately placed relative to occupants; relocation of the diffusers became a central activity during the renovation; diffuser relocation should be a recognized and planned part of any renovation project.

Nighttime cool complaints continue and most likely are a result of the inability to increase zone temperature setpoints for nighttime operation. This results from using pneumatic thermostats and may be exacerbated by the minimum stops for the VAV boxes being set too high. Although more expensive, a direct digital control (DDC) system extended to the VAV boxes would allow more flexibility to control these zones. Using large perimeter zones so that the perimeter skin loads are not separately controlled from the interior loads may also exacerbate this condition.

Figure 5: Broken Diffuser

Diffuser - Not long after occupancy mechanical problems with the diffusers began to appear. Some diffusers broke at the floor flange as shown in Figure 5. The locking ring sometimes fell off so that the diffuser was loose in the floor. Also some occupants would remove the basket damper because it became stuck. Without the basket the diffuser plate position was slightly lower than the ring presenting a problem for chair rollers and potentially a tripping hazard. Titus has improved and replaced all defective flanges. The maintenance staff monitors the diffuser adjustment activities of occupants to ensure that adjustments are being made properly.

Carpet tiles - Carpet problems have resulted from the original installation of a newly offered cushion-backed carpet tile. Apparently the combination of an unsheathed cushion backing material and overly aggressive glue resulted in de-lamination when carpets were pulled up. The carpet supplier is replacing the tiles with new 50 cm x 50 cm (19.6 in x 19.6 in) standard, non-cushioned carpet tiles.

Floor panels -The floor panels are not screwed down. This would appear to compromise the integrity of the floor system but does make changing the panels a little easier. However, the raised floor installation uses a stringer system, which is common in computer room applications. Typically, the panels with corner screws were designed for use without stringers in office applications (i.e., post support system). Structural integrity is provided by diagonal seismic bracing at regular intervals that was engineered for the local seismic zone.

Perimeter offices - Some offices have no independent control since they are built-up from lightweight partitions after occupancy and therefore are subject to the control of the zone in which they are located. This did not appear to be a significant problem. The original design included some perimeter offices that are provided with dedicated VAV boxes.

Furniture layout – The modular furniture was laid out on a diagonal for aesthetic reasons. However, this diagonal layout does not correlate well with the diffuser layout, which was done with a standard rectangular grid. This points to the need for coordination between the design and installation of the furniture and floor systems.

Maintenance – Some large particle debris resides in the diffuser baskets. This apparently is not a problem and the facility manager sees no reason to clean them out regularly, thus helping to keep maintenance costs low (or at least does not add to maintenance cost).

Renovation – The facility manager reports that contractors find working with the raised floor system very easy, which helps to lower renovation costs. In this regard the 0.61 m (2 ft) high plenum is a distinct advantage – the electrical contractors can work in the underfloor plenum during normal working hours, thereby reducing overtime costs associated with having to take up floor panels in workstations during off hours. Also, drilling access holes in floor panels can be accomplished without special tools.

Date Reviewed: June 2000

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