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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.
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.
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.
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.
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.
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.
Reviewed: June 2000