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BC Hydro
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Figure
1: Podium Building
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Building Design
Features
UFAD System Characteristics
UFAD System Performance |
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Building
Use:
Corporate
offices of BC Hydro, British Columbia Electric Utility
Location:
Edmonds Center, Burnaby, BC Canada
Design Team:
| Owner/Developer: |
BC
Hydro |
| Architect: |
Architectura |
| Mechanical
Design: |
Keen
Engineering Vancouver |
| Contractors: |
PCL
Contractors |
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Size:
18-story office tower of 27,000 m2 (290,000 ft2)
and two 3-story “podium” buildings of 9,300 m2 (100,000
ft2) each
Construction Status:
Completed in the early 1990’s.
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Building
Design Features
A similar construction method was employed for the office tower and podium
buildings comprising this project, except that the podium buildings are planned
around a central courtyard area. The external envelope consists of curtain walls with an insulation value of R12,
and double-glazed, green tinted window units with a shading coefficient of 0.6. The glazing accounts for 60% of the envelope area.
Spatially, the podium buildings are predominately open-plan. In addition, the perimeter zone contains a number of private offices, created with lightweight
partitioning, while conference rooms and mechanical services are located in the
central core zone. Internal
finishes include a suspended acoustical tile ceiling and embedded fluorescent
lighting fixtures.
Figure 2: BC Hydro Office Tower |
Figure
3:Typical Perimeter Office |
Top
Underfloor
Air Distribution (UFAD) System Characteristics
Design Intent
To provide a state of the art energy efficient example and to accommodate a
high rate of churn with the raised floor system.
Design/Configuration
| Plenum
height: |
0.45
m (18 in) |
| Diffuser
types: |
Swirl
diffusers, supplied by Krantz are used throughout the buildings |
| Raised
Floor: |
0.61
m (24 in) concrete-core panels, supplied by Tate. |
Supply
Air
Temperature: |
Nominal
17°C (63°F), varies with load |
UFAD
System
Types: |
Constant
volume, variable temperature (CAV-VT) perimeter and interior
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Each
of the three buildings features 0.45 m (18 in.) high plenums and a
concrete-core raised floor system throughout.
Within workplace areas, 0.61 m (2 ft) square carpet tiles have been
laid, non-coincident with the access floor panels, and accommodate round swirl
diffusers in both perimeter and interior areas.
Although the underfloor plenum contains no ducting, plenum partitioning
has been installed to delineate perimeter, interior and conference room zones.
The perimeter zones extend from the external wall to a depth on plan of
only 1.2 m (4 ft). Each floor of
the podium buildings contains two air-handling units (AHUs), located at
opposite corners of the building. For
the office tower, supply air from the AHUs at the top and bottom of the
building is delivered to each floor via stub-outs from trunk ducts located in
the central area of the building.
Operation
Interior
zones are operated as a constant air volume-variable temperature (CAV-VT)
system. The supply air temperature
is varied in response to an average of interior temperatures measured by a
series of sensors linked to a Honeywell Excel energy management and control
system (EMCS), as illustrated in Figure 4 (typical for office tower AHU).
Perimeter
zones are served by a CAV-VT system consisting of 2-pipe fan coil units that
draw return air through specially built duct chases located on the outer walls,
allowing air to be drawn from near the ceiling. A room-air temperature sensor controls the coil on the fan coil unit,
and the supply water for these units is changed from heating- to cooling-mode
on a seasonal basis. Round swirl
diffusers supply variable-temperature air to the 1.2 m (4 ft) perimeter zone.
The proximity of swirl diffusers serving the interior zone augments the
high demand for supply air typical of perimeter zones. Under normal operating conditions, air is returned to the AHU via return
grilles and lighting fixtures located in the ceiling.
In
contrast to the open plan work areas described above, the conference rooms are
enclosed spaces served by a VAV system. Responding
to signals from a room thermostat, supply air is drawn from within the interior
plenum and supplied to a partitioned space and then through diffusers to the
room using a variable speed fan, as illustrated in Figure 5.
A
similar UFAD system operates in the podium buildings with the exception of the
AHU configurations. Each of the three floors is served by two AHUs receiving
return air from ceiling plenums, under typical operating conditions. When in
economizer mode, air is exhausted through relief dampers located in the
courtyard walls.
Top
UFAD System Performance
These
buildings appear to demonstrate the “forgiving” nature of well-designed
UFAD systems: despite a churn rate of approximately 50% per year, most
diffusers are not relocated. As a
result, a number of diffusers are now located beneath desks and other
inappropriate places (Figure 6).Nevertheless,
very few complaints are received from occupants.
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.)
The
designer acknowledges that the floor-to-floor air distribution in the office
tower could be improved by installing motorized control dampers at each floor
takeoff to improve temperature control.
Overall, although the system consumes fan energy during cooling and heating periods due
to the use of fan coil units in the perimeter zones, reheating is virtually
eliminated with this design. The high ceiling return dictates that, in cooling
mode, the warmest air is used as opposed to cooler air from the occupied
portion of the space. However, during winter this warm return air reduces
heating energy, which is important for this relatively cool climate.
There appears to be potential for overlap between heating and cooling due to the
close proximity of perimeter and interior system diffusers.
Date
Reviewed: September 1999
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BC Hydro