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BC
Hydro
|
Figure
1: Podium Building
|
Building
Design Features
UFAD System Characteristics
UFAD System Performance |
|
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 |
|
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. |
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 |
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 |
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.
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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