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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

Edmonds Center, Burnaby, BC Canada

Design Team:
Owner/Developer: BC Hydro
Architect: Architectura
Mechanical Design:    Keen Engineering Vancouver
Contractors: PCL Contractors

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.


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 
Nominal 17°C (63°F), varies with load
UFAD System 

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.

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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