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More Than Skin Deep

An integrated facade strategy helps designers create more comfortable and better-performing glass buildings.

July 2010
From Architectural Record

By Joann Gonchar, AIA

Frankfurt has a mild climate, with long, benign shoulder seasons, making it well suited for such an approach. But a double-skin can also be incorporated into a coordinated strategy for energy conservation and occupant comfort in buildings in more extreme environments, as illustrated by the $271 million headquarters for public utility Manitoba Hydro. The 700,000-square-foot building opened in September in downtown Winnipeg, Canada - a city with short and humid summers and long and brutal winters. It has the dubious distinction of being the coldest city on the planet with a population of 600,000 or more.

Even though Winnipeg has a harsh climate, its new Manitoba Hydro building is clad completely in glass.

Photo: © Eduard Hueber/Archphoto

The cladding systems include double-skin curtain walls with automated windows that open to vent excess heat.

Photo: Gerry Kopelow

South-facing winter gardens precondition outdoor air before it is distributed to the rest of the building.

Photo: © Eduard Hueber/Archphoto

 

A.Fresh air enters south-facing winter gardens.

B.Air is humidified or dehumidified by the water features, depending on the season.

C.Air is distributed via underfloor displacement ventilation.

D.Radiant ceilings add or remove heat as needed.

E. A chiller fed by 280 geothermal wells transfers heat to or from pipes running through the radiant ceilings.

F. Air drawn through office spaces is vented through two-story atria at the north end of the building.

G. The air flows to the solar chimney and is exhausted upward in the summer.

H.In winter, the exhaust air travels through a heat exchanger and then warms the parking garage.

I.Sand-filled pipes absorb the sun's heat to help maintain the stack effect on cool summer nights.

 

Illustration: Bryan Christie Design

 

1 Solar Chimney
2  North Atrium
3  Offices
4  Double-skin Facade
5  Winter Garden
6  Green roof

 

Despite the harsh conditions, the client and its design team, led by Toronto-based Kuwabara Payne McKenna Blumberg Architects (KPMB), opted for a highly transparent structure. But by deploying a host of tightly coordinated features, including a double-skin, they've created a tower expected to consume only a third of the energy of a code-compliant office building.

Manitoba Hydro's massing, the product of in-depth site analysis, includes two 18-story office blocks separated by a service core on top of a three-story podium. The blocks are set at angles to one another, forming the long legs of a triangle, with dominant exposures to the west and east-northeast. To the north, at the triangle's apex, is a finlike solar chimney that extends several stories beyond the roof. And at the opposite end, forming the triangle's base, are three stacked atrium spaces, or winter gardens, each six stories tall.

This configuration, and especially the south-facing atria, allow the building to make the most of Winnipeg's unique atmospheric conditions: Although frigid in winter, the city's skies are among the clearest in Canada. "Even when it is cold, it is almost always sunny," points out Transsolar's Auer, whose firm also served as this project's environmental consultant.

The winter gardens were conceived to take advantage of this free solar energy. The 90-foot-long and 30-foot-wide space acts almost like an expanded double skin, providing a chamber for preconditioning outdoor air before it is distributed to the office areas through an underfloor displacement ventilation system.

Fresh air enters each atrium through the louvers in the south-facing insulated glazing. During the winter, it is warmed by the sun and humidified by 80-foot-tall fountains made of tensioned mylar ribbons that carry water along their length. In the summer, chilled water runs along the ribbons, helping remove humidity from the air. The winter gardens are the building's "lungs," says Bruce Kuwabara, KPMB principal.

Once the air is introduced into the offices, heat is added or absorbed, depending on the season, by radiant ceilings. During the summer, the stack effect draws the air upward through the solar chimney and out of the building. But in the winter, the heat in the air is recovered and used to warm a below-grade parking garage.

The long, exposed faces of the office blocks are clad with a more typically dimensioned double skin. The system includes a 49-inch-deep cavity enclosed by an IGU on the exterior and a single lite on the interior. Both inner and outer skins are of low-iron glass, incorporating low-E coatings, but of differing performance levels: Somewhat counterintuitively, the outer skin's coating allows much of the sun's radiant energy to pass through the glass into the cavity. However, the inner skin includes a higher-performing pyrolytic, or baked-on, coating. It reflects a large portion of the solar radiation back into the cavity while helping maintain comfortable temperatures for office areas immediately adjacent to the curtain wall. "The goal was to collect as much heat [in the cavity] as possible," explains John Peterson, KPMB project architect.

The combination of coatings is so effective that excess heat often builds between the inner and outer curtain-wall layers whenever outdoor temperatures rise above 41 degrees. But at those times, the BMS opens operable windows in the outer skin to vent the cavity. The system also controls automated blinds to further block unwanted solar heat gain and control glare. Occupants can open windows, as well, on the curtain wall's interior skin to introduce more fresh air if they desire.

 

Originally published in the July 2010 issue of Architectural Record
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