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Design strategies
One of ATA Architects’ strategies focuses on increasing the U-value of typical glazed assemblies using passive methods. Although films and additional glazing panes do increase the U-value of a window, they do not have the vast increase that may be required for the 2030 Challenge. The cost and the return on such an investment is also typically too high and too long for clients to digest. Increasing the number of panes and adding films also reduces the visible light permitted into the building which can be counterproductive during our long winters. ATA’s approach is to use typical glazing in different ways and arrangements to allow this standard technology to perform in an exceptional way.
One of this author’s focuses, published in the May 2014 edition of Construction Canada, is the heated plume of air occurring outside a window on a cold, calm day. (See the May 2014 edition of Construction Canada for this author’s previous article, “Glazing Performance and Sustainable Design.” Visit www.constructioncanada.net/glazing-performance-and-sustainable-design). This plume becomes a vital insulator for the building, increasing the temperature of the inside glass face. The higher the temperature of this inner face of glass, the less energy the HVAC system has to expend and the more comfortable
the environment.
The plume is delicate. On windy days, it is blown away, chilling the window by several degrees in the winter. This is no different than the wind chill effect felt on human skin. Even a slow-velocity exterior wind will remove this exterior plume. There are several strategies implemented to attempt to maintain this air layer. These strategies take place after reducing the overall glazing percentage, and ensuring assemblies have good insulation values and low infiltration rates. These strategies are also implemented at the very first day of design, and are not late add-ons (Figure 2).
Window location and size
In the Delta house, a residential project located in Smithville, Ont., the windows were centred and expanded along the leeward side of the building, while reduced along the windward side. The shape of the house, designed in a wind tunnel, is the form of an aerodynamic delta, separating the wind in an organized fashion to create a wind buffered area along the leeward side of the building.
The windows, located on the south façade are tipped forward to reflect the summer sun away from the building, while filling the living areas with natural light. The house was also planted into the ground, thereby minimizing the exposure to the wind (Figure 3).
Window materials
The mullions around an IG unit are typically lower performing than the glazing it supports. Vinyl and fibreglass perform better than metal aluminum frames because of the high conductivity of metal. The larger the mullion and the more internal steel the mullions have inside them, the greater the potential conductivity. A building with large exposed exterior steel mullions, unless they have been totally thermally decoupled from the interior, operates very much like a heat sink on an electronic component—continually drawing energy out or into the building depending on the temperature outside. Steel window shades can have the same effect.
Long horizontal windows are great when it comes to maximizing natural lighting throughout the building, but they require additional structure to provide a lintel over the large openings. If these lintels are steel, they can also greatly increase the possibility of thermal bridges through the building. These lintels usually punch through insulated areas easily erasing any gains that have been made by daylighting the building. Vertical windows require less backing structure, and may be better-suited for the cold climate environment.
Window shutters
Insulated window shutters are also another option to reduce energy loss/gain through glazing. In Canada’s cold climate, shutters on the inside of the building may cause condensation issues. In the warm season, interior shutters will still absorb the energy created by the sun and subsequently will be released into the interior.
On the outside of the building, an automated shutter system could open and close, depending on the occupancy of the building. Glazing and natural light are of no value if it is nighttime or no one is home. A shutter is an opportunity to add an insulation layer to an underperforming glazing system. ATA is currently constructing two homes in Mississauga, Ont., with sliding insulated doors overlapping windows to provide insulation.
Another method for insulating is providing a wind blocking hood around glazing, the same way a hood on a jacket works in the winter. Even on windy days, with the hood drawn, a bubble of body heat forms around the wearer’s face, held in place by the hood. The same strategy can be used for building façades. See Figure 4.
The hoods on the future LJM Development’s Think Tower in Burlington, Ont., will be constructed out of fibreglass and be designed to maintain the window plume during the winter wind. There are two lines of defence for this strategy. The first is the building shape. The building turns its back to the winter wind to create a low-velocity pocket of air in front of the main glazing area (Figure 5). The second line of defence is individual hoods surrounding a predefined glazing area. The geometry and size of the hoods are very important, and can be tuned with CFD software.
In Figures 6 and 7, two models were created in Autodesk Revit and Autodesk CFD. Two punch windows were modelled within a steel stud wall, one employing a 600-mm (24-in.) deep fibreglass hood extending out from the wall. Different velocities of –20 C (–4 F) wind were then directed at the windows at a 45-degree angle to see the effect on the air plume.
It was found using the CFD data even with no wind the hood design keeps the interior face of the window approximately 2 C (3.6 F) warmer than without a hood. Although this is experimental at this point, and a real-world test needs to be completed, this simple geometry may be able to increase the performance of typical windows (Figures 8 and 9).
Conclusion
The strategies listed in this article are only a few ideas on how buildings can form to provide an energy-related function. The strategies may inch us toward where architects will need to be in 15 years to successfully meet the 2030 Challenge. Between now and then, efforts need to be made pushing all technology levels. Architects must ensure they stop following ‘rules of thumb’ in design, and start utilizing early design modelling software to push in the right direction. When it comes to glazing, a good understanding of the building climate and a strategic plan on how to use it in a sustainable manner is crucial.
Mark Driedger, LEED AP, is a sustainable designer, intern architect, and associate at ATA Architects Inc. He is an adjunct professor at Lawrence Technological University near Detroit, Mich. Driedger continues to integrate science with design, and can be contacted via e-mail at mark@ataarchitectsinc.com.
