Rolling blackouts in California and utility outages in flood-ravaged regions have focused renewed attention on resilient architecture, designing homes that bounce back from major storms and operate independently. Could you still live in your house if the power went out and gas wasn’t available? It’s an increasingly vital issue to contemplate, one addressed in my award-winning book Designing for Disaster.
Back-up generators are a time-honored solution to power outages. However, today’s most sustainable homes rely on passive tactics to provide air conditioning or heat after a storm – even during normal times. Windows and window walls are integral elements of this strategy.
Local climate dictates the optimal approach. In southern regions, the key consideration would be the ability to cool the house when there’s no electricity to run air conditioning. The ideal situation is when you can open windows and window walls on either side of a room to create cross ventilation as they did in the days before mechanical air conditioning.
The size and placement of the inlets and outlets affect how much air circulates. Outlet openings need to be at least as big as inlets to get the most benefit. It also helps if one side of the house is oriented to capture prevailing breezes.
Another approach, which works even if you can’t take advantage of prevailing winds, is to create stack ventilation within the house. Stack ventilation relies on the buoyancy of warm air to rise and exit through openings at ceiling height. Cooler outside air replaces rising warm air.
The effect could be accomplished by opening windows walls on the first floor, allowing natural convection to draw air through the house using natural convection, and venting the air through windows on the upper level. The system works even better when you have the benefit of ceiling fans to circulate air.
The strategy’s effectiveness can be magnified by cooling breezes with water before they reach your house. When water evaporates, it absorbs heat from the surrounding air. You could place pools, ponds, or fountains immediately outside windows or in the courtyard to aid in the process.
Window walls can be part of a passive heating strategy in colder climates. The ideal situation is when you have lots of glass facing south. In the winter, ample fenestration allows sunlight into the house when the sun is low in the sky. Porch overhangs and eaves can block the sunlight during the summer when the sun is high in the sky.
Solar heat needs to be collected in a so-called thermal mass. A tile or concrete floor will work, as will brick or stone. In well-insulated homes in moderate climates, furnishings, and drywall may store enough heat. Darker colors, which absorb more heat than light-colored surfaces, are a better choice if you go this route. Thermal masses warm during the day and release heat at night to warm the house.
Formulas are used to optimize how much glazing and thermal storage you need by climate. If you painstakingly follow the guidelines, it’s possible to use the sun to provide all the heat your home needs.
The energy characteristics of windows and window walls are essential to this equation. In colder climates, you would want a glass with a low U-factor—0.30 is considered very good. The lower the U-factor, the more energy-efficient it is. In warmer climates, the window’s shading coefficient may be more critical. You want a window with a low solar heat gain coefficient to prevent overheating.
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