Windcatchers are a great example of the marriage between architectural design and the environment to help keep your house cool. For more than a thousand years, windcatchers have existed in and around the Persian Gulf, providing natural ventilation and passive cooling.
Keeping cool through the summer involves controlling how all the elements in the house interact with solar energy. “Passive solar desig is all the things that you can do when you’re designing a building to basically naturally condition it and make it a better place to live,” says David Wright, an architect who has been in the sustainable design movement for nearly five decades. The principles of passive solar design are core to building houses that can keep us comfy without using much energy.
Your home should be oriented in such a way that it can take advantage of the naturally occurring wind patterns. By paying attention to which way the summer breeze blows, you can better plan where entrances and windows will be placed to naturally cool your house.
It is a good idea to protect the exterior from direct sunlight. If you live in a place surrounded by trees, they provide excellent natural shade; deciduous trees in particular are effective at blocking the sun during the hot months and then letting in the winter sun when you need it. You can install protective coverings like canvas, awnings or overhangs to prevent the sun from hitting the roof and walls of your house directly. Getting the depth of the overhang is crucial: Too deep and you lose your winter sun, too shallow and you’ve got too much summer heat. The proper measurements will depend on your location. You can make those calculations yourself using many available tools and guides online. Providing shade for windows that are south and north facing is much easier than those that are eastward or westward because as the sun sets it shines through windows at much lower angles during the afternoons.
The key to creating good cross-ventilation is figuring out where the wind is coming from. “You want to make sure you open windows on the west and the south where you can pick up those winds and then you need to get the wind back out,” says Vivan Loftness, a professor of architecture. “The more windows you can open, the more flow you’re going to get through the house. But if you want to speed up the wind, there’s a general rule of thumb that says you should have fewer open on the windward side and more open on the leeward side.” The Venturi effect comes into play when the wind is drawn into the house through a smaller opening, it speeds up inside of the house, making the breeze feel stronger.
Using what designers call the stack effect, you can draw hot air towards the top of your house and move it away from pooling nearer the ground where people tend to live. Creating a ventilation tower through high ceilings and a narrower opening, funnels the hot air into the tower. This motion pulls cooler air into the lower living spaces. You can create this tower by either placing windows higher up, like clerestory windows or skylights, or simply by creating spaces like atriums that have higher ceilings than the rest of the room. The greater the height difference between the peak height and the ground, the greater the effect. If you already have an attic, you can also create an attic hatch; in order to make sure that you’re not just recycling stale air, crack open a window to introduce some fresh air.
Insulating your roof and the attic prevents all the heat that builds up as sunlight hits the roof from entering your house. Building your roof out of reflective materials is another way of making sure that less heat is absorbed through the roof.This means using materials that are lighter in color. “Now the roofing industry has been developing dark colored roofing shingles that happen to be highly reflective,” says Loftness. “In other words, color and reflectivity used to be just like the windows. There used to be one choice: if you wanted to be highly reflective, you had to put a white roof on. But today they’ve figured out a way to make coatings that aren’t white, but that actually are highly reflective.”
Heavy, thick materials like most earthen walls have a lot more thermal mass, which allows them to store excess heat during the day, which is then removed later at night by cool air. Through this process masonry materials are better at passively cooling homes because they essentially have a lot more capacity to store the heat that would otherwise get transferred to the air inside the house.
The houses we build now will need to withstand a lot more heat in the decades to come. Designing them to stay cooler in extreme temperatures is just one of the steps we can take to alleviate our demands on polluting energy systems.
When we begin to design sustainability, we begin to design resilient homes. Resiliency is going to become increasingly important as storms and fires threaten how reliable our power is going to be. “Imagine the power goes down in your house for a week and your home has been designed with a central air conditioning system and it hasn’t doesn’t have very good shading, if any,” Loftness explains. “In many cases, many of the windows don’t even open. You can open the front door and maybe there’s a window or two that has been sealed shut for the last 10 years. You would be very hard pressed to stay in that home in the afternoon, or even at all. And so, resiliency is an important word for us to understand because the power is going to go out on us for lots of reasons.”
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