With the threat of global warming and through-the-roof rates for utilities, the quest to keep our homes cool has never been so urgent. Our solution in today's world has been overwhelmingly to battle nature on its own terms: we consume great quantities of electricity in a futile bid to operate air conditioners that blow warm air into a heat-trapped world already riddled with them. This creates a vicious and unsustainable cycle. But imagine if there were another way, a way that was in harmony with nature rather than against it. Turning to the sunny, dry edges of the globe, we have a treasure chest of ancient building techniques that created luxurious comfort on a total of zero watts of electricity. They are not humble tents, but passive, high-technology climatic systems refined over centuries of experimentation and innovation. By learning from desert wisdom, both old and ageless, we might recapture precepts for a sustainable and resilient future.
Desert philosophy is not to cool it, but to moderate heat. It understands that the desert climate is extreme: hot during the day and instantaneously cool at night. The aim is to retard heat during the day and initiate cooling during the night. This is done through an amalgamation of design strategies in the form of orientation, materials, and imaginative use of air and water. The earliest and most rudimentary principle is one of using thermal mass. Dense walls built by societies in the past, utilizing mud brick, adobe, or stone, were accessed. These soak up and hold an awful lot of heat. On the warm days, the sun's heat is poured upon these walls, and rather than letting the heat in instantly, the heavy material holds it in, just like water holds a sponge. This keeps the building interior quite cool during the day. And then, out under the crisp desert night sky, the heat that's been trapped in the walls leaks slowly back out and heats up the inside rooms and provides a secure, temperate haven. And with planning, therefore, the desert house orientation and shape are carefully designed. The dwellings tend to be compact in size and connected by mutual walls in an effort to reduce surface exposure to the strong sun.
Windows are slender, positioned strategically, and usually shaded by extensive overhangs or wooden lattices called mashrabiya. They serve for ventilation and external visibility, and not the protection from direct sunlight. The traditional example of this is the courtyard house, a Middle Eastern structure on the coast of North Africa. The courtyard is the center of the house and yet an advanced climate machine. It is typically surrounded by tall walls that cast shade in the rest of the rooms. During sunlight, the air in the courtyard gets warm and rises. This sucks cooler air from shaded rooms around it, forming a natural convection current that cools the house. At night, it reverses; the courtyard floor, maybe stone, dispels the cold that it absorbed during the night sky and forms a scoop of cooled air that descends and flows into the rooms. Maybe the most clever invention of desert design is the windcatcher, or badgir as it just so happens to be called in Persia, malqaf in Egypt. It is a tower built atop a building designed to capture the slightest of breezes at a higher elevation, where air is cooler and less dusty.
The dominant wind vents into the openings of the windcatcher. When the wind is trapped in the building, it is channeled downwards along the tower and into the living area below. But the really clever thing is that most commonly it is combined with a qanat, or underwater aqueduct. Often, the base of the windcatcher shaft passes over a small water reservoir or over the entrance to a qanat. As the dry, hot outside air travels down the shaft, it passes over the surface of the cold water. The air is cooled and humidified by evaporation simultaneously, and is a cold wind upon entry into the house. No wind is needed for the windcatcher to function. The top of the tower is warmed by the sun-heated top, and it ascends. The ascending air pulls in cooler air from ground levels or the house itself, another ongoing, passive ventilation system. Another low-tech, high-performance approach is light and color. Take a walk through any old desert town, and observe that buildings are nearly ubiquitous in white or light earth color.
Light colors possess a high albedo, or the ability to reflect a large percentage of the sun's radiative energy without absorbing it. That easy fix keeps the entire building from gaining an enormous amount of heat. The curving, narrow alleys between buildings are also a planned design element. The shaded canyons are cool walkways where tall, solid walls on either side shield the sun for most of the day. It is released during nighttime, yet the confined space is so small that this warm air has no space to blow and instead keeps a cooler microclimate than the sidewalks around for passersby to walk under. Their worth is far from in constructing mud-brick homes in contemporary cities, but overall in respecting their timelessness. Architects are using these concepts in innovative green architecture today, a domain of study known as "bioclimatic architecture." We encounter it in buildings that employ huge, open concrete walls or floors as thermal mass, heating up and then releasing heat at night, just like adobe.
We may observe it in the courtyard's revival, transformed here as an interior atrium of a tall office building admitting daylight and stack-effect ventilation. New refinements of the windcatcher, equipped with dampers and filters, are employed to cut sharply the demand for mechanical air conditioning of big buildings. Even evaporative cooling, an ancient technology, is being upmodernized. While not possible everywhere, in warm, dry conditions, new systems can draw on the sun to energize pumps that fog water onto roofs or blow air through moist pads, cooling with but a fraction of the energy of vintage AC.
The change of heart is generally most important: we need to design buildings that respond naturally to where they are. Rather than use machinery to repair a poorly constructed box, we can use the box itself to control the climate naturally. At its core, desert architecture is an exercise in humility and ingenuity. Our ancestors lacked our technology but had a rich, tactile understanding of their own environment.
They came to understand the sun, the wind, and the stars, and they constructed their houses in modest conversation with these forces. With the age of the ills of excessive use of energy, that kind of wisdom is required more than ever before. It advises that comfort need not be derived from a power station. Perhaps it is due to wall thickness, the wind direction, and the simple, deep geometry of a shaded courtyard. In looking back to these ancient solutions, we are not retrograde; we are learning a wiser, more elegant, and more sustainable path.