Passive Cooling Design Techniques: 3 Ways to Stay Cool with No AC!
Have you ever seen pictures or videos of people living in hot, tropical regions without air conditioning, and wondered, How do they do it?
For some of us, air conditioning has become almost synonymous with comfort. It’s easy to forget that humans have lived without mechanical cooling for thousands of years—and still live this way in many hot parts of the world. Don’t underestimate natural ventilation!
Did you know that air conditioning accounts for nearly 12% of the energy consumption in the average American home?
This has a major impact on our environment.
And if the power goes out? We’re left sweltering and sweating! The idea of resilience—living in a way that allows us to thrive in relationship to our environment and stay agile when disruptions come up—is more relevant than ever. Rethinking our approach to cooling is a key part of that.
I’m not saying our homes should all feel like dark caves, but we don’t always have to rely on mechanical cooling. There’s a middle ground. We can stay comfortable while being mindful of our energy consumption.
Let’s explore some passive cooling design techniques you can use to stay comfortable and efficient.
Elemental Design: Engaging with Hot Climates
When I design a structure, I like to consider the environment I’m building in, and how the elements of nature show up.
I take an approach inspired by the Chinese system of Feng Shui, and by the ancient Indian practice of Vaastu Shastra. The two systems have a lot in common, because they consider the relationships between the elements: earth, air, fire, water, and ether. (Actually, Vaastu focuses on four elements: earth, air, fire, and water. But I digress!)
In Taoist philosophy, we find the concept of Wu Xing—it explains how each element is balanced, controlled, and supported by the others. For example, fire is controlled by water, and supported by wood.
It makes sense, right?
So when I’m designing a building in a hot climate, I can balance that heat by introducing water in some way, shape, or form. I might design a pool near the structure, or a green roof with vegetation on it. A green roof will help cool the area through evapotranspiration—plants release moisture, which absorbs heat as it evaporates, thereby cooling the area.
A metal roof, on the other hand, will heat up very fast!
I call this approach “Elemental Design.”
In Wu Xing, water sometimes behaves like air. It makes sense if you think about humidity. The air holds moisture, right? So we can also design air elements into buildings to cool the fire element. Basically, we want to get the air moving as naturally as possible.
Moving Air: Pressure Zones
First, let’s talk about pressure zones.
High and low-pressure zones play a crucial role in passive cooling. They influence how air moves within and around a building. If you understand pressure zones, you can design spaces that naturally encourage airflow.
High-Pressure Zones: These are areas where the air is denser and more compressed. High pressure occurs when air molecules are packed closely together. This can happen because of cooler temperatures (molecules cluster up and move slowly when they’re cold), or because of external forces like the wind.
Low-Pressure Zones: In contrast, low-pressure zones have less dense air, with molecules spread further apart. This often occurs when air is heated, causing it to expand and become lighter. Wind patterns can also create low pressure zones, as can the design of a structure, which funnels air around it in a specific direction.
Why Are Pressure Zones Important in Passive Cooling?
The movement of air from high-pressure to low-pressure zones makes passive cooling possible.
Air naturally flows from high-pressure areas to low-pressure areas. It’s trying to find balance. So by designing a building with intentional pressure differences, you can create natural airflow, and this can help cool the interior.
For example, when wind hits one side of a building, it creates a high-pressure zone on that side and a low-pressure zone on the opposite side. Air will then move through the building from the high-pressure to the low-pressure side, providing ventilation and cooling.
The stack effect is a great example of pressure zones in action.
The Power of the Stack Effect
When air in or around a structure warms up, it becomes less dense and rises. That creates a low pressure zone at the base of the structure. What flows into this low pressure space? Cooler, denser, high-pressure air!
As that cool air heats up, it also rises . . . drawing in another fresh flow of cooler air at the base.
This effect creates natural airflow that moves from the bottom of a structure, out through the top.
This keeps the building cool.
That’s the stack effect! (It’s also called the “chimney effect.”)
You can design your building to take advantage of the stack effect by “stacking” windows at different heights, with larger openings at the bottom, and smaller openings at the top. Now you’ve got a natural ventilation system that keeps air moving through your home without mechanics.
Examples of the Stack Effect
Atriums and Ventilation Shafts: Open spaces within buildings that allow air to circulate freely.
Windcatchers: These were popular in ancient Persia! They’re still common features in hot, arid climates, like the Middle East and North Africa. Windcatchers look like towers with openings at the top.
Some even have a central shaft connected to underground tubes, providing additional cooling.
As it leaves the tower, the air—now cool—flows through the lower levels of the building.
Solar Chimneys: Like a windcatcher or an actual chimney, a solar chimney consists of a tower, usuallypainted black or made of heat-absorbing material. The exterior of the chimney absorbs sunlight and heats the air inside the shaft.
That air is now low-pressure and rises up through the chimney. This creates an upward draft, which pulls in cooler air from the building’s exterior.
The chimney effect brings in a constant cycle of refreshing air as long as the sun is shining!
Breezeways: A breezeway is usually designed like an open passage or corridor between parts of your building (though it can take other forms). It’s aligned with the prevailing winds in your area. When these winds hit one side of your building, they’re channeled through the breezeway, into and around your home, creating a continuous flow of air.
When wind hits one side of a building, it creates a high pressure zone. On the opposite side, a low pressure zone forms. This difference in pressure encourages air to move from the high-pressure area to the low-pressure area.
By opening windows and doors on the low pressure wings of the breezeway, you can enhance this effect, allowing air to flow through the breezeway and circulate around your home.
The result?
A constant, refreshing breeze that keeps your living spaces cool and comfortable.
Imagine the wind as a river of air.
When it encounters your building, it has to go somewhere. The positive pressure zone, where the wind hits, pushes air into the breezeway. As the air moves through, it naturally seeks out the lower pressure zone on the other side of the building. This movement of air not only cools the areas it passes through, but also encourages air circulation around the exterior of your home.
Now let’s imagine you open some windows on one side of your building.
The airflow a breezeway creates can pull the warm, stagnant air out of your home. If you’ve ever noticed your curtains being “sucked” outside your windows, this is what’s happening.
If you open windows on the other side of your house as well, the breeze can flow both into and out of your home, giving you cross-ventilation.
Tips for Better Cross Ventilation
I know, it seems straightforward. Just open windows on opposite sides of a room, and you’ll get cross ventilation, right?
Well, yes . . . but also no.
With cross ventilation, our goal is to invite the air to move throughout our interior space. If the windows are directly across from one another, sure the wind will blow through the room . . . but it might not actually circulate. It’ll just blow in a straight line from one side of the room to the other. Then you’ve got a room with a cool-feeling “corridor,” and hot sides.
Instead, try to stagger your window placement on opposite or adjacent walls.
For example, place the windows in opposite walls, diagonal from one another. This encourages the air to move around the room. The idea is to create a natural push-pull effect, so the breeze moves through the space in a dynamic way.
Just think about the wind as a river current, and imagine where the water would flow based on where your windows are.
Enhanced Airflow by Design
If you understand how to work with high and low-pressure zones in and around your building, you can harness the prevailing winds (even if they’re not ideal). For instance, aligning a building with prevailing winds can create a consistent high-pressure zone on the windward side, driving air through the structure.
Here are a few things to consider in the early stages of design.
Orientation: Position your building to take advantage of prevailing winds, creating natural high and low-pressure zones.
Openings and Ventilation: Place windows, vents, and other openings to encourage airflow from high to low-pressure areas. For example, put larger openings on the windward side (high pressure) and smaller openings on the leeward side (low pressure).
Landscaping: Use trees, hedges, or other structures to direct wind to certain parts of the building, so the “river of air” will flow in an efficient way.
Couplas, Oculi, and Dome Roofs: Use these architectural features to help direct and “sculpt” the movement of air.
Venturi Effect: This principle explains how air pressure increases when it passes through a constricted space, creating a cooling breeze. If air enters a wide space, and then that space gets narrower, the air speeds up as it passes through the narrow space.
Cooling Tubes & Earth Air Tunnels
Beneath the earth’s surface—about six to ten feet underground—the temperature remains pretty stable, regardless of whether we’re in the middle of summer or there’s two feet of snow on the ground.
We can tap into this stability to keep our homes cool.
Cooling tubes involve a mini-windcatcher installed somewhere on the grounds in the path of prevailing winds. It captures the wind and sends it through underground tubes or tunnels, where the earth’s temperature naturally cools the air. The tubes then carry the air up into your home, cooling the rooms.
Cooling tubes work great alone, but you can really get the air flowing if you pair them with a solar chimney!
If you’re designing a large structure (or a complex of buildings), you might want a system that can handle a bigger load of air. In that case, earth air tunnels are a good option. They work on the same principle as cooling tubes, but they’re often combined with other elements of an HVAC system to help handle the load.
Working with Water: Evaporative & Radiant Cooling
Water is another powerful tool in passive cooling design. As I mentioned above when I was talking about elemental design, the element of water cools fire. Let’s talk about a few ways we can use water in our building designs to naturally reduce heat.
Evaporative Cooling
In evaporative cooling, we’re using the natural cooling effect of water evaporation to lower temperatures. Water absorbs heat, which lowers the temperature in the air.
Pools and Water Features: Placing water features, like pools or fountains, near windows or in courtyards can help cool the air as it enters a building. The Persians took full advantage of this by placing beautiful pools near their buildings. They’re often in courtyards, or outside of the building to capture the prevailing winds.
Green Roofs (aka Living Roofs): A green roof is covered in living plants! Sometimes it’s only partially covered, but in other cases the entire roof is abundant with grass, bushes, or shrubs. Green roofs hold water in their soil, and can be designed with water retention systems to cool the building below.
Underground Water Channels: You can incorporate these into windcatchers or ventilation shafts to cool incoming air.
Radiant Cooling
If you’re familiar with radiant heating—where heat is distributed through the floor through pipes or tubes—radiant cooling will make sense. Cool water flows through tubes in the ceiling to absorb heat from the space below. Radiant cooling is great in dry climates where evaporative cooling might not be enough.
Shading: Protecting Against Solar Heat Gain
Even if your building has excellent cross ventilation, you might still need extra protection from the sun’s heat. Shading is one of the simplest and most effective ways to reduce solar heat gain. It’s classic for a reason!
Shading Techniques
Overhangs and Shade Structures: Design these to cover all of your windows during the hot summer months. If you live in an extremely hot region, consider shading entire walls.
Western Sun Protection: The afternoon sun is often the hottest, so minimizing western-facing windows or using deep porches and shade structures is a great approach.
Deciduous Trees and Vines: Planting these to the west can provide shade in the summer while allowing sunlight in during the winter.
Material & Design Choices: Building for Coolness
Some building materials absorb heat. This is a great design feature if you live in a cooler climate. In that case, we want “thermal mass”—materials that absorb heat during the day and release it at night.
But if you already live in a hot climate, we want to reduce thermal mass.
So we can build with materials that minimize heat absorption and reflect sunlight. Here are a few ways you can incorporate that into your design.
Minimize Surface Volume: A two-story house, for example, has less roof surface area exposed to the sun than a single-story house of the same square footage.
High-Performance Windows: Opt for windows with a low U-value to reduce heat gain. Casement windows are a popular choice, since they’re so airtight that they’re more resistant to heat. And on the sunny side of a building, Solar Heat Gain Coefficient windows help keep heat out.
Earth & Wood Materials: These have natural insulating properties that help maintain a cooler interior temperature.
White Roofs: Reflect sunlight and reduce heat absorption.
A Return to Resilient Design
If you combine these methods and tailor them to your climate (and the microclimate on your property), you can create a comfortable, resilient home that doesn’t rely too heavily on mechanical cooling systems.
While modern technology offers convenient solutions, the wisdom of passive design lies in its simplicity and sustainability.
By rethinking our approach to cooling, we not only reduce our energy consumption but also reconnect with the natural world—a world that provides everything we need to stay cool when our designs exist in harmony with it.
