The basic principles in passive cooling are to slow or prevent the sun from heating up your house by blocking it where possible, to use natural cooling breezes (such as ocean breezes), use evapotranspiration from trees and water, and use temperature differences to create air movement, thus constant cooling breezes.
Thermal chimney - This works on similar principles of moving air around with temperature differences, but with a single chimney. Often, this is a simple black chimney that heats up, causing warm air to be drawn out of the house and pulling cool air in through a covered porch or backyard filled with old growth trees, etc.
You can use these principles in your existing home. For instance, in one home I was renting, I wanted to reduce or eliminate air conditioning. I created more shade near the home with moringa and other trees and plants. We created a bean trellis to shade and screen the south facing bathroom which had a big window.
We then opened the attic trap door just a bit, knowing that heat would rise into the attic, the attic heat would escape from the vent, and cool air would be pulled through open windows through the shady areas of our yard throughout the house.
This worked very well. I could feel a nice, light, cooler breeze even with no wind outside, while standing in the kitchen or sitting at my desk. Though a couple people in the house insisted on air conditioning, we were able to keep it off for at least 2 months longer than usual, and use it less when it was on.
Thermal chimney.
Here’s a thermal chimney combined with passive geothermal cooling. Below 6-8 feet, the earth remains at a steady temperature. When a pipe runs through the ground, it cools the air off. The chimney draws hot air out of the home, creating enough of a draw to pull air through the underground pipes where it cools off before it enters the home.
This method was used in a straw bale house in the high drylands at Quail Springs in California, where temperatures routinely surpassed 100F in summer. The pipe ran for 100 feet, and cooled the house by 10-15 degrees F. The builder said if he ran it about 300 feet, he felt it could cool the home 25F or more.
This ground source geothermal cooling and heating is gaining popularity and recognition. A number of companies now install these systems in regular homes, with heat pumps to assist the transfer of heat/cool. These use far less energy than gas heaters or central air conditioning. They can be pricey to install but the cost can be reduced by doing some of the work yourself or working with neighbors to install a "microgrid."
Double roof/shade - The roof is an area that gains tremendous heat from the sun. If you’ve ever been in an attic in the summertime, you know about this. Adding a second layer with some air space in between creates an insulation barrier that can significantly cool the house.
Simple and inexpensive pole barn concept.
The above helps cool down the containers substantially, which could be used as storage, offices, or ? Use other techniques for cooling mentioned here to reduce heat even further. This type of design mimics the cracker house “breezeway” concept below.
Wind - Breezeways - a very common way to cool homes in the tropics is to position them to catch the wind. There are many ways to do this. I’ve been in homes in the tropics that were so cleverly designed that mild, cooling ocean breezes were sent throughout the home, flowing through every room before escaping from the top vent.
Many old “Florida cracker houses” had breezeways that faced the prevailing winds. These winds would sweep through, and also into the rooms of the house, cooling the rooms. In Miami, I visited one of these with a long, narrow hallway and doors at each end. With room doors left open, you could almost always feel a breeze through this hallway and into the rooms. Outside, trees lined the entrance, creating a kind of wind tunnel effect that accentuated the wind patterns and cooled the air.
The above breezeway keeps the sun off the home walls and creates a wind tunnel that sends a breeze into the home. In Spain, these wind tunnels, which could also be created by trees or arbors, might lead to a courtyard in an apartment building several stories tall. The wind would flow up through the courtyard and into the open windows surrounding the yard. The sun/shade aspects in the courtyard could add to this “draw” of air. It is quite an effective cooling method especially in dryer climates and many buildings in Spain are built with courtyards for this reason.
This is very aesthetic and the architecture also sends the ocean breeze throughout the house.
This modern version could gain more cooling by combining the evapotranspiration from the pond with well placed trees. People like the looks of features like this pond but often don’t know that they are functional as well. v
Trees. Remember from our earlier lesson on trees that they act as evaporative coolers. They literally remove heat from underneath their canopy and transpire it into the air during the hottest part of the day.
It’s noticeably cooler under large trees than it is under an awning or porch roof. Value large, old growth trees for their energy savings! The more there are in an area, the more pronounced the effect is, so let your neighbors know about this benefit as well. This effect works in both dry and humid climates.
This home uses several of the above elements to passively heat and cool the home in different seasons.
Fans. A low energy way to reduce heat discomfort is to use fans. Living in hot and humid Florida, I was determined to find a way to live with the heat. So I shut off the AC vent to my room and turned on my ceiling fan. My roof was shaded by a large tree, and I had tall windows which allowed a cross breeze. The fan ensured air was always moving even when there was minimal breeze. The room never got hotter than 82F even on hot and sunny days.
The best lesson was that the fan kept the humidity under control. Mold can’t form well in moving air. This became especially apparent when I went out of town for a month. When I got back, my roommates had turned off my fan (which I kept running 24/7 in humid summer months), and there was mildew everywhere as a result. A very graphic demonstration of the power of moving air.
The other thing that I noticed was just how much a constant breeze helped keep me comfortable. If I shut the fan off I would feel instantly hotter. The ceiling fan seemed especially useful as it moves a lot of air, but gently. I’ve used personal fans and other types of fans blowing directly on me and they weren’t as comfortable. I may have more tolerance of heat and humidity than most - or maybe I just acclimatized to it. In any case, a ceiling fan can help make you feel comfortable at a higher thermostat setting than you otherwise might want to try.
Cracker houses - We covered a simple version but there are more elaborate versions as well. Several features of old southern homes created passive cooling that could keep the home quite comfortable.
The cupola in the center had windows that could open and would create a draft, similar to a thermal chimney that would let hot air out, while sucking cooler air through the windows and keeping a passive breeze going. A covered porch would often surround the entire house, keeping the sun from hitting the windows and cooling air down before it enters the house.
The homes were often raised, allowing cool air to rise from under the house and reducing flooding risk.
A modern home using cracker style features including covered porch, cupola effect, shade, and open windows circulating cooler air. Imagine live oaks surrounding this home, accentuating the evaporative cooling effect.
This is a Malaysian version that works on similar principles.
A typical Malaysian site design. Note that the kitchen is in a separate structure which keeps the kitchen heat out of the house. Cracker houses sometimes had outdoor kitchens as well that could be used in summer. We’ve created an outdoor kitchen on our wide porch area.
Saltbox - a design from the 1600’s in the US, this house is built to protect from both winter cold and winds, and summer heat.
Though many saltbox houses didn’t incorporate passive elements, they could have. In this version, the porch and large shade trees allow cooling breezes to come into the house, while shading the home from the sun in summer.
In winter, a wind break and sloped roof shove the cold winds over the house instead of into the windows and the steep slope helped ensure snow would slip off the roof. As well, the lower sun is able to pass through the branches of the deciduous trees and heat the home.
This Salt Box uses several of the passive features we’ve looked at - a double roof, thermal chimney, breezeways to capture cool air (not shown in this illustration), and earth cooling.
Humidity is of concern in hot and humid areas and fans and breezes may not handle all of it for everybody. Some green architects have experimented with using textured concrete and materials like hempcrete to absorb and regulate humidity.
This is an area where a lot more work could be done as many people feel they need air conditioning to keep humidity under control even if temperatures are comfortable. One of the most intriguing solutions I've seen was an indoor fountain developed by a student at a university as a prototype, that had a dessicant in it that absorbed humidity from the air and sent it into the water. This was never released (that I could find) but it's an idea worth exploring. Dehumidifiers can use more energy than an air conditioner so aren't really an energy conscious solution.
See some patterns here? Shade, breezes, protecting key areas from sun heat, directing heat out, cool air in, using the earth to cool things down.
You can apply many of these concepts and elements to existing structures. Some of them, like attic vents, are already built into many homes, but you can amplify their effectiveness through thoughtful design. Passive heating and cooling are “lost technologies” as far as most builders are concerned. They aren't trained to get the maximum benefit from these techniques, but most of these approaches are not difficult or expensive.