Designing a home without consideration for the local climate can make it unlivable without depending on air conditioning. And if you are concerned about the environment and climate change, air conditioning is bad news! With most electrical grids using fossil fuels to generate electricity, not only is air conditioning expensive to install and operate, it increases the use of carbon-based fuels whose emissions are driving climate change. It’s a perverse feedback loop. The climate is getting hotter. So more air conditioning is installed to make buildings more comfortable, and even habitable. This leads to more fuel being burnt to generate electricity, leading to more emissions, leading, over time, to a hotter climate.
Which is why designing a building from the start, in a way that keeps it cool without using air-conditioning, or at least minimizing the size and energy use of the air conditioning installed, is so important. Such a building is called a passively cooled building, or a passively designed building.
What are passively cooled buildings?
Passively cooled buildings are designed with an understanding of the local climate. It is an approach that aims to use natural air conditioning for cooling, ventilating and lighting without using mechanical or electronic devices.
Some home designs are made to use passive cooling exclusively, while others combine passive cooling and mechanical cooling systems to create a hybrid air conditioning system. Whichever method is used, passive cooling is a cost-effective, environmentally friendly solution that needs to focus on how it can be integrated into homes.
And there is actually even a standard, for designing a house in such a way that the need for heating and cooling is avoided, or minimized in very harsh climates – Passivehaus.
Some design concepts for a passively designed building
Understand the local climate
This requires a knowledge of weather patterns and the movement of the sun. The latitude of the site should be known, along with the paths the sun follows in various seasons. Weather information, including temperature, rainfall, cloud cover and wind speed also needs to be understood.
Correct building orientation
Orient the building in a way that minimizes unwanted heat gain when it’s hot, and captures the energy of the sun when it is cold. This usually involves aligning the building so its long side runs from east to west. Additionally the building can be oriented in a way to capture winter sun, whilst keeping the sun out in summer.
Design the building and use materials such as bulk insulation and radiant barriers, to keep heat out when it’s hot, and keep heat in, when it’s cool. This works hand in hand with the orientation and shape/form of the building. Window positioning, and the type of window glazing and frame are also important.
Minimize unwanted air movement.
Hot air leaking into a building is unwanted when trying to keep a building cool. A passively designed building also needs to be built in such a way that holes and cracks that allow unwanted air movement are eliminated. On the other hand, it should also be built to effectively capture cooling breezes. In other words, it should be possible to control air movement – by either opening up to allow air to move through the building, or shutting it up, and having it tightly sealed, to minimize unwanted air movement.
Thermal mass is material that doesn’t change temperature much in response to heat. Often heavy construction materials have good thermal mass. A lot of thermal mass is good when its at a comfortable temperature. On the other hand a lot of thermal mass at an uncomfortable temperature will just sustain the discomfort! A passively designed house needs to make appropriate use of thermal mass, as best suited to the local climate. For example in a desert climate, with cold nights and hot days, thermal mass can keep the house cool in the day, and warm at night.
Want to learn more about passive design? Our course Solar Passive Design is a great introduction!