There are two types of cooling for passive solar homes: stuff that cools the house and stuff that cools the people inside the house. Humans do not react to heat in the same way as building materials, after all! There are two main ways of cooling a home's inhabitants:

• Active cooling from evaporative coolers and air conditioning.
• Human-targeted cooling from ceiling and other fans.

If you're building a passive solar home, you really don't want to use expensive cooling systems... but you don't always have a choice. Some climates, locations, and buildings simply cannot cope with the required cooling load by using only passive systems. Wherever possible, you should target passive options or energy-efficient active systems like heat pumps.

Air-con and coolers

Of the two types of active cooler, evaporative models are more energy-efficient. However, they only work well in hot, dry climates, as their function is based around adding cool moisture to the air. That doesn't work in hot, humid areas.

Air conditioning is the final resort in green homes. If you can avoid it, do so – it's not very efficient, it's expensive to run, and it's just not eco-friendly. Thankfully, energy-efficient models (relatively speaking) are available, so make sure you get the most efficient one you can afford. You should also ensure you buy a model that is the right size for your needs: too big and it won't dehumidify the air properly, too small and you'll still be hot.

Ceiling and other fans

The alternative to active cooling is to install fans. The most popular residential models are ceiling-mounted, with big paddle blades , and can be switched to either push warm air down into the room or pull it up to the ceiling to cool. Running a fan can help with the home's ventilation as well, encouraging warm air to escape.

Although fans do not actually cool the air in the home, they can make the residents feel cooler. Moving air strips the "boundary layer" of warmth away from the body – the cocoon of warm air that sits close to, and is warmed by, the skin. The effect is to make a room feel up to 4°F cooler than it actually is, especially in very humid, hot areas where the skin is unable to cool itself effectively because of limited evaporation.

Fans work in any climate and are relatively cheap to run. They can also be combined with air conditioning to augment efficiency: in hot, humid climates, air con can be set up to 6°F higher if a ceiling fan is running. Each degree saves about 8% of cooling costs.