Staying cool
For thousands of years, people kept cool with shade, fans, thick walls, open windows and water. Today, air conditioning cools homes, schools, hospitals, cars and offices around the world. It changed where people live and how buildings are designed.
Cooling before air conditioning
| Method | Where and how |
|---|---|
| Wind catchers | Towers on buildings in ancient Persia caught breezes and funnelled them indoors |
| Evaporative cooling | Ancient Egyptians hung wet reeds in windows; evaporating water cooled the air |
| Thick walls | Adobe and stone absorbed heat during the day |
| Ice | Ice blocks and fans cooled rooms in the 1800s |
Inventing air conditioning
| Year | Event |
|---|---|
| 1820s | Michael Faraday shows that compressing and evaporating ammonia can chill air |
| 1902 | Willis Carrier, a 25-year-old engineer, designs a system to control temperature and humidity in a Brooklyn printing plant, where damp air was wrinkling paper |
| 1920s | Movie theatres install air conditioning; summer "blockbusters" become popular partly because theatres were cool |
| 1930s | First room air conditioners for homes |
| 1950s | Home air conditioning becomes common in the U.S. |
| 1970s–1990s | Central air spreads; ozone-safe refrigerants replace CFCs |
| Today | About 2 billion air conditioning units worldwide |
Carrier’s original goal wasn’t comfort at all; it was to control humidity for printing.
How air conditioning works
An air conditioner works like a refrigerator. It doesn’t create cold; it moves heat from inside to outside, using a refrigerant.
| Step | Part | What happens |
|---|---|---|
| 1 | Evaporator coil (indoors) | Cold liquid refrigerant absorbs heat from indoor air and evaporates into a gas |
| 2 | Fan | Blows warm indoor air across the cold coil; cooled air returns to the room |
| 3 | Compressor (outdoors) | Squeezes the gas, making it hot and high-pressure |
| 4 | Condenser coil (outdoors) | The hot gas releases heat to the outside air and condenses into a liquid |
| 5 | Expansion valve | Pressure drops and the liquid becomes very cold again |
Removing humidity
As warm indoor air passes over the cold evaporator coil, water vapour condenses into liquid, like water drops on a cold glass. This water drips into a pan and drains outside. Drier air feels more comfortable, because sweat evaporates more easily.
Heat pumps
A heat pump is an air conditioner that can run in reverse.
- In summer, it moves heat from inside to outside (cooling).
- In winter, it moves heat from outside air (or the ground) to inside (heating).
Even cold winter air contains heat energy. Modern cold-climate heat pumps work well in much of Canada down to about −25 °C or lower. They can deliver two to four times more heat than the electricity they use, so they’re much more efficient than electric baseboard heaters. Many Canadian governments offer rebates to help families switch.
Benefits
| Benefit | Example |
|---|---|
| Health | Prevents heat stroke and deaths during heat waves |
| Hospitals | Keeps operating rooms and medicines at safe temperatures |
| Technology | Cools data centres full of computers |
| Food | Keeps food fresh in stores and warehouses |
| Growth of hot regions | Made cities in hot climates more livable |
During the 2021 heat dome in British Columbia, many of those who died were in homes without air conditioning. Since then, BC has helped provide free air conditioners to people most at risk.
Environmental concerns
| Concern | Details |
|---|---|
| Energy use | Air conditioning uses a large share of electricity in hot regions, especially during heat waves |
| Greenhouse gases | If electricity comes from fossil fuels, AC adds to climate change, which then increases the need for AC |
| Refrigerants | Old CFC refrigerants damaged the ozone layer; some newer ones (HFCs) are powerful greenhouse gases being phased down |
| Heat outdoors | AC units release heat outside, warming cities |
Solutions
- More efficient air conditioners and heat pumps
- Climate-friendly refrigerants
- Better building insulation, shading and light-coloured or green roofs
- Planting trees for shade
- Clean electricity from renewable sources
Common mistakes
- Thinking air conditioners make cold. They move heat out.
- Thinking you can cool a room with a fridge or AC unit inside the room only. The heat must go outside.
- Thinking heat pumps don’t work in Canada. Modern models work in cold climates.
Try it yourself
- Wrap a wet cloth around one thermometer and leave another dry. Put both in front of a fan. Compare readings. This is evaporative cooling.
- Place a glass of ice water on a warm, humid day. Explain where the water on the outside comes from.
- Find out if your home has air conditioning or a heat pump, and how it works.
Quick recap
- People cooled buildings with shade, wind and evaporation for thousands of years.
- Willis Carrier invented modern air conditioning in 1902 to control humidity.
- Air conditioners move heat from inside to outside using a refrigerant cycle.
- Heat pumps can heat and cool efficiently, even in Canadian winters.
- AC saves lives but uses lots of energy, so efficiency matters.