Air conditioning facts for kids
Air conditioning, often called A/C or air con, is a way to remove heat from a closed space. This makes the inside temperature more comfortable. Sometimes, it also carefully controls how much moisture is in the air. You can cool air using a machine called an 'air conditioner'. Other ways include using natural methods like passive cooling or ventilative cooling. Air conditioning is part of a bigger group of systems known as HVAC. Heat pumps are similar to air conditioners but can both heat and cool a space.
Air conditioners usually work using a process called vapor-compression refrigeration. They come in many sizes. Some are small for cars or single rooms. Others are huge and can cool entire buildings. Air source heat pumps are becoming more common in colder places. They can both heat and cool.
Air conditioners can help reduce deaths when temperatures are very high. In 2016, about 1.6 billion air conditioning units were used worldwide. The United Nations has asked for air conditioning technology to be more sustainable. This helps fight climate change. They also suggest using other methods like passive cooling, evaporative cooling, and better thermal insulation.
Contents
History of Cooling
People have tried to cool spaces for a very long time. Even in ancient times, like in the city of Hamoukar in modern Syria, buildings had double walls. This allowed air to flow through and help cool the homes. Ancient Egyptian buildings also used many natural cooling tricks. These ideas spread across North Africa, the Middle East, and India.
These natural cooling methods were popular until the 1900s. Then, machines that used power to cool became more common. Today, engineers are looking back at these old building designs. They are using ancient ideas to create new, energy-saving buildings.
Air conditioners help keep the inside of a building cool and steady. This happens even when the weather outside changes a lot. They also let people live comfortably in very hot parts of the world. However, they are now criticized because they use a lot of electricity. This adds to climate change. They can also make the areas around large cities hotter.
Early Discoveries
Many scientists and inventors helped create modern air conditioning.
- In 1558, Giambattista della Porta found a way to make ice much colder. He mixed it with a substance called potassium nitrate.
- In 1620, Cornelis Drebbel showed King James I of England how to cool a large hall. He used troughs and vats of water.
- In 1758, Benjamin Franklin and John Hadley experimented with evaporation. They found that evaporating liquids like alcohol could make objects very cold. They even froze water on a thermometer bulb.
- In 1820, Michael Faraday discovered that compressing and then letting ammonia evaporate could cool air.
- In 1842, John Gorrie, a doctor in Florida, used a compressor to make ice. He used this ice to cool his patients. He dreamed of cooling entire cities. He got a patent in 1851, but his idea didn't become a reality.
- In 1851, James Harrison in Australia made the first mechanical ice-making machine.
The First Air Conditioners
Electricity made it possible to build effective cooling units.
- In 1901, Willis Carrier built what is known as the first modern electrical air conditioning unit.
- In 1902, he installed his first system in a printing company in New York. His invention controlled both temperature and humidity. This was important for printing paper and ink correctly.
- Later, Carrier and others started The Carrier Air Conditioning Company of America.
- In 1906, Stuart W. Cramer used the term "air conditioning." He was trying to add moisture to the air in his textile mill. Willis Carrier liked the term and used it for his company.
Air conditioning for homes soon became popular.
- In 1914, the first home air conditioner was installed in Minneapolis.
- In 1931, H.H. Schultz and J.Q. Sherman created the window air conditioner. These units went on sale in 1932.
- In 1939, Packard became the first car company to offer air conditioning in its cars.
How Air Conditioning Spread
Many new ideas in the late 1900s made air conditioners more common.
- In 1945, Robert Sherman invented a portable window air conditioner. It could cool, heat, humidify, dehumidify, and filter air.
- The first inverter air conditioners, which are more energy-efficient, came out in the early 1980s.
Air conditioner use tends to increase as household incomes rise in warmer areas. By 2050, global economic growth is expected to cause about 85% of the increase in air conditioner use. The other 15% is due to climate change.
By 2016, about 1.6 billion air conditioning units were used worldwide. More than half of these were in China and the USA. Experts predict that this number will grow to about 4 billion units by 2050. The biggest increases are expected in India and China. In the US, about 87% of homes had air conditioning systems by 2015.
How Air Conditioners Work
Air conditioners cool air using a process called the vapor-compression cycle. This cycle uses a special liquid called a refrigerant. The refrigerant changes between a gas and a liquid to move heat.
- It absorbs heat from inside your home.
- Then, it releases that heat outside.
Some air conditioners can also remove moisture from the air. This happens when the evaporator coil gets very cold. It makes the air less humid, usually between 30% and 60% relative humidity. Many modern systems have a special dehumidification mode. In this mode, the fan slows down to cool the evaporator more and collect more water.
Heating with Air Conditioners
Some air conditioning systems can reverse their cycle. They act like a heat pump and can heat your home instead of cooling it. These are often called "reverse cycle air conditioners." Heat pumps are much more energy-efficient than electric heaters. They move heat from the outside air or ground into your home.
When a heat pump is heating, the indoor coil becomes hot, and the outdoor unit releases cold air. Most air source heat pumps become less efficient when outdoor temperatures drop below 4°C (40°F). This is because ice can form on the outdoor coil. To fix this, the system temporarily switches back to cooling mode to melt the ice. Some systems also have electric heaters to keep the indoor air warm during this defrosting.
Newer models work better in cold weather, even down to -14°F (-25°C). However, ice can still form, requiring a defrost cycle. Because of this, heat pumps are sometimes used with other heating systems, like gas furnaces. The heat pump works efficiently in milder temperatures, and the other heater takes over when it's very cold.
Measuring Performance
The efficiency of an air conditioning system is measured by its coefficient of performance (COP). A higher COP means lower running costs. In the U.S., air conditioner power is often measured in "tons of refrigeration." One ton equals the cooling power of 12,000 BTUs per hour. Home systems usually range from 1 to 5 tons.
Efficiency is also rated by the seasonal energy efficiency ratio (SEER). This ratio shows how well an air conditioner uses energy over a whole cooling season. Removing moisture from the air before cooling it can greatly reduce energy costs.
How Air Conditioners are Controlled
Wireless Remote Control
Many air conditioners use a wireless remote control. This remote sends commands to the air conditioner using infrared light. You can't see this light because its wavelength is beyond what human eyes can see. These remotes are common for mini-split air conditioners because they are easy to use and portable. Some window and central air conditioners also use them.
Wired Controller
A wired controller, also called a "wired thermostat," is fixed to a wall. It controls the air conditioner by turning heating or cooling on or off. It uses sensors to measure temperature.
- Older mechanical thermostats use metal strips that bend with temperature changes.
- Newer electronic thermostats use special sensors to send electronic signals to control the unit.
These controllers are often used in hotel rooms. They are wired directly into the air conditioner, so they don't need batteries.
Types of Air Conditioners
There are many different types of air conditioners, each designed for different needs.
| Types | Typical Capacity* | Air supply | Mounting | Typical application |
|---|---|---|---|---|
| Mini-split | small – large | Direct | Wall | Residential |
| Window | very small – small | Direct | Window | Residential |
| Portable | very small – small | Direct / Ducted | Floor | Residential, remote areas |
| Ducted (individual) | small – very large | Ducted | Ceiling | Residential, commercial |
| Ducted (central) | medium – very large | Ducted | Ceiling | Residential, commercial |
| Ceiling suspended | medium – large | Direct | Ceiling | Commercial |
| Cassette | medium – large | Direct / Ducted | Ceiling | Commercial |
| Floor standing | medium – large | Direct / Ducted | Floor | Commercial |
| Packaged | very large | Direct / Ducted | Floor | Commercial |
| Packaged RTU (Rooftop Unit) | very large | Ducted | Rooftop | Commercial |
* where the typical capacity is in kilowatt as follows:
- very small: <1.5 kW
- small: 1.5–3.5 kW
- medium: 4.2–7.1 kW
- large: 7.2–14 kW
- very large: >14 kW
Mini-split and Multi-split Systems
Ductless systems, like mini-splits, cool and heat one or a few rooms without needing air ducts. Multi-split systems can cool up to eight rooms independently. Each room has its own indoor unit, connected to a single outdoor unit.
The first mini-split system was sold in Japan in 1961 by Toshiba. Mitsubishi Electric sold the first wall-mounted mini-split in 1968. These were popular in Japan because homes were often small. In 1969, the first mini-split came to the US. Daikin invented multi-zone ductless systems in 1973. They also invented variable refrigerant flow (VRF) systems in 1982. VRF systems are like larger multi-split systems. They use smaller pipes to carry refrigerant, saving space and allowing individual room control.
Ducted Central Systems
Split-system central air conditioners have two main parts.
- An outdoor unit (the condenser) releases heat outside.
- An indoor unit (the evaporator, or Fan Coil Unit) absorbs heat from inside.
The refrigerant flows between these two units through pipes. The indoor unit then sends cool air through ducts to different rooms.
Portable Units
A portable air conditioner is a unit on wheels. It has an indoor part connected to an outdoor part by flexible pipes. These are similar to mini-split units but can be moved.
Some portable units have a hose that vents hot air outside. These can be "monoblock" (collect water in a bucket) or "air-to-air" (re-evaporate water and send it out the hose). Portable units draw indoor air and push it outside, which can make them less efficient. Many portable air conditioners also offer heating and dehumidifying functions.
Window Units and Packaged Terminal Units (PTAC)
PTAC units and window air conditioners are similar. They are installed in a window frame or a wall opening. They have a partition that separates the indoor and outdoor parts. PTAC systems can also provide heat. They might use electric heaters or reverse the refrigerant flow to act as a heat pump.
Packaged Air Conditioners
Packaged air conditioners combine all the parts of a central system into one unit. They deliver air, sometimes through ducts, to the spaces that need cooling. These units can be placed outdoors (like rooftop units) or indoors. They can be cooled by air or water.
Types of Compressors
The compressor is a key part of an air conditioner. It squeezes the refrigerant gas, which helps it change temperature and pressure.
| Compressor types | Common applications | Typical capacity | Efficiency | Durability | Repairability |
|---|---|---|---|---|---|
| Reciprocating | Refrigerator, Walk-in freezer, portable air conditioners | small – large | very low (small capacity)
medium (large capacity) |
very low | medium |
| Rotary vane | Residential mini splits | small | low | low | easy |
| Scroll | Commercial and central systems, VRF | medium | medium | medium | easy |
| Rotary screw | Commercial chiller | medium – large | medium | medium | hard |
| Centrifugal | Commercial chiller | very large | medium | high | hard |
| Maglev Centrifugal | Commercial chiller | very large | high | very high | very hard |
Scroll Compressors
A scroll compressor uses two spiral shapes that fit together. One spiral stays still, and the other orbits around it. This motion squeezes the refrigerant. These compressors are more efficient because they have fewer moving parts than other types.
Screw Compressors
Screw compressors use two spiral rotors that mesh very closely. As the screws turn, they trap and squeeze the gas. The gas enters at one end and is forced out the other as the space between the spirals gets smaller. This change in volume is how the gas is compressed.
How Air Conditioners Adjust Cooling Power
Air conditioning systems can change how much cooling they provide. Here are some common ways:
Variable-Speed Compressor
This system uses a special device called an inverter to control the speed of the compressor motor. By changing the compressor's speed, the system can adjust how much refrigerant flows. This is the most efficient way to control an air conditioner's cooling power. It can be up to 58% more efficient than systems that run at a fixed speed.
Impact of Air Conditioning
Health Benefits
In hot weather, air conditioning can prevent serious health problems. These include heat stroke, dehydration, and electrolyte imbalances. Heat waves are a major cause of weather-related deaths. A study in 2020 found that places with less air conditioning had more heat-related deaths and hospital visits. For example, a heatwave in France in 2003 caused about 15,000 deaths.
Air conditioning, with its filters and humidity control, can create a clean and safe environment. This is very important in hospital operating rooms. It can also help people with allergies, especially to mold. However, if cooling towers are not cleaned properly, they can spread germs like Legionella pneumophila, which causes Legionnaires' disease. Regular cleaning with chlorine can prevent this.
Economic Effects
Air conditioning first helped industries like printing and large factories. Soon, it spread to government offices. Studies showed that productivity increased by about 24% in places with air conditioning.
Air conditioning also changed where people lived, especially in the United States starting in the 1970s. More people moved to warmer areas like the Sun Belt. Also, the number of deaths during summer heat waves became more even across the US.
The widespread use of air conditioning is a big reason for the increase in global electricity demand. A 2018 report found that the energy used for cooling in the US was more than the combined energy use of billions of people in Africa, Latin America, the Middle East, and Asia (not including China).
Environmental Effects
In 2016, cooling spaces, including air conditioning, used a lot of energy worldwide. Most of this was electricity. A 2018 report predicts that electricity use for cooling will greatly increase by 2050. This means that greenhouse gas emissions from cooling will also double. There is a strong effort to make air conditioners more energy-efficient. The UN Environment Programme (UNEP) and the IEA believe that if air conditioners were twice as efficient, huge amounts of greenhouse gases could be saved.
Refrigerants, the chemicals used in air conditioners, have caused environmental problems. Older refrigerants like CFCs and HCFCs damaged the ozone layer. Newer ones like HFCs contribute to climate change. These issues happen when refrigerants leak into the atmosphere. Newer HFO refrigerants are designed to be much safer for the ozone layer and have a lower impact on global warming.
Without international agreements like the Kigali Amendment, HFCs would have made global temperatures rise even more. The amendment helps reduce this increase.
Other ways to cool buildings without constant air conditioning include passive cooling, natural ventilation, using shades to block sunlight, and planting trees.
Social Effects
People with lower incomes often have less access to air conditioning. This can lead to more heat-related deaths and hospitalizations. Studies in cities like Phoenix, Arizona, and Chicago, Illinois, show that lower-income areas and certain communities, often due to past unfair housing practices, experience higher temperatures and have less access to cooling. This is because these areas often have more heat-absorbing materials and less green space.
To help, some cities offer public cooling spaces for people who don't have air conditioning at home.
Other Cooling Techniques
Buildings designed with natural cooling methods are often cheaper to build and maintain. They also use less energy than buildings with traditional air conditioning. While these methods can cool a building by many degrees, they need to be designed carefully for each specific location.
Many techniques can make buildings more comfortable and cooler:
Passive Cooling
Passive cooling uses natural forces like wind and evaporation to cool a building. This includes designing buildings to let breezes flow through or using features like "windcatchers" that direct cool air inside.
Daytime Radiative Cooling
Passive daytime radiative cooling (PDRC) surfaces are special materials that reflect sunlight and heat back into space. They can cool buildings without using any energy or causing pollution. These surfaces can be paints or films applied to roofs and walls. They can significantly lower energy use and costs, especially in homes. Experts predict a large market for PDRC by 2025.
Fans
People have used Hand fans since ancient times. Large fans built into buildings, like the punkah, were powered by people.
In the 2nd century, a Chinese inventor named Ding Huan created a rotary fan for air conditioning. It had seven large wheels and was powered by prisoners. Later, in the Tang dynasty, Emperor Xuanzong had a "Cool Hall" with water-powered fan wheels and fountains for cooling. Rotary fans became even more common in the Song dynasty.
Thermal Buffering
In places that get cold at night or in winter, buildings can store heat. This heat can be stored in the earth or in heavy walls. Air is then drawn past these materials to heat or cool it.
In areas where it freezes in winter, snow and ice can be collected and stored in ice houses. This ancient technique, over 3,700 years old in the Middle East, was used to cool things later in the summer. Wealthy Europeans also practiced this in the 1600s. Eventually, mechanical ice-making machines replaced this practice.
Evaporative Cooling
In dry, hot climates, evaporative cooling can be used. This involves placing water at the air intake. As air passes over the water, it cools down and becomes more humid before entering the house. This is why fountains in hot, dry climates are like fireplaces in cold climates.
Evaporative coolers don't work as well when the air is very humid. This is because there isn't much dry air for them to work with. Unlike other air conditioners, evaporative coolers bring in outside air, cool it through wet pads, and then push the warmer indoor air out through an open door or window.
See Also
In Spanish: Acondicionamiento de aire para niños
- Air filter
- Air purifier
- Cleanroom
- Crankcase heater
- Energy recovery ventilation
- Indoor air quality
- Particulates
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