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How Does An Air Conditioner Work?

What’s the best way to keep your kitchen cool on a hot summer day? If your first thought is, “Open the refrigerator door,” you’re way off track. Every bit of heat that a refrigerator absorbs through its cool box is expelled through the metal fins at the back. In fact, because of the machine’s inefficiency, you’ll make the room even hotter. However, using a refrigerator to cool a home isn’t as crazy as it may appear: with a few minor modifications, it works almost exactly like an air conditioner. Let us investigate further!

How to Avoid Cooling Your Kitchen

A fundamental physics law known as the conservation of energy states that you cannot create or destroy energy: if you have some energy that you don’t want (such as heat in your kitchen), you cannot eliminate it. All you can do is change it into another form or relocate it. When you open your refrigerator door in the hope of cooling the kitchen, all of the heat that is drawn in must go somewhere else. It can only exit through the back of the machine. You may have noticed that the grid of fins on the back of a refrigerator gets quite hot—this is because they radiate all of the heat that would normally be inside. More information on how refrigerators work can be found in our article.

How to Construct an Air Conditioner

But don’t despair! Instead of allowing science to defeat us, we must learn how to use it correctly.

Assume you build your house around a refrigerator, with half of the machine (the chiller cabinet) inside and the other half (the grid of hot fins at the back) outside. If you leave the door open, you now have a fully functional air conditioner. It draws heat from inside your home and expels it outside, gradually cooling it down.

The most basic air conditioners work almost exactly like this, except they have fans on both sides to circulate air more quickly. They also contain a heating element, allowing them to both warm and cool the air in a room on cold days. HVACs are another name for machines like this (heating and ventilation air conditioning units). More complex air conditioners use long ducts to distribute warmed or cooled air throughout a building, but they all work in the same way.

How an HVAC air conditioner functions

  • Warm air from the room is drawn in through a grille at the machine’s base.
  • The air flows over some chiller pipes that circulate a coolant fluid. This section of the machine functions similarly to the chiller cabinet in a refrigerator. It cools the incoming air and removes any excess moisture with a dehumidifier.
  • The air is then passed over a heating element (similar to the one in a fan heater). On a cold day, this part of the unit can be turned all the way up so that the HVAC acts as a heater.
  • A fan at the top forces the air back into the room through another grille. When the heating element is turned down, the air that returns to the room is much cooler, and the room gradually cools down.
  • In the meantime, coolant (a volatile liquid that evaporates quickly) circulates through the chiller pipes. As it does so, it absorbs heat from the air passing through the pipes and evaporates, transforming from a cool liquid to a hotter gas. It transports this heat from the inside of the room to the outside of the building, where it releases it to the outside air. How? The coolant flows through a compressor unit and some condensing pipes, just like in a refrigerator, to turn it back into a cool liquid ready to cycle around the loop again.
  • What becomes of the heat? There are numerous metal plates in the unit outside the building that dissipates heat into the atmosphere. To speed up the process, an electric fan blows air past them.
  • The heat inside the building gradually escapes into the outside air over time.

Car air conditioners

Car air conditioners function similarly to those found in homes and offices, albeit on a much smaller scale. The chiller (which includes an expansion valve and an evaporator) is installed behind the dashboard, while the heat dissipater (which includes a compressor unit and a condenser) is installed near the radiator grille (where the air blows past as you drive), and the two are linked by a circuit of pipes through which coolant flows when the air conditioning is turned on. Unlike a static unit in a building, which is entirely powered by electricity, a car’s compressor unit is powered by the crankshaft (driven by the engine, in other words). A heater (to adjust the temperature of the passenger compartment) and a dehumidifier (also known as a receiver/dryer unit) are usually included. The coolant cycles between gas and liquid, high and low pressure, and high and low temperature, just like in standard air conditioning.

How does car air conditioning work?

Have you ever wondered how your car’s air conditioning keeps you cool? It goes something like this…

  • The evaporator absorbs heat from the passenger compartment, causing the coolant contained within it to boil and transform from a low-pressure liquid to a low-pressure gas.
  • The heat is carried away by the coolant as it flows out of the compartment and into the compressor. It is a low-pressure, low-temperature gas that enters the compressor.
  • The coolant is squeezed by the compressor into a high-pressure, high-temperature gas.
  • The coolant flows into the condenser and (surprise, surprise) condenses: it loses heat to the atmosphere and returns to a high-pressure, low-temperature liquid, which flows into the expansion valve (via the receiver/dryer, not shown).
  • The coolant can expand into a low-pressure liquid thanks to the expansion valve.
  • The evaporator is filled with low-pressure liquid coolant, and the cycle is repeated. Heat is sucked from the passenger compartment to the outside air over time, cooling the car.

The Environmental Impact of Air Conditioners

You probably enjoy the feeling of cool air on a hot day, but don’t forget about the law of conservation of energy! In our universe, there is always a cost to getting something good. In this case, the cost is the energy required to run the air conditioning unit; using energy has an impact on both your wallet and the planet in the form of environmental issues such as global warming.

Environmentalists argue that we should use less air conditioning, which sounds easier than it is in extreme heat. It’s important to remember that air conditioning isn’t just for luxury or comfort: an air-conditioned room can make you much more productive at work, and it can have important health benefits as well; some public-health experts believe that the greater use of air conditioning in the United States is one reason why there are fewer heat-related deaths there than in Europe, where air conditioning is less popular. It’s sometimes argued that if people don’t have air conditioning, they’re more likely to use inefficient devices like electric fans (rearranging hot air instead of removing it and generating heat with their electric motors). However, the largest electric desk fans (typically rated at 25-50 watts) use a fraction of the electricity that the smallest air conditioners (typically rated at 750-1000 watts) do; you could use 20-30 fans and consume the same or less power than a compact AC unit! [1]

So, what is the environmental impact? First, let’s look at energy. Every time you turn on your car’s air conditioner, you add 10-20% to your fuel consumption (and an extra 10–20 percent to the price you pay at the gas station). Your vehicle will emit significantly more CO2 and pollute the environment. [2] Opening a window instead is often a better option at low speeds, but at higher speeds, you create air resistance (drag) and waste more energy than you save. Using the air conditioner at home will significantly increase your electricity bill; when physicist Tom Murphy scientifically tested his air conditioning, he discovered he used “more electrical energy in two days than we normally expend in a month.” Other strategies include leaving your windows open all night but closing them tightly first thing in the morning and throughout the day to keep hot air out of your home. Even if you can’t live without air conditioning in extremely hot climates, you can dramatically reduce how much it costs you (and how much energy you use) by simply turning the thermostat to a slightly higher setting.

Air conditioning units used to have another negative impact on the environment. Until the late twentieth century, most coolant chemicals known as chlorofluorocarbons (CFCs) (so named because they are made of the chemicals chlorine, fluorine, and carbon) were widely used in refrigerators. When old air conditioners and refrigerators were disassembled for scrap, the coolant chemicals escaped into the atmosphere. As they rose into the stratosphere (the upper atmosphere), they rapidly depleted the Earth’s ozone layer, which acts as a natural sunscreen, shielding us from the Sun’s harmful ultraviolet rays. Most modern air conditioners avoid CFCs (which are now banned in many countries as part of a global agreement known as the Montreal Protocol) and instead use alternative coolant chemicals (typically halogenated chlorofluorocarbons or HCFCs). If you look closely at our top photo, you’ll notice that the fan has a green “Ozone friendly” label on it, indicating that it contains no CFC coolants.

Is it here to stay?

We won’t be getting rid of our air conditioners anytime soon, whether we like it or not; in the United States, for example, all trends are pointing in the opposite direction. According to a US Energy Information Administration (EIA) survey conducted in 2009, 87 percent of US households now have air conditioning, with a dramatic increase in every region of the country since 1980. Changing expectations have contributed to this trend: according to the same survey, approximately 90% of new homes now have air conditioning. Affluent homes are more likely to have centralized air conditioning systems that cool the entire structure, whereas poorer homes rely on smaller, room-based air conditioning units that are fitted to windows or walls. Although centralized systems are far and away the most popular in the South, Midwest, and West, room-based units remain far more popular in the colder Northeast. Not surprisingly, according to a 2015 EIA study, residential air conditioning consumes 18% of US household electricity, accounts for 12% of total home energy costs, and causes a dramatic increase in consumption during the summer months.

Who created the air conditioner?

Thank Willis Carrier if you couldn’t live without air conditioning (1876–1950). In the early decades of the twentieth century, he was the man who pioneered this “cool stuff.” Here’s one of his early designs—notice how similar it is to my quick sketch above. How does it function? A fan draws warm air from a room (1), mixes it with fresh air (2), conditions it, and blows it back into the room (3). Heat is removed from the duct by the refrigerator chiller pipes (4), which are fed and controlled by a system of pumps, compressors, valves, and thermostats (5).

Air coolers that evaporate

If the thought of high electric bills and environmental damage makes you want to avoid air conditioning, evaporative air coolers are another option to consider.

Evaporative cooling may appear complicated, but it is something we are all familiar with. Dogs stay cool without air conditioners by sticking their tongues out and panting; hot runners do the same by sweating profusely to remove heat from their bodies. When liquid water evaporates and turns to water vapor, it absorbs heat from something nearby, known as the latent heat of evaporation (a panting dog or a sweating athlete, perhaps). To put this science into practice, we can use evaporation to remove heat from a room if we have a convenient supply of water nearby.

Portable air coolers (also known as evaporative air coolers or “swamp coolers”) resemble air conditioners on wheels but operate in a completely different manner. Whereas an air conditioner works like a refrigerator, expanding and then compressing a coolant chemical to transfer heat from inside a building to outside, an air cooler draws in hot air, cools it by passing it through or near water, and then blows it back into the room. There are two distinct types of air coolers:

One of them circulates air through a water-filled “sponge,” evaporating droplets of water into the air, cooling it while increasing humidity. This is known as direct evaporation because the air and water come into direct contact and exchange heat.
In a slightly different configuration, incoming air is routed through a heat exchanger, with cool water flowing in the opposite direction. Because the water and air do not come into contact here, this is referred to as indirect evaporation. Indirect evaporation involves moving two streams of fluid instead of one, which necessitates the use of an additional fan/pump and thus consumes more energy.

Air coolers are less expensive to operate than air conditioners, but they do not provide as much cooling. They are much more portable; on the downside, they have internal tanks that must be periodically refilled with water (and ice, if desired, to improve performance) or permanently connected to a water supply with a length of garden hose. They work best in hot, dry climates with low humidity (less than about 60%) because lower humidity means more effective evaporation and cooling.

Unlike air conditioners, which work best when doors and windows are closed, air coolers require good airflow near an open window (where dry fresh air comes in) and an open door. When you think about it, the water you’re adding to the airflow is “soaking” up heat from the room, and if you constantly expel moist air while allowing dry air to enter, you’re constantly removing heat. Air coolers that use direct evaporation (adding water) can also be used as humidifiers, but the doors and windows must be kept closed to allow the humidity to rise.

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The article above was written by the BestTopReviewsOnline team, which includes many of the US’s most knowledgeable technical experts. Our team includes well-known writers with extensive experience in mobile phones, computing, technology, photography, and other fields.

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