How Air Conditioners work (The Not-So Technical Explination)

How do air conditioners work?

Everyone in Houston definitely understands what air conditioners do, but how do they do it? Well, that's probably a question not so frequently asked. I mean, have you thought at all about your air conditioner today? I'm and HVAC technician so my answer is a little biased but i'm willing to bet most of us didn't wake up today and start pondering the mechanics of our air conditioning system. Air conditioners, like our cell phones or the internet for example, are the sort of things we tend to use and enjoy without ever giving their technical inner workings much thought. We expect these conveniences to be in our lives and with us just about everywhere we go, but we don't really focus on their physical properties or mechanics as much as we do their features and the enhancements they provide in our lives (unless we are without them!).

Air conditioning then, is perhaps one of those modern necessities that most of us probably don't think about that much at all, and when compared to our phones or the internet, i'm betting air conditioning probably comes in last place in the time-of-thought race. Why? Well, not only has air conditioning been around a little bit longer than cell phones or the internet, making majority of us born within the era of modern air conditioning and already acclimated to having air conditioning in our everyday lives but we also don't really see or interact with our HVAC systems that much like we do our phones or the internet. Not to mention the physical air our HVAC systems condition and the results they accomplish is invisible, so air conditioning has got the whole 'out of sight out of mind' thing applied to it, making it even easier to over-look.

Air conditioning has become such a common everyday feature in our lives that it's just hard to imagine how life was and is without it. When it comes to air conditioning we just seem to automatically expect it everywhere we go - We don't ask ourselves before going out to dine at any particular restaurant, "Does this restaurant i'm going to have central air and heat?", we just expect a comfortable air conditioned environment when we go out and never give that question any thought while we're busy weighing out other important things like what type of food we want to eat. But to think that not so long ago air conditioning was nonexistent is an interesting thing to imagine and really helps give us a perspective on everything air conditioning has enhanced our lives with and provides us with and also just how often we take it for granted and how frequently it gets over-looked. Let's take a brief look at the introduction of air conditioning to Houston:

Houston Early A/C History Time Line

Date Info
1922 Rice Hotel's Cafeteria - The first public room to be air conditioned in Houston.
1923 Second National Bank - The first public building to be air conditioned in Houston.
1925 The Majestic Theatre - The first theatre to be air conditioned in Houston.
1927 Following the Majestic Theatre's incorporation of air conditioning, all theatres located on Main Street in Houston become air conditioned.
1932 The first private home in Houston is air conditioned.
1938 The Houston Chamber of Commerce reports there are 427 air conditioning systems installed in Houston, including 126 private homes. Houston's 1938 population: 400,000.
1950s During the 1950s all businesses and homes began being constructed with air conditioning. Houston is dubbed "The Air Conditioning Capital of the World".
1965 In 1965 the world would see the first domed stadium - The Astrodome. Not only was this the first domed stadium, but the first air conditioned stadium as well.

On a personal note, I tend to think air conditioning is one of the most important developments in our history as well as one of the most over-looked. So just how important is air conditioning? Like the discovery of electricity, HVAC is pretty important. So important in fact, that it's literally laid the foundation for and in some way paved a road to pretty much everything else we know and love and probably take for granted as much as we do air conditioning, such as the internet for example - The internet is a place we can go and gain insight and information on just about anything we want and has changed history forever. But it's true, without air conditioning to cool the servers and data centers that power the web, it never would have come into existence. And before the internet, when people would read and gain information from articles printed in books and newspapers, without air conditioning the mass production of printed paper would also not exist. in fact, this is why and how modern air conditioning was invented in the first place in Brooklyn N.Y. back in 1902 by a young electrical engineer named Willis Haviland Carrier, the coolest inventor ever.

Willis Haviland Carrier

So does the name 'Carrier' sound familiar to you? You may have heard it before in the news or seen it around the net or on various pieces of air conditioning equipment (maybe even your own). After inventing the air conditioner, Willis Haviland Carrier realized he stumbled upon something pretty significant and ended up founding what would become one of the largest and most popular brands of HVAC equipment manufacturers in the world - The Carrier Corporation. So what and why did Mr.Carrier create an air conditioner? He was tasked a pretty tough assignment for his time at a Brooklyn N.Y. paper printing and publishing company known as Sackett-Wilhelms - Reduce the humidity in this building so we can mass print and publish things on paper. See, before the invention of modern air conditioning, stock paper that was being stored in buildings prior to ever hitting the printing press would absorb moisture, causing the paper to jam inside printing machines, become a breeding ground for mold, and cause issues with the ink being printed on the paper (like getting the ink to dry and layer correctly onto the paper it's being printed on). So, Mr. Carrier being the engineer that he was, basically chilled some metal pipes and blew air across these cold pipes, thus cooling the air. And, since cold air can't hold as much moisture as hot air, the humidity levels in the printing company's paper storage area leveled out and their printing techniques took off and so did modern air conditioning as we now know it. Pretty soon air conditioners started popping up all over the place making our lives comfortable, healthier and giving birth to most of the modern world as we know it today. So many things we use every day are now possible due air conditioning and it's safe to say any form of modern mass production was somehow given birth because of air conditioning. From the mass production of paper and milk to the silicon chips inside computers and advancements in medicine - None of this would be possible at the level it is today without some form of air conditioning. So how does air conditioning actually work anyway? Does an air conditioner still consist of a bunch of chilled pipes with air blowing across them like Mr.Carrier developed for the paper company? Yes and no. Let's explore and discuss the inner workings of the machine that has done so much and changed the world for the better into the cool place it has become today.

"It's not so much the heat as it is the humidity!"

That's a phrase we all know very well in Houston. Humidity is what makes our hot summers unbearable and it's what makes the long summer days seem even warmer than they actually are. Why is this though? Temperature and humidity are actually 2 complete different things, and when we put them together we get the Heat Index, or "How it actually feels". On a hot summer day outside at 90°F, if the humidity is low, it probably feels like 90 degrees, which is tolerable. However, if the humidity is high like it is always in Houston, it can feel like your standing and sweating in a molten lava pit well above 90°F. When humidity and temperature combine at high levels, the Heat Index, or the way it actually feels rises to unbearable levels (a common occurrence in Houston) and the weather man gives us "Heat Index" warnings and reminds us to drink fluids. Modern air conditioners immediately became a perfect fit for areas such as Houston because they dehumidify and lower the temperature of the air, but how do they do it? Air conditioners work by taking advantage of certain things that happen when matter changes state.

"Bwhaat? Wait a minute.. I thought this was the non-technical version of how air conditioning works?"

Hey! Don't worry I'll keep this simple, because it really is simple and it's just a common process that goes on all around us all the time. If you can understand how water is a liquid and can turn into a gas called steam, and viceversa, then you'll understand air conditioning by the end of reading this article: Air conditioners pump refrigerant through pipes, and in various areas of these pipes, they change the state of the refrigerant they are pumping from a liquid state to a gas state, and from gas state back into a liquid state. Simple, like boiling a pot of water - You boil the water and it turns into steam.

Water's Different States of Matter

So why is changing the state of matter important to making our homes and businesses cool and dehumidified? Well, air conditioners use this process of changing the state of refrigerant from a liquid into a gas in order to absorb lots of heat from the air in our homes and offices, in turn removing heat from the air inside our homes and businesses, which makes the air in our homes and businesses cooler and dehumidified. That is to say, when something is 'cold', it's simply lacking heat, and as air conditioners absorb and remove heat from the air, they make the air cold. I won't go through all the technical stuff with all the different components that make up an air conditioner and how they all work to accomplish this process of removing heat from the air, instead ill use the example of a pot of boiling water on a stove. You may think a boiling a pot of water has nothing to do with the inner workings of an air conditioner because the water is getting hotter, but it's the exact same process. The water is simply absorbing heat created by a stove in the same way a sponge absorbs spilled milk. From now on let's try to think in terms of absorbing heat and transferring heat with our examples. Let's think about a pot of cold water on a hot stove for a moment and compare it to an air conditioner and a home. We fill up a pot with cold water at 33°F and set it on the stove. We turn the stove on and begin applying heat to a pot that contains liquid water at 33°F and the water begins to absorb this heat and consequently the water begins to warm and rise in temperature. By using a thermometer we notice the temperature of the water beginning to rise and monitor this rise in temperature from 33°F all the way up to 212°F and suddenly the thermometer just stops rising and bubbles begin to form in the water.

"What the? What is going on? Why isn't the temperature getting hotter? Is my thermometer broken or having an issue going beyond 212°F?"

Not quite, this is normal, your thermometer is fine and doing what it's designed to do! Let me explain why:

Water boiling at 212 degrees F

As it turns out, there are different forms of energy when it comes to various things absorbing heat. Sensible Heat Energy (the temperature, which we can sense with a thermometer) and Latent Heat Energy (the part we cant sense with a thermometer). Technically speaking, latent heat energy is the energy required to change matter from one state to another, which as we can see with the pot of water beggining to boil, this process requires alot of energy (notice how the thermometer sticks at 212°F and doesn't rise for a long time no matter how high you turn up your stove). Thermometers only measure sensible heat, or changes in temperature, which is why the thermometer is stuck at 212°F, because it simply cannot sense the rise in latent heat that's occuring within the water once the water reaches 212°F. The whole time the water is at 212°F it's readily absorbing heat from the stove without rising in temperature and it's doing this in order to facilitate a change in state, and that's alot of heat! This is the same principal that air conditioners exploit with refrigerants inside pipes in order to absorb heat from the air in our homes and offices, in turn making the air 'cold'. Now, back to the boiling water:

Once the water in the pot reaches 212°F you probably noticed bubbles beginning to form and hot steam beginning to rise up from the pot of boiling water - This is the water changing state from a liquid into a gas because the water has finally absorbed enough energy in the form of latent heat energy to make a change in the state in matter, yet the thermometer is again stuck at 212°F. And, it is this process of changing state from a liquid (water) into a gas (steam) that is keeping your thermometer stuck at 212°F. Why? Because in order for matter to change state it requires a lot of heat energy to make this change of state physically occur, and with water the magical number that makes this change happen is 212°F. Because of this, the entire pot of water will remain at 212°F until all the water has evaporated into a gas, or steam. So what's going on here? The water absorbs sensible heat energy (change in temperature) from 33°F all the way to 212°F which we can see on our thermometer, once the water reaches 212°F it begins to absorb latent heat energy (change in state) as it begins to boil in order to change states of matter, and this is the part we cannot pick up with our thermometer. That is to say, the entire time the water is boiling, it's absorbing great amounts of heat energy in the form of latent heat energy and using that energy to change the state of the water from a liquid into a gas. Even though the flame or the surface of your stove may be well beyond double the temperature of the water which the stove is heating, the water continues to absorb this heat and remain at 212°F in order to change states and it's not until all the water has changed into a gas state (steam) that the steam can then begin to absorb more sensible heat and reach temperatures beyond that of 212°F. Air conditioners do the same thing but instead of boiling water they boil refrigerant, which boils at a much lower temperature than water at around 40°F. And instead of using a stove to heat up a pot of water in order to make water boil and change states, an air conditioner uses the heat contained within the air in our homes and offices to boil a refrigerant into a different state. The pot of water was absorbing heat generated by the stove whereas an air conditioner absorbs the heat from the air in a confined space such as your home, thus cooling that space. It's all about transferring heat by taking advantage of phase changes in matter. Since the refrigerant in an air conditioning system boils at 40°F, the air in our home's is hot enough to make this boiling process occur like we are seeing with the stove and the boiling pot of water.

Speaking of transferring things, lets transfer the boiling pot of water example into the air conditioner example for a better understanding: Remember, all we are doing is absorbing heat from something with both these examples, thus removing heat from whatever it is we are absorbing heat from, and in turn making that thing colder. With the boiling water example, our heat source came from a stove which was constantly turned on and creating lots of heat, and the water sitting in the pot on top of the stove is what we used to absorb all the heat created by the stove by changing water into steam. In an air conditioning example, refrigerant in bunch of cold pipes changes state from a liquid to a gas, absorbing heat out of the air in our homes, which makes our homes air colder. Unlike the stove which can be turned on and off and existed as a constant source of heat, our homes gain heat due to several other factors - Most of the heat that enters our homes comes from the sun - It shines through our windows and hot outdoor air enters our homes through air gaps like open windows and doors and other air gaps in our homes outer envelope. These things all add heat to our homes air which makes us uncomfortable and then we want to turn on the air conditioner. Other heat sources in our homes include electronics like televisions, cooking stoves and ovens, and even people. As the temperature rises in our homes due to these sources of heat infiltration, the air conditioner's thermostat notices, and once the indoor temperature gets higher than what the thermostat is set at, it kicks on the air conditioner to remove heat from our homes which makes it feel cooler. Inside the air conditioning system the whole 'boiling pot of water' analogy takes place which readily absorbs heat using a phase change in matter, except instead of using a stove and water, air conditioners use the hot air in our homes and refrigerant. The refrigerant absorbs the heat out of the air inside your home, and that big air conditioning unit sitting outside of your home with the fan spinning on it then blows all that heat outside of your home. Just go put your hand over the outside unit when your A/C system is running and you'll notice the air blowing out of it is hot air - That's all the heat that was absorbed from your home's indoor air now being removed out of your home and blown outside! It's like a conveyor belt made of refrigerant that carries heat from the inside of your home to outside your home, in turn making your home cooler. Now that's pretty cool.