If a kitchen sells houses, then it’s only fair to say that a refrigerator sells kitchens. It’s a must-have, day-to-day appliance that a household certainly wouldn’t be the same without.
Just imagine a hot summer day without a fridge or a long day at work without a cool refreshment to come home to — wouldn’t that be terrible?
It’s easy to take our fridge’s cooling powers for granted, but if you’ve ever stopped to wonder how it keeps doing what it does, then this article is for you.
If you haven’t — well, it doesn’t hurt to know!
How does a refrigerator work?
A refrigerator follows a heat-exchanging cycle that involves the refrigerant flowing through the coils of your fridge. The refrigerant changes from a liquid state to a vapor state to absorb the heat inside the appliance.
The absorbed heat is then released outside the fridge and the cycle repeats.
You might have imagined that your fridge cools everything inside it by simply blowing freezing air into its compartments, but the science of it can’t be any more different.
Believe it or not, your fridge actually absorbs heat inside the compartments instead, and then transfers all that heat outside the appliance. It repeats this process until your set temperature is achieved and stabilized.
By eliminating heat from the food you put inside a closed space, you limit the growth of bacteria in them, thus slowing down their decomposition and preventing them from spoiling too soon.
This is all possible through the process of evaporation. To recap what we’ve learned in our grade school chemistry classes, evaporation is when a liquid turns into vapor and absorbs the heat around it.
It’s what happens when it’s too hot and our body starts sweating to cool down. In the same principle, your refrigerator produces liquid that turns into vapor as it enters the compartments.
Once the vapor has absorbed all the heat inside the fridge, it’s ushered outside so it can release the absorbed heat into the environment around the appliance instead. It’s why the back of your refrigerator is so hot to touch — that’s where all the heat comes out!
But mind you — only the absorbed heat is released. The vapor that does all the absorption is compressed back into liquid so it can be transformed into vapor again, and the cycle is thus repeated to maintain freezing temperatures.
Are you still with us? If yes, then good.
But if this still sounds too confusing for you, don’t worry. We can still break it down to a more straightforward step-by-step guide you can follow.
In simple steps, here is what happens during the refrigeration cycle:
- Step 1: Liquid Refrigerant Travels to the Evaporator
- Step 2: Heat Is Absorbed; Liquid Refrigerant Turns to Vapor
- Step 3: Refrigerant Vapor Returns to the Compressor
- Step 4: Heat Is Released through the Condenser
- Step 5: Cycle Repeats
Step 1: Liquid Refrigerant Travels to the Evaporator
The refrigeration cycle wouldn’t be possible without a chemical compound called ‘refrigerant’, which is typically stored in the compressor where the cycle begins.
The refrigerant starts in liquid form, eventually turning into vapor as pressure changes throughout the cycle, and then back to liquid again as it restarts.
As such, we’ll begin explaining the refrigeration cycle with the refrigerant in its initial liquid state.
To turn it into vapor without setting the appliance at high temperatures, the refrigerant has to be converted from a high-pressure liquid to a low-pressure one. This change in pressure also changes the boiling point of the liquid.
We know the boiling point of water is extreme at 100°C (212°F), but this temperature is relative to the sea level with the atmospheric pressure of 1 bar. Lowering this bar (i.e. lowering the pressure) also lowers the boiling point of water.
Where you stand right now, for example, water might boil at 100°C.
But if you were to climb up Mount Everest where the atmospheric pressure is about 0.3 bar — about 1/3 of the atmospheric pressure we’re used to — the boiling point of your liquid comes down to about 70°C (158°F).
Applying the same principle to your refrigerant, to convert it from liquid to vapor without setting a high temperature, all you have to do is change the pressure. This is possible using a throttling device.
Behind your refrigerator, you might notice a capillary tube or expansion valve attached to the compressor. That’s your throttling device!
As its name might suggest, the throttling device’s responsibility is to regulate the flow of the liquid refrigerant. It does this by obstructing its regular flow so that it’s forced to expand pressure and temperature as it travels along the rest of the tube.
Liquid refrigerant enters the capillary tube at high pressure and temperature and then exits it at lower pressure and temperature.
Once the liquid refrigerant has cooled down, it travels to the evaporator coils found in the back of the compartments of your fridge.
Step 2: Heat Is Absorbed; Liquid Refrigerant Turns to Vapor
Once this cool liquid refrigerant enters the evaporator coils, heat absorption begins.
Your fridge might have evaporator fans stationed near the coils. These fans can help regulate air circulation across the compartments so that all the heat is redirected toward the evaporator while the refrigerant is present to absorb it.
As heat across the space is absorbed, the compartment cools down while the high-pressure liquid refrigerant turns into a low-pressure vapor.
Remember how the change in pressure changes the boiling point of a liquid without compromising the temperature of its environment? That’s what happens as liquid refrigerant is turned into refrigerant vapor!
Step 3: Refrigerant Vapor Returns to the Compressor
Once all heat required to maintain a set temperature is absorbed, the refrigerant vapor now has to be returned to its original high-pressure liquid state so that the cycle can restart.
After exiting the evaporator coils, the refrigerant vapor returns to the compressor, where it’s compressed into a superheated high-pressure vapor.
However, unlike liquid where pressure is changed without altering the temperature, the temperature of compressed vapor — which is in a gas state — increases as the pressure does.
The compressor then needs to get rid of the hot temperature first before the refrigerant vapor is effectively returned to its liquid state.
You might ask how, and the answer is simple: via the condenser coils, of course!
Step 4: Heat Is Released through the Condenser
Have you ever wondered why the space behind your refrigerator is always hot? Well, here’s your answer — it’s all part of the refrigeration process!
Having exchanged its cool temperature with the heat it absorbed from inside the fridge, the refrigerant vapor now must exchange the heat again so it returns to its liquid state.
And because the inside of the fridge has to stay cold, the heat can only be exchanged outside of the fridge. This is made possible through a larger set of coils located at the back of the unit.
This part of your fridge is more commonly known as the condenser coils. As the high-temperature refrigerant vapor passes through it, heat from the absorption and compression is liberated to the appliance’s nearby surroundings.
With the heat removed from the vapor, the refrigerant is now converted back into a liquid state.
Step 5: Cycle Repeats
After a couple of heat exchanges, we now have a high-pressure, high-temperature refrigerant liquid again!
Once it exits the condenser, the refrigerant is once more fed into the throttling device so it changes pressure and temperature — and thus the cycle repeats.
By repeating this cycle over and over, your refrigerator creates a continuous cooling effect that meets your desired temperature and preserves the items inside the appliance.
Main Components of a Refrigerator
Every part of your refrigerator plays a role in keeping the appliance running, but the refrigeration cycle wouldn’t be possible without the following four parts: the compressor, the throttling device, the evaporator coils, and the condenser coils.
The refrigeration cycle can be summed up in four stops as we’ve listed above. Each stop is regulated by a device that plays a vital role in exchanging heat.
Here’s a short introduction to each of them.
1. The Compressor
The compressor is commonly referred to as the heart of your refrigerator. Think of the refrigerant as the blood that flows through your veins, which would make the compressor the heart that pumps it and keeps the body going.
You can also think of it as a bicycle pump. Heat increases as air is compressed, and then pumped into another vessel.
Likewise, the compressor ‘pumps’ low-pressure vapor to increase its pressure. As pressure goes higher, so does its temperature, after which it is then directed to another device.
In brand-new refrigerators, the refrigerant is stored here, waiting to be released into a throttling device.
Have you ever noticed how there’s a constant thrumming noise coming from your refrigerator? That’s actually the compressor in action!
But the compressor doesn’t always have to be in action. When the refrigerator meets your set temperature — or when it gets too cold — the compressor has to be turned off to avoid overfreezing. Thermostats inside the fridge help read the temperature in the compartments and signal the control panel to stop the compressor. When the temperature reading begins to rise as the fridge warms up, the compressor is signaled to start again. Your refrigerator normally fluctuates between temperatures as the appliance stabilizes this setting, so you might notice that the unit seems to be turning on or off on its own. For non-inverter fridge models, starting the compressor may make a lot of noise and consume too much energy. Meanwhile, rather than turning off the compressor, inverter models only signal it to slow down. This is why you’ll notice that this type of fridge is quieter.
2. Throttling Device
The throttling device is sometimes referred to as an expansion device because that’s what it does — it expands the liquid refrigerant so that its pressure and temperature are lowered.
It functions like a nozzle of an aerosol spray. The contents of the bottle are liquid, but once you press on the nozzle, they are released as tiny droplets that look like mist.
Similarly, when liquid refrigerant exits the throttling device, a portion of it is vaporized like mist. This comes with the lowering of pressure.
This wet mist — or liquefied gas — retains liquid particles which help absorb heat from conditioned spaces.
3. Evaporator Coils
The evaporator coils are your indoor heat exchangers. They’re usually found at the back of the compartments, often behind a back panel.
As the liquid refrigerant travels through the evaporator coils and absorbs heat from the conditioned space, it evaporates — hence the name of the device — and cools the compartment down.
It’s no different than sweating!
For more efficient cooling, most refrigerators have an evaporator fan which helps regulate air circulation inside the appliance and maintain different temperature levels.
But remember — the cold air doesn’t come from the evaporator fan itself but from the evaporator coils. Your refrigerator can still chill your food even when the fan malfunctions.
But if your evaporator coils stop working, forget about slow cooling effects — your refrigerator won’t cool at all.
When the cool temperature of your refrigerant meets the warm temperature inside the compartments, condensation can form. Due to low-temperature settings, these condensations can turn to ice and frost. Frost formation along the evaporator coils is a common setback. They can obstruct the cooling process, but don’t worry — they’re preventable! Defrosting your fridge once a month helps get rid of ice buildup along these indoor coils. We also recommend leaving an inch of space between the coils and your food. This ensures proper airflow between them and reduces the risk of the food’s heat directly coming into contact with the vapor traveling through the coils.
4. Condenser Coils
If the evaporator coils are the indoor heat exchanger, your condenser coils are the outdoor ones.
Condensers are built the same way evaporators are, but they function differently. Where the evaporators absorb, the condensers release.
Once the heat from the compressed refrigerant vapor is released, it transforms back into its liquid state, and the cycle begins again.
As such, the condensers are connected to the throttling or expansion device for a seamless refrigeration cycle.
Similar to your evaporator coils, the condensers may also employ a ventilation system that helps release heat more effectively. A condenser fan spreads the hot air across the coils so more heat is liberated from the vapor.
Also like evaporator coils, the condenser coils can be prone to obstructions such as dust or lint buildup. We recommend cleaning your fridge once a month and brushing up or vacuuming the condensers while you’re at it! Ensure also that there are at least two inches of space between the fridge body and the surface it’s standing against. This helps release the heat from the vapor more effectively. If the heat from the vapor isn’t removed properly, your appliance might experience overheating issues, as well as trouble cooling efficiently.
As a bonus item on the list, we’re adding refrigerant to the crucial parts of the refrigeration cycle. After all, the cycle would just be a concept if you don’t have the refrigerant running through it.
Here, we’d like to introduce you to the most common types of refrigerants in the market.
While there are various refrigerants in existence, modern refrigerators typically use either of these two: the R-134a or the R-600a.
This type of refrigerant is widely used because of its environmental properties.
Before the introduction of the R-134a in the market, refrigerators used the R-22 which contributed greatly to the depletion of the planet’s ozone layer.
Nowadays, the R-134a is a standard among refrigerators. But while it doesn’t contribute to ozone depletion, this refrigerant gas still has its environmental caveat.
It’s a potent greenhouse gas, which means it actively traps heat in the atmosphere that could take a dozen to hundred years to dissipate.
In terms of greenhouse gas emissions, the R-600a fares better than the R-134a in that it’s guaranteed to have 0 global warming potential.
It also cools more efficiently than the R-134a. Its biggest catch, however, is that it’s highly flammable and that it poses more health risks.
Few refrigerators use it for this matter and the ones that do employ this refrigerant only use small doses of it.
Though it is flammable, rest assured that a refrigerator absolutely cannot emit enough gas to start a widescale fire on its own. As such, R-600a refrigerants are used in frost-free refrigerators.
Types of Cooling Systems
Modern refrigerators can be classified by the type of cooling system they use: direct-cool or frost-free.
Direct cooling uses less energy but demands manual defrosting of the unit. Frost-free refrigerators, meanwhile, use heating systems to automatically melt frost buildup in the appliance.
The differences between direct cooling and a frost-free refrigerator can be broken down into five factors: operation, capacity, maintenance, energy consumption, and market price.
Here’s a table to lay it down for you.
|Factor||Direct-Cool Refrigerator||Frost-Free Refrigerator|
|Operation||It uses the evaporator coils to directly cool its compartments without the employment of a fan system.It also doesn’t have heating elements to melt frost build-up automatically.||It uses a fan system in addition to the evaporator coils to distribute cool air in the compartments.It also employs heating elements that automatically defrost the compartments, especially the freezer, throughout the day.|
|Capacity||It is typically limited to 12 cu. ft. It’s good for cooling specific items such as beverages or ice, but won’t do well with more items.||It can go up to 30 cu. ft. Its fan system allows it to cool larger compartments and store more items.|
|Maintenance||This type of fridge requires manual defrosting more than a frost-free refrigerator, but its simpler construction means there are fewer parts to maintain.||This type of fridge requires less effort to defrost, but its additional parts also mean more parts to maintain.|
|Energy Consumption||Without a fan or heating system, a direct-cool refrigerator consumes less energy.||With independent fan and heating systems, a frost-free refrigerator can consume more energy.|
|Market Price||Direct-cool refrigerators sell for more economical prices.||Frost-free refrigerators may sell for higher prices in the market.|
The main difference between a direct-cool refrigerator and a frost-free refrigerator is how they operate.
Direct-cool refrigerators do not have a fan system. Ergo, the cooling effect comes from the evaporation process alone.
As we’ve mentioned before, the refrigeration cycle can still work even without a fan to regulate the airflow inside a compartment, albeit this could limit the number of compartments it can effectively cool.
On the other hand, a frost-free refrigerator uses one or more fan systems to circulate cold air into its compartments evenly. This allows it to keep food fresh for a longer duration.
Moreover, frost-free refrigerators have heating elements that allow them to automatically defrost the unit multiple times a day.
Direct-cool refrigerators do not have heating elements and thus require manual defrosting of the unit once there’s enough ice buildup in its compartments, particularly in the freezer.
The lack of an independent air circulation system in direct-cool refrigerators limits its dimensions to about 12 cu. ft. That might not sound much at first, but that’s already standard measurement for a household fridge for a small family.
The nature of its cooling system, however, makes a direct-cool refrigerator better suited for industrial cooling. If you’re looking for a fridge to just keep your food chilled and fit in a small space, this is the type of fridge you’d want to purchase.
But if you’re looking to store a week’s worth of groceries to feed a family of five or six, a frost-free refrigerator could be your best friend. This type of fridge can offer up to 30 cu. ft. of storage.
French door or side-by-side models usually incorporate this type of cooling system as it can cool larger spaces. This makes it perfect for residential use.
As we’ve mentioned above, a direct-cool refrigerator needs to be manually defrosted. In most cases, you’ll have to defrost and clean it weekly.
That already sounds like a hassle, we understand, but the brighter side to it is that a direct-cool refrigerator has fewer mechanical parts. Ergo, lesser risk of running into technical errors.
Meanwhile, a frost-free refrigerator needs only to be force defrosted and cleaned once a month. But with more moving parts, they’re more likely to give you mechanical issues, especially involving their fan system.
Remember that a refrigerator can get rickety as it ages. Over the years, a frost-free refrigerator might cost you more effort in maintenance than a direct-cool one.
4. Energy Consumption
Since direct-cool refrigerators use no fan or heating systems, they naturally consume less energy.
On the other hand, a frost-free refrigerator’s additional systems can consume more power.
This issue with energy consumption, however, can easily be offset by inverter systems. As we’ve briefly introduced, an inverter refrigerator saves energy by only slowing the compressor down instead of repeatedly turning it on and off.
Inverter systems aren’t just limited to frost-free refrigerators, though. Direct-cool refrigerators can also offer inverter models — in that case, its energy-saving function is doubled!
5. Market Price
With all its additional technologies, a frost-free refrigerator typically costs more than a direct-cool one. But we still think it’s a worthwhile investment!
Frost-free refrigerators offer you convenience, and with their larger capacities, you can consider them a homemaker.
Meanwhile, a direct-cool refrigerator costs less for fewer technologies. If you want an appliance to plug into your home office to store drinks or dessert leftovers, this type of refrigerator would be perfect for you!
Your refrigerator might look like it runs on complicated methods, but it doesn’t get any more complicated than any scientific processes you learned in middle school.
Think of the water cycle and how rain forms — it’s very similar to that, give and take a few steps.
Understanding your fridge further can also help you make better choices, either in buying a new fridge or maintaining the one you’re using now.