How does a refrigerator work?

Refrigerator 101: How Does A Refrigerator Work?

A refrigerator today is almost always taken for granted; it is large, un-sexy – and yes, kind of boring. It just…stands there. But when it was first invented, it was a godsend.

Back then, preserving food meant salting or drenching meat in vinegar to stop food from spoiling quickly (a theory on how adobo came to be). Rich people also paid a lot of money to transport ice blocks from across the world all the way to the Philippines just to enjoy an ice-cold drink.

The refrigerator changed all of that. Now, food preservation was made easy – and it makes ice-making accessible too!

The purpose of refrigeration

All foods contain mostly harmless beneficial “gut bacteria”. Some foods, like yogurt and bread, are literally made out of bacteria (lactobacillus and yeast). When these bacteria grow too fast, they will cause food spoilage.

The basic idea behind refrigeration is to slow down the process of decomposition by slowing down the growth of bacteria in our food.

The refrigerator does this by providing a consistent low-temperature environment. So the question is, how does a refrigerator work?

The cooling process

A common misconception about how refrigerators work is that they blow cold air into their compartments to bring the temperature down. This is not the case. What they actually do is take the heat out of the air inside and transfer it outside. This is done through the process of evaporation.

When a liquid evaporates in to the air, it absorbs heat. This is why your skin feels cold after rubbing your hands with alcohol. This is also why we sweat when our body temperature gets too hot.

A refrigerator works by harnessing the power of evaporation to cool down its interior, but makes it so that the resulting vapor won’t escape. Instead, it gets reverted back to its liquid form to start the cycle all over again.

The refrigeration cycle

The refrigeration cycle is deceivingly simple – it only requires four main parts to achieve it. The cycle goes like this:

Expansion Valve

Expansion Valve

Also known as the capillary tube, this part greatly reduces the pressure of the liquid refrigerant, bringing its boiling point down.

Fridge Evaporator

Evaporator

The low pressure liquid is passed along the evaporator coils where – you guessed it – it will gradually evaporate.

As stated earlier, evaporation absorbs heat inside the the fridge compartments, which brings the temperature down.

Refrigerator Compressor

Compressor

By now, the low pressure liquid has already evaporated into low-pressure gas. To restart the process, the fridge needs to turn it back into high-pressure liquid. It achieves this in two phases.

The first phase is where the compressor comes in. Otherwise known as the “heart” of the refrigerator, the compressor increases the pressure of the refrigerant gas, turning it into hot high-pressure vapor.

Refrigerator Condenser

Condenser

The next phase turns that hot high-pressure gas into warm high-pressure liquid.

To do this, the compressor pumps the refrigerant along the condenser.

Condensers are the finned coils at the back of the refrigerator. On newer models, they can be hidden inside the fridge wall.

This is where the hot refrigerant gas turns back into liquid. The liquid then gets pumped back to the expansion valve to start the cycle over again.


Thermostat

The thermostat is outside of the refrigeration cycle, but it is an important part in regulating the cycle.

Its job is to monitor the temperature inside the fridge – when the ref gets too cold, it switches the compressor off; when it gets too warm, it turns it on again.

A short discourse on non-inverter vs. inverter refs

This is why refrigerators (especially non-inverter ones) turn on and off and then on again periodically. This is because non-inverter refs only have two “speeds” – on and off.

Meanwhile, inverter refrigerators are continuously switched on; it doesn’t go from “zero to one hundred” just like a non-inverter, instead it maintains the desired temperature by only pulling in the right amount of energy to the compressor. This translates to energy savings – and yes, a smaller electricity bill.

The longer and more detailed discourse of the inverter technology and how it works can be found here. [coming soon!]

Types of refrigerant gases

If the compressor is the heart of the fridge, then the refrigerant gas is its blood. This is the gas that gets evaporated and condensed to cool down our refs.

There are many kinds of refrigerant gases in use today for refrigerators, air conditioners, and other commercial applications. Each one of them have different properties.

Back in the day, the most common refrigerant gas was Freon (R-12). However, Freon is a CFC (chlorofluorocarbons) that damages the ozone layer. Freon has been phased out in lieu of more environment-friendly refrigerants because of this.

The two most common refrigerants for refrigerators today are R-134a and the newer R-600a. Here’s the difference between the two:

R-134a (Norflurane)

  • Global Warming Potential: 1430 (Medium)
  • Ozone Depletion Potential: 0
  • Flammability: No

R-600a (Isobutane)

  • Global Warming Potential: 3 (Low)
  • Ozone Depletion Potential: 0
  • Flammability: Yes

Also worth noting: R-600a is more efficient, requiring a shorter time to reach -21°C (60 minutes) compared to R-134a (135 minutes) [1].

On flammability

You may be worried about the inherent flammability of R-600a, but refrigerators use only small amounts of this gas. Fridges need ~50g of this gas to function – 66% lower than when using R-134a [2]. This amount won’t pose that much danger of your refrigerator blowing up or being engulfed in flames – it’s still flammable though. If you suspect that your refrigerant is leaking, call a professional.

Types of cooling systems

All refrigerators create cold air the same way, but they can differ in their way of distributing it throughout the compartments. Refrigerators are categorized as either direct cooling or fan cooling. These are their differences:

Direct Cooling

This is the traditional cooling system. It relies on the evaporator to cool the air with no aid for circulation.

With this system, you don’t have a way to evenly distribute the cold air inside the fridge. This uneven cooling is the reason why frost appears in the freezer box which you’ll have to defrost.

Fan Cooling (No Frost)

A fan cooling refrigerator still uses the evaporator to cool the air, but it uses several internal fans to evenly circulate the cold air inside the fridge.

In the Philippines, the term ‘fan cooling’ is used interchangeably with the term ‘no frost‘, but they are not synonymous.

‘Fan cooling’ is a type of cooling system, while ‘no frost’ is a type of defrosting system; it just so happens that all fan cooling models being offered in the Philippines are no frost.

A refrigerator can only be considered a ‘no frost’ if it has a heating element in the freezer box to periodically melt the built-up frost on the freezer walls.

Conclusion

While most people can go about their lives not knowing how a refrigerator works, it can be worthwhile to study. Knowing so will provide you with information to make better decisions when buying for a new refrigerator. It can also help you improve its performance to get more from it – or at the very least, not break your fridge.

FURTHER READING: Refrigerator Buying Guide

Sources:
https://sciencing.com/evaporation-cause-cooling-5315235.html
https://www.danfoss.com/en/about-danfoss/our-businesses/cooling/the-fridge-how-it-works/
https://hydrocarbons21.com/articles/9680/alternative_refrigerants_cited_as_key_climate_solution_by_drawdown_australia

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