How a Fridge Works
Your refrigerator gets taken for granted, admit it. It’s always on, it controls itself. Cycles refrigeration when it needs to, and turns itself off when the temperature is satisfied. Have you seen the recent Maytag commercial featuring the fridge? It is basically the only appliance in your kitchen that is constantly on.
Have you ever wondered what goes on inside there? Behind the insulated walls of plastic laminate. What does the curly thing on the back do? That’s the condenser. If you have ever wanted to know how a fridge works, this post should help you understand the awesome basics of refrigeration, heat, and energy. I am counting on you to connect those dots.
Before we get into the simple explanation of how the refrigerator in your kitchen works, and basically every type of refrigeration unit such as air conditioning units or freezers. They all work using the same, exact principles of refrigeration. I am getting these principles, and paraphrasing them, from the book Modern Refrigeration & Air Conditioning. Just so you know the resource before we begin.
It may help to have the additional page open, it’s another post on the site – a drawing of the basic 4 step refrigeration cycle. There should be a sweet Paint picture up for this one as well lol but the other drawing is more technical and can help you understand. Totally up to you though.
How a Fridge Works
The example the book opens with is of a canoe. A leaky one at that. Pretend we are in a leaking canoe. We need to remove the water right? How could we do this? We have no buckets or cups but we do have sponges.
We can soak up some water, it’s a small leak, and then wring the sponge out overboard. Staying afloat yeah what. We can keep doing it again and again so we can stay out fishing for longer.
This is how a fridge operates.
A fridge removes heat from the inside, brings that heat outside of the fridge, and then loses it.
It wrings itself out, outside of the refrigerated space. Then, it repeats the cycle. The refrigerant goes back in, picks up any heat from inside the fridge, comes back out, etc. So simple now yeah? Moments ago it was a mystery box that always hummed in the background. Now you know even more, that quickly.
Just like the sponge and canoe example, the refrigerant inside the tubes keeps repeating the process over and over until the refrigerated space, the inside of your freezer, fridge, a/c unit, hits the desired temperature setting.
In the refrigerator heat instead of water is being transferred. When the liquid refrigerant inside evaporates because of the heat inside, heat is absorbed by it. Boom – energy transfer.
This happens inside the evaporator and occurs as the refrigerant changes from a liquid to a gas or vapor. This is why these units use refrigerant. It has different properties than say, water.
Freon for example has a different boiling point than water. So for it to remain a liquid, it needs to stay at a certain pressure. It is unable to do this as it flows through the various stages of the cycle, as it absorbs and then transfers heat around. Still following yes?
How is it Accomplished?
After the refrigerant has absorbed the heat from the inside and turned into a gas, it is discharged to the condensing unit on the outside of the refrigerated space. On a regular old fridge this is usually that coiled thing across the back, with the twists, turns, and fins. This is the place where the refrigerant is going to give up the heat it picked up.
It’s going to wring out its sponge.
The condenser works just the opposite of the evaporator. Inside the evaporator, liquid refrigerant enters one end and absorbs heat as it makes its way through. When it reaches the end of the evaporator, it has all become a gas.
As you now now, the high pressure, high temperature gas now hits the condenser. As it goes through, and the surrounding air around the tubes and fins touches the outside, it gives up the heat.
When it reaches the end of the condenser the refrigerant has cooled and is a liquid again. That simple refrigeration cycle is generally repeated until a desired temperature set point is reached. Whether it is 40 F in your fridge or 72 F in your house.
Heat can get inside a fridge through leaks or simply when you open it. Believe me, I heard enough about that growing up.
My Dad made you plan your openings. Seriously. He would yell, and you would get in trouble if you had the door open for more than a few seconds. He strategically placed like items in there for ease of grabbing quickly. You had to plan what you’d be getting in one swoop. Don’t even think about opening it twice in succession because you forgot something mister. Forgot the bread accidentally this time? Guess your sandwich is breadless this time.
More heat is introduced every time you put something in that isn’t as cold as the fridge already is, like new groceries.
Keep in mind that heat is never destroyed in the refrigerated process. It is removed from one spot and then wrung out in another. That is how they all work and is the basics of every refrigeration cycle you see or feel. In your car, on the plane, in condo, a deep freezer, a morgue.
Question, comment, or suggestion? You know what to do, please feel free to leave or send one. If you’d like to contribute let me know.
Again, this was pretty much taken from the book Modern Refrigeration & Air Conditioning.
Along with the boiler series books, these are the main core books I recommend for people looking to understand engineering basics a little bit more, or to get into serious building engineering. To be a true one at least.
That core of books was standard issue in my day. back in my day…