6.4 Refrigerators
6.4 RefrigeratorsIt might seem like your refrigerator works by "making things cold," but physically, it does the opposite. A refrigerator is a heat mover. Its job is to extract thermal energy from the cool interior and push it out into the warmer kitchen.
Because heat naturally wants to flow from hot to cold, moving it in the reverse direction requires work—and that work requires electricity
Text description of the Refrigeration Cycle image.
The image illustrates a diagram of the refrigeration cycle, divided into two sections representing low and high pressure. On the left, the blue section is labeled "Low Pressure" and depicts cool liquid flowing through a coiled tube, marked as the evaporator. Snowflake symbols and the text "COOL AIR" are included to signify cooling. On the right, the orange section is labeled "High Pressure" and shows hot liquid moving through a similar coiled tube, designated as the condenser, accompanied by red circles and the text "HOT AIR" to indicate heating. At the center of the diagram, a compressor connects the two sections, with arrows indicating the flow direction. An expansion valve is positioned between the evaporator and condenser, illustrating the complete cycle.
The principle of operation of a refrigerator is similar to an air conditioner. It moves the heat energy from inside to outside. There are four basic components in a refrigerator and their functions are as follows:
- The expansion valve acts like a nozzle. High-pressure liquid refrigerant squeezes through it and suddenly expands into a low-pressure zone. Key physics: When a fluid expands rapidly, its temperature drops. This is the same reason aerosol cans feel cold when sprayed. Now the refrigerant is cold and ready to absorb heat.
- Evaporator - These are the coils you might see inside the freezer or behind the back panel. The cold, low-pressure refrigerant flows through them and evaporates (turns from liquid to gas). Why this matters: Evaporation requires energy. The refrigerant steals that energy as heat from the air and food inside the fridge. Result: Your food cools down, and the refrigerant warms up as it carries that heat away.
- Compressor - This is the refrigerator's 'engine'—and the part that uses the most electricity. The compressor squeezes the now-warm refrigerant gas, increasing its pressure and temperature dramatically (think of pumping up a bike tire: the pump gets hot). This compression step requires significant electrical work. The refrigerant leaves the compressor hotter than the kitchen air, so it can now release its heat outward.
- Condenser - These are the black coils you might feel on the back or bottom of your fridge. The hot, high-pressure refrigerant flows through them. Because the refrigerant is now hotter than the kitchen air, heat naturally flows out of the coils and into the room. The refrigerant condenses back into a liquid, ready to repeat the cycle. Why you feel warmth: That heat you sometimes feel near your fridge? That's the heat originally taken from your food, plus the energy used by the compressor."
How Does a Refrigerator Work?
How does a Refrigerator Work? (3D Animation) (4:10)
Transcript: How does a Refrigerator Work? (3D Animation) (4:10)
Have you wondered how the refrigerator in your home works. Refrigerators which have become an integral part of every household works on some simple and scientific principles starting from a simple and basic model this video will elaborate on the workings of a modern refrigerator and its High Energy Efficiency.
Simply a cold liquid is continuously passed inside the refrigerator around the object to be cooled. Now let's see how this continuously moving cold liquid is achieved inside the refriger Ator. The most crucial component of the refrigerator is a device named throttling device. Here a capillary tube with a small diameter is taken as the throttling device and cold water is produced from the throttling phenomenon.
For Effective throttling the refrigerant should be in a liquid state at high pressure. The throttling device is a huge obstruction to the flow so a huge pressure drop occurs when liquid passes through the throttling device. Due to the drop in pressure the boiling point of the liquid drops and turns it into vapor. The energy required for the refrigerant liquid to evaporate comes from the refrigerant so its temperature drops.
Now we have converted the room temperature liquid at high pressure to cold and low pressurized Vapor but the thing to be noted is that only a small portion of the liquid is evaporated. Then the liquid is passed through the object to be cooled. During the heat absorption process the refrigerant further evaporates and all the remaining refrigerant turns into pure Vapor.
Since there is a change of phasee In the period the temperature of the liquid does not change. This heat exchange system is called evaporator. By the clever use of evaporator fans inside the refrigerator one can maintain different temperature levels inside the refrigerator so we have achieved the refrigeration effect inside of our refrigerator.
Now if we can convert the cold low press vapor into the state before that is high press liquid we will be able to repeat the same process again. Now at first we have to convert the low press vapor into High Press vapor and for that we use a compressor as you can see that a reciprocating type compressor is used here however the compressor is also compressing gas with pressure so the temperature inevitably Rises.
Now we've converted the refrigerant into High Press Vapor. To convert the vapor into a liquid state we introduce another heat exchanger which is fitted outside of the refrigerator thus it will liberate heat to the surroundings and its temperature will reach its normal level. This heat exchanger is known as a condenser.
Now the refrigerant is back in its normal state so it can be fed into the throttling device again. Just by repeating this process again and again we will be able to achieve a continuous cooling effect. This is the most basic refrigerator ever.
This refrigerator will work perfectly in theory but in practice we will experience different sorts of issues let's see what these issues are and how to overcome them. One major issue is the frost developed in the freezer compartment. The air in the compartment has moisture content which will turn into Frost when it comes in contact with the evaporator coil.
Such ice coating prevents further heat exchange and the refrigerator becomes inefficient over time. To overcome this issue heating rods are used to remove the frost produced and the condensate is collected in the refrigerator somewhere near the compressor.
Moreover in modern refrigerators you won't be able to see the condenser fins on the back of the refrigerator instead they use a compact condenser system that uses a cooling fan and the same heat rejection system is achieved here. Cold air cools the hot High Press vapor and returned to the throttling device.
In modern refrigerators you may not see the throttling device as presented here because the throttling device can also have a long wire shape instead of a curly spring shape. A filter dryer is used to remove any moisture content present in the refrigerant that might become trapped in the compressor operation.
We hope this video gave you a clear insight into the workings of a modern refrigerator thanks for watching the video.
Did you know that different refrigerator styles have different energy efficiencies? For decades, the only common design was the top-freezer model. But is that design the most efficient?
Contrary to popular belief, the answer is no. The most efficient configuration is typically a refrigerator with the freezer on the bottom. This is because of how air moves: warm air rises and cold air sinks. A bottom-freezer design takes advantage of this natural behavior to conserve energy.
Below is an image of the most common types of refrigerators available, along with their relative efficiencies.
Text description of the Refrigerator Types image.
Diagram of four refrigerator types shown in order from the least energy use to the most energy use, bottom freezer, four door, top freezer, and side by side.
6.4.1 Energy Efficiency of a Refrigerator
6.4.1 Energy Efficiency of a RefrigeratorMost of the energy used by a refrigerator is used to pump heat out of the cabinet. A small amount is used to keep the cabinet from sweating, to defrost the refrigerator, and to illuminate the interior.
The efficiency of a refrigerator is based on the energy consumed per year for a given size. The efficiency of a refrigerator is expressed in volume cooled per unit electric energy per day. Volume is measured in cubic feet and electrical energy is measured in kilowatt-hours.
The energy efficiency of refrigerators and freezers has improved dramatically over the past three decades. The most energy efficient refrigerator of 2025 was a Samsung RS24T5202. It has the capacity of most other models (27.4 ft3), but uses only 546 kWh/year.
You can explore more types of energy efficient appliances on the energy star website. Also, Energy Star as a calculator to determine how much energy you could save by upgrading your current fridge to one that is more efficient!
Energy Guide Labels
Refrigerators now come with an EnergyGuide label that tells you in kilowatt-hours (kWh) how much electricity a particular model uses in a year. The smaller the number, the less energy the refrigerator uses and the less it will cost you to operate.
- Full-sized refrigerators that exceed the federal standard by 15% or more (and full-sized freezers that exceed it by 10%) qualify for the ENERGY STAR label.
- Compact refrigerators and freezers must exceed the standard by 20% to qualify for ENERGY STAR.
How to keep your refrigerator running efficiently
- Keep your refrigerator or freezer at the following temperatures: 37–40°F for the fresh food compartment of the refrigerator, 0–5°F for the freezer section. Use a thermometer to check inside temperatures.
- Regularly defrost manual-defrost refrigerators and freezers; don't allow frost to build up more than 1/4 inch.
- Make sure your refrigerator and freezer door seals are airtight. Check the seal on door gaskets periodically by closing the door on a dollar bill. If it pulls out easily, you may need a new gasket.
- Keep the doors closed as much as possible and make sure they are closed tightly.
- To ensure proper cooling of its contents, don't crowd food items. Too many dishes obstruct air circulation.
- Cover liquids and wrap foods stored in the refrigerator. Uncovered foods release moisture and make the compressor work harder.
- Replace paper wrappings on food items with aluminum foil or plastic wrap. Paper is an insulator.
- Placement of the refrigerator is very important. Direct sunlight and close contact with hot appliances will make the compressor work harder. More importantly, heat from the compressor and condensing coil must be able to escape freely, or it will cause the same problem. Don't suffocate the refrigerator by enclosing it tightly in cabinets or against the wall.
- Regularly brush off or vacuum the refrigerator coils on the back or bottom of the unit.
- Because most refrigerators reject heat from the bottom and/or back, they need adequate clearance to allow sufficient airflow. While no specific studies have been done to calculate the optimum clearance space, one general rule-of-thumb is to double the space recommended by manufacturers for refrigerator installation. Another rule-of-thumb is to allow 2 inches of air flow around the refrigerator.
- Don't keep that old, inefficient fridge running day and night in the garage for those few occasions when you need extra refreshments. A 15-year-old refrigerator could cost $100–$150 per year.