Refrigeration cycle: Definition, Diagram

What is a Refrigeration cycle?

The refrigeration cycle is a process that removes heat from a space or substance to lower its temperature. It consists of four main stages: compression, condensation, expansion, and evaporation, where a refrigerant circulates through components like the compressor, condenser, expansion valve, and evaporator.

This cycle is used in air conditioning, refrigeration, and heat pump systems.

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Refrigeration cycle in HVAC:

The refrigeration cycle in HVAC systems follows four key stages: compression, condensation, expansion, and evaporation.

Here’s how each stage works:

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Stages of Refrigeration cycle:

Stage	Component	Function	State of Refrigerant
Compression	Compressor	Increases pressure and temperature of refrigerant gas.	High-pressure gas
Condensation	Condenser	Releases heat, turning refrigerant gas into liquid.	High-pressure liquid
Expansion	Expansion Valve	Reduces pressure and temperature of refrigerant.	Low-pressure liquid
Evaporation	Evaporator	Absorbs heat, turning refrigerant liquid into gas.	Low-pressure gas

Lets discuss in brief:

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1. Compression (High-Pressure, High-Temperature Gas):

• The refrigerant enters the compressor as a low-pressure gas.
• The compressor (typically a scroll, rotary, or reciprocating type) increases the pressure of the refrigerant, raising its temperature and energy level.
• The high-pressure, high-temperature superheated gas leaves the compressor and moves to the condenser.

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2. Condensation (High-Pressure Liquid)

• The condenser (usually an air-cooled or water-cooled coil) removes heat from the refrigerant.
• As the refrigerant loses heat to the surrounding air or water, it condenses into a high-pressure liquid.
• This phase change releases the heat absorbed during the evaporation phase.
• The refrigerant exits the condenser as a high-pressure, medium-temperature liquid.

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3. Expansion (Low-Pressure, Low-Temperature Liquid)

• The expansion valve (or capillary tube, thermal expansion valve, or electronic expansion valve) controls the flow of refrigerant into the evaporator.
• It rapidly reduces the refrigerant’s pressure, causing a drop in temperature.
• The refrigerant becomes a low-pressure, cold liquid mixed with some vapor as it moves into the evaporator.

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4. Evaporation (Heat Absorption, Cooling Effect)

• In the evaporator, warm indoor air blows over the cold refrigerant coils.
• The refrigerant absorbs heat from the air, causing it to boil and turn into a low-pressure vapor.
• This phase change removes heat from the air, cooling the indoor space.
• The refrigerant, now a low-pressure gas, returns to the compressor to repeat the cycle.

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Key Takeaways:

• Compressor: Increases pressure and temperature of refrigerant.
• Condenser: Releases heat, converting gas to liquid.
• Expansion Valve: Drops pressure and temperature of refrigerant.
• Evaporator: Absorbs heat, cooling the air.

This continuous loop enables HVAC systems to regulate indoor temperatures efficiently.

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Other Courses:

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Video Demonstration: Refrigeration cycle explained in youtube.