Vapour Compression Cycle Definition, Working Principle, Optimal Efficiency COP & 6 Comparison with VARS system [PDF]

In this article, we shall have a brief overview of the Vapour compression cycle. We have also provided a PDF for the same.

A Vapour compression cycle generally known as VCC is a refrigeration cycle. In this cycle, the refrigerant is sealed condition in an airtight mechanism and is compressed in a compressor which permits the transfer of heat energy. The refrigerant absorbs heat from one place and releases it to another place. The system repeats over and over again and absorbs heat at low pressure from the refrigerant space.

Main Components of Vapour Compression Cycle

The main parts of the Vapour Compression Cycle are as follows

  • Evaporator
  • Suction line
  • Compressor
  • Discharge Line
  • Condenser
  • Receiver Tank
  • Liquid line
  • Expansion Valve
Main Components of Vapour Compression Cycle
Actual vapour Compression cycle
Actual vapour Compression Refrigeration


Evaporator provides the heat transfer surface through which heat can pass from the refrigerant space into the refrigerant.

Suction line

The Suction Line carries the low-pressure vapor refrigerant from the evaporator to the inlet of the compressor.


The function of the compressor is to compress the vapor refrigerant to temperature and pressure to such a point so that it may be easily condensed.

Discharge Line

The Discharge line coveys the high-pressure and high-temperature refrigerant from the compressor to the condenser.


The Condenser provides a heat transfer surface and cools down the refrigerant by water spray or blow of air.

Receiver tank

The Receiver tank stores the liquid refrigerant coming from the condenser and supplies it to the evaporator as per requirements.

Liquid line

Liquid Line carries the liquid refrigerant from the receiver to the expansion valve.

Expansion valve

It supplies the proper quantity of liquid refrigerant to the evaporator after reducing the pressure.

Working principle of Vapour Compression Cycle

  • During the suction stroke of the compressor, wet Vapour refrigerant is drawn from the evaporator and compressed adiabatically to high pressure and high temperature
  • The high-pressure Vapour refrigeration is then cooled in the condenser at constant pressure
  • The high-pressure liquid refrigerant is there expanded through a throttle valve or expansion valve and lower its pressure and temperature.
  • The low-temperature vapor refrigerant absorbs heat from the evaporator at constant pressure and cools the space.
  • The vapor refrigerant enters the compressor during the suction stroke and the cycle is repeated.

In this cycle, a large amount of work is required to compress the vapor refrigerant for increasing its pressure.

COP of Vapour Refrigerant Cycle


  • h1 = Specific enthalpy of refrigerant before compression.
  • h2 = Specific enthalpy of refrigerant after compression.
  • h3 = Specific enthalpy of refrigerant after cooling.
  • h4 = Specific enthalpy of refrigerant after expansion.

Therefore, COP is equal to (Refrigerating effect/Work-done) represented as follows

{(h1-h4)/(h2-h1)} = {(h1-h3)/(h2-h1)}

[As h3 = h4]


Actual Vapour Compression Cycle

The actual Vapour compression cycle differs from the standard cycle due to the following reasons

  • Liquid refrigerant in the condenser is subcooled to ensure 100% liquid enters the expansion valve.
  • The vapor usually leaves the evaporator and is superheated to prevent droplets of liquid within the compressor.
  • Isentropic expansion does not occur due to friction and other losses.
  • Pressure drop takes place in the evaporator and condenser due to
  • Friction.

Description Of Vapour Compression Cycle

  • Process a-b-c represents the flow of refrigerant in the evaporator at suction pressure and temperature T2.
  • Process c-d represents a drop in pressure due to suction valve resistance to the compressor.
  • Process d-e represents the addition of heat to the refrigerant from the cylinder wall.
  • Process e-f represents the actual compression of refrigerant in the compressor.
  • Process f-g represents the cooling of the refrigerant at the compressor exit line as heating d-c.
  • Process g-h represents pressure drop due to resistance of the discharge valve.
  • Process h-ij-k represents desuperheating of vapor to a dry state and removal of latent heat and sub-cooling of refrigerant.
  • Process k-a represents the throttling of sub-cooled refrigerant from condenser pressure to evaporator pressure.

Comparison of Vapour Compression and Vapour Absorption System

Vapour Compression SystemVapour Abortion System
The system has more weak, tear, and noise due to moving parts in the compressor.The system is quiet in operation due to less number of moving parts.
Mechanical energy is supplied.Heat energy is supplied.
The supply of energy is low. 1/2 to 1/3 of refrigerating effect.The supply of energy is high. 1.5 of refrigerating effect.
Poor performance of partial loads.Performance is not affected by load variations.
Charging of refrigerant is simple.Charging of refrigerant is difficult.
Chances of leakage of refrigerant.No leakage of refrigerant due to the absence of a compressor.

working of Vapour Compression Cycle

Video By Vector Solutions Industrial


what is the definition of actual vapour compression cycle or actual VCR cycle

The actual vapor compression cycle, or actual VCR cycle, is a process used in refrigeration and air conditioning. It involves compressing a refrigerant, condensing it, expanding it, and then evaporating it to transfer heat from a lower-temperature environment to a higher-temperature one. It enables efficient cooling and refrigeration by utilizing the properties of the refrigerant to change phase between liquid and vapor at different temperatures and pressures.

What is the COP of VCR Cycle

The COP (Coefficient of Performance) of a VCR (Vapor Compression Refrigeration) cycle measures its efficiency by determining the amount of cooling or refrigeration achieved per unit of work input. A higher COP signifies a more efficient system that delivers greater cooling or refrigeration while using less energy.

Applications of VCR Cycle

Applications of VCR (Vapor Compression Refrigeration) Cycle:

  • Domestic and commercial refrigeration
  • Air conditioning
  • Industrial cooling
  • Food processing
  • Medical and pharmaceutical storage
  • Cold chain logistics
  • Automotive air conditioning
  • Refrigerated transport
  • Process cooling in industrial applications.


In conclusion, The vapor compression cycle is a widely used process in refrigeration and air conditioning. It involves compressing a refrigerant vapor, turning it into a high-pressure liquid, and then expanding it to a low-pressure vapor, which absorbs heat from the surroundings. The efficiency of this cycle is measured by the coefficient of performance (COP), which considers the system’s design and conditions. While vapor absorption systems have advantages in specific applications, the vapor compression cycle is preferred for its efficiency, cost-effectiveness, and versatility. Ongoing advancements in its design and efficiency contribute to more energy-efficient and eco-friendly cooling systems.


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