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Difference Between Heat Engine and Heat Pump

Last updated date: 09th Apr 2024
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An Introduction to Heat Engine and Heat Pump

Heat engines and heat pumps are intriguing machines with numerous uses in a variety of industries and aspects of daily life. Although they have diverse goals, these devices use the laws of thermodynamics to transmit and manipulate heat energy. Consider the air conditioner in your home, which effectively cools down the indoor environment by extracting heat and transferring it outside. This instance exemplifies a heat pump in action, showcasing its ability to regulate temperatures. By exploring the difference between heat engine and heat pump, we can gain insight into their respective functions and applications in our daily lives.

Heat Engine:

Heat engines use thermal energy to produce mechanical work. They frequently follow a cycle of operations that include absorbing heat from a high-temperature source, converting that heat into work, and then dissipating extra heat into a low-temperature sink. The internal combustion engine used in cars is a real-world example of a heat engine since it burns gasoline to provide the thermal energy required to do mechanical labour.

The work done will be,

Where Q₁ is heat removed and Q₂ is the heat supplied.

Coefficient of performance $=\frac{{{Q}_{2}}-{{Q}_{1}}}{{{Q}_{2}}}$

Heat Engine

Image: Heat Engine

Heat Pump:

The equipment that is used to absorb heat from low temperatures and supply it to high temperatures is called a heat pump. The heat pump operates by providing temperatures that range from ambient to high, or from low to high, increasing the rate of heat transfer. The Coefficient of performance of the heat pump is always greater than that of the refrigerator. The rate of heat transport affects this. Heat absorbed and work done by the pump replace heat rejected.

It uses heat energy from a source with a lower temperature to change mechanical energy into heat energy from a source with a higher temperature. In contrast to natural convection, heat pumps transport heat energy in the opposite direction. The Clausius assertion is the foundation of the heat pump. In the winter, homes are heated with it. Water heating and commercial heating are both accomplished by heat pumps.

Heat Pump

Image: Heat Pump

Difference Between Heat Engine and Heat Pump:

Understanding the difference between heat engine and heat pump is essential to understanding how each plays a unique part in energy conversion and transfer. Heat pumps excel at transporting heat from a low-temperature source to a higher-temperature sink for heating or cooling purposes. Heat engines concentrate on transforming thermal energy into mechanical effort.

The table describes the difference between heat engine and heat pump:



Heat Engine

Heat Pump


Convert thermal energy into mechanical work.

Transfer heat from a low-temperature source to a high-temperature sink.

Energy Transfer

Focus on converting heat into useful work.

Focus on moving heat from one location to another.


The efficiency measures work output compared to heat input.

Efficiency is evaluated by comparing the output to energy input using the coefficient of performance (COP).

Kelvin-Planck Statement

The Kelvin-Planck statement, which states that it is impossible to design a heat engine that exclusively generates work without any heat transfer, governs heat engines. To transform some of the thermal energy into productive work, some heat must constantly be released to a lower-temperature sink.

Heat pumps are not governed by the Kelvin-Planck statement.


Gas turbines, internal combustion engines.

Heating and cooling systems, refrigerators, and air conditioners.

Heat Engine And Heat Pump Examples:

The examples of heat engines are as follows:

  • Vehicles Engines: In these types of engines of vehicles, chemical energy from fuels like petrol or diesel is converted into heat through combustion. The resulting heat is transformed into mechanical work, propelling the vehicle.

  • Steam Turbines: In power plants, high-pressure steam is produced by heating water using fuels like coal, natural gas, or nuclear energy. This steam is used in steam turbines. The steam's thermal energy powers the turbine, which rotates mechanically to produce electricity.

The examples of heat pumps are as follows:

  • Appliances like refrigerators and freezers transmit heat from within to outside in order to keep food cool.

  • Our comfort is ensured by heat pumps, which are used in HVAC (heating, ventilation, and air conditioning) systems, which transport heat to offer both heating and cooling.


The two unique technologies of heat engines and heat pumps have various uses and ways of operation. Heat engines, which transform thermal energy into mechanical work, are frequently employed in power and transportation engines. They adhere to the Kelvin-Planck hypothesis, which calls for heat to be transferred to a sink with a lower temperature. While heat pumps, on the other hand, are made to move heat from a low-temperature source to a high-temperature sink. They are used in a variety of systems, including cooling, heating, and refrigeration. Heat pumps are primarily concerned with the transport of heat, whereas heat engines concentrate on transforming heat energy into usable work. Heat pumps are evaluated using the coefficient of performance (COP) to identify their output in relation to energy input, whereas the efficiency of heat engines is determined by their work output in relation to heat input.

In many areas, including thermodynamics, engineering, and energy systems, it is essential to comprehend the difference between heat engines and heat pumps. It makes it possible for us to understand their special uses and applications, which eventually helps power production, transportation, and sustainable energy practises improve.

FAQs on Difference Between Heat Engine and Heat Pump

1. Can a heat engine also function as a heat pump?

Yes, in theory. When used in reverse, certain reversible heat engines act as heat pumps by transporting heat from a cold reservoir to a hot reservoir. However, actual implementations could call for other plans and factors.

2. Are there any unusual examples of heat engines and heat pumps?

Yes, there are some uncommon instances, such as thermoelectric heat pumps that employ the Seebeck effect to create a temperature differential and thermoacoustic heat engines that transform heat into sound waves.

3. How does the idea of entropy apply to heat engines and heat pumps?

The rules of thermodynamics, which include the idea of entropy, apply to both heat engines and heat pumps. Entropy measures a system's disorder or unpredictability, and changes in it are correlated with the movement of heat and work.