Category: Education

Heat Pump And Hess Law Of Constant Heat Summation

Heat Pump

Heat Pump

The heat pump is a reverse heat engine. In simple words, the heat pump is used to provide heat energy to the thermal reservoir. The heat pump is based on Carnot’s cycle. The heat pump is used to absorb heat from the cold space and give it to the warmer one. The heat pump transfers heat from the cold body to the hot body using an external agent to supply the mechanical energy. The external work done on the heat pump also gets converted into heat energy. The heat transferred to the hot reservoir by the heat engine is given by

Qh = Qc +W

Qh is the heat transferred

Qc is the heat absorbed from the cold reservoir

W is the external work done

The heat pumps are of two types: air to air heat pump and geothermal heat pump. Air to air heat pump uses the outdoor air whereas geothermal heat pump uses underground (water or earth) temperature as the source of heating or cooling.

For home heating, a heat engine absorbs the heat from the outside air, heats it more and transfers it inside the house. In a refrigerator, a heat pump is used to remove the heat out of the fridge.

Application of heat pump

  • Heat engine is used to heat up the enclosed space like the rooms of the house, workplace etc.
  • Water can be heated using a heat pump.
  • The process fluid is heated by heat pumps in industries

Coefficient of Performance of Heat Pump

The coefficient of performance of the heat pump is given by the ratio of the energy given for the heating to the input electric energy that is being used in the process.

Coefficient of performance = Qh/W =  Qh/Qh– Qc

Advantages of heat pump

The heat pump is cheaper. It is easier to run when compared to a boiler. The heat pumps are smaller in size and fuel storage is not required. They are very safe to use since it does not release any harmful gas. Heat pumps require less maintenance and last longer when compared to combustion-based systems.

Working of a heat pump

The heat pump works by transferring heat by circulating a substance called the refrigerant through the evaporation and condensation process. Two exchanger coils are provided. In one coil the refrigerant gets evaporated at a lower pressure and it absorbs heat from the surroundings. The refrigerant is then compressed and sent to the other coil. In the second coil, the refrigerant is condensed at high pressure. Now the refrigerant releases the heat it absorbed earlier.

Refrigerators and air conditioners are examples of heat pumps operating in cooling mode. The cycle of the heat pump is reversible. It can be used for heating in winter and cooling in summer.

Do check BYJU’S pages on more thermodynamics related topics like Hess law of constant heat summation. According to Hess law, the heat energy changes accompanying a chemical reaction remain at a constant temperature.