Heat Pump : Introduction, Working, Types, and their Applications.

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Heat Pump

A heat pump is a device that takes heat from one source and moves it to another location through electrical or mechanical means. In other word- A device that transfers heat from a colder area to a hotter area by using mechanical energy, as in a refrigerator.

Heat pumps moves thermal energy in the opposite direction of spontaneous heat transfer, by observing the heat from a clod space and releasing it to a warmer one. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink.
A Condenser, an Expansion valve ,an Evaporator and a compressor are the main part of the heat pump. The heat transfer medium circulated through these components is called refrigerant.

  • Lord Kelvin describes the theory of underlying heat pump in 1852.
  • The First heat pump was developed by the Peter von Rittinger in 1855-1857.

Working of Heat Pump 

Heat pump transfer heat by circulating a substance called a refrigerant through a cycle of evaporator and condensation. A compressor pump the refrigerant between two heat exchanger coils. The refrigerant is evaporated at low pressure in a coil and absorbs heat from its surrounding. the refrigerant is then compressed en route of the other coil, where it condenses at high pressure. At this point it releases the heat it absorbed earlier in the cycle.

Refrigerator and air conditioners are both example of the heat pump operating in the cooling mode.  A refrigerator is essentially an insulated box with a heat pump system connected to it. the evaporator coil is located in side the box , usually in the freezer compartment. usually behind or underneath the unit where the condenser coil is located. Similarly an air conditioner transfer heat from inside a house to the out doors.

Coefficient of Performance and Efficiency of Heat Pump

A refrigerator takes out heat from a lower temperature T2, and released it to a higher temperature T1..
for this process to take place , work has to be done on the system.


In the case , we defined the Coefficient of performance as :
             COP =  Q2/W
where,
  • Q2 is the heat taken from the system
  • W is work done on the refrigerator.
similar to heat engine after a cycle the refrigerator returns its original state hence dell U = 0.
so,                   
                      W= Q1-Q2
therefore,
                   COP = Q2/(Q1-Q2)
A refrigerator will not be able to function without external work so it coefficient of performance can never be infinite.
For Heat Engine Efficiency:
efficiency = WQ1.
where,
W = work done by the engine.
Q1=heat taken from the source.
after each cycle the engine returned to its initial state so, total internal energy, dell U=0.
so,           
                W=Q1-Q2
hence the heat engine efficiency is :
               Efficiency = (Q1-Q2)/Q1.
or,            Efficiency = 1-(Q2/Q1).
so for Q2=0, efficiency will be 100% but in actual this is not possible because there will be some loss of energy in the system. hence for every engine there is a limit for the efficiency. The efficiency is maximum a reversible engine such as Carnot heat engine.

Types of Heat Pump

There are three main types of heat pump.
1. Air Source type Heat Pump :
In expansive to install and commonly used air source heat pumps function well in moderate climates , using outside air as a medium for heat exchange.
2. Water Source type Heat Pump:
Water source heat pump dissipate heat by way of water instead of air . The require well ,lake or other water source. 
3. Ground Source type Heat Pump : 
This type of heat pump is also known as geothermal heat pumps. It take advantage of thermal energy stored underground , transferring heat in a similar manner to air source to heat pump. Due to the constant pressure of the ground , the offer much more efficient operation , however installation is pricier and more complicated due to the need for excavation and installation of underground.

There are also the some sub type of Heat pump are as follows-

1. Hybrid Heat Pump:
The hybrid heat pump are the combo type of heat pump use for very warm. the are also two type-
  • Ground and air  source heat pump combos:In this, with air source system leading the way when air is warm outside, but switching to ground source when temperature drop..
  • Heat pump and gas / oil boiler combo:where simultaneous operation can offer more consistent warmth at a higher level of efficiency. it is commonly used in homes with existing boiler system.
2. Solar Heat Pump:
Used in conjunction with air and geothermal heat pump. Solar heat pump integrates solar panels as power supply for the system ,with a solar geothermal setup. It is therefore possible to heat or cool your entire home by renewable energy.

3. Absorption or Gas  fired Heat Pump:
 Driven by another heat source other then electricity (solar/geothermal/gas) , these system are more typical to industrial applications.

Applications of Heat Pump 

Heat pump are used in water heating applications, It is used in such as for the generating domestic hot water for- Mines, Hospitals, Prisons, Schools , Hotels, Hostels. It used to heat or preheat water for swimming pools or heating potable water for use by homes and industry.
usually heat is extracted from out door air and transferred to an indoor water tanks , another variety heat from indoor air to assists in cooling the space.












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