Environmental Impact

Heat pumps require a refrigerant to work correctly. The most commonly used refrigerant used in heat pumps was chlorofluorocarbons (CFCs). This changed in August 1987 with the Montreal Protocol which banned or restricted the manufacture of CFCs. In the 1990s, hydrofluorocarbons (HFCs) were developed to replace CFCs as they have minimal ozone depletion potential. However, they still pose a serious risk to the environment as they have strong greenhouse gas effects as stated in the Kyoto Protocol.

Heat pumps have another impact in that they produce noise since the require moving parts to work. In air source heat pumps an external unit containing moving mechanical parts (usually fans) produces noise. There are no established standards for noise barriers or noise protection. However, the United States only allows heat pumps to produce 55 decibels of noise during the day (about the noise level of background conversation in a restaurant) and 45 decibels at night (about the noise level of calls). This is to protect us from any adverse health effects and to protect the welfare of residential areas.



Heat Pump: https://en.wikipedia.org/wiki/Heat_pump

Freon: https://en.wikipedia.org/wiki/Freon

Kyoto Protocol: https://en.wikipedia.org/wiki/Kyoto_Protocol

Montreal Protocol: https://en.wikipedia.org/wiki/Montreal_Protocol

Useful Sources

i found two websites with very useful information on heat pumps and how they work

this is from a company that makes industrial heat pump


this was written by a physics professor at University of California


Engineering Details

Heat Pumps

Heat pumps are simply devices designed to use work to move heat in the opposite direction it typically would flow and thus do not create heat. There are several types of heat pumps and while each of these heat pumps achieves the same end result, they operate on different engineering principles.

Mechanical heat pump

The pressure of a refrigerant is increased via a compressor which thereby raises the boiling temperature. Two types of mechanical heat pumps exist. They either operate on the principle of direct expansion or operate by using a vessel to separate gaseous and fluid refrigerant known as the pump system. Mechanical heat pumps are the most common type of heat pump and are usually the most feasible to install.

Direct Expansion System

direct expansion system


Pump System

pump system


Gas Engine heat pump

This heat pump operates on the same principles as a mechanical heat pump, however, rather than using an electrical pump to drive the compressor, a gas powered engine is used to drive the compressor.

Absorption heat pump

These heat pumps work by using thermal energy to evaporate refrigerant which is then absorbed into a medium. Examples of absorption heat pumps include Lithium-Bromide and Water and Ammonia. This type of heat pump is useful when both heating and cooling are necessary.

absorption heat pump


Adsorption heat pump

This type of heat pump is based around the same principles as the absorption heat pump, but uses a solid medium for absorption rather than a fluid. Some examples of this would be Silica gel and water, zeolite and water, and active carbon/salt and ammonia.

Trans-critical CO2 heat pump

When above 31 degrees Celsius, Carbon Dioxide liquid and gas are indistinguishable. This is called a trans-critical range. This phenomenon allows heat to be released at a range of temperatures.



The blue line shows the transcritical cycle. The steps are as follows:

1 – 2 Compression to transcritical pressure
2 – 3 Gas cooling in transcritical area
3 – 4 Expansion
4 – 5 Evaporation
5 – 1 Superheating

Hybrid Heat pump

These pumps are a combination of the mechanical and absorption heat pumps. They use a mixture such as Ammonia and Water. Changes in the composition of this mixture allow heat to be emitted at a range of temperatures. This can lead to higher efficiency.




Thermoacoustic heat pump

This type of heat pump is not yet commercially available. It works on the principle that sound waves and temperature are related and one can generate the other.








Clausius Statement and Kelvin Statement

Heat pumps can be explained by the Clausius and Kelvin Statements.  This being “Heat can not be transferred from cold to hot by itself” and “Heat can not be converted 100 % to work” respectively.  Heat pumps work by adding energy to a system to move heat from areas of colder concentrations to warmer areas as seen in the graphic below .

Heat Pump

The efficiency of a heat pump can be calculated with the equation

Efficiency Equation

Heat pumps always have an efficiency greater than 1.


Brief History of the Heat Pump

As one can see in the advancements of recent technology, the heat pump we know today has only existed for a few decades.  But as seen below, the theory for a heat pump has been around since the mid-1700’s and the first heat pump came to be in the early 1850’s. This technology however, was not applied successfully until 1945 by John Sumner.

• 1748 – William Cullen demonstrates artificial refrigeration
• 1834 – Jacob Perkins builds a practical refrigerator with diethyl ether
• 1852 – Lord Kelvin describes the theory underlying heat pump
• 1855-1857 – Peter von Rittinger develops and builds the first heat pump.
• 1945 – John Sumner installs an experimental water source heat pump that fed a central heating system to heat council buildings
• 1948 – Robert C. Webber is credited as developing and building the first ground heat pump
• 1951 – First large scale installation, reversible gas powered water source heat pump

*retrieved from google 12/7/2017