Compression and absorption heat pumps are the two main types of heat pumps, and they differ in internal architectures and working principles. Compression heat pumps are reliant on mechanical energy driven by electricity to power a compression within the heat pump. On the other hand, absorption heat pumps run heat as an energy source. This heat can be produced from electricity, fuel-burning sources as well as naturally occurring heat sources. Regardless of the type, a heat pump is often more efficient in terms of energy than a gas furnace. However, it produces less heat and is appropriate for low-heating applications.
There are finer divisions in the heat-pump family which branch into the following:
· Air-to-Water: Electricity is used to drive a refrigeration compressor.
· Air Source Heat Pumps: These heat pumps get energy from the surrounding air, and are drawn across the heat exchanger within the unit. In this case, the temperature is highly dependent on the ambient temperature, and the weather itself.
· Ground Source Heat Pumps: Here the working principle is like that of a geothermal power station, in the sense that the heat pump itself draws energy from groundwater, which maintains a constant temperature throughout the year. This heat is augmented with fuel-burning sources to improve the fuel economy of the heat pump.
· Water Loop Heat Pumps: Waterflow from rivers is used as the heat source/sink for this type of heat pumps.
See the summary of this part in this infographic – 4 Basic Types of Heat Pumps [Infographic]
About Absorption Heat Pumps
Absorption heat pumps rely on a thermodynamically sealed circuit which contains a special ammonia-water solution acting as the medium for heat transfer. In this solution, the ammonia acts as the primary refrigerant and the water allows heat to be absorbed. This is a stark contrast to the traditional refrigerants used by air-to-water electric heat pumps or air conditioners wherein fluorinated refrigerants (most commonly the R410A refrigerant) is used. Although they are known to have a less damaging impact on the environment, there is still a significant amount of global warming potential associated with these refrigerants. Therefore, their use is not completely harmless. On the other hand, ammonia is naturally forming a chemical with virtually no impact on the ozone layer. Moreover, the combined water and ammonia solution features zero ODP and zero GWP, with virtually no environmental impact.
There are some drawbacks to using ammonia for residential purposes, however. With ammonia refrigerant being toxic and flammable, heat pump installations in a commercial context are often installed outdoors, and come with sealed ammonia circuits. Therefore, contact with the dangerous fluid is minimized during service and maintenance runs. Moreover, with the use of a sealed system to contain the ammonia refrigerant, it is less likely t hat the flammable ammonia will escape into the surrounding atmosphere and pose a threat to people. Despite these benefits, it is often not possible in a residential setting wherein the main heat pump unit is located somewhere within the home or near people.
The Working Principle of an Absorption Heat Pump
The function of an absorption heat pump is dependent on a well-orchestrated heat exchange mechanism based around heat exchangers, condensers, evaporators and an ammonia-water solution.
The ammonia refrigerant of the heat pump is initially expanded before being pumped into the evaporator at low pressure and temperature. Much like an air-source heat pump, heat is drawn from the surrounding air to evaporate the ammonia.
To introduce more heat into the system, a gas burner is lighted (as is the case in most gas-absorption heat pumps), and the ammonia refrigerant is heated further. Once the ammonia from the refrigerant solution has evaporated, it is guided into the condenser chambers, and exchanges heat with the water from the main heating system. Due to the heat absorption by the water, the ammonia evaporates condenses again and is returned to the evaporator chamber. Here, the cycle restarts as the ammonia heats up and evaporates once again.
The water in the solution acts as the absorber for the ammonia once it has been condensed again. This reabsorption generates more heat and is recirculated by the heat pump. It’s important to note that, this absorbent water is completely different from the exchanger’s water supply and serve different purposes within the absorption heat pump.
Gas-absorption heat pumps function as high-efficiency solutions to low-requirement heating and can be used with traditional boilers for reduced emissions and economical ratings. Their functionality is simple and provides a lower cost, and smaller carbon footprint solution to heating through heat pumps.
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