The two main heat pumptypes ------------
Discuss with Professional heat pump manufacturer:China PalmAlmost all heat pumps currently in operation are either based on a vapour compression, or on an absorption cycle. These two principles will be briefly discussed in the following two sections. Theoretically, heat pumping can be achieved by many more thermodynamic cycles and processes. These include Stirling and Vuilleumier cycles, single-phase cycles (e.g. with air, CO2 or noble gases), solid-vapour sorption systems, hybrid systems (notably combining the vapour compression and absorption cycle) and electromagnetic and acoustic processes. Some of these are entering the market or have reached technical maturity, and could become significant in the future.[table=98%][tr][td=1,3,92%]
Vapour compressionThe great majority of heat pumps work on the principle of the vapour compression cycle. The main components in such a heat pump system are the compressor, the expansion valve and two heat exchangers referred to as evaporator and condenser. The components are connected to form a closed circuit, as shown in Figure 1. A volatile liquid, known as the working fluid or refrigerant, circulates through the four components.In the evaporator the temperature of the liquid working fluid is kept lower than the temperature of the heat source, causing heat to flow from the heat source to the liquid, and the working fluid evaporates. Vapour from the evaporator is compressed to a higher pressure and temperature. The hot vapour then enters the condenser, where it condenses and gives off useful heat. Finally, the high-pressure working fluid is expanded to the evaporator pressure and temperature in the expansion valve. The working fluid is returned to its original state and once again enters the evaporator. The compressor is usually driven by an electric motor and sometimes by a combustion engine.
- An electric motor drives the compressor (see Figure 1) with very low energy losses. The overall energy efficiency of the heat pump strongly depends on the efficiency by which the electricity is generated. This is discussed in the section on Heat pump performance. [size=10pt]洓沎/size][/size]
[*]When the compressor is driven by a gas or diesel engine (see Figure 2), heat from the cooling water and exhaust gas is used in addition to the condenser heat.
[*]Industrial vapour compression type heat pumps often use the process fluid itself as working fluid in an open cycle. These heat pumps are generally referred to as mechanical vapour recompressors, or MVRs; refer to the section on Heat pumps in industry. [size=10pt]洓沎/size][/size]
[/td][td=1,1,50%][align=right]Figure 1: Closed cycle, electric-motor-driven vapour compression heat pump[/align]

[/td][/tr][tr][td=1,1,50%][align=right]Figure 2: Closed cycle, engine-driven vapour compression heat pump.[/align]

[/td][/tr][tr][td=1,1,50%][align=right]Figure 3: Absorption heat pump[/align]

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AbsorptionAbsorption heat pumps are thermally driven, which means that heat rather than mechanical energy is supplied to drive the cycle. Absorption heat pumps for space conditioning are often gas-fired, while industrial installations are usually driven by high-pressure steam or waste heat.Absorption systems utilise the ability of liquids or salts to absorb the vapour of the working fluid. The most common working pairs for absorption systems are:
- water (working fluid) and lithium bromide (absorbent); and
- ammonia (working fluid) and water (absorbent).
For heat transformers, which through the same absorption processes can upgrade waste heat without requiring an external heat source, refer to the section on Heat pumps in industry.