Absorption chillers and heat pumps- Ammonia-water systems.Theory

The binary ammonia-water mixture (NH ₃ -H ₂ O) is intended for liquid absorption machines, which are trithermal heat converters [BE 9 734] whose main applications are, on the one hand, industrial refrigeration, using superheated steam, hot water or exhaust gases and, on the other hand, domestic heat pumps using natural gas (or LPG) as an energy source.

This binary mixture differs from the H ₂ O-LiBr water-lithium bromide mixture [BE 9 735] not least in the pressure level and the fact that the vapor is a mixture, which has important consequences for the design of absorption machines and the technology used. As in the case of H ₂ O-LiBr, the refrigerant has no impact on the greenhouse effect or the ozone layer.

Compared with H ₂ O-LiBr systems, NH ₃ -H ₂ O single-stage machines enable access to evaporation temperatures well below 0°C, making them very attractive, whether for industrial refrigeration or heat pump operation applied to home heating. On the other hand, they offer lower coefficients of performance (COP).

The GAX (Generator, Absorber, heat eXchanger) cycle takes advantage of the solution's wide temperature range to recover heat from the absorber, using part of the latent heat of absorption to increase the COP. This cycle works well when the thermal amplitude between desorption and absorption is large, and that between condensation and evaporation is not very high.

Applications of these different cycles in liquid absorption machines are presented in the article [BE 9 738] dedicated to their technology.

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