heat driven ammonia absorption refrigeration plants
At the end of the 19th century most refrigeration equipment was based on the absorption principle. This technology did not need electrical energy, its main driving energy heat source came from a steam boiler or a burner.
Later in the 1950s, due to low energy prices the hermetic compressors came on the market and the absorption technology was moved into the background. It remained used only in a few niche areas where its high reliability and ability to cool down to extremely low temperature was an advantage.
At the end of the last century, after the first energy crisis, absorption technology has again attracted attention, as it can be powered by residual heat, thus reducing primary energy consumption.
Nowadays thermodynamic processes of absorption combined with modern control techniques result in high-efficient plants. They are the most environmental friendly and energy-saving form of refrigeration through the use of the natural refrigerant ammonia and the drive with residual heat.
Refrigeration means to extract heat. A refrigeration system extracts heat at low temperatures and rejects it to the higher ambient temperature.
This is done by the help of a working fluid called the refrigerant. This fluid evaporates at a low pressure and temperature and extracts the heat from the medium that have to be cooled. Later on, the vaporized refrigerant has to be liquified again, this is done by increasing the pressure high enough to be able to condensate at ambient temperature.
The increase of pressure is done by a compressor which needs mechanical energy to be driven. This driving energy is normally electricity but it could also be mechanical energy from an engine or a turbine.
On an absorption refrigeration plant the mechanical compressor is substituted by a liquid solution circuit.
An additional fluid is needed to absorb the refrigerant gas coming from the evaporator. Using ammonia as refrigerant the best absorbent is water. This water will be enriched with ammonia and is pumped to the desorber or boiler, where a heat source is used to separate ammonia and water by evaporation. As in conventional refrigeration systems the high pressure refrigerant gas is liquified and sent to the evaporator.
In this way thermal energy can be used to create refrigeration.
Using ammonia absorption refrigeration systems presents many advantages:
