Heat pumps and absorption chillers enable a low-temperature source of energy to be converted into a high-temperature source.
Absorption chillers use heat as a form of energy to drive the cooling process. Unlike compression systems, which require a mechanical compressor, they use an absorption circuit to generate the difference in pressures that enables the refrigerant to provide cooling. The fluid used is a mixture of water (refrigerant) and lithium bromide (solvent).
The absorption process involves three separate flows, each of a different temperature:
- a high-temperature source to provide the energy for driving the cooling process
- a low-temperature source, to produce the cooling effect
- an intermediate temperature loop which removes the ambient heat (slightly above ambient temperature)
An absorption heat pump operates in a similar way to a chiller. The difference between the two machines is in the temperature levels of the “cold” and “intermediate” loops. With a heat pump, the cold loop recovers energy at a temperature of around 30-40˚C and the intermediate loop operates at a temperature that is sufficiently high to provide heating.
Detailed functioning of equipment
- The desorber or generator provides the “backflow” element of the thermal compression system. The refrigerant is separated from the solution by evaporation at an absolute pressure of around 50 mbar and a temperature ranging from 65-75˚C.
- The condenser collects and condenses vapor from the compressed refrigerant supplied from the desorber. The liquid refrigerant then flows toward the evaporator.
- The evaporator allows the refrigerant to evaporate at very low pressure (8 mbar absolute), and at a temperature of 4˚C,
- The absorber is the “aspirating” part of the thermal system. The refrigerant vapor produced in the evaporator is absorbed by a salt-rich solution (about 62%). The solution is diluted during this process and is re-routed toward a generator, via a pump.
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