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Chair for Energy Conversion TechnologyAbsorption Chillers

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Absorption Chillers

Depending on the pressure in absorption chillers as well as in compression chillers different boiling and dew points of the refrigerant are used. In case of the compression chillers an electrically driven compressor is applied for the pressure rise of the vapourous refrigerant on the condenser level.
In sorption chillers there is additionally used a second working fluid circle (solvent circle) where the refrigerant vapour is liquified and due to the low specific volume it can be brought up to a higher pressure level by a solution pump with minimal electrical expense.

Bild 1: Funktionsweise einer einstufigen Absorptionskälteanlage

The evaporator is located on a pressure level where the refrigerant evaporates at 4-13°C. The therefore required enthalpy of evaporation is for example withdrawn from the water of a cooling ceiling of which a room is air-conditioned.

The originated refrigant vapour is absorbed in the absorber by the concentrated solvent (absorbed or "liquified" see above) whereby the originated heat is purched by cooling water.

The solution is lifted on a higher pressure level by an electrically or thermally driven solution pump. Through a supply of solar generated driving heat, waste heat from a cogeneration unit or district heat with a temperature of 60-105°C the refrigerant vapour of the generator is extracted out of the solution.

Afterwards the circle equals that of a compression chiller. In the condenser the refrigerant vampour is liquified with fed cooling water at 30-40°C. Now the refrigerant can reevaporate again in the evaporator.

Cost efficiency measures are possible like in many other circles: The concentrated solution originated in the generator first preheats the diluted solution coming from the absorber in the solution heat exchanger. Than it is able to reabsorb refrigerant in the absorber.

The following Image shows a system characteristic in the normally used vapour pressure diagram.

Bild 2: lg p, -1/T - Diagramm für H2O/LiBr


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