The basic process of cold generation is the compression of a refrigerant fluid, which causes evaporation of the liquid at low temperatures and pressures and condensation of the vapour at higher temperatures and pressures. Instead of mechanical compression like in electrical air — conditioners, thermal driven chillers use thermal energy for the compression of the fluid.

The basic principle of the thermal compression is the ab — or adsorption of the refrigerant in a liquid or solid material. Whereas absorption chillers use the liquid lithium-bromide in adsorption chillers solid adsorbents like silica gel or zeolites are used. In both machines the refrigerant is water, which results in the technical task that the machine has to be operated at very low pressures in a vacuum tight containment.

In our chiller we use silica gel as adsorbent. Silica gel is a porous glass with a high capacity of adsorbing water vapour. For that reason it is used as desiccant in various applications.

The working process of the adsorption chiller is described below (compare figure 1).

Step 1: Desorption — Drying of the adsorbent

The adsorbent is dried by heat input. Water vapour is set free, flows in the condenser and is liquefied there under heat emission. When the material is dry, the heat input in the adsorber is stopped and the upper check valve closes.

Step 2: Adsorption — water vapour is adsorbed at the surface of the adsorbent

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After a cool down phase the reverse reaction and the evaporation of the liquid condensate starts. The lower check valve to the evaporator opens and the dry adsorbent aspirates water vapour. In the evaporator, water evaporates and generates cold, which can be used for air-conditioning. During the adsorption process heat is rejected which has to be dissipated.

Step 3: Return of condensate

In a final step the liquid condensate is returned to the evaporator and the circuit is closed.

In order to achieve a continuous cold production two adsorbers work in combination, i. e. one adsorber desorbs while the other adsorber generates cold by adsorbing in the meantime.

water vapour liquid process water check valves condensate return driving heat heat rejection cold generation

2. Construction Principles

SorTech AG has developed and patented two construction principles, which are important for achieving a compact and lightweight chiller design: