Within the last years a lot of research in the field of solar supported desiccant and evaporative cooling (DEC) systems was done and many system variations were developed /1-10/. The solar input is typically "collected” by solar water collectors, the energy is then stored or directly used in the process for heating up the return air flow for regenerating the desiccant wheel.

The use of solar air collectors as energy source was analysed within simulation studies. The idea of keeping the system as simple as possible was supported by the promising results of the simulations. Thus the pilot plant in Freiburg uses directly solar heated air as exclusive energy source for the cooling case. Figure 1 shows the flow pattern and the different process steps in the temperature-humidity-diagram.

The general aim is to cool and to dry the ambient air. Therefore ambient air is
dehumidified by adsorbing the water vapour to a silicagel bed or some other hygroscopic
material between point 1 and 2. Due to the heat of adsorption the air is warmed up. For

The regeneration of the dehumidification wheel is done by air heated up in the solar air collectors (point 1 to 9). For regeneration air with high temperature and low relative humidity is needed. Therefore the regeneration temperature should reach 45 to 90°C /11/ depending on the cooling load.

Beside dehumidification and cooling, the DEC-plant is also used for humidification and/or heating of supply air or for pure ventilation of the rooms only. The operation modes internally numbered from one to five are:

• Modus 1 — Heating: The desiccant wheel is used as heat recovery wheel. Both wheels are used to warm up the inlet air by cooling down the outlet air. For meeting the room conditions the air is additionally heated by the backup heater and/ or solar gains.

• Modus 2 — Heat Recovery: The desiccant wheel is used as heat recovery wheel. Both wheels are used to warm up the inlet air by cooling down the outlet air. No additional heating is needed.

• Modus 3 — Free Ventilation: For realising the demanded air change rate the ventilators are delivering the inlet and outlet air. No other components of the plant are active.

• Modus 4 — Adiabatic Cooling: The inlet air is cooled down within the heat recovery wheel by humidified outlet air and/or by humidifying the inlet air.

• Modus 5 — Desiccant and Evaporative Cooling: The air is treated as described above.