Today most of cooling demand is satisfied with electrically driven compressor chillers. Due to global warming, cooling demand will increase worldwide. Therefore alternative refrigeration methods need to be improved to preserve limited energy resources. One opportunity is thermally driven chillers, which perform absorption cycle process. In this principle main energy input is done by heat and only a little electricity. This heat can be either produced conventionally by combustion or sustainably with solar thermal collectors. Like any other electrical driven chiller, all heat brought into the process need to get rejected by a recooler. In case of thermally driven chiller, heat rejection amount is much higher. This causes higher system cost compared to electrical driven chiller and blocks larger market diffusion of thermally driven chiller. Therefore improved heat rejection concepts are necessary also to maximise solar utilisation.In this thesis measurements were performed on a dry cooling tower extended with an adiabatic precooling system to increase recooling capabilities. This system has a simple and cheap design and needs less maintenance to remain hygienic quality. During measurements a correlation between evaporation water flow and fan speed to heat rejection was found and with normalisation it was possible to predict heat rejection dependent on these two operation factors for given ambient air conditions. At the start, measurements were performed and the test rig was evaluated to ensure high accuracy. The sensor alignment in the test rig was insufficient; therefore evaporation, which causes precooling effect, was calculated instead measured by relative humidity sensors.The measurements attest that the system has high precooling effectiveness up to 10 K below ambient temperature for appropriate conditions. Under such conditions almost doubled heat rejection was measured.To quantify the impact to a thermally driven chiller supplied by solar heat on a theoretical basis, a model including solar thermal collector and cooling tower was developed. Extended with meteorological data for a chosen location, supplied cold of the chiller and consumed electricity for the cooling tower fan was calculated for a single day and for period of one year. Using adiabatic precooling enables two optimisation methods; first increased chillers cold output and second reduced electrical fan consumption. Here simulation has shown huge electrical energy saving potential of sixty-nine percent on the one hand, or nine percent more supplied cold on the other hand compared to ordinary dry recooling. However while analysing results for increasing supplied cold, it was found a high dependency to available heat produced by solar thermal collectors.In future work, the adiabatic precooling system should prove its advantages in a field study to achieve knowledge about its long term behaviour