The overall performance of a thermal system simulated with TRNSYS and in particularly of the heat rejection technologies is strongly influenced by the type of components employed in the simulation and the control strategy of the system.

The control strategy of the present system is as follows. The cooling load has to be satisfied with water at 7°C and the chilled water returns from the load at 12.5°C. It is supposed that all the cooling production is absorbed by the loads. Solar collectors heat up the hot storage and the pump of the solar collector loop is started as the difference between collector outlet and storage bottom temperature

exceeds 8 °C. Water from the top of the storage is sent to the generator of the absorption chiller. The start up Temperature of the chiller is set to 72°C and the air-cooled heat exchanger or the cooling tower start up matches with it. In this study the fans were not controlled nor with a variable frequency Drives (VFDs) neither with two speed motor steps. Controlling a motor with a VFD is of author’s interest and this technology will be considered for the next activities [12]. As can be noted the system control strategy is kept very simple to avoid complications in the simulation.

The investigation is carried out for three different Italian sites: Bolzano (latitude 46°30’ N) with an alpine climate, Rome (latitude 41°54’ N) with a Mediterranean climate and Palermo (latitude 38° 7′ N) with a very hot climate. This should give an idea on how different locations lead to different energy and economic performance of the heat rejection equipment Each location was simulated for both the heat rejection technologies: dry cooler and wet cooling tower. The solar collector slope was varied for each location and was equal to 35, 30 and 25°.

Since the choice of the heat rejection technology gets influenced by economic considerations, the definition of the installation and running costs is of primary interest. The economic parameters assumed for the present analysis are reported in Table 1.