Thermo-hygrometric behaviour of Roman thermal buildings: the “Indirizzo” Baths of Catania (Sicily)

Abstract Roman baths represent an interesting slice of the ancient culture and an emblematic step in the process of civilization. Their heating system is a meaningful example of the outstanding level of technological progress achieved by the Romans in the art of building. However, while their mode of operation is sufficiently known, there is uncertainty regarding temperatures and relative humidity (RH) maintained in the heated rooms, thermal level and expulsion process of hot flue gases, presence of window glazing and concamerationes . In order to overcome such uncertainty, a multidisciplinary approach − based on in situ analyses, topographic and 3D laser scanning surveys and computational fluid dynamics (CFD) simulations − has been developed by studying the main features of the “Indirizzo” Baths of Catania (Sicily), which represent one of the best-preserved hypocausted thermal buildings anywhere in the Roman Empire. Results show that temperatures in the caldarium ranged between 30 and 35 °C, with a RH of around 60 ÷ 70%, while the thermal level of hot gases inside the hypocaust fluctuated from about 90 to 125 °C, in function of the outdoor climate. Moreover, the original presence of windowpanes and concamerationes has been confirmed, as they were necessary to guarantee appropriate indoor thermal sensations and to prevent burns by touching the heated surfaces. These outcomes may constitute a useful support for better understanding the operation of other similar Roman thermal complexes.