An Original Approach to Active Climate Control Based on Equilibrium Moisture Content (EMC) as Set Point in a Middle-Age Building in Palermo, Italy

In the frame of a more sustainable approach to climate control, a long term strategy has been developed and is under advanced phase of implementation by technical staff of the University of Palermo in an important building, Palazzo Steri, owned by the University. The monumental room under climate control, the Sala dei Baroni (also known as Sala Magna), has a precious wooden ceiling where the previously loadbearing elements are covered with wooden painted panels. Many of them, painted in the fourteenth c, underwent important restorations in the past due to climate related damage (cracks, warpings, paint layer delamination) and biological infestations. The room is currently undergoing an important installation, using an HVAC system designed differently from the standard approach to climate control. The adopted design approach deals with the control of the air surrounding the wooden artifact as a function of the potential Equilibrium Moisture Content (EMC) that the panels could achieve. EMC is a synthetic parameter useful in correlating the response of panel paintings to climate fluctuations, and the behaviour of wooden objects may be better expressed as a function of EMC than to Relative Humidity (RH) fluctuations alone. Indeed, the correlation between a specified climate expressed with a parameter that takes into account both T and RH as experienced by wood is more correct. In this case-study the benefits of such an approach are even greater: due to the fact that it is possible to obtain the same EMC values with different combinations of Temperature and Relative Humidity values, the climate can be kept stable around the objects in the way the objects would feel it, meanings that the same EMC values (or hygro-mechanical stability of the artifacts) can be obtained in different seasons by adapting the Relative Humidity to the corresponding EMC value, letting the system free to follow the Temperature seasonal variations without compromising its stability.