Indoor climatic conditions of ancient buildings by numerical simulation and thermographic measurements

The preservation of historic buildings and monuments needs the knowledge of local climate in order to evaluate the mass and energy flows interesting structures and indoor spaces. Special attention shall be paid to the indoor air control in buildings hosting frescos or paintings. The equilibrium conditions of the surfaces are defined by the values of temperature, velocity and humidity contents of the indoor air. The influence on the preservation is clear but the air and pollutants flows, the convective and radiative energy exchanges, vary with the local conditions. The knowledge of the indoor air conditions and of the internal surface temperature allows the calculation of these flows. These indoor values can be measured, but it is often difficult to perform a correct evaluation and to avoid any modification of the air velocity and temperature fields by conventional probes themselves. In this context, the use of numerical codes is a useful tool. In fact a numerical simulation allows the calculation of the indoor parameters in a large number of internal points, also because of the performances of modem computers. Two or three-dimensional model can be used, radiative and convective heat transfer problems can be treated both in steady state and in transient mode. The aim of this work is to set up an investigation method allowing predicting the best indoor conditions for the preservation of the frescos and the correct schedule of the number of visitors. The case study is a typical example of this problems bound to the fresco's maintenance, the Camera Picta (St George Castle, Mantova — Italy). The reported example presents a synergetic effect of results obtained by measurements and by a numerical study. JR Thermography effectively measures surface temperature on walls according to a special procedure. The data measured are the boundary conditions fed to the numerical code. The solution of the mass, energy and momentum equations allows the evaluation of the local values of indoor air parameters. Comparison of measured and calculated values for air parameters is brought over and some indications on possible application of this methodology to design a proper Heating Ventilation Air Conditioning system are pointed out.