Humidity and air temperature measurement by quantitative infrared thermography

Abstract

Quantitative infrared thermography is used to measure the humid air conditions in equilibrium with a building surface. The method is based on accurate temperature measuring as the driving parameter of the physical process. At the same time, the thermographic system produces images of the wall surface behind the device and so can measures the wall's temperature, as well. This is a part of a project dealing with the full monitoring of the indoor environment on thermodynamic basis. The use of a special ancillary device called IRpsicro and a dedicated procedure allows the measurement of the air temperature, relative humidity and speed using only IR thermography. This knowledge is fundamental to know and quantify the moisture exchange process between the porous material and the boundary. As a consequence thereof the evaporative process can be studied on quantitative basis. Essentially, IRpsicro enable the wet and dry bulb temperature measurements needed by the psycrometric method. Equations to achieve indirectly the hygrometric quantities of air are presented. Results obtained in laboratory-controlled conditions are compared with standard measurements of temperature and relative humidity. The paper illustrates a current application of the system in order to evaluate the decay of a heritage building covered by frescoes. An accurate global view of the building envelope is produced with images corrected for the geometric and radiometric distortions.