Correction of thermal bridges to improve the effectiveness of heat treatment for insect pest control in flour mills

Flour mill products constitute an ideal substrate for the growth of various species of pests such as arthropods, rodents and microorganisms. These pests determine quality reduction of the flour milling industry products and other products derived from further processing. An alternative to chemical treatments for the control of insect pests in flour mills is represented by methods based on heat treatment of the indoor environment. The heat treatment consists in raising the air temperature inside the building between 45°C and 55°C-60°C for a time interval of 36-48 hours, in order to eliminate all life stages of insect pests for both dehydration and irreversible alterations in lipid and protein levels. However, since some mill building components can provide a refuge for insects from the heat, also their surface temperatures should accomplish the abovementioned requirements in order to guarantee the effectiveness of the heat treatment. Therefore, in our previous work the improvement of thermal performance of the mill was simulated by correcting thermal bridges through building interventions suitable to reduce heat losses during the heat treatment. The aim of the present study was to improve the thermal performance of another mill characterised by materials and building techniques different from those previously studied. Specifically, the existing insulation of the external walls of this mill was made of expanded clay. The results demonstrated that insulation of the external walls of the analysed mill had a relevant role in the correction of thermal bridges. Although the existing insulation made it possible to obtain higher temperatures of the inside surface of external walls, it produced higher losses of heat flux across the thermal bridges than those recorded in the flour mill analysed in the previous study