Thermal Insulation of a Flour Mill to Improve Effectiveness of the Heat Treatment for Insect Pest Control

One of the major problems that are found in flour mills, and more generally in industries for the processing and storage of food, concerns the control of insect pests. Insects can develop and are responsible for contamination that can determine the non-conformity of productions to the norms and regulations. An alternative to chemical treatments for the control of insect pests in flour mills is given by methods based on heat treatment of indoor environment. The heat treatment consists in raising the temperature of the surfaces where the insects live by increasing the air temperature inside the building. The optimum air temperature for the effectiveness of the heat treatment ranges between 47 °C and 55 °C and must be maintained for a period of 36÷48 hours to eliminate all life stages of insect pests both for dehydration and for irreversible alterations in lipid and protein levels. The most widely used system for heat treatment in flour mills is based on heaters powered by electricity which are usually integrated with fans to ensure a uniform air temperature inside the buildings. The objective of this research was to analyse the heat transfer of a number of building elements belonging to a flour mill located in Eastern Sicily (Italy) in order to highlight the weakness of the building thermal behaviour. Firstly, building materials and components, such as floors, external walls, windows, pillars and beams, were analysed. Next, thermal characteristics of the indoor environment were studied before and during the heat treatment. Specifically, air temperature and relative humidity inside and outside the building were measured by means of data-loggers; surface temperatures of the building components were measured by using a thermal camera; thermal conductivities of the building materials were collected from materials catalogues. The monitoring of the microclimatic parameters inside and outside the building before and during the heat treatment revealed that a relevant heat loss occurred across thermal bridges which were previously identified by analysing digital images provided by the thermal camera. On the one hand, thermal bridges represented a weakness of the thermal treatment since insects found refuge in areas of the building characterized by lower surface temperatures; on the other hand they caused a huge expenditure of electrical energy in order to maintain indoor air temperature within the optimal range. Therefore, the building components which constituted the thermal bridges were analysed with the aim of studying the contributions of different insulation materials on heat loss. Simulations were carried out by using different insulation solutions to quantify heat loss reduction. A set of possible solutions was reported in this paper