HVAC (Heating, Ventilation and Air Conditioning) systems are usually designed to ensure thermal comfort conditions (temperature, ventilation and humidity) inside a public building or an industrial plant. These systems become critical when they are organically incorporated into more complex process plants, in which it is necessary to have well-specified air requirements needed by the production cycle. In the chemical and pharmaceutical industry, there are many examples of companies in which the HVAC systems are playing an enabling role for the productivity of the department in which they are inserted. These industries, in fact, have, some laboratories in which tricky production phases take place. The laboratories require the retention of stringent internal environmental conditions and the careful control of ventilation, to prevent the proliferation of bacteria, viruses and other harmful microorganisms. A lot of laboratories areas must keep sterility conditions, which is achieved also thanks to the correct operation of the thermal ventilation plant and to the moisture control. For chemical and pharmaceutical companies, moreover, the exact control of the temperature and humidity conditions is an important parameter for the certification of the production process.
In such companies, therefore, it is essential to ensure high values of availability for service facilities, including HVAC systems, in order to minimize the costs of plant downtime that would result from a failure of such systems. In these kinds of industries, in fact, faults of air conditioning systems can cause stopping of the work process and even throwing away some of the produced goods[1]. In addition, any stops would involve considerable time of non-production related to the restoration of optimal temperature and humidity conditions. Such reversals may be definitely costly and complex for the company, especially for the need to "rehabilitate" the production process.
For all these reasons, the proper maintenance of an HVAC system is critical both when it would become uncertified for the production process, both in different contexts, such as in the case of commercial buildings, in which thermal comfort is economically significant.