PSI - Issue 77

Alexander Čaja et al. / Procedia Structural Integrity 77 (2026) 177 – 182 Author name / Structural Integrity Procedia 00 (2026) 000 – 000

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desire to create a controlled and hygienic environment has its roots in more than a century ago – especially in the field of healthcare, where it was about preventing infections – the requirements for so-called cleanrooms are the product of technological progress in recent decades. Their importance today goes far beyond medicine and is becoming a key element in various industrial sectors. According to ISO 14644-1, a cleanroom is defined as: “A room in which the concentration of particles in the air is controlled and which is constructed and used in a way that minimizes the introduction, generation and retention of particles inside the room and in which other relevant parameters, such as temperature, humidity and pressure, are monitored.” In addition to operating rooms, where the priority is to protect the patient from microbial contamination, strict conditions are also imposed on areas intended for the production of medicines, electronics or micromechanical components. In these cases, the main risk is not infection, but damage or deterioration of sensitive products due to the presence of impurities. From the point of view of their use, we distinguish two main categories of clean rooms: • areas for working with inanimate materials - such as laboratories, pharmaceutical or microelectronic production, where contamination can affect the quality of the product or significantly shorten its lifespan, • medical areas - especially operating rooms and intensive care units, where absolute cleanliness is essential to prevent the transmission of microorganisms that can cause serious infections in the patient. One of the main tools for ensuring the required class of cleanliness is controlled air exchange. Traditionally, cleanrooms have used very high air changes (e.g. 20–40 ACH – air changes per hour), often with laminar flow, to minimize particle concentrations (Bhattacharya et al., 2023). However, such settings are very energy intensive and often exceed real needs, leading to unnecessary energy waste (Chen et al., 2023). Cleanrooms are classified according to the cleanliness of their air – historically according to Federal Standard 209 and currently according to ISO 14644 – which evaluates the number of particles ≥ 0.5 µm per defined volume of air. The key is therefore to ensure optimal forced air exchange with adequate treatment (filtration, humidification, heating and cooling). In the design and operation of cleanrooms, it is crucial to monitor the way the air moves in the room. The flow can be laminar (even and directed) or turbulent (swirling and less predictable). This character is influenced by the type of air-handling elements – specifically the way in which the air supply and exhaust is distributed – and is determined depending on the required cleanliness class according to the relevant standards. The standards specify exactly what type of outlets should be used for air supply and exhaust and also define their location. The combination of these factors significantly affects the resulting direction and behavior of the air flow in the space. Modern approaches to the design and operation of HVAC systems in clean rooms are therefore increasingly focused on optimizing air exchange. The goal is to find a balance between ensuring the required environmental quality and minimizing energy consumption. Research shows that excessive air exchange may not always lead to improved cleanliness, especially if factors such as the movement of people, opening doors or the configuration of distribution elements are not taken into account (Bhattacharya et al., 2023; Nikoopayan Tak et al., 2023). At the same time, it turns out that the energy consumption of HVAC systems in clean rooms can be several times higher than in conventional buildings. In some cases, the energy consumption for ensuring air cleanliness can represent up to 50–70% of the total energy balance of the facility (Chen et al., 2024). Therefore, it is necessary to look for solutions that enable dynamic control of air exchange based on current conditions in the space. This study focuses on analyzing the impact of different air exchange rates on the environmental quality in operating rooms, with an emphasis on particle concentration, temperature-humidity parameters and thermal comfort. The research combines experimental measurements and CFD simulations, with the aim of designing energy-efficient solutions that also meet strict hygiene standards.

Nomenclature CFD

Computational Fluid Dynamics HVAC Heating, Ventilation and Air Conditioning PMV Predicted mean vote PPD Predicted percentage of dissatisfied v sup

Speed of air flowing from the supply distribution element Volumetric flow rate of the supply distribution element

V sup