Air change per hour and inlet area: Effects on ultrafine particle concentration and thermal comfort in an operating room

The Heating, Ventilation and Air Conditioning (HVAC) system in an Operating Room (OR) has two main functions: evacuate contaminants to guarantee an elevated Indoor Air Quality (IAQ) and ensure the thermal comfort of the occupants. The UltraFine Particles (UFP) generated during the surgical operation can cause health-related risks at higher concentrations if inhaled for a prolonged time. In this work, the authors have developed a transient model to simulate the thermofluid dynamic conditions, UFP transport and thermal comfort inside an OR equipped with a Laminar AirFlow (LAF) system. The effects of the Air Change per Hour (ACH) and inlet area on the unidirectional airflow, UFP concentration and thermal comfort have been studied here for the first time, considering the constraints imposed by the standards. An increase of ACH above the minimum value imposed by the standards can ensure two advantages: obtaining both thermal comfort conditions for the surgical staff and very low UFP concentrations. Moreover, larger ACH values ensure the unidirectional airflow and avoid the disruption caused by the thermal plume. Excessive ACH values do not bring additional cleanness to the OR, while increasing energy consumption.