Controlling respiratory contaminants in airborne infection isolation rooms (AIIRs) is essential to minimize transmission risk and protect healthcare workers. While background ventilation is a widely used and effective engineering strategy for infection control, source-oriented local ventilation offers a more targeted alternative. This study explores a ceiling-mounted local exhaust concept for AIIRs, designed to capture coughing particles in a practical and flexible way. We employed the Eulerian-Lagrangian framework to simulate transient airflow and particle dispersion in AIIRs. Four exhaust configurations were tested under different coughing behaviors. Our findings reveal that the capture efficiency of the above-chest exhaust drops from 97% to 7% with a change in coughing angle, while the ceiling-mounted exhaust maintains an efficiency of 20–40%. The ceiling-mounted solution exhibits higher capture stability and greater resilience across different conditions. Subsequent trajectory analysis of 16 variants identifies the influence of heat-source arrangement and ventilation flow direction on particle transport. A real-ward case study further indicates that the ceiling-mounted local exhaust system can suppress the initial concentration peak in the breathing zone, demonstrating short-term exposure reduction under a representative clinical layout. Overall, this work presents an adaptive, source-oriented ceiling-mounted local exhaust approach for effective short-term removal of coughing particles in AIIRs.

In hospitals, it is essential to control the pathogen transmission for health aspects in addition to ensuring occupant comfort. High occupant density and frequent movement of staff and visitors accelerate pathogen spread, making hospitals at risk of airborne transmission. From the perspective of engineering controls, ventilation remains one of the most efficient and reliable strategies for mitigating airborne transmission. The key challenge, therefore, is not whether to ventilate, but how to design systems appropriately, operate them correctly, and ensure sufficient adaptability to varying indoorconditions in hospitals.This thesis examines two representative scenarios. The first scenario is surgical site infection in operating rooms, where maintaining an ultraclean environment is essential to prevent wound contamination. The second is respiratory infection in patient rooms, driven by human respiratory activities; here, the goal is early mitigation of exhaled particles to prevent onward spread.Computational fluid dynamics is employed to assess system performance across operating conditions. A literature review first characterizes emission sources in each scenario, with particular attention to particle size distributions. These characteristics inform the modeling strategy, either Lagrangian discrete-particle tracking or an Eulerian passive-scalar formulation. To preserve realism, the operating-room simulations replicate the actual room configuration, while the patient-room simulations implement the realistic human respiration model. Quantitative metrics are used to compare designs and sensitivities and to reveal how system behavior changes under different settings.For the hybrid operating room, the results demonstrate that the current Temperature-controlled Airflow installation establishes two distinct ventilation zones: a central zone with strong contaminant transport capacity and a peripheral zone where the short distance to the exhausts enables effective contaminant removal. In patient rooms, the work captured the full evolution of cough-generated air–particle mixtures, from an initial stage where particle motion is dominated by size, through an intermediate period of dispersion shaped by the thermal plume, and to a final stage of background ventilation removal. The intermediate period, typically between 5 and 23 s after a cough, was revealed as a critical window for local exhaust intervention. Simulations of different configurations showed that a ceiling-mounted system leveraging the body’s thermal plume offers a robust and effective solution. Furthermore, the analyses highlight the role of background ventilation in determining the optimal placement and performance of such ceiling-mounted systems, offering practical guidance for their application in patient care environments.Based on the analysis, this thesis advances the understanding of ventilationdriven contaminant transport in hospitals and establishes ventilation as a dynamic tool for infection control rather than a fixed design parameter. It emphasizes resilience and adaptability as key to creating safer healthcare environments.

På sjukhus måste inomhusmiljön inte bara säkerställa komfort utan också begränsa smittspridning. En hög patientbeläggning och frekvent rörlighet av personal och besökare påskyndar spridningen av patogener. Det gör sjukhus särskilt sårbara för luftburen smitta. Detta gör sjukhus särskilt utsatta för luftburen smittspridning. Ur ett ekonomiskt perspektiv anses ventilation ofta vara kostsamt, men det är fortfarande en av de mest effektiva och tillförlitliga strategierna för att minska luftburen smittspridning. Den viktigaste frågan är därför inte om man ska ventilera, utan hur man skall utforma systemen på rätt sätt, använda dem korrekt och säkerställa tillräcklig flexibilitet för varierande kliniska förhållanden. I denna avhandling undersöks två representativa scenarier för sjukhusinfektioner. Det första är infektioner i operationssalen, där det är viktigt att upprätthålla en ultraren miljö för att förhindra kontaminering av sår. Det andra är luftvägsinfektioner i patientrum orsakade av människors andningsaktivitet. Här är målet att tidigt minska partikelhalten från utandningsluft för att förhindra vidare spridning.Numeriska strömningsberäkningar används för att utvärdera systemprestanda under olika driftsförhållanden. En litteraturgenomgång karakteriserar först utsläppskällor i varje scenario, med särskild uppmärksamhet på partikelstorleksfördelningen. Detta ligger till grund för modelleringsstrategin –antingen Lagrangesk diskret partikelspårning eller en Eulerisk passiv skalärformulering. För att bevara realismen replikerar operationssalssimuleringarna den verkliga rumskonfigurationen, medan patientrumssimuleringarna implementerar en realistisk modell för mänsklig andning. Kvantitativa mått används för att jämföra konstruktioner och känsligheter och för att visa hur systemets beteende förändras under olika förhållanden.För hybridoperationssalen visar resultaten att den nuvarande TcAFinstallationen skapar två distinkta ventilationszoner: en central zon med stark transport av föroreningar och en perifert belägen zon där korta avstånd till evakueringspunkterna möjliggör effektiv evakuering av föroreningar. I patientrummen utforskades alla förlopp av luft-partikelblandningar som genereras vid hostning, från ett inledande skede där partikelrörelsen domineras av momentum, genom en mellanperiod av partikelspridning som formas av den termiska plymen, till ett slutskede av partikelupptagning i bakgrundsventilation. Mellanperioden, vanligtvis mellan 5 och 23 sekunder efter hosta, visade sig vara en kritiskt tidsram för lokal partikeltransport. Simuleringar av olika konfigurationer visade att ett takmonterat system som utnyttjar kroppens termiska plym erbjuder en robust och effektiv lösning. Dessutom visar analyserna bakgrundsventilationens roll för att bestämma den optimala placeringen och prestandan för sådana takmonterade system. Det ger praktisk vägledning för deras tillämpning i patientvårdsmiljöer.Baserat på analysen bidrar denna avhandling till en ökad förståelse av ventilationsdriven transport av föroreningar i sjukhus och etablerar ventilation som ett dynamiskt verktyg för infektionskontroll snarare än en fast designparameter. Den betonar att resiliens och anpassningsförmåga är nyckeln till att skapa säkrare vårdmiljöer.

Accurate modeling of exhalation dynamics is essential in estimating infection rates. In this study, we analyzed the predictive capabilities of three Unsteady Reynolds-Averaged Navier–Stokes (URANS)-based turbulence models: Realizable k–ε, renormalization group (RNG) k–ε, and shear-stress transport (SST) k–ω for sinusoidal exhalation. The exhaled jet flow extends over a distance from the exhalation source, normalized by the exhalation source diameter, and was analyzed across the jet region. Furthermore, this region was divided into three sub-regions: near-field, transitional, and fully developed field for turbulence evaluation. These models were validated against time-resolved particle image velocimetry data and empirical measurements under quiescent ventilation conditions. Results from the centerline velocity decay profiles demonstrated that each model exhibited performance across the sub-regions of the exhaled jet. Using three performance metrics for quantitative validation, the RNG k–ε model demonstrated superior performance overall across the jet flow region. When sectioned into sub-regions, its performance is better in transitional and fully developed regions due to its enhanced strain-term formulation. Meanwhile, the SST k–ω model provides superior accuracy in near-wall shear and boundary–layer interactions. The Realizable k–ε model performs well in the transitional region but underperforms in the near-field and fully developed regions. These results advance the characterization of breath-generated flows, providing insights into airborne transmission dynamics that can inform the optimization of ventilation strategies and mitigation measures in indoor environments. Semi-empirical equations, derived using the best-performing region-specific URANS models, estimate centerline velocities during exhalation (0 < t < 2 s) in developed field regions.

Laminar airflow (LAF) is essential for maintaining a sterile environment in operating rooms, but its rapid unidirectional flow decay leads to low airflow efficiency and increases energy consumption. The objective of this study is to investigate the energy-saving and air quality benefits of using a low-turbulence air curtain around laminar airflow, which is referred to as protective laminar airflow (PLAF). Numerical simulations were used to model airflow and particle transport, and a series of experiments were conducted in a real operating room at St. Olavs Hospital, Norway, to validate the simulation results. The findings indicate that when the unidirectional airflow supply velocity is maintained at 0.25 m/s, combined with an air curtain that has the width of 2 cm and the velocity of 1.5 m/s, the PLAF system outperforms the conventional LAF system operating at a unidirectional airflow supply velocity of 0.30 m/s. This configuration results in a 17.3% energy saving, showing the potential of this airflow distribution strategy to enhance both cleanliness and energy efficiency.

This study evaluated the performance of a newly proposed hybrid ventilation strategy, a temperature-controlled airflow system, in an operating room under different working conditions. The influence of obstacles and ventilation rates on air patterns and airborne contamination concentration is investigated. Numerical simulation based on computational fluid dynamics techniques was applied to obtain high-resolution whole-field flow movement and particle dispersion. The results show that obstacles like surgical lamps considerably weaken the central supply of air and introduce mixing air movement above the operating table. It is also found that due to the presence of surgical lamps, the air exchange rate should be increased to obtain a similar performance as in the ideal room configuration.

In recent years, pandemic outbreaks have raised concerns about the spread of respiratory infections and their impact on public health. Since the pathogen emission during human respiration is recognized as the primary source, characterizing the physical properties of exhaled particles and airflow has become a crucial focus of attention. This article critically reviews experimental studies in exhaled particles and airflow, examines the uncertainty introduced by different measurement methods, analyzes how it is reflected in measurement outcomes, and provides an in-depth understanding of particle size distribution and airflow behaviors of human respiration. The measurement techniques assessment highlights the variability among particle sizing techniques in detection size range, collection efficiency, hydration status of captured particles, and experimental protocols. A combination of sampling-based instruments and laser imaging systems is recommended for particle sizing to cover a wider detection range, with refined setups in thermal conditions, sampling distance, volume, and duration. Meanwhile, it identifies the complementary nature of qualitative and quantitative measurements of airflow characterization techniques. Image recording systems plus data reconstruction programs are suggested to capture dynamic airflow features while accuracy validation by other techniques is required at the same time. Subsequent analysis of the measurement data showed that the various experimental measurements provided substantial information, but they also revealed disagreements and challenges in quantification. The dominance of submicron aerosols in exhaled particles and jet-like transport in exhaled airflow is obvious. More efforts should be made to measure particles larger than 20 μm, capture airflow dynamics in a high temporal and spatial resolution, and quantify the impact of face coverings to improve the understanding of human respiratory emissions.

This article investigates the efficacy of temperature-controlled airflow systems in modern operating rooms for contaminant control, a critical factor in preventing surgical site infections. We have conducted experimental measurements in an operating room equipped with temperature-controlled ventilation to map the airflow field and contaminant dispersion (airborne particles with diameters ranging from 0.5 to 1 μm). The results were used to validate the computational fluid dynamics code, which was then employed to simulate and examine different conditions, including contaminant release locations and air supply rates. Realizable k-epsilon and passive scalar models were utilized to simulate airflow and airborne particle phases. We assessed the airflow distribution and contaminant dispersion, utilizing indices such as ventilation and air change efficiency scales. The analysis provided quantitative insights into the distribution and removal of contaminants, as well as the speed at which the room air was replaced. Contamination was found to be effectively reduced when contaminants were released near exhaust outlets or under central unidirectional inlets. The presence of the operating table caused a big distortion of the central downward airflow, forming a horizontal air barrier at the periphery. Under this unique interior configuration, an appropriate air supply ratio between central and periphery zones was required to achieve optimal overall ventilation performance.