Effective Ventilation Strategies for Mitigating Infection Risks in Hospitals

BEEE CPD Seminar: Effective Ventilation Strategies for Mitigating Infection Risks in Hospitals [7 May 2025, Hong Kong, China]

Speakers: Prof. Lee Wai Ming, Eric (CityU), Prof. Liu Chun Ho (HKU) and Prof. Wong Ling Tim (PolyU)

Facilitator: Prof. Mui Kwok Wai, Horace (PolyU)

Part 1: Effective Ventilation Strategies in Hospital Environments

Bio: Prof. Ling Tim Wong is the Associate Head and Associate Professor in the Department of Building Environment and Energy Engineering at The Hong Kong Polytechnic University. He received the Hans B. Thorelli Award in 2006 and 2011 and the Emerald Literati Network Award for Excellence. He is a working commission member (W062) of the Council for Research and Innovation in Building and Construction and organized the 34th CIBW062 International Symposium in Hong Kong in 2008. He is the Editor-in-Chief of the journal AIR.

Abstract: This session will focus on the latest developments in effective ventilation strategies. We will explore critical design parameters, including Air Changes per Hour (ACH), optimal designs, and energy consumption considerations for healthcare-associated infections (HAls) and airborne virus transmission. The insights will inform practical guidelines to mitigate airborne transmission risks in General Human Occupied Areas (GHOAs), ensuring a safer environment for patients and healthcare workers.

Part 2: Outdoor Urban Morphology and Virus Transmission

Bio: Prof. Chun Ho Liu is an Associate Professor in the Department of Mechanical Engineering at The University of Hong Kong. His research focuses on air pollution physics and chemistry, geophysical turbulence, and scientific computing. He currently investigates the urban atmospheric boundary layer, using large-scale computer models to examine how urban morphology modifies transport processes, refining land-surface parameterizations, particularly urban roughness.

Abstract: This seminar will explore how the physical layout of urban environments influences the spread of airborne viruses as passive scalars. We examine how urban structures can mitigate or exacerbate virus transmission. Key findings indicate that urban morphology-such as building density, street orientation, and green spaces-plays crucial roles in determining airflows and pollutant dispersion, affecting viral particle concentration and transmission likelihood in densely populated areas.

Part 3: Dynamics of In-Pipe Environment

Bio: Ir Prof. Eric Wai Ming Lee is a Professor in the Department of Architecture and Civil Engineering at City University of Hong Kong. His research expertise includes building water supply and drainage systems and computational modeling of multi-phase flow. Prof. Lee is an active member of the HKIE and contributes to various technical committees under HKSAR Government departments.

Abstract: Air pressure fluctuations in building drainage systems can cause problems if proper venting is not provided. Excessive positive pressure may push foul air into the building through the trap seal, while excessive negative pressure can empty the trap seal. To reduce these fluctuations, cross-vents connect the drainage stack to the vent stack every two or three floors. This study uses computational fluid dynamics techniques to investigate cross-vent design.

Joint Symposium 2023 Shaping the Future: Trends and Insights for Tomorrow Technologies Development in Greater Bay Area [23 November 2023, Hong Kong, China]

Airborne transmission significantly contributes to healthcare-associated infections (HAIs) in hospitals. Computational simulations using parametric assessments can be a powerful tool for evaluating and optimizing the effectiveness of ventilation strategies in indoor environments. Still, they can be computationally expensive and resource-intensive due to the many factors affecting airflow and contaminant distribution. This study utilized a computational fluid dynamics (CFD) model coupled with a genetic algorithm (GA) to determine ventilation strategies that minimize the exposure risk of infectious pathogen deposition in a general inpatient ward cubicle. The proposed model iteratively evaluated diverse design solutions with fewer CFD simulations than the traditional approach. It was found that the optimal combination of ventilation strategies largely depends on the position of the source patient. In general, a ventilation configuration of 9 air changes per hour (ACH), three ceiling supply air diffusers of 0.36 m2, and six nearby exhaust units of 0.04 m2 with a 30% exhaust flow rate of the supply air at a height of 0.8 m was identified as the most effective in mitigating infection transmission within the ward cubicle, regardless of the source location. This study provides insights for the further design and operation of hospitals, and can aid in developing evidence-based guidelines for hospital ventilation and infection control. The proposed CFD model and a GA offer an evaluation tool for optimizing ventilation strategy effectiveness to minimize the exposure risk of airborne infectious pathogen deposition.

Water Supply and Drainage for Buildings CIB W062 48th international Symposium [29-31 August 2023, Leuven, Belgium]

Multiple COVID-19 outbreaks in high-rise residential buildings were found to be caused by the vertical spread of the virus along the building. Although such a transmission pathway was speculated to be one of the reasons for COVID-19 cases observed at top-floor residential units along a vertical column, empirical evidence and experimental results have yet to be obtained. To evaluate the effects of toilet ventilation on the spread of bathroom bioaerosols, a set of tracer gas experiments were conducted in a full-scale, 3-floor mock-up toilet experimental research facility. Using a novel IoT-enabled tracer gas sensing network, tracer gas dispersion from the lower floor toilet to the upper floor toilet and the roof under the 16 combinations of opening windows and exhaust fans was evaluated. Experimental results confirmed the potential vertical transmission pathway through toilet ventilation. Residents of both units are suggested to close the windows and switch on the exhaust fans of the toilet to minimize the risk of airborne infection via vertical transmission effectively.

Seminar on Indoor Air Quality in Long Term Care Settings and RCHEs [9 June 2023]

Local study tour co-organized by GTPlatform and HKPC with expert from engineering and hospital-care specialties to discuss about indoor air quality in long term care settings and RCHEs.

Water Supply and Drainage for Buildings CIB W062 47th international Symposium [23-26 October 2022, Taichung, Taiwan]

The vertical airborne transmissions of the SARS-CoV-2 virus induced by toilet ventilation and poorly maintained drainage system have been suspected to be the culprits of many in-building COVID-19 outbreaks in Hong Kong. To establish a testing ground for identifying the potential transmission pathways and the influences of the environmental factors in promoting these transmissions, a full-scale, 3-floor mock-up toilet experimental research facility was constructed at The Hong Kong Polytechnic University. The facility consists of two fully functioning toilets built according to the layout and dimensions of the toilet of a single-person public housing flat. The toilets are equipped with an operable plumbing and drainage system with the drainage-ventilating pipe extended 1 m above the roof, an electrical system, an openable window, an exhaust fan, and a sliding door. Toilet ventilation experiments using a novel tracer gas system were conducted in this mock-up facility to identify the potential transmission pathways from the lower floor to the upper floor and subsequently to the roof. Experimental results confirmed that the re-entrance of airborne particles was feasible. This mock-up toilet provides a testing ground for numerous research opportunities concerning toilet ventilation, bioaerosol transmission and plumbing and drainage system, and acknowledges the importance of physical setups for experimental research and validation of computer simulations.

Technical Seminars and Annual Technical Conference (ATC) [17 September 2022]

A public sharing on building ventilation and bioaerosol transmission, and an in-depth discussion on the development and the applications of a novel wireless tracer gas system developed in this study.

PolyU Research Postgraduate Summer School Industrial Centre Virtual Tour and online lecture [22 July 2022]

Sharing on the research elements and project details of this study to talented local and overseas senior undergraduates and master’s students.

Indoor Air 2022 – the 17th International Conference of the International Society of Indoor Air Quality & Climate [12–16 June 2022, Kuopio, Finland]

With focus on urbanization, population, and sustainable housing, tiny house movement have gained momentum in recent years. In high-density populated regions such as Hong Kong, non-existence of standards on minimum amount of living space per capita and chronic housing shortage have led to rise in tiny residential units with size less than 18m2. As we perceive a future in tiny affordable homes, it is necessary to implement strategies that make it more sustainable. This study utilizes a hybrid model that integrates the physical simulation method with data driven approaches to comprehend key relationships within buildings physical configuration, material specifications and operational conditions to recommend energy saving strategies at a minimal time compared to conventional energy estimation approaches. The study indicates that establishing a minimum area per occupant along with indoor set-point temperature control can be decisive factors in reducing the annual cooling energy consumption of tiny residential units.

HKIE Technical seminar on Indoor air quality against COVID-19 [27 April 2022]

A public sharing on the scientific mechanism behind the indoor bioaerosol transportation and the role of ventilation in preventing the spread of the pandemic. The ways to ensure effective indoor ventilation, the requirements of air exchange and suggestions on spatial arrangements at the dine-in premises and households were presented.

Effective Indoor Air Quality Management for Clinics and Health Centres – IAQ webinar for medical centers [10 December 2021, HKPC, Hong Kong]

Sharing on typical IAQ problems and improvement strategies for health facilities to the owners and facility managers for clinics and health centres.

The 46th CIBW062 International Symposium of Water Supply and Drainage for Buildings [26-27 October 2021, Taichung City, Taiwan]

An international sharing on the measurement results of air pressure in a ventilation section of a 150-mm diameter stack during a branch pipe discharge at a flow rate of 1-4 L/s.