His research interests are in building environment engineering. His current research topics include city climate/environment, environment studies of infection and indoor environment. His work led to the findings of the roles played by airflow in the 2003 Amoy Gardens SARS outbreak. He carried out research on hospital ventilation in preparation for influenza pandemics for Hospital Authority and WHO. He contributed to the dynamic theory of natural ventilation and hospital ventilation. He publishes over 200 journal articles in engineering, environment, climate and health journals including Indoor Air, Climate Dynamics, PNAS and New England Journal of Medicine with over 4500 SCI citations (SCI h-index = 39). He led and co-authored 2009 WHO guidelines on natural ventilation. His research has been supported by 2 RGC CRF, 12 RGC GRF, 1 Horizon2020, 4 RFCID and 3 NSFC grants as PI since 2000 (>HK$40m). His work has also been supported by WHO, Boeing and Microsoft.

He currently serves as President, Academy of Fellows of International Society of Indoor Air Quality (ISIAQ). He was the President of Indoor Air 2014. He gave plenary/keynote/invited talks in >80 conferences on topics ranging from environment control of infection, natural ventilation to city climate and environment.

He received the State Scientific and Technological Progress Award (Second Prize) in 2010, Best Paper Awards of the Indoor Air in 2008 and 2011, the Rydberg Gold Medal of SCANVAC in 2014, and the Inoue Memorial Award, SHASE, Japan in 2016. He was elected a Fellow of ASHRAE, ISIAQ, HKIE, and IMechE. He is a chartered engineer (CEng) with UK Engineering Council.