30 under 30: Engineering Hong Kong’s vertical cities

Hong Kong and Mainland China have some of the highest urban densities in the world. How does this ‘vertical’ context influence innovation?

Zhengguang Liu: In ultra-dense, vertical cities – such as Hong Kong and many Mainland China megacities – conventional sustainability approaches based on incremental efficiency gains reach their limits quickly.

Spatial constraints, limited roof area and tightly coupled infrastructure mean that optimising individual components is no longer sufficient. This context forces a shift in thinking: buildings must be treated as active nodes within a wider urban energy system rather than isolated energy consumers.

Much of my work focuses on how building-integrated photovoltaics and demand-side flexibility can unlock system-level decarbonisation in environments where space, capacity and redundancy are constrained.

Jill Leung: In Hong Kong and Mainland China, density and verticality push us to innovate beyond standard practice. Extremely high occupant and equipment densities require advanced load prediction, dynamic zoning and AI-assisted chiller and air-side optimisation to maintain comfort while cutting energy use.

Space constraints drive modular, prefabricated, multi-trade integrated mechanical, electrical and plumbing (MiMEP) systems that fit tight plantrooms and enable staged retrofits. Onsite renewables move beyond roofs to building-integrated photovoltaics (PVs) on façades, and hybrid PV and solar thermal (PVT) systems that provide electricity and useful heat. Micro wind turbines are also being explored.

Tsz Kai Charles Lam: Vertical city conditions have pushed us to design sustainability as a three-dimensional, operational discipline – where plant, air paths, controls, logistics and user behaviour must work together at height, speed and scale.

In that context, innovation is less about inventing new standards and more about re-engineering how international best practice is applied to dense, mixed-use towers and campuses with long operating hours and complex stakeholder interfaces.

In ultra-dense districts, we cannot treat buildings as isolated assets; we have to optimise clusters such as shared central plants and district energy interfaces, and we need resilient maintenance strategies that work in constrained plantrooms and vertically distributed risers.

That ‘stacked’ complexity forces earlier, more integrated decisions: separating sensible vs latent cooling demands, and designing for 24/7 tenancy diversity (for example, retail, offices and serviced apartments in one tower). Retrofit phasing has to be planned carefully so that decarbonisation happens without disrupting business continuity.

Building services in the region are dominated by cooling and humidity challenges. What is the biggest hurdle to achieving true net zero in a subtropical climate?

Zhengguang Liu:  The biggest hurdle is not cooling demand itself, but the rigid coupling between thermal comfort, humidity control and conservative operational strategies. In humid subtropical climates, maintaining wellness often locks systems into inflexible modes of operation, leaving little room for optimisation. My research explores how thermal storage, system inertia and predictive control can decouple when cooling is generated from when it is used. This allows energy use, carbon emissions and comfort to be optimised simultaneously, rather than forcing trade-offs that undermine performance or wellbeing.

Jill Leung: The biggest hurdle is managing rapidly rising cooling and dehumidification loads without over-reliance on energy-intensive systems. Climate change is increasing temperature and humidity, which drives up latent and sensible loads, and lowers equipment efficiency. To approach true net zero, we must dissect cooling load components rigorously, then reduce demand through façade optimisation, airtightness, moisture control and heat recovery. In parallel, we must promote behaviour change via green tenancy and incentive schemes, and encourage acceptance of higher setpoints. This load reduction underpins efficient, wellness-focused system design.

Tsz Kai Charles Lam: The biggest hurdle is latent load. We have to remove moisture safely and efficiently during long operating hours, without overcooling or compromising indoor air quality and comfort. Research focused on Hong Kong shows the latent portion can dominate ventilation cooling load (reported around 80% in one study) and it is highly sensitive to outdoor moisture, making dehumidification energy a core barrier to ‘true’ net zero in our climate.