Hong Kong is one of the most densely populated areas in the world with most residents working and living in high-rise towers and residential apartment blocks. Working with local partners Sino-Land and Hong Kong Polytechnic University, Arup has developed a small-scale, in-building hydro-power generation system that makes use of the unused water pressure in the potable water pipelines of high-rise buildings. I think the result could bring energy savings to many sites across this crowded city – and possibly others around our rapidly urbanising world.
High-rise needs high-pressure water
The dominance of high-rise buildings in Hong Kong (between 30-40 storeys on average) means the pressure in local municipal fresh water supply pipelines is usually very high (6-8 bar), in order to ensure consistent water supply throughout the city. Pressure reducing valves (PRV) are used to protect the water facilities of the city’s towers from this extreme high pressure. And when a micro hydro generation set replaces the typical PRV system, the energy that would otherwise be lost, can be extracted by the pressure difference.
The hydro-power generation system combines an external hydroelectric generator and a highly efficient vertical-axis spherical turbine that dips into flowing water and reclaims residual pressure. This micro hydro-turbine, the first in the world to work in a high-rise context, has been installed at residential buildings Olympian City 2 and Lee Tung Avenue in Hong Kong.
Intelligent energy saving
Hydro-electricity is a very clean source of energy, and represents an intelligent energy saving response in a city where there often isn’t space for wind turbines or solar panels. In the demonstration in Olympian City 2 where a 100W turbine is used, the electricity generated by this system can power the lighting in a lift lobby, saving 876 kWh per year for only 5m water head consumption. This represents a 600 kg CO2 annual emission saving, which is equivalent to planting 30 trees to offset the emission. To date, nine similar 16W turbines have been installed at a second address in Hong Kong and have been running since the beginning of 2016.
A new building standard?
With so many existing and potential high-rise sites, in-building hydro power generation could help dense cities like Hong Kong make significant cumulative energy savings. Similar to the heat and energy recovery system for heating, ventilation and air conditioning (HVAC) in buildings, this energy saving technology could become a new building standard around the world.