Prof. Defilla, President Assistant of APSEC, was invited to speak at the International Smart City Congress held last week in hybrid mode in Algiers, where he was the only offsite speaker. In his presentation held under the title “Engineering Net Zero in Cities”, he pointed out to the lessons Algeria can learn from Chinese cities. 

In China the subways and high-speed railways are the transit axis along which cities grow internally and are being interconnected among each other and developed along the model of transit-oriented development. 37 Chinese cities have now their own subway system as backbone for passenger transport, helping to diminish urban congestion and keeping transport efficient and clean. The Chinese high-speed railway system has grown rapidly in recent years with increasing number of lines that can be travelled at speed of 350 km/h. In the coming years the magnetic levitation technology will increase this speed to 600 km/h. 

Keeping cities liveable and inclusive means cities should have a sufficient proportion of affordable housing, preferably in the neighbourhood of subway stations, allowing people without cars to conveniently use the subway system. A new objective for cities with developed tertiary or service economy is to create mixed districts with residential and tertiary economic activity. Jobs and residences should be close to each other. 

The great challenge of cities is to use the new city-scale technologies to make cities clean. The concept of positive energy district has been tested several years ago in Germany. It should now be adapted to a high-density city. The technologies are photovoltaic in both, rooftop as well as building-integrated photovoltaic, combined with seasonal energy storage, heat pumps, performance contracts for buildings and incentive smartphone games for residents. Among these new technologies, district cooling is especially trendy. It is much more energy efficient than individual cooling and can be combined with urban renewable energy. Another source of urban energy is wastewater. Today, wastewater treatment can become an energy supplier, whose surplus energy can be injected into the electricity grid. 

As a recommendation for a country with strongly developing demography, Algeria should build as many as possible positive energy districts around subway stations with affordable housing for the low-income groups and all essential services, including jobs, to be found within walking distance.