What is a digital twin? A virtual clone of a real system, such as a factory, a building or a city, which uses data to mirror its current state and behaviour .

After working all of his life as a sound technician for the Bulgarian state television, Emil is now retired. He lives in a 120 square meter house in Gorni Lozen, a village not far from Sofia, but only uses its ground floor and basement because he can’t afford to heat the whole of it.

The city has a climate that is good for agriculture : one fifth of Turkey's fruit and vegetable exports and more than 30% of its greenhouse areas come from just this one region.

Each year over 3.5 million tourists from all over the world visit Pompeii to admire the ruins left by the eruption of the Vesuvius that, in 79 AD, engulfed it together with the nearby city of Herculaneum.

In the city, the famous Cabanyal district which had been home to a local fishing community for a long time, has recently been transformed into a testing ground for numerous energy efficiency techniques.

In architecture, there are two kinds of sustainability: one simpler, smaller, and ethical in its relationship with the environment and with people; and another which is “fashionable”, used as a label in a speculative way, without an understanding of what it really means.

Maguy Soldevila is a former art teacher. Some years ago, she quit the frenzy and the pollution of the French city of Lyon to move into a typical house of the 1960s, in the small village of Sail-sous-Couzan.

The Turkish city of Antalya, on the country’s southwest coast, is perhaps best known internationally as a holiday destination. But as one of Turkey’s largest cities, Antalya is home to around 2.

Cities, with their concentration of services, economic opportunity, mobility and social interaction, have proved endlessly attractive to humans.

Transforming districts into near-zero energy consumption urban areas could be a reality in the next few decades.

The quest towards low energy consumption in city districts requires many changes not only at building level, but also at district level.

Energy consumption in the non-residential sector, such as public and industrial buildings, is typically about 40% higher than in the residential sector.

There is much need to develop energy efficient solutions for residential buildings in Europe. The EU-funded project, MeeFS , due to be completed by the end of 2015, is developing an innovative multifunctional and energy efficient façade system to retrofit residential buildings.

CARTIF III is a new building that forms part of an applied research institute, called the CARTIF Technology Centre, based in Valladolid, Spain. This building is singular.

Three public non-residential buildings will be revamped during the next four years in three countries with different climates; namely in Turkey, Belgium and Spain.

Innovative solutions are required to improve the energy efficiency of the existing residential building stock in Europe. But combining such innovation with better management and new business models creates unique retrofitting opportunities .

Cities substantially contribute to European air pollution as they are the source of about 36% of the total CO 2 emissions. Modern cities therefore raise sustainability concerns.

Imagine a city could halve its energy consumption, costs and greenhouse gas emissions. This would get closer to levels that would ensure sustainability of resources.

Those who live in low-energy buildings are not experts. But energy professionals have been aware of the importance of meeting their needs, right from conception stage.

Tackling energy loss from buildings is one of the key objectives to reach greater sustainability, when it comes to energy consumption.