Smart city

#SmartCity: New York City about to go green?

Archive January 2016

The days are numbered for waste and mismanagement. For a number of years now the construction sector has been targeted with ambitious goals for reducing energy consumption. In France a new era began with the passing of environmental measures under the ‘Grenelle I’ and ‘Grenelle II’ Laws. In fact the building sector, which alone accounts for 42.5% of all energy consumption in France, is a key factor in the transition to more environmentally-friendly energy systems. The ‘RT2012’ thermal regulation currently in force for buildings has already led to the appearance of new buildings that require only a third of the heat they used to consume under the previous regulations. Thus RT2012 has made low consumption the norm in new buildings and, in the wake of the Paris Agreement on Climate Change Action, the next set of rules (RT2020) will go much further. By 2020 It is likely to impose as the ‘standard’, at least for new constructions, that they should be energy-plus buildings, i.e. producing more energy than they consume.

Bouygues Immobilier and Elithis pioneers in the environmentally-friendly tertiary building market 


Construction sector firms already have several years of hindsight in this field.  Some pioneering companies have paved the way, removing any doubts as to the feasibility of such energy-efficient buildings. In the new era of energy-plus buildings, the Elithis tower in Dijon in eastern France – named after the engineering firm that built it and has its own offices in it – which opened in 2009, marked the entry of the service sector into the positive energy era. The company is about to make headlines again; by the end of the year it will open the first residential tower block of this type, a 17-storey building in Strasbourg. Bouygues Immobilier is also a forerunner in this field. The Green Office building delivered by the Bouygues Group in Meudon in the southwestern suburbs of Paris in 2011 is often cited as a case study. With 23,000 m2 of floorspace, it is currently the largest energy-plus building designed for tertiary-sector use. It has 4,200m2 of photovoltaic panels, a Combined Heat and Power unit running on vegetable oil, plus natural ventilation and the use of ‘natural’ materials. Broadly speaking, an ‘energy-plus’ house or apartment works on ‘passive house’ principles – i.e. it is designed to allow minimal energy consumption – but it pushes these principles to the limit. It draws maximum contributions from solar energy and internal heat sources, leaving the heating boiler to step in as backup on the coldest, bleakest winter days.

We’re now looking to recover the free heat provided by the sun by using orientation – by having windows face south and by limiting exposure to wind.

Thierry Bièvre

All this is now attainable because a number of different systems have converged. When you talk about an ‘energy-plus’ building you are also talking about bioclimatic architecture. “This was not necessarily the case for the first generation of buildings, which focused more on using technology. Since then we’ve realised that such technology can be expensive to maintain”, reveals Thierry Bièvre, President of the Elithis Engineering Group, which specialises in energy efficiency.

The industry is now looking to recover the free heat provided by the sun by using orientation – by having windows face south and by limiting exposure to wind. The residential Elithis Danube tower in Strasbourg, which is due to open at the end of the year, is the model for this type of energy efficiency.

The Elithis Danube has a very large south-facing façade, with wide glass bay windows, in contrast to a north-facing façade that is shaped like the prow of a ship – very narrow, very slim. This aerodynamic shape ensures minimum exposure to wind and cold. The insulation also needs to be faultless, so as to minimise heat loss and reduce air currents. In recent years a lot of progress has been made in building materials; they now provide better thermal insulation and also have a smaller environmental footprint. An insulation layer on the outside of the building and the elimination of heat loss through weak points in the structure  (‘thermal bridges) significantly reduce the need for heating, which is the main source of energy consumption. 

The building’s external insulation has to act as a skin, i.e. it needs to be able to respond to the range of temperatures the building will be exposed to throughout the year.

If the work has been done well, a passive building will not consume more than 15 kWh/m2/year for heating purposes. “The building’s external insulation has to act as a skin, i.e. it needs to be able to respond to the range of temperatures the building will be exposed to throughout the year, a delicate balance to achieve,” explains Thierry Bièvre. Paradoxically, you do not necessarily need high-performance external insulation, as a building might find itself with excess heat at certain times of the year, resulting in a ‘thermos’ effect.

The cost of electricity from PV solar panels is now competitive

Regard d'expert

Emmanuel François


Smart Building Alliance

The price of photovoltaic panels is now an eighth of what it was ten years ago

In addition, energy-plus buildings make extensive use of renewable energy. They usually use double-flow ventilation systems, which take the heat from stale air in the home and use it to heat new air filtered in from the exterior. A ventilator then diffuses this preheated new air into the main rooms. These systems thus use heat generated inside the home – from domestic appliances and electronic equipment. In order to make them ‘energy-plus’, these buildings also have their own means of producing energy, most often using solar panels.  This is a reliable, proven technology, whose cost has fallen considerably in recent years, mainly due to cheaper installation costs.  “The price of photovoltaic panels is now an eighth of what it was ten years ago,” points out Emmanuel François, President of the Smart Building Alliance. The upshot is that the cost of electricity produced from photovoltaic panels is now very competitive compared with electricity supplied by the grid. It has now become cost-effective for buildings to consume the energy they have produced themselves.



Bouygues Immobilier

Sometimes other less conventional renewable energies are used. For example, French real estate developer Bouygues Immobilier’s second Green Office, the Spring Building, is equipped – in addition to its 6,500m2 of PV panels – with a geothermal system for producing heat and cooling, and a system of rainwater capture for flushing the toilets. Last but not least, the energy-plus building draws on digital technologies. Regulating temperature in this type of structure is a very delicate process, so the energy system needs to be managed so as to respond as closely as possible to the needs and daily habits of the people renting homes there. In fact, from very early on home automation has played a vital role in the development of this style of construction, so as to avoid wasting energy of course, but more than that. “Home automation has allowed us to demonstrate the efficiency of this style of building and also to develop our knowledge of temperature regulation,” underlines Thierry Bièvre.

 “Home automation has allowed us to demonstrate the efficiency of this style of building and also to develop our knowledge of temperature regulation”

Home automation systems underpinned by artificial intelligence 

Using digital technology to help manage a building’s energy systems is only in its infancy and low-energy-consuming buildings are set to become much ‘smarter’. In the next few years we are likely to see a qualitative leap forward in the development of integrated home automation systems based on artificial intelligence (AI), including systems that will turn off the air conditioning when the home automation control centre detects that you have opened a window; or that will know when the occupant arrives home without anyone having to push any buttons or do anything at all. Early home automation systems were already capable of this kind of action. “But the way these systems react is not always appropriate to the situation,” says Emmanuel François, explaining: “AI-based installations can take into account far more sophisticated parameters.” Packed full of sensors, the smart building will be capable of regulating itself using self-learning systems which closely mirror the needs of the building’s residents – and not just according to pre-set scenarios. Advanced solutions are appearing on the market. For example, Ethilis has just launched a system called Alad’hun, which is a sort of virtual energy advisor for home occupiers. Meanwhile Bouygues Immobilier is using technology developed by Lyon, France-based startup Ubiant in its Flexom homes. Ubiant’s Cloud platform Hemis autonomously regulates the temperature in these homes and guarantees to meet a pre-determined consumption target.

Bio facades uSING MICROALGAE biomass

cabinet XTU

Real estate developers have equally high expectations of the development of storage systems to back up renewable energy sources, which are by nature intermittent. Innovative systems are emerging in the form of hydrogen fuel cells, or more traditional zinc-air batteries. French start-up Sylfen,  based in Grenoble, has for example developed a renewable energy storage solution which transforms into hydrogen any surplus power created locally, and conversely, can re-convert the energy from the hydrogen fuel cell back into electricity whenever needed. “However, district heating systems – micro power plants which produce hot water for an entire city district – are still to a certain extent viable,” stresses Emmanuel François, who argues that renewable energy should be stored using a mix of different solutions. In the same vein, new systems of energy production are emerging. Some are highly innovative, such as bio-facades incorporating microalgae biomass and photovoltaic windows. As regards insulation, green roofs are fast making headway. These are highly beneficial for acoustic and thermal insulation for buildings – for example they reduce heat loss through the roof during the cold season and reduce to an absolute minimum the need for air conditioning in the summer.

Digital modelling, a highly useful tool for low-cost designing 

Meanwhile digital modelling is playing a vital role in making the construction of these environmentally-friendly buildings more widespread. Digital tools can produce simulations of a number of hypotheses – based on data on the building structure and the materials to be used – before deciding on the final plan. Firstly, digital modelling enables architects and designers to assess a building’s energy performance, using thermal simulations incorporating historical variables on humidity, temperature and sunshine. Secondly, it produces a fast analysis of the environmental quality of the building using data files incorporated in the software. This approach has the huge double advantage of both reducing design costs and helping to avoid errors.

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Thierry Bièvre believes that nothing now stands in the way of the construction industry being able to create energy-plus buildings at market prices and that once a number of general preconceptions are swept away, this kind of building could be constructed on a large scale by 2020. “Some leading firms have a good mastery of the field, while others are still shying away,” he reveals, adding: “Some of those that are hanging back are still harbouring misconceptions that die hard: the costs will prove too high, the projects are likely to be overly complex, it’s still not feasible to use only low-carbon energy, and so on.” Eight years after the first plans were drawn up, the French Observatory for low energy buildings today lists only 437 conventional positive energy buildings – comprising private houses, apartment buildings and offices – already built or under construction. That’s really not very many. And with carbon reduction deadline dates fast approaching, it’s clear that all the players in the building sector need to start working together to make progress in this vital field.  

By Olivier Discazeaux