Fighting energy waste in buildings
- Europe’s buildings account for 40% of its energy use and up to 40% of its CO₂ emissions.
- From France to the Netherlands to Denmark, new initiatives are beginning to deliver convincing results.
Is Europe an energy sieve? The continent’s property sector accounts for 40% of its energy costs and up to 40% of its CO₂ emissions, similar to the US. The main reason is an ageing property inventory: pre-1945 buildings account for almost 30% of the total energy used by European buildings. In light of this, renovating old housing is at the forefront of efforts to cut down on waste.
The problem is that renovating an old house or flat isn’t all that simple. If not properly carried out, the work can damage a building, resulting in increased humidity, dampness and poor air quality. “The good news is that there are effective solutions,” says Vilhjalmur Nielsen of the civil-engineering department at the Technical University of Denmark (DTU). “A huge amount of research has shown that it’s possible to reduce energy consumption by at least 50% by insulating old buildings.”
“The real challenge lies in choosing the right methods and materials,” adds Frédéric Laroche, head of the Réhafutur project. “Renovation is a multidisciplinary issue.” This French project, which operates near Lille, involves testing a number of insulation techniques using eco-materials in a 350-m² house, working closely with all trades, from carpenters to electricians. The building is packed with sensors that provide data for long-term studies of each solution to identify which performs best over time.
A unique challenge with every building
To achieve large-scale success, renovating Europe’s properties requires bringing together expertise from engineers, businesses, public authorities, architects, universities, and more. This is the goal that DTU and its partners are seeking to achieve with their REBUS (Renovating Buildings Sustainably) project, launched in the spring of 2016 with funding of almost €11 million. It focuses on the renovation of social housing, which accounts for 30% of properties in Denmark.
France’s Biofluides company also hopes to have an impact on collective housing. Its solution is based on heat recovery from warm wastewater – which has an average temperature of 29° C – from residents’ showers, washing machines and dishwashers, which is then reinjected into the pump used to heat water for the building. The results are promising – the 70 buildings fitted with this technology require four times less energy to produce the same amount of hot water. As a result, residents have seen their energy bills fall by an average of 40%. Moving beyond housing, other buildings have their own challenges stemming from their environment or purpose. For instance, the energy requirements of a primary school are very different from those of a hospital open 24 hours a day.
The new departmental-archives building in Lille highlights this issue: proper preservation of its documents requires specific temperature and humidity levels. Instead of trying to maintain a fixed temperature through air-conditioning, the building, opened in 2014, was designed to allow the temperature to vary between 16° C and 25° C while preventing variations of more than one degree per 24 hours in order to avoid thermal shock, which could damage the archives. The building’s thickness, perfect weatherproofing, triple glazing and insulating carpentry, as well as its stainless-steel skin, which is designed to reflect solar rays, all play a part. The building is also capable of generating its own energy. With 300 m² of solar panels on the roof, it requires only a 16-kg cogeneration boiler to control the temperature over an area of 10,000 m².
Eindhoven’s green U
Across the entire campus, the Eindhoven Technical University (TU/e) is currently modelling a successful renovation. The work, which has already won a host of environmental awards, will transform the university’s main building into one of the greenest complexes in the Netherlands. The heating and cooling systems in most of the buildings will no longer be powered by gas but by one of Europe’s biggest geothermal systems. The system already stores heat and cold separately in a tank underneath the entire campus. Electricity will be supplied by solar panels, which will provide 500,000 MWh per year, equivalent to the energy used by 75,000 homes. Lit by a system of smart, low-power LEDs that can adapt to the needs of each visitor, the project is a new step forward in an energy strategy that has already allowed TU/e to reduce its gas consumption by more than 50% over 15 years.¨
Buildings’ energy efficiency is also part of a broader context. “More will happen in the next five years than has happened in the last 60,” explains Laurent Cantat-Lampin, sales director at RTE, the company responsible for managing France’s highvoltage electricity grids. “In 10 years, the amount of green electricity has tripled in Europe. However, grids aren’t designed to manage such flows, which are variable by their very nature.” This can cause absurd situations. “In Denmark, we have to stop some wind turbines on windy days because the grid isn’t smart or flexible enough to absorb the influx of energy,” says Henrik Madsen, head of DTU’s Computing and Applied Science department. Making better use of this energy means looking beyond the building scale and focusing on neighbourhoods or even entire cities. “The most sustainable, effective and cheapest solutions can only be implemented on a large scale,” says Madsen. This is particularly true when it comes to storage: at the building level, solutions for storing excess wind or solar energy are either impossible or too costly. At the neighbourhood level, they become profitable.
The good news is that Europe brings a wealth of assets to the table. “We’re ahead in terms of smart, automated and flexible systems that facilitate the integration, storage and distribution of renewable energy flows,” Madsen points out. As part of the CITIES (Centre for IT-Intelligent Energy System) project, he and his colleagues are working to help Denmark achieve its target of a fully renewable urban energy supply by 2050. This includes developing tools capable of managing all aspects of an energy system using forecasting, monitoring and optimisation. For example, the researchers have developed thermal mass storage solutions within buildings, using the ability of certain heavy materials (such as concrete, brick and mudbrick) to store, then release heat or cold. “Used on a single site, the storage time can reach six to 12 hours. At the neighbourhood level, it can extend to two to three days.” The challenge lies in creating “energy-buffer” buildings that absorb variations in energy generation and consumption by acting on the heating and cooling systems in real time. This development will allow the much-discussed smart grids to constantly balance energy supply and demand. However, Nielsen points out that a number of obstacles still remain. “Making buildings smart enough to achieve the full potential of a smart grid isn’t always easy, technically speaking.” One limitation is the need to install extremely accurate sensors. The challenges are also financial, as it is necessary to develop standardised solutions, which are consequently less expensive on a large scale.
Across Europe, solutions that focus on entire urban areas are delivering convincing results. Launched in 2000, the BedZED project has completely transformed Beddington’s 2,500 m₂ of homes, offices, retail premises, green spaces, and cultural and healthcare centres in South London. The result is an 88% drop in energy consumption for heating and 57% for hot water. Another iconic project is the Northern Harbour district in Copenhagen. Managed by DTU with government support, the EnergyLab Nordhavn project has a budget of €17 million and is helping the city cope with its growing population. Its work demonstrates how electricity and heating, energy-saving buildings and electricity transmission can all be integrated into a smart, flexible and optimised energy system. Nordhavn’s computerised control systems communicate with the energy systems in individual homes and offices right down to the radiators, heralding the smart cities of the future.
Temperatures in cities need to fall – and fast. But how?
Streets swelter, entire neighbourhoods are transformed into baking ovens, and residents are left exhausted by stifling heat. “Higher temperatures in cities are an increasingly noticeable issue, particularly at night,” says Thomas Auer, an expert on sustainable construction at the Technical
University of Munich (TUM). “The heat produced by the sun, traffic and air-conditioning systems is absorbed by the tarmac and the walls of buildings during the day, and is then released at night.” Worsened by dark building exteriors and a lack of green spaces, which promote cooling, the formation of urban heat islands (UHIs) is becoming an issue of concern, especially with global warming set to further exacerbate this phenomenon. During the heatwave of 2003, which was responsible for the premature deaths of 70,000 people in Europe, the temperature difference between major European cities and rural areas exceeded eight degrees Celsius.
What can be done to alleviate this? “Reflective construction materials can minimise UHIs,” says Auer. Other researchers, like TUM’s Philipp Molter, are testing “skins” designed for use in the building envelope. In his laboratory, he and his team are working on the Flexcover project, which has created self-regulating windows modelled on human skin. Just like the skin’s pores, which can open and close in response to the temperature, they form an envelope that can “breathe”, adapting the building’s temperature to the conditions outside.
Rethinking urban design
Even so, the real response won’t be found at the building level or even at the neighbourhood level, says Auer. Our whole approach to urban design needs a rethink, particularly when it comes to new districts. “Reducing urban density isn’t necessarily useful. However, we need to create a roadmap that we can use to adapt cities to the climate, to promote wind circulation in new urban areas using specially-designed corridors, like in Hong Kong, or to increase the surface area devoted to green spaces while ensuring these spaces are distributed across the city.” The transformation will take decades, but a number of major cities have already started. New York, for example, has painted the roofs of around 100 buildings white to reduce the amount of energy consumed. Since then, airconditioning bills have fallen by 10% for five-storey buildings. What’s more, while Helsinki and Copenhagen are leading the way in Europe, Paris has been looking into urban renovation for around a decade, and Moscow has plans to redesign 3,000 major roads as part of My Street, a huge urban renovation project begun in 2015.