Efficiency potential in buildings


The silkworm uses its saliva to spin a well-insulated cocoon that protects it from weather conditions while the pupa undergoes metamorphosis. Silk is prized for its low density and insulating properties.

Efficiency potential in buildings

Sustainable modernisation of old buildings

To achieve the greatest impact, it makes sense to start where the most energy is used and the greatest efficiency potential lies: buildings. Research institutes and representatives of the building sector at national and international level are developing efficient insulation materials and new renovation technologies for the huge numbers of old buildings. One of them is Empa, the Swiss materials research facility, whose work we present in the following section.

Switzerland is dependent on imports of gas and petroleum products for three-quarters of the energy it needs. Foreign dependence is actually eighty per cent if the primary energy needed to generate electricity is also included. Switzerland has a total of 1.64 million residential buildings that account for around 46 per cent of total domestic end consumption, putting them in the highest consumption category. In 2011 roughly 3.5 million tonnes of heating oil and 3.1 billion cubic metres of gas were used for heating in Switzerland. The use of fossil fuels can thus be reduced if the demand for heat is also lowered.


Buildings erected between 1920 and 1970 need around 200 kilowatt hours per year of energy for heating and hot water for every square meter. At the beginning of the 1980s, stricter structural standards were introduced in response to the oil crises. New buildings that comply with the MINERGIE or MINERGIE-P standard consume between 30 and 50 kilowatt hours per square metre annually for heating, cooling, ventilation and hot water, which is less than 25 per cent of the energy consumed by an old building. Today, however, the rate of energy-saving building modernisations is very low. The focus of energy laws and technical innovations on new buildings neglects the fact that long-term building energy demand will be determined by structures that were built before the year 2000 (see graphic on page 17).

One effective model is therefore to modernise old buildings materials with high energy consumption. The federal government recognises a high efficiency potential in buildings and also focuses on this area in its energy strategy. To reduce total energy consumption of buildings 28 terawatt hours by 2050 compared to the trend scenario, the rate of energy-saving modernisations of existing buildings should be drastically increased. How can this ambitious goal be reached in practical terms?

The costs for energy today are too low for building modernisations to be worthwhile from a purely financial point of view. On the other hand, a full-scale modernisation can create added value in terms of comfort and also brings buildings into line with today's needs with respect to floor plans and layouts. A full-scale modernisation includes all aspects of living: energy supply, ventilation, floor layout and natural lighting, as well as heat insulation and building technology.


The greatest optimisation potential in heating energy lies in heat insulation. Different materials and components can be used to limit the amount of heat lost through the building's shell. If the façade of a historical building has to be protected, an inner lining made of insulated plaster is ideally suited. A plaster lining is also much easier to apply in winding staircases, rounded arches and retaining walls than insulation panels that first have to be painstakingly cut to size. The Swiss material research facility, Empa (see box on page 19), worked with an industrial partner to develop a plaster made of aerogel that has better insulating properties than a polystyrene panel. Because of its appearance, aerogel is sometimes referred to as frozen smoke. It owes its insulating property to its low density: the material consists of around five per cent silica – the rest is air. It is a purely mineral product that can be applied inside with no problem because no harmful organic substances are produced. This special product was launched on the market at the end of 2012 and is a significant technological innovation in heat insulation.


Another approach is to explore how it would be possible to store the excess heat produced in the summer months to use during the winter months. Global radiation, i.e. the direct and diffuse sun's rays, runs contrary to the annual heating curve. When the demand for heat is high, global radiation is low, and vice-versa. Excess solar energy is lost today because the possibilities for long-term heat storage are still in an experimental phase. Research work is underway to try and use the energy collected by solar cells to create a highly concentrated sodium hydroxide (NaOH) lye. Water is then re-added to the lye, which releases heat in this process. The advantage of this chemical storage principle is that the heat can be stored without being lost, making it an extremely efficient storage method. The question of how much a kilowatt hour of stored heat costs has not yet been answered, and it will likely still take some time until this solution becomes marketable.


Conventional building renovation is often more of a repair than a modernisation intended for generations to come. Instead of getting a building in shape for the long term, many of the changes focus on individual, urgent measures that will not unnecessarily lower the returns from a property. People forget that after fifty years of use and low maintenance costs, massive investments have to be made in a building so that it can be reasonably used for another fifty years.

With this in mind, Empa got involved in the CCEM-Retrofit project, which worked with industrial partners to come up with solutions for sustainable renovation of multi-family houses and residential housing developments. The resulting concept is simple: a largely prefabricated, new building shell is placed over the existing building. Value-adding enhancements can be attached to this new shell which guarantees that the building meets the highest standards of energy efficiency and comfort after renovation. The usually massive external shell of the old building is generally used as a retaining sub-construction for the new, highly insulating façade lining. The insulation layer is used to integrate a ventilation system, meaning that extensive modifications inside the building can be avoided. Laser technology measures the existing building exactly so that the façade elements can be more or less prefabricated. There are several advantages to prefabricating the renovation modules: not only do they simplify the construction process, but they also make it easy to coordinate the work since the inside can be continuously inhabited during construction.


Even greater efficiency can be achieved if the renovation isn't just restricted to a single building, but is extended over a larger unit. To this end, the building typology of a district has to be captured. This may identify several buildings suitable to be torn down and replaced by a new energy-saving building, while other buildings are comprehensively modernised using the process described above. Historical, protected buildings could potentially be used to store heat on a seasonal basis because these buildings often have the necessary space. The buildings are then connected to one another by what is called an “energy hub”. The various functions of energy management are brought together in a district's energy hub: from distribution to conversion and storage of heat, cold and electricity. Decentralised, renewable generation facilities can be connected to the energy hub and supply some of the electricity. If the individual buildings or consumption units are also equipped with control and communication modules, consumption can be ideally controlled within the district and adjusted to fluctuating generation. This creates a flexible network unit that functions as a virtual power plant (see article on pages 20-21).

Several districts with smart energy systems can be connected to form larger, intelligent units. By doing this, entire parts of cities and agglomerations can be connected to the regional electricity grid, which in turn is connected to the national grid. The goal is always to keep the energy flows at the lowest possible grid level. The supply model of the future is based on the principle of using the irregular and decentralised generation from new renewable energies at regional level if possible, i.e. to distribute it or to store the excess. This would reduce the need for grid expansion. This doesn't, however, eliminate the need to set up a high-performance super grid that transports electricity over long distances.



What are the advantages of the approach pursued in the CCEM-Retrofit project for housing renovation over conventional building renovation?

In addition to saving energy, a full-scale modernisation also takes into account today's housing standards. Our approach also allows the living space to be enlarged, for example, by converting balconies into winter gardens. In both pilot projects the existing roof was removed and replaced by an additional apartment. This additional living space was actually what made the projects economically viable in the first place.

How can building owners be motivated to modernise their old buildings, apart from offering them financial and tax incentives?

Many multi-family homes constructed between 1950 and 1970 are ideally situated but no longer meet our current expectations in terms of comfort and energy efficiency. While they no longer belong in the top tier of buildings, a full-scale modernisation pushes them back up into the higher echelons. This means that the owner once again has a property that meets modern standards and generates commensurate returns.

How should a building owner decide between maintenance, full-scale modernisation or a completely new building? Are there any decision-making aids?

We have developed a tool called Retrofit Advisor that helps owners of multi-family houses easily determine their property's potential. The financial, environmental and social impact of various options including painting, a full-scale modernisation in line with the Retrofit concept and reconstruction can be compared with one another. The user can set individual priorities and compare different variants side-by-side. The first analysis serves as a basis for detailed planning. We are currently working on enhancing the Retrofit Advisor in a European research project and transferring it to an Internet platform.

Are there already practical models for how energy-saving optimisations can be implemented at district level or for entire parts of cities?

The first models exist and various municipal energy supply companies are moving in this direction. The core questions that have not yet been definitively answered include the ideal size of a network, the technical solutions which should be used in the energy hub, the control technology, and of course also the legal aspects as to whether there is an mandatory connection and how billing is to be handled.

The speed of innovation in the building sector is relatively low. What is needed for successful technology transfer?

Construction investments are generally very expensive and geared toward the long term. The result is that building developers tend to be more risk averse – they want to be sure that the technical solutions proposed actually work in practice. This creates a relatively large hurdle to transferring the results from research to practice. The most efficient way to encourage technology transfer is trial projects that test new solutions for their suitability for practical application under realistic conditions. For this reason, Empa joined forces with technology partners from the ETH domain to develop the NEST concept: a research and technology transfer platform on which new results from research and development can be tested and demonstrated on a 1:1 scale.

The efficiency potential in buildings is around fifty per cent. What is the potential of mobility and industry?

Technically speaking, a lot of progress has been made in efficiency in mobility in the last few decades. The main thrusts are more efficient engines, hybridisation and lightweight design. I think the biggest challenge is the continuous growth in mobility. All of the gains made in efficiency over the last few years are being cancelled out by increased consumption.

I am more optimistic about the industrial sector, where efficiency measures that make good economic sense are implemented relatively quickly. New technical developments will further encourage this development. The industrial sector can play an important role in the context of local energy networks because it often has a load profile complementary to the housing sector, meaning that industrial companies can function, e.g. as buyers of excess electricity, and feed process heat into the hub, in return.

Are efficiency measures enough to decouple energy demand from population and economic growth or do we also have to think about sufficiency in the future?

As the example of mobility shows, we will not reach the goals set through efficiency measures alone. Whether we as a society are able to voluntarily limit our consumption and what the economic impact of a step like this is, is difficult to say. I think, though, that we need to have this discussion to see which solutions would be feasible and if they would be met with widespread acceptance. If we extrapolate the European and North American resource consumption to the global level, it becomes immediately clear that we are living far beyond our means. Per capita energy demand in developing and emerging economies is a fraction of our demand. But the rest of humanity has the same right to economic development and prosperity as we do. Unless we achieve totally unexpected technological breakthroughs in the next few years, we will have to deal with the issue of how to distribute access to resources in a more equitable manner. This can only mean getting by with less. This step does not necessarily have to be associated with a lower standard of living, however.

Empa is an interdisciplinary research and service institution for material sciences and technological development within the ETH domain. Empa takes on research contracts for various industrial partners, creates studies and assessments, and is involved in university-level training and education. Empa has sites in Dübendorf, St. Gallen and Thun, and employs around 940 people, 140 of which are doctoral students. The focal areas of research include nanostructured materials, material for energy technologies and new drive technologies.

More information can be found at:

For more on the Retrofit programme:

Energy consumption of residential buildings by year of construction
(source: Empa)